Multiscale Simulation Techniques

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Multiscale Simulation Techniques

Final Report

Final Report programme MuSTTechnology Foundation STW

Enabling new technologyin the top sectors

Enabling new technologyEnabling new technologyEnabling new technology

MuST

3 Perspectiefprogramme MuST

Table of contents

04 Preface

08 Summary

11 Programme objectives and results

15 Conclusions and recommendations

20 Herman Wijshoff: ‘It would be good if research programmes were organised for a longer period’

25 STW, Questions and answers about the MuST programme

30 Interviews with principal investigators

84 Personal experiences of PhD students, staff and users

116 Final symposium of the MuST programme

120 Appendix Output: List of publications

134 Colophon

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Preface

The Multiscale Simulation Techniques (MuST) programme was launched seven years

ago as one of the first Perspective programmes of the Dutch Technology Foundation,

STW. The objective of the MuST programme has been to make significant progress

in the area of computational techniques for engineering problems exhibiting a wide

range of length or time scales, and in the application of these techniques to advanced

industrial problems. In addition, aligned with the above primary objective, the

programme endeavoured to build a community of research organisation sharing tools,

techniques and strategies in multiscale simulation and engineering and, moreover, to

establish a platform for cooperation with industry, international research organisations

and for further development of scientific education.

Numerical simulation is nowadays well established as part of the trinity of modern

science and engineering: Theory, Experiment and Simulation. In virtually all advanced

industries, notably in the high-tech sector, numerical simulation forms an indispensable

instrument in R&D portfolios. On the one hand, numerical simulation provides a flexible

analysis tool that can be operated at relatively low expense, with low throughput

time, and in a completely general and non-intrusive manner. On the other hand,

numerical simulation enables systematic design, control and optimization of products

and processes and allows for sensitivity and inverse analyses. Despite the significant

advancement of numerical-simulation techniques over the past decades, boosted by

exponential growth in computing power, fundament developments are still required to

harness the enormous potential of numerical simulation for multiscale problems.

The adjective multiscale refers to the interdependence of phenomena on distinctly

different length or time scales. Many problems in science and engineering exhibit

multiscale behaviour, in that an adequate description of their properties on a length

scale of engineering interest must account for phenomena that occur on much smaller


length or time scales. In computational simulations of multiscale problems, a complete,

explicit description of the microscale behaviour would generally result in prohibitive

computational complexity, far beyond the reach of current and prospective computing

resources. Moreover, it is not generally necessary to describe microscopic phenomena

in complete detail to arrive at a reliable model of the macroscopic properties of a

system or process. Yet, a sufficiently accurate description of the macroscopic behaviour

requires that the microscopic phenomena be accounted for in some simplified, reduced

form. Multiscale simulation techniques aim to obtain results with the accuracy of a

microscopic model at the computational expense of a macroscopic model.

The Multiscale Simulation Techniques programme has generated a variety of new

computational techniques for industrial multiscale problems. Moreover, MuST has made

a significant contribution to bridging the knowledge-transfer gap between academia

and industry in this area. The programme has also spawned many successful new

academic-industrial and academic-academic collaborations. Therefore, despite the fact

that many challenges are still outstanding in this broad, complicated and multi-faceted

field, it is safe to conclude that the MuST programme has been successful in achieving

its original goals. The MuST programme has laid a theoretical, methodological and

infrastructural foundation, which can serve Dutch industry and future generations of

researchers.

One of the most important products of the MuST programme has been human capital.

MuST has offered a large group of young researchers the opportunity to venture into

and contribute to the exciting field of numerical simulation techniques for multiscale

problems, and to develop into independent researchers. The large majority of the PhD

and postdoctoral students in the MuST programme have finalized their projects or will

do so in the near future. Many of them have found positions in industry or academia,


both nationally and internationally, where the training and education that they have

received in the MuST programme enables them to make valuable contributions.

This final report of the Multiscale Simulation Techniques programme gives an overview

of the scientific achievements of the programme. Moreover, it provides accounts of

personal endeavours and experiences of junior researchers, principal investigators,

industrial partners and others who have been involved in the programme.

I would like to take this opportunity also to give acknowledgments. The first

programme director of the Multiscale Simulation Techniques programme, René de Borst,

has been instrumental in defining, setting up and shaping the MuST programme. I

thank all project leaders, junior researchers and project contributors for their diligence

and their contribution to the program’s results. Acknowledgments to Technology

Foundation STW are due for providing the basis of MuST. In particular, I would like to

thank the STW-officers who have guided the setup of MuST and the program officers

who have supported MuST: Chris Mombers, Corine Meuleman, Stefan Jongerius and

Lotje Wansbeek. I would also like to thank the members of the programme committee,

Herman Wijshoff, Frans Klever, Ardi Dortmans, Rene Duursma, Marc Geers, Fred van

Keulen and Jaap van der Vegt, for their role in the definition of the programme and their

support. Finally, I would like to thank Claud Biemans for her role in establishing this

final report.

Harald van Brummelen


By the end of 2007 the STW-programme Multiscale Simulation Techniques (MuST) started, as one of the first Perspectief programmes. The total budget was at least 4.5 million euro, complemented by contributions of participating companies (users).

Multiscale simulation techniques create a numerical bridge between physical and chemical processes at small scales and behaviour of materials and fluids at large scales. These methods make it possible to predict material and fluid properties in a relatively inexpensive and fast way. They are highly important for increasing the competitiveness of the Dutch industry.

The main objective of the programme was to significantly advance the state-of-the-

art in numerical simulation techniques for industrial systems and processes that exhibit a wide range of length and time scales. The programme facilitated the development of fundamentally new models, techniques, algorithms and software, and the transfer of knowledge in this area between academia and industry.

In 2007, ten projects were selected, and in 2009 another three projects from the STW-Open Technology Programme were added to MuST. Research groups from the universities in Eindhoven, Delft, Twente, Groningen and CWI in Amsterdam participated in the programme. Altogether twenty-five PhD students, thirteen postdocs and several Master students were working in the projects.

By 1 October 2013 the MuST programme resulted in fifty-two peer-reviewed journal publications, twenty-one publications were under review or in preparation, and fifty refereed conference proceedings had appeared. Although the major part of the research has been done, several projects are still running. The last project will end in 2015.

More than sixty representatives from over thirty companies (industrial companies, small or medium-sized companies, and technological institutes) have been involved with the MuST projects. Apart from in-kind contributions, the companies provided 198,000 euro in cash.

Summary


In addition to the regular user committee meetings, several programme-level plenary meetings were organised to facilitate networking and exchange of knowledge and ideas.

The MuST programme has made a significant contribution to the scientific development of the field of multiscale simulation techniques and simulation-based engineering. For this final report many protagonists were interviewed.

After an overview of the Programme objectives and results (page 11) and the Conclusions and recommendations (page 15), Herman Wijshoff talks about his experiences as a member of the MuST programme committee (page 20). In STW, Questions and answers about the MuST programme STW looks back at the organisation of MuST programme.

The principal investigators of all the thirteen projects talk about the scientific and utilisation aspects of their work and they showcase the highlights of the research of their group in the Interviews from page 30. Several PhD students and a staff member talk about their personal experiences during their research in the projects. (from page 84). The interviews with participants from big and small companies (also from page 84) give a feeling about the reality of networking in the MuST programme and the usefulness of the research for the participating companies. Page 116 highlights the Final Symposium of the MuST programme that was organised in May 2013. In the appendix all scientific publications that resulted from the programme are listed.


The main objective of the Multiscale Simulation Techniques programme has been to significantly advance the state-of-the-art in numerical simulation techniques for industrial systems and processes that exhibit a wide range of length and time scales. This main objective encompasses both the development of fundamentally new models, techniques, algorithms and software, and the transfer of knowledge in this area between academia and industry. The main objective of the MuST programme engenders the following three-fold ambition:

— Scientific development of the field of multiscale simulation and engineering.

— Building a community of research organisations sharing tools, techniques and strategies in multiscale simulation and engineering.

— Establish a platform for cooperation with industry, international research organisations and for further development of scientific education.

Scientific developmentThe MuST projects, thirteen in total, are concisely elaborated by the respective principal investigator and junior researchers in the interviews. The contributions of these projects to the arsenal of numerical simulation techniques for multiscale problems have been numerous. Examples include new discrete particle methods and corresponding efficient data structures and algorithms, optimal adaptive discretization methods for large-displacement fluid-structure inter action, network models for fibrous materials, adaptive particle-continuum models for streamer discharges and molecular-dynamics techniques for material interfaces.

In addition to the aforementioned enhance-ment of the knowledge basis, the MuST programme has made a substantial contribution to the human capital in the area of multiscale simulation techniques. Within the programme, fourteen PhD students have received their PhD, while another five PhDs students will defend their thesis in the near future. Another five PhD students, appointed on STW-OTP projects which where retroactively appended to the MuST programme, are expected to finalize their projects by the end of 2014. In addition,

Programme objectives and results


large and medium-sized enterprises and research institutes participated in the user committees of the MuST projects; see, for examples, the interviews with Gertjan Kloosterman (Dassault), Piet Kok (Tata Steel), Famke Kraaijeveld (Shell), Ed Pols (Van der Heide B.V.) and Sander Gielen (TNO) on pages 101-112. The user committees convened on a regular basis, typically semi-annually, to discuss progress within the projects and to consider new research directions, opportunities for knowledge utilization and follow-up research. The user committees have formed an effective instrument in the dissemination of knowledge within the MuST programme. In addition to the user-committee meetings, which were held on a project level, several programme-level plenary meetings were organized, to strengthen coherence, to provide further network opportunities and to facilitate knowledge spill overs.

The MuST programme has been successful in achieving its community-building objective. The programme has resulted in important and fruitful new academic/academic and academic/industrial partnerships. Several new follow-up projects have already emerged, for instance, within the FES NanoNextNL programme, the Open Technology Programme, and the recent STW-TKI HTSM programmes. In addition, the MuST programme has lead to, for instance, part-time appointments of industrial participants at academic counterparts, to joint supervision of final projects of BSc and MSc students, and to appointments on industrial advisory boards. More generally, the MuST programme has provided a comprehensive overview and awareness of, on the one hand, the Dutch academic environment in the area of multiscale computational techniques and,

thirteen Postdoctoral researchers have worked within the MuST programme.

The MuST programme has so far resulted in fifty-two journal publications1. In addition, twenty-one journal publications are currently under review or are in preparation and fifty refereed conference proceedings have appeared. Because several projects are still in progress and the output from recently finished projects is not yet completely consolidated, it is anticipated that the overall output of the programme will increase even more. Many publications have appeared in top-tier journals in the field. An aggregated overview of the output of MuST is provided in the List of publications.

The Multiscale Simulation Techniques programme has also contributed to the development of various open-source software packages, such as the MercuryDPM package (www.mercurydpm.org) for discrete-particle simulations and the Nutils library (www.nutils.org) for finite-element computations. Furthermore, many specialized user-defined subroutines for commercial software packages have been developed within the context of MuST.

Community buildingThe Multiscale Simulation Techniques programme has assembled researchers from nineteen different research groups, affiliated with the three universities of technology in the Netherlands, namely, Delft University of Technology, Eindhoven University of Technology and University of Twente, with the University of Groningen and with the Centre for Mathematics and Computer Science. In total, more than sixty industrial representatives from over thirty


and of the 3TU Center of Excellence Multiscale Phenomena in Fluids and Solids. The enhanced contacts between the MuST researchers have also contributed to the establishment of the NWO graduate programme Fluid and Solid Mechanics; see www.3tufsm.nl > gp-fsm.

Within the various MuST projects, there have been extensive collaborations with international research organisations, in particular, via user committees and via extended research visits of the principal investigators and junior researchers; see, for instance, the interviews with Stefan Luding on page 64 and with Timo van Opstal on page 91.

on the other hand, the main industrial parties in this field and their needs and challenges. The MuST programme has not only led to an infrastructure in terms of concepts and methodologies, but also in terms of personal contacts.

Platform functionThe Multiscale Simulation Techniques programme has provided an effective platform for cooperation between academic and industrial partners, from which many successful academic/industrial collaborations have emerged; see the above Section ‘Community building’. The MuST community sustains strong ties with several other organisations and networks. Many of the principal investigators in MuST are affiliated with the national research schools for fluid and solid mechanics, the J.M. Burgerscenter (JMBC) and the Engineering Mechanics (EM) graduate school, respectively. Accordingly, virtually all junior researchers in the MuST programme have been embedded in one of these two research schools. Moreover, the connections in MuST have contributed to further collaborations between the two research schools, e.g., admission to and recognition of mutual courses. In addition, MuST has been instrumental in the establishment of the course Advanced Topics in Solid Mechanics within the programme of the EM graduate school. The connection between MuST researchers affiliated with the EM and JMBC graduate schools has moreover led to exploratory discussions on a joint JMBC/EM course on multiscale phenomena and techniques.The MuST community also represents a significant section of the 3TU Center of Competence in Fluid and Solid Mechanics, 1 Reference date: 1 October 2013


— The MuST programme has made a significant contribution to the scientific development of the field of multiscale simulation techniques and simulation-based engineering. Due to the focus on solid mechanics and materials, which emerged in the initial stages of the programme, the main contribution has been in these areas. However, important scientific contributions to other fields have been established as well, in accordance with the intended generic scope of MuST.

— Multiscale simulation techniques continue to form a very active field of research, nationally and internationally. The MuST programme has played an important role in keeping the level of Dutch multiscale science and engineering at par in the international

research arena. MuST has also catalyzed new initiatives, such as the Multiscale Institute at Eindhoven University of Technology.

— The MuST programme has made a significant contribution to the development and improvement of new numerical techniques for multiscale problems in the Netherlands, including discrete-particle methods, molecular-dynamics, numerical homogenization, fibrous-network models and adaptive methods.

— The building of a community of research organisations in multiscale simulation and engineering has been predominantly successful. The MuST programme has assembled many of the most important academic researchers in computational fluid and solid mechanics in the Netherlands and connected them with researchers in relevant industries. Existing contacts have been reinforced and new academic-industrial, academic-academic and even industrial-industrial contacts have emerged as a result of the programme.

— Several programme symposia have been organised with plenary presentations of all projects and interactive poster presentations by junior researchers. These programme symposia have provided an effective means for networking, reinforcing coherence and establishing knowledge spill overs.

— The MuST programme has yielded a high

Conclusions and recommendations


scientific output: so far, fifty-two journal publications have appeared, twenty-one journal papers have been submitted or are currently in preparation and fifty refereed conference proceedings have appeared. Because several projects are still in progress (the last project in the programme is scheduled to end in February 2015), the overall output of the programme is anticipated to increase even more.

— Active participation of industries in the MuST programme has been promoted by cash and in-kind contributions. The active participation of industries has been successful in most projects, but not

uniformly throughout the programme. In some projects, industrial participation faded. Three main causes can be identified:• In some projects, the industrial

partners could not fulfill their intended role and/or obligations on account of internal strategic realignments related to the financial crisis;

• Close collaboration with industry in the context of a programme with a generic methodological scope is nontrivial, since industries are often focused on solving specific problems directly connected


has been established in the educational programme of the Engineering Mechanics graduate school. The two programme symposia have also strengthened coherence. Further enhancement of coherence in the programme was impeded by three main causes:• Due to the extensive start-up period

of the projects, spanning almost three years, the projects were out of phase. The junior researchers in the first cohort were in the final stages of their project when the final cohort started;

• In the organisational setup of the MuST programme, only a single person was charged with coordination, namely the programme director. Due to the departure of the first programme director, the process of providing and reinforcing coherence was halted over an extended period;

• As a result of the generic character of MuST, the interaction between projects has generally been indirect and, consequently, no larger clusters emerged.

In relation to the last item, it has to be remarked that the wide scope of the programme on the other hand provided a good basis for establishing new contacts.

— The programme covered a single round of calls for projects. Coherence, continuity and reinforcement of the MuST community and, notably, academic-industrial partnerships would have benefited from an extended programme

with their business. In addition, numerical simulation, despite its high technological relevance in advanced industries as a research tool, is generally pre-competitive and the impact on day-to-day operations is often indirect;

• The research in a few projects deviated significantly from the original proposal.

— Coherence in the programme was partly accounted for by participation of most of the junior researchers in meetings of the Engineering Mechanics and JMBC graduate schools. A new course on multiscale aspects in interface problems

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scale-bridging numerical methods for high-tech materials.

— Multiscale science forms a broad and complicated research field. Despite the significant progress that has been achieved within the MuST programme, many questions and challenges are still open, and many opportunities for application in industrial environments are still unexplored. To maintain the strong position of fluid and solid mechanics in the Netherlands in the area of simulation techniques for multiscale problems, further consolidated research programmes are required.

— Knowledge transfer from academia to industry via software is a recurring challenge in many programmes and projects. The challenge emanates from the fact that software platforms that provide dedicated support, such as commercial software and general-purpose third-party open-source software, do not generally provide enough flexibility to implement advanced state-of-the-art numerical techniques, while in-house codes which do provide the necessary flexibility, are often not adequately supported. There is no one-size-fits-all solution to this problem. Continuity of the academic-industrial collaboration over an extended period is an important factor in bridging the gap. Another partial solution would be to allocate budget to enable academic groups to release and support their software in open-source form. In this manner, the role of software as output of research projects can also be reinforced.

— The intermediate role of research institutes such as TNO between academia and industry can be further

with multiple calls. Dedicated long-term relationships between academia and industry are generally necessary to establish effective interaction. It typically takes eight years to progress from first theories to applications. Academic-industrial collaborations over an extended period are therefore particularly important to research programmes addressing generic methodological subjects, such as Multiscale Simulation Techniques. MuST projects in which the industrial-academic collaboration was particularly successful have resulted in follow-up projects or are anticipated to do so in the near future. Such follow-ups will however occur external to the MuST programme and, generally, without mutual interaction.

— Continuity of research programmes addressing the development of numerical-simulation techniques, and academic-industrial knowledge transfer via software, are often challenging: Academic codes are generally developed within a specific context without regard of long-term support. Commercial codes and general-purpose open-source platforms, which typically provide better support, are generally unsuitable for developing novel and advanced numerical techniques.

Recommendations — To reinforce the Multiscale-Simulation-

Techniques community, a follow-up programme should be organized, encompassing the most successful academic-industrial partnerships in the MuST programme. It is recommended that such a follow-up programme targets a more specific area with high potential for academic-industrial partnerships, e.g.,


should then be started in a confined time window to retain coherence.

— To ensure continuity of the STW support and administration of a research programme, it is recommended that each programme is assigned a deputy program officer in addition to the program officer. Monitoring of projects can be further improved, for instance, by having annual project-review meetings between the STW-program officers and the programme director or the managing board. It is to be noted that the latter measure has already been installed in later Perspective programmes.

formalized in research programmes to strengthen continuity. Intermediation of TNO moreover provides an effective and fertile route of dissemination of research on multiscale computational methods to small and medium-sized enterprises, which, as opposed to large high-tech enterprises, do not generally have the research capabilities and organisational infrastructure to optimally benefit from and actively support the development and application of such methods.

— To enhance coherence in research programmes, it is imperative that all projects are started in a confined time window. Multiple, sequential calls for proposals within a research programme can benefit continuity and effectiveness of academic-industrial collaborations. The projects granted within each round

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‘ It would be good if research programmes were organised for a longer period’

Herman Wijshoff


As a researcher at the Research and Develop ment department of Océ Technologies Dr. Herman Wijshoff has a long-time experience with collaborations between industry and universities. Since 1997 he has been involved in the inkjet research programme, in close co-operation with the University of Twente in Enschede, where he received his PhD degree in 2008. Wijshoff is also university researcher at Eindhoven University of Technology. We meet at Océ R&D in Venlo, where we talk about his experiences as a member of the MuST programme committee.

How did you get involved in the MuST programme?‘Since more than ten years it is my duty to look for academic partners that can contribute to the trinity of theory, measurement and simulation technologies, in a way that enables Océ to make progress. My own first experience of doing fundamental research with an academic partner was sixteen years ago when we were developing a print head that generates droplets using acoustic principles, together with Prof. Henk Tijdeman in Twente. With Prof. Detlef Lohse we started a research programme on drop formation and the influence of air bubbles. Trough this STW-project our academic network quickly grew. I manage these collaboration projects on inkjet now, together with my colleague Hans Reinten. In this capacity we are asked to take part in all kinds of committees, like the Phenomenological Physics advisory board of FOM, jury panels for STW, the advisory boards of the J.M. Burgerscentrum and the Graduate School for Engineering Mechanics. So we know many people, including René de Borst and Harald van Brummelen, who were starting up the MuST programme. They asked me to join the programme committee. Together we discussed about how this programme should be organised.’‘At that time we were working at Océ on quite a few fluid-solid interaction problems, which in our case is for example the behaviour of ink droplets on printing media. We are studying 10 micron droplets, penetrating

Interview


We try to understand how paper deforms under influence of heat and humidity, experimentally as well as numerically. As a result of this meeting we have defined an M2i project together, to study paper as an advanced material.’‘Another topic was delamination of thin layers. The newest generation print heads is based on the thin layered structures of piezo crystals in silicon MEMS structures. These print heads are not meant to be disposed off after a short time, they should operate at least for five years. Therefore delamination of thin layered structures is a hot topic for Océ now. We have a NanoNextNL project on this subject now, together with groups at Delft that we met during a MuST day.’‘During the last MuST programme meeting Stefan Luding presented his work on porous media. That stimulated me to read Kazem Yazdchi’s PhD thesis and this again provided me new ideas for collaboration. In this way every general MuST meeting was useful.’

How hard is it nowadays to find funding for numerical developments?‘This period is not easy. Numerical work is typically one of the fields where budgets are easily cut. And when we start a new numerical collaboration project at Océ, it will be probably part of a new programme. And unfortunately every time these programmes conjure up some new construction, which implies another quarrel about contracts, IP-regulations and so on. Our company lawyers always say: ‘Hey, there you are again? Do you have some new contract issue?’ ‘It would be good if research programmes were organised for a longer period with a wider scope. There are examples of FOM programmes, like Dispersed multiphase flow, that were organised in different phases.

100 nm sized coating particles on paper, to produce up to 10 meter long print. So we had to control the quality at all scales from 100 nm to 10 m, and all physical processes that take place on time scales from microseconds, like the behaviour of small droplets, to many years for the colour fastness of the print. Multiscale methods are indispensable to do this.’‘In the programme committee we actually decided to focus the MuST programme more on solids and less on fluids. The idea was that the FOM programme Dispersed multiphase flow was ending and we knew that FOM wanted to start a new programme focussed on fluids, called Changing flow. This was actually cancelled later on. Personally, I was disappointed, because most of our own questions were related to fluids. I was even considering to give up my position in the programme committee, knowing that we could not work on our fluid related topics. But in retrospect I must say that the focus on solids worked out very well for us.’

New collaborations

Once the MuST Programme started, Océ got involved with several projects. How did that go?‘Ron Peerlings and Marc Geers studied the behaviour of cardboard, in a first meeting they mentioned the use for emergency shelters in third world countries. When used in the tropics the cardboard faces conditions of high temperatures and high humidity. Peerlings and Geers wanted to find out how the strength of cardboard can be preserved, using multiscale methods. The presentation of this project, at one of the general MuST programme meetings, triggered us. There are many similarities with the influence of ink droplets on printing media.


committee. Our role was mainly facilitating the general meetings, and I think especially the mid term programme day brought several projects together. But to be honest, I would not have spent more energy on the programmatic level of MuST. That would have taken everybody’s time, also from professors and PhD students.’‘When you are talking about numerical codes you got a point. But without big investments you cannot develop an open platform. We did not plan to do that from the beginning, and I sincerely doubt if it would have been useful. Open platforms that are successful operate on a much larger scale than the MuST programme. With this diversity of topics I think lots of resources would have been spent on something we would not have been able to bring to a usable level. When MuST started, OpenFoam was still at an initial stage. The best thing is to stick to current developments. In a new programme we could consider to use OpenFoam, and other platforms that exist for fluid dynamics and other fields. There is no need to re-invent the wheel.’

Generic projects

Are companies interested in collaborating with projects when they are very generic?‘For big companies that is no problem. Involving small-sized companies is a problem in general. I don’t know how to do that. Many small-sized companies have relatively short-term vision and PhD projects are often beyond their horizon. Programmes trying to associate these companies, initiated in the past, are therefore often not very succesful. Of course there are exceptions. What works better is probably TNO’s technology transfer.’‘It can be problematic too that the project administration has to be organised according

After five years there was a second call. The quality of the second call programme was absolutely better than in the first round. Initially you cannot know which projects are going to work out well, but after five years the most promising developments are visible. I think that the quality of programmes could still improve with a third call.’

Administrative fuss

Is Océ also collaborating with foreign universities?‘Until last year I was only looking for academic partners in the Netherlands. That was more than enough, and funding possibilities were also plenty. But in the last years everything is getting more difficult and that is not going to get better soon. At the moment we are examining the chances Brussels is offering, but it is hard to find our way around there. Unlike Océ, University of Twente has for example their own people in Brussels. Maybe we should join forces. In NanoNextNL circles we have the same kind of discussion.’‘At the moment we are involved with a COST action, Smart and green interfaces: from single bubbles and drops to industrial, environmental and biomedical applications, which is really relevant to our inkjet process. But I do know that Océ will not easily act as chairholder of such projects. The administrative fuss connected to them is tremendous, so we rather join a more experienced party.’

There have been comments about the lack of coherence between the MuST projects. How do you think about that?‘In the beginning there has not been much interaction between the different MuST projects, to the knowledge of the programme


Do you think it is problematic that PhD’s move on to another country once they finish their project?‘Well, it hardly ever happens in our projects and when we really want to work with someone we do our best to persuade this person to stay. The last time it happened we could make a deal that this researcher stayed with us for three months to pass on his work, before accepting another job.’

Is there going to be a follow up for the MuST programme?‘Yes, but we are still discussing if it should be organised like a Perspectief programme or rather like a Partnership programme. One of the comments on the Perspectief programmes is that they should be more focussed, but I would regret that. I liked the broad framework of the MuST programme. It paid off through the contacts we made with the projects on porous media, coatings, and delamination. Those topics are quite far from each other, and I have been acquainted with these subjects because of the wide scope of the MuST programme.’

to accounting standards, also for the justification of hours and use of equipment. Océ once had to withdraw their contribution that consisted of the use of equipment, because we used a simple notebook, which was not accountable. These things can also be problematic for small-sized companies.’‘We would never ask a PhD student to do a project on ink composition, because we don’t want these kinds of results to be published. But numerical projects are often generic and well suited for PhD projects. Scientifically the most interesting aspect is the core of a numerical programme. We need numerical specialists to find out how in general we solve these problems, what kind of discretisation method is needed. Those things can be published without any problem. At the moment we have more than twenty PhD students from various programmes working on some aspect of the inkjet printing process.’

Researchers in the MuST programme sometimes experienced a dilemma, the choice of spending time on solving problems for a company versus writing publications.‘I suppose that people forget that the business world in the Netherlands is really small. When you solve some problem for a company like Philips, Océ or Shell, soon everybody knows it. But it is hard to make these achievements visible in a way that is also recognized in the academic world. So I do understand this feeling, because there is nothing written in black on white. Companies do not publish many papers and universities only count publications. That is why they cause an avalanche of papers. Sometimes papers appear to be written just to increase the numbers instead of to contribute to science.’


MuST, together with SmartSiP, is STW’s first Perspectief programme. In 2006 STW had the idea to combine several projects, globally in the same research area, to gain momentum in that field. By that time the areas computational material science and systems in package were defined and Dutch researchers in general were asked to write a programme proposal for both subjects. Subsequently two calls were opened and every interested researcher could apply with a project proposal. That is how MuST (and SmartSiP) started. In this interview STW looks back at the organisation of the MuST programme.

In retrospective, how does STW assess the organisation of the programme? Have things been changed meanwhile?In 2007 STW changed the organisational set-up of the Perspectief programmes, in a way that a larger quantity of qualitatively good programmes became eligible for funding. The Perspectief-programme became an open competition for programme ideas, followed by an open competition for projects within the allocated programme-ideas. The present set-up, four years old by now, is an open competition for complete programmes including projects, to further enhance and secure coherence and co-operation within a programme.

Regarding the organisation of Perspectief programmes STW has learned a lot of the MuST programme, among others. The organisation has been adapted so that it focuses more on coherence and co-operation, which had been intended from the beginning. One example is that nowadays we organise a meeting of the programme commission with the STW-program officer every year to discuss the status of the entire programme and to adapt it if necessary.

How generic and coherent does a research programme like MuST have to be?STW does not want to decide about generality, including cohesion, as a quality. STW facilitates an independent expert review by referees and a jury. Evaluation of the former Perspectief programmes showed

STW, Questions and answers about the MuST programme


they should be willing to invest in the implementation. In practice the project should bring the algorithms to a level where companies can assess the value, so they can decide if they want to bring it to a higher level. This pathway is different for each and every project and algorithm.

Is there a way that STW can prevent research results getting lost when PhD students leave?We do not believe that research results get lost. Often we see that researchers continue doing their research, either within the university or in a company. That helps to secure continuity.But algorithms are hard to keep: in many cases only the programmer understands the code and special software is hardly ever well maintained. Decay of code could be prevented by good education and supervision of programming PhD students. One advice: try to continue building on existing software whenever possible, and try to avoid using ad-hoc codes and reinventing the wheel. But we have to admit that it is hard to build upon existing software, when developing fundamentally new algorithms and methods. Still researchers can do things to improve the situation, like adding extra comments in their code, and adding them to their publications or creating a Wiki that is commonly available.

Does STW try to relieve the administrative burdens of projects for applicants and users?STW realises very well that project administration can be experienced as a burden and minimising the administration continuously is a point of special interest for us. But research funding has to go hand in hand with a certain amount of organisation, guarantees and accountability,

that cohesion between the projects is an important condition. With our Perspectief-set-up today, that also focuses on co-operation and coherence, we see that the programmes obtain stronger networks, produce more excellent research, which results in more knowledge transfer between the participants.

Utilisation of software developed in research programmes has its own issues. Academic credits are absent, patents are hard to obtain and researchers struggle with the question how much time to spend on implementation. What are the experiences and policies of STW about this issue?It is true indeed that software takes a special position. The mission of STW is knowledge transfer, so the development of applicable algorithms fits well within the objectives of STW. Obtaining a patent only fits within STW’s objectives, when the patent enhances knowledge transfer. In most cases it is possible to transfer software directly to an interested party, or to publish it in open source format, comparable with a publication. Another question is who has to make the effort to implement algorithms, that have been developed in a project, for a company. That is absolutely not meant to be part of the work within the research funded by STW. There are several ways to deal with this issue. The main ‘products’ of the STW funded research are the excellent researchers. Because of the intensive contact between researchers and companies through the user committee meetings every six months, PhD students often end up working at one of the contributing companies in the project. That creates possibilities to develop software further, make it user-friendly and to implement it. When a certain company is really interested in some special software,


is problematic when these agreements do not match with company policies. Then STW looks for a solution in close consultation with the company.

University funding is under pressure. Is that a reason to adjust STW-project funding?No, it is not STW’s responsibility to counter-balance budget cuts. But researchers tend to be more oriented towards funding by organisations like STW, when universities cut their research budgets. STW divides the resources in open competition through the process of peer review, involving (inter)national experts, followed by the assessment of a professional jury. This process secures the high quality of the awarded research projects.

and unfortunately a part of the paperwork has to be done by the beneficiaries. That is unpleasant and STW tries to give as much help as possible to reduce the administrative burden. And STW will never ask for paperwork for the sake of the paperwork.

Also, STW has relatively little administrative obligations for participating companies. The fact that STW is a publicly financed organisation, guarantees that we do not offer illegal state support. That is also why matters regarding co-financing and intellectual property have to be well-regulated. Fortunately we can use standardised agreements, that are well equipped and adapted and in fact they are ready to be signed in a moment. Sometimes it


Companies are still very enthusiastic about participating in STW-projects, thanks to the researchers who have successfully involved companies in the utilisation of their research. And also thanks to the companies that have found their way to the research institutions to meet their need for innovation. Especially in times of financial decline it is wise to invest R&D budget in STW-research, because it opens doors towards a multitude of generated knowledge. Working in public-private consortia, like Perspectief programmes, is an ideal instrument to yield more than the product of its component parts. Apart from industry-university relationships also new university-university relationships and industry-industry relationships arise. This proves that the STW-policy works and that companies find their way towards innovation through co-operation in financial troubled times.

Does STW have ideas about stimulating the participation of small and medium-sized companies in these programmes?The organisation of our co-financing facilitates exactly the participation of small and medium-sized companies in our projects and programmes and we experience an increasing involvement of these companies. Often they participate in the form of a consortium with other companies. In the programmes the participation of a big contributor is regularly required to acquire enough co-financing. But, there is no minimum amount of co-financing for a participating company, so in that way there is no obstacle. Moreover, within the STW-projects there is no competition between participating companies; one rather speaks of ‘conculega’s’ in Dutch, which means competitor and colleague in one. Companies

Researchers desire to be able to work in a flexible way in a project. Circumstances can change, contributing companies can strike out a new course or they can go bankrupt. New understandings can be a reason to change the direction of research. To what extent is it a problem to change the direction of a STW-project underway?That is no problem. Circumstances and insights change inevitably. It is wise to allow for the freedom to reorganise the research, so that project leaders and researchers can deal with new situations and understanding, to come to the optimal result. Every six months we organise a meeting for each project where the researchers, contributing companies and a representative of STW gather. That is a good moment to adapt a project, if necessary.

Does STW play a part in stimulating long-term relationships between researchers and companies?Stimulating contacts between researchers and companies is core business of STW. The organisation of our programmes and projects, with user committee meetings for everybody who is involved twice a year where everyone gets to know another, creates a robust network between researchers, users and STW. Those networks still exist and are useful long after a project has ended. In addition, for instance all Perspectief programmes organise an annual meeting for all participants of all projects to improve cross-fertilisation. On a regular basis STW organises, by special request or not, match-making meetings between researchers and companies to stimulate this co-operation.

Does STW experience that co-financing by companies is under pressure?


have to take the initiative. A potential new MuST2 programme will have to prove itself in open competition with other programme ideas. We believe that a good consortium with commitment of industry and smaller businesses will be able to create a good profile to compete in the Perspectief-call or as a Partnership programme.

with common interests are looking for mutual synergy. To conclude, recently we made it possible to start up an initiative within the Partnership programme as a consortium, for the benefit of small and medium-sized companies.

There can be a tension between the questions from the participating companies and the academic interpretation of those issues. What are STW’s ideas about this? What is a good way to unite the expectations of users and researchers?Bringing together expectations of companies and researchers is something that is embedded in all STW-processes. Already when a proposal is submitted the applicants have to elaborate about utilisation possibilities. In the peer-review process scientific quality and utilisation strategy quality have the same standing. Also, every six months these expectations are on the agenda in user committee meetings and, if necessary, they are readjusted. All these efforts cannot prevent that frictions arise in mutual expectations, every now and then. There is also a responsibility of the participants; always communicate clearly and speak out, keep to your agreements or discuss why you want to change course. Keep in mind that a contented co-financier may also be a future co-financier or, the other way round, as a company consider that the brilliant researcher can fuel tomorrows innovations.

What are STW’s ideas and desires regarding a follow-up of the MuST programmme?STW realises that a follow-up can anchor the MuST research and prevent the evaporation of this large-scale co-operation. However, the researchers and the companies involved


32 Dynamics of aerosols in turbulence

Bernard Geurts

36 Multiscale mechanics of fibrous networks ‘From fibre to tissue’

Ron Peerlings

40 A multiscale approach towards integrated cohesive interface elements

Marc Geers

44 A multiscale methodology for the analysis of metallic interfaces

Erik van der Giessen

48 Multiscale computational poromechanics

Jacques Huyghe and Joris Remmers

52 New simulation techniques for flows interacting with transforming structures

Hester Bijl

56 Multiscale model adaptation for dynamic performance of multiphase materials

Sergio Turteltaub

60 The start up of lighting and lightning: Streamer discharges in lamp ignition, electric switches and materials processing

Ute Ebert

64 Hierarchical multiscale modelling. A single data structure for micro-macro and multi-phase/field models

Stefan Luding

68 Multiscale simulation of multi-material adherence

Bert de With

72 Adaptive multiscale methods for airbag-deployment-safety simulations

Harald van Brummelen

76 Experimental and computational techniques for the design of impact-resistant materials

Bert Sluys

80 Lagrangian ‘mixing analysis’ of heat transfer: a new way for thermal optimisation

Michel Speetjens

Interviews with principal investigators


Dynamics of aerosols in turbulence

Prof.dr.ir Bernard Geurts

University of Twente | Duration: 1/11/2008 to 30/11/2011


IntroductionCombustion fumes emitted by diesel trucks are one of the main causes of air pollution. Filters catching the small sized soot particles in the fumes can partly solve the problem, but using them costs extra energy and the filter can clog up. There might be a smart way to help catching away the soot. Particles in a gas stream tend to migrate towards the surface of a pipe, a phenomenon called turbophoresis. In the truck there is a large temperature difference between the cold surface of the exhaust pipe and the hot exhaust fumes. This temperature gradient enhances the movement of particles towards the surface of the exhaust pipe, a process called thermophoresis. The question is how we can make use of thermophoresis in order to direct the migration of particles in a flow, for instance towards a filter.

Science and utilisationBernard Geurts holds a chair in Multiscale Modelling and Simulations and his work concentrates on multiphase flows. Talking about this project his enthusiasm immediately returns. Geurts: ‘This work is in the veins of my group’.The objective of the project was to build an efficient multiscale fluid mechanics model with particles undergoing phase transitions. Physically a gas flow with particles or aerosol transport is a complicated process, especially when the sizes of the particles change by collisions and phase transitions like condensation and evaporation. The flow of exhaust fumes is basically determined by the velocity of the gas phase, but it is affected by by the soot particles in the gas flow, or in the case of an aerosol by the moving droplets. Geurts: ‘We wanted to develop a consistent multiscale model in which different length

and time scales were represented. Building the coupling between the scales was one of the biggest challenges.’The concentration and energy, mass and momentum of the particles, derived from the lower scale model are coupled to the continuum scale, which describes the gas flow by Navier-Stokes equations and produces the picture of the overall transport behaviour. The particle processes have to be taken into account on a much shorter length and time scale, and e.g. the temperature and mass of the particles can be put into a discrete Lagrangian point-particle model. Form factors of the particles could be important, but that’s on the verge of the impossible. The differential equations become increasingly more complex when ever more properties of the particles are taken into account. Geurts: ‘For a soot particle 30x30x30 grid points in 3D might be needed, that’s beyond the limits of computing capacity and costs. You need to add a little well dosed imagination in order to reduce the complexity somewhat and be able to deal with the problem within the limitations of expensive computer time. As a mathematician I have to decide how many details I can leave out, without destroying the general picture. Computations get faster and cheaper as information is omitted, but then they are meaningful only in a well defined working area. It’s always a matter of compromise to get an average view of the problem, but you can even work out a theory for the procedure to homogenize the terms in order to make the results a little smoother. In this way you can generate a cheaper model, which is efficient enough but not very general. It’s like holding a wet bar of soap. Squeeze it and it shoots out of the other side of your hand. That’s the game and you can do

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problems is in demand. And the work often takes longer than the funding. Two PhD students in Geurts’ group are working on similar projects dealing with turbulent flows with phase changes. One project is part of the FOM Droplets in turbulent flow Programme. Geurts: ‘It focusses on mathematically the same problem, but now we take the process of evaporation and condensation into account, like in the sudden appearance of fog. In this FOM programme eight PhD students collaborate with simulations and experiments, unlike this MuST project, in which there was only one PhD and no experiments. A current STW-project deals with pyrolysis of wood chips, also a problem of particles with a position, temperature, mass and velocity. In the future we will study the dispersion of an aerosol from a medical inhaler into the lungs: we could find out how big the droplets are, where they end up in the lungs and what the chemical composition is.’

nice and decent mathematics with it’.Truck producer DAF took part in the user committee, the company was interested in how many particles can be caught using a temperature gradient, in order to develop cleaner diesel exhaust devices. Other users were software developers ANSYS and ASCOMP, who were interested in the algorithms and computational methods developed in this project.The project was discontinued midterm, when it became clear that the expectations of the project leader and the junior researcher on the project, Briti Deb, had diverged.

HighlightsNo papers in scientific journals appeared, but there have been contributions to a Burgers Centre workshop and to a number of international conferences.

Follow up projectsA more fundamental look at technological

1 Automobile exhaust gas. Photo: Rderijcke Wikimedia Commons


OutputGeurts: ‘We wanted to contribute to an engineering tool for designing industrial processes and we had commercial software partners who were interested in the end product. We were building a new method in our own code. Making software is ‘interesting’, but only in the British meaning of the word. It does not count for your track record. Young people in the beginning of their career should not spend too much time implementing software for partners. From the perspective of their scientific record this is time wasted. The only output that counts in the scientific world is a thesis and scientific papers that contain the ideas. It’s a bridge too far to go from thesis to implementation in our partner’s commercial software. To make this step you need some bright people with a lot of time. In a project like this it could be done by an experienced post-doc, who can pick the fruits from the work of a PhD student and translate the models to community code, for either commercial or open source platforms like OpenFoam.’

PeopleBriti Deb is working on another PhD project at the University of Tartu, Estonia.


Multiscale mechanics of fibrous networks ‘From fibre to tissue’

Dr.ir. Ron Peerlings

Eindhoven University of Technology | Duration: 1/08/2008 to 22/1/2013


IntroductionCelebrities in illuminating gowns light up stages since Philips showcased this kind of wearable technology at a German consumer electronics fair in 2006. Philips is developing electronic textiles, not just for fashion stars to shine, but mainly for medical applications. LED light sources could provide a medical treatment for skin problems or relieve lower back pain. Sensors embedded in textile could monitor your health. Even if the conducting wires and electronic components in the textile are protected by a polymer encapsulation they are relatively vulnerable. When textile deforms the yarns and wires rotate and slip over each other and high tensions occur, damaging the relatively rigid conductive wires and electronic components. Lesser goddesses might want to wear their dresses for more than one night and for medical applications durability of electronic textiles is of course a major issue.Cracks in cardboard, easily formed while creasing or folding the material, originate from broken fibres and bonds at the micro level. For economic and environmental reasons less material and recycled (shorter) fibres are used for the production of modern cardboard, making the material even more vulnerable. A model describing cardboard or paper as a uniform material is unrealistic because the interactions between the fibres forming the network structure have to be taken into account. On the small scale the problem of crack forming can be described in a similar way as the damage occurring in electronic textiles. A good model for the failure of networks of fibres should describe the interactions between hundreds of thousands fibres, but it would take weeks or months to compute all the interactions involved. Ron Peerlings: ‘We wanted to

take into account the network structure of the materials and build a bridge between application-scale models and the models for individual fibres.’

Science and utilisationPeerlings’ group worked on similar problems before this MuST project started. Ron says he was lucky that his former master student Lars Beex (see page 86), who had worked on the cardboard problem as a master student, was interested in the PhD position: ‘I had to compete for him with a colleague.’ The biggest challenge was to model the behaviour of a complete product with a length scale of tens of centimetres to meters, whereas the size of fibres and yarns is in the order of microns or millimetres. Lars Beex supervised, among others, master students Cyriel Verberne and David Wilbrink who built small scale models and characterized electronic textiles experimentally. The master students did experiments on the stretching and punching of a 10 by 10 cm piece of electronic textile and parametrized the microscale model. Lars Beex focussed on the core of the project, the generic computational tools to bridge the scales.Peerlings: ‘Philips was a good supporter of the project. They provided electronic textile samples and paid a fee to the master students who were doing their work in the company’s lab. That was very attractive and students also regard Philips as a potential employer. When an industrial partner pulls harder, the project shifts a little towards them.’Users committee members Smurfit Kappa, Kenniscentrum Papier en Karton and Océ were interested in the modelling of cardboard and paper. Peerlings: ‘The fibre model appears to be not as realistic yet compared

1/2 Microscopic images of fibrous materials: paper and electronic textile.

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to atoms, but when I pull one yarn there’s friction when it slips over the others. Once released it does not slip back. We had to account for this dissipation effect. Another main issue was how to select the grid points that are taken into account. We proposed a new summation rule that works out better for our kind of materials than existing methods. We’ve delivered the proof of principle that our model works for electronic textile. Lars Beex was very productive and there will be six refereed publications in the end.’

Follow up projectsPeerlings: ‘New projects are a bit difficult these days. The expected contribution from industrial partners in new projects has increased, and for most potential partners this is a problem. Potential partners say they have to make choices. That’s a pity because I would like to continue. There are few exceptions, like Océ. They got involved during this project and at the moment we have a joint M2i project about the effect of moisture on paper. The reaction of an individual fibre on moisture is partially known, and we want to characterize it experimentally.

to the electronic textile. We noticed there was a gap between the level of detail of our knowledge and what a paper producer can practically use.’‘We also wanted to work on biological fibre networks like collagen, that’s why Philips Medical Systems and QTis/e were members of the users committee. But biological tissues are adaptive, they react on mechanical loads and that was a bit too ambitious for this project. We tried to set up a graduation project for a master student but no student applied.’I don’t think our users will start using our methods tomorrow but we have made a step towards the usability of this kind of network models. We laid a foundation for applications.’

HighlightsLars Beex set up a discrete model based on a method known for atomistics, the quasi-continuum method. This method had never been used for fibrous materials. Peerlings: ‘We had to add some effects that are irrelevant in atomistics. Interactions of atoms are reversible. In our models, the contact points of the yarns in textile are equivalent

3 Two steps in the quasicontinuum method. In the left image the full lattice model is shown. In the center, an interpolation triangulation is superimposed on the lattice model and a small number of lattice points are used to sample the governing equations in the right image.

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The interaction of many fibres in a network will be affected by moisture too. Fibres are connected to each other and they can come loose or make new bonds. A sheet of paper will react in a certain way and we want to relate that to fibre scale processes.’It would be great to continue under similar conditions and make a next step in a second MuST-like programme. Industrial partners would certainly be interested. It seems to me MuST fits without any difficulty into multiple Roadmaps of the Topsectors defined by the Ministry.

PeopleLars Beex is Lecturer at the Institute of Advanced Materials and Mechanics, Cardiff University, UK.Cyriel Verberne is engineer at Tegema (engineering services).David Wilbrink is trainee supply chain at AkzoNobel.

Co-applicantsDr.ir P.H.M. Bovendeerd (TU/e), Prof.dr.ir. Marc Geers (TU/e)


A multiscale approach towards integrated cohesive interface elements

Prof.dr.ir. Marc Geers



IntroductionBendable, rollable, and foldable displays and solar cells are lighter and thinner than conventional devices, and can be used for many new applications. The flexibility affects the way in which connections between electronic components are designed. The maximum elastic deformation of 10 cm straight copper wire is less than 1 mm, whereas a similar piece of synthetic rubber can easily stretch up to twice its length. The electrical wiring can be shaped like a spring, but still this is not a long-lasting solution. In time the copper separates from the polymer substrate and the flexible electronic device may fail. Comparable problems occur in polymer coated steel, used for food packaging or even in pre-coated vascular stents. After delamination the steel corrodes, the food decays, or the stent coating releases prematurely during unfolding.Observed through a microscope, the process of delamination in stretchable electronics becomes visible through the formation of many tiny polymeric fibrils, much thinner than hair. These fibrils can break or detach from the interface. The multiscale physics of this complex delamination process is yet poorly understood.

Science and utilisationThe energy needed to separate the bonded layers at an interface can be measured in the lab. It turns out to be several thousands of Joules per meter square for a copper-rubber system. With existing macroscopic models it was possible to predict the process of delamination with a limited degree of accuracy. The observed mechanisms at the molecular scale cannot trivially explain what is measured at the macroscopic level. The known mechanisms of physical

adhesion of fibrils account for only 1 Joule per meter square. ‘The physics incorporated in the macroscopic model is incomplete’, says Marc Geers, ‘so the predictive value of the macroscopic model remains limited’. Identifying the origin of this apparent contradiction between the macro- and molecular scale was one of the biggest challenges in this project. Geers: ‘So far, we have incorporated physical mechanisms reaching 100 J/m2 after scale bridging, so something is still missing’. Postdoc Mathieu Solar in Groningen studied the physical mechanisms of stretching and detaching molecular chains in a polymer network. This part of the work has been finished. In Eindhoven, PhD student Bart Vossen developed the generic multiscale model. At this moment, he is taking a closer look at the dissipation and delamination at the length scale of fibrils. Geers: ‘We need quantitative input resulting from the microscopic model from Groningen. Even though some numbers will still be missing, we expect to be able to continue with the multiscale model nevertheless. The qualitative multiscale model and the physical insight is the major outcome of this project. Results could have been more quantitative if we could have worked in a synchronous manner. But those are things you cannot control.’The fibrils are modelled on two different scales, which can be connected. Geers: ‘Looking at the fibril scale means that we had to make a choice for a specific material, PDMS (a silicone rubber), which is used in flexible electronics, for instance by Philips, one of the users. A master student is working on a series of experiments to measure the deformation and mechanics of a single fibril, which is quite complicated. The mechanics of traditional rubberlike materials is not

1 Copper wire shaped like a spring.

2 Electron microscope image of fibrils.

3 Fibrillation at the interface between copper and rubber.

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times a user does not have the resources to do what we have planned.’‘Helianthos was another user, producing flexible solar cells. Nuon, who took over Helianthos, also decided to discontinue these activities because of the global competition in this sector. Tata Steel has been involved from the beginning as well. They are interested in packaging materials. Delamination of a pre-coated steel is also a fibrillation problem. Their biggest issue is that microscale damage of coated steel cannot be easily detected, whereas it is noticed at a later stage when the packaged products get spoiled. Berend Boelen of Tata Steel did research on the mechanisms of delamination and we used his data in the project.’‘Other users are people from software companies. Dassault Systèmes Simulia (see page 101) is one of them. They might pick up what we are doing in this project. We are building a generic multiscale approach and try to develop strategies to solve dedicated multiscale problems. The scale transition method to tackle an interface problem at a small scale and to couple it to a macroscopic delamination process is generic. Besides our specific problems of flexible electronics and fibrillation it must be possible to deal with other issues. But in our project we have to focus, we cannot work on five application problems at the same time.’

straightforward applicable to these delicate structures in which molecular chains tend to line up to a great extent.’‘We are fortunate to have many diverse users in this project. Philips’ contact person, Olaf van der Sluis, is also part-time assistant professor at our department, so communication is easy. Another user was Polymer Vision, producer of a fancy product, rollable displays. In 2009 the company was sold to the Taiwanese firm Wistron. In 2012 they shut discontinued their activities in the Netherlands for global market reasons. Regretful, since all intellectual property and know-how is now in the hands of others. As a part of the project, a master student did experimental work for Polymer Vision, which could be finished timely. We always define master projects along with our research projects. That works out fine, because many

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better macroscopic model in which the observed conflicts between the scales are repaired. A more representative model, that has a similar performance at the macroscale level, but which is more realistic at the lower scales. If we do not reach that point within the limited time of this project, we will continue in follow-up work.’

PeopleBart Vossen will finish his PhD research project in 2015.Dr. Mathieu Solar is at Martin Luther University Halle-Wittenberg, Germany.

Co-applicantsDr.ir. Piet Schreurs (TU/e), Dr.ir. Leon Govaert (TU/e), Prof.dr.ir. Erik van der Giessen (RUG).

HighlightsWith a coarse-grained molecular dynamics study Mathieu Solar and Erik van der Giessen in Groningen investigated the competition between physical mechanisms at the microscale to determine the overall work of separation. The results are valuable for future developments of continuum models for adhesion on polymer surfaces. Bart Vossen developed the generic multiscale model, which couples the fine scale to the application scale.

Follow up projectsGeers: ‘We still have some work to do. We have to bridge the gap between measured and computed work of separation. Furthermore, there are good indications that it will be possible to construct a significantly

Van der Giessen watches a discussion of material researchers working with an electron microscope.


A multiscale methodology for the analysis of metallic interfaces

Prof.dr.ir. Erik van der Giessen

University of Groningen | Duration: 1/09/2008 to 30/4/2014


IntroductionWithout dislocations in steel, cars would not exist. It would not be possible to produce the body of a car from a metal sheet, to change the shape of metals like we are used to. The structure of metals is built up of smaller or bigger grains with different crystal orientations. Dislocations are defects in the crystal lattice of the grains, lines of atoms which are out of place. The surfaces between the grains are known as grain boundaries, the most important kind of interfaces in metals. When a metal is deformed, atomic positions change and dislocations propagate through the crystal structure. It turns out that dislocations interact in special ways with interfaces. The movement of dislocations changes at grain boundaries. Interfaces can generate new dislocations and in other cases dislocations can be absorbed.By trial-and-error, steel manufacturers have learnt to manipulate the size and composition of metal microstructures, in order to improve the performance of the material. Until now an engineering model that included the processes at the atomic scale and microscale did not exist. This project aimed at establishing a generic way to bridge the events between the three scales —atomistic, mesoscopic and macroscopic—, to reach the level which is useful in industry.

Science and utilisationOne of the main challenges is to understand what happens at the atomic scale when dislocations move. The essence of the atomic behaviour is collected and sent to the mesoscale. At this scale the effect of many dislocations interacting with interfaces is modelled, and the general behaviour is sent to the continuum scale which is usable for practical applications. Van der

Giessen: ‘We tried to build the complete chain, atomic scale, mesoscale, continuum scale and their connections. Experiments have shown that scale effects are important especially for metals with small grains, having relatively large interfaces. Those scale effects especially affect the plasticity of the metal. They are very significant, but not included in the continuum models used by product designers today. Knowing the behaviour of small grain metals is important by definition in miniature applications, like microelectromechanical systems (MEMS). Yet, there are more size effects in MEMS. For little gears, for instance, with a size of fractions of millimetres the effect of friction is strong because the amount of surface is relatively large. As a consequence, these things don’t operate, they just don’t go around. Friction involves plastic deformation of the ‘hills’ of rough surfaces, so this is another reason why we want to know what is going on at that small scale.’PhD student Sebastián Echeverri Restrepo in Delft has worked on the molecular dynamics model of the atomic scale level. He will receive his PhD at the end of 2013. Postdoc Xiaoming Liu still works part-time in Groningen (part-time at the Chinese Academy of Sciences in Beijing, China), modelling the collective behaviour of dislocations at the mesoscale. PhD student Paul van Beers continues to work in Eindhoven on the continuum scale model. Van der Giessen: ‘The last is probably the most difficult part of the project. I’m afraid we may not be able to deliver a ready-made continuum model in the end, because some aspects turned out to be much more difficult than we had hoped.’The users of this project (Tata Steel [see page 106], Philips) are interested in applications at the continuum level. Van der

1 Model of dislocations in steel by Sebastián Echeverri Restrepo.

2 Atomistics picture of the local geometry of grain boundaries in steel.

3 Poster of Lorentz workshop on Scale transitions in space and time for materials, 2009.

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way, with large effects on the behaviour of dislocations. It makes a difference if a dislocation ends at a certain atomic plane or another. Yet you want to get rid of these effects on the transition to the mesolevel, so in order to get a good representation of the average behaviour you have to find a way to level them off. However, when you do a simulation or even an experiment, you can get results that deviate very much from the average.’‘At the mesolevel we regard not just one, but a train of dislocations, which may repel or attract each other and represent a lot of energy with a large effect on the total behaviour. This is why it’s important to include the mesoscale in the model. On this level we have found a very simple relation between the yield stress, the stress of dislocations sliding along an interface, and the number of dislocations waiting. That was quite ingenious and the people in Eindhoven are using this result now.’‘It was a little bit problematic that the project ran simultaneously at three locations. It was a chain of activities in a time span of maximum five years. The big challenge was to run the three scales synchronously and to let them interact simultaneously. In the

Giessen: ‘Modelling on smaller scales costs a lot of time and a lot of detailed initial data have to be added. Our users don’t want to do this, it’s too elaborate for them. We need to extract the essence and transfer that to the models they use, so they can do fast computations for their applications.’

HighlightsVan der Giessen: ‘At the smallest scale we needed to build atomic interfaces. A logical thing to do was to look for the lowest energy states, but it turned out there was a enormous spectrum of low energy states and we don’t know if they are all realistic because we cannot measure them. But we have learnt a lot about the behaviour of dislocations and the perturbation of atomic positions near interfaces at the atomic scale. Atoms at interfaces are distributed in a chaotic

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4 Steel microstructure.

5 Plastic deformation by sliding of an edge dislocation. The blue arrows show the dislocation direction, the grey area shows the sliding zone and the green dashed line shows the dislocation line. {Image: Chris-tophe Dang Ngoc Chan/Wikimedia Commons]


Follow up projectsVan der Giessen: ‘I would like to continue with this approach, but as of yet nothing has been planned. In this project we have not been able to study all kinds of interactions between dislocations and interfaces. Now we know how to tackle the problem, it is a good moment to study those other aspects.’

PeopleXiaoming Liu has a position at the Chinese Academy of Sciences in Beijing, and he’s working on the project in Groningen till the end of June 2013.Sebastián Echeverri Restrepo is now at SKF Research in Nieuwegein, working in a multiscale modelling research group.Paul van Beers will finish his PhD research in Eindhoven in 2014.

Co-applicantsProf.dr.ir. M.G.D. Geers, Dr.ir. V.G. Kouznetsova (TU/e); Prof.dr. B. Thijsse, Dr. L. Nicola (TUD).

beginning we did not know very well which kind of information we had to exchange. Numerous discussion sessions were needed to establish this, before we could collaborate effectively. Now we know how to do this and that’s already one of the main successes of this project! First we have to identify what we need to know from another and what one is able to provide. Then you can start doing initial preparations for each level, without the exact final results. If you can anticipate on the kind of information you are going to receive from another level it is possible to get an idea of how the world looks like at the scale you work at and to work towards the information the next level needs. For this particular problem we now know what that is. If we could continue to do a similar job from a different perspective we would know how to start.’


Multiscale computational poromechanics

Dr.ir. Jacques Huyghe and dr.ir. Joris Remmers



IntroductionAn intervertebral disc consists of porous material filled with fluid. The cartilage in the disc looses its water binding capacity in time and the water content can vary from 90% in babies to 50% at the age of 80. The effect of the decreasing water content is that cracks form more easily, which can cause a painful hernia. The process of crack formation in cartilage is comparable to the mechanism of cracking earth layers by hydraulic fracturing. This technology is used to break shale rocks in order to release petroleum or shale gas, but also for the production of geothermic energy. A lot of research has been done on cracks in solids, but there’s still a lot to learn about crack formation in porous solid-fluid mixtures.

Science and utilisation‘We always work at the interface between civil engineering, mining and biomechanics’, says Jacques Huyghe in his office in Eindhoven, where his colleague Joris Remmers joins him for the interview. ‘We believe in creating win-win situations when we find applications in both fields.’ In this project the most important challenge was to develop the model. Once a microcrack starts growing in a porous medium, the crack fills with fluid, attenuating the tendency of a crack to grow. The stability of a crack is connected to what is happening at the microscale at the tip of the crack. In a multiscale model of crack formation in porous media, small mistakes in the effects at the microscale have a catastrophic effect on the validity at the applications scale. Huyghe: ‘We hoped that our user Shell would provide experimental results, so we could validate the model, but that did not happen. It was hard for them to give us instructions, they

were hardly prepared for this subject. I think that’s going to change in the coming years. It’s good that our former student dr. Famke Kraaijeveld (see page 103) works there now.’Other companies in the user committee were Dassault Systèmes, the developer of Abaqus software, and Habanera, (software, now Dynaflow), Procter & Gamble and Petrobras (Brazillian oil company). Remmers: ‘I was very happy with the user meetings twice a year. It’s very good to get feedback, moments of reflection and exchange with people from industry on a regular basis. In the general MuST programme meetings it was harder for the PhD students to keep track of the diversity of other projects. But it’s good that they can present their work there in a familiar environment.’

HighlightsPhD student Faisal Irzal worked in 2D at large deformations that occur at the crack tip. It was not possible to simplify the model at this scale. He succeeded to include all terms. Remmers: ‘He was the first one to do this and we published a paper about it. When this part was finished we could have switched to a 3D model, but then we learned about a new numerical technology, isogeometric analysis, in which Abaqus was interested. One of our group members had done a postdoc in Texas with Tom Hughes, and he came back with this new method. We encountered the problem that we could not take into account all the higher order derivatives in our standard element discretisation. Faisal came up with the idea to do this in isogeometric analysis, and after consulting our users we jumped on that train. The field in which we work is developing continuously, you don’t want to be tied down to a programme exactly as it was written a few years ago.’

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Huyghe: ‘One of the remarkable things PhD student Francesco Pizzocolo could prove was that cracks in porous material propagate in a step-wise way. We did not expect this. The formation of cracks in metals occurs in a much smoother way. But he recognized it in his simulations and then we did experiments with hydrogels and the effect turned out to be real. We don’t know yet which material parameter causes the effect. In a way it is connected to the liquid flow, but we did not find a quantitative relation yet. We wrote a paper about it, which is accepted for publication. The intermittent crack propagation could be related to earthquakes and aftershocks. We discussed it with seismologists, but it is still hypothetical.’

Follow up projectsHuyghe: ‘Considering the growing attention for shale gas, we expect increasing interest in our work. We already have a new hydraulic fracturing project from the top sector Energy. We are going to adapt the model in a way it can be used for 3D simulations. This project got to the point of proving that it is possible. Now we are making a next step. Together

with Procter & Gamble we also started a new STW-project on crack formation, but now in diapers. The problem is a little bit different. One of the problems they have is that the first layer of gel grains is swelling so perfectly that it blocks new liquid from entering. So they made a harder shell around the grains of the first layer, to temporarily attenuate the swelling. We want to know how this swelling exactly works.’

PeopleFrancesco Pizzocolo is Geomechanics Scientist at TNO. He expects to receive his PhD in April 2014.Faisal Irzal received his PhD in October 2013.

Co-applicantsProf.dr.ir. R. de Borst (TU/e).

1 A herniated intervertebral disc. The white represents fractures occurring from the centre nucleus pulposus to the outer annulus bro-sus. [From: F Kraaijeveld. Propaga-ting discontinuities in ionized porous media. PhD thesis, Technische universiteit Eindhoven, 2009.]

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2 (a) Pressure distribution at the time step before the crack propaga-tes through another element. (b) Pressure distribution at the time step after that crack propagated. [From: Master thesis Ernst Remij, Technische universiteit Eindhoven, 2013.]

3 Step-wise scheme of the propa-gation of a typical crack. [From: Piz-zocolo, F., J.M. Huyghe, K. Ito. Mode I crack propagation in hydrogels is step wise. Engineering Fracture Mechanics (2012).]


New simulation techniques for flows interacting with transforming structures

Prof.dr.ir. Hester Bijl

Delft University of Technology | Duration 01/05/2008 to 14/08/2014


IntroductionAt first sight there are no similarities between spinning yarns from molten polymers and the solidification of steel in a casting mould, but both industrial processes are based on the same physical processes of interacting fluids and structures. Crystallizing polymers interact with cooling air flows, solidifying steel interacts with flows in the casting steel that is still liquid. Both processes are very sensitive to slight changes in the liquid or solid phase or the flow. It’s hard to keep the quality of polymer yarns constant, and initial formed solid steel at the wall of the casting cup can come loose and get stuck in the machine. A multiscale model for fluid-structure interactions could help to improve the industrial production of these and other goods.

Science and utilisationHester Bijl’s group has experience with fluid-structure interaction models, but in this project the combination with changing temperatures and fluid-solid phase transitions is new. ‘We couple multiple physical systems, which we used to solve apart from each other, with different scales in space and in time’, she says. ‘We also have to take heat transfer into account, which makes it even more difficult to compute what happens in an accurate and stable way. Existing simulation models can diverge, although the physics behind them is accurate. Both Tata Steel and Diolen were struggling with these kinds of problems. That is why we wanted to pick it up. Now we are able to couple existing solidification models to a flow in a numerically stable way.

‘We had to stop working on the polymer problem, because shortly after the start of

the project Diolen went bankrupt. Instead we took up a new problem: uncertainties in the parameters of the model. We never know material properties precisely. And the accuracy of the computer model is limited: we cannot have complete resolution at all scales. Slight changes in material properties in time can have a huge effect on the stability of the model. We are studying how one can account for and quantify these uncertainties and how to reduce them. PhD student Jouke de Baar is working on this part of the project, and Richard Dwight (see page 98 ) helped to set up the framework for taking into account the uncertainties.’

‘PhD student Jasper Kreeft focussed on the discretization of the partial differential equations conserving the physical properties of the system. PhD student Vahid Kazemi-Kamyab developed the thermal coupling algorithm. In this part of the work we encountered some complications since we found that the already available iterative solution algorithm for incompressible flows did not have the correct temporal accuracy. Having solved that problem we moved to the coupling design. Since we wanted to develop a generic algorithm which can tackle various applications, a larger portion of the time was allocated to the design of stable, accurate, and efficient numerical procedures for the coupling. As a result, we unfortunately did not get the time to work on the particular applications I mentioned earlier. The user committees of STW-projects are inspiring, but I find it hard to have a very direct impact on the business of the users. This is different for, so-called, third money stream projects where you perform research for a company, often in very close collaboration.’

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exchange. It works for fluids and structures with huge temperature variations. At the same time we have clarified the theory of one of the standard models for computing unsteady incompressible flows. The better understanding allowed us to create a new model resulting in an enormous improvement in time-accuracy, which we demonstrated in OpenFoam. That is a big step forward, and one that can be applied throughout the industry with minimal effort and cost to improve everyone’s codes and results. A personal highlight is that the principal developer of OpenFoam, Prof. Hrvoje Jasak, is coming to work in my group for one day per week, to better exchange knowledge and expertise.’

Follow up projects‘We are further speeding up the solution of coupled problems using coarse meshes

‘One way to have impact on the business of users is, in our case, through implementation of our methods in open-source software. We used the flow solver OpenFoam, which – thanks to free access to the source code – we could easily couple to our solid-mechanics solver. The contact person from Tata Steel, Eelco van Vliet, also uses OpenFoam. Other users of the project were commercial software companies, Numeca, Ansys and Open Engineering, who were more interested in the knowledge developed. When they think that the methods we develop are interesting they must first implement them in their own software before they can take advantage of them.’

Highlights‘The most important outcome is that we now have a stable and efficient coupling algorithm for flows and structures with heat

1 Decomposition of velocity field. It shows the curl-free components (left), the harmonic components (top) and the total velocity field, for different vortical strengths and different polynomial order. From: J.J. Kreeft, A. Palha, M.I. Gerritsma, Mimetic framework on curvilinear quadrilaterals of arbitrary order, submitted, arXiv:1111.4304, 2013.


problems that does not exist when working with free and open software like OpenFoam.’

PeopleJasper Kreeft is Researcher Fluid Flow at Shell Global Solutions.Vahid Kazemi-Kamyab received his PhD on 13 September 2013.Jouke de Baar is still working on the project until the summer of 2014.Richard Dwight is assistant professor at the Faculty of Aerospace Engineering in Delft.

Co-applicantsProf.dr.ir. Sybrand van der Zwaag (TUD); Dr.ir. Alexander van Zuijlen (TUD).

and variable-fidelity models. The field of application is wind turbines. It sounds quite different, but large wind turbines at sea can suffer from fluid-structure interactions, a coupled problem where different scales play a role.’

‘In addition, we tried to organise a big open source follow-up project. Together with Kees Vuik and Mark Roest from Vortech, a scientific computing company I set up the Dutch OpenFoam Users Group in 2010, because we saw great opportunities. Open source software is a good way to work together with industry, the methods implemented are directly available for use. However, use of open-source software in industry has major drawbacks as well: continuity, limited availability of a help-desk, quality management, user-friendliness and version management are issues. Luckily for popular open source codes, like OpenFoam, companies have been started-up that can help with these issues. Our idea was to use the research project, where methods would be developed for complex problems involving fluid flows, to link Dutch partners and to stimulate developments relevant for industry, academia and institutes like TNO. In this way we wanted to make a big step in the Netherlands. But our proposal was rejected, it was considered to be too fragmented with that diversity of parties concerned. I am a firm believer in open source-software, but I do understand it’s hard for companies to switch completely. Nevertheless in some cases there are clear advantages. We work together with various companies interested in massive computations with up to 10,000 parallel processors. That is going to be very expensive when you need to buy a licence for each processor. This is one of the


Multiscale model adaptation for dynamic performance of multiphase materials

Dr. Sergio R. Turteltaub

Delft University of Technology | Duration: 01/01/2009 to 15/10/2013


IntroductionSteel companies are interested in developing new kinds of steel that are very strong, which allow designers to create energy-efficient lightweight structures. Typically, an increase in stiffness may be achieved at the expense of ductility. However, a steel requires sufficient ductility so it can be stamped into useful objects, like the body of a car. One way to achieve an optimal compromise between strength and ductility is to create a steel that is composed of different types of crystal structures, or phases, each with a different purpose. One such multiphase steel is known as the Transformation Induced Plasticity (TRIP) steel. Its microstructure consists of austenite grains (face-centred cubic crystals) embedded in a matrix of ferrite (body centred cubic crystal). This material is initially ductile, and it becomes very hard to deform when the austenite turns into martensite (tetragonal crystal structure) during plastic deformation. That’s a desirable quality because once the body of a car is stamped, you don’t want any deformations. But the steel should also not get brittle. In case a car crashes it should not break. Knowing more about how different phases in steel affect the macroscopic properties is essential for the development of innovative varieties of steel.

Science and utilisation‘It’s a giant step to connect microstructures in steel with something usable for someone who wants to construct a building or an aeroplane’ says Sergio Turteltaub in his office at the Faculty of Aerospace Engineering in Delft. ‘The differences between the micro, meso and continuum scales are very big. At the smallest scale we need to collect qualitative data, and we need to transfer the most important information to the next scale.

It was challenging to do the computations in an efficient way.’Initially two PhD students, in Delft and Groningen, were working at the project, but the student in Groningen stopped after eighteen months and postdoc Prabhat Agnihotri took over. Sourena Yadegari in Delft first focussed on the thermal effects in multi-phase steel during the forming, later he switched to the application of the multiscale method (from a meso- to a macroscale). He will receive his PhD in 2013. Prabhat Agnihotri has worked on strain-rate dependency aspects at the sub-micron scale and will continue on the multiscale aspects from the micro- to the mesoscale.Turteltaub: ‘It is nice to have a new multiscale method, but even nicer when somebody is going to use it. Steel producers can roughly control microstructures in steel as the result of certain manufacturing routes. Now we can simulate the effect of microstructures on the properties of the end product. One of the questions of our user Tata Steel was what happens when the austenite is deposited in layers instead of dispersed in the ferrite bulk material. It’s not easy to get answers by doing experiments; too many factors are hard to control. In our simulations we can easily change just the distribution of the austenite particles, everything else stays exactly the same. That’s hard to do under experimental conditions. We have found that the shear strength is reduced for steel with banded microstructures.’‘We have adapted the project to the expertise of Piet Kok, research scientist at Tata Steel [see page 106]. He is specialised in generating geometrical microstructures. He is happy that we use his invention and we are glad to use his programme. We used Piet’s models, his computonium, in our simulations.’


Highlights

‘One of the goals of this project was to get a

better model for this material. In our model the

thermal part is much better than it used to be.

We published a paper about this aspect in 2012.’

‘Recently we have written another paper on

the application of the multiscale method of

this work. We have developed a new method to

calculate an approximation of what happens at

the smallest scale in a relatively efficient way.

We chose to use an adaptive method with two

types of so called homogenisation methods.

The first method, direct numerical simulation

with a finite element model, transfers many

details to the next scale, which takes a lot of

computational time. In order to use this method,

you have to find out which volume elements

are representative for the properties of the

microstructure, and use the model only for

these elements. The other method, known as

the Generalized Grain Cluster Method, can be

used for the other volume elements. It is fast,

but does not have the same accuracy.’

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1 Dispersed and banded samples of TRIP steel.

2 Representative volume elements for aggregates of steel grains.


Co-applicantsProf.dr.ir. A.S.J. Suiker (TUD);Prof.dr.ir. E. van der Giessen (RUG).

‘Many multiscale users do not know if their

representative volume elements are really

representative. You can check it with a

numerical experiment. For instance a typical

TRIP steel may contain 12% of austenite

(in volume). If a microscopic volume element contains only one grain of austenite (which occupies 12% of the microscopic volume element), it is however not representative for the microstructure since it only represents one crystalline orientation. A large number of grains in one volume element are essential for a good result. It’s never going to be perfect, we work to the limits of what a computer can do. An adaptive method needs to be robust in different circumstances. In general it’s very difficult to switch between homogenisation schemes when they are very different. The advantage of the current approach is that there is a seamless integration between the direct numerical simulation and the generalized grain cluster method.’

Follow up projects‘We have developed the method now but still we did not use it for a large-scale sample, which was the original goal. We would like to do a simulation that can be tested on a larger scale. Tata is interested in the effects of banded structures, but now for another type of steel. It’s not clear if we can work on that problem in this project, or if we are going to continue to do the work in another way.’

PeopleSourena Yadegari will start working at Continental AG in Germany at the end of 2013.Prabhat K. Agnihotri is postdoc at the University of Groningen.


The start up of lighting and lightning:

Streamer discharges in lamp ignition, electric switches and materials processing

Prof.dr. Ute Ebert

Centrum Wiskunde & Informatica | Duration: 1/11/2008 to 31/8/2013


IntroductionIn 1750 Benjamin Franklin, the inventor of the lightning rod, published a proposal to fly a kite in a storm in order to prove that lightning is generated by electricity. A few years later he succeeded to extract electric sparks from clouds, followed by other investigators who were electrocuted, because they did not think of using proper insulation. After many more experiments and theory we still do not entirely understand these electric discharges with their multiple scales in space and time. Lightning is a complicated phenomenon where initially free electrons are accelerated in large electric fields, hit gas molecules and thus create more charged particles and eventually weakly ionized plasma. First in the streamer phase the self-generated electric fields of the plasma channels dominate the motion. Hundred thousands of streamers explore space and prepare the path of hot leader channels. When the leader channels have created an electric short-circuit between cloud and ground, return strokes along these plasma channels heat the gas further and create the major light emission and also the thunder of a lightning stroke. Similar processes occur in plasma technology and high voltage engineering.

Science and utilisation‘This MuST project has been very instrumental for us between other research projects,’ says Ute Ebert. ‘It came right in time to strengthen our computational work. This work is very generic. It’s not restricted to one specific application. We could really concentrate on the development of theory.’ The project is strongly coupled to precise plasma physics experiments in Eindhoven. Ebert: ‘The experiments we do are at a macroscopic scale. It’s still virtually impossible to measure an electric

field sufficiently locally in space and time in the active zone of a streamer discharge; we have to get data from our computations. In simulations it’s possible to focus on small scale characteristics while the experiments show large-scale phenomena. Somewhere experiment and model have to meet.’The ignition of gas discharge lamps follows similar physical processes as the streamer phase in lightning. Ana Sobota studied the process at Eindhoven University of Technology in close collaboration with Philips Lighting. In high local electric fields free electrons initiate ionization avalanches that can grow out into space-charge regions. Due to the enhanced electric fields created by the space charges, the streamer discharge can penetrate into regions where the background electric field would be too low for ionization avalanches. Sobota did experiments and set up simulations of what happens during ignition. Ebert: ‘For the start-up of a lamp this discharge should take place in the volume, not along the lamp’s dielectric wall. We want to understand the ignition process and try to avoid discharges along the walls. The researchers at Philips Lightning were very happy with these results. However, the management of the company decided to stop the development of gas discharge lamps, and to switch over completely to the development of LED lights.’‘Another user is the Van der Heide Group, a lightning protection company (see page 109). They were so excited about the present collaboration that they joined a new project as well. We are looking at tips of long objects, that eject counter-streamers and counter-leaders, that can join with approaching streamer and leader discharges hence directing lightning strikes to these tips. Sometimes discharges appear at unexpected places or exhibit unexpected behaviour. A

1 The development of an electric discharge. Hundreds of positive streamers are generated at a high voltage electrode. Ohmic friction causes some streamers to heat up to bright leaders. Pictures are taken with shutter times increasing from 50 nanoseconds to 1 microsecond. [From: Experimental study of hard X-rays emitted from meter-scale positive discharges in air, P.O. Koch-kin, C.V. Nguyen, A.P.J. van Deursen, U. Ebert, J. Phys. D.: Appl. Phys. 45 425202 (2012).]

2 Light emitted from a sprite streamer emerging from the sharpened edge of a relaxation-ionization wave in the ionosphere. This wave produces diffuse optical emissions observed as a halo. [From: Emergence of sprite streamers from screening-ionisation waves in the lower ionosphere, A. Luque, U. Ebert, Nature Geoscience 2 757-760 (2009).]

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HighlightsEbert: ‘Chao Li developed a sophisticated hybrid code. In some parts of the discharge we follow every free electron with a Monte Carlo code, but there is a large area with many electrons which is very uniform, that we describe with a density approximation. Chao succeeded to connect the two models in a 3D simulation, a very complicated project. This work was very instrumental and we are receiving a lot of recognition for it.’Alejandro Luque reviewed density models (also called reaction-drift-diffusion models) that are often used for simulations of streamer electrical discharges, detailing their physical foundations, their range of validity and the most relevant numerical algorithms. He managed to resolve the multiple length scales in a streamer discharge without high

streamer can flatten out horizontally, as if it hits a barrier, and at the same time suddenly change diameter. Then we get what we call pollard willow (Dutch: knotwilg) streamers. We also see that discharges suddenly seem to propagate perpendicular to the electric field, in our so-called onion streamers. It looks like the background charge and the background ionization of a previous discharge play a role here.’‘Altogether five postdocs worked on this project, some only for short periods, Chao Li, Alejandro Luque, Sasa Dujko, Diana Mihailova, and Anbang Sun. They all had worked on other projects in my group before, so they could easily join in and help to set up this project. They built up many new codes, and now we are able to do 3D and hybrid simulations.’‘PhD students Lei Liu and Gideon Wormeester are still working on the project until the summer of this year.And we are busy documenting the code on our website, where it’s available for other users. I know there’s a need for this code, although it’s not used by many people yet. I know that ABB Corporate Research, a multinational in high voltage technology is interested.’

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allow transporting electricity from solar panels in the Sahara desert or from water power in Scandinavia to Western Europe with little losses. In these last two projects we collaborate with ABB Corporate Research. And we have a new project in the open competition - projectruimte - of FOM where we will study the interaction of high energy cosmic rays and thunderstorms.’

PeopleAna Sobota has defended her PhD in April 2011 and is postdoc at CNRS Ecole Polytechnique, Paris.Gideon Wormeester expects to receive his PhD in August 2013.Lei Liu has received his PhD in July 2013.Alejandro Luque is on a tenure track position at the Institute for Astrophysics of Andalusia (IAA-CSIC), in Granada, Spain.Chao Li is Research Engineer at Textkernel in Amsterdam.Sasa Dujko is Associate Professor at the University of Belgrade.Diana Mikhailova is postdoc at Université Paul Sabatier and CNRS, France.Anbang Sun is still postdoctoral researcher at CWI in Amsterdam.

Co-applicantsProf.dr. Willem Hundsdorfer (CWI); Dr.ir. Jan van Dijk (TU/e).

computational costs. These highlights were published in a special issue of the Journal of Computational Physics (231(3)) in 2012. Ebert: ‘Another highlight is a paper Luque and I wrote in 2009 in Nature Geoscience. It was the first publication of a quantitative theory in atmospheric electricity.’

Follow up projectsEbert: ‘I built up long term relationships with other researchers in electrical engineering, plasma physics, geophysics, and companies. In December 2009 three projects were approved in the STW-programme ‘Building on Transient Plasmas’. In November 2011 we got a new project in the Open Technology Programme of STW. And in February this year we received a grant from the Shell-NWO programme to study high voltage DC circuit breakers. DC electricity networks would

3 Onion-streamer discharge in 600 mbar artificial air. [From: A Peculiar Streamer Morphology Created by a Complex Voltage Pulse, S. Nijdam et.al., IEEE Trans. on Plasma Sci. 39 2216 (2011).]

4 Electron density in the region where a streamer grows. The rows show three different models: the extended fluid model (first row), par-ticle model (second row) and hybrid model (third row). [From: A compari-son of 3D particle, fluid and hybrid simulations for negative streamers, Chao Li et.al. Plasma Sources Sci. Technol. 21 055019 (2012).]


Hierarchical multiscale modelling

A single data structure for micro-macro and multi-phase/field models

Prof.dr. Stefan Luding

University of Twente | Duration: 1/11/2008 to 31/10/2013


IntroductionMany systems in nature and industry consist of different phases: particles or fibres of different materials, shapes and sizes, in combination with flowing liquids or gases, that can be affected by fields like gravity, temperature differences or electromagnetic fields. One example is the sedimentation of bio-mass, sand and clay particles in the floodplain of a river. It is a great challenge to model the behaviour of multiple particles and fluids in such complicated situations. Fields and phases affect each other constantly at different length scales. A multiscale model that overcomes these complications will be applicable for other natural phenomena like avalanches or countless industrial processes.

Science and utilisationIn 2007 Stefan Luding was appointed as professor for multiscale mechanics at the University of Twente. ‘My first working day when I arrived here was 2 October 2007’, he says. ‘I spent my first two nights finishing writing this project. By then a meso-scale method for solving the interaction between fluids and particles at a scale of the distance between the particles did not exist. The interaction between particles and fluids can be described by various, often distinct numerical methods; in existing methods the liquid properties were either not very precise, or too precise. In the first case something will be missing, and in the last case your simulations will run endlessly. Our idea was to start a monolithic code (where the distinct methods are combined at the basis, from the beginning) from a meso-scale, intermediate resolution and when we observe that something is missing we switch to a finer resolution. That is the hierarchical multiscale modelling idea. The idea was that once we developed the

new method, also an electromagnetic field or temperature field could be solved on the same grid and data-structure as the fluid, but we have not reached that point yet; it turned out to be a bit too ambitious for this project. It was an explorative project and it turned out to be even more fundamental than the proposal I wrote. The work was supposed to be focussed on numerical methods, but there were unforeseen technical problems in modelling the fluid together with the particles. Fortunately, the PhD students achieved much more than expected at the theoretical level.’PhD student Kazem Yazdchi (see page 88) constructed flow-models at the basic, highly resolved scale with liquid flowing through grids of motionless particles, with the goal to understand how macroscopic properties like permeability and drag can be predicted from the microstructure and described at all densities. PhD student Vitaliy Ogarko worked on both optimizing the particle code and the continuum theory for very differently sized particles. Dr. Saurabh Srivastava was bridging and combining the methods. Users were Boehringer Ingelheim Pharma, Procter & Gamble, various universities and research institutes, and several software companies like DEM Solutions. Luding: ‘DEM Solutions is a British company that sells commercial particle solvers, which can be coupled to liquid solvers, and they tackle many solid-liquid problems with their software and as consultants. The idea was that the PhD students would spend about a quarter of their time at companies of the users or partners. DEM Solutions wanted to improve their own code, which would have been possible with the help of Ogarko, but that turned out to be complicated. As a Russian citizen, Vitaliy Ogarko could not get the permission to spend months in the UK. There still was

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1 Some examples of multiphase phenomena occurring at various length scales. From left to right: Nanoparticles for self-cleaning surf-aces, gases (like bubbles) in a liquid, flow in porous media and industrial chemical reactors. [Thesis Kazem Yazdchi, p.12]

2 Streamline patterns around (a) circle, (b) square and (c) ellipse. The color shows the magnitude of the horizontal velocity. [Thesis Kazem Yazdchi, p.129]

methodology built in already from the start. The coupling of particles and fluids is still not finished. Five years ago I didn’t regard and recognize open source software as valorisation, but now I do. Still you don’t get credits for it. It is also output, I urge my students to put it on their resumes. It might be a Dutch disease, but here these developments are not honoured. The years of development of new computer simulations, algorithms and usable software are hardly ever valued; models and codes are regarded as things you just use. They are too often taken for granted – one can appreciate their value only after one tries to do it by one self. It is good that it is possible to do this kind of work in a STW-project and provide a service to the community.’

HighlightsKazem Yazdchi performed numerous simulations on fluid flow through fibrous materials.

some exchange, by email, but that is never as efficient as visiting a place. Many other mostly shorter visits to the users fortunately could take place, and many of them visited University of Twente during the last years. For the PhD students it was good to meet the users on a regular basis, to get their input and to hear about the work floor applications; that keeps their feet on the ground.’ ‘We developed and worked towards a new open source code, in which our commercial user was not interested, because it was hard to implement on their system. When the implementation takes too much time a commercial software developer looses interest – unless he has a client that needs the know-how directly. Nevertheless some of the project results make our open source software unique and will surely be implemented and adopted by users in the future. For example (1) we can deal with strongly different particles sizes now, and (2) we have the micro-macro coarse graining

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3 Horizontal velocity contours for ordered arrays (square configu-ration) of particles at different diameters, d, and porosity ε. [Thesis Kazem Yazdchi, p.168]

when it is compressed. This did not work for three moments, but it did work out for five moments. This is a strong prediction and we still want to test it experimentally with our partners.’

Follow up projects‘I applied for a few follow-up projects, in the Netherlands. Some are successful if they are application oriented – fundamental modelling research is not appreciated these days. And I wrote a big application for EU funding, which takes a lot of time, but if successful one can really make big steps forwards.’

PeopleKazem Yazdchi finished his PhD on 28. November 2012 and is now at Bosch Transmission Technology.Vitaliy Ogarko will finish his PhD at the University of Twente by the end of 2013.

Vitaly Ogarko took two major steps in the development of the particle method. Luding: ‘The first step was to simulate (using hierarchical multiscale grids) in an efficient way particles with size variations of a factor up to one-thousand, where just the particle-size is another multiscale aspect. We could not do this when we started. He is a very capable programmer and he came to this result within a few months. He also was able to provide the recipe for how many hierarchical layers are needed and how to distribute the particles across them to simulate a certain size distribution in the most efficient way. Afterwards he got interested in kinetic theory, which is in the realm of statistical physics. In that field we could make a multiscale step in a direction we had never foreseen. A loose density particles sample can be described by the three-moments of its size distribution, which is known since a while. We wanted to predict when a liquid crystallises or becomes a glass


Multiscale simulation of multi-material adherence

Prof.dr. Bert de With



IntroductionPolymers are used in electronics to protect the circuits from water and damage. For this good adhesion and low water penetrability are required. Epoxy and other polymer coatings are also in widespread use as anti-corrosion protection, for instance to protect metal hulls of ships from the corrosive effects of water. The coating must be long-lasting so that frequent repair does not keep the ship out of service. The polymer layer must be able to withstand salt water and high pressure washing with water in a dry dock. But coatings are sensitive to delamination – the adhesion between the metal surface and the polymer deteriorates. Also water is able to penetrate in an epoxy layer. This can affect a vessel’s performance and durability. Similar problems occur in electronics protected by polymer coatings; which was the main topic of this biggest project of the MuST programme.

Science and utilisation‘With the results of this work we can improve the understanding of adhesion and reduce the permeability of polymer coatings’, says Bert de With, the project leader. Initially four PhD students started, one focussing on experimental work and the others on three different modelling levels: the molecular scale, mesoscale and macroscopic scale. The idea was to couple the various levels in a later stage. Fidel Valega Mackenzie, in Barend Thijsse’s group in Delft, modelled different varieties of crosslinking of epoxy macromolecules in a quantitative way on the molecular scale with Molecular Dynamics (MD). De With: ‘Crosslinking is a reaction between the reactive groups of the epoxy macromolecule. It’s essential to take this bonding into

account, because it has a large effect on the molecular interaction parameters, essential for the delamination process.’Gökhan Kacar in Bert de With’s group in Eindhoven studied crosslinking at the mesoscale and the interaction of the cross-linking network with the substrate using the coarse-grained simulation method Dissipative Particle Dynamics (DPD), with water as an important factor in adhesion. Nico Reuvers studied the penetration of water in nylon coatings experimentally with Nuclear Magnetic Resonance in the group of Olaf Adan in Eindhoven. Experiments are essential to validate and calibrate the numerical models. De With: ‘We wanted to find out how fast water penetrates and how the profile of water in a cross-section of the polymer layer looks like. Ideally the experiments should have been done on epoxy coatings, but compared to other polymers they do not absorb a lot of water, that’s why they are widely used to protect electronic circuits. As the water content is less than 1%, it is very hard to measure. Amide polymers like nylon contain typically 5% water, that is why nylon was chosen for the experiments. From nylon we could also learn about the diffusion of ions in polymers, which was also quite new. An outstanding experimental method was developed for these measurements.’‘The fourth PhD student in Delft was supposed to work on the macroscopic scale, but he stopped after a little while and this part was taken over by postdoc Mohammad Samimi. But he got a nice job offer in industry after one year, and then this part of the project ended. Because of the loss of the macroscopic part of the project we did not arrive at absolute macroscopic adhesion quantities.’The user committee consisted of TNO, NXP,

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we map these results of the mesoscopic model back to Molecular Dynamics, the densities are far from real. It took a while before we could adapt the DPD-model in a way that these volumes are adjustable. Now the crosslinking is representative, we find realistic crosslinking levels of typically 90%. The next step is to go back to the interface in Molecular Dynamics, where we can compute molecular parameters like the interface energy, which is proportional to the delamination energy. Departing from the coarse grained structure we can pretty quickly set up an MD model now, with the long term and long range order of a global structure. It would be hard to do this in MD directly for a polymer with a molecular weight of, say 6000 or so, because the computation time is everlasting. These are two major methodological steps we took, and they are very generic. They can also be used for any other substrate, such as silicon oxide

Akzo, Océ and Boschman, a small electronics company. De With: ‘The committee functioned as a think tank, reflecting and advising. All companies are interested in metal oxide – polymer transitions. The original idea was to do experiments at TNO but that was not effectuated, but they had a very stimulating coaching role (see page 112).’

HighlightsDe With: ‘We were looking at a substrate of aluminium oxide covered by an epoxy layer. The first thing we did was to describe the crosslinking of epoxy side chains at the right time and length scales with Dissipative Particle Dynamics (DPD). That was rather problematic. We did a coarse graining for typical chemically recognizable parts of the polymer molecule, like urethane, polyester, ether, benzene and amide groups, and we created pseudo-atoms for these groups. The problem with this DPD method is that all the bead volumes are assumed to be equal. That cannot be right because the volumes of chemical groups can diverge 300%. When

2 Left: Initial ensemble of a DGE-BA-DETA polymer with 30 molecules of DGEBA and 10 of DETA (DGEBA = Bisphenol A diglycidyl ether, DETA = Diethylene triamide). Displayed in blue are amine groups, in black every epoxide group available for cross-linking. Right: Same polymer after nearly 70% of the epoxy has been cross-linked. From the work of Fidel Valega Mackenzie.

1 Nico Reuvers’ thesis.

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as this project has been, they finance two PhD students at most. And you need to put in some money of your own, when you want to do some investments. For a project with three or four PhD’s we are looking at EU funding. We have contact with Portuguese and Italian groups that could contribute. We are trying to find the balance between the big effort it takes to write such a project and our chances of success, because it’s a lot of paperwork.’

PeopleNico Reuvers started working at ASML after finishing his PhD.Fidel Valega Mackenzie expects to receive his PhD in 2014. Gökhan Kacar expects to receive his PhD in January 2014.Mohammad Samimi is structural engineer at Allseas, Delft.

Co-applicantsProf.dr.ir. O.C.G. Adan, (TU/e); Prof.dr. Barend Thijsse, (TUD); Prof.dr.ir. Fred van Keulen, (TUD); Prof.dr.ir. Kouchi Zhang, (TUD).

or copper oxide, and any other polymer. The next step is to focus on the aluminium oxide surface with kinks, dislocations, pores, and different orientations of the beads.’‘I was delighted that we could get a good idea of the geometrical structure of a crosslinked system, although the method is pretty much simplified. Beforehand I had not thought this was possible. It’s good to be optimistic, but it appears that in these processes more problems arise than one ever imagines. With a little collaboration and splitting up tasks, we could tackle a pretty big and complex problem.’

Follow up projects‘Especially AkzoNobel stimulated us to continue this work. They said, now that we have these tools, we should go ahead and tackle other problems. I would like to do another project with Barend Thijsse, AkzoNobel and maybe TNO, our collaboration was very satisfying. But it is not simple nowadays to find funding for this kind of work. A standard STW-project is not as big

3 Water attack on an alumina site bonded to an amine group in a poly-mer. From the work of Fidel Valega Mackenzie.


Adaptive multiscale methods for airbag-development-safety simulations

Prof.dr.ir. Harald van Brummelen

Eindhoven University of Technology | Duration: 1/9/2009 tot 30/11/2013


IntroductionSince the introduction of airbags, the number of casualties in car crashes has very much decreased. Strangely enough, in relatively low impact car crashes the mortality rate has gone up. Usually the victims are small-sized adults and children, who are struck by the inflating airbag. Airbags deploy with a displacement force of five kilonewton and impacting an airbag which is not yet fully inflated has a similar effect as crashing into a concrete wall. To improve the safety of airbags it is essential to investigate precisely how airbags unfold and to get a better view on the dynamics of the inflating airbag.

Science and utilisationIt is not easy to describe the deployment of airbags in a numerical model. When a car crashes, a signal triggers the inflator of the airbag, which is an explosive mechanism that shoots a gas into the airbag. The transition from the complicatedly folded initial configuration to what is more or less an inflated balloon is complex. Two different models are needed to describe the inflation process: one on the small scale for the initial inflation, when gas flows into the smallest creases in the material, and a model on the large scale that describes the path to the final configuration of the inflated airbag. Van Brummelen: ‘The inflating airbag represents a fluid-structure-interaction problem, which is our field of expertise. The initial supersonic gas flow is very complex, it has direct impact on the airbag material, and it slows down quickly. It was necessary to know how the gas fills the little folds before we could describe the initial stage of the deployment process. We could only hope that the dynamics are not too sensitive to the precise manner in which the airbag is folded. In that

case one airbag would be much safer than another. However, experience shows that this is not the case. It is interesting that the large scale dynamics is relatively insensitive to the exact configuration on the small scale, which makes the deployment of airbags a nice multiscale problem. Existing models do not resolve the gas flow in the airbag, and therefore give an incorrect description of the dynamics. At first we were dealing with the deployment of airbags in 2D. We are now working on a 3D model which is indispensable for realistic situations.’Initially this project was not awarded in the MuST programme. It was added later when it was approved for the STW-Open Technology Programme. Van Brummelen: ‘This is a quite specific project. Although it was evaluated as a good proposal, I think at first it did not fit into the overall contours of MuST.’The principal user of the project is TNO Automotive Safety Solution (TASS). This company develops software to improve the safety of cars and they use simulation software to study the behaviour of airbags. In the past, TASS operated under the umbrella of TNO, but now it is an independent business. Van Brummelen: ‘TASS is in a good position to transfer this project to other parties, because the most important airbag producers in the world use their software. When we started this project, TASS had just decided to reinforce this part of their business. They installed a new team that would develop code for airbag simulations. This project was therefore very complementary. Our research is very fundamental, and this project was also intended to provide TASS a perspective on future possibilities. Their practical aims and our scientific questions were aligned to a large extend. One of the fundamental


over to another person with other priorities. When there is a period of two years between the conception and the start of a project, the environment can change completely. We have looked at other potential partners, but for this application area, that was not easy. There are no airbag developers in the Netherlands, and going abroad did not seem to be logical.’

Highlights‘PhD student Timo van Opstal (see page 91) is doing very well. He has already published several papers and the work for his thesis is more or less complete. I’m very enthusiastic about the first 3D results. Although the extension to more realistic flow models is still in progress, the current 3D simulations already provide a very nice illustration of what we are actually doing. This project also provided new important insights in the model elements that are indispensable for good airbag-deployment predictions. At the start we thought we could use either viscous or inviscid models to describe the gas flow. However, we found that inviscid models are useless. At the small scale it is necessary to take self-contact of the airbag fabric into account. Viscous flow models

questions TASS wanted to answer was how one can say something about what happens at the smallest scales, without having to include very sophisticated flow models, which would be prohibitively complex or result in excessive computation times.’The original plan was to do a large part of the work at TASS. However, that was impeded by the market crash in 2009, soon after the project had started. ‘The crisis and its enormous impact on the automotive industry had significant consequences for the project. When we wrote the proposal the market was booming, but now TASS had to diminish their contribution. We decided to give the project a more fundamental focus. I think that this has worked out very well. Unfortunately, we could not make the strong connection with the application that we originally envisaged. TASS intended to pick up the fundamental insights and implement them in their codes, but that part was never realised. They still share their expertise with us, but they could not follow up on the large scale computations on the deployment of airbags. That is a pity, but that was the reality.’‘Initially also ESA expressed their interest in joining this project. However, once we started their contact person retired and he handed it


some ideas. We could focus on the reverse process, deflation, for instance in vacuum sealing. Such a change of perspective could open doors for new application partners that are interested in such processes.’

PeopleTimo van Opstal will defend his thesis in December 2013.

Co-applicantsProf.dr.ir. René de Borst (TU/e).

prevent such self-contact automatically, without any additional measures. Inviscid flow models, on the other hand, have the nasty side effect that the airbag fabric in narrow folds is instead attracted towards itself. This is extremely awkward in numerical simulations and, moreover, it is the opposite of what happens in reality. Inviscid flows therefore require a complicated algorithm that explicitly prevents self-contact of the airbag fabric. This was the topic of the first two papers that we wrote. We also worked on model adaptivity; how to connect the small-scale model to the large-scale model in an optimal manner. Our investigations have been preliminary, but they give a perspective on how to solve this, which can be the starting point of further research.’

Follow up projects‘At the moment we are talking with TASS about future work, but it is not clear yet what their strategic agenda is going to be. The automotive industry is only now starting to recover from the crisis. Fundamental new developments are still on hold. Without support of application partners it is unrealistic to think that we can proceed with this work in the same way. But we do have

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1 3D simulations of the deploy-ment of an airbag, made by Timo van Opstal.


Experimental and computational techniques for the design of impact-resistant materials

Prof.dr.ir. Bert Sluys

Delft University of Technology | Duration: 1/4/2010 to 1/3/2015


IntroductionModern protective materials, like glass grains embedded in polymers are commonly developed for civil and defence applications by trial and error. These impact-resistant materials can be damaged by extreme dynamical loadings. At the macroscopic scale matrix embedded particle materials seem to be homogeneous, but the effects of an explosive impact are to be found at the microscale. After an impact microcracks form in the polymer, and glass grains detach from the polymer matrix. If loading continues these microcracks extend into bigger macrocracks. Testing experimentally how these materials behave under dynamic loadings is quite expensive. High-quality equipment and well-educated technicians are required, and all kinds of safety measures have to be taken regarding the explosions that take place in the setup. It is also complicated to prepare test samples. A numerical multiscale methodology makes it easier to improve and optimize these materials. Until now such models do not exist.

Science and utilisationBert Sluys: ‘This project has two main challenges. We have to tackle many experimental issues, and we have to couple experimental data to new numerical multiscale methods, in order to understand what happens inside the protective materials. We have to distinguish the material behaviour from structural inertia effects, and that is a difficult task.’PhD student Jitang Fan is testing dynamical loadings of a polymer material filled with little glass particles with a modified horizontal Split-Hopkinson bar, in close collaboration with TNO [see also page 93 and 112]. A transparent sample with a well

defined microstructure is placed between long bars and an explosion generates a pressure wave that travels through the material. Crack formation and microcracks in the material are measured at different time and length scales. Sluys: ‘To create a perfect one-dimensional pulse is an experimental challenge. The sample also needs to be firmly attached to the bars and therefore we are looking for the right kind of glue at the moment. You need to be creative during the process. Once we solved these purely practical problems we can make a series of measurements and filter out the various effects. With a diameter of 7 cm our setup deviates from the international standard, because of its small size. And usually Split-Hopkinson bars are placed vertically, but once loaded it is hard to keep the bars straight. ‘In 2010 Saumya Weerathunge started as the first PhD student on this project. Together with prof. Daniël Rixen she is developing a generic numerical multiscale method, that is independent of the material used. In the models small meshes are needed to take the behaviour of all the small grains into account, which gives rise to long computation times. Saumya is developing efficient methods for time integration and discretisation. For personal reasons this part of the project was interrupted. PhD student Amin Karamnejad is working on a multiphysics model and also on the numerical part of the multiscale model. Sluys: ‘We have a system with a progressing wave and the finite-element model we use at the lower scale has an artefact of waves bouncing at artificial boundaries, which is not a realistic response. We need to cancel out this effect and that is part of the work of Amin, together with the development of a very good constitutive law that includes

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1 Direct numerical simulation model for cracking in heterogene-ous quasi-brittle materials under dynamic loading. A. Karamnejad, V. Nguyen, L.J. Sluys, A multiscale rate dependent crack model for quasi-brittle heterogeneous materials, Engineering Fracture Mechanics, 104, 96-113, May 2013.


at dynamic multiscale applications. We have developed a computational homogenisation scheme for a range of dynamic loadings. We have shown that it works, independent of the size of the representative volume elements, which is a big issue in multiscale modelling. About this result Amin wrote his first paper in Engineering Fracture Mechanics and two congress papers; he is doing very well. Of course the nicest results are to be expected in the third and fourth year of this project. We are going to couple the experimental and numerical multiscale work and validate the models. After that we can optimize the protective materials with the multiphysics, multiscale model.’

Follow up projectsWith researchers in Eindhoven Sluys is working on a new project about optimizing fibrous polymer materials. The stiffness of fibrous materials has different values in different directions. The optimization depends on the amount, thickness and length of the fibres, and their orientation. Sluys: ‘Initially we want to construct a static multiscale model that combines ductile and

temperature effects. Since we do not have data for the polymer material yet, Amin works on a model to study damage in concrete. At the lower scale we use a constitutive model that is very specific for the material used. But once the scheme works for concrete, it is relatively easy to plug in the constitutive model for another material and follow the same procedure for polymers with glass particles.’‘Initially Jaap Weerheim has been the driving force behind this project. He has the experimental expertise and he is Jitang’s supervisor. He works for TNO three days a week and he works here at the TU Delft for the rest of his time. Multiscale modelling is a very important issue for TNO, they have started a major project and they closely follow what we do. The idea is that we develop procedures and, in consultation with STW, TNO will decide how they want to use the results.’ Other users of the project are the NLR and the software companies Ansys and Dynaflow.

Highlights‘The specific and new thing we do is looking

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2 Multiscale model and different Representative Volume Element sizes. A. Karamnejad, V. Nguyen, L.J. Sluys, A multiscale rate dependent crack model for quasi-brittle hete-rogeneous materials, Engineering Fracture Mechanics, 104, 96-113, May 2013.


brittle failure, later maybe also a dynamic version. We need to model the constitutive and numerical part of this system and then we can use the numerical technique we developed in the current MuST project. The experimental results of this MuST project may also be used to test these fibrous materials.’

PeopleSaumya Weerathunge Kadawathagedara stopped working on the project on 1-4-2014.Jitang Fan will be working on the project until 1-11-2014.Amin Karamnejad will be working on the project until 1-3-2015.

Co-applicantsDr.ir. J. Weerheijm (TUD)Prof.dr.ir. Daniël Rixen (TUD).


Lagrangian ‘mixing analysis’ of heat transfer: a new way for thermal optimisation

Dr. Michel Speetjens



IntroductionStatic mixers have been used for the continuous mixing of fluid materials in industry since they were invented in 1965 by the Arthur D. Little Company. They were licensed to the Kenics Corporation and marketed as Kenics Motionless Mixers, with diameters that vary from millimetres to meters. Static mixers are used for many different applications, like mixing two-component adhesives, wastewater treatment and polymer production. What makes them especially interesting is that they can be used to improve heat transfer during the mixing of fluids. But these static mixers have been developed using empirical relations and fundamental understanding of the three dimensional behaviour of the mixing system is limited, and the physics behind the connection between mixing and heat transfer is poorly understood. This project aims at optimizing the shape of the mixer elements, to achieve the best mixing and heat transfer results in laminar flows, with lower pump capacities, saving lots of electricity, time and money.

Science and utilisationIn his office in Eindhoven Michel Speetjens shows me examples of transparent static mixers that are lying on his desk. ‘We are looking at structures in the flow field’, he says, ‘which are actually particle trajectories in laminar mixing systems. And we try to link heat transfer to the role of mixing.’This project is one of three projects that could not originally be funded in the MuST programme, but that were shortly after funded in the Open Technology Programme and were added to the MuST programme in view of their strong thematic connection. According to the reviewers, the multiscale

aspect was not clear enough. Speetjens: ‘Then we applied successfully for the STW-Open Technology Programme, and then this project was added retroactively to MuST. We were surprised, because we did not expect that after the previous rejection. But do I believe we fit into the MuST programme. We look at mixing connected to heat transfer from a Langrangian point of view: we define heat exchange in terms of ‘flow’ of a virtual ‘fluid’. Coherent structures arise in the particle trajectories, and there we find an enormous range of physical length scales: from large scale eddies of the size of the system itself, to minuscule structures, which altogether determine the topology of the flow and the mixing behaviour.’Laminar flows, characterized by low Reynolds numbers, are common in fluids with high viscosity, like polymer solutions. But also in small systems, like a lab-on-a-chip, flows tend to be laminar. Speetjens: ‘In our lab we study centimetre sized systems, but we can translate the results to much smaller systems characterized by the same Reynolds numbers. What makes it special is that our studies are three dimensional, while other work in this field is basically two-dimensional. 3D structures and bifurcations complicate the situation tremendously and they are hard to visualise.’Two PhD students work on this project. Özge Baskan (see page 96) started in November 2010. She is doing experiments to measure flow fields and heat transfer. Our partner CSIRO is developing a rotated arc mixer that we use for our case study. The radial flow is generated by two windows in the axial flow tube, which is placed inside another, rotating tube. The geometry of this system makes it easy to measure the flow field and it is easy to describe it in a numerical model.

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1 Basic Kenics element for heat-transfer and mixing applications.

2 Two dimensional setup.

3 Rotated arc mixer.


mixing structures that are formed in the three dimensional flow lines. Speetjens: ‘Commercial software already has the possibility to determine flow lines, but when you zoom in to the small-scale structures − and that is what we want to do − these models show major errors. At first sight the flow lines look like disordered spaghetti, but in a way they have to be organised. We have to identify those elements that control the mixing behaviour and their connection with heat transfer.’The interests of researchers and users of this project are essentially analogous. Speetjens: ‘We like it very much when industries are interested in our work, and they do have interesting questions. For us it’s also good to know what is going on in industrial situations. The main companies in the user committee are Primix, a producer of static mixers and heat exchangers, and the research department of DSM, where we

Under certain symplifying assumptions the evolution in the axial direction can be represented by a time evolution and a stationary three-dimensional system can be translated to a two-dimensional time dependent system. The setup Baskan uses is a 2D version of CSIRO’s rotated arc mixer. It consists of a round reservoir, filled with a 1 cm layer of silicon oil. The flow in this layer can be forced by two or more belts in the rim of the mixer, which are alternatingly rotating, to reorient the flow field. Using hot water reservoirs in the rim, the temperature of the reservoir can be regulated, in order to do the heat transfer measurements. Another experiment is a 3D case study of a static mixer in a tube, equivalent to a real industrial situation. Since January 2011 Esubalew Demissie focuses on the numerical part of the project. So far he has worked on technical issues to obtain a reliable code for the


Follow up projects‘It is clear that there will be many unanswered questions when we finish this project. We are already thinking of doing a follow up STW-project with two PhD students. We try to develop our tools now in a generic way, so that we are not tied to a certain geometry, and we have laid the foundation for examining heat transfer, but we want to look at it in a more universal way. During a sabbatical leave this year I want to acquire more detailed knowledge of this subject. Major advances are being made in microfluidics at the moment, but there are many open problems. Once we know how to control coherent flow structures for mixing and heat-transfer purposes, we will have new possibilities.’

PeopleÖzge Baskan and Esubalew Demissie will be working on the project until the end of 2014.

Co-applicantsProf. dr. Herman Clercx (TU/e).

planned an extended research visit for Özge. The participants from Primix do not have a scientific background, but they are very much interested. They know that we will not produce a completely optimized mixer/heat-exchanger in these four years, but for them all insight that is gained is useful. Another participant is Guy Metcalfe of CSIRO, the Australian TNO. He plays a double role. He is very actively researching the application of these systems, and he is also a potential user. I have worked with him before, when I was a postdoc, so I already knew him very well before this project. CSIRO wants to build bridges between the scientific world and industry. They aim to transform fundamental scientific knowledge of mixing and heat-transfer behaviour into useful mixing devices and heat exchangers within five years. In some cases their rotated arc mixer uses just twenty percent of the energy that is traditionally needed when applying a Kenics mixer.’

Highlights‘Özge has already published a paper on measurements of a three dimensional flow field created with a Primix mixer element, which is a nice result.’‘Esubalew has developed software that works now. We can import a flow field from a commercial computational-fluid-dynamics software package and then we can see how the mixing works for laminar flows. It has been a lot of work, but it is essential to have good software for this goal. We are going to apply this code on the rotated arc mixer and on Kenics mixers and then we have planned to write a paper about the results. The next step will be to take on heat flows.’


86 Next project top secret

Lars Beex

88 The project still feels like my baby

Kazem Yazdchi

91 Inspiration from Texas

Timo van Opstal

93 Sometimes I feel like a worker

Jitang Fan

96 At each step I learn something new

Özge Baskan

98 Synthesis of measurements and models

Richard Dwight

101 User committees are very effective

Gertjan Kloosterman

103 Stimulate contributing companies to share experiences

Famke Kraaijeveld

106 People are key to the project

Piet Kok

109 Ute Ebert’s project was a stepping stone

Ed Pols

112 TNO can bring results further towards applications

Sander Gielen

Personal experiences of PhD students, staff and users


‘If I had known in advance what would come out of this project, I certainly would have jumped to the opportunity. I’m very happy with the results’ says Lars Beex, shortly after receiving his PhD in October 2012. When he finished his master studies cum laude in 2008 in the same group, the section Mechanics of Materials, faculty of Mechanical Engineering, Eindhoven University of Technology, he had no clear idea of what his future would look like. A few companies offered him jobs, and he could pursue his academic career in Eindhoven with two options for PhD projects. Beex: ‘In my opinion those opportunities in industry were not very challenging. It just seemed nicer to continue working on the subject of my master studies, the modelling of fibrous materials. When I graduated I had the feeling: is this it? I had expected that the study would have

demanded more of me. I also got an offer for an experimental PhD project, but I favoured the theoretical part of this work. Now I found out that I like to do research and I will continue to do so.’

‘We developed a new methodology based on a model for atomic grids, taking into account irreversible processes in fibres by adding dissipation. The papers we published are very theoretical. Before these models can be used for applications there’s still a lot of work that has to be done. I’m happy that master students were involved in the project; they took care of the link towards utilisation. The essential step we wanted to make in this project is the coupling between the scales in a multiscale model, and that’s what I did. The simulations you can do with that methodology are much larger in the end.

‘ Next project top secret’

Lars Beex

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1 Lars Beex’s PhD ceremony.


Anyway, it would be nice if our work will be continued in follow-up projects and we can hopefully see the fruits of our work in a couple of years.’

Beex liked the experience of working with industrial partners: ‘It’s nice to see what’s going on in industry and I was happy that other people besides my advisor were interested in my work. However, I can imagine that some companies like to have something implemented, which is not new at the academic level and does take a lot of time. I can imagine this could slow down the progress of my work, although it’s nice that you don’t have to wait if someone is ever going to use and appreciate it in the future. Anyway, this did not happen in my PhD project, I was very happy with our partner’s attitude . And the way of working with master students keeps everybody happy.’After his graduation Lars Beex started as lecturer at Cardiff University. Beex: ‘Just like Ron Peerlings (see page 36), I will write my own research projects there. The topic of my first project is top secret!’ He laughs. ‘Well actually I would like to work on one of Ron’s ideas. The model we developed can also be used for biological tissues. A few things have to be adapted in the model, and changing it will take a few years time. Once that is fixed we can work towards new applications.


Kazem Yazdchi has worked on the MuST project ‘Hierachical multiscale modeling’ together with Saurabh Srivastava and Vitaly Ogarko, lead by Prof. Stefan Luding (see page 64) in Twente. He graduated in December 2012, when he had already started to work at the competence centre of Bosch Transmission Technology in Tilburg. This international company with more than 900 employees focuses on production and innovations in the field of transmission technology.

Luxury positionYazdchi originally comes from Isfahan, Iran. He did a bachelor and master in mechanical engineering in Tehran. ‘When I finished my studies in Iran my main challenge was to have a new experience abroad, being at an international university with international students,’ he says.

There were a couple of reasons to look for an academic position in the Netherlands. Yazdchi: ’I had many friends that were going abroad for a PhD and normally Netherlands was one of the targets because of the three good technical universities and for international students the Netherlands is easy to enter. Actually, before Twente I had also applied at Manchester University but then there were quite a lot of issues about visa and those kind of things. And it was nice that two of my cousins were studying here, one in Delft at Aerospace Engineering, the other at the university of Amsterdam. I also had three other offers for academic positions, in Barcelona, in Vancouver, and in Trondheim in Norway. That was actually quite a luxury position.’Yazdchi saw an advertisement for this project on a Dutch website and he applied

‘ The project still feels like my baby’

Kazem Yazdchi


I could use this knowledge for a real product. It is not only practical and a completely different atmosphere in here, but the topic I work on is also not exactly the same, it’s more on the metallurgical and material science side. I’m dealing with developing new processes or optimising a current process. We are trying to optimise the heat treatment and phase transitions in steel, to see how steel behaves at different temperature and times. We are tuning the temperature and time of annealing or hardening and we even have nitriting and oxidizing facilities. Because of my knowledge of simulation and modelling, I’m partly also involved as a consultant with another group.’‘I think my work here is very close to what Tata Steel does in the MuST projects. We have a couple of colleagues who are actually coming from Tata Steel and now joined our group. Bosch participates also in STW-projects, and we are continuously supporting PhD projects of the M2i institute, not only inside the Netherlands, but also in Austria, Germany and Belgium. Bosch is a growing company and they are active in working with universities and supporting research projects. There is a good future in here, that’s why I came.’

Friends‘It’s hard to say now where I will be in five years. I miss some of the activities and challenges I have in academic, but at the same time everything is new and I’m really enjoying it. I cannot guarantee what will happen in two or three years. The type of discussions and way of looking at the problems is a little bit different here. With Stefan we talked more about technical things, we take time to see different possibilities. Here we need to see how we

successfully. ‘I was invited to come for a month to work with Stefan Luding. It was a pre-involvement, both of us were seeing how it was going. It was summertime, everything was beautiful and fantastic. After this month Stefan offered me the position. I was the first person working in this project. After six months another PhD student came in, Vitaly Ogarko. And then after three months the postdoc Saurabh Srivastava arrived. I think we complemented each other very well, because my background was on the physics and mechanical side, Vitaly was more on mathematics and theory, and the postdoc was specialised in programming. We were combining all the knowledge we had.’

‘I was not only working to bring input to the project, but I really had the chance to develop myself and my skills. In that sense I was lucky to be in that situation. I did my PhD in exactly in four years. One part of the output of the project is software for solid fluid interaction with a phase flow. It is based on the initial data I derived during the first two years. The postdoc, Saurabh Srivastava, the Indian guy, implemented this information in a C++ programming package. I think by now it is online, so people can comment on its use.’

Tough decisionIt was a tough decision Yazdchi had to make between continuing his academic career or looking for a job in industry. ‘Before accepting this job I had a chance to start a postdoc position in Eindhoven. But again I decided to have some other experience. During many years of study I was mainly a theoretician with a simulations background. I thought it would be good to have some experience in a real factory. I chose for interaction with people and production and I wanted to see if


can solve the problem right now, with any solution. We need to produce right now. Here it’s more money issues and not so many people are interested in pure physics.’‘Looking back I think I did a really nice PhD project. I feel lucky it was relatively big. Three people were involved, other projects in our group normally have one, or two. MuST meetings were always nice. I had a couple of friends working on other projects within this multiscale programme. I saw them at least once a year when we met with all the projects. One of them, Sourena Yadegari, is in Delft with Sergio Turteltaub and his research is in the field I am working in now. He was asking me how it looks like here, because he is also making a choice between staying in academia and working in industry.Sometimes in the weekend I still have contact with Stefan. Although I do not have so much time for it anymore, the project still feels like my baby.’


‘There’s a good balance in my work between theory and programming’, says Timo van Opstal, PhD student in the project Adaptive Multiscale Methods for Airbag-Deployment-Safety Simulations, lead by Harald van Brummelen [see page 72]. Timo met his supervisor during his master studies in Delft at the faculty of Aerospace Engineering. ‘Harald invited me to work on this project in Eindhoven. My background was fluid structure interaction, which suited very well.’ At the moment of the interview, Timo has just started writing his thesis. The defense is planned in December. The thesis will be based on four papers, of which two have already been published. ‘Shortly after the start of the project, Harald had the idea to work with a boundary element method for the discretisation of the flow of air in the airbag. That seemed to be a logical step and

soon it became clear that it was the best way forward. With this method, one only requires a computational mesh on the boundary of the fluid domain, not for the fluid domain inside the airbag. Since a computational mesh on the boundary is anyway required to represent the airbag, this poses no restriction. The internal domain of an airbag changes dramatically in the deployment process, changing from an intricately folded configuration to a fully inflated bulbous shape in only milliseconds. We therefore refer to airbag deployment as a geometric multiscale problem. This enormous change in the geometry of the fluid domain precludes methods based on a mesh in the interior of the airbag.’

Model adaptivityThe boundary element method became a

‘ Inspiration from Texas’

Timo van Opstal

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1/2 Promotie van Timo van Opstal 12.12.2013.


between students and professors. Everybody is trying to be involved with other projects. Exchanging experiences is very motivating. Sometimes you get new ideas about your own project in this way and others give direct input to your work. Encouraged by everyone’s experiences in Texas we also focus on the exchange of ideas in our group in Eindhoven. It is exciting to hear everything about the variety of projects of Harald van Brummelen, ranging from collision relations, flow in thin gases, and tumour growth to droplets.’

UsefulnessVan Opstal is still not absolutely sure about his future after obtaining his PhD. He feels that an academic career suits him well, but he does not rule out a job at a company. In his project Van Opstal collaborates with Mervyn Lewis from TNO Automotive Safety Solution, a company that develops technical and embedded software, among others for the automotive industry. ‘I asked him what the important research topics are for TASS and how they deal with them, and how things work out in practice. The idea is that they can extend their software with the methods I develop. They use a different kind of software, but I believe Mervyn Lewis is very well able to implement what I do in their system. He is excited about the work and the results. He tries to convince his managers now about the usefulness of this project.’

red line in Van Opstal’s work, and it took him to Texas. Van Opstal: ‘In the boundary element method you need to make restrictive assumptions about the flow, and those assumptions are not valid everywhere in the process. It is necessary to split the domain in an area where you can use boundary elements in a Stokes model and an area where finite elements in a Navier-Stokes model are more appropriate. Important questions are how these models can be coupled and where the model interface has to be defined, so that the errors are minimized. Answers to these questions can be found in model adaptivity. Seminal work on this subject has been performed at the Institute for Computational Engineering and Sciences of the University of Texas at Austin. I was welcomed into the group of Dr. Oden, where most of the work on model adaptivity is performed. Even though my intended supervisor, Serge Prudhomme, was just leaving to Polytechnique Montreal, I had fruitful collaborations with other people to finish the project I came for.’‘Another reason to stay a few months in the USA was to have a taste of how things work in another organisation in another country. Other members of our group who went to Texas were excited about their experiences, and I also liked it very much. Regularly they organise presentations and work meetings with discussions between students and


Jitang Fan is one of the three PhD students in the project Experimental and computational techniques for the design of impact-resistant materials headed by Prof. Bert Sluys in Delft (see page 76). He studied solid mechanics and properties of materials at the Chinese Academy of Sciences in Shenyang, near Beijing. He finished his master studies in 2008 and subsequently he worked as a researcher at a university in Hong Kong. ‘I was looking for a PhD abroad and I found this project with Google search and the keywords solid mechanics and materials and then immediately this project popped up’, he says. ‘I sent an email to Bert Sluys and he asked me to come over. It was the only project I tried. In the beginning I got a one year contract and I started working with Jaap Weerheijm, professor at TU Delft and senior research scientist at TNO, as my daily

supervisor. I had never studied high speed loading before, this was new to me. After an evaluation, Jaap told me it was going well, and I could continue to work here for another three years. Now only one and a half year is left, so I should hurry up to finish my tensile and compression tests.’

Explosion‘My project is measuring the impact resistance of polymer materials. The properties change under high speed loading. The first thing I did was building up a good horizontal split-Hopkinson Bar experiment. Using this equipment we can measure the material properties under different loading weights.’ The polymer sample is placed in a holder between the ends of two straight metal bars. At the end of one bar an explosion, triggered by high pressure

‘ Sometimes I feel like a worker’

Jitang Fan

1

1 Tightening bolts to fix his polymer sample in the horizontal split-Hopkinson Bar.


aluminium alloy, and the material of the grabbing part has to be made of the same material, otherwise the bar or the grab will break. I screw the sample in the holder and I also tighten it with many bolts. The bolts are made of steel, because aluminium is not strong enough, it breaks. These steel bolts also get ruined when I do the test several times.’

One glass particleFan starts mounting his sample. He cuts off a piece of polymer that fits in the holder. He uses sand paper to smoothen the surface. Fan: ‘When the surface is very smooth you can see what happened inside the sample after the experiment.’ It takes a lot of time to tighten the sample very precisely with twelve bolts. Some bolts are larger than others. ‘Sometimes the bolt holes deform

air, creates a stress wave that propagates through the bar and the specimen, causing plastic deformation and cracks in the polymer. ‘First I had to measure the stress and strain of the bar, and now I use those material parameters to calculate the stress and strain of the sample material.’Fan proposes to show me his set-up, so we head for his lab. Fan: ‘In the beginning it was very difficult to attach the sample holder cage to the bar, because when there’s an impact the bar vibrates with quite high frequencies. One part of the experiment is a compression test, which is quite easy to do, another part is the tensile test. For this experiment you have to grab the material very tight, not to loose it during the tensile loading, and that is very difficult. I have worked half a year to correct this problem, but now I can do it. The bar is made of

Clau

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through the impact’, he says, ‘and when that happens I make them bigger and use bigger bolts. I almost finished a series of experiments with different loading rates from 500 to 3000 per second. I also did tests for which I made a piece of polymer with just one small glass particle exactly in the centre and then I did the tensile test. I wanted to know what the effect is of one particle in the polymer. I study how cracks initiate and how they grow.The other two PhD’s do a different kind of work; modelling and simulation. Sometimes I send my experimental results to them and they use the data in their models. We have user meetings twice a year, with Jaap Weerheijm and some other persons from TNO and STW. The three PhD students present their work there and we discuss future work. If I suffer from some problem I can consult with them and then we find a way to deal with it.’When the sample is finally fixed I hear a loud explosion and the polymer is torn apart. ‘Broken from the centre, that’s nice,’ says Fan. ‘These are good data. I keep the parts because I want to study them with a scanning electron microscope to look at cracks inside and at the surface of the sample, which is quite expensive to do.’While dismounting his sample Fan shows me a crooked bolt. ‘You see? Sometimes I feel like a worker. I do like seven experiments per day. I scare the people in the offices, so I do my tests during lunch time and at four or fiveo’clock in the afternoon. During the day I analyse the results. In the end I will write a paper. If Jaap has an open position when I finish my PhD. I would like to continue working with him. He and the people I work with here give me a lot of support.’


Özge Baskan

Özge Baskan is doing her PhD at Eindhoven Technical University in the MuST project Lagrangian “mixing analysis” of heat transfer: a new way for thermal optimisation, supervised by Herman Clerx and Michel Speetjens (see page 80). She focuses on the experimental and physical side of the work, while her colleague, PhD student Esubalew Demissie, is working on the numerical part of the project.Baskan did her bachelor and master in aerospace engineering at the Middle East Technical University in Ankara, Turkey. After graduation she went to the Von Karman Institute for Fluid Dynamics, near Brussels in Belgium, for a second master. Baskan: ‘First I did some courses there about fluid dynamics and then I did experimental work on breathing and the flow of air in lungs. I had a set-up for mimicking the expansion and contraction of lung airways. When I finished the course I was

looking for a PhD I decided to come to the Netherlands, because the conditions are good here for a PhD student, and there are many international students around.’

Unexpected thingsÖzge Baskan takes me to the lab at the Department of Applied Physics. At the moment of the interview the setup is not in use, but in the previous months she did a series of heat-transfer and velocity-field measurements in a mixing system with chaotic advection. The installation looks like a circular tray with a diameter of several decimetres, which is filled with a thin layer of liquid. She uses an infrared camera to examine temperature fields, and a CCD camera for velocity field measurements.The setup mimics the behaviour of flow in the cross sectional area inside in-line mixers.

‘ At each step I learn something new’


In the liquid layer time periodic flow fields are created with rotating belts in the boundary, that run in turns. Baskan: ‘In the beginning I applied magnetic forcing in stead of the belts. For this I had to use salt water that was getting dirty and became opaque after a while. That is not good for optical measurement systems. So we decided to change the system and to work with silicon oil.’In order to diminish some effects of the bottom layer Baskan uses two layers of liquid; a glycerol in water solution at the bottom and the silicon oil on top. But when something goes wrong the two layers can mix. ‘Then I have to clean everything and put new liquid in. It is not easy to work with silicon oil, it sticks and it is hard to remove. Those things take a lot of time. We can also apply temperature conditions at the boundary of the system, to create a heat flux from the boundary to the centre of the system, which is even more difficult. I fill a basin around the rim with hot water of a constant temperature. When I do an experiment, the temperature of the fluid changes. Before I can perform another experiment, I have to wait until the effect of the previous experiment levels off. Also, when something goes wrong with the initial conditions of the experiment, I have to wait until the setup gets stable again. Many unexpected things happen when you are doing experiments, but I like that side of the work.’

Night workBaskan doesn’t want to do experiments during the day because there are construction works going on near the Applied Physics building. ‘You always feel that the building is shaking. So I start my experiments after 5 p.m. and I shut down in the morning. During the day I do simulations or process

my data. At this moment I am working on a paper about the evolution of temperature fields in a domain with time-periodic flow field, representing the cross sectional area of an inline mixer. We see that there are persistent patterns in the system. Maybe the amplitudes of these patterns are changing, but the structures stay the same. Before designing the setup, I did many simulations. So I already knew what was supposed to come out. And indeed the intensity of these structures are well fitted to an exponential function in the first few periods, as suggested by the simulations, then, due to the heat losses in the system the intensity is not changing anymore, but the patterns remain the same.’Baskan has several plans for future experiments. She wants to do experiments with four instead of two rotating belts, to change the parameter space. And there is another experimental facility at the department of Mechanical Engineering where she supervises a master student who is working on it now. ‘We are going to implement Laser-Induced-Fluorescence techniques for the measurement of temperature fields in this setup. We have to use a fluorescent liquid and when there are temperature differences in the system the colour intensities change. At the moment we are looking for a liquid with the proper viscosity.’In the future Özge wants to go back to Turkey. ‘I want to remain in the academic world , but I think it’s not easy to find an academic position in Turkey. There are nice laboratories, but they are still developing. Maybe I will stay here for a few years to get a postdoc and some more experience in a different country. I like what I do now, at each step I learn something new and this makes me happy.’


‘ Synthesis of measurements and models’

‘I was amazed how little measurement data is available on the solidification of steel – even in basic situations like steel cooling in a small cup. The only information Tata Steel gets about what is going on inside the much more complex continuous casting case is when the whole thing breaks down, and there is liquid steel all over the floor. That data is hard to use’, says Richard Dwight, in his office at the Faculty of Aerospace Engineering in Delft. He joined Hester Bijl’s MuST project (see page 52), New simulation techniques for flows interacting with transforming structures, in 2010. ‘I’m an assistant professor, acting as PhD student Jouke de Baar’s daily supervisor. My role in the project was bringing experiment and simulation together, combining them to get more insight into real physical processes. We got completely different results from our preliminary model

and the experimental data. There was really no error information or confidence in either the experiment or the model. In that situation the only recourse is expert knowledge; the same knowledge that built the models in the first place. This was a big challenge.’

Uncertainty quantificationRichard Dwight studied mathematics in Cambridge, UK, and did his PhD on efficient methods to numerically simulate the compressible Navier-Stokes equations governing aerodynamics, at the Deutsches Zentrum für Luft- und Raumfahrt (DLR) in Braunschweig, Germany. He remained working there as a researcher after his graduation, until he got the offer for a position in Delft. Dwight: ‘At the DLR I was starting to get interested in uncertainty quantification and I knew that Hester Bijl

Richard Dwight


it’s impossible to reconstruct everything from a few strain gauges. But we’ll also find out how to better instrument future turbines.’

Long bridgeWorking together with industrial partners during the MuST project reminds him of his work at DLR. ‘DLR is a large and well funded institute, whose role is to form a bridge between academia and industry. And that is a long bridge. Before a scientific paper can be used in industry there is a lot of work that has to be done. Typically it took five years before somebody in industry started to use my work. And from the first scientific paper until a method is mature enough for the DLR to take an interest, can be another five years. Those are the kind of time scales we are talking about. Connecting universities directly with the users risks therefore quite a strong conflict of requirements and expectations. If we work directly on the problems that the users specify, we would not be able to publish at all. If we worked exclusively in our own world, the users would quickly lose interest. The challenge is to communicate expectations so that no one is disappointed, and find out in what ways users and academics can best help each other.’Like Hester Bijl, Richard Dwight prefers to work with open source software. ‘There’s a lot of time wasted in reproduction of work. In science the codes are almost always ad hoc. They are cobbled together for one specific application of one specific method, and only just work for that. This is not necessarily a problem, except that they are not presentable and are therefore not shared. I would not mind if publication of journal articles in numerical analysis was conditional on submitting a minimal, clean

was a leader in that. When I had a six month sabbatical I came to Delft and I liked it here.’‘The unifying theme of my research is combining simulations with experiments to get closer to the truth. The mathematical tools we use come from statistics and numerical analysis, two fields with a lot to learn from each other. At this interface there are many opportunities for new methods. Broadly speaking, we relate measurement data to simulations predictions using a statistical model. Probability allows us to quantify our level of knowledge. In MuST the most interesting work for me has been the analysis of intrinsic error in models themselves (in particular turbulence models). In the numerical analysis community this is a source of error that is often neglected, because there is no easy way to quantify it without experiments. Notwithstanding it is the dominant error in most simulations. We came up with some of the first estimates for this error; trying it out was the nicest part of the project.Hester Bijl is encouraging Dwight to apply for STW-projects. ‘I have some nice ideas. I would like to bring these methods a little bit closer to practical applications, like wind turbines. Wind turbines experience vibrations due to all sorts of different effects, which cause reduced life and high maintenance costs. If the blades start to oscillate strongly, you want to know what happened there, is it a gust from the flow, or some structural resonance? Turbines are well instrumented by default with accelerometers, and strain gauges can be placed in the tower. That’s going to be our data source. We want to find out what happened by matching the observed data with simulation. The biggest challenges is limited data, because we don’t have many measurements of the flow, and


reference implementation of the proposed method. Journals demand that contributions are sufficiently detailed for the results to be reproducible – that’s a fundamental part of science. Reproducibility could be enabled enormously by having code available. That would accelerate everyone’s investigations.’


‘Simulation tools can be used to gain insight, try out ideas without having to make prototypes and therefore saving costs in product development’ says Gertjan Kloosterman, as we speak in the Dutch office of Dassault Systèmes in Maarssen. The company, also called the 3D EXPERIENCE Company, is a world leader in 3D design software, 3D Digital Mock Up and Product Lifecycle Management solutions. In 2005 Dassault Systèmes acquired ABAQUS Inc., a simulation software company, and Abaqus, the software suite for finite element analysis, is now part of the SIMULIA brand of Dassault Systèmes.In 2002 Kloosterman received a PhD from the University of Twente for his research on finite element simulations. Now he works for the SIMULIA brand of Dassault Systèmes as a consultant and trainer. ‘One

of my roles is to listen to what customers want and to learn what’s going on at universities’, he says. ‘Academic researchers try to invent new algorithms to describe new physical phenomena. I communicate the most promising developments to our R&D department. When there’s similar customer demand from different parts of the world they might start implementing new simulation software.’

Service providerKloosterman is involved in the user committees of four MuST projects. ‘Multiscale simulations are very attractive and fit very well in our activities. During my PhD I already got to know many people from the research groups that are involved in the MuST programme. And many participants, universities as well as companies, are

‘ User committees are very effective’

Gertjan Kloosterman


very complex material model, and it works and has predictive power, superb! In the project of Marc Geers (see page 40), who worked on fibrils, something came out that was quite an eye-opener to me: the lack of equilibrium of cohesive elements. They wrote a paper about it. I realised that it was something I struggled with many years ago, and now somebody found a reason for it.’‘Van der Giessen’s project (see page 44) about molecular dynamics and how that works out over different scales to the properties of an interface was really fantastic. It’s very impressive to see that this is possible at all.’‘It’s funny to see in Huyghe’s project (see page 48) that they discover something that’s only logical, but nobody wants to believe it: the non-continuous crack formation.’

Maintenance‘As long as it is properly documented, we don’t care what kind of software researchers use to write their code, we can always reconstruct it. But there is a problem when a PhD student departs. When the knowledge is gone it does not take long before the code stops working. A code needs maintenance, otherwise it’s dead When a code is designed as a plug-in for commercial software − that does not necessarily have to be ours − then chances are higher it will still be used after a few years. Commercial software companies take care of updates, so that software can be used on new platforms.’

customers. As I was interested in the topic, taking part in the user committees automatically came my way. In the beginning I shared the job with a colleague, until he left the company.’‘User committees are very effective as a networking possibility and to maintain contacts. It’s good to listen to customers or potential customers on a regular basis. And it’s interesting to keep in contact with universities. Many academic researchers are future customers of our software. Our goal is to build long-lasting relationships.’‘My role is a bit different from other users. We act as a service provider between researchers and companies who want to utilise the technology. We are taking part with the perspective of making some of these technologies available in the future.’Kloosterman participated in the MuST introduction day where he saw many different aspects of the programme. ‘The four projects we were asked to join are closely related to finite element implementations and some researchers use Abaqus. The finite element method is very general, so even if one uses another solver the results can almost directly be transferred to another method. Of course this holds only for the upper level in multiscale methods, and sometimes for the middle scale. On the smallest scales discrete dislocation modelling or other molecular methods are used.’

Open discussions‘Every project has contributed to my level of knowledge. I’m really excited about the interaction with the researchers and the very open discussions during the user-committee meetings. Most of all I’m inspired by the finite element part of the projects. The group of Sergio Turteltaub (see page 56) has built a


Famke Kraaijeveld is geomechanical specialist/researcher at Shell. She received her PhD on Propagating discontinuities in ionized porous media in October 2009, from Eindhoven University of Technology, where Jacques Huyghe was her co-supervisor. Before she left she had been working together with PhD student Francesco Pizzocolo for a few months. ‘When Jacques involved me in writing the application for the POROMULT MuST project (see page 48)’, she says ‘I could not have imagined that I would take part in this project as the representative of a user. Shell was in the user committee of my PhD project, which was also funded by STW. When I almost finished they offered me this job. As the project is a continuation of my PhD work, I had the right background to take a chair in the user committee. It was nice to look at this project from a different

perspective, and see how useful the learnings are for Shell.’

ContainmentKraaijeveld works in a team that focuses on containment of fluids in soil. ‘We make models of the subsurface to study if and where problems may occur during drilling, oil production and injection of fluids. When we drill new wells we need to know the pressure locally on forehand to decide what kind of drilling mud we have to use in order to prevent failures. Furthermore, deformation of the subsurface is predicted to map possible risks. Also, we need to be able to measure and predict where fluids go after injection for safety and legislation. Our models cover large production areas.’‘In the past simple linear-elastic models were sufficiently predictive, but now we need to

‘ Stimulate contributing companies to share experiences’

Famke Kraaijeveld


numerical work. After two years the researchers in this project decided to stick to 2D models and to look at new methods, which is theoretically interesting. But for us that is not good enough. We cannot work with 2D, because the world is 3D. We are sponsoring the research project and we cannot influence the research direction. That is a good thing because research has to stay pure. When the researchers decide to change the research direction, it can either be bad for us, or it can also become more interesting. But we contribute energy and money and we like to get something in return. Now the results are several papers, but we still do not know if a method is going to work out for us. As far as I know nothing was implemented in commercial software. This could raise the threshold for us to join a new project.’There are no plans yet for contributing to a follow-up of this project. Kraaijeveld: ‘I am personally interested in this work and I think that we will work together in the future. But as long as it has not been proven that the methods work in 3D, I cannot convince the people at Shell to put in more energy. Also, I think it would have been good if POROMULT had collaborated more with other groups in Eindhoven. I know that there are several groups that work on these topics. Sometimes they collaborate but sometimes they also act as competitors. They should try to work together and create a win-win situation. In the same way we can also improve the exchange of information here at Shell. In our office in Rijswijk, we support several STW-projects, but I do not have an overview. We can organise that better.’

User committeeIn the user committee Kraaijeveld met Gertjan Kloosterman of Dassault Systèmes.

consider non-linear processes, for instance because we have to deal with geological faults. Special locations and production methods require better soil models, so we add new technologies to our software.’‘Hydraulic fracturing research takes place in Shell, but in our team we currently do not work on that subject. When we started the project with STW, we thought that we would work on this subject, but a reorganisation in Shell changed the direction of our work. We have only limited data available, but I think we would have shared more data if a student had worked here with us to test different fracture models. On the other hand, the software that was developed in this project was not ready for that. Setting up an experiment to compare lab results and fracture modelling would be a good idea for another project.’

Research directionShell often does long term research in collaboration with international universities, in Joint Industry Projects (JIPs). Kraaijeveld: ‘I like to work with the technical universities, to be connected to bright people and smart research. Also the research equipment at universities is sometimes better and they have more time. There is one thing at Shell that causes problems for collaboration in an STW-project: we change our position every four years. So there’s only a slight chance that an assignment matches the period of a project. When we are interested for personal reasons we can choose to stay connected with a project. Otherwise we hand it over to a new person, which does not always work out very well for the project.’‘I still think that the POROMULT project is nice and promising. But I am a bit disappointed about the progress of the


‘In Shell we also use Abaqus software for finite element analysis. We talked about the modelling methods that were used in this project. The problem for Abaqus was that there were no examples that could be used to make implementations. From our perspective it was really hard to give examples because we could not share any data. So we were stuck.’‘One of the nice things of STW-projects is the opportunity to get into contact with other companies that are no competitors. They share the same research interest. For Shell it is good when Dassault Systèmes picks up the results, because usually we work with commercial software. And it is nice for Dassault Systèmes to meet companies in the energy branch as new potential customers.’‘The good thing of the user meetings is that the communication is straightforward and open. Everybody can share experiences and speak freely about methods that work and the ones that don’t, and about how difficult it is to make implementations. Those are the things that are easier to share with words; you cannot learn them from scientific papers.’‘Looking back it would have been a good idea if I had presented the work we do at Shell at one of the user meetings. It could have created an opportunity to show how things go in practice and what problems we encounter. It would create a better understanding between all parties what the problem to solve is and what the expectations are. Now there were presentations about the research work in the project, but it would have been better if we had created two-way communication. The other participants do not know much about the problems we face in our work. I think it would be good to stimulate contributing companies to share experiences during the user meetings.’


Piet Kok is researcher at the applications and engineering centre of the R&D department of Tata Steel in IJmuiden. With 400 employees in five buildings, it’s the biggest R&D department of the company. Another 200 researchers are based in the UK. Piet Kok’s work focuses on steel applications like for example packaging and automotive applications. Kok: ‘We want to work towards stronger kinds of steel that are lighter and easy to transform. Those are conflicting properties, because the stronger steel gets, the harder it is to change its shape. We have found a solution: a kind of steel that is easy to shape at high temperatures, but once it cools down it regains its superior strength. We use a combination of different microstructures and different hard and soft phases in the metal. In order to understand which way to go we use models. Computers

are cheaper than experiments. Brain power is not expensive.’Tata Steel is involved with several MuST projects. Piet Kok himself participates in the user committees of Van der Giessen’s (see page 44) and Turteltaub’s (see page 56) projects where he gives presentations of how he uses or could use the results of their work. Kok: ‘Sometimes I spend half of my time to Turteltaub’s project, in other months there are just a few emails. I would say it’s one day a week in general. For Van der Giessen’s project I spend one day in two or three weeks. Van der Giessen’s project is rather fundamental. Our aim was to get more knowledge about all the scales of his model. We try to understand what is happening at the atomic scale, but there’s hardly any practical use for us there. The lowest scale that’s important for our aims is

‘ People are key to the project’

Piet Kok


possible in projects. Generally I have a good idea of how a project is going to work out. The only thing you can’t foresee is how a PhD student will perform: there are big differences. People are key to the project, not so much the topic of research.’‘We cannot test our computonium in the steel factory, changing little things in the production process causes tremendous stress there. Everything has to stay the same as much as possible. We have proofing installations in the lab, where we can replicate processes. And we can do transformation tests to check our predictions. The power of modelling is that you are able to create structures that cannot be produced. That’s nice to do, but it’s also useful. In this way we are able to create microstructures with superior qualities. Afterwards we have to convince everyone here that it is also possible to use them.’

Facilities and collaborationsTata Steel in IJmuiden has good computing facilities. Kok: ‘There’s a CAD room next door with a cluster of twenty-four connected pc’s for parallel computing. If necessary we can go to SARA in Amsterdam. We have a selection of dedicated software, which we also need to support our customers. We pay the full amount, where universities get discounts. My microstructures are built with finite element methods and for this work we can use two big software brands, Marc and Abaqus. I think that the code generated in Turteltaub’s project is generally available. We have no objections, because it’s all very precompetitive. But you need to be an expert to be able to work with that code, and experts there are only few.’Only from conferences and publications I have an idea where we stand in the steel

the microscale. We don’t sell microstructures, but knowing their properties is indispensable for understanding what happens at the macroscale.’

ComputoniumAt Tata Steel Piet Kok is the person who builds models of steel microstructures. ‘We look at the results of academic research and then we develop smart derived models that fit our purposes. We have a whole lot to learn about mechanical properties of steel grains, like hardness. All the experiments we do are at the macro level, like tensile-strength tests. For us it is important to be able to add mechanical properties to the microscale level to our model.’ That is why the results of Sergio Turteltaub’s project are very useful for this work. ‘We generate the microstructures in our model and they add the mechanical microscale properties. Sergio Turteltaub is very enthusiastic about this way of collaboration. When I heard about his work I immediately recognised the opportunity, and they did too.’Kok didn’t know yet that Sergio Turteltaub calls his microstructure models ‘computonium’, but he likes the word. ‘It’s the mathematical translation of a steel microstructure, very visual, so you can check what you are doing. You can twist and pull at the structure and see what happens.’‘We are working together to a great extent, which is very good for the exchange of knowledge. We keep on asking questions to each other, we’re very happy about that. I did not know Sergio Turteltaub and Akke Suiker and the PhD student before this project. I will not say we are friends, but it almost feels like that. I would like to continue working with them in the future. It’s ideal to work in this way, but I understand this is not always

1 Banded computonium structure, with cross sections in x =0, y =0 and z =0 planes.

2 Computonium example, with cross sections in x =0, y =0 and z =0 planes.

21


once that train gets going, it will not stop for a while.’Research projects at Tata Steel can last a short period, but also many years. Kok: ‘That’s the time we need to design a new way of producing steel, like replacing the furnaces. But usually we work at three to five year projects. Four years, like we have now in the MuST programme, is nice. Of course all parties have to be flexible. When new insights arise, you need to be able to choose another way to continue the research. The most important thing is that everybody who is involved can improve themselves.’

world with our simulations. I don’t think steel companies publish everything they do in this field. I believe that our direct competitors in Europe are at the same level. We do have European collaborations in this field. Actually the EU originated from the European Coal and Steel Community, in which six European nations collaborated. Nowadays there’s the Research Fund for Coal and Steel, subsidised by Brussels. Herein European steel companies collaborate with academic partners. Those projects are bigger than these STW-projects, but it takes at least two years to start up a programme. You really have to seek motivation before entering. But


The multiscale simulation interview tour leads to unexpected places. In his home village Buitenpost, in Friesland, not far from Groningen I meet Ir. Ed Pols. We are a few kilometres from Kollum, where Van der Heide, the company he works for, is based.The history of the company goes back to 1927, when a coppersmith, Pieter ‘Bliksem’ (‘Lightning’ in English) started mounting copper rods on farmhouse roofs, to protect them from lightning strikes. Shortly after the second World War Tjisse Van der Heide took over the business in Kollum, and under his guidance the company grew to a nationwide enterprise. Nowadays the Van der Heide group is based in six towns all over the country and almost half of the employees, 115 people, work in the lightning protection business, which makes it the most important company of its kind in the Netherlands and

probably even the biggest in the world. Other specialities of Van der Heide are cathodic protection, electric safety and corrosion prevention. Since 2011 the company is part of the Oranjewoud holding.Although retired, Ed Pols still works at least one day per week as advisor for the company. ‘I am sort of addicted to my job’, he says. Twentyfive years ago he moved to Groningen. ‘With my background in physics it was not easy to find a job in the north of the country, so I was very happy when I found this job. This business has not changed much since Franklin, but it has been fascinating since I started to work here.’

Raise the standingThe link between lightning protection and multiscale modelling is not very obvious. ‘My manager came up with the idea to

‘ Ute Ebert’s project was a stepping stone’

Ed Pols


for participating in a follow-up project of Ute Ebert and Eindhoven University of Technology in the STW-programme Building on Transient Plasmas. The project is called Understanding Lightning: From Terrestrial Gamma-Ray Flashes to Lightning Protection. We expect that we will get some useful information from this project. We put forward some questions from real-life situations. Developments in the world of lightning protection are slow. Most companies use identical methods, but there are a few exceptions. One is the use of ‘early streamer emission devices’. Supposedly these devices send out upward streamers when lightning strikes, so the device will be hit. These systems pretend to be able to win the race toward the lightnings downward leaders. However, the producers and the conventional lightning protection world are quarreling, and that’s no scientific dispute but pure emotion. With Understanding Lightning we would like to get a scientific point of view on this topic.’

Small branch‘Another model of lightning protection is used by a US-based company that we know very well. They use large umbrella’s filled with long needles that are supposed to send out ions. In this way the local electric field is diminished and lightning will strike preferentially somewhere else. The story sounds great, but there is little scientific evidence. They are doing experiments on a test site in Singapore and when something evolves out of it we would like to look at it in the Understanding Lightning project.’‘I would also like to do experiments in a natural environment, that is the only way to do serious lightning research. But in the Netherlands we don’t have enough thunderstorms. We try to join colleagues in

collaborate with scientists and support scientific research to raise the standing of the company. As the biggest company we have relatively high overhead costs, so in general we are a little more expensive. We have to show we are worth it. The company has always been committed to innovation. My manager met with Ute Ebert (see page 60) at a conference and she gave him some papers. Then he approached me because it is my job to translate theoretical information, and that’s how I got involved with Ute Ebert’s MuST project. She has a different approach towards lightning, studying things like sprites, but her group was also working on models for the initial stages of streamers. We thought that it was really interesting, so we decided to participate, although we knew it would not be directly profitable for the company.’‘Now I understand much better how streamers evolve. The models developed in the MuST project make it evident and they are sustained by the experiments. So far there has been no practical value for the company. Actually the results confirm existing models for lightning protection. That is also useful, to know that the foundations of our work are reliable.’

Pure emotion‘Our academic network has grown since we took part in the project. And since we participate we are taken seriously. Before we started some people in the project had the idea that small and medium-sized enterprises are just knocking together their products without any further ideas, but now we are talking on a different level and contacts have considerably improved. So it’s not only the research topic that is valuable.’‘The MuST project was a stepping stone


the USA and the researchers in Singapore. It would be nice if they could place some Franklin bars and early streamer emission devices, so they can compare the preferences of thunderbolts. But our branch is very small, there are about twenty companies with altogether not even 500 employees, it is hard to finance this kind of research. So we are very happy with the activities in the STW-projects. Departing from the results of these projects we want to define follow-up research, we want to stay involved. Even now that market circumstances are difficult, we don’t want to cut down our expenses on scientific collaborations. These projects deserve a long-term vision.’


Sander Gielen was involved with the Multiscale simulation of multimaterial adherence project, lead by Bert de With (see page 60). As senior technologist at TNO, he’s involved in the technological developments of the company. ‘I monitor what happens in the field of model development and I focus on what is needed to make these models applicable in industry. As miniaturization advances, multiscale modelling is getting more and more important. We keep on trying to get more functionality from materials, using material properties on smaller scales. We have to bridge the gap between the scale of the functionality of the material and the scale of applications. Multiscale modelling brings together several kinds of expertise. It requires working in a multidisciplinary way, which is not really encouraged by the faculty structure of our universities. Fortunately,

these boundaries were well crossed in this project, having interaction between physics, chemistry, and mechanical engineering.’

New stepsBesides other industries, TNO supports also industries in the field of packaging and protective coatings for electronics. ‘More and more new packages appear on the market, with ever more functionality and several chips in one box and we notice that the current epoxy packages may not be good enough anymore. With industrial parties we investigate if we can improve processes, designs or materials. NXP and Boschman Technologies were on the user committee of this MuST project, two companies we knew very well from other TNO projects. We were solving similar problems with them and we had also previously studied the

‘TNO can bring results further towards applications’

Sander Gielen


perspective. In this way we learn about the direction of technological developments.’ ‘In order to find qualified TNO personnel, I also observe the students that are working in the projects. When I have identified potential candidates, then we have some goal-oriented talks with students from STW-projects, and in this way we regularly find new employees. During the MuST programme I met PhD student Fidel Valega Mackenzie. We offered him a job and he accepted.’

Balance‘An issue is to ensure that the results of these projects are not lost. Of course all the PhD students write a nice comprehensive thesis in the end, but that does not mean that everything can be used in practice. At TNO we in general do mirror projects, programmes with equivalent themes and we strive to find interaction with STW-programmes. We also give feedback to STW what we see as the questions from the academic perspective and from the utilization perspective. There is always a grey area and I think that this is also a challenge for STW to figure out what type of project fits best in its field. On the one hand STW is initiating programmes on industrial request, with topics brought up by companies. But in the end it’s all about the academic interpretation, because PhD students and postdocs carry out the projects. There is always a tension between the outcome and the accessibility of the results in a later stage. My personal opinion is that TNO can and will play a role there. TNO is in a position to pick up on results and bring them further toward applications. The point is that we can realise the complete chain of contributing parties from fundamentals to application. We have to discuss what everybody’s role is in this chain

effect of moisture on epoxy packages. We shared some details of our research with the academic partners of this MuST project, because we realized several things were beyond our comprehension. We were eager to learn if those topics could be clarified. And I believe they were.’‘Some people say that we have been doing multiscale modelling for so long now, that there’s nothing new about it anymore. But I can see that in this MuST project there were definitely new steps taken, and I am happy that we understand a few things much better now. One of the PhD students visualized beautifully how an epoxy detaches from a metal frame. Now we can really understand why that happens in this way.’

Small companiesThe main reason for TNO to join the project was to be able to transfer the results to industry. ‘We notice that fairly few companies are able to absorb this abstract matter. Only big companies such as Philips, NXP, and ASML can do that. Our role as TNO is to transfer this kind of science also to smaller companies, like Boschman. Boschman produces injection-moulding machines that spray polymer coatings on electronics. The company wants to know if they can change something about their equipment to make better packages; that’s their competitive edge. It’s business when their machines make better components than those of their competitors. We can make specific derived multiscale models, aimed at dedicated processes for these smaller companies.’‘We are also interested in the other MuST projects, so we often participated in the general meetings. These STW-projects are focused on industrial questions, but we know that they are approached from an academic


and how we can use our resources, that are becoming ever scarcer, in an efficient way.’Gielen is in favour of a MuST 2 programme. ‘The MuST programme has uncovered many more applications and new developments, but we have to raise things to a higher level to make good products. Industry is looking for answers to specific questions, while on the other side of the spectrum we are trying to find generic solutions. The MuST programme was quite diverse and provided many answers. A challenge will be to find an even better balance between application and fundamentals in the successor.’


The symposium was opened by programme director Prof. Harald van Brummelen.with a presentation on multiscale simulation techniques and on general aspects of the MuST programme. In his presentation, Van Brummelen pointed out that modern science and engineering are characterized by the trinity of theory, experiments and simulations. Simulations enable virtual experiments at relatively low costs, using non-intrusive methods with low throughput times. In addition, numerical simulations are enabling for the design and optimization of products and processes. On the other hand, the conceptual and computational complexity of simulations are still a challenge, especially for problems that exhibit multiple length and/or time scales. For such problems, new models and techniques have to be developed. In addition, new numerical methods require new skills and often those are not compatible

Final symposium of the MuST programme

22 May 2013, Nieuwegein


and academic participants in an informal setting. The plenary presentations and poster presentations resulted in enthusiastic and fruitful discussions between the - more than sixty - participants of the symposium. The symposium was closed by Van Brummelen with a retrospective of the day and of the overall programme, and a perspective on future developments. As a result of the programme, academic/industrial and academic/academic collaborations had clearly been initiated and intensified, and even new industrial/industrial interactions had emerged. Van Brummelen expressed that, despite the overall success of the programme with regard to establishing and intensifying collaborations, it was evident that not all projects had been equally successful in this respect. For several projects, the effect of

with industrial organisational infrastructures. Outside the scientific community multiscale methods are still relatively unknown, and although many challenges in science and engineering and in industrial applications pertain to multiscale aspects, the first dictionary that includes the word multiscale has yet to be published.The day continued with plenary presentations of the project leaders of all thirteen projects. The presentations provided a comprehensive overview of the recent scientific highlights, new academic/industrial and academic/academic collaborations, the impact on applications and the status of the various projects. During the lunch break, a poster session was held, in which the junior researchers in the projects discussed the details of their work with the industrial


of the MuST-programme, he and the STW-programme office would remain committed to the projects that had not yet been completed.

the financial crisis was noticeable, and the industrial counterparts had been impacted in such a manner that knowledge transfer had been impeded. With regard to the development of the field, Van Brummelen expressed that, in addition to providing scientific progress, the MuST programme had contributed to additions in the course programmes of the EM and JMBC graduate schools and to new initiatives, such as the Eindhoven Multiscale Institute at TU Eindhoven and the 3TU Centre of Excellence for Multiscale Phenomena in Fluids and Solids. Van Brummelen ended with a word of thanks to the participants, to the initiator and former programme-director, Prof. René de Borst, and to the people of the STW-programme office, and emphasized that that, although this had been the final symposium


123 10103 – Geurts

123 10104 – Peerlings

124 10108 - Geers

125 10109 – Van der Giessen

125 10112 - Huyghe

127 10113 – Bijl/Dwight

128 10117 – Turteltaub

128 10118 – Ebert

130 10120 – Luding

131 10121 – De With

132 10476 – Van Brummelen

133 11054 – Speetjens

133 10615 – Sluys

Appendix

Output: List of publications


Criteria

1) At least one researcher, paid by

the STW-project, was involved as

(co-)author;

2) If this researcher, paid by the

STW-project, was involved for

less than six months with the

project, one of the (co-)applicants

has to be (co-)author;

3) Publications of researchers,

paid by the STW-project, that

appeared less than three months

before the date of appointment

on the STW-project are not taken

into account.

Output: List of publicationsReference date September 30, 2013.


10103 – Geurts

International conference proceedings1. Deb, B.S. and Ghazaryan, L. and Geurts, B.J. and Clercx, H.J.H. and Kuerten, J.G.M. and van der

Geld, C.W.M. The effect of phase transitions on the droplet size distribution in homogeneous isotropic turbulence. Proceedings of the V European Conference on Computational Fluid Dynamics ECCOMAS CFD 2010, 14-17 June 2010, Lisbon, Portugal. pp. 1-10. Eccomas.

2. Deb, B.S., Ghazaryan, L., Geurts, B.J., Clercx, H.J.H., Kuerten, J.G.M., Geld, C. van der: 2011. Effect of evaporation and condensation on droplet size distribution in turbulence. ERCOFTAC Series, 2011, 15,DOI: 10.1007/978-94-007-2482-23.

10104 – Peerlings

Thesis1. Multiscale quasicontinuum modelling of fibrous materials, L.A.A. Beex. PhD thesis, 2012.

Journal papers2. L.A.A. Beex, R.H.J. Peerlings, M.G.D. Geers, A quasicontinuum methodology for multiscale

analysis of discrete microstructural models. International Journal for Numerical Methods in Engineering 87, 701-718, 2011.

3. D.V. Wilbrink, L.A.A. Beex, R.H.J. Peerlings, A discrete network model for bond failure and frictional sliding in fibrous materials. International Journal of Solids and Structures 50, 1354-1363, 2013.

4. L.A.A. Beex, C.W. Verberne, R.H.J. Peerlings, Experimental identification of a lattice model for woven fabrics: application to electronic textile. Accepted for publication in Composites: Part A 48, 82-92, 2013.

Submitted journal papers5. L.A.A. Beex, R.H.J. Peerlings, M.G.D. Geers, Central summation in the quasicontinuum method.6. L.A.A. Beex, R.H.J. Peerlings, M.G.D. Geers, A multiscale quasicontinuum method for

dissipative lattice models and discrete networks.7. L.A.A. Beex, R.H.J. Peerlings, M.G.D. Geers, A multiscale quasicontinuum framework for lattice

models with bond failure and fiber sliding.

International conferences8. L.A.A. Beex, R.H.J. Peerlings, Mechanical modelling of paperboard to predict failure during

converting, 10th US National Congress on Computational Mechanics, Columbus, USA, 2009.9. L.A.A. Beex, R.H.J. Peerlings, M.G.D. Geers, From macroscopic to mesoscopic modeling of

paperboard, 4th European Conference on Computational Mechanics, Paris, France, 2010.10. L.A.A. Beex, R.H.J. Peerlings, M.G.D. Geers, Summation rules for the quasicontinuum method,

5th International Conference on Multiscale Materials Modelling, Freiburg, Germany, 2010.


11. L.A.A. Beex, R.H.J. Peerlings, M.G.D. Geers, Novel summation rules for the quasicontinuum method, 11th US National Congress on Computational Mechanics, Minneapolis, USA, 2011.

12. R.H.J. Peerlings, L.A.A. Beex, M.G.D. Geers, Mechanical modelling of paper at Eindhoven University of Technology, 2nd SimPaper Workshop, Milano, Italy, 2011.

13. R.H.J. Peerlings, L.A.A. Beex, M.G.D. Geers, A quasicontinuum approach to modelling discrete microstructures, 23th Congress of the International Union of Theoretical and Applied Mechanics, Beijing, China, 2012.

14. L.A.A. Beex, R.H.J. Peerlings, M.G.D. Geers, A virtual-power-based quasicontinuum method for dissipative lattice models, 6th International Conference on Multiscale Materials Modelling, Singapore, 2012.

Outreach15. L.A.A. Beex, R.H.J. Peerlings, How can computational models prevent paperboard cracking?,

Knowledge days of the Dutch Paper and Cardboard Conglomerate, Enspijk, 2009.16. L.A.A. Beex, R.H.J. Peerlings, M.G.D. Geers, Multiscale mechanics of fibrous networks,

International Vaalsbroek Scientific Meeting of Royal DSM N.V., Vaalsbroek, 2010.17. L.A.A. Beex, R.H.J. Peerlings, M.G.D. Geers, Multiscale mechanics of fibrous networks,

Multiscale Simulation Techniques Programme Day, Nieuwegein, 2010.18. Multi-schaal mechanica van vezelnetwerken, Jaarverslag 2010 Technologiestichting STW,

2011.19. L.A.A. Beex, R.H.J. Peerlings, M.G.D. Geers, Multiscale mechanics of fibrous networks,

Multiscale Simulation Techniques Programme Day, Nieuwegein, 2012.

10108 - Geers

Journal papers1. M.Y.J.R. Solar, E. van der Giessen: Polymer-polymer adhesion via connector chains: An MD

study of the competition between bulk dissipation and connector pull‐out. Comput. Mat. Science 64 (2012), 187-191.

2. Vossen, B.G., Schreurs, P.J.G., Sluis, O. van der & Geers, M.G.D.. On the lack of rotational equilibrium in cohesive zone elements. Computer Methods in Applied Mechanics and Engineering 254 (2013), 146-153.

Submitted journal paper3. Vossen, B.G., Schreurs, P.J.G., Sluis, O. van der & Geers, M.G.D., Multiscale modelling of

delamination through fibrillation. Journal of the Mechanics and Physics of Solids, submitted.

Remark: Two more journal papers to be expected from the work of Bart Vossen.


10109 – Van der Giessen

Journal papers1. S. Echeverri Restrepo and B.J. Thijsse: Towards a virtual laboratory for grain boundaries and

dislocations. Mater. Res. Soc. Symp. Proc. 1224, 137–142.2. S. Echeverri Restrepo and B.J. Thijsse: A genetic algorithm for generating grain boundaries,

Modell. Simul. Mater. Sci. Eng., 21 (2013) 055017. doi:10.1088/0965-0393/21/5/055017.3. S. Echeverri Restrepo and B.J. Thijsse: Atomistic relaxation of systems containing plasticity

elements, Comput. Mater. Sci., 73 (2013), 154-160.

Submitted journal papers4. S. Echeverri Restrepo and B.J. Thijsse: Molecular statics calculation of the Peierls stress in

aluminum, Phys. Rev. B, submitted.5. P.R.M. van Beers, G.J. McShane, V.G. Kouznetsova and M.G.D. Geers. Grain boundary interface

mechanics in strain gradient crystal plasticity. Submitted and first revision Journal of the Mechanics and Physics of Solids.

Papers to be submitted and in preparation6. S. Echeverri Restrepo and B.J. Thijsse: Using artificial neural networks to predict grain

boundary energies, Phys. Rev. B, to be submitted.7. S. Echeverri Restrepo, A. Stukoskwi, X.M. Liu and B.J. Thijsse: Atomic-level simulation study of

dislocation-grain boundary interaction. In preparation.8. X.M. Liu, L. Nicola, Y.G. Wei, E. van der Giessen: Breakdown of continuum dislocation pileup

model. Philosophical Magazine, to be submitted.9. P.R.M. van Beers, V.G. Kouznetsova and M.G.D. Geers. Analysis of energetic contributions in

modelling grain boundary behaviour in strain gradient crystal plasticity. In preparation.

10112 - Huyghe

Thesis1. F. Irzal, The role of fluid in fractured porous media. (2013).

Journal papers2. F. Pizzocolo, J.M. Huyghe, K. Ito. Mode I crack propagation in hydrogels is step wise.

Engineering Fracture Mechanics 97 (2013) 72–79.3. Faisal Irzal, Joris J. C. Remmers, Clemens V. Verhoosel and René de Borst Isogeometric finite

element analysis of poroelasticity International Journal for Numerical and Analytical Methods in Geomechanics 37 (2013), 1891-1907. DOI: 10.1002/nag.2195.

4. Irzal, F., Remmers, J.J.C., Verhoosel, C.V. & Borst, R. de (2013). An isogeometric analysis approach to poroelasticity. International Journal for Numerical and Analytical methods in geomechanics, (2013), accepted for publication.


5. Irzal, F., Remmers, J.J.C., Huyghe, J.M.R.J. & Borst, R. de (2012). A large deformation formulation for fluid flow in a progressively fracturing porous material. Computer Methods in Applied Mechanics and Engineering, 256 (2013), pp.29-37.

Submitted journal papers6. E.W. Remij, F. Pizzocolo, J.J.C. Remmers, D.M.J. Smeulders, J.M. Huyghe. Nucleation and mixed

mode propagation in a porous material. Transport in Porous Media, submitted.7. Faisal Irzal, Joris J. C. Remmers, Clemens V. Verhoosel, Rene de Borst, An isogeometric

analysis Bezier interface element for mechanical and poromechanical fracture problems, International Journal for Numerical Methods in Engineering, submitted.

International conference proceedings8. E.W. Remij, F. Pizzocolo, J.J.C Remmers, D. Smeulders, J.M. Huyghe (2013), Nucleation and

mixed mode crack propagation in porous material, 5th Biot Conference on Poromechanics, July 10-12, 2013, Vienna, Austria.

9. F. Irzal, J.J.C Remmers, C.V. Verhoosel, R. de Borst (2013), An isogeometric analysis approach to fluid flow in a fractured porous medium, 5th Biot Conference on Poromechanics, July 10-12, 2013, Vienna, Austria. 3 F. Irzal, J.J.C. Remmers, J.M. Huyghe, R. de Borst, K. Ito, A two-scale approach for propagating cracks in a fluid-saturated porous material, in IOP conference series: Materials Science and Engineering: Proceedings of WCCM/APCOM; Editors: N. Khalili, Sydney, Australia, WCCM343R1, (2010). 4 F. Irzal, J.J.C. Remmers, J.M. Huyghe, R. de Borst, K. Ito, A finite strain, partition of unity based cohesive zone formulation for propagating cracks in porous media, in European congress of Computational Mechanics (pp. 1038-1/2).; Paris, France, (2010). 5 F. Pizzocolo , J.M. Huyghe, J.J.C. Remmers , K. Ito , R. de Borst. A mixed hybrid formulation for 2D poroelasticity with discontinuity. Proceedings of European Fracture Conference, Dresden, Germany, 2010.

10. J.M. Huyghe F. Pizzocolo, F. Kraaijeveld, J.J.C. Remmers, K. Ito, R. De Borst. Mesh-free, load-free crack propagation as a model of the degenerating intervertebral disc. Mathematical and physical aspects of porous media. Conference in honour of Pieter Raats, Wageningen, The Netherlands.

11. F. Kraaijeveld, F. Pizzocolo, J.M. Huyghe. Step wise propagation of cracks in poroelastic media. USNCCM VI, Los Angeles, CA, August 2010.

12. J.M. Huyghe, F. Kraaijeveld, P.R. van den Broek, F. Pizzocolo, Y. Schröder, Synergy between geo- and biomechanics., in Proceedings of the 17th UK National Conference on Computational Mechanics in Engineering; Editors: C. Sansour, 13-19, The Spencer Institute, Nottingham, UK, Book Chapter ISBN 978 0853582557 (2009)


10113 – Bijl/Dwight

Journal papers1. J.J. Kreeft, B. Koren, A new formulation of Kapila’s five equation model for compressible two-

fluid flow, and its numerical treatment, Journal of Computational Physics, 229 (2010), 6220-6242.

2. M. Bouwman, A. Palha, J.J. Kreeft, M. Gerritsma, A conservative spectral element method for curvilinear domains, in Lecture Notes in Computational Science and Engineering (2011), 76, 111-119.

Submitted journal papers3. J.J. Kreeft, A. Palha, M.I. Gerritsma, Mimetic framework on curvilinear quadrilaterals of

arbitrary order, (70 pages), Submitted to Journal Foundations of Computational Mathematics, 2011.

4. J.J. Kreeft, M.I. Gerritsma, Mixed mimetic spectral element method for Stokes flow: a pointwise divergence-free solution, Submitted to Journal of Computational Physics, 2012.

International conference proceedings5. J.J. Kreeft, A. Palha, M.I. Gerritsma, Mimetic spectral element method for generalized

convection-diffusion problems, in Proceedings of ECCOMAS CFD 2010, Lisbon (Portugal).6. Palha, J.J. Kreeft, M.I. Gerritsma, Numerical solution of convection-diffusion equations with

the discretization of the Lie derivative, in Proceedings of ECCOMAS CFD 2010, Lisbon (Portugal).

7. J.J. Kreeft, M. Weghs, A.H. van Zuijlen, H. Bijl, Multi-level and Quasi-Newton Acceleration for Strongly Coupled Partitioned Fluid Structure Interaction, in Proceedings of Coupled Problems 2011, Kos (Greece).

8. J.J. Kreeft, B. Koren, A new model and numerical method for compressible two-fluid flow, in Proceedings of ECCOMAS 2012, Vienna (Austria).

9. B. Koren, J.J. Kreeft, A new model and numerical method for compressible two-fluid Euler flow, in Proceedings of HYP 2012, Padova (Italy).

10. J.J. Kreeft, M.I. Gerritsma, Higher-Order compatible finite elements for curvilinear quadrilaterals and hexahedrals, In Proceedings of ICOSAHOM 2012.

11. Kazemi Kamyab, V, Zuijlen, AH van & Bijl, H (2011). Higher Order Time Integration Schemes for Thermal Coupling of Flows and Structures. In M. Papadrakakis, E. Onate & B. Schrefler (Eds.), Computational Methods for Coupled Problems in Science and Engineering V (pp. 1-11). Barcelona, Spain: International Center for Numerical Methods in Engineering (CIMNE).


10117 – Turteltaub

Journal papers1. Yadegari, S.; Turteltaub, S.; Suiker, A. S. J., Coupled thermomechanical analysis of

transformation-induced plasticity in multiphase steels, Mechanics of Materials 53 (2012), 1-14, DOI: 10.1016/j.mechmat.2012.05.002.

Submitted journal papers2. S. Yadegari, S. Turteltaub, A.S.J. Suiker, P.J.J. Kok, Analysis of banded microstructures in

multiphase steels assisted by transformation-induced plasticity, submitted to Computational Materials Science.

3. S. Yadegari, S. Turteltaub, A.S.J. Suiker, Generalized grain cluster method for multiscale response of multiphase materials (to be submitted).

10118 – Ebert

Theses1. Ana Sobota, Breakdown processes in HID lamps, 11 april 2011.2. Lei Liu, Studies on the Discretization of Plasma Transport Equations, 4 juli 2013.3. Gideon Wormeester, Propagation mechanisms of positive streamers in different gases, 29

augustus 2013.

Journal papers4. Probing photo-ionization: Simulations of positive streamers in varying N2:O2 mixtures, G.

Wormeester, S. Pancheshnyi, A. Luque, S. Nijdam, U. Ebert, J. Phys. D: Appl. Phys. 43, 505201 (2010).

5. Sprites in varying air density: charge conservation, glowing negative trails and changing velocity, A. Luque, U. Ebert, Geophys. Res. Lett. 37, L06806 (2010).

6. Review of recent results on streamer discharges and their relevance for sprites and lightning, U. Ebert, S. Nijdam, C. Li, A. Luque, T.M.P. Briels, E.M. van Veldhuizen, J. Geophys. Res. 115, A00E43 (2010).

7. Spatially hybrid computations for streamer discharges with generic features of pulled fronts: I. Planar fronts, C. Li, U. Ebert, W. Hundsdorfer, J. Comput. Phys. 229, 200-220 (2010).

8. Emergence of sprite streamers from screening-ionization waves in the lower ionosphere, A. Luque, U. Ebert, Nature Geoscience 2, 757-760 (2009).

9. 3D hybrid computations for streamer discharges and production of run-away electrons, C. Li, U. Ebert, W. Hundsdorfer, J. Phys. D: Appl. Phys. 42, 202003 (2009).

10. The role of metastables in the formation of an argon discharge in a two-pin geometry, A. Sobota, F. Manders, E.M. van Veldhuizen, J. van Dijk, M. Haverlag, IEEE Trans. Plasma Sci. 38, 2289-2299 (2010).

11. Speed of streamers in argon over a flat surface of a dielectric, A. Sobota, A. Lebouvier, N.J.


Kramer, E.M. van Veldhuizen, W.W. Stoffels, F. Manders and M. Haverlag, J. Phys. D: Appl. Phys. 42, 015211 (2009).

12. Discharge Ignition Near a Dielectric, A. Sobota, E.M. van Veldhuizen, and W.W. Stoffels, IEEE Trans. Plasma Sci. 36, 912-913 (2008).

13. Statistical time lags in ac discharges, A. Sobota, J.H.M Kanters, E.M. Van Veldhuizen, F. Manders & M. Haverlag, Journal of Physics D: Applied Physics, 44, 135203 (2011).

14. Facilitating breakdown in noble gases at near-atmospheric pressure using antennas, A. Sobota, M.F. Gendre, F. Manders, E.M. van Veldhuizen & M. Haverlag, Journal of Physics D: Applied Physics, 44, 155205 (2011)

15. Ac breakdown in near-atmospheric pressure noble gases: I. Experiment, A. Sobota, J.H.M Kanters, F. Manders, M.F. Gendre, J. Hendriks, E.M. van Veldhuizen & M. Haverlag, Journal of Physics D: Applied Physics, 44, 224002 (2011).

16. Ac breakdown in near-atmospheric pressure noble gases: II. Simulations, A. Sobota, J. van Dijk & M. Haverlag, Journal of Physics D: Applied Physics, 44, 224003 (2011).

17. Mass conservative finite volume discretization of the continuity equations in multi-component mixtures, K.S.C. Peerenboom, J. van Dijk, J.H.M. Ten Thije Boonkkamp, L. Liu, W.J. Goedheer & J.J.A.M van der Mullen, J. Comp. Phys, 230, 3525 (2011).

18. Feather-like structures in positive streamers, G. Wormeester, S. Nijdam & U. Ebert, Jap. J. Appl. Phys. 50, 08JA01 (2011).

19. Boltzmann equation analysis of electron transport in N2-O2 streamer discharge, S. Dujko, U. Ebert, R.D. White & Z.Lj. Petrovic, Jap. J. Appl. Phys. 50, 08JC01 (2011).

20. Probing background ionization: Positive streamers with a varying pulse repetition rate and with a radioactive admixture, S. Nijdam, G. Wormeester, E.M. van Veldhuizen & U. Ebert, J. Phys. D: Appl. Phys. 44, 455201 (2011).

21. The complete-flux scheme – Error analysis and application to plasma simulation, L. Liu, J. van Dijk, J.H.M. ten Thije Boonkkamp, D.B. Mihailova and J.J.A.M. van der Mullen, J. Comput. and Appl. Math. 250, 229 (2013).

22. Extension of the complete flux scheme to systems of conservation laws. Thije Boonkkamp, J.H.M. ten, Dijk, J. van, Liu, L. & Peerenboom, K.S.C. Journal of Scientific Computing 53, 552 (2012).

23. Spatially hybrid computations for streamer discharges: II. Fully 3D simulations, Chao Li, Ute Ebert, Willem Hundsdorfer, J. Comput. Phys. 231, 1020 (2012).

24. Simulated avalanche formation around streamers in an overvolted air gap, Chao Li, Ute Ebert, Willem Hundsdorfer, IEEE Trans. Plasma Sci. 39, 2256 (2011).

25. A comparison of 3D fluid, particle and hybrid model for negative streamers, Chao Li, Jannis Teunissen, Margreet Nool, Willem Hundsdorfer, Ute Ebert, Plasma Sources Sci. Technol. 21, 055019 (2012).

International conference proceedings26. Propagation mechanisms of positive streamers in air and other N2:O2 mixtures: photo-

ionization versus background ionization, G. Wormeester, S. Nijdam, S. Pancheshnyi, A. Luque, E.M. van Veldhuizen, U. Ebert, refereed proceedings of ESCAMPIG 2010.


27. Feather-like structures in positive streamers, G. Wormeester, S. Nijdam, U. Ebert, refereed proceedings of 63rd GEC/ 7th ICRP, July 2010.

28. AC ignition of HID lamps - statistical and formative lag times, A. Sobota, J. H. M. Kanters, E. M. van Veldhuizen, F. Manders, M. Haverlag, proceedings of LS (Light Sources) 12, Eindhoven, 2010.

29. AC ignition of HID lamps, A. Sobota, J. H. M. Kanters, E. M. van Veldhuizen, F. Manders, M. Haverlag, proceedings of GD (Gas Discharges) XVIII, Greifswald 2010.

30. Electron transport data in N2-O2 streamer plasma discharges, S. Dujko, U. Ebert, R. White, Z. Lj. Petrovic , 25th Summer School and International Symposium on the Physics of Ionized Gases, Donji Milanovac, Serbia, Aug/Sept 2010.

31. S. Dujko ,U. Ebert, R. White, Z.Lj. Petrovic , Boltzmann equation analysis and Monte Carlo simulation of electron transport in N2-O2 streamer discharge, refereed proceedings of 63rd GEC/ 7th ICRP, July 2010.

32. How photo-ionization and background ionization affect streamers and sprites, G. Wormeester, S. Nijdam, A. Luque & U. Ebert, Int. Conf. Atmospheric Electricity, Rio de Janeiro, Brazil, Aug 2011.

33. Streamer simulations with highly accurate transport data, G. Wormeester, S.Dujko & U. Ebert, Int. Conf. Phenomena in Ionized Gases, Belfast, United Kingdom, Aug 2011.

34. Derivation and test of high order fluid model for streamer discharges. A.Markosyan, S. Dujko, U. Ebert. Proceedings of the Scientific Computing in Electrical Engineering, SCEE2012, 11-14, September, 2012, ETH Zurich, Switzerland; pp. 107-108.

35. High order fluid model for streamer discharge. S. Dujko, A. Markosyan, R.D. White and U. Ebert, 26th Summer School and International Symposium on the Physics of Ionized Gases, August 27th-31st, 2012 Zrenjanin, Serbia (edt. M. Kuraica and Z. Mijatovic , ISBN: 978-86-7031-242-5), pp. 345-348.

10120 – Luding

Thesis1. K. Yazdchi, Micro-Macro Relations for Flow through Fibrous Media, Utwente, 28 nov. 2012.

Journal papers2. A. R. Thornton, T. Weinhart, V. Ogarko, and S. Luding, Multiscale Methods for Multi-

Component Granular Materials, Comp. Methods in Mater. Science, 13, 197-212, 2013.3. A. Narvaez, K. Yazdchi, S. Luding, and J. Harting, From creeping to inertial flow in porous

media: a lattice Boltzmann - finite element study, J. Stat. Mech., P02038, 2013.4. K. Yazdchi, and S. Luding, Upscaling and microstructural analysis of the flow-structure

relation perpendicular to random, parallel fiber arrays, Chem. Eng. Sci. 98, 173-185, 2013.5. K. Yazdchi, S. Srivastava, and S. Luding, Microstructural effects on the permeability of periodic

fibrous porous media, Int. J. Multiphase Flow, 37, 956-966, 2011.6. K. Yazdchi, S. Luding, Towards unified drag laws for inertial flow through fibrous materials,

Chemical Engineering Journal, 207-208, 35-48, 2012.


7. 6. K. Yazdchi, S. Srivastava and S. Luding, Micro-macro relations for flow through random arrays of cylinders, Composites Part A, 43, 2007-2020, 2012.

8. 7. V. Ogarko, and S. Luding, Equation of state and jamming density for equivalent bi- and polydisperse, smooth, hard sphere systems, Journal of Chemical Physics, 136, 124508, 2012.

9. 8. V. Ogarko, and S. Luding, A fast multilevel algorithm for contact detection of arbitrarily polydisperse objects, Computer Physics Communications, 183, 931-936, 2012.

International conference proceedings10. K. Yazdchi, S. Srivastava, and S. Luding, FEM-DEM simulation of two-way fluid-solid

interaction in fibrous porous media, Powders and Grains 2013, 1015-1018.11. K. Yazdchi and S. Luding, Fibrous random materials: From microstructure to macroscopic

properties, Powders and Grains 2013, 1142-1145.12. K. Yazdchi, S. Srivastava and S. Luding, On the validity of the Carman-Kozeny equation in

random fibrous media, Particles 2011.13. V. Ogarko, S. Luding, A study on the influence of the particle packing fraction on the

performance of a multilevel contact detection algorithm, Particles 2011.14. S. Srivastava, A. Patra, Interior penalty and mixed discontinuous Galerkin method for

elasticity, ACOMEN 2011.15. K. Yazdchi, S. Srivastava and S. Luding, On the transition from creeping to inertial flow in

arrays of cylinders, IMECE 2010.16. K. Yazdchi, S. Srivastava and S. Luding, Multiscale permeability of particulate and porous

media, World Congress Particle Technology 6, 2010.17. 1K. Yazdchi, M. Salehi, On Viscoelasticity in CNT-Reinforced Polymer Composites, Proceedings

of IMECE, 2010.18. V. Ogarko, S. Luding, Data structures and algorithms for contact detection in numerical

simulation of discrete particle systems, World Congress Particle Technology 6, 2010.

10121 – de With

Thesis1. N.J.W. Reuvers (2012): Water and ion transport in nylon as studied by NMR. Eindhoven

Universtity of Technology.

Journal papers2. Kacar, G., Peters, E.A.J.F. & With, G. de (2013). Mesoscopic simulations for the molecular and

network structure of a thermoset polymer. Soft Matter, 9, 5785-5793.3. G. Kacar, E. A. J. F. Peters and G. de With, A generalized method for parameterization of

dissipative particle dynamics for variable bead volumes, Europhysics Letters, 102 (4), 1-6.4. G. Kacar, E. A. J. F. Peters and G. de With, Structure of a thermoset polymer near an alumina

substrate as studie by dissipative particle dynamics. Journal of Physical Chemistry C, 2010, 114 (1), pp 370-382.


5. N.J.W. Reuvers, O.C.G. Adan, H.P. Huinink, H.R. Fischer (2012): Quantitative Water Uptake Study in Thin Nylon-6 Films with NMR Imaging, Macromolecules 2012 45 (4), 1937-1945.

Journal papers in preparation and submitted6. G. Kacar, E. A. J. F. Peters and G. de With, Back-mapping of molecular structures form coarse-

grained structures, in preparation.7. N.J.W. Reuvers, H.P. Huinink, O.C.G. Adan, S.J. Garcia, J.M.C. Mol. Water transport in nylon 6 films

as measured by EIS and MRI. Submitted.8. N.J.W. Reuvers, H.P. Huinink, H.R. Fischer and O.C.G. Adan. Plasticization during water uptake.

Submitted.9. N.J.W. Reuvers, H.P. Huinink, H.R. Fischer and O.C.G. Adan. Influence of monovalent ions on

water transport into nylon 6 films. Submitted.10. N.J.W. Reuvers, H.P. Huinink, H.R. Fischer and O.C.G. Adan. Transport of divalent ions through

nylon 6 films. Submitted.

International conference proceedings11. Fidel Valega and Barend J. Thijsse, Atomistic simulations of the mechanical response

of copper/polybutadiene joints under stress, in Mechanical Behavior at Small Scales – Experiments and Modeling, edited by J. Lou, E. Lilleodden, B. Boyce, L.Lu, P.M. Derlet, D. Weygand, J. Li, M.D. Uchic, E. Le Bourhis (Mater. Res. Soc. Symp. Proc. 1224, Warrendale, PA, 2010) 1224-FF10-09.

12. Fidel Valega and Barend J. Thijsse, Atomistic modeling of Alumina/Epoxy adhesion, in Defects and Microstructure complexity in Materials. (Mater. Res. Soc. Symp 2013).

10476 – van Brummelen

Journal papers1. T.M. van Opstal, S.J. Hulshoff, C.V. Verhoosel. A robust solution procedure for the transonic

small-disturbance equation in fluid-structure interactions, Open Aerospace Engineering Journal, 4 (2011) 1-10.

2. T.M. van Opstal, E.H. van Brummelen, R. de Borst, M.L. Lewis. A finite-element/boundary-element method for large-displacement fluid-structure interaction, Computational Mechanics, 50 (2012) 779-880, special issue on computational fluid mechanics and fluid-structure interaction.

3. T.M. van Opstal and E.H. van Brummelen, A finite-element/boundary-element method for large- displacement fluid-structure interaction with potential flow, Comput. Methods Appl. Mech. Engrg. 266 (2013), 57-69.

Journal papers in preparation and submitted4. Q. Du, T.M. van Opstal, S. Prudhomme, P. Seleson, K.G. van der Zee. Goal-oriented adaptivity

for concurrent coupling methods based on phase-field modeling (in preparation).


5. T.M. van Opstal, P.T. Bauman, S. Prudhomme, E.H. van Brummelen. Goal-oriented model adaptivity for viscous, incompressible flow (submitted to Computers and Mathematics with Applications).

International conference proceedings6. T.M. van Opstal, E.H. van Brummelen. Finite element/boundary element coupling for airbag

deployment IV International Conference on Computational Methods for Coupled Problems in Science and Engineering (Kos, Greece), 2011.

7. T.M. van Opstal, E.H. van Brummelen. Model comparison for inflatables using boundary element techniques, First ECCOMAS Young Investigators Conference (Aveiro, Portugal), 2012, 155:1-10.

11054 – Speetjens

Journal papers1. Mosovksy, B.A., Speetjens, M.F.M. & Meiss, J.D. (2013). Finite-time transport in volume-

preserving flows. Phys. Rev Lett. (in press).2. Jilisen, R.T.M., Bloemen, P.R. & Speetjens, M.F.M. (2013). Three-dimensional flow

measurements in a static mixer. AIChE J, 159, 1746-1761.3. Speetjens, M.F.M. (2012). A generalised Lagrangian formalism for thermal analysis of laminar

convective heat transfer. Int. J. Thermal Sci., 61, 79-93.

10615 – Sluys

Journal paper1. A. Karamnejad, V.P. Nguyen, L.J. Sluys (2013), A multiscale rate dependent crack model for

quasi-brittle, heterogeneous materials. Engineering Fracture Mechanics 104 (2013) 96-113.

International conference proceedings2. A. Karamnejad, V.P. Nguyen, L.J. Sluys (2013), A rate-dependent multi-scale crack model for

concrete. FraMCos-8 2013, Toledo, Spain.3. A. Karamnejad, V.P. Nguyen, L.J. Sluys (2012), A two-scale rate dependent crack model for

quasi-brittle, materials under dynamic loading. WCCM 2012, Sao Paulo, Brazil.

Colophon


Final Report STW-programme

Multiscale Simulation Techniques (MuST)

Publisher

Technology Foundation STWP.O. Box 30213502 GA UtrechtThe NetherlandsT +31 (0)30 600 12 11F +31 (0)30 601 44 08E [email protected]

www.stw.nl

Text and interviews

Claud Biemans, www.frontlinie.nl

Editors

Ir. Stefan Jongerius, STWAstrid van der Stroom, STW

Photography

Bram Saeys, Eindhoven

Design

Room for ID’s, Nieuwegein

Printer

Zwaan printmedia, Wormerveer

Publication

May 2014

ISBN/EAN

978-90-73461-97-0

www.stw.nl

Multiscale Simulation Techniques

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