ADVANTAGE - Engineering Simulation & 3-D Design · PDF fileChoosing the right simulation...

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SPOTLIGHT ON ANSOFT

ANSYS Advantage • Volume II, Issue 4, 2008www.ansys.com 1

EDITORIAL

This entry of ANSYS into the electronic design softwareindustry broadens the company’s range of simulation solutions. Furthermore, adding Ansoft electromagneticsand electromechanical functionality to ANSYS technologiesfor structural and fluid dynamics simulations greatlyexpands the range of multiphysics simulations that canbe performed — especially those involving mechatronics.

With these comprehensive multiphysics solutions,electronics engineers can readily evaluate stresses insemiconductor packages and printed circuit boards aswell as assess reliability of hand-held devices undergoingshock and vibration. They can study various coolingstrategies for electronics and better understand heat flowin high-density packages. All of this can be accomplishedwhile also optimizing the design of radio-frequency andmicrowave components or studying signal and powerintegrity of high-performance electronics. The various simulations can be tied together within the ANSYS Workbench framework for a smooth exchange of databetween various field solvers and design tools; the infor-mation can be linked with ANSYS Engineering KnowledgeManager (EKM) software for managing simulation data.

Such a unified approach, breadth of engineeringsolutions and depth of multiphysics technologies givesdevelopment teams the tools they need in a competitiveenvironment, where the ability to design mechatronics-based systems better and faster will likely be decisive for agrowing number of companies in the coming years. ■

John Krouse, Senior Editor and Industry Analyst

A Big Step Forward in MechatronicsThe acquisition of Ansoft expands the breadth of multiphysics capabilitiesfrom ANSYS and gives engineers a powerful range of simulation tools for systems, blending together mechanical and electronics designs.

Mechatronics-based products combine mechanicalassemblies with electronics, intelligent control systems,electromagnetics and electromechanical components. Theyare all around us — and growing exponentially. Electronics-based hand-held products, unheard of years ago, are nowcommonplace, and traditionally all-mechanical productssuch as cars, planes, toys and appliances now haveincreasing levels of electronic circuitry.

One formidable barrier in developing these mechatronicssystems is that mechanical and electronics developmentprocesses are usually not performed in an integrated manner.Mechanical computer-aided design (MCAD) and electronicdesign automation (EDA) systems typically are incompatibleand do not exchange data smoothly. These different disciplines often work independently — risking problemsdownstream when subsystems are pieced together, resultingin missed opportunities to collaborate in optimizing the system’s overall multiphysics performance. In developmentof a stealth fighter aircraft, for example, designing the exteriorshape of the plane to minimize reflection of electromagneticwaves from ground radar may not result in optimal aero-dynamics and might limit options for designing the landing gearor weapon delivery systems.

A big step forward in bringing together these otherwiseseparate physics was taken recently with the ANSYS, Inc.acquisition of Ansoft Corporation — a provider of EDA software and simulation tools for electromagnetics, electro-mechanical, circuit and electronic systems. For more on thisimportant development, see the industry spotlight section inthis issue for a history of Ansoft, a lineup of software products, the synergy of the two companies’ solutions,and case studies showing how companies put thesetechnologies to work.

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SPOTLIGHT ON ANSOFT

20 A History of InnovationAnsoft has a long history of developing leading simulationsolutions for the electronics industry.

23 ANSYS and Ansoft: The Power of SynergyIntegrating Ansoft tools with technologies from ANSYS combines the best of both worlds for developing electronic products.

26 Aligned with the ANSYS VisionThe Ansoft product suite will help deliver benefits to theentire ANSYS engineering simulation community.

27 Electric Motors Advanced by “Ultra” Power StorageElectromechanical simulation tools aid in the design flow of hybrid–electric systems.

29 Microwave Simulation, Macro BenefitsElectromagnetic simulation finds applications in high-performance antenna systems and electronics.

31 Impeding InterferencePanasonic improves signal integrity design for a remote surveillance camera using electronics design software from Ansoft.

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www.ansys.comANSYS Advantage • Volume II, Issue 4, 20082

CONTENTS

Table of ContentsFEATURES

4 AUTOMOTIVE

First to the Finish LineIn a sport where winning is often decided by split seconds,the BMW Sauber F1 Team uses fluid dynamics solutions fromANSYS to lower lap times through improved vehicle aerodynamics.

8 INDUSTRIAL EQUIPMENT

New Check Valves Swing into ActionANSYS multiphysics simulation and design optimization determine petrochemical check valve flow characteristicsovernight — a task that otherwise could take years to complete.

11 ANALYSIS TOOLS

Making an ImpactModern explicit solutions enable the study of blast or high-impact scenarios.

15 THOUGHT LEADER

Multiphysics MaestroAn industry visionary shares insights into the evolution of multiphysics solutions and future challenges to overcome.

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CONTENTS

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SIMULATION @ WORK33 AUTOMOTIVE

Decreasing the Shock in Shock Absorbers Engineering simulation improves valve design for an automotive shock absorber.

34 ENERGY

Scheduling Replacements SmartlySimulation is used to effectively predict crack growth that could lead to power plant valve failure.

36 TURBOMACHINERY

What’s Shakin’?The combination of 3-D structural dynamics, ANSYS Workbenchand classical rotordynamics modeling techniques helps solverotating machinery vibration problems.

38 PROCESS INDUSTRIES

Designing Safe CrackersFluid and structural simulation combine to help researchersanalyze a variety of stresses on catalytic cracking equipment.

DEPARTMENTS40 ANALYSIS TOOLS

Multibody Dynamics: Rigid and Flexible MethodsChoosing the right simulation method for dynamic assembliesdoesn’t have to be risky.

43 ANALYSIS TOOLS

Extensive Multiphase Flow Capabilities Fluid dynamics simulation provides a wide range of multiphaseflow capabilities to meet challenging industrial needs.

46 TIPS AND TRICKS

Analyzing Viscoelastic Materials Mechanical solutions from ANSYS have convenient tools for calculating deformation of materials in which stiffnesschanges as a function of loading, time and temperature.

48 ACADEMIC

Small Bubbles, Large Benefit Air injection simulations show promise for reducing ship dragby injecting air bubbles to reduce skin friction along the hull of a vessel.

49 OUTSIDE THE BOX

Snowflake by SnowflakeSimulation provides insight about snow safety.

For ANSYS, Inc. sales information, call 1.866.267.9724, or visit www.ansys.com.For address changes, contact [email protected] subscribe to ANSYS Advantage, go to www.ansys.com/subscribe.

Executive EditorFran Hensler

Managing EditorChris Reeves

Senior Editor andIndustry AnalystJohn Krouse

Art DirectorSusan Wheeler

EditorsErik FergusonMarty MundyShane Moeykens

Ad Sales ManagerHelen Renshaw

Graphics ContributorGregg M. Webber

Editorial AdvisorKelly Wall

ANSYS Advantage is published for ANSYS, Inc. customers, partners and others interested in the field of design and analysis applications.

Neither ANSYS, Inc. nor the senior editor nor Miller Creative Group guarantees or warrants accuracy or completeness of the material contained in this publication.

ANSYS, ANSYS Workbench, Ansoft Designer, CFX, AUTODYN, FLUENT, GAMBIT, POLYFLOW, Airpak, DesignSpace, FIDAP, Flotran, Iceboard, Icechip, Icemax, Icepak,FloWizard, FLOWLAB, G/Turbo, MixSim, Nexxim, Q3D Extractor, Maxwell, Simplorer, Mechanical, Professional, Structural, DesignModeler, TGrid, AI*Environment, ASAS,AQWA, AutoReaGas, Blademodeler, DesignXplorer, Drop Test, ED, Engineering Knowledge Manager, Emag, Fatigue, Icepro, Icewave, Mesh Morpher, ParaMesh, TAS,TASSTRESS, TASFET, TurboGrid, Vista, VT Accelerator, CADOE, CoolSim, SIwave, Turbo Package Analyzer, RMxprt, PExprt, HFSS, Full-Wave SPICE, Simulation DrivenProduct Development and any and all ANSYS, Inc. brand, product, service, and feature names, logos and slogans are registered trademarks or trademarks of ANSYS, Inc.or its subsidiaries located in the United States or other countries. ICEM CFD is a trademark licensed by ANSYS, Inc. All other brand, product, service and feature names ortrademarks are the property of their respective owners.

© 2008 ANSYS, Inc. All rights reserved.

About the CoverAnsoft is a leading developerof high-performance electronicdesign automation software.Learn about this expertise in the Spotlight on Ansoftbeginning on page 19.

DesignerMiller Creative Group

Circulation ManagerSharon Everts

36 49


AUTOMOTIVE

First to the Finish LineIn a sport where winning is often decided by split seconds, the BMW Sauber F1 Team uses fluid dynamics solutions from ANSYS to lower lap times through improved vehicle aerodynamics.By John Krouse, Senior Editor and Industry Analyst, ANSYS Advantage

Formula 1 (F1) race cars arestrange-looking beasts, resemblingStar Wars fighting machines more thanmotor vehicles. The numerous odd-shaped appendages, exposed tiresand open cockpit all contribute to con-siderable air resistance. Indeed, theaerodynamic drag of these cars isworse than that of a brick.

The reason for such low aero-dynamics is that F1 rules mandatethese configurations — along withstandardized tires and restrictions onengine development — to limit carspeeds, thereby making for a slower,safer and more exciting race in which vehicles are more evenly matched.

Nevertheless, within these evolvingrestrictions, aerodynamics is a key per-formance driver for teams wanting toimprove car lap times by the fractions ofa second needed to win races, accordingto Willem Toet, head of aerodynamics for the BMW Sauber F1 Team.

Given these demands, developingoptimal racecar aerodynamics is ahuge engineering challenge involving awide range of conflicting requirements.In straightaways, highest speeds at fullthrottle are gained with aerodynamic“slippery” vehicles, in which compo-nents exposed to the air stream areintegrated. These include the chassis,underbody, engine cover with air inlets,

vehicle nose, side pods with coolinginlets, wheels, brakes, suspension and exhaust system.

During cornering, braking, acceler-ating and high-speed maneuvering inthe pack, the key is road-holding ability from downward forces pro-duced by airfoil surfaces on thevehicle. At speeds above 170 km/h(106 mph), this force against the tracktypically equals total vehicle weight sothat the car could drive upside downacross the ceiling — at least in theory.

These high downward forcesinevitably increase air resistance andlower the vehicle’s top speed, however.The aerodynamicist must balance


AUTOMOTIVE

these trade-offs so that the time gainedon the bends is not lost on the straight-aways. Every part of the bodyworkmust be designed to provide maximumdownward force with a minimum ofdrag. Moreover, downward force at thefront and rear of the vehicle must becarefully apportioned depending oncharacteristics of individual racetracks.Also, aerodynamic parts such as fins,diffusers, wings and barge boardsmust provide optimal downward forcewithout interfering with air inlets orengine cooling. The aerodynamicdesign from the front of the car to therear depends on the shape and place-ment of all these components, and thevehicle reacts extremely sensitively tothe slightest design alterations.

Compounding these technicalcomplexities, teams have only ninemonths to develop a new car. Chassis,engine, transmission and, above all,aerodynamic concept must be right at the very first attempt. There is notime for multiple prototype cycles,and, when the first tests are held in January, it is generally too late for wholesale changes. Furthermore,during the racing season the idea of“standing still” with the same design isan alien concept. “At practically everyone of the 18 races, teams makesome kind of improvement so thattheir cars at the end of the seasonhave very little in common with theoriginal designs,” said Toet. “With arace scheduled every two weeks, theclock is ticking to make performance-enhancing modifications on their carsbefore competitors do.”

Simulation is a Must-Have ToolIn contending with the above

technical challenges and demandingtimetables, today’s racing aero-dynamicists simply cannot rely onintuition or trial-and-error methods.Rather, engineering simulation hasbecome a standard part of vehicledevelopment for most teams.

Finite element analysis becameuniversally used in the racing industryas early as the 1980s, while simula-tions of air flow appeared in the early

to mid-1990s. In recent years, com-putational fluid dynamics (CFD)simulation has experienced a realboom period in racecar designbecause of the ability to quickly and cost-effectively study aero-dynamic efficiency and investigatethe impact of design modificationand alternative what-if changes on vehicle performance.

Fluid flow simulations are usedextensively in these applications and range from the stationary analysisof individual components (wing profiles, for example) up to investiga-tions of the entire vehicle as well asnon-stationary simulations, such asinteractions within the vehicle whenovertaking another car. Also coveredare fluid flow considerations that areoutside the field of aerodynamics,such as sloshing inside a fuel tank.

Demonstrating a commitment toexpanding its use of CFD, the BMWSauber F1 Team recently upgraded its high-performance supercomputercluster specifically developed for efficiently processing these simu-lations. Made by DALCO AG ofSwitzerland, the cluster has a peakcomputing speed in excess of 50 teraflops (one trillion calculations per second) with a compute sectionbased on Intel® Xeon® 5160 dual-core and E5472 quad-core processors.With this processing power and theefficiency of fluid dynamics solutionsfrom ANSYS, BMW Sauber F1 Team’s

engineers can process full-vehiclesimulations in a matter of a few hours,instead of the weeks otherwiserequired on conventional machines.

Aerodynamicists tune the configuration of the rear diffuserto provide different downward force strength depending oncharacteristics of individual tracks. Top to bottom showsdesigns used in the 2007 season for races at Montreal,Canada; Barcelona, Spain; and Monza, Italy.

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AUTOMOTIVE

“The big difference with CFD compared to wind tunnels is that younot only get results, but you also get an understanding of what goes on.Wind tunnel testing remains importantwith experimental work and CFD complementing each other,” saidTheissen. He noted that comparativewind tunnel measurements are alsoused for calibration and validation ofthe fluid flow calculations to increasethe accuracy and reliability of simula-tion results. The range and detail of data collected, reproducibility of the results, and a better understandingof complex aerodynamic interactionsare all strong arguments in favor ofCFD simulations.

In an expanding range of studies,simulation is used to overcome limita-tions of wind tunnel testing. Becausevehicles generally are stationary forwind tunnel tests, for example, evidence concerning air-flow char-acteristics can be rather vague inmany regions. Also, wind tunnel testsare of little use in investigating heatingand cooling effects because theengine is not running and brakes arenot at operating temperature. In con-trast, fluid dynamics simulations takeall these factors into account, and calculations can be applied to allphysical parameters, including those

Top view of the current model BMW Sauber F1.08 shows the aerodynamic complexity of a Formula 1 racecar.

Fluid Dynamics Complements Wind Tunnels“The latest upgrade of our super-

computer was a decisive reinforcementof our CFD capacity. Unlike other teams,we didn’t plan to build a second windtunnel. Instead, we have used the keyrelationship commitment with our high-performance computing (HPC) partners,including ANSYS, to continue to developand exploit the expanding potential forCFD that high-performance computinggives us,” explained Mario Theissen,BMW Motorsport director.

He added that wind tunnel testingwill continue as an important designelement of their Formula 1 racing cardesign. The BMW Sauber F1 Team’swind tunnel generates wind speeds upto 300 km/h (188 mph) and featureswhat is known as a “rolling road” thatcan simulate the interaction betweenthe vehicle and the road surface. Usingthe wind tunnel, engineers can readilysee the effect, on the actual vehicle, ofminor adjustments made on the spotto part geometries and orientations.


AUTOMOTIVE

involving variations in multiple inter-related parameters. In the finalanalysis, however, it is the testing onthe racetrack itself that is the actualyardstick for evaluating the successof the aerodynamic methods in useand deciding to what extent theyhave been effective.

Coping with New RegulationsBeginning with the 2009 racing

season, new regulations for the con-figuration of Formula 1 cars willdrastically limit the use of aerodynamicsurfaces. Many components, such aswinglets to direct airflow, will becomehistory. These constraints will certainlyresult in slower lap times, and perform-ance of all the racing teams will likelybecome more closely matched.

“New regulatory changes do notmean that CFD simulations willbecome less important or that thework of aerodynamicists will diminish,”Toet emphasized. “On the contrary,

demands of the new motor sports rulesare pushing aerodynamic designs fur-ther than ever and radically increasingthe efforts of teams to maintain optimumperformance.” He noted that the frontwing will be completely re-engineered,for example, to compensate for the lack of winglets, which are responsible

for producing sufficient down force in critical situations. “Now more than ever,CFD continues to be a major factor influencing overall lap times and anindispensable tool in the development ofFormula 1 racecars.” ■

The author thanks freelance writer Ulrich Feldhausfor contributing portions of the material in this article.


INDUSTRIAL EQUIPMENT

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For over 60 years, Cameron’sValves and Measurement group hassupplied full port check valves for oil,gas and petrochemical applications.Manufactured under the well-knownbrand Tom WheatleyTM, theserobust and reliable valves con-tain a disk-shaped clapper atthe end of a pivoted arm that isforced shut by reverse flow ofthe medium, such as naturalgas, crude oil or refined petroleum products. Throughthis action, the valve providesinstantaneous protection ofcompressors and otherupstream equipment costinghundreds of thousands of dollars.Using such valves helps avoid operational downtime expenses thatcan reach into the millions of dollars.

In one recent project, Cameron’sengineers used a range of tech-nologies from ANSYS to develop anew line of check valves. Primarydesign goals were to reduce pressurelosses in the valve and to increase thetime the valve would stay fully open in low-flow conditions — particularlyduring system startup, when pipelinesare often not operating at full flow forweeks, months or even years.

Reducing Pressure LossesTo reduce pressure losses, engi-

neers used ANSYS CFX fluid flowsoftware to locate areas of maximumturbulence inside the valve body. TheANSYS CFX product was used in

conjunction with ANSYS DesignXplorersoftware for design of experiments(DOEs) to optimize the shape of theclapper disk for greater flow efficiencyin fully open and partially closed posi-tions. By efficiently performing manysequential fluid flow analyses, ANSYSDesignXplorer software goes throughmultiple iterations and quickly con-verges on a target solution: in this case,the disk shape causing the leastamount of pressure loss. In this goal-driven approach, Cameron’s engineersused on-screen slider bars to changethe various input parameters andimmediately view output parametersdisplayed as color-coded 3-D response

surfaces that guide the way to an optimal design.

In this iterative process, the useof ANSYS DesignModeler technologywas critical in preparing the range ofgeometries for efficient part meshingwith each iteration, as well as gener-ating the fluid portion of the model for analysis. The tool readily importedCAD geometry from its nativeAutodesk® Inventor® format and created a parameterized model,enabling engineers to modify compo-nent geometries anywhere in theprocess simply by changing a fewkey values. Through this process, theengineering team was able to achieve

New Check ValvesSwing into ActionANSYS multiphysics simulation and design optimization determinepetrochemical check valve flow characteristics overnight — a task that otherwise could take years to complete.By Christophe Avdjian, Design Development Manager, Engineered Valves, Cameron Inc., Vitrolles, France

ANSYS CFX software results show areas of turbulence inside the valve body, indicating areas that could be modified to reduce pressure losses. The contours represent velocity.

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an almost three-fold improvement inpressure loss using the new design.

Longer Open TimesSimilarly, Cameron’s engineers

used ANSYS DesignXplorer andANSYS DesignModeler technologies inconjunction with ANSYS Mechanicalsoftware to optimize the weight of thearm and clapper without overstressingor deforming the parts. This simulationreduced the mass and inertia of theassembly up to 50 percent, resulting inless weight pulling down on the clapperand, therefore, longer open time for thevalve during low-flow conditions. Opentime was further increased by a multi-physics optimization of the angle of theclapper and arm assembly, performedusing the ANSYS DesignXplorer tool inconjunction with both ANSYS CFX andANSYS Mechanical technology in thesame set of simulations. The end resultwas a dramatic improvement in low-flow performance, with the valveremaining open for flow rates nearly 75 percent lower than nominal ratesof other comparable check valves.

In addition, engineers used theANSYS Mechanical product by itself in analyzing stresses and non-linear contact in pressure-containing

portions of the valve body assemblyas well as shock forces and deflec-tions of the clapper in its emergency“slam shut” mode of operation.Cameron’s Tom Wheatley experiencecombined with the latest tools fromANSYS has enabled the develop-ment of a new generation of checkvalve that provides a higher level ofperformance than was previouslyavailable. The valves are tentativelyscheduled to arrive on the marketearly in 2009.

Evaluating Full Range of CharacteristicsCameron’s engineers are also

using ANSYS CFX and ANSYSDesignXplorer tools to compile a reference database of valve perform-ance under a wide range of flowrates and fluid types for each of the 50 different sizes and pressureclasses of the new valve. The angu-lar position of the arm and clapperassembly depends on the effects ofthe inlet fluid, gravity and externalforces, so typically up to two weeksare required to perform the manydetailed calculations for a limitedoperational range of one valve size.This can result in delays in gettingback to the customer with solutions.

Even with ordinary simulation andmodeling processes, determining theperformance characteristics for everyconceivable feed condition for all 50valves would be a daunting task, taking years to complete. Cameron’sgoal was to develop an approach thatleveraged the capabilities of tech-nologies from ANSYS for performingthe needed calculations practicallyovernight. Together, Cameron’s engi-neers and an ANSYS team in Lyon,France developed a streamlined, auto-mated approach that achieved thisgoal by linking ANSYS CFX softwarewith the ANSYS DesignXplorer tool in such a way as to analyze virtually thousands of inlet flow-rate and angular position combinations withoutuser intervention, for the entire rangeof feed conditions on each valve size.

During this automated process,ANSYS DesignXplorer softwareexplores a range of possible angularpositions of the arm and disk. Multiplemeshes are automatically generated

This response surface plot shows flow, arm angle and pressure loss data that can be usedby engineers to optimize the design of the check valve.

Pressure decreases in the valve assembly as thearm and clapper move from full-close to full-openpositions.

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Trade-off plots show how ANSYS DesignXplorer software starts with more than 5,000 design-of-experiments calculation points (top left) and iteratively converges, as the equilibrium condition of the clapper is narrowed, toward a single curve (bottom right). This indicates pressure loss as a function ofinput flow rate for valve equilibrium — that is, when the arm and disk assembly is on the verge of closing.

using the parametric-driven geometryfrom the ANSYS DesignModeler tooland then imported into ANSYS CFXsoftware to determine pressure loss in relation to valve input flow rate.ANSYS CFX software also computesthe torque at the rotation axis of thearm generated by the fluid acting onthe clapper.

These ANSYS CFX outputs arecollected by ANSYS DesignXplorersoftware for every successive simula-tion representing up to 15 differentstages of valve closure positions fromfully open to fully closed and input flowrate from minimum to maximum. Toverify the torque equilibrium conditionsof the arm and disk assembly, engi-neers created a derived parameter inthe ANSYS DesignXplorer tool to per-mit summing three separate torquesacting on the assembly: fluid-inducedtorque, external forces–generated

Analysis with ANSYS Mechanical software indicatesstress distribution in the optimized arm and clapperdisk assembly.

torque, and torque from the weight ofthe arm and disk as a function of angleand center of gravity.

A goal-driven optimization was thenperformed to determine the clapperangle for each inlet flow rate at whichtotal torque equals zero — the point atwhich the valve is in equilibrium — forall valve feed conditions. From agenerated sample of 5,000 points,the Cameron engineering team usedANSYS DesignXplorer technology to iterate through the multitude of solutions and generate trade-off plotsas it converged to the ultimate objectiveof a single curve showing pressure lossas a function of input flow rate for valve equilibrium. This line of points— essentially a flow performance curvefor a wide range of feed conditions —was generated for each of the 50valves, thus providing solutions in hoursrather than weeks. ■

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THOUGHT LEADER

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How did you become focused onengineering simulation, and specif-ically on multiphysics?

I graduated in 1973 with a civilengineering degree from the Uni-versity of Padua in Italy. I stayedthere to pursue an academic teaching career in constructiontechnologies and mechanics.Research in these fields included

work in the fledgling technologies of finite element analysis (FEA), computer-aided engineering (CAE) andintelligent digital prototyping (iDP).

Throughout the 1970s and 1980s, computer powerincreased dramatically and enabled more complex prob-lems to be handled by engineering analysis codes, suchas those available from ANSYS, Inc. A growing number of simulation applications were directed at representingthe real-world loads and constraints engineers mustalways take into account — that is, multiple interactingphysics such as structural, fluid dynamics, thermal andelectromagnetics.

Capabilities for modeling and analyzing multiphysicsproblems unleashed a wave of engineering tools that havetransformed the way engineers design, develop, retrofitand enhance products in an expanding range of indus-tries. The integration of multiphysics simulation intoengineering processes was my vision from the start andremains so today.

You recognized the emerging trends in multiphysics simulation quite early. How did you leverage this tech-nology into a commercial opportunity?

During the 1980s, industrial companies quickly sawthe benefits of computer-aided engineering, so in 1984 I founded EnginSoft S.p.A. for technology transfer ofthese solutions — mostly doing consulting in the Italianmarket. As a complementary enterprise, in the 1990s weset up ESTECO, a research laboratory for engineering optimization and IT technologies, which these days fall within the field of process integration and designoptimization (PIDO).

The concept behind PIDO is to refine designs quicklyand effectively by blending simulation into product devel-opment processes, rather than performing these studiesas a separate function. At ESTECO, we subsequentlylaunched modeFRONTIER™ optimization software forcompanies to implement PIDO in their particular productdevelopment activities. Essentially, the software controlsthe simulation of a wide range of design variables andquickly converges on a solution that best meets all engineering requirements.

Today EnginSoft has a staff of over 200 and more than800 clients worldwide. We have been an ANSYS channelpartner in Italy since 2003 and have had links to CFX software for computational fluid dynamics (CFD) for over15 years. The long-standing relationship with ANSYS isone of EnginSoft’s major strengths.

In the early years, was multiphysics less of an issue, sinceindividual engineering simulation disciplines such as FEAand CFD were done separately for the most part?

Yes and no. From the outset, EnginSoft applied anapproach aimed at multiple disciplines in what we calledCAE solutions for the design chain. We developed ancil-lary software for transferring models and data from onedomain to another — for instance, from finite difference-based CFD to FEA-based structural analysis.

This was cumbersome, but it met customer require-ments for the physics to be coupled, even thoughindirectly. So to some extent, what is known today asmultiphysics is the approach we used for multiple disci-plines two decades ago. Since then, the approach haswidened to encompass a range of multiphysics andmulti-scale technologies as well as manufacturingprocess simulation.

How does technology from ANSYS fit into your current range of activities?

The multiphysics approach of software from ANSYS goes hand in hand with our design process optimization concept for multiple disciplines, withANSYS structural and mechanical modeling software as well as fluid dynamics and meshing technologies

Multiphysics MaestroAn industry visionary shares insights into the evolution of multiphysics solutions and future challenges to overcome.EnginSoft S.p.A., headquartered in Italy and established in 1984, focuses on engineering technology and design process innovation. Company founder and CEO Stefano Odorizzi was interviewed by Keith Hanna, ANSYS corporate marketing director in Europe, about the role of multiphysics in engineering simulation.

Dr. Stefano Odorizzi

THOUGHT LEADER

performing critical functions in the workflow. We have usedthis combination with considerable success at many companies, including the auto supplier Mazzucconi and the Piaggio motorcycle and motorbike company. (Seeaccompanying sidebar stories.)

We are currently engaged in two European Union collaborative projects with the aerospace and automotiveindustries that involve multiphysics and design optimizationfor all levels of a design process, from component to systemlevel right up to the early production concept phase.

What do you see as the major challenges currently facingthe engineering community in making further progresswith multiphysics simulation?

As multiphysics and advanced modeling methodsbecome more advanced, simulation-based engineering andscience will be indispensable in meeting the technologicalchallenges of the 21st century. The process will not be “simulation as usual” for narrow studies ofindividual parts and assemblies, but it will be focused oncomplex, interrelated engineering systems and on analysisresults that meet specified standards of precision and reliability. Hence, engineering simulation will develop newmethods, technologies, procedures, processes and plan-ning strategies. All these will be key elements for achievingprogress in engineering and science. To reap these benefits,however, four significant obstacles must be overcome.

First, we must revolutionize the way we conceive andperform simulation. In this respect, the mass success ofcomputer-based engineering simulation may be its ownworst enemy, because the knowledge base, methods andpractices that enabled its achievements to date nowthreaten to stifle its prospects for the future because oforganizational inertia and a reluctance to implement newapproaches.

Second, we must make significant advances in sup-porting technologies, including those for structuring theway in which models are built and organized. These tech-nologies have a huge impact on the complexity, solutiontime and memory capacity required, and, even today,some of the most complex turbulent-flow problems can-not currently be solved on the world’s largest and fastestcomputers. If progress continues at the rate of Moore’slaw, such solutions may not become practical for decadesunless effective multiscale modeling technologies aredeveloped to represent the entire range of complexities,from minute individual component details up to broad system-level characteristics.

Third, meaningful advances in simulation-based engineering and sciences will require dramatic changes ineducation. Interdisciplinary education in computationalscience and computing technology must be greatlyimproved. Interdisciplinary programs in computational science must be encouraged, and the traditional bound-aries between disciplines in higher education must bedissolved for information to be exchanged smoothlybetween scientists and engineers collaborating withinteams from multiple disciplines.

Fourth, because of the interdisciplinary character and complexity of simulation, we must change the manner in which research is funded. Incremental, short-term research efforts are inadequate and instead shouldbe replaced by long-term programs of high-risk research.Moreover, progress in such research will require the creation of interdisciplinary teams that work together onleading-edge simulation problems.

If applied mathematics and computer sciencemethodologies are focused on computational science atthis broad scale in overcoming the above barriers, there isample evidence that developments in multiphysics andrelated new disciplines could significantly impact virtuallyevery aspect of human experience.

Where do you see engineering simulation going in thenext 10 to 20 years?

From the perspective of EnginSoft, simulation-based optimization will undoubtedly be used for morerealistic decision-making in support of engineeringdesign, product manufacturing and field service activities. Tremendous strides are already being madein technologies and approaches for managing thehuge amounts of simulation-based data.

Also, among the world’s leading engineering simulation software suppliers, ANSYS, Inc. has theright long-term vision and is making significant invest-ments both in the core disciplines of science andengineering and in the development of algorithms andcomputational procedures for dynamic multiscale,multiphysics applications.

Do I personally think we will get to a point where science fiction becomes science fact within the nextdecade or two, where design engineers focus most oftheir efforts on imagining product variants and productinnovations while computers churn away in the back-ground spitting out predictions in real time? I really dothink these dreams will become reality in my lifetime. ■

THOUGHT LEADER


In one recent project, EnginSoft used multi-physics technologies in the study of a 1.3 liter dieselengine cylinder head, made by the casting and pre-machining supplier company Mazzucconi for Italianautomaker Fiat. In this study, ANSYS Structural software was used in comparing residual stressesdue to casting process, pre-machining and heattreatment. This set of simulations represented leading-edge engineering simulation technology thatrequired a wide range of physical transient values(temperature and deformation, for example) to be computed using control-volume meshing andtransferred to the ANSYS Structural model. “To myknowledge, this is the first time that the overall project and production process of such a complexcast component was thoroughly simulated by working in a single environment,” noted Luca Pirola,technical manager of Mazzucconi. “It’s amazing howpowerful the tool is to analyze the logic of the problem, as well as to optimize the entire processand synthesize and document the results for decision-making.”

Mazzucconi Uses Simulation Throughout the Entire Process

This detailed finite element model contains more than 26,000 solid elements toaccurately represent the intricacies of the Mazzucconi engine block casting.

ANSYS Structural software was used to determine residual stresses in the engineblock to optimize casting, machining, heat treatment and other production processes.


THOUGHT LEADER

The Research and Development Center for Piaggio group approached EnginSoft to perform multiphysics optimization studies on one of theirmotorcycle engines. The goal was to shorten productdevelopment time and reduce costs by refining thedesign with engineering simulation instead of numerous prototype test cycles. The majorchallenge was in developing an environmentallyfriendly engine that conformed to stringent emissionsstandards while maintaining high performance interms of low fuel consumption, reduced noise andhigh reliability.

Piaggio engineers first created a 1-D functionalmodel representing the entire engine system, takinginto account the full set of structural and fluiddynamics parameters for meeting all of the enginepower, torque and energy requirements. Pressure,velocity and temperature output values from the 1-Dmodel served as an input for ANSYS Structural soft-ware to calculate the structural behavior of enginematerials. The 1-D results were also used as an inputfor ANSYS CFX software to calculate the complexfluid mechanics and conjugate heat transfer of theengine cooling system.

Piaggio Boosts Motorcycle Engine Performanceby 15 Percent

This CAD model shows details of the Piaggio engine, for which the structuralbehavior of parts and materials was determined with ANSYS Structural software.

1717


Geometry of the engine cooling system was imported into ANSYS CFX software to study fluid mechanics andheat transfer of the system.

THOUGHT LEADER

The modeFRONTIER softwaremanaged this multi-variable simu-lation process providing input to the1-D code (more than 20 parameterswere taken into account), along withthe physical and geometrical para-meters of the gaskets and cylinderheads for both ANSYS Structural andANSYS CFX simulation. This designmethodology met the project time andcost goals and provided an addedbenefit of improving engine perform-ance by 15 percent. In this way,ANSYS Multiphysics technology anda collaborative optimization approachhelped Piaggio gain a significantadvantage in a fiercely competitiveglobal market.

In July 2008, ANSYS, Inc. acquired Ansoft Corporation.As a leading developer of high-performance electronicdesign automation (EDA) software, Ansoft is worldrenowned for expertise in electromagnetic, circuit and system simulation. The acquisition of Ansoft is the firstforay by ANSYS into the broader electronic design soft-ware industry and will enhance the breadth, depth, usabilityand inter-operability of the expanded ANSYS portfolio of engineering simulation solutions.

Ansoft software allows engineers to simulate component-level behavior, combine this behavior with

circuit elements and functional blocks, and optimize system performance under actual operating conditions. Tosolve the underlying physics of the components, Ansofttools use finite element and other simulation methods toaccurately characterize the electromagnetic behavior. Thispart of the process is similar to many structural mechanicsor fluid dynamics simulations from ANSYS, in that geometry is meshed and solved for a single component.Ansoft also provides tools to allow this model of the component, or a reduced-order equivalent representation,to be used as part of a full system-level simulation.


ANSOFT: HISTORY

Ansoft, a leading developer of high-performance elec-tronic design automation software, is now a subsidiary ofANSYS, Inc. We founded Ansoft to meet the design challengesof modern high-performance electronic and electro-mechanical systems by linking electromagnetic fieldsimulation with circuit and system-level design. Today’selectronics products relentlessly become more dense,operate at higher speeds and grow in functionality. To be competitive in this dynamic market, engineers must be able to simulate the true behavior of these products by includingthe electromagnetic coupling. Additionally, the convergence of electronics and mechanics in many applications, such as hybrid electric vehicles, has driven the need to uniteelectromechanical system simulation with rigorous three-dimensional electromagnetic field modeling. Ansoft softwareallows engineers to simulate component-level behavior,combine this behavior with circuit elements and functionalblocks, and optimize system performance under actual operating conditions. The key to Ansoft’s success is solvingthe physics underlying electrical and electronics productsusing finite element and other simulation methods andenabling these physics-based solutions to be used in system-level simulations.

The Ansoft and ANSYS combination will address theexploding global demand for more automated and functionalproducts in a wide range of industries: alternative energy,wireless technology, high-speed digital devices, and auto-motive and aerospace applications. The combination of ourtwo world-class engineering organizations can already delivermany of the tools engineers require to meet these globaltrends. We are very excited about our future together — working as one company, we will deliver an unprecedentedrange of simulation technology, from electromagnetics to thermal, fluid flow to structural, physical to behavioral. Togetherwe will deliver Simulation Driven Product Development acrossthe entire spectrum of engineered products.

Zoltan CendesChief Technology Officer and General Manager Ansoft LLC

A History of InnovationAnsoft has a long history of developing leading simulation solutions for the electronics industry.By Mark Ravenstahl, Director, Marketing Communications, Ansoft LLC

Ansoft grew out of research conducted at CarnegieMellon University by Zoltan J. Cendes, Ph.D., and his colleagues. Dr. Cendes’ early research focused onlow-frequency magnetic and electrostatic field compu-tations. The original software developed by Dr. Cendesand his colleagues — Maxwell — was equipped with apowerful Delaunay mesh-generation algorithm thatautomated the meshing process and made the soft-ware very easy to use. In 1984, with the technologydeveloped to the point at which the principals believedit could be turned into a business and Dr. Cendes wasconvinced that electromagnetics was being under-utilized, Ansoft was formed.

In the 1980s, Ansoft started doing cutting-edgeresearch on high-frequency microwave fields. Ansoftdeveloped new types of elements — called edge elements — that ultimately solved the “spuriousmodes” problem that had been plaguing researchers infinite element modeling of electromagnetic (EM)

devices. This development opened the doorfor the finite element method (FEM) to beemployed in electrical engineering applica-tions. In 1990, Ansoft shipped the first versionof HFSS (High-Frequency Structure Simulator)technology, which has become the industrystandard for computing electromagnetic

properties of arbitrary 3-D components andstructures. Following that, revenue from HFSSand other Ansoft-developed products for signalintegrity analysis and electromechanical systemsimulation grew at a 25 percent compound average growth rate.

Propelled by the strength of HFSS, Ansoftgrew to become a leading developer of high-performance electronic design automation (EDA)software. The unique ability of the products from


Ansoft has expanded its research anddevelopment efforts beyond electromagnetics

to include circuit and system simulation.Today, the Ansoft product suite focuses onimproving physical design by leveragingadvanced electromagnetic-field simulatorsdynamically linked to powerful circuit andsystem simulation. These capabilitiesallow engineers to eliminate physical prototypes, maximize product perform-ance and greatly reduce time to market.

With the acquisition of Ansoft byANSYS, two world-class engineering organi-zations are brought together — includingexperienced professionals with depth of knowl-edge in both simulation and a variety of industries.

Ansoft’s target applications are divided intotwo segments: high-performance electronicsand electromechanical systems. ■

ANSOFT: HISTORY

Ansoft to leverage electromagnetics across component, circuit and system design hasallowed companies worldwide to designmobile communication, internet access,broadband networking components andsystems, integrated circuits (ICs) andprinted circuit boards (PCBs), as well aselectromechanical systems such as automotive components and power elec-tronics systems. In April 1996, Ansoftcompleted its initial public offering andbegan trading on the NASDAQ stockexchange under the symbol “ANST.” In 2008, Dr. Cendes received the Institute of Electrical and Electronics Engineers (IEEE) Antennas andPropagation Society (AP-S) DistinguishedAchievement Award for contributions to the wide-spread use of user-friendly software tools forelectromagnetic analysis and design.

High-Performance Electronics

RF and Microwave

Radio frequency (RF) and microwave applications are a prime segment of the high-performance electronics market. These applications include high-frequency components and circuits found in the transmitter and receiverportions of communication systems, radar systems, satellites and cellular telephones. Market demands forreduced cost, size, weight and battery consumption force component and system developers to consider electro-magnetic effects within the design process. Modern high-performance RF modules have continually increasingdesign complexity, density, package parasitics and chip-to-chip interactions. The Ansoft high-performance RF andmicrowave solution targets these challenges with full-system verification, multi-chip simulation and package interconnect parasitic extraction, ensuring successful development of next-generation RF and microwave designs.

Signal and Power Integrity

Engineers designing servers, storage devices, multimedia personal computers, entertainment systems and tele-com systems have driven the industry trend to replace legacy shared-parallel buses with high-speed,point-to-point serial buses. Standard interfaces like XAUI, XFI, Serial ATA, PCI Express™, HDMI™ and FB-DIMMhave emerged to provide greater throughput using serial signaling rates of 3 to10 gigabytes per second. While thistrend has greatly reduced the number of traces and connections within the system, it creates electromagnetic inter-ference between the multiple connectors, transmission lines and vias on PCBs. High package pin count andgigahertz-speed data rates translate into extremely fast I/O switching and high transient power sinking. Simul-taneously, the average PCB size is decreasing, power density is increasing, and power delivery requirements aretightening. Engineers apply full-wave electromagnetic field simulation to precisely analyze power nets and planesusing layout geometry. The signal- and power-integrity solutions of Ansoft allow engineers to solve these gigahertz-speed and power-integrity design challenges.



ANSOFT: HISTORY

Electromechanical Systems

Electromechanical systems are another major segment for Ansoft products. The software is used in the automo-tive, aerospace and industrial automation industries. The technologies integrate mechanical, electronic and controltechnology to create synergistic physical systems: This convergence of electronics with mechanics has renderedineffective iterative design methodologies in which individual design groups are focused on a single aspect of asystem. From the initial design stage, modern electromechanical systems are designed with consideration of boththe system and the interoperability of components and circuits. The Ansoft electromechanical design solution cap-tures the interactions between electromechanical components, electronic circuits and control logic. This powerfulmultiple domain approach to design captures the underlying physics that governs all electrical behavior, allowingengineers to accurately model, simulate and validate the component, circuit and system-level performancerequired for electromechanical system design.

The Maxwell comprehensive electromagnetic field simulation software package assists engineers taskedwith designing and analyzing 3-D and 2-D structures,such as motors, actuators, transformers and other electric and electromechanical devices.

The Simplorer multi-domain simulation software tool isused for the design of complex power electronic anddrive systems.

RMxprt software speeds the design and optimizationprocess of rotating electric machines.

The PExprt product speeds the design and optimizationprocess of transformers and inductors for power electronics.

For more information on products from Ansoft, visit www.ansoft.com.

High-Performance Electronics Products

The SIwave product analyzes complex PCB and IC packages.

Q3D Extractor software efficiently performs the 3-D and 2-D quasi-static electromagnetic field simulationrequired for the extraction of resistance, inductance,capacitance and conductance (RLCG) parameters froman interconnect structure. It automatically generates anequivalent SPICE subcircuit model.

The Turbo Package Analyzer (TPA) tool automates theanalysis of — and produces lumped or distributedresistance, inductance and capacitance (RLC) modelsfor — all complex semiconductor packages.

Electromechanical Systems Products

HFSS is a 3-D full-wave FEA-based product that allowsusers to extract parasitic parameters (S, Y, Z), visualize3-D electromagnetic fields (near- and far-field) and generate Full-Wave SPICE models. HFSS utilizes a 3-Dfull-wave finite element method field solver to computethe electrical behavior of complex components of arbitrary shape and user-defined material properties.

The Nexxim product is an advanced circuit simulatorthat addresses the increasingly complex, nonlinear andfull-wave circuit behavior of gigabit-speed serial interconnects, radio frequency complementary metaloxide semiconductor circuits and GaAs/SiGe radio fre-quency integrated circuits.

Ansoft Designer software is an integrated schematicand design-management front end linking to Nexxim,HFSS and other field simulators.

power generation and power deliveryindustries. Many of the companies inthese industries — large and small, OEMsas well as suppliers — have continued torely on mechanical and fluid simulationsolutions from ANSYS in their productdevelopment initiatives. With the recentacquisition of Ansoft, the range of solutions for the electronics engineeringcommunity has expanded, comple-menting the comprehensive capabilitiesof ANSYS Multiphysics technology.

The resulting breadth of solu-tions from ANSYS is unparalleled, providing electronics engineers witha range of simulation tools across multiple domains. In assessing relia-bility, design teams can use ANSYSMechanical software to study struc-tural and thermomechanical stressesin semiconductor components,

electronics packages, printed circuitboards and complete systems. Engineers can incorporate nonlinearphenomena — including solder jointfatigue, delamination and creep —into product design and can conductmodal, shock and vibration analysis.They can also use ANSYS AUTODYNsoftware to conduct drop-test simulation for optimizing productreliability and performance.

ANSYS provides a variety ofvertical electronics cooling simula-tion tools as well as powerfulgeneral-purpose computationalfluid dynamics solutions to meetthe requirements of product minia-turization and high-power densities.ANSYS Icepak thermal managementsoftware simulates fluid flow, con-duction and radiation heat transfer in various package, board and system-level designs. For evaluatingadvanced cooling systems, fluiddynamics technology from ANSYScan be used in fan and acousticdesign, micro-channel analysis,emersion and phase-change cooling.Fluid dynamics solutions also simu-late semiconductor manufacturingprocesses including etching, photo-lithography and chemical vapordeposition, as well as semiconductorpackage manufacturing applicationssuch as encapsulation and curing.

The addition of Ansoft solutionsto the ANSYS suite of technolo-gies brings electronics engineers an


ANSOFT: SYNERGY

ANSYS and Ansoft:The Power of SynergyIntegrating Ansoft tools with technologies from ANSYS combines the best of both worlds for developing electronic products.By Fadi Ben Achour, Director of Electronics Industry Marketing, ANSYS, Inc.

The electronics industry facesimmense challenges in the globalarena in which engineers mustaddress conflicting requirements toincrease product functionality whilereducing size and weight, loweringenergy consumption and complyingwith stricter government regulations.Pressures from all sides are com-pounded by shrinking design cyclesto meet narrowing windows of business opportunity.

Companies meeting these chal-lenges reap considerable benefits byleveraging growth opportunities in a widerange of electronics segments, includingconsumer, communications and compu-tational sectors. Furthermore, there is increasing penetration of electronicssystems and electromechanical appli-cations in the aerospace, automotive,

Drop-test simulation of a graphics card performed in ANSYS AUTODYN software


ANSOFT: SYNERGY

24

expanded range of electromagneticsimulation capabilities. In high-frequency applications, engineerscan use the Ansoft flagship HFSSsoftware to conduct full-wave 3-D electromagnetic simulationsessential in designing radiofrequency and microwave compo-nents and systems widely used inradar, antenna, medical device and various wireless applications. Furthermore, HFSS with Ansoft 2.5-D vertical simulation software(SIwave for full-wave and TurboPackage Analyzer for quasistaticanalysis) form a powerful toolset useful in design and analysis for signal– and power-integrity applications and electromagneticcompliance. Such analysis is criticalin designing high-speed electronicscomponents and systems, such assemiconductor packages, telecom-munication equipment, servers, PCs and hand-held devices. Thesehigh-frequency electromagneticcapabilities are dynamically linked to Nexxim software, a state-of-the-art time and frequency domain circuitsimulator that provides an integrationof high-frequency electromagneticsimulation and advanced circuitdesign and simulation.

For electromechanical and low- frequency applications, Ansoft expands

ANSYS product offerings with generaland vertical electromagnetic tools aswell as system level simulation tools.Maxwell 3-D electromagnetic fieldsimulation software from Ansoft isused for the design and analysis ofmotors, transformers and otherelectromechanical devices commonto automotive, aerospace and indus-trial systems. Specialized verticallow-frequency software from Ansoftincludes PExprt software for designingtransformers and inductors, and theRMxprt tool for analyzing rotatingelectric machines. These tools arecomplemented by Simplorer software— a multi-domain system simu-lation software used for designinghigh-performance electromechanical systems. These technologies comple-ment the multiphysics, mechanical

and fluid dynamics simulation capabilities from ANSYS.

The combined simulation tech-nologies from ANSYS and Ansoftprovide the electronics community with extensive solver, meshing, pre-and post-processing, and system- and circuit-level simulation capabilities.ANSYS offers a range of mechanicalsimulation technologies including automatic contact detection, exten-sive material models and element types — such as direct coupled-fieldelements — as well as rigid body andexplicit dynamics capabilities. Fluiddynamics technologies includedynamic and moving mesh features,chemical species mixing and reactingflows, specialized models for rotatingmachinery, and extensive turbulencemodels. Physics-based meshing from

Thermomechanical stress analysis conducted with the ANSYS Mechanical product on a ball grid array IC package

Thermal management of a network server simulated with ANSYS Icepak technology


ANSOFT: SYNERGY

25

Signal and power integrity studied with Nexxim and SIwave software from Ansoft

Maxwell software from Ansoft performing 3-D electromagnetic simulation of an electric motor

ANSYS has various algorithms andelement types including hexahedraland tetrahedral meshes, and prism,pyramid, quad, tri and bar elements.The acquisition of Ansoft furtherexpands these technologies byadding capabil it ies such astangential vector f inite element formulations, trans-finite elementmethods and adaptive finiteelement meshing capabilities.

To tie all this together andimprove efficiency and usability,ANSYS has a variety of advancedinfrastructure and data managementcapabilities that provide for auto-matic data exchange betweenvarious solvers. This data exchange— along with two-way MCAD inte-gration and advanced Six Sigmatools — is achieved through theANSYS Workbench framework.Management of simulation data andprocesses is handled by ANSYSEngineering Knowledge Manager(EKM) software, which enables multiple levels of the enterprise toaddress issues associated with data backup and archiving, trace-ability and audit trail, processautomation, collaboration, captureof engineering expertise and intel-lectual property protection.

The Ansoft acquisition is a con-tinuation of the ANSYS strategy of

providing the engineering communitywith an integrated and compre-hensive multiphysics solution. The benefits of this multi-domainapproach are highlighted in thedevelopment of hybrid vehicles, forexample. Here, engineers not onlyface the challenge of designing theelectric motor and battery systems,but also the need to continuallyimprove aerodynamics, engine per-formance and stability, underhoodthermal management, passengercomfort and crash-test rating. Thehigh end of the automobile industryis seeing more electronics-basedfeatures, such as accident avoidanceand automatic parking systems aswell as navigation devices and enter-tainment centers.

In such automotive applications,the combined ANSYS and Ansofttechnologies provide comprehensivemechanical, fluid dynamics and elec-tromagnetics capabilities for all typesof multiphysics applications. Usingthese tools, engineers can study theinter-related effects of various roador weather conditions on vehiclebehavior, for example, as well as the complex interactions amongvarious components. In the end, themultiphysics and multi-systemdesign approach will result in auto-motive designs that achieve an

optimal balance between car per-formance, gas consumption, weight,environmental impact and safety.

Similarly, in the development of products as diverse as global positioning units, cell phones, MP3players and other hand-held devices,engineers will be able to use multi-physics analyses to optimize thermaldesign and mechanical reliability, aswell as to conduct extensive electro-magnetic analysis and designantenna systems. Most important isthat designers in a variety of indus-tries will have a unified designapproach at their disposal, whichenables simulation to drive the entiredesign process. ■


ANSOFT: INTEGRATION

Aligned with the ANSYS VisionThe Ansoft product suite will help deliver benefits to the entire ANSYS engineering simulation community. By Barry Christenson, Director of Product Management, ANSYS, Inc.

The ANSYS vision involves a solid base of advanced technologies that enables virtualprototyping. Process compression speeds up the simulation effort. And finally, dynamiccollaboration results in innovative products. The ANSYS Workbench platform providesthe framework for the process, combining the steps in a truly coupled fashion.

development efforts at ANSYS have the opportunity to link1-D circuit and 3-D high-fidelity simulation applicationsthrough reduced-order models and co-simulation tech-niques. Ultimately, this will provide a tightly integratedenvironment for simulating complete systems that includeboth control and hardware elements.

Historically, Ansoft has shared the ANSYS vision formultiphysics simulation by creating straightforward ways forsolvers to exchange data. For upcoming releases, the com-bined development team will consider ways to harmonizethat exchange mechanism and deliver true multiphysicsintegration between all of the core solver products.

Process compression is about delivering software solutions that remove significant time and effort from users’typical simulation methods. Maxwell and RMxprt productsfrom Ansoft deliver superior performance for electric motordesign and analysis. This solution enables users to definemotor parameters in a tabular user interface, perform a 3-Dsimulation and examine the resulting motor performancecharacteristics very quickly. Additionally, Ansoft’s high- performance electronic design products are very effective inshortening the design cycle of high-frequency and high-speed electronic components and systems.

Just as ANSYS has designed its core products to beCAD independent, Ansoft products have interfaces with allmajor ECAD systems. Thus, over time, the fundamentalANSYS alignment with MCAD systems will be expanded to include a comprehensive list of major ECAD systemsavailable today.

Bringing these Ansoft and existing ANSYS technologiestogether will create a dynamic engineering simulation collaboration environment that defines and communicatesthe process for electronics simulation. For example, in anelectric motor drive system application, this solution willallow one engineer to model the power control system,another to develop the motor hardware, and still another tosimulate the mechanism, and all three together can under-stand the effects of the physics coupling.

As the Ansoft technologies are fully integrated into the product suite from ANSYS, customers will find that they can simulate their products in ways they never imagined possible. ■

The Ansoft product suite is not merely a strong addi-tion to the considerable tool kit from ANSYS; it will alsoadvance the vision for Simulation Driven Product Develop-ment. For the combined community of Ansoft and ANSYSusers, some benefits of this depth of solution will be real-ized immediately; even more value will be revealed ininnovative ways throughout long-term product develop-ment. The Ansoft technology integration will allow users toperform simulated tests that would otherwise not be possi-ble, a process that is critical to customers exploring andexpanding operational boundaries in developing leading-edge products and processes.

Delivering world-class technologies has been part ofthe ANSYS strategy for developing — and acquiring —new capabilities. Ansoft solver products HFSS andMaxwell, for high-frequency electromagnetic and low-frequency electromechanical simulations respectively, add two world-class leaders in their physics areas.

The ANSYS vision for virtual prototyping targets thesimulation of complete systems. To date, the company provides comprehensive multiphysics, meshing and high-performance solvers for high-fidelity 3-D productsimulation. Ansoft brings a new concept to the portfoliowith the Simplorer product for simulating 1-D systemsmodeled through a schematic, or circuit, interface. Future


ANSOFT: ELECTROMECHANICAL

www.ansys.com 27

Electric Motors Advanced by “Ultra” Power StorageElectromechanical simulation tools aid in the design flow of hybrid–electric systems.By John M. Miller, Vice President Advanced Transportation, Maxwell Technologies, Inc., California, U.S.A.Marius Rosu, Group Leader Simplorer Modeling, Ansoft LLC

In the energy storage industry, electric double-layer capacitors arebecoming widely accepted both instand-alone applications and in com-bination with batteries. Also known asultracapacitors, these devices com-bine a relatively vast electrode surfacearea with a molecular-scale chargeseparation distance, providing capaci-tances that are several orders ofmagnitude higher than more commonelectrostatic or electrolytic capacitors.As the technical and economic benefits of these power-dense components become more widelyunderstood, there is increased interestin the active combination of ultra-capacitors as electrical storageelements with energy-optimized bat-teries, such as nickel metal-hydrideand lithium-ion, as the means to offerreliable energy storage over wide temperature and operational limits.

Computer simulation of ultra-capacitors and advanced batteries is becoming more widespread as the engineering community becomes better attuned to global climate change and the subsequent demandfor more efficient energy storage systems. Examples of ultracapacitorsworking in combination with advancedbatteries continue to proliferate, primarilyin the electric and hybrid–electric commercial transportation segmentssuch as transit buses and trains. Insuch systems, brushless DC (BLDC)motors and their component powerelectronics play a significant role in

increasing the overall system efficiency.These motors supplement the output ofthe internal combustion engine whenextra power is needed. They are alsoused to start the engine, as opposed tothe conventional starter and solenoidmethod.

When designing a variable-speeddrive for a BLDC motor, however,designers face a variety of problemsdue to the combination of several engineering domains interacting in the device. Some of the majorchallenges include magnetic designfor linear and rotating electricalmachines; power electronics designfor converters, inverters and DC links;mechanical design for the load profileand oscillations; control design fordigital and analog signal compo-nents; and multiphysics interactiondesign for electromagnetic compati-bility (EMC) and interference (EMI)requirements.

To address the variable-speeddesign requirements in a hybrid–electric system, engineers can employa comprehensive design flow includingseveral electronic design automationtools from Ansoft. Their first step is toselect a feasible design for the givenrated performance specifications of theelectrical machine — for example, cur-rent, torque or speed. RMxprt software,a tool designated for the electricaldesign of rotating machines, allowsdesigners to create a machine modelby entering rotor, stator and ratinginformation in addition to cost functionsinto a parameterized input module.

To validate the initial design produced by the RMxprt tool, themodel is transferred to Maxwell electro-magnetic field simulation software toperform a finite element analysis.Maxwell technology provides thedesigners with critical parameters,including flux linkage versus current for

Hybrid–electric system topology in Simplorer software from Ansoft

MAXWELL FEA

Battery Ultracapacitor Modules at 175V-dc

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ANSOFT: ELECTROMECHANICAL


different angular positions of the rotor. The rotor positioninformation is then used in the controller to synchronize thetriggering of each phase of the stator coils with the positionof the rotor. To account for unwanted, or parasitic, effects onthe bus bar interconnects in the ultracapacitor design, Q3D Extractor parasitic extraction software can be used to compute resistance, inductance, capacitance and conductance (RLCG) parameters and automaticallygenerate an equivalent subcircuit computed at nominal frequency or S-parameters (signal scattering coefficients)calculated for a large spectrum of frequencies.

Ultimately, the analyzed characteristics of different components within the entire power system topology arethen assembled within the Simplorer electomechanical simulation software package to verify the complete drivesystem. When the BLDC model is imported from Maxwellsoftware to the Simplorer tool, the analog-digital character-istics of the circuitry can be modeled. Mixed-signal circuitscan then be simulated with both block diagram– and statemachine diagram–based representations of the controller,allowing the performance of the system to be optimized.

The simulation of the complete drive system enables theverification of the C-code that will be running on a digital signal processor (DSP) or embedded controller, since suchcode can be part of the system-level simulation. In Simplorersoftware, multi-domain components (power electronics,mechanical, hydraulic and thermal) are available to enablemore complex study on existing power system design. Engineers can use Simplorer software to create the entiredesign analysis framework because of the variety of compo-nents in the Simplorer tool’s signal characteristics librarydedicated to measuring the performance and design qualityof the power system.

The motor’s electronic controller contains three-phasebi-directional drivers, which drive high-current DC powerand are independently controlled by a block diagramscheme and a state machine diagram. The state machine–based scheme compares the rotor position to determinewhen the output phase should be advanced. The block diagram uses a hysteresis, or history-dependent, controlscheme to chop the phase currents between upper andlower admissible band values in order to allow the electricalmotor to develop a sufficient electromagnetic torque to sustain the mechanical load. As an immediate consequenceof the hysteresis band control and power inverter switchingfrequency, the ripples induced in the electromagnetic torqueand the harmonic content of the currents affect the overallperformance of the system.

At heavy system loads, the ultracapacitor experienceshigh bursts of power, from both charging and discharging. Thiseventually will lead to corresponding high carbon loading,which, combined with high current cycling, eventually leads toa reduction in component life. The construction must berobust enough to tolerate high electrical, thermal and mech-anical stresses. Hybrid–electric system designers benefit fromAnsoft software because the tools provide a comprehensivedesign flow capable of addressing multi-domain and mixed-signal design by allowing a coupled analysis of the motor,circuit, controller and drive systems. ■

Maxwell interface showing brushless DC (BLDC) geometry

Profile of brushless DC electromagnetic torque response from simulation results

Simulation profile of brushless DC phase currents during continuous operation

Q3D Extractor interface showing the structure of the ultracapacitor busbar interconnects


ANSOFT: HIGH FREQUENCY

www.ansys.com 29

Microwave Simulation,Macro BenefitsElectromagnetic simulation finds applications in high-performance antenna systems and electronics.By Lawrence Williams, Director, Business DevelopmentSteve Rousselle, Technical Director, Ansoft LLC

Engineers have long relied onMaxwell’s equations to model the high-frequency performance of wave-guiding structures, such as striplineand microstrip transmission lines, connectors and coaxial lines. Analytical expressions for specific dis-continuities, such as the impedancestep, open- and short-circuited lines,coupled lines, bends, gaps and junctions, are used by microwave engi-neers to create matching networks,couplers, power distribution networks,filters and antennas. In the final layout,these models may couple to oneanother through parasitic electro-magnetics, thus creating circuitperformance that is different than wasintended. Additionally, an engineer maywish to create new components forwhich there are no available models inthe circuit library.

For these and other reasons, electromagnetic field solvers were created that allow the direct solution of Maxwell’s equations to extract accu-rate models of distributed and parasiticeffects. The best electromagnetic sim-ulation tools are capable of full 3-D simulation, allowing engineers todesign, analyze and refine microwavecomponents virtually, avoiding costlyand time-intensive prototypes andexperimental work. Engineers use thesetools for Simulation Driven ProductDevelopment in order to visualize theelectromagnetic fields in their device,understand the device’s electricalbehavior to an unprecedented degree,and build virtual products that work aspredicted when manufactured.

Today’s microwave and radio frequency (RF) design challenges gofar beyond the addition of a few electromagnetics-based models to acircuit. The trend in RF, microwave and high-performance electronics productdesign is toward accurate prediction ofcomprehensive system-level behaviorwith electromagnetic simulation at thecore. Engineers now simulate largerand more sophisticated design prob-lems. For phased array antennasystems, for example, designers cansimulate the antenna elements as wellas the supporting feed network and active circuits behind the array.Other antenna system designers are focusing on the environment inwhich the antenna operates — the performance of an antenna beneath aradome, for example, or the interactionof a mobile handset and the body of an automobile.

A phased array antenna system,like those on an unmanned aerial vehicle, presents an excellent casestudy that illustrates the larger system-level designs that are possible today.The ultimate goals of the simulation are to design the antenna and its

electronic feed network and then inte-grate the antenna subsystem into anunmanned aircraft.

Ideally, the ground-mappingX-band antenna system would delivera flat, equal power versus distanceradiation pattern. Achieving the shapedbeam is highly dependent upon veryprecise control of the relative amplitudeand phase at each element. This control is often limited by the perform-ance of nonlinear, real-world poweramplifiers. To achieve the desired radiation pattern, each antenna in thearray receives a different amplitude and phase. As a result, amplifier gain compression will vary among the transistor-based amplifiers in the array.A typical power amplifier will produce a fixed gain and flat phase as a functionof input power until a certain point is reached. It cannot produce ever-increasing output power as the inputpower is increased. Eventually, thedevice exhibits nonlinear behavior, andits output power compresses while the gain decreases. Using the Nexximresults from harmonic balance circuitsimulation of a simple bipolar junctiontransistor (BJT) power amplifier circuit,

16-element active phased array antenna placed on an unmanned aerial vehicle platform

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ANSOFT: HIGH FREQUENCY

the resulting plot of the circuit gainversus input power shows that thegain is nearly constant until roughly -8 dBm input. Beyond -8 dBm, thegain rolls off quickly.

Transmit power is important to thedesign of an airborne radar system.Greater power translates into a longerrange over which the aircraft can senseaggressors and targets. However,increased power also may result inundesired degradation to the radiationpatterns caused by nonlinear behaviorof the power amplifiers.

Ideal elevation plane radiation pat-tern exhibits a shaped-beam region toprovide equal power illumination on theground. Ripples in the main beam arepermitted to make the array excitationmore realizable. In this case, the pattern’s first four side lobes were suppressed to -30 dB to avoid radia-tion along and above the horizon. Toachieve this pattern, a very specificamplitude and phase distribution alongthe array was required. Indeed, theamplitude distribution has a dynamicrange of over 15 dB. As the input powerto the feed is increased, some of thepower amplifiers will experience gaincompression before others, thus disrupting the prescribed distribution,which in turn degrades the far-field radiation pattern. When the input powerincreases over 10 dBm, simulationwithin the Ansoft Designer environmentshows that the shaped main beamregion is mostly unaffected. However,the first four side lobes begin to riseabove the -30 dB level. When the inputpower reaches 14 dBm, the far-fieldshows significant degradation due tothe nonuniform gain compressionacross the array.

Powerful 3-D electromagnetic fieldsolvers have long been used by engi-neers to design complex microwave

components. These solvers continueto transform and extend productdesign, especially when linked withadvanced circuit simulation. RF,microwave and high-performanceelectronics product design nowdemands accurate prediction of system-level behavior and can includerigorous electromagnetic simulation atthe core. Simulations of an active-phased-array antenna system wereperformed using coupled harmonicbalance and finite element simulation.

Plot of gain and output power as a function of input power, at 10 GHz, demonstrating gain compression

Far-field radiation simulation using HFSS software (elevation cut) for 0 dBm (blue), +10 dBm (orange) and +14 dBm (red) input. At 0 dBm, the pattern’s first four side lobes are suppressed to -30 dBm to avoid radiation along and above the horizon. At higher inputs, the far-field radiation rises above the -30 dBm level, increasing aircraft visibility and vulnerability.

The effect of the nonlinearities of thetransmit power amplifiers was observedto degrade the far-field radiation patternas the input power was increased. Thisadvanced simulation method allowsengineers to fully understand the effectsof electromagnetics and nonlinear circuits so that specific design choicescan be made. ■

References[1] Rousselle S., Miller, M., Sligar, A.,

“Complex Antenna System Simulation Uses EM Software,” Defense Electronics,December 2007.

[2] Williams, L., Rousselle, S., “Electromagneticsat the Core of Complex Microwave SystemDesign,” IEEE Microwave, to be published in 2008.

[3] Elliott, R.S., Stern, G.J., “A New Technique for Shaped Beam Synthesis of EquispacedArrays,” IEEE Transactions on Antennas andPropagation, Vol. AP–32, No. 10, October 1984.

Cosecant-squared beam shape in the elevation plane provides equal power illumination versus distance for ground mapping radar.

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ANSOFT: SIGNAL INTEGRITY

In a unique network camera devicethat permits remote visual monitoringfor surveillance and security applica-tions, Panasonic used a standardEthernet connection to transmit videoand audio signals, allowing remotemonitoring from any location. Thecamera was designed to rotate, panand zoom by commands issued by theuser. Within the control electronics inthe camera body, three module printed circuit boards (PCBs) were connectedby a high-speed, low-voltage differen-tial signaling (LVDS) channel withribbon cables and associated connec-tors. After building and testing theinitial prototype, the designers of theLVDS network camera realized thatdevice performance would be subopti-mal, causing them to face a difficultchoice: They could either re-spin andtest or adopt a new design approachthat involved advanced simulation.With a critical deadline looming, man-agement decided that simulation wasthe best choice.

Working together with Panasonic,Ansoft created a methodology that

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enabled engineers to simulate com-plex high-speed PCBs and meetchallenging noise and performancespecifications. The team used a refer-ence design board for a consumerelectronics device as an example toillustrate how to accurately predictand suppress board resonances andresulting radiated emissions.

Panasonic engineers modeled thefull LVDS channel using a combinationof HFSS, Nexxim and Ansoft Designersoftware. The channel included threePCBs (video, mechanical controllerand central processing unit) and twoMolex® FFP/FPC surface mount con-nectors. Additionally, the team usedthe HFSS tool to extract Full-WaveSPICE and S-parameter models forthe PCBs. Similarly, they created W-element and 2.5-D planar modelsfor the connectors using Nexxim andAnsoft Designer software. The engi-neering team then inserted theindividual models into a circuit simula-tor to form the complete channel. Withthe full channel assembled, the circuitsimulator then provided a channel

Vias are plated holes that connect copper tracksor traces from one layer of a PCB to another.

Pads are surfaces on PCB boards to whichcomponents can be mounted.

Traces are the electronic pathways that trans-mit signals from one component to another.

Timing skew occurs when a clock signal travelsalong traces and reaches its component destinations at different times.

Today’s printed circuit board (PCB) designers face competing challenges of smaller,higher-density applications coupled with high-frequency and high-speed signaling. A multitudeof standards now exist that utilize high-speedserial signaling. The higher speeds give rise togreater demands on PCB designs to meet signalintegrity (SI), power integrity (PI) and electro-magnetic interference (EMI) specifications. Thechallenge becomes especially acute for low-cost commercial devices in which traditional signal-integrity design rules may be ignored inexchange for a board with fewer power andground planes or a higher-density design withless than optimum signal routing.

SI, PI and EMI design once were consid-ered separate disciplines, each with its owndesign rules, analysis methods and measure-ment techniques. A more modern approach isto recognize that there is a strong interdepend-ence among the three and that optimum boarddesign requires an integrated approach. A signal-integrity problem, for example, may leaddirectly to an EMI problem. This article illus-trates the new approach, and the importantdesign considerations, through an overview of an LVDS application.

Image © istockphoto/alienhelix

ImpedingInterferencePanasonic improves signal integrity design for a remote surveillance camera using electronicsdesign software from Ansoft.By Hiroshi Higashitani, Panasonic Electronic Devices Co. Ltd., Japan Aki Nakatani, Ansoft LLC

Diagram of PCBs and connectors


ANSOFT: SIGNAL INTEGRITY

impedance map, similar to time domain reflectometer results.The system’s initial design had a significant impedance problem along the video board.

Upon further examination of the video board’s layout, the team found that a pad and via were the root cause of the impedance problems. The impedance mismatch wasthe result of a step change in the width of the trace located near the via. Beyond the impedance mismatch,the team determined that the original trace routing wouldalso lead to skew.

Panasonic engineers addressed the skew and imped-ance mismatch in two steps. First, they reconfigured thetrace routing so that the total length of each trace in the differential pair was equal; this was accomplished by

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A comparison of the impedance maps for the original and improved designsfor a full LVDS channel; in the later map, impedance is greatly improved.

ba

overlapping the traces. They resolved the impedance mismatch, on the other hand, by eliminating the width stepchange in the routing to the via and by optimizing the pad and antipad radii. This was done by parameterizing the pad and antipad geometries in HFSS software.

Once they identified optimal routing and via geome-tries, the engineers focused on the impedance peak of oneof the connectors. Polyamide strips were placed on thesurface of the connector over certain sections. With theirhigher permittivity, the polyamide strips caused the localelectric fields to be more tightly concentrated. Hence, thecapacitance of the transmission line increased, and thecharacteristic impedance fell. Finally, Panasonic engineersadded a common mode noise filter to the circuit to reducecommon mode signals while permitting differential signals.Having made these changes, they generated a secondimpedance map and found that the impedance variationswere significantly reduced.

By addressing the signal integrity problems in the PCBsand the connectors, the team confirmed that they hadimproved the channel’s electromagnetic interference per-formance. In the initial design, the LVDS signal wasscattered whenever it encountered an impedance disconti-nuity. The scattered energy had to go somewhere; some ofit scattered back toward the transmitter, some of it coupledto other propagation modes, especially common mode,and still other energy coupled into parallel plate resonantmodes within the PCB. This energy could then radiate toproduce unwanted EMI. Solving the SI problem, therefore,had a direct effect on the radiated emissions of the system.Experimental measurements of the camera’s radiated emis-sions before and after the modifications clearly showed areduction as well. By adopting a circuit and 3-D electro-magnetic cosimulation approach, the design team savedabout two months on a second prototype build and aboutone month on lab measurements. ■

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BleedsGroup of Concentric Disks

Geometry of the shock absorber


AUTOMOTIVE

Decreasing theShock in ShockAbsorbersEngineering simulation improves valve design for an automotive shock absorber.By Marcelo Kruger, Geraldo Severi, Martin Kessler and Regis Ataides, ESSS, Florianópolis, Brazil

Sergio Vanucci, Pedro Barau and Robson Iezzo, Magneti Marelli Cofap, Campinas, Brazil

Automotive design requires consid-eration of a large number of factorsincluding passenger comfort. Suspen-sion design — more specifically, shockabsorbers — requires special attentionfrom engineers in order to improve ridequality. Without shock absorbers, avehicle would have an uncomfortablejolting motion, as energy stored in thespring is released to the vehicle. Shockabsorbers dampen spring vibrations byturning the kinetic energy from thesprings into heat that is dissipatedthrough a hydraulic fluid.

Engineers at Magneti Marelli Cofapin São Paulo, Brazil — a division of theinternational company that is com-mitted to the design and production ofhigh-tech systems and components forthe automotive sector — have beendeveloping a shock absorber systemthat is controlled mainly by valvesemploying circular disks. For low velo-cities, the fluid passes through smallbleeds, or holes, on the disks, with thepassage area defined by the number of

bleeds. For high-velocity conditions, adifferent method is used.

In order to improve the shockabsorber design and obtain a betterunderstanding of hydraulic fluid flow,engineers from both Magneti MarelliCofap and Engineering Simulation andScientific Software (ESSS), an ANSYSchannel partner in South America, col-laborated on an engineering simulationanalysis. The team built a computationalmodel of the shock absorber for the low-velocity condition in order to understandthe flow physics that occur in the valve,to evaluate dispersion of forces at thedisks and to compare the results againstexperimental data.

To evaluate the flow pattern andmeasure the forces, the engineeringteam used ANSYS ICEM CFD meshingsoftware to generate a computationalmesh consisting of tetrahedral andprisms elements and containing 1 millionnodes. Simulation of the steady-stateflow was performed using the k-epsilonturbulence model in ANSYS CFX fluid

flow software. The team considered threeconfigurations of bleeds (two, eight and 16bleeds) under three velocity conditions foreach configuration at the inlet. Theyobtained the pressure field on the regionsof interest at the valve using the CFX-Postpost-processor and generated a plot offorce (at the valve) versus velocity. Theresults showed very good agreement withexperimental data.

The reliability of the results has givenMagneti Marelli Cofap engineers increasedconfidence in the computational modeland, by comparing the different configura-tions, has provided them with a betterunderstanding of the complexity of theflow pattern. Simulation has imparted useful insights that the engineers now rely upon to make important decisionsconcerning the improvement of shockabsorber efficiency. ■

Computational mesh Streamlines in the shock absorber for the eight-bleed configuration

During a scheduledoutage in 2000, aninspection was performedon a check valve in use ata fossil fuel power plantin the United States.Working with the utility,Structural Integrity Asso-ciates found that thecracks circled the valve

seat on the inside of thevalve body. At that time, they

attributed the cracks to thermalfatigue, although creep was always a concern for compo-nents, such as this valve, that operate at temperatures of1,000 degrees F or higher. Structural Integrity worked together with the utility to measure crack depths in order toallow for monitoring of damage progression during futureshutdown inspections.

Subsequently, the analysis team agreed to re-inspect thevalve body during an upcoming outage scheduled for 2007.For this later shutdown, the inspection included examiningthe valve for furthercracking, incorporatingthose findings into asimulation designed topredict future deterior-ation, and, in a shortturnaround time, deter-mining if the valve wassuitable for continuedservice with or withoutrepairs.


The fleet of power generation equipment in the UnitedStates is of an advanced age, particularly in the case of fossil fuel plants. Many facilities have boilers, piping systems or other components that may be nearing the endof their useful lives due to damage accumulated duringoperation. Components susceptible to service-related dam-age typically are inspected to detect this damage duringtightly controlled and scheduled shutdown periods, or out-ages. These outage schedules are often developed yearsin advance by the utility and have little margin for change.

Damaged components fall into two basic categories:those that are damaged but still viable for continued useand those that are in danger of failure and need to bereplaced. Because part replacement is costly, it is most efficient to continue using parts as long as possible. Safetyand the desire to avoid component failure that can lead tounplanned shutdowns, however, make it essential that component viability be estimated correctly.

Scheduling Replacements SmartlySimulation is used to effectively predict crack growth that could lead to power plant valve failure.By Dan Peters, Structural Integrity Associates, Inc., Ohio, U.S.A.

The valve model showing the location of the crack on the inner surface of the valveand the direction of propagation of the crack through the wall

Crack Location

ENERGY

Temperature distribution in the valve at 532 seconds into a transient analysis of the valve behavior during a shutdown event

Crack Propagation Direction


ENERGY

The first steps involved creating a computer model ofthe valve using SolidWorks®, which was completed inexpectation of the 2007 outage. The developers of themodel created and designated its features, based on adrawing of the valve geometry, such that one could modifythem in the future to match the actual measurements foundduring inspection.

Structural Integrity used Creep-FatiguePro® — softwaredeveloped for the Electric Power Research Institute — toperform a crack growth analysis. As part of this analysis, theStructural Integrity team needed to understand both thepressure stresses experienced by the valve during standardoperation and the thermal stresses experienced during theshutdown process.

Due to the desire to keep shutdown time as short as possible, the team set up static and transient stressanalyses prior to the actual outage using the ANSYS Workbench framework and the SolidWorks model that hadbeen created. The ANSYS Workbench 11.0 environmentwas helpful in that it would later provide a seamless and fastinterface for updating the model and the analysis in the fieldbased on actual “as cast” dimensions.

The team used the ANSYS Workbench platform to runthe complete transient thermal stress analysis coupled witha multi-step static stress analysis. To obtain stresses alonga path, the switch to the traditional ANSYS Mechanicalinterface still had to be made, but it was easily automated,with the file structure in the ANSYS Workbench environmentmaking this process much easier than in prior versions.

The transient thermal stress analysis used a convectivecondition applied to the internal surface and a step temp-erature change to model the shutdown event. A multi-stepstatic thermal stress analysis was then run to determine thestresses based on the temperature distribution at variouspoints in time.

The pressure and thermal stresses then were normalizedusing stress transfer functions and were used as inputs into

the crack growth software. The calculation of creep andfatigue crack growth is not a trivial concept. It was handledwithout difficulty, however, with Creep-Fatigue PRO softwareand the ANSYS Workbench environment, which was able toexport stress analysis results that could easily be used togenerate the input to the crack growth software.

Structural Integrity used this methodology, beginningwith the measurements taken in 2000, to study the advanceof the crack propagation between 2000 and 2007. Theycompared these results to measurement data acquired in 2007. There was good correlation between thesimulation predictions and the measured data, validating theprediction process.

By using this methodology to then analyze the valve forfurther use, analysis results showed that an expensivereplacement of the valve was not immediately needed. Thecrack growth rates in this valve were low, and the valve couldbe operated safely potentially for many more years with con-tinued monitoring of the valve at future outages. The crackgrowth model will be updated with ongoing plant operationaldata to provide a continuing picture of the crack growth ratesfor the future. The client was able to make decisions quicklyduring the outage because the analysis was completed within two days of the completion of the valve inspection,thereby minimizing the length of the outage and avoiding anextremely expensive replacement of the valve. ■

Outside of the valve Internal view of the valve

Stress distribution in the valve at 532 seconds into a transient analysis of the valvebehavior during a shutdown event

careeves

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TURBOMACHINERY

What’s Shakin’?The combination of 3-D structural dynamics, ANSYS Workbenchand classical rotordynamics modeling techniques helps solverotating machinery vibration problems.By Josh Lorenz, Senior Principal Mechanical Engineer, Kato Engineering Inc., Minnesota, U.S.A.

In the electric power generationindustry, the ability to design and pro-duce reliable and long-lasting rotatingmachines is, in part, dependent on theability to control machinery vibration.Due to the dynamics of rotatingmachinery parts, mechanical vibrationcan’t be eliminated completely, butdesigning machines that meet industrystandards for acceptable vibration levels is a crucial part of the productdesign process. Kato Engineering hasbeen in the business of designing suchmachines since the 1920s.

Kato Engineering uses 3-D struc-tural modeling tools from ANSYS toincrease their ability to simulate andpredict machine vibration. Classicrotordynamics modeling techniquesinvolving spreadsheet-style programswith axisymmetric beam elementsolutions have been around for manyyears and are very useful tools. However, there are times when the

complex 3-D structural details of arotating machine cannot be cast

into the form of an axisymmetricbeam element model with

sufficient accuracy. Forcritical applications andnew designs in whichvibration prediction isof the utmost impor-tance, simulation using

software from ANSYSallows Kato Engineering to

bridge the gap between rotor-dynamics spreadsheet modeling

techniques and real-world vibrationbehavior.

Recently, Kato engineers inheriteda relatively large common shaftmotor–generator design with unfavor-able vibration performance. Their taskwas to modify the design, making itmore reliable and easier to produce.This included improving the vibrationcharacteristics of the machine.

In order to tackle this type ofproblem using structural softwaretools from ANSYS, the engineers atKato performed frequency sweepharmonic response analyses using a mixed-element modeling tech-nique. This method combines the efficiency of beam element models— for the rotating portion of themachine — with more structurallycomplex 3-D shell and solid elements that represent the sur-rounding stationary structures. Thesesurrounding structures include themachine frame, mounting structure,foundation and other components.

The simulation results providedstructural vibration displacements andphase angles at each node of the

model for all of the frequencies considered. Using the time–historypost-processor, the team at Kato tookdata from nodes in the model wheresensors would be installed during real-world vibration tests of the equipmentand examined the predicted magni-tude of the vibration response versusfrequency. Later, the engineering teamcompared the simulation results withmachine vibration Bode plots obtainedduring vibration testing of the produc-tion equipment.

An important portion of the rotor-dynamic analyses focused on thebearing connections between rotatingand stationary structures. Through the use of ANSYS Parametric Design Language (APDL) and MATRIX27 elements in software from ANSYS, theengineering team allowed for the inclu-sion of complex bearing stiffness anddamping phenomena in the simulationmodel. They were able to include thebearing stiffness and damping charac-teristics, as a function of rotationalspeed as well as all of the cross-coupled stiffness and damping termsthat are important in the simulation ofthe bearing behavior. While thesetypes of bearing behaviors have longbeen a part of spreadsheet-style rotor-dynamics programs, the Kato teamwas now able to efficiently incorporatethese behaviors into 3-D full-modelvibration simulations using the flexibleAPDL structure and data input–outputoptions. Speed-dependent bearingstiffness and damping coefficients —calculated using dedicated bearingperformance software — were curve-fit and programmed into the structuralmodel using an APDL routine.

A portion of the finite element mesh for theshaft of a motor–generator

Contour plot of vibration displacement for the whole assembly at a particular forcing frequency


TURBOMACHINERY

www.ansys.com 37

The ANSYS Workbench framework has been a verypowerful tool for Kato Engineering with regard to simu-lation model construction time. Using the ANSYSWorkbench environment, the team was able to make thetransition more quickly from CAD geometry to complexfinite element meshes. Where 3-D structural model creation for a machine previously may have taken a week,it was now taking only a day or two with the enhancedgeometry and meshing capabilities of ANSYS Workbench.

For this particular application, the Kato engineering teamwas able to predict the steady-state vibration response ofthe redesigned machine to a reasonable degree of accuracyusing structural simulation tools. While the modeling tech-nique relied on the placement of rotor imbalance forces,which were somewhat nebulous in reality, the team was ableto get good correlation between simulation and test resultsusing reasonable assumptions for expected magnitudes andlocations of rotor imbalance. By iterating with the simulationmodel during the design phase, Kato engineers were able todetermine that, if they control the imbalance of the rotor to acertain degree and at certain locations, they can expect tomeet targets in terms of machine vibrations. The improvedsteady-state vibration performance of the redesignedmachine provided a significant boost for customer confidence in Kato Engineering’s capability to produce a reliable product. ■ Comparison of simulation and test data at one of the vibration

sensor locations, indicating trends

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In the petrochemical industry, cat-alytic cracking is one of the major stepsin the process of splitting large hydro-carbon molecules into smaller, moreuseful components for gasoline and jetfuel. The cracking system itself consistsof a reactor and a regenerator that areinterconnected by a catalyst pipelinenetwork. During the cracking process,the system undergoes mechanicalloading — from wind, internal pressurebuildup and the weight of the catalystmaterial — and experiences thermalstresses caused by the repeated tem-perature changes to the system’s walls.

At the request of chemical equip-ment manufacturer JSC Neftehimproekt,the Computational Mechanics Lab-oratory (CompMechLab) at St. Peters-burg State Polytechnical University in Russia performed a 3-D structural analysis of a catalytic cracker, taking intoaccount the effects of external fluid flow as well as overall mechanical and thermal stresses. In their evaluation ofhow these effects would impact thecracking system, the CompMechLabengineers chose software from ANSYSfor the selection of the cracker construc-tion and materials.

A primary goal of the simulationwas to choose wall thickness values forthe reactor, regenerator and pipelineconnections, taking into considerationthe physical effects on the systemstructure at all operating conditions. Byextension, this would allow creation of a list of requirements for third-partysuppliers of structural components.

Within ANSYS Mechanical soft-ware, CompMechLab used multi-layershell elements, including SHELL131 to perform thermal analysis andSHELL181 for structural analysis. The reactor and regenerator walls

consisted of two layers: an externallayer of steel and an internal concretelining. Applying these shell elementsalso led to a reduced number ofdegrees of freedom, which savedcomputational resources.

The weight of the catalyst pipelinenetwork is about half as much as the reactor and regenerator vessels. It was very important to take thesecomponents — including connectingnose pieces, bellows expansion jointsand spring bearings — into considera-tion. Bellows expansion joints are usedin the construction to compensate for

the displacement variations caused bychanging temperature loads on the cata-lyst pipelines and to reduce structuralloads on the nose pieces. These jointsare deformable parts that independentlyfunction in an elastic manner whenundergoing axial, lateral or rotationalmovement. For the global model, theCompMechLab team simulated thesecomponents using MASS21 point masselements in appropriate locations relativeto the reactor and regenerator vessels.

CompMechLab’s simulation processfocused on analyzing the stiffness of thebellows expansion joints and also the


PROCESS INDUSTRIES

Designing Safe CrackersFluid and structural simulation combine to help researchers analyze avariety of stresses on catalytic cracking equipment.By Alexander Michailov, Igor Voinov and Alexey Borovkov, Computational Mechanics Laboratory (CompMechLab), St. Petersburg State Polytechnical University, St. Petersburg, Russia

Pressure distribution on the catalytic cracking equipment surfacesdue to the external air flow (represented by the streamlines)


PROCESS INDUSTRIES

forces on the system’s spring bearings,which are used to decrease the gravita-tional loads acting on the nose pieces.The forces on the spring bearings can becounteracted by varying seven thicknessand dimensional parameters. Each of thefive bellows expansion joints also hasthree stiffness values to vary, giving 22independent parameters in total. Foreach parameter variation, CompMech-Lab engineers analyzed two sets of operating conditions: the normal working conditions (temperature range 521 degrees C to 740 degrees C, maxi-mum pressure 0.3 MPa) and the designlimit conditions (temperature range 555 degrees C to 790 degrees C, maximum pressure 0.8 MPa).

By varying the 22 parameters,researchers performed a series of com-putations that focused on decreasing theload on the nose pieces. Included in thisprocess was a computational fluiddynamics (CFD) analysis of the wind’simpact on the system’s external pressuredistribution. Using ANSYS CFX software,the analysis team simulated the air flowaround the cracker with the built-in shearstress transport (SST) k-ω turbulencemodel, which is a robust model reliablefor a wide class of air flow situations.

The wind-induced pressure data fromANSYS CFX output was then inter-polated onto the elements of the structural model in ANSYS Mechanicalsoftware, thus adding to the load contributions from internal pressure distributions, gravity, thermal stress andforces contributed from the catalystweight.

The global structural analysismodel, which included computingstress distributions on the system and their equivalent displacement vectors, assumed linear behavior ofthe concrete and steel material. Usingcodes and standards of the Russian oil and gas industry, CompMechLabengineers determined the maximumallowable stresses for the differentparts of the cracking system at partic-ular wall thickness values, taking into consideration safety factors fordifferent operating regimes includingstartup, normal working conditions andshutdown. Comparing the stresses calculated by ANSYS Mechanical soft-ware to those allowed by industrystandards, the analysis team was ableto validate whether a particular wallmaterial thickness was acceptable orwhether the stresses were too high, in

which case another analysis iterationwould be required using an increasedthickness.

Following the global model analysis,CompMechLab created a more detailedsubmodel for thermostructural andcyclic loading analysis of the upper partof the reactor with consideration of thewelded joint between the reactor casingand plenum. The team carried out thisstep to obtain the reinforcement ringthicknesses in the zones of the nosepiece connections to the reactor, whichare areas of high stress concentration.Based on these detailed analysis results,engineers selected the zone with thehighest stress — known as the criticalzone — and perfomed cyclic strengthanalysis on that zone.

Following the analysis processusing software from ANSYS, the designteam was able to select appropriatedimensions for all of the structural component parameters. In summary,the CompMechLab engineers utilizedthe simulation method developed herefor analyses of two different crackingsystems and, as a result, were able toperform their analyses and issue theirtechnical report for a greatly pleasedclient in a period of just six weeks. ■

(a) 3-D solid model of the cracking system, (b) location of the spring bearings and bellows expansion joints, and vector (c) and contour (d) representations of the mechanical loadsthat are caused by internal and external pressures, gravity and catalyst density, and that are acting on the equipment

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ANALYSIS TOOLS

Assuming that parts of a dynamic assembly act as purely rigid bodies is like assuming that the earth is flat: Thetruth won’t be known until the assumptions are challenged.There is always an element of risk involved with challengingthe status quo, but, luckily, using ANSYS Flexible Dynamicstechnology is less risky than falling off the edge of the earth.

When challenged with prototyping a new mechanicalassembly, most engineering departments turn to a rigiddynamics software program, and for good reason. Theadvantages of simulating an assembly as a collection of rigidparts connected by joints are undeniable: It is much faster,more design ideas can be investigated in the same amountof time, and a product development team can be more productive. But this time savings comes at the expense ofinsight, and, sometimes, what isn’t known about a newdesign can come back to haunt a well-meaning team.Unknowns can include:

• Will our assembly survive the first cycle, or will one ofthe parts buckle, break or deform so severely that thesystem locks up?

• Will the assembly vibrate so much that nobody will buy it?

• Will our warranty department have to deal with the big,expensive problem of material fatigue?

• Is this a huge career-limiting mistake that our designteam can’t collectively afford to make?

To gain the insight required to answer the above questions (and many others), part and joint flexibility needsto be included in the simulation.

Rigid dynamics simulation can demonstrate how quicklyan assembly’s parts are moving, how fast the parts areaccelerating or decelerating, and what the forces are at thejoints between the parts at any time during the dynamic tran-sient. The total solution time for many rigid dynamicssimulations is often measured in seconds, because the num-ber of degrees of freedom is low and all parts are assumedto be infinitely stiff. This fast solve time makes rigid dynamicsextremely attractive to those with looming deadlines.

On the other hand, flexible dynamics provides thesesame part velocities and acceleration data, plus completedeformation, stress and strain data. While this is the informa-tion needed to really understand the design, total solutiontime is longer. Because of this, relying on flexible dynamics inthe early stages of design development has never beencommercially viable.

Smart engineers have been trying to combine the bene-fits of the fast solve times of rigid dynamics with thecomplete performance information that comes only fromrunning a flexible FEA simulation. Several methods havebeen developed over the past 20 years with varying degreesof success.

Rigid Dynamics Loads to Static Simulation MethodThe most basic and most widely used method of com-

bining the benefits of rigid dynamics with those gained byusing flexible system modeling is to transfer loads from a rigid dynamics run and use those loads on a structurallystatic system. This marriage of dissimilar technologies hassome pros and cons.

Multibody Dynamics:Rigid and Flexible MethodsChoosing the right simulation method for dynamic assemblies doesn’t have to be risky.By Steve Pilz, Senior Product Manager, ANSYS, Inc.

Rigid flexible assembly of truck suspension


Pro

• Dynamic loading on parts is captured accurately, so there is no need to estimate how far to scale upa static load to approximate a dynamic load. This widely practiced approach is sometimesconservative, and sometimes it is not.

• Static structural simulations are some of the most efficient FEA-based solutions that accuratelymodel flexibility.

Con

• The process forces the engineer to choose the transient time points at which to transfer to the structural static simulation.

• Using this method, it is extremely easy to overlook the worst-case loading combinations for all butthe simplest assemblies, so the wise engineerusing this method applies a very large margin ofsafety when relying on results.

ANALYSIS TOOLS

Predominantly rigid assembly with selective flexibility added to presumed weak links

Craig–Bampton MethodA more sophisticated technique of combining rigid and

flexible benefits is the Craig–Bampton method. Using this technique, the flexibility of a system is captured via a model–dynamic solution. The mode shapes and frequencies, or eigenvalues and eigenvectors, are then fed tothe rigid dynamics model so that part flexibility is accountedfor during a transient. While less of a forced marriage thanthe previous technique, the Craig–Bampton method is alsoblessed with pronounced strengths and weaknesses.

Pro

• A modal analysis is one of the most efficient of alldynamic simulations.

• The rigid dynamics reduced-order model gains flexibility at the lowest computational cost, and this has made the method popular with those requiring additional simulation fidelity.

Con

• The method is inherently limited to linear responsesdue to its reliance on modal analysis results. Thismeans it is not capable of accurately modeling:

– Anything other than linear materials: no material plas-ticity, hyperelasticity or viscoelasticity is possible

– Real-world nonlinear contact, with or without frictionand or changing contact status

– Large deflection

• The method is complicated and consumes much engineering time. Little has been done to automate, or at least streamline, the linking of the modal resultswith the rigid reduced-order model, likely because of the inherent limitations of the Craig–Bamptonmethod itself.

• Design iterations are painful. Because there is signifi-cant manual interaction and data reading, writing andtranslating, it is nearly impossible to keep up withchanges to a 3-D CAD model.

Load transfer from rigid dynamics simulation model (top) to staticstructural model (bottom)


• Financial cost is typically very high because twoexpensive programs must be used, often from differentsoftware companies, and these programs are typicallyrun by two different engineers who have been trainedon one system but not both.

Rigid and Flexible Dynamics MethodThe most modern method of combining the benefits of

rigid and flexible dynamics is to create a general-purposesoftware system that can be used to model full-rigid dynamics with reduced-order models or a full-flexibledynamics assembly, or any combination thereof. For thismethod, an engineer uses reduced-order models in purerigid dynamics and is able to keep pace with rapidly evolvingdesign proposals because of the fast solve times afforded bythe explicit solver. To gain further insight, the rigid model is modified with the addition of flexible component(s), and aflexible or rigid and flexible system is analyzed.

While some software suppliers have pieces of the rigidand flexible dynamics method, only ANSYS offers this typeof system — and it has been in commercial use for nearlytwo years. To consummate the relationship between rigid and flexible dynamics, the ANSYS Rigid Dynamicsproduct is used as an add-on to ANSYS Structural, ANSYSMechanical or ANSYS Multiphysics software.

Pro

• A single geometry model is used for both rigid and flexible dynamics. This model is typically an easy-to-visualize 3-D model from ANSYS DesignModelersoftware or a CAD system.

• The same user interface is employed for both rigid and flexible dynamics, so users of one have very littleto learn to be able to run the other.

• Models can be converted from rigid to flexible in minutes in as few as four mouse clicks.

• Design iterations are easy. Change the CAD model,click update, and resolve the rigid, rigid and flexible, orfull-flexible model.

• The limitations of the Craig–Bampton method do notapply: that is, you are able to model nonlinear contactas well as material nonlinearities at the same time, if desired.

Con

• While creating a rigid and flexible model with contactand material nonlinearities is easy to do, sometimesthese nonlinearities cause conflicting convergence targets for the solver. Overcoming these conflicts and getting a converged solution can require someexpertise in nonlinear simulations.

• Solver requirements are higher than either of the previous two methods, which has always been thenature of a full-nonlinear transient dynamic simulation.However, new time integration schemes and parallelprocessing or high-performance computing can bevery effective at reducing CPU demands.

Because some brave soul challenged the assumptionthat the earth was flat, falling off the edge of the world is lessof a concern than it was centuries ago. As the state of the artin engineering simulation software continues to improve, andmore engineers begin to use rigid and flexible dynamics during product development, failed product designs willbecome less of a concern as well. ■

ReferencesPilz, S., “Multibody Dynamics: Rigid, Flexible and Everything in Between,”ANSYS Advantage, Volume 2, Issue 2, 2008, pp. 20–23.

Combined rigid–flexible assembly with flexible member stresses

ANALYSIS TOOLS

ANSYS Advantage • Volume II, Issue 4, 2008www.ansys.com 43434343www.ansys.com 4343

ANALYSIS TOOLS

Multiphase flow is the simultane-ous flow of materials with differentstates, such as gas, liquid or solid, orwith different chemical properties, forexample gas bubbles in a liquid or oil

droplets dispersed in water. Multiphaseflows are commonly encountered in

a wide variety of industrial applications,ranging from evaporation in distillation columns to sloshingin fuel tanks, and from spray painting to cyclonic particleseparators.

Multiphase flows are much more difficult to model thanflows of just a single fluid. A complete description of theflow requires solving mass, momentum and energy equa-tions for each of the phases. These equations are morecomplex than for single-phase flows because they containadditional terms that govern the exchange of mass,momentum and energy between the phases. Because ofthe wide range of physical phenomena present and themany possible different flow regimes, the exact form ofthese interphase exchange terms is not always completelyknown. Multiphase flow models, therefore, often still includeempirically derived terms that continue to evolve asresearch progresses.

Leading fluid flow simulation products from ANSYSoffer a comprehensive suite of multiphase flow models thatcover most relevant industrial situations. ANSYS sets thestandard for multiphase flow simulation not only by offeringthe widest range of multiphase capabilities but also through

extensive experience and knowledgein the application of these capabilities.Understanding the different types ofmultiphase flow models will assist in theselection of the most appropriate modelfor a multiphase application.

Free-Surface Multiphase FlowsOne type of multiphase flow is free sur-

face. With free-surface flows, there are twoor more immiscible fluids, each of which isdescribed as being continuous in significantparts of the flow domain. There are clearlyrecognizable regions that contain either one or the otherfluid, although the shape and location of these regions mayvary with time. These regions are large enough that they canbe covered by multiple grid cells in the fluid dynamicsmodel. The shape and location of the interface between thefluids is usually of interest.

ANSYS POLYFLOW software uses a deforming meshmethod to calculate the free-surface shape of viscous fluidsflowing into an open domain. In this case, as the fluidmoves, the domain is remeshed so that the mesh followsthe exact shape of the fluid interface. This allows for veryefficient and accurate predictions of blow molding andextrusion processes.

ANSYS FLUENT and ANSYS CFX software use the volume-of-fluid (VOF) method to describe free-surfaceflows.

ExtensiveMultiphase Flow CapabilitiesFluid dynamics simulation provides a widerange of multiphase flow capabilities to meetchallenging industrial needs.By André Bakker, Lead Product Manager, ANSYS, Inc.

Blow molding of a waterfountain canister modeledwith ANSYS POLYFLOWsoftware. The color indicatesthe thickness distribution.

Volume fraction of solid particles in a stirred tank as calculatedwith the Eulerian-granular multiphase flow model in ANSYS FLUENTsoftware. These simulations can be used to determine the optimumconfiguration of the mixing impellers.


ANALYSIS TOOLS

With the VOF approach, the whole flow domain is meshed witha fixed mesh. The motion and the local volume fraction of the phases are calculated along with the shape of the interfacebetween the phases. At any point in space, there is only one orthe other of the two fluid phases, so there is only one velocityfield at every location. It is common, therefore, to solve onlyone velocity field, although in cases in which the velocity differ-ence along the interface is large, robustness and accuracy ofthe calculations is improved if two separate velocity fields aresolved. The shape of the fluid interface does not have to matchthe shape of the mesh. Different interface tracking methods areavailable with different levels of accuracy, calculation speedand numerical robustness.

Typical examples of the use of the VOF model are flowssuch as ships moving through water, dam break scenarios,fuel tank sloshing, stratified flows (distinct layers of differentfluids), slug flows (very large gas bubbles moving through aliquid in a pipe) and droplet breakup at inkjet printer nozzles.

Dispersed Multiphase FlowsIn dispersed multiphase flows, there is one continuous

phase and one or more dispersed phases. The dispersedphases consist of many discrete small droplets, bubbles orparticles that are distributed throughout the continuous phase.Usually, the size of these is small compared with the flowdomain, and often they are smaller than the grid cell size. Frequently, there are too many particles to calculate the motionof each individually. The two most common methods used tomodel these systems in a manageable fashion are the Eulerian

Wave formation around a seafaring vessel as modeled using the volume-of-fluid free surface model in ANSYS CFX software.Simulation and image by Philippe Godin and Robin Steed. Cargo ship image © istockphoto/dan_prat.

Gas and solids distribution in a three-phase bubble column as calculatedusing the Eulerian multiphase flowmodel. The light-blue iso-surface shows the region with the highest gas fraction. The color on the columnwall indicates the concentration of the solid catalyst particles.


ANALYSIS TOOLS

Particle trajectories in a cyclone separator are shown as calculated withthe discrete particle tracking model. The color indicates the particlediameter. The larger particles (red and green) exit from the bottom asintended. Some of the smaller particles (blue) exit from the top, reducingthe separation efficiency. Multiphase technology from ANSYS can beused to optimize the separation efficiency for different particle propertiesand size distributions.

method and the Lagrangian method. Both methods areavailable in ANSYS FLUENT and ANSYS CFX software.

The Eulerian method describes the system as mixedcontinuous phases and solves the equations of mass,momentum and energy for each phase. Droplets, bubblesand particles are not tracked individually. The equations ofmotion include the effects of the interphase drag force andother relevant forces that occur in dispersed multiphasesystems. Typical results of the calculations are the localvelocities, temperature and volume fractions of eachphase. Interface shapes are not explicitly calculated. Thereare several variations of the Eulerian multiphase model. Incases in which the velocity difference between the phasesis relatively small, it is often possible to simplify the modelby solving just one equation of motion for the mixture,instead of equations for each phase. Also, for bubbles ordroplets, the effects of breakup and coalescence can be included in the model to calculate their size distribution.For solid particles in a fluid or gas, special Eulerian-granularmodels are available that can take into account the effectsof particle collision, friction and packing density. The Eulerian method is commonly used for fluidized beds, bubble columns, mixing tanks, sedimentation, slurry flows,and pneumatic transport and hydrotransport systems.

The Lagrangian particle tracking method (LTM) calcu-lates the trajectories of individual particles, drops orbubbles in the continuous phase. It is also known as the discrete phase model (DPM). In practice, this method ismost useful when the particles or droplets occupy a smallpart of the total volume, usually less than 10 percent, and areheavier than the continuous phase. In cases in which thenumber of particles is too large to calculate, it is possible tosimplify the model just by calculating a statistically significantnumber of particle streams. The effects of the particles on theflow of the continuous phase can be taken into account andvice versa. Mass transfer effects, such as evaporation and condensation, and chemical reactions, such as combus-tion, can be included. Examples of applications in which theLagrangian model is used are sprays of droplets in air, suchas paint, or solid particles in air, such as fine powders in asthma medication inhalers.

Steady State or Time DependentMultiphase flow calculations can be either steady state

or time dependent. Steady-state calculations are most suitable when the final solution is independent of the initialconditions and there are distinct inflow boundaries for theindividual phases. Other situations are commonly modeledas time dependent. Because of the additional equationsand the need to model many flows as time dependent, multiphase flow modeling is computationally intensive.Luckily, fluid dynamics software from ANSYS works efficiently on parallel computing systems so that modelturnaround times remain reasonable.

Because of the large number of industrial multiphaseapplications, ANSYS continues to invest in research anddevelopment in this important area. The ongoing develop-ment effort will result in continuous improvement of thealready comprehensive multiphase flow modeling capa-bilities from ANSYS. ■

Iso-surfaces of water vapor for a pumpoperating with developing cavitationCourtesy Vansan Makina Sanayi


TIPS AND TRICKS

Viscoelastic materials have aninteresting mix of material propertiesthat exhibit viscous behavior (like thegradual deformation of molasses) aswell as elasticity (like a rubber bandthat stretches instantaneously andquickly returns to its original stateonce a load is removed). The clearestway to visualize the behavior of amaterial containing both elastic andviscous components is to think of a spring (exerting forces to return to itsunstressed state) in series with adashpot (a damper that resists suddenmotion, similar to the pneumatic cylinder that prevents a storm doorfrom slamming shut). With these prop-erties, the stresses of a viscoelasticmaterial gradually relax over timewhen a constant displacement isapplied. Conversely, under a constantapplied force, elastic strains continueto accumulate the more it is deformed.

Various materials exhibit viscoelas-ticity, with deformation depending onload, time and temperature. That is,given enough loading over a period oftime, many materials will graduallyundergo some level of deformation —and the process may speed up as thematerial gets hotter. For example, anamorphous solid such as glass may act more like a liquid at elevated tem-peratures, at which its time-dependentresponse can be measured in seconds.On the other hand, at room tempera-ture, its stiffness is much greater, soglass may still flow, but the time-dependent response is measured inyears or decades.

Viscoelastic behavior is similarlyfound in other materials such aswood, polymers, human tissue andsolid rocket propellants, to name afew. Because of this complex behavior,the use of linear material properties is generally inadequate in accuratelydetermining the final shape of a viscoelastic material, the time takento arrive at that geometry, and thestresses on the part. In these cases,the material’s viscoelasticity must betaken into account in the simulation.

Viscoelastic Material ModelsIn mechanical solutions from

ANSYS, viscoelasticity is implementedthrough the use of Prony series. Theshear and volumetric responses areseparated, and the well-known rela-tionships between shear modulus Gand bulk modulus K are shown below:

Instead of having constant valuesfor G and K (and by extension, elasticmodulus E and Poisson’s ratio ν), theseare represented by Prony series in viscoelasticity:

These equations imply that theshear and bulk moduli are representedby a decaying function of time t. Simplystated, the user provides pairs of rela-tive moduli α i and relaxation time τ i,which represent the amount of stiffnesslost at a given rate.

For simplicity, only the shear termG will be considered for subsequentdiscussions. Start off at time t equal to0 with the full stiffness (instantaneousshear moduli). Hence:

This implies that the sum of theinput relative moduli α i must be lessthan or equal to 1.0. Consider theextreme case at infinite time, whichgives:

This means that the infinite modu-lus α∞ represents the percentage ofremaining stiffness. The user-input rela-tive moduli α i, on the other hand, is thepercentage of stiffness that is lost, withτ i representing the time constant.

Example ProblemFigure 1 shows a rubber bumper

being compressed by two rigid bodiesin which the right body is fixed and theleft body is displaced to compress therubber part in the middle. The rubberbumper was defined with a neo-Hookean hyperelastic material modelin ANSYS Workbench Simulation.

Analyzing Viscoelastic MaterialsMechanical solutions from ANSYS have convenient tools for calculating deformation of materials in which stiffness changes as a function of loading, time and temperature.By Sheldon Imaoka, Technical Support Engineer, ANSYS, Inc.


TIPS AND TRICKS

A Commands object was insertedunder the rubber part with the following contents:

tb,prony,MATID,1,1,sheartbdata,1,0.5,100

For this example, a single Pronypair was defined for the shear behavior.The TB command activates the defini-tion of the Prony pair, and the TBDATAcommand defines the Prony pair values. In this case, a relative modulusof 0.5 was assumed to have a relax-ation time of 100 seconds. This meansthat at infinite time, half of the shearstiffness will be lost at a decay rate,such that at 100 seconds 0.5(e-1), or 18 percent, of the stiffness is relaxed.

Figure 2 shows the maximumequivalent stress in the rubber part as a function of time. Note that thedecay is rapid in the beginning. This is due to the exponential function inthe Prony series. The responsebecomes asymptotic, showing thatthe maximum stress at time equal to1,000 seconds decreases to nearlyhalf of the maximum stress at thebeginning of the solution, as expected.Note that relaxation starts to occur atthe beginning of the solution, and thismodel experiences a multiaxial state ofstress, explaining why the long-termmaximum stress value is not exactlyhalf of the peak value.

Figure 3 displays the model at timeequal to 10 seconds. Note the self-contact that occurs due to the largeimposed displacement. A comparisonwith Figure 4 — displaying equivalentstress at time equal to 1,000 seconds —shows not only the reduction of stressbut also some redistribution that occursdue to stress relaxation.

In this way, the Prony series provides an effective tool in mechanicalsolutions from ANSYS for calculatingdeformation of materials where stiffnesschanges as a function of loading, timeand temperature. ■

Contact the author [email protected] for the completepaper from which this column is excerpted.

Figure 1. A rubber bumper (the graypart in the middle) is compressed bya fixed and moveable body on itsright and left.

Figure 2. Maximum equivalent stress in therubber part as a function of time

Figure 3. Model at 10 seconds, where self-contactoccurs due to the large imposed displacement

Figure 4. Equivalent stress at 1,000 seconds showingreduction in stress and some redistribution due to stressrelaxation

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Fluids Simulation for Viscoelastic MaterialsViscoelastic materials experience behavior

that may be characterized as both viscous andsolid. In addition to tools for addressing deforma-tion (ANSYS Mechanical software), the ANSYSportfolio also contains technology in ANSYSPOLYFLOW software that can be used to investi-gate deformation as well as applications that are more fluids related, such as rubber profileextrusion, blow molding or fiber spinning. Bothmodeling approaches reveal a great deal aboutthe uncommon behavior of the wide range of vis-coelastic materials.

Given the recent rise in energycosts and the desire to reduce CO2

emissions, demand for energy-efficientships is growing. Fuel consumption fora ship can be reduced by lowering theresistance of the hull as it movesthrough the water. This resistance canbe decomposed into skin friction, formdrag and wave drag. Although the relative importance of these threecomponents varies by vessel type,skin friction is generally the largestconstituent. For relatively slow-movinglarge vessels such as tankers, skin friction may represent as much as 70 percent of total drag. Therefore,researchers in the marine hydro-dynamics field have been making aconcerted effort to reduce skin friction.Among the methods that have beenproposed, covering the wetted surfaceof a ship with air bubbles is consideredthe most promising.

The concept of using air bubblesto reduce skin friction is not new. Thiseffect has been confirmed in manybench-scale studies, but there are sig-nificant problems to overcome beforeapplying this method to actual vessels.The energy required to pump air to thebottom of the ship increases in propor-tion to the flow rate and the draft of thevessel. Additionally, the efficiency ofthe propeller decreases in the bubblyflow regime. In order to achieve a netenergy savings, the position of the airinjectors, the mean bubble diameterand the volumetric flow rate of air mustbe optimized.

In a recently conducted full-scalestudy using a 126-meter-long cementcarrier, researchers at the University of

Small Bubbles,Large BenefitAir injection simulations show promise forreducing ship drag by injecting air bubbles toreduce skin friction along the hull of a vessel.By Takafumi Kawamura and Asako Murakami, Department of Systems Innovation, The University of Tokyo, Japan

Tokyo confirmed that fuel consumptioncan be reduced by 5 percent by injecting air bubbles into the boundarylayer at the bottom of the hull near thebow. In this project, the research teamused fluid flow simulation to predict thedistribution of air around the hull andestimate the reduction in skin friction.They developed an original bubbleflow model for modeling the air volumefraction and the velocity of the airphase and implemented it in ANSYSFLUENT software using a set of user-defined scalar (UDS) transportequations. This bubble model wastuned against data collected frombench-scale experiments

The ANSYS FLUENT simulationsrevealed that 34 percent of the wettedsurface area of the hull is covered with air bubbles and estimated a 10percent reduction in total resistance.

Mesh on the hull surface generated by GAMBIT software. Air injection was modeled as a mass fluxthrough the specified region near the bow.

The computational results also sug-gested that energy savings are greaterin the ballast condition than in the fullyloaded condition. These predictionswere consistent with results obtainedfrom tests conducted with the cementcarrier vessel.

In the near future, it is possiblethat many ships will be equipped withair bubble injection systems. Fordesigning such ships, computationalflow simulation will be a powerful toolgiven the costs of full-scale testingand the difficulties associated withscaling up bench test results to actualvessel performance. ■

ReferencesKawamura, T., Ito, A., Hinatsu, M., “NumericalSimulation of Bubbly Flow Around a MarinePropeller,” Proceedings of FEDSM2007,5th Joint ASME/JSME Fluids EngineeringConference, 2007, San Diego, California, U.S.A.

Air bubbles, shown here as a white sheet of bubbles, are injected along the ship’s hull, shown in red,in order to reduce the ship’s drag.


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OUTSIDE THE BOX

Snowflake bySnowflakeSimulation provides insight about snow safety.By ANSYS Advantage Editorial Staff with the assistance of Zoe Courville, CRREL, New Hampshire, U.S.A.

For many, the romantic dream ofwinter weather is sitting beside aroaring fire with a hot drink while snowdrifts gently to the ground outside.However, the reality can be more of anightmare. According to the NationalSnow and Ice Data Center in Colorado,U.S.A., seasonal snow affects up to 33 percent of the earth’s total land surface, 98 percent of which occurs inthe Northern Hemisphere. With snowaccumulation come transportationchallenges, natural events such as avalanches, and increased demandsrelated to maintaining our human support infrastructure, including elec-tricity and fuel supply. To betteraddress these challenges, researchersare taking a closer look at snow defor-mation — a factor that is related toeach of these scenarios.

Snow, which is actually an aggre-gate of ice grains, can be considered at three scales: the micro-scale (10-3

meters), the local scale (1 meter), and the landscape scale (104 meters).Landscape-scale snow properties canbe derived from local-scale snow datausing distributed or statistical models.Local-scale snow properties, however,depend strongly on heterogeneities andlayering at the micro-scale. Represen-tative elemental volumes (REVs) are ableto model local-scale snow; however,they do not take into account micro-mechanical factors that are fundamentalin explaining deformation.

To account for the micro-scale factors, researchers at the Cold RegionsResearch and Engineering Lab (CRREL)use a discrete element method (DEM) to explicitly model the dynamics ofsnow particle assemblies and the micro-mechanical interaction processesbetween the grains. DEM was selectedfor its ability to model materials thatundergo large-scale discontinuousdeformations that depend on micro-scale contact processes, internalbreakage of contact bonds and com-paction of broken fragments.

CRREL’s DEM model, calledµSnow, stores the particle shapes,

velocities and locations; finds contacts;calculates contact forces and moments;calculates conditions for contact bondformation, growth and rupture; and calculates movement for each particlewithin the aggregate. This explicit repre-sentation provides a way to identify theimportant processes that control snowdeformation and directly compare phys-ical experiments to simulation.

Recently, CRREL began combininga fluid flow model with µSnow toaccount for the flow and diffusion of airand water vapor in snow. Researcherssimulated pressure-driven air flowthrough 3-D models of snow samplesand found that modeled results closelymatched measured values.

In the future, this methodology foraddressing the complexity of the prob-lem by providing a way to incorporateindividual mechanisms into the largersnow model can lead to better predic-tions and understanding for a wholerange of snow-related scenarios. So asyou sit having happy thoughts whilesnow gently falls outside your home,think of the science that lies behind thesafety of snow tires, avalanche bestpractices and making sure that yourhome stays warm through those wintermonths. ■Air flow patterns through a 3-D model of a snow sample

A cubic µSnow model sample from CRREL,25 millimeters on edge with a 2-D cross-sectional plane; the particle diameter is about1 millimeter and the density is 30 percent


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