Computational simulation of marine devices by coupled ...
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Computational simulation of marine devices by coupled seakeeping and control system analysis tools Treball Final de Màster Facultat de Nàutica de Barcelona Universitat Politècnica de Catalunya Treball realitzat per: Bárbara Alcayde Romo Dirigit per: Prof. Julio García Espinosa Dr. Borja Serván Camas Màster en Enginyeria Naval i Oceànica (MUENO) Barcelona, Juliol 2020 Departament de Ciència i Enginyeria Nàutiques
Transcript of Computational simulation of marine devices by coupled ...
Computational simulation of marine devices by coupled seakeeping and
control system analysis tools
Treball Final de Màster
Facultat de Nàutica de Barcelona Universitat Politècnica de Catalunya
Treball realitzat per:
Bárbara Alcayde Romo
Dirigit per:
Prof. Julio García Espinosa Dr. Borja Serván Camas
Màster en Enginyeria Naval i Oceànica (MUENO)
Barcelona, Juliol 2020
Departament de Ciència i Enginyeria Nàutiques
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Dedication
To my grandmothers,
Mari and Filo.
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Acknowledgements
Many people have helped me, either directly or indirectly, to carry out this Master's Thesis,
sharing their knowledge, experiences and concerns, solving doubts, or supporting and
motivating me to continue with the work.
I would like to thank my supervisors, Professor Julio García and Dr. Borja Serván, for all their
help, from their motivational words to their knowledge that they have shared with me. I am
very grateful to have had the opportunity to develop this project with them since it has
allowed me to reinforce, strengthen and expand the knowledge acquired during the studies.
Finally, I would like to thank Jonathan Colom from CIMNE for his great support and his
programming advice. I am also very grateful to Ovidi Casals and Rosa Peyrau from CompassIS
for their technical assistance.
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Table of contents
List of figures ................................................................................................................................. xi
List of tables ................................................................................................................................. xv
Summary ....................................................................................................................................... 3
Resumen ........................................................................................................................................ 5
Glossary ......................................................................................................................................... 7
Chapter 1. Introduction ................................................................................................................ 9
1.1 Scope ............................................................................................................................. 9
1.2 Content description ..................................................................................................... 10
1.3 Previous concepts ....................................................................................................... 11
PART I: SIMULINK-SEAFEM COUPLING SYSTEM ........................................................................ 13
Chapter 2: Programs description ............................................................................................... 15
2.1 Introduction ................................................................................................................ 15
2.2 SeaFEM basic description ............................................................................................ 15
2.2.1 Information processing in SeaFEM .......................................................................... 16
2.2.2 Tcl extension ............................................................................................................ 17
2.3 Simulink description .................................................................................................... 20
2.4 Description of the TCL language ................................................................................. 21
2.5 Summary ..................................................................................................................... 23
Chapter 3: Communication interface development .................................................................. 25
3.1 Introduction ................................................................................................................ 25
3.2 Communication Interface concept definition ............................................................. 25
3.3 Approach ..................................................................................................................... 27
3.4 Communication between two Tcl scripts .................................................................... 27
3.5 Direct communication interface in Simulink ............................................................... 29
3.6 Communication Interface between Simulink and a TCL script ................................... 31
3.6.1 Simulink model ........................................................................................................ 33
3.6.2 Tcl script code .......................................................................................................... 33
3.7 Comunication interface between Simulink and SeaFem ............................................ 37
3.7.1 Simulink model ........................................................................................................ 45
3.7.2 TCL script code ........................................................................................................ 48
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3.8 Summary ..................................................................................................................... 51
Chapter 4 Program case: oscillating water column device ....................................................... 53
4.1 Introduction ................................................................................................................ 53
4.2 Approach ..................................................................................................................... 53
4.3 Development ............................................................................................................... 53
Chapter 5: Program case: fins effect on a Wigley hull .............................................................. 57
5.1 Introduction ................................................................................................................ 57
5.2 Approach ..................................................................................................................... 57
5.3 Development ............................................................................................................... 58
5.3.1 Modifications on the TCL script ............................................................................... 58
5.3.2 Modifications on Simulink ....................................................................................... 58
5.3.3 Modifications on SeaFEM ........................................................................................ 60
PART II: VERIFICATION................................................................................................................ 61
Chapter 6: Analysis of an oscillating water column device ....................................................... 63
6.1 Introduction ................................................................................................................ 63
6.2 Oscillating water column description .......................................................................... 63
6.3 Turbine model ............................................................................................................. 64
6.4 Model description ....................................................................................................... 64
6.5 Verification case: produced power ............................................................................. 65
Chapter 7. Fins effect control algorithm .................................................................................... 67
7.1 Introduction ................................................................................................................ 67
7.2 Fins model ................................................................................................................... 67
7.3 Environment and computational domain ................................................................... 72
7.4 Case: Fins effect in a sea without waves ..................................................................... 73
7.5 Case: Fins effect in irregular sea ................................................................................. 74
Chapter 8: Conclusions ............................................................................................................... 77
APPENDICES ................................................................................................................................ 79
Appendix A: Previous concepts .................................................................................................. 81
A.1 Introduction ................................................................................................................ 81
A.2 Rolling tests ................................................................................................................. 81
A.3 Wave spectrums .......................................................................................................... 81
Appendix B: Simulink blocks description ................................................................................... 83
B.1 Introduction ................................................................................................................ 83
B.2 TCP/IP Client Send block ............................................................................................. 83
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B.3 TCP/IP Client Receive block ..................................................................................... 84
B.4 Mux and Demux ...................................................................................................... 86
Appendix C: Communication interface development ............................................................... 87
C.1 Introduction ................................................................................................................ 87
C.2 TCL to TCL communication .......................................................................................... 87
C.3 Simulink TCL communication ...................................................................................... 88
C.4 Simulink to SeaFEM Communication .......................................................................... 93
Appendix D: OWC codes ........................................................................................................... 107
D.1 Introduction .............................................................................................................. 107
D.2 TCL code .................................................................................................................... 107
D.3 Simulink file description ............................................................................................ 110
Appendix E: Fins effect control ................................................................................................ 113
E.1 Introduction .............................................................................................................. 113
E.2 TCL code .................................................................................................................... 113
Appendix F: Fins effect control verification ............................................................................. 125
F.1 Verification case: Sea without waves ........................................................................ 126
F.2 Verification case: Sea with waves ............................................................................. 129
F.3 Summary ................................................................................................................... 133
References ................................................................................................................................ 135
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List of figures
Figure 1. Images of the different parts of the communication process between Simulink and
SeaFem. ....................................................................................................................................... 10
Figure 2. Definitions of coordinate system ................................................................................. 11
Figure 3. Body dynamics solver algorithm integrated with the wave diffraction-radiation solver
and mooring solver. .................................................................................................................... 17
Figure 4. SeaFEM data capture with activated TCL extension. ................................................... 18
Figure 5. Simplified scheme of the dynamic integration solver of SeaFEM. ............................... 19
Figure 6. Simplex communication. .............................................................................................. 25
Figure 7. Half Duplex Communication. ....................................................................................... 26
Figure 8. Duplex Communication. ............................................................................................... 26
Figure 9. Communication interface development followed process. ......................................... 27
Figure 10. Communication between two TCL scripts process. ................................................... 28
Figure 11. Capture of the communication between the TCL scripts. ......................................... 29
Figure 12. Scheme of the TCP/IP communication system. ......................................................... 30
Figure 13. Signal received by the TCP/IP Receive block. ............................................................. 31
Figure 14. Tcl to Simulink communication Interface process. .................................................... 32
Figure 15. Communication scheme in Simulink. ......................................................................... 33
Figure 16. Data Received in Simulink. ......................................................................................... 37
Figure 17. Diagram of the communication process between SeaFEM and Simulink. ................ 38
Figure 18. Simulink structure. ..................................................................................................... 39
Figure 19. Simulink process. ........................................................................................................ 40
Figure 20. Structures of the Simulink model and the TCL script. ................................................ 41
Figure 21. Initiate Problem diagram. .......................................................................................... 42
Figure 22. Start New Step diagram. ............................................................................................ 43
Figure 23. Start New Iteration diagram. ..................................................................................... 43
Figure 24. Finish Iteration diagram. ............................................................................................ 43
Figure 25. Finish Step diagram. ................................................................................................... 44
Figure 26. Start New Iteration diagram. ..................................................................................... 45
Figure 27. Finish Problem diagram. ............................................................................................. 45
Figure 28. Simulink general structure. ........................................................................................ 46
Figure 29. Simulink general scheme. ........................................................................................... 47
Figure 30. Description of the data transfer between Simulink and SeaFEM. ............................. 53
Figure 31. Scheme of the general communication procedure between the Simulink and
SeaFEM. ....................................................................................................................................... 54
Figure 32. Scheme of the communication procedure between the Simulink and SeaFEM. ....... 55
Figure 33. Scheme of the general communication procedure between the Simulink and
SeaFEM. ....................................................................................................................................... 56
Figure 34. Description of the data transfer between Simulink and SeaFEM. ............................. 57
Figure 35. Parts of the movement equation solved by Simulink and SeaFEM. .......................... 58
Figure 36. Simulink general scheme. ........................................................................................... 59
Figure 37. Simulink Finish Iteration subsystem. .......................................................................... 60
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Figure 38. Scheme of the oscillating water columns (OWCs) operating system. ....................... 63
Figure 39. Isometric view of the computational domain (Length in meters). ............................ 64
Figure 40. Mesh scheme. ............................................................................................................ 65
Figure 41. Pressure in the OWC. ................................................................................................. 66
Figure 42. Power produced in the OWC...................................................................................... 66
Figure 43. Principles of roll reduction by fin stabilizer.(Kawazoe, Nishikido, & Wada, 1993) .... 68
Figure 44. Localizing active fins on ship hull and stabilizing fin angles. (Rahimuddin, Maimun, &
Gani, 2014)(Kula, 2015) ............................................................................................................... 69
Figure 45. Directions of lift force and drag force.(Kim & Kim, 2011) .......................................... 69
Figure 46. Fin-induced forces and moments.(Lihua, Peng, Songtao, Ming, & Jia, 2018) ............ 70
Figure 47. Simulink scheme. Fixed fins. ...................................................................................... 71
Figure 48. Simulink scheme. Active fins. ..................................................................................... 72
Figure 49. Wigley hull model. ...................................................................................................... 72
Figure 50. Wigley hull generated mesh....................................................................................... 73
Figure 51. Roll movement. Fins effect in a sea without waves. .................................................. 73
Figure 52. Roll velocity. Fins effect in a sea without waves. ....................................................... 74
Figure 53. Roll acceleration. Fins effect in a sea without waves................................................. 74
Figure 54. Roll movement. Fins effect in irregular sea. .............................................................. 75
Figure 55. Roll velocity. Fins effect in irregular sea. .................................................................... 76
Figure 56. Roll acceleration. Fins effect in irregular sea. ............................................................ 76
Figure 57: Block TCP/IP Client Send. ........................................................................................... 83
Figure 58: Block TCP/IP Client Receive ........................................................................................ 84
Figure 59: Block TCP/IP Client Receive with Blocking mode activated ....................................... 84
Figure 60: Block TCP/IP Client Receive Blocking mode not activated ......................................... 84
Figure 61. Representation of a FIFO (queue) with enqueue and dequeue operations. ............. 85
Figure 62. Mux block. .................................................................................................................. 86
Figure 63. Demux block. .............................................................................................................. 86
Figure 64. Simulink client configuration...................................................................................... 88
Figure 65: Block parameters TCP/IP Receive .............................................................................. 89
Figure 66: Block parameters TCP/IP Send ................................................................................... 89
Figure 67: Block parameters Data Type Conversion ................................................................... 90
Figure 68: Simulink general scheme ........................................................................................... 94
Figure 69: Block Parameters TCP/IP Receive .............................................................................. 95
Figure 70: Block Parameters Demux ........................................................................................... 95
Figure 71: Block Parameters Data Type Conversion ................................................................... 96
Figure 72: Block Parameters If .................................................................................................... 96
Figure 73: Block Parameters Merge ............................................................................................ 97
Figure 74: Block Parameters TCP/IP Send ................................................................................... 97
Figure 75. Action 0 - Initiate Problem ......................................................................................... 98
Figure 76. Action 1 - Start New Step ........................................................................................... 98
Figure 77. Action 2 - Start New Iteration .................................................................................... 99
Figure 78. Action 3 - Finish Iteration ........................................................................................... 99
Figure 79. Action 4 - Finish Time Step ....................................................................................... 100
Figure 80. Action 5 - Finish Problem ......................................................................................... 100
Figure 81. Simulink general scheme. OWC. .............................................................................. 110
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Figure 82. Simulink subsystem: Finish iteration. OWC. ............................................................ 111
Figure 83. Simulink subsystem: Finish iteration. Pressure calculation subsystem. OWC. ........ 111
Figure 84. Simulink subsystem: Finish iteration. Pressure calculation. OWC. .......................... 112
Figure 85. Simulink general scheme. Active fins installed on a Wigley hull.............................. 121
Figure 86. Start New Iteration. Active fins installed on a Wigley hull. ...................................... 122
Figure 87. Operations subsystem. Active fins installed on a Wigley hull. ................................. 123
Figure 88. General roll moment and angular roll velocity curve. ............................................. 126
Figure 89. Roll movement. Ship without fins. Sea without waves. ........................................... 126
Figure 90. Roll movement. Fixed fins. Sea without waves. ....................................................... 127
Figure 91. Curve Mx-wx. Fixed fins. Sea without waves. .......................................................... 127
Figure 92. Roll movement. Fixed fins. Sea without waves. Verification. .................................. 128
Figure 93. Roll movement. Active fins. Sea without waves. ..................................................... 128
Figure 94. Mx-wx curve. Active fins. Sea without waves. ......................................................... 129
Figure 95. Roll movement. Active fins. Sea without waves. Verification. ................................. 129
Figure 96. Roll movement. Ship without fins. Sea with waves. ................................................ 130
Figure 97. Roll movement. Fixed fins. Sea with waves. ............................................................ 130
Figure 98. Mx-wx curve. Active fins. Sea with waves. ............................................................... 131
Figure 99. Roll movement. Fixed fins. Sea with waves. Verification. ........................................ 131
Figure 100. Roll movement. Active fins. Sea with waves. ......................................................... 132
Figure 101. Roll movement. Active fins. Sea with waves. Verification. .................................... 132
Figure 102. Roll movement. Active fins. Sea with waves. Verification. .................................... 133
Figure 103. Roll movement comparison for the three considered cases. Sea without waves. 134
Figure 104. Roll movement comparison for the three considered cases. Sea with waves. ..... 134
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List of tables
Table 1. SeaFEM TCL procedures execution point and task. ...................................................... 20
Table 2. Simulink Instrumet Control Toolbox blocks description. .............................................. 21
Table 3. Process flags and tasks. ................................................................................................. 40
Table 4. Tasks correspondence with flag value. .......................................................................... 42
Table 5. Wave data. OWC. .......................................................................................................... 65
Table 6. Wave data. Fins analysis on irregular sea. ..................................................................... 75
Table 7. Waves data. Sea with waves. ...................................................................................... 129
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Computational simulation of marine devices by coupled seakeeping and
control system analysis tools
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Summary
The aim of this Master’s Thesis is to extend the functionalities of a simulation of marine
devices program, SeaFEM, by coupling it to a control simulation program, Simulink, through a
communication interface following a TCP/IP protocol. Thus, more complex external loads could
be applied on the model to simulate.
To verify and demonstrate the correct functioning of the suggested system it has been used to
solve two situations: finding the power produced from the flux going through the turbine of an
Oscillating Water Column device and finding the reduction of the roll due to the effect of the
stabilizing fins installed onboard a Wigley type hull introducing a control algorithm. Finally, this
last case has been applied in more adverse sea conditions similar to reality.
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Resumen
En este Trabajo Final de Máster se ha pretendido extender las capacidades de un programa de
simulación de artefactos marinos, SeaFEM, acoplándolo con un programa de simulación de
control, Simulink, mediante una interfaz de comunicación siguiendo un protocolo TCP/IP. De
esta manera, se podrían aplicar cargas externas más complejas y bajo un algoritmo de control
sobre el modelo a simular.
Para verificar y demostrar el correcto funcionamiento del sistema propuesto se han resuelto
dos situaciones: conocer la potencia producida a partir del flujo que circula a través de la
turbina de una columna de agua oscilante y la reducción del balance debida al efecto de las
aletas estabilizadoras instaladas en un casco de tipo Wigley introduciendo así un algoritmo de
control. Finalmente, este último caso se ha aplicado en unas condiciones de mar más adversas,
similares a las reales.
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Glossary
a Inertial moment of the virtual mass around a longitudinal axis
𝐴𝑗 Wave amplitude
b Damping coefficient
c Restoring coefficient
CD Drag coefficient
CL Lift coefficient
D Drag forcé
d2θ/d2t2 Angular acceleration
dθ/dt Angular velocity
F factor to calibrate
Fz_fin fin vertical force
𝐻13
Significant wave height
L Lift forcé
MX Rolling momento
MF Fins momento
p pressure (Kpa)
P Power (Kw)
Q Flux (m3/s)
Rx Tilt
S (m2) Surface
S (w) Wave spectrum
𝑇1 Mean wave period
Troll fundamental period of the ship
U Ship velocity vector
Vs Forward ship velocity
Vz_fin Velocity of the fluid respect to a system of reference located in the fin
𝑤𝑗 Circular frequency
wx Roll angular velocity
yp Rolling arm
αE Angle of attack
αF Angle of attack
αP Pitch angle
∆𝑤 Constant difference between successive frequencies
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𝜖𝑗 Random phase angle of wave component number j
Acceleration
Velocities
θ Movements
Λ Ratio of aspect
φ Angular amplitude
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Chapter 1. Introduction
Times are noticeably changing for engineering. Currently we find structures such as wave
energy converters or marine wind power generation plants, something that a few years ago
was almost unthinkable. For this reason it is essential to find an association between the
product, nature and life, so that they play a joint role. Not only to create innovative designs,
but also to offer optimal functionality, guaranteeing safety and safeguarding sustainability for
ecological well-being. But how can we include these three elements in the design processes of
the structures? To achieve this, it is necessary to make realistic computational simulations that
take into account the precise geometry and properties of different materials, realistic
representations of physical and natural processes, and rational predictions of people's
experiences.
1.1 Scope
The aim of this Master's thesis is to develop a communication interface that couples a
seakeeping program (SeaFEM) with a control system analysis tool (Simulink) to obtain a
simulation that approaches reality more properly. Communicating with Simulink enlarges the
functionalities of SeaFEM since it allows adding a control on how the program applies loads on
the model.
Since SeaFEM has a powerful TCL interface, the commands that govern the communication
between the programs will be collected in a TCL script. SeaFEM TCL enables users to enhance
simulations without recourse to external compiled subroutines by accessing to advanced
features, including operations on internal structures and execution/communication with
external programs.
Several recent studies try to communicate Simulink with other programs to enhance their
capabilities. The procedure followed until these days consisted of creating a block from an S-
function type that used C MEX file (Sysel, 2009), which is complex from the user’s point of
view. Now, Simulink offers a new pack of tools called Instrument Control Toolbox that
facilitates the connection with any device. Among the different protocols that the pack offers
to stablish the communication the TCP/IP protocol has been chosen for the development of
this project.
The procedure of the simulation using the communication interface is the following. The
geometry of a model will be generated in SeaFEM (Figure 1. A) and parameters as current,
waves and other boundary conditions will be configured. From those conditions, SeaFem will
obtain displacements, velocities and accelerations values. Those values will be sent to a
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Simulink file (Figure 1.B) that will use them to calculate the loads to be applied on the model.
A control system can also be added on those loads. The resulting forces and moments will be
sent back to SeaFEM that will apply them on the model (Figure 1.D). As mentioned, a TCL code
will govern all the communication procedures between the programs (Figure 1.C).
Figure 1. Images of the different parts of the communication process between Simulink and SeaFem.
Once the communication interface structure has been defined, several tests have been carried
out to verify its correct functioning. These tests are described in the following section.
1.2 Content description
As already mentioned, this project aims to couple two programs in order to apply complex
loads on a model. For this, it is necessary to design the communication interface and verify
that it works correctly to finally apply it to a specific case. Thus, this project is divided in two
parts: Simulink-SeaFEM coupling system and verification.
In the first part, the process followed to establish the communication interface between both
programs is described. This part includes the design of a general structure and two customized
applications for future applications in the second part of this project.
A
C
D
B
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As mentioned, in the second part, the general communication structure is applied on two
different situations in order to verify the correct functioning: an oscillating water column
(OWC) and a ship Wigley type hull. On the first situation the intention is to calculate the power
obtained from the flux through the turbine of an OWC. The results obtained from calculating
only using SeaFEM and using the coupling system have been compared concluding on a
satisfactory functioning. Once the loads on a model are correctly applied, in the second
situation the intention is to add a control algorithm. For that, a pair of fins acting on a Wigley
hull has been simulated. Several tests considering different fins and sea conditions have been
carried out. The verification method followed is described. Finally, the fins control algorithm
from the previous part is applied in two sea situations to analyze their effect on the decreasing
of ship roll movement: without waves and considering more adverse sea conditions, irregular
sea. As expected, in both situations, the fins have a significant impact on the reduction of the
ship roll movements.
1.3 Previous concepts
This section pretends to introduce the movements of the ship. The study of the dynamic
behavior of a ship considers six movements depending on its six freedom degrees as a rigid
body; this means, three translations and three rotations. The movements of a ship are referred
to a Cartesian coordinate system which origin is located on the waterplane; coinciding with the
x-axis in the longitudinal direction; the y-axis with the transversal direction and the z-axis with
the vertical(Newman, 1979).
The translation in the x-axis is called “surging”; on the y-axis, “swaying” and on the vertical
axis heaving. The rotation around the x-axis is called rolling, on the y-axis, pitching and in the
vertical axis yawing. In Figure 2 the six movements are shown.
Figure 2. Definitions of coordinate system
The surging of a ship is closely related with the effects of the propeller system and is studied in
relation with the resistance and propulsion problems. The yawing and the swaying depend on
the propeller system and on the govern device installed, being usually studied under
manoeuvrability aspects (Faltinsen, 1993).
The heaving, pitching and rolling are the movements related with the resistance, the
propulsion and the manoeuvrability not contained in the vertical plane. These last three
movements compose the object of study that is normally designated Dynamics of the ship and
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are those that have a greater influence on the determination of the habitability conditions
onboard, as in the effect of the forces induced by the waves acting on the ship.
The interaction of the movements together with the manoeuvrability of the ship and the
vertical movements is significant, thus, the manoeuvrability studies are frequently included in
the dynamics of the ship. It is already known that the yawing has an important impact on the
roll, especially in high velocities.
It is also important to mention that only three of these movements are purely oscillatory since
it exists in them restoring forces or moments when the ship is moved from her equilibrium
state: heaving, rolling and pitching. In the surging, swaying and yawing, the ship does not
return to her initial equilibrium state when it is displaced from it.
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PART I: SIMULINK-SEAFEM COUPLING
SYSTEM
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Chapter 2: Programs description
2.1 Introduction
In this chapter the programs involved in this project as well as the programming language used
to stablish the communication between them are described. The reasons for choosing these
programs for the development of this project will also be remarked.
2.2 SeaFEM basic description
Tdyn is a simulation software that includes a complete set of simulation tools, in a single
computing environment, which allows to solve almost any sort of engineering analysis,
including problems of structural calculation, fluid dynamics, heat transfer , coupled, multi-
physical and seakeeping. Tdyn is made up of three analysis packages: Tdyn CFD + HT,
RamSeries and SeaFEM.
SeaFEM is a module that includes the Tdyn program that offers a set of advanced tools for
simulating the behavior of the sea that allows analysis of the effect of waves, wind and
currents on naval and oceanic structures, as well as for maneuverability studies. The program
covers a wide range of applications such as ships, semi-submersible platforms and TLP type,
FPSO systems, marine wind turbines and oceanic energy generation devices.
SeaFem has been developed at the International Center for Numerical Methods Applied to
Engineering, CIMNE, of the UPC, in collaboration with the company Compass Ingeniería y
Sistemas.
With a new generation solver, SeaFEM allows realistic simulations of 3D wave radiation
diffraction models with multiple bodies, by solving potential flow equations in the time
domain, using the finite element method in non-mesh structured. It also allows solving first
and second order diffraction-radiation equations with real sea states.
In contrast to other programs that simulate the behavior of the sea, which do so in the
frequency domain and with the Boundary Elements Method, SeaFEM works in the time
domain and bases its operation on the Elements Method Finite. The advantage of this method
is that complex geometries can be represented as it allows the use of unstructured meshes.
This Tdyn module is built in GID which is a universal, adaptable and easy to use pre and post
processor, developed by CIMNE. In this way, the operation of this program is based on a set of
steps that must take place consecutively: the pre-process and the post-process.
The preprocess includes the model definition steps:
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- Geometric representation
o Element geometry
o Geometry of the study area
o Definition of the open sea area
- Definition of Tdyn data
o Simulation Type
o General Data
o Problem Description
o Environment Data
o Time Data
o Body Data
o Initial Conditions
o Numerical Data
o Boundary Conditions
- Mesh generation
Finally, the part in which the results are analyzed is the Postprocess.
2.2.1 Information processing in SeaFEM
When designing a program it is necessary to think first on the algorithm that the new program
will have allowing creating a general scheme. In this case, the program will follow and adapt to
the algorithm that governs SeaFEM. In this section the general algorithm of the program is
explained as well as the sequence of the different intern calculations. Thus, this section will
clarify the decisions taken in the following chapter regarding the communication interface
development.
A relaxation algorithm based on the Aitken method is used to accelerate convergence within
each loop (Serván Camas, 2016).In this way, the dynamic solver is implemented in SeaFEM by
means of three nested loops shown in Figure 3.
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Figure 3. Body dynamics solver algorithm integrated with the wave diffraction-radiation solver and mooring
solver.
- Time marching loop: In the time marching loop the information from the previous
time step is used as initial values of the iterative procedure. This is the most
external loop in the program and refers to the time step.
- Solver loop: Hydrodynamic loads are calculated in the Solver Loop. This loop will
perform iterations in which will solve the linear system corresponding to the
problem of wave diffraction radiation. The program will iterate until the condition
of convergence of hydrodynamic loads is reached along with the kinematics of the
body.
- Body dynamics loop: The body dynamics loop is the inner loop. Within this loop,
wave diffraction and radiation loads remain unchanged, hydrostatic forces are
updated based on body position, and the rest of loads will be updated in each
iteration.
2.2.2 Tcl extension
Occasionally, the program does not have incorporated the functionalities that the user wants
to perform. For this reason SeaFEM offers the possibility of extending them by adding a TCL
script in the configuration of the program. Thus, SeaFem distribution includes a basic TCL
installation that allows implementing new capabilities in SeaFem. As the aim of this project is
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connecting SeaFem with Simulink in order to extend the capabilities of the program to
calculate external loads and add a control system on them, the TCL extension facility has been
used.
The SeaFem extension is activated when the check-box is selected in the TCL Data section of
the General Data part in the problem definition. The route to the location of the TCL script that
the program is going to read should also be indicated as shown in Figure 4.
Figure 4. SeaFEM data capture with activated TCL extension.
SeaFem has implemented some standard SeaFEM TCL event procedures (SeaFEM Theory
Manual, n.d.). These procedures have specific names that SeaFem recognizes as well as a
specific syntax in the definition of values. For this project the procedures that we are going to
use include:
- TdynTcl_InitiateProblem
- TdynTcl_StartNewStep
- TdynTcl_StartNewIteration
- TdynTcl_FinishIteration
- TdynTcl_FinishStep
- TdynTcl_FinishProblem
These procedures correspond to different parts of the loops described in the previous section
and illustrated in Figure 3. In order to understand more easily in which points are those loops
located and allow the access to these procedures a generalized example is presented. Thus,
the following figure pretends illustrating how SeaFEM process the data to achieve results to
apply to the model. In this general case it has been considered that firstly the program does
not reach the convergence and it has to begin again until it reaches the convergence in the
next iteration. In the graphic it is supposed that the process has already begun
(TdynTcl_InitiateProblem) continuing in the following way:
- Beginning of the time loop (TdynTcl_StartNewStep): the information from the
previous time step is used as initial values of the iterative procedure.
1) Begins to count time and iterations.
- Solver loop and Body Dynamics loop (TdynTcl_StartNewIteration): The program
will iterate until the condition of convergence of hydrodynamic loads is reached
along with the kinematics of the body
2) As convergence is not reached the iteration is manteined i = 0; the following time step
begins.
19
3) The program returns to the beginning of the time step (TdynTcl_StartNewStep). It is a
new time step t = 1 but in the same iteration i = 0.
- SeaFEM studies again the hidrodynamic loads convergence.
4) In this case convergence is reached. Thus, iteration finishes. (TdynTcl_FinishIteration).
5) The program ads a new time step (TdynTcl_FinsihStep).
6) The program ads the new data (TdynTcl_StartNewStep) to carry out the calculus in the
new iteration i =1 and time step t = 2.
The program will continue this process until the desired time duration for this simulation is
reached. Once reached, the program will activate the endings orders (TdynTcl_FinishProblem).
Figure 5. Simplified scheme of the dynamic integration solver of SeaFEM.
The following Table 1 clarifies and summarizes in which point of the loop are located the
procedures and which is their task.
20
Procedure Point of execution Task
TdynTcl_InitiateProblem Called at the beginning of the
execution, once all the data
structures have been created.
This procedure runs the
execution of the program.
TdynTcl_StartNewStep Called at the beginning of the
time marching loop.
The previous time step is used
as initial values of the iterative
procedure.
TdynTcl_StartNewIteration
Called at the beginning of the
solver and body dynamics loop.
Convergence study.
TdynTcl_FinishIteration Called when the convergence is
reached.
Ads a new iteration.
TdynTcl_FinishStep Called once the current step is
finished.
Ads a new time step.
TdynTcl_FinishProblem This procedure is called at the
end of the execution of the
current problem.
Closes and stops the
procedures and execution of
the program.
Table 1. SeaFEM TCL procedures execution point and task.
Using the aforementioned procedures, information can be introduced and extracted from
SeaFEM at computational time.
2.3 Simulink description
Simulink is a graphical programming environment for modeling, simulating and analyzing
multidomain dynamical systems developed by MathWorks. Its primary interface is a graphical
block diagramming tool and a customizable set of block libraries. It offers a good quality
integration with the rest of the MATLAB environment and can either drive MATLAB or be
scripted from it. Simulink is used in automatic control and digital signal processing for
multidomain simulation and model-based design.
In essence, Simulink is a visual programming environment, which works on the Matlab
programming environment. Simulink provides the user a packet of tools that allows sending
and receiving information by means of a different communication protocols called Instrument
Control Toolbox.
The Instrument Control Toolbox was designed to connect MATLAB directly to instruments such
as oscilloscopes, function generators, signal analyzers, power supplies, and analytical
instruments (Instrument Control Toolbox 2 User ’s Guide, n.d.). The toolbox connects to the
instruments via instrument drivers such as IVI and VXIplug&play or via text-based SCPI
commands over commonly used communication protocols such as GPIB, VISA, TCP/IP, and
UDP. The user can also control and acquire data from test equipment without writing code.
But the functionality that we are interested in for this project is that allows generating data in
MATLAB to send out to an instrument or read data into MATLAB for analysis and visualization.
The packet contains the blocks of the Table 2.
21
As it has been mentioned, for this project:
- The TCP/IP Communication protocol will be used.
- Only TCP/IP Client Receive block and TCP/IP Client Send block will be used.
- Both of the blocks are for use as TCP/IP clients. They do not work as TCP/IP servers.
Block Description
Query Instrument Query or read instrument data
To Instrument Send simulation data to instrument
Serial Configuration Configure parameters for serial port
Serial Receive Receive binary data over serial port
Serial Send Send binary data over serial port
TCP/IP Client Receive block Send binary data over serial port
TCP/IP Client Send block Send data over TCP/IP to specified remote
machine
UDP Receive Receive data over UDP network from
specified remote machine
UDP Send Send data over UDP network to specified
remote machine
Table 2. Simulink Instrumet Control Toolbox blocks description.
2.4 Description of the TCL language
Tcl (Tool Command Language) is a high-level, general-purpose, interpreted, dynamic
programming language. It was designed with the goal of being very simple but powerful. Tcl
casts everything into the mold of a command, even programming constructs like variable
assignment and procedure definition. Tcl supports multiple programming paradigms, including
object-oriented, imperative and functional programming or procedural styles.
It is commonly used embedded into C applications, for rapid prototyping, scripted applications,
GUIs, and testing. Tcl interpreters are available for many operating systems, allowing Tcl code
to run on a wide variety of systems. Because Tcl is a very compact language, it is used on
embedded systems platforms, both in its full form and in several other small-footprint
versions.
22
The popular combination of Tcl with the Tk extension is referred to as Tcl/Tk, and enables
building a graphical user interface (GUI) natively in Tcl. Tcl/Tk is included in the standard
Python installation in the form of Tkinter.
It was first created by John Osterhout in 1989.
A socket is defined by a pair of local and remote IP addresses, a transport protocol and a pair
of local and remote port numbers. In order for two programs to communicate with each other,
certain requirements must be met:
- That one program is able to locate the other.
- That both programs are capable of exchanging any sequence of octets, that is, data
relevant to their purpose.
For this, the three resources that originate the concept of socket are necessary:
- A communications protocol, which allows the exchange of octets.
- A pair of Network Protocol addresses (IP Address, if TCP / IP Protocol is used), which
identifies the source and remote computer.
- A pair of port numbers, which identifies a program within each computer.
There are two distinct types of socket network applications: Server and Client. Servers and
Clients have different behaviors; therefore, the process of creating them is different. What
follows is the general model for creating a streaming TCP/IP Server and Client.
- Server
o Initialize Winsock.
o Create a socket.
o Bind the socket.
o Listen on the socket for a client.
o Accept a connection from a client.
o Receive and send data.
o Disconnect.
- Client
o Initialize Winsock.
o Create a socket.
o Connect to the server.
o Send and receive data.
o Disconnect.
Sockets allow implementing a client-server or peer to peer architecture. The communication
must be initiated by one of the programs called the client program. The second program waits
for another to initiate communication, for this reason it is called the server program.
A socket is an existing process or thread on the client machine and the server machine, which
ultimately serves the server and client program to read and write the information. This
information will be transmitted by the different network layers.
23
When a client connects to the server a new socket is created, in this way, the server can
continue to wait for connections in the main socket and communicate with the connected
client, in the same way a socket is established in the client in a local port.
A server application usually listens for a specific port waiting for a client connection request.
Once it is received the client and the server connect so that they can communicate with each
other. During this process, the client is assigned to a port number, through which it sends
requests to the server and receives the corresponding responses from it.
Similarly, the server obtains a new local port number that will help it to continue listening to
each connection request from the original port. Similarly connect a socket to this local port.
2.5 Summary
Once the programs and the communication language used in this project have been described,
the facilities offered by their tools to implement it can be listed.
TCL is the best option since SeaFEM incorporates a TCL extension that allows enlarging the
capabilities of the program. Furthermore, this Language allows creating a simple structure to
communicate the clients with the server.
The tools package Instrument Control Toolbox of Simulink, for its parts, allows Simulink to
send and receive information from other devices through a TCP/IP protocol. Thanks to the
presentation and the format of the tools, the Package offers a visual and intuitive handling.
24
25
Transmitter Receiver
Chapter 3: Communication interface
development
3.1 Introduction
In this chapter, the process followed to transmit data between Simulink and SeaFEM through a
TCL script is detailed. Before detailing each step of the design process some concepts
regarding the communication interface concept will be revised.
Several tests have been made in this project in order to develop the communication interface
between SeaFEM and Simulink increasing the difficulty each time. For each test a general
example is presented.
3.2 Communication Interface concept definition
The interfaces are responsible for preparing the data so that they can travel through the
transmission medium. If the transmission medium is copper the data can be represented as
voltage or current levels and if it is optical fiber the data must be represented by light pulses.
The protocol, in turn, is responsible for establishing the rules that govern the exchange of data
between two devices.
One method of characterizing lines, terminal devices, computers and modems is by their mode
of transmission or communication. The three kinds of transmission modes are simplex, half-
duplex and full-duplex.
- Simplex communication: Simplex or unidirectional transmission (See Figure 6) only
occurs in one direction, disabling the receiver from responding to the transmitter.
Normally simplex transmission is not used where human-machine interaction is
required. Examples of simplex transmission are: TV and radio broadcasting,
unidirectional paging, etc.
Figure 6. Simplex communication.
26
Transmitter
Receiver
Receiver
Transmitter
- Half Duplex Communication: Half-duplex transmission (See Figure 7) allows
transmission in both directions; however, transmission can occur only in one direction
at a time. Both transmitter and receiver share a single frequency. A typical example of
half-duplex is the civil band radio (CB) where the operator can transmit or receive, but
cannot perform both functions simultaneously on the same channel. When the
operator has completed the transmission, the other party must be advised that it can
start transmitting (e.g. saying "change").
Figure 7. Half Duplex Communication.
- Duplex Communication: Full-duplex transmission (fdx) (See Figure 8) allows the
transmission in both directions, but simultaneously on the same channel. There are
two frequencies: one to transmit and another to receive. In the telecommunications
field abound the examples. The most typical case is telephony, where the transmitter
and receiver communicate simultaneously using the same channel, but using two
frequencies.
Figure 8. Duplex Communication.
A protocol is the language with which devices communicate on the network. It is the way in
which the devices of a network exchange information. For example, two computers connected
in the same network but with different protocols could never communicate, for this, it is
necessary that both "speak" the same language, therefore, the TCP / IP protocol was created
for Internet communications. It is necessary to have this communication protocol installed in
order to allow any computer to connect to the Internet. They can be well implemented in
hardware (network cards), software (drivers), or a combination of both.
Then, a more appropriate way to define it would be: it is a set of conventions related to data
format, transmission methods, network topology, bus accesses and control procedures in
general necessary for communication between two or more equipment and services.
Transmitter
Receiver
Receiver
Transmitter
27
3.3 Approach
Several tests have been made in this project in order to develop the communication interface
between SeaFEM and Simulink increasing the difficulty each time. This means that the first
tests were trying to communicate the programs with themselves and then tried to
communicate the programs with each other.
Figure 9 shows the followed communication interface development process. On the first step
it is necessary to be able to send and receive data from a channel in TCL and in Simulink,
separately. Once both programs work, on the second step it has to be possible to transfer data
between TCL and Simulink. Finally, on a third step the communication interface between
Simulink and SeaFEM through a TCL Script can be developed. The following sections describe
each step.
Figure 9. Communication interface development followed process.
3.4 Communication between two Tcl scripts
The first step to develop the communication interface between the two programs is to know
how to communicate a program with itself. In TCL language it is possible to communicate two
scripts, acting as server and client, through a channel. For that, once the socket is opened and
the channel is assigned, the server begins the communication between them begins. In order
to check that the communication works satisfactorily the server sends the data back to the
client.
Figure 10 describes the communication process between the server and client scripts. As
shown, the client assigns a channel and both scripts try to connect to the channel. If the server
is not able to connect to the channel the connection aborts and ends. If the server
satisfactorily connects to the channel the communication between the two programs can
begin.
1st 2nd 3rd
TCL
SIMULINK
SEAFEM
Tcl to Tcl
communication
Direct Interface
Communication
Communication
between Tcl and
Simulink
Communication
between
SeaFem and
Simulink
28
In order to establish a communication between the scripts a loop has been created in such way
that the server will ask a message to the client and wait for it, the client will answer and the
server will ask a message and wait again.
Figure 10. Communication between two TCL scripts process.
Client script
The client assigns the channel and waits for the server to connect. Then, the client asks the
user to write a message and sends it to the channel.
Sever script
The procedure that performs the server actions is called proc Receive_Data.
As mentioned, the server tries to connect to the channel and configures it. Then,
communication loop where the data transfer takes place is defined. Finally, the socket is
closed.
SERVER CLIENT
Open socket
Channel
configuration
Channel asignement
Connection
YES
NO Exit
Wait for client data
Introduce message to send to server
Send message to channel
Get message from the channel
Send message to channel
Receive server response
Loop
29
The different commands of the codes can be found in the Appendix C (p. 87). Figure 11 shows
an example of an established communication between the two scripts on the Command
Windows.
Figure 11. Capture of the communication between the TCL scripts.
3.5 Direct communication interface in Simulink
Following with the communication interface development process described in
Figure 9, the remaining part of the first step (data transfer involves one program) is
implementing a Simulink model to send and receive data through a channel. The process,
described in the example below, requires using the blocks from the Instrument Control
Toolbox pack.
Sending and Receiving Data over a TCP/IP Network
This example details how to build a simple model using the Instrument Control Toolbox blocks
in the library block in conjunction with other blocks in the Simulink library. It also illustrates a
different possibility of communication since, unlike the previous TCL case, the data is sent to
an echo server using TCP/IP protocol.
As mentioned, it is necessary to create an echo server on the machine that simulates sending a
signal to the TCP/IP send block and echoes the result back to the Send block to send data.
Then, the TCP/IP Receive block will read that same data back into the model.
The steps to create this communication example are listed and described below:
Step 1: Create an Echo Server
Step 2: Create a New Model
Step 3: Open the Block Library
Step 4: Drag the Instrument Control Toolbox Blocks into the Model
Step 5: Drag the Sine Wave and Scope Blocks to Complete the Model
Step 6: Connect the Blocks
Step 7: Specify the Block Parameter Values
Step 8: Specify the Block Priorities
Step 9: Run the Simulation
Step 10: View the Result
30
- Step 1. Create an Echo Server: this step consists opens a port on the computer to work
as an echo server that sends and receives signals via TCP/IP. To create an echo server
(in this example port 50000 was used) the following command in MATLAB should be
used:
echotcpip('on', 50000)
- Step 2. Create a New Model: open an empty Editor window.
- Step 3. Open the Block Library: In this example the blocks on the Instrument Control
Toolbox node are used.
- Step 4. Drag the Instrument Control Toolbox Blocks into the Model: For this example
the blocks used are the TCP/IP Client Send and the TCP/IP Client Receive. A Scope
block is used to display the data received by the TCP/IP Receive block.
- Step 5. Drag the Sine Wave and Scope Blocks to Complete the Model
- Step 6. Connect the Blocks: Once all the blocks are on the editor window the Sine Wave
block and the TCP/IP Client Send block are connected as shown in Figure 12. In the
same way, the output port of the TCP/IP Client Receive block and the input port of the
Scope block are connected.
Figure 12. Scheme of the TCP/IP communication system.
- Step 7. Specify the Block Parameter Values: In this part the parameters for the blocks in
the model are configured.
o TCP/IP Client Send Block configuration: The Remote Address and the Port fields are set with the address of the echo server.
o TCP/IP Client Receive Block configuration: The Remote Address and the Port fields are set with the address of the echo server.
o Sine Wave Block configuration: the Sample Time Field of this block must match the one in the TCP/IP Client Receive Block.
- Step 8. Specify the Block Priorities: the order in which Simulink should process the
blocks is specified on the Properties section by assigning a priority number. In this case,
the priority of TCP/IP Client Send and TCP/IP Receive is set to 1 and 2, respectively. In
the Configuration Parameters dialog box, the Type field is set to Fixed-step and
the Solver field to discrete (no continuous states).
31
- Step 9. Run the Simulation: While the simulation runs, the status bar at the bottom of
the Simulink Editor updates the progress of the simulation.
- Step 10. View the Result: The Scope block shows the graph in Figure 13 correspondent
to the signal received by the TCP/IP Client Receive block.
Figure 13. Signal received by the TCP/IP Receive block.
3.6 Communication Interface between Simulink and a TCL script
Once it is known how to communicate TCL and Simulink separately, the second step, following
the scheme in
Figure 9, is to communicate the programs between them. The following example was used to
stables the communication between Simulink and TCL.
In this example, the following iterative operation is solved:
𝑂𝑢𝑡𝑛𝑢𝑚 = 2(2 + 𝑖) 𝑖 = 0,1,2, … ,50
𝐼𝑛𝑡𝑜𝑢𝑡 = (𝑖 + 0.98888999999) 𝑖 = 0,1,2, … ,50
Both values, Outnum and Intout1, are calculated in the TCL script and sent to Simulink. Once
Simulink has received the values it shows them on a graph. In order to check that the process
works successfully Simulink will send the values back to TCL and be shown on the Command
Window. Thus, Simulink will act as a client and TCL as the server. Figure 14 shows the process
1 In this example Intout is used to introduce the error to check that Simulink reads properly an integer
that has been transformed to double.
32
of the communication between TCL and Simulink. The functioning is very similar to the
communication between two TCL scripts.
Figure 14. Tcl to Simulink communication Interface process.
Thus, in this example, two values are sent and received and will be interpreted as a vector for
both programs:
(intout, outnum)
TCL SIMULIN
K
Open socket
Accept client
connection
Connects to channel
Connection
YES
NO Exit
Operations
Receive data
Transform data and send
Receive data and transform
Send data
Loop
Show
data
Close socket and channel
33
The Simulink model and the TCL script code implemented are described in detail in the
following sections.
3.6.1 Simulink model
Figure 15 shows the communication scheme in Simulink. The blocks used are the following:
- TCP/IP Client Receive: The remote address and port must be indicated in the data
reception block. Since two data will be received, it must be indicated as a vector [1
2].
- TCP/IP Client Send: In the data sending block the Remote address and the Port
must coincide with those previously indicated in the TCP/IP Client Receive block.
- Scope: shows the values received on a graph.
- Display: shows the values received.
- Data Type Converter: In this case, this tool is added to check if the values were
received in the correct format.
Figure 15. Communication scheme in Simulink.
3.6.2 Tcl script code
As shown in the Figure 14, the TCL has to perform the following tasks:
- Open a socket.
- Accept the connection of the client.
- Operate.
- Send data.
- Receive data.
- Transform data.
- Close the socket.
34
All those tasks compose the different procedures of the code. The procedures have to be
written in certain order so the process runs as in the Figure 14.
As it is already known, in TCL, the code begins describing the procedures and after begins the
main program, in which the procedures are called.
- Procedures description:
o Proc close_socket
o Proc accept_client_connection
o Proc open_socket
o Proc send_data
o Proc receive_data
- Main program:
o Variables description
o Open socket
o Operation loop
o Send data
o Receive data
o Close socket
Now the procedures are going to be described in detail.
- Proc close_socket: This procedure closes the channel in which the communication
takes place.
- Proc accept_client_connection: This procedure configures the channel and determines
if the communication between programs has been stablished correctly. If the
communication is successful the connection will be set to value 1, otherwise an error
message will appear indicating that the client tried to connect to server.
35
- Proc open_socket: In this procedure the channel and port where the communication
will take place are defined.
- Proc send_data: This procedure sends data to Simulink.
- Proc receive_data: this procedure sets the size of the data packet that we want to
receive from Simulink and reads the data. In this example we will receive 2 doubles (2
packs of 8 bytes).
As mentioned, all those procedures are going to be called in a particular order in the Main
program.
- Variables description and Open socket: Since Simulink can only act as a Client, the
TCL script will obligatorily act as a server. As described in the previous section, a
server socket begins defining the socket, the port in which the communication will
take place (in the example the port will be 9901) and the channel. The channel is
defined by opening the socket on the wished port.
36
- Operation loop: In the main program the operations loop also has to be described.
In this example the loop operation takes into account the error in the
transformation of the data in its sending and reception. The expression “set
intout” introduces the error to check that Simulink reads properly an integer that
has been transformed to double.
- Send data: Before sending the data it is necessary to transform it to the correct
format by using the command “binary format”2.
Once the data is transformed, the sending procedure can be called defining the data to
be sent and the channel. In order to verify that the process is successful, a message
that shows the data that has been sent to Simulink can be added.
- Receive data: Now the program is going to receive data from Simulink. The data
will be received and transformed into the readable format for TCL. Once again, a
verification message that shows the values received can be added.
- Close socket: Finally, and to ensure that the process of sending information does
not interfere with future tasks, it is necessary to close the channel and the port
that has been used. To achieve this purpose, the procedures created above will be
called.
2 Binary is a built-in Tcl command, performs conversions on the bytes in a string, rather than the
characters. The most commonly used binary type commands are the following: binary format formatString ?arg arg ...? binary scan string formatString ?varName varName ...?
Binary facilitates the direct manipulation of bytes in a string, and can interpret those bytes in various ways. Binary scan is used to extract data, and binary format is used to generate data.
37
Figure 16 shows the graphic obtained in Simulink in which appear two lines that correspond to
the two different operations of the loop. The blue line corresponds to the outnum values and
the yellow line to the intout values.
Figure 16. Data Received in Simulink.
3.7 Comunication interface between Simulink and SeaFem
Once the data transfer between TCL and Simulink works successfully, the third step (See
Figure 9) which is communicating Simulink and SeaFEM through a TCL script can be developed.
Before describing the designing process, it is opportune to mention that it has been designed
in such way, that it is as intuitive as possible and that the user has to make the minimum
modifications when using it for different applications. Meaning, it is expected that the user
only has to modify the operational part to add the required functions to obtain the external
forces and moments but not the communication algorithm. The place where the user should
add those calculi is inside a Simulink box called Operations.
In the example used to illustrate this section it is considered that there is a SeaFEM model of a
body and the intention is to apply an external force on it. That external force has been
calculated in Simulink and sent to SeaFEM.
As it can be intuit, until this moment iterative processes have been treated. In the cases seen
until now there were loops and, in each loop there was a data reception, a calculus and a
sending of the result. From now on, each loop will be called Time Step.
38
As explained in the previous chapter, SeaFEM works with three loops to control the
convergence of its results. The communication interface developed in this project has been
designed following the steps succession of SeaFEM. Thus, there will be different time steps on
each one of the iterations until SeaFEM reaches the convergence.
The diagram in figure shows a general preliminary scheme of the first time step of the iterative
communication process between the two programs. The process would be the following (see
Figure 17):
- Simulink calculates the external forces acting on the model and sends them to
SeaFEM.
- SeaFEM applies the forces on the body and calculates the new displacements.
- SeaFEM sends the new displacements to Simulink.
- SeaFEM will calculate the convergence of the results. If the results converge a new
iteration with new displacement values will begin. If not a new time step inside the
iteration will begin and SeaFEM will recalculate the displacements asking values to
Simulink until convergence is reached.
Figure 17. Diagram of the communication process between SeaFEM and Simulink.
Thus, it can be clearly observed that Simulink is going to act as the client role and SeaFEM as
the server. Once assigned the role to each program the client general scheme can be defined.
Figure 18 shows general structure of the Simulink part. The functioning of the diagram
beginning at time t = 0 would be the following:
…
YES/NO YES/NO
Convergence
Control
Send displacements
Send forces
Convergence
Control
SIMULINK SEAFEM
tn = t
tn = t + 1
…
39
- Simulink, as it has preconfigured the role of Client, needs to be the first to receive
data. For this reason, in this step, Simulink makes a first reception and delivery of
empty data, in order to activate the program. This data will be used later to
indicate which task the program is going to develop.
- Simulink receives from SeaFEM the displacements.
o If there is not any operation to be solved the program ends and exits.
- Otherwise, Simulink solves the operations required to obtain the forces from the
displacements.
- Simulink sends the obtained forces to SeaFEM.
- SeaFEM studies the convergence.
o If it reaches the convergence a new iteration begins (it = it+1) and the
process continues.
o If convergence is not reached a new time step begins in the same iteration.
Figure 18. Simulink structure.
In order to send several values in each time step it is grouped in a vector. In this case, the
intention is to obtain forces (fx, fy, fz) from the displacements (dx, dy, dz) in the three
directions (x-,y- , z-):
(dx, dy, dz, fx, fy, fz)
It is also necessary that this vector includes a value indicating which task Simulink has to
develop (flag) and the time increase (dt). Thus, the vector used has two new components:
(flag, dt, dx, dy, dz, fx, fy, fz)
it = it + 1 t = t + dt
it=0
NO
RECEIVE
SEND
RECEIVE
OPERAT
E
SEND
CONVERGENCE
END YES
EXIT
t = 0
YES NO
SIMULINK
40
Figure 19. Simulink process.
Figure 19 shows the same process of figure but the different actions that take place have been
grouped in four tasks and each task has been assigned to a different number called Flag.
Flag Task
0 Initialization
1 Iteration
2 Convergence
3 End
Table 3. Process flags and tasks.
Once the client structure is determined the structure of the TCL script can be planned. Figure
20 shows the relation between the TCL code and Simulink. The following tasks previously
defined can be distinguished (See Table 3):
- 0 → Initialization: the first reception and delivery from Simulink that was empty
has been used to begin the program by receiving a flag value 0 and a time step.
- 1 → Iteration: When Simulinks receives the flag value 1 and the displacements
from SeaFEM operates to obtain the forces and sends them back to the channel.
- 2 → Convergence: If convergence is not reached Simulink receives the flag value 2
and the process begins again on a new time step (t = t+1). Otherwise, a new
iteration begins (it = it + 1). This steps makes reference to the time step.
it = it + 1 t = t + dt
it=0
NO
RECEIVE
SEND
RECEIVE
OPERAT
E
SEND
CONVERGENCE
END YES
EXIT
t = 0
YES NO
SIMULINK
Convergence
End
Iteration
Initialization
41
- 3 → End: Simulink receives the flag value 3 and ends the communication.
Figure 20. Structures of the Simulink model and the TCL script.
To adequate the defined steps to the loops in the TCL code and to SeaFEM the iteration and
convergence steps have been divided into the beginning and end of the loop.
- Iteration:
o Start New Iteration
o Finish Iteration
- Convergence:
o Start New Step
o Finish Time Step
Thus, the sequence of steps is:
Send [0,…]
Receive
For (time)
While (it)
Send [1,…]
Operations
Receive
Send [2,…]
Receive
Send [3,…]
TCL
it = it + 1 t = t + dt
it=0
NO
RECEIVE
SEND
RECEIVE
OPERAT
E
SEND
CONVERGENCE
END YES
EXIT
t = 0
YES NO
SIMULINK
42
Flag Name of the task
0 Initiate Problem
1 Start New Step
2 Start New Iteration
3 Finish Iteration
4 Finish Time Step
5 Finish Problem
Table 4. Tasks correspondence with flag value.
Now that the tasks are defined and the general structure of the communication has been
established, an example of the process is described in detail.
1. Initiate Problem (Flag 0) (t = 0):
- TCL opens the socket stablishing the channel in which the data transfer takes place.
- We launch SeaFEM to calculate. SeaFEM connects to the channel and waits for the
Client to connect.
- We launch Simulink to calculate. Simulink tries to connect to the channel.
- TCL accepts the client connection. Now both programs are connected on the
channel waiting for an action.
- SeaFEM sends a time increment, dt, to the channel.
- TCL sends value flag 0 and the time increment, dt, to Simulink.
- Simulink initiates the problem and stores the value of the time increment, dt.
Figure 21. Initiate Problem diagram.
2. Start New Step (Flag 1) (t=0): This step enters to the time loop and there is only a
delivery and reception of data. As shown in Figure 20 the time increases if there is no
convergence meaning at the end of the time step.
SIMULINK TCL SEAFEM
Initiate
Problem
(Flag 0) Conection
Wait
Receive
Send
Open socket
Accept Client
Conection
Send (0,…)
Receive
Wait
Conection
Store dt
43
Figure 22. Start New Step diagram.
3. Start New Iteration (Flag 2) (t = 0): As SeaFEM has not developed any calculus yet it is
assumed that convergence is not reached. There is only a delivery and reception of
data since iterations have not been initialized yet.
Figure 23. Start New Iteration diagram.
4. Finish Iteration (Flag 3) (t = 0):
- As SeaFEM has not arrived to the end of the calculation process the program sends
the displacements to the channel.
- TCL collects the displacements and sends them to the channel.
- Simulink receives the displacements from the channel and operates them to obtain
the forces.
- Simulink sends the forces to the channel.
- Tcl collects the forces from the channel and orders SeaFEM to apply them to the
model.
Figure 24. Finish Iteration diagram.
Send (1,…)
Receive
Send
Start New Step
(Flag 1) Receive
Send (2,…)
Receive
it = it+1
Receive
Send
Start New
Iteration
(Flag 2)
NO
END
OPERATIONS
Send (3,…)
Receive
Receive Finish Iteration
(Flag 3)
Send
Send (dx, dy, dz)
Receive (fx, fy, fz)
44
Once SeaFEM has received the displacements the program checks the convergence.
Depending if convergence is found or not a different step will succeed. Let us comment first
the no convergence situation.
5A. Finish Time Step (Flag 4) (t = 0):
- If convergence is not reached TCL send the value flag 4 to the channel.
- Simulink receives the flag value from the channel and ads a new time step (t = t +
dt). In this step iterations are initialized (it = 0).
- Simulink sends the new time step to the channel.
- TCL receives the new time step from the channel.
Figure 25. Finish Step diagram.
6A. Finish Iteration (Flag 3) (t = t + dt): Simulink calculates the forces again and sends
them back to SeaFEM until convergence is reached (
Figure 24).
Let us comment now the situation in which Simulink and SeaFEM converge to a result. In that
situation the program goes back to the second flag 2. Start New Step. It is possible that
convergence is not reached at the first time step (t = 0). We consider that this situation takes
places at a certain time step (t = t + dt).
5B. Start New Iteration (Flag 2) (t = t + dt) (it = 0):
- TCL sends the value flag 2 to the channel.
- Simulink receives the flag from the channel and ads a new iteration.
- Simulink sends the information to the channel.
- TCL receives the information from the channel.
CONVERGENCE
NO Receive Send (4,…)
Receive
Finish Step
(Flag 4)
it = 0
t = t + dt
Send
45
Figure 26. Start New Iteration diagram.
6A. Finish Iteration (Flag 3) (t = t + dt) (it = it + 1): Simulink begins the calculation process
to obtain the forces from the displacements received from SeaFEM (
Figure 24).
The program is going to iterate until SeaFEM sends all the displacements to Simulink. Then, the
execution ends and the communication is closed. For this explanation we are going to assume
the program ends at certain time step (t = t + dt) and at a certain iteration (it = it + 1).
7. Finish problem (t = t + dt) (it = it + 1):
- There are not more displacements that SeaFEM can send to Simulink.
- TCL sends to the channel the value flag 5.
- Simulink receives the flag value and disconnects from the channel.
- TCL closes the socket and the channel disconnecting SeaFEM.
Figure 27. Finish Problem diagram.
After the Finish Problem step, SeaFEM has applied to the model all the forces received from
Simulink. Now SeaFEM is able to show the simulation postprocess.
In the following sections the TCL code and the Simulink model developed are going to be
described.
3.7.1 Simulink model
As described above Simulink is expected to perform different tasks depending on a condition
imposed by the flag value. In Simulink those tasks are called actions.
Send (2,…)
Receive
it = it+1
Receive
Send
Start New
Iteration
(Flag 2)
Send (5,…)
EXIT
END
YES
Receive Finish Problem
(Flag 5)
46
The following vector, that TCL sent to the channel, arrives to the receive block:
(flag, dt, dx, dy, dz, fx, fy, fz)
This vector is discomposed into the flag and the other components. The flag indicates to the
conditional block which action to perform while the other components are needed in every
action. The results of each action are grouped and sent to the channel. This process is shown in
Figure 28.
Figure 28. Simulink general structure.
The diagram in Figure 28 shows the general configuration of the Simulink model. As can be
seen, the program receives a vector and breaks it down into its different component values.
One of them, the flag, must be converted to a correct format. This value indicates to the
conditional block what action should be performed. The other values go to the different
actions. The output elements of the actions are grouped and sent to the channel.
RECEIVE (dt, dx, dy,
fx, fy, fz)
SEND (dt, dx, dy,
fx, fy, fz)
ACTION 0
ACTION 1
ACTION 2
ACTION 3
CONDITIONAL
ACTION 4
ACTION 5
(flag)
(dt, dx, dy, fx, fy, fz)
47
Figure 29. Simulink general scheme.
48
The most relevant blocks used to create the model are:
- TCP/IP Client Receive Block: This block receives data from the channel. The channel in
which the communication takes place has is configured in this block indicating the
remote address and the port. The data that is going to be received has to be also
defined.
- Demux: This block allows separating the data that arrives in the form of a vector in its
components.
- Data Type Conversion: This block transforms the value of the flag into a readable
format.
- Mux: Unlike the Demux block, this block allows recomposing the vector.
- If: This block allows entering the condition that imposes the flag value for the program
to perform the different actions.
- Merge: This block should be added whenever an If block is used.
- TCP/IP Client Send Block: The same configuration data as in the TCP/IP Client Receive
is entered in this block.
As mentioned previously, the actions that Simulink are the following Appendix C (p. 93):
- ACTION 0 – Initiate Problem: This action corresponds to the beginning of the program.
The value of the time increment, dt, is stored in the variable dt_.
- ACTION 1 – Start New Step: Simulink does not perform any task in this action.
- ACTION 2 – Start New Iteration: This action counts the iterations.
- ACTION 3 – Finish Iteration: In this action the forces are obtained from the
displacements.
- ACTION 4 – Finish Time Step: In this action iterations are initialized and time
increased.
- ACTION 5 – Finish Problem: The Stop block disconnects Simulink from the channel.
3.7.2 TCL script code
As mentioned above, the TCL code will follow the structure shown in Figure 20. To describe
the code it is going to be divided into three parts: procedures created specifically for this
project, procedures that are already created for SeaFEM and the main program. The code can
be found in the Appendix C (p. 93).
The procedures that were created for this project are:
- proc close_socket: in this procedure the communication channel is closed.
- proc accept_client_connection: in this procedure the buffer size of the channel is set.
The value 1 is also assigned to the connection variable to confirm that the connection
with the client has been successful.
- proc open_socket: In this procedure the socket is created and the channel where
communication between programs will take place is defined. The messages that you
want SeaFem to display on the screen will also be added to check that the process is
progressing correctly. Finally, the vwait command instructs the program to wait until
49
the connection with the client is accepted. This was defined in the previous procedure.
This means that the moment we call the procedure accept_client_conection within
the creation of the socket, the program will stop until the variable connection takes
the value 1. Then SeaFem will display a message indicating that the connection was
established correctly and on which channel it will take place.
- proc send_data: In this procedure the data is sent.
- proc receive_data: In this procedure, the format for receiving the data is defined. In
this case it is a vector of 7 doubles (8 bytes).
Now the procedures that are previously defined in the SeaFem program are described.
proc TdynTcl_InitiateProblem
proc TdynTcl_StartNewStep
proc TdynTcl_StartNewIteration
proc TdynTcl_FinishIteration
proc TdynTcl_FinishStep
proc TdynTcl_FinishProblem
- proc TdynTcl_InitiateProblem (flag 0): This procedure opens the channel in which the
communication will take place by calling the procedure open_socket. Both programs,
Simulink and SeaFEM, connect to the channel. The vector (flag, dt, dx, dy, dz, fx, fy, fz)
is defined by adding the term func_.
The command [:: mather :: create_function waves" dx; "] assigns the values of
SeaFEM to the functions created before. The process is repeated with every function.
50
Once SeaFem data is collected, it must be transformed to the appropriate format for
its correct reading. This data can already be sent to the channel.
Finally, the data in the channel is received and converted to a readable format.
- proc TdynTcl_StartNewStep (flag 1): For this project this procedure only sends and
receives data.
- proc TdynTcl_StartNewIteration (flag 2): This procedure sends the displacement
values from SeaFEM to the channel and receives the forces from the channel. Then
SeaFEM receives the instruction to apply the forces on the model.
o The values of the displacements in SeaFem will be evaluated using the
command :: mather :: evaluate_function $ func_dx. The process must be
repeated with every function.
o The data will be transformed to the format suitable for its correct reading and
sent to the channel.
o Data from the channel is received and transformed back to the original format.
o The TdynTcl_Set_Body_Loads command indicates SeaFEM to apply the forces
received from Simulink on the model.
51
- proc TdynTcl_FinishStep (flag 4): For this project this procedure only sends and
receives data.
- proc TdynTcl_FinishProblem (flag 5): This procedure ends the communication process
(channel and server_socket) by calling the procedure close_socket. The last remaining
data is transformed to the correct format and sent to the channel.
3.8 Summary
In this chapter, the different steps followed to establish the communication between Simulink
and SeaFEM through a TCL script have been described. As shown in the
Figure 9, the programs have been connected to themselves, then, Simulink with a TCL script
and, finally, the desired communication have been established.
In order to facilitate the creation process of the communication interface between the two
programs making it more intuitive it has been applied to a general case that will be useful for
the following chapters. In this case, it has been considered that SeaFEM will apply a load on a
model. Simulink will calculate the load from the displacement, velocity and acceleration data
that SeaFEM will send in each time step. This process will be repeated until reaching the
selected simulation time. This process is illustrated in Figure 17.
As shown, one of the most important points for the interface design is to understand which
program and why should develop the client role and the server role. Since Simulink is already
preconfigured as a client this role has been assigned whereas SeaFEM would be the one
demanding information.
Once the roles have been assigned, the program that will define the structure and the
algorithm has been chosen. The conclusion has been that SeaFEM is the best option since, as
52
mentioned previously, it offers the possibility of extending the functionalities by adding a TCL
script in the configuration of the program.
Among the procedures it offers, the following have been chosen:
- TdynTcl_InitiateProblem
- TdynTcl_StartNewStep
- TdynTcl_StartNewIteration
- TdynTcl_FinishIteration
- TdynTcl_FinishStep
- TdynTcl_FinishProblem
Hereafter, the diagrams from Figure 3 and Figure 5 have been taken as a basis and
complementary functioning schemes have been designed in Simulink and TCL following its
structure. Finally, the tasks developed in each procedure have been chosen and the programs
that can be found in the Appendix C (p. 93) created.
53
Chapter 4 Program case: oscillating
water column device
4.1 Introduction
Once determined a general model to establish the connection between Simulink and SeaFEM
some modifications can be carried out to adapt it in different cases. In this chapter and in the
following one, two examples for future applications will be described. In this first case it will be
adapted to simulate an oscillating water column device. The intention is to obtain the
produced energy from the flux passing through the turbine.
4.2 Approach
As mentioned, in this situation Simulink will calcúlate the pressure due to the flux that
circulates through the cilinder and sends it to SeaFEM to be applied on the model. Figure 30
shows the general communication scheme.
Figure 30. Description of the data transfer between Simulink and SeaFEM.
4.3 Development
The development process description is divided in three parts that reference the three
involved files: TCL, Simulink and SeaFEM. The detailed explanation and the complete codes can
be found in the Appendix D (p. 107). As described in the previous chapter, the operations that
Simulink has to perform to obtain the pressure from the flux take place in the step Finish
Iteration.
Figure 31 shows a general communication scheme between TCL and Simulink. In each
procedure of the TCL script a different value is assigned to the flag and sent to Simulink.
Depending on that flag value Simulink is going to develop a different action. It can be noticed
that flag values 1 and 2 correspond to the time and iteration loops, respectively, from SeaFEM.
Pressure
Flux
SEAFEM SIMULINK
54
Figure 31. Scheme of the general communication procedure between the Simulink and SeaFEM.
- Initiate Problem: The program begins in this step and corresponds to the flag value
0. The TCL develops the following tasks:
o Socket definition and opening
o Variables definition
o Functions creation (time and flux)
o Evaluate time function
o Send time and flag to Simulink
o Receive time from Simulink
Simulink receives the flag value and the time increase which is stored and sent
back to TCL. The relation between the tasks in the TCL script and the with the
Simulink actions is shown in Figure 32.
TdynTcl_InitiateProblem
TdynTcl_StartNewStep
TdynTcl_StartNewIteration
TdynTcl_FinishIteration
TdynTcl_FinishStep
TdynTcl_FinishProblem
RECEIVE
SEND
For (0: time)
[counts time]
RECEIVE
SEND
While (body_iterations)
[counts iterations]
RECEIVE
SEND
RECEIVE
OPERATIONS
SEND
RECEIVE
SEND
RECEIVE
END
START
FLAG 0
FLAG 1
FLAG 2
FLAG 3
FLAG 4
FLAG 5
TCL SIMULINK
55
Figure 32. Scheme of the communication procedure between the Simulink and SeaFEM.
- Start New Step: In this section both, TCL and Simulink, send and receive data. This
section corresponds with flag value 1.
- Start New Iteration: TCL and Simulink send and receive data. Simulink counts
iterations and stores the value. This section corresponds with flag value 2.
RECEIVE
Time increase (dt)
is stored
SEND
FLAG 0
TCL SIMULINK
- Socket definition
- Variables definition
- Call procedure Open_Socket
….
- Functions creation (time and flux)
- Functions Evaluation (time)
- Convert and send data
- Recieve and convert data dt
56
RECEIVE
Operations
SEND
FLAG 3, flux, dt
TCL SIMULINK
- Variables definition
….
- Functions Evaluation (flux)
- Convert and send data
- Recieve and convert data dt, pressure
- Finish Iteration: In this section that corresponds with flag value 3 the pressure is
obtained from the flux. Figure 33 shows the scheme of the succession of tasks that
Tcl and Simulink perform.
o TCL evaluates the flux received from SeaFEM.
o TCL sends the time increase, the flag value 3 and the flux to the channel.
o Simulink receives the flux from the channel and calculates the pressure.
o Simulink sends the pressure obtained to the channel.
o TCL receives the flux from the channel and sends it to SeaFEM.
o SeaFEM applies the pressure on the model.
Figure 33. Scheme of the general communication procedure between the Simulink and SeaFEM.
- Finish Time Step: In this section correspondent with flag value 4 both, TCL and
Simulink, send and receive data. Simulink counts time and stores the value. In this
step Simulink also initializes the iterations.
- Finish program: In this section correspondent with flag value 5 the communication
between programs ends.
57
Chapter 5: Program case: fins effect on
a Wigley hull
5.1 Introduction
In this chapter, the modifications that have been carried out on the general coupling case
between Simulink and SeaFEM to adapt it to a one of the cases of interest in this project: to be
able to simulate the effect of the stabilizing fins on a Wigley hull. This allows illustrating an
application example of the program showing the points that should be modified.
5.2 Approach
In this situation the intention was to be able to simulate the behavior of stabilizing fin installed
on a Wigley hull. The general idea is that Simulink calculates the moment generated by the
stabilizing fins and sends it to SeaFEM to be applied on the model. For its part, SeaFEM should
send to Simulink the data necessary to calculate the moment. (See Figure 34).
Figure 34. Description of the data transfer between Simulink and SeaFEM.
Departing from the movement equation:
𝑎𝑑2𝜃
𝑑2𝑡2+ 𝑏
𝑑𝜃
𝑑𝑡+ 𝑐𝜃 = ∑ 𝑀
(5.1)
Where the first term represents the inertial moment, d2θ/d2t2 is the angular acceleration and
a is the inertial moment of the virtual mass around a longitudinal axis. The second term
represents the damping moment, dθ/dt the angular velocity and b the damping coefficient.
The third term cθ represents the restoring moment, θ is the angular amplitude and c is the
coefficient that makes the ship returns to the equilibrium position when the ship is displaced
from it (Patil, Chandra Dubey, & Anantha Subramanian, 2019)(P.G. Howlett, 2006).
, , 𝜃
Forces and moments
SEAFEM SIMULINK
58
The movement equation can be written as:
𝐼 + 𝐵 + 𝐶𝜃 = ∑ 𝑀 (5.2)
In the case of a ship equipped with fins, considering the x-direction, the external moments are
the rolling moment MX and MF the moment due to the fins. The first one is solved by SeaFEM
and the second one by Simulink.
𝐼 + 𝐵 + 𝐶𝜃 = 𝑀𝑥 + 𝑀𝐹
Figure 35. Parts of the movement equation solved by Simulink and SeaFEM.
Figure 35 shows the communication process scheme. SeaFEM will send the angular amplitude,
velocity and acceleration to Simulink that will use these data to obtain a fin moment. This
moment will be sent back to SeaFEM that will apply it to the ship and obtain new angular
values to send to Simulink.
5.3 Development
As in the previous chapter, the explanation is divided in three parts that reference the three
involved files: TCL, Simulin and SeaFEM. The detailed explanation and the complete codes can
be found in the Appendix E (p. 113).
5.3.1 Modifications on the TCL script
This scenario is more complicated than the previous since in this one the intention is to send
displacements, velocities and accelerations and receive forces and moments. Thus, all of them
should be defined in the script and added in the places where the data transference takes
place.
5.3.2 Modifications on Simulink
As in the TCL script, the new data that Simulink is going to use in its calculus should be defined.
The convenient iterative moment for Simulink to calculate the moment produced by the
stabilizing fins is in the Finish Iteration as shown in Figure 36. In this point SeaFEM will have
finished its intern calculus obtaining new displacement, velocity and acceleration values of the
correspondent time step and will be prepared to receive new forces and moments to apply to
the model. Figure 37 shows the extraction of the velocities and loads needed.
SeaFEM Simulink
59
Figure 36. Simulink general scheme.
60
Figure 37. Simulink Finish Iteration subsystem.
5.3.3 Modifications on SeaFEM
The unique modification on SeaFEM is indicating the program the external forces or moments
to be applied on the model. In this case, the fins generate a moment in the x-direction, Mx. It
must be indicated as mx_tcl.
Dem
ux
Div
ides
vel
oci
ties
an
d
mo
men
ts in
co
mp
on
ents
Sub
syst
em
Intr
od
uce
fu
nct
ion
s h
ere
61
PART II: VERIFICATION
62
63
Chapter 6: Analysis of an oscillating
water column device
6.1 Introduction
In Chapter 3 (p. 37), the adaptation process of a general communication model between
SeaFEM and Simulink to a case which intention was to know the power obtained in an
oscillating water column device was described. Thus, in this chapter the application on a model
is described and the obtained results, verified.
6.2 Oscillating water column description
Inexhaustible and trustworthy, wave power has long been considered as one of the most
promising renewable energy sources. Wave Energy Converters (WECs) convert wave power
into electricity.
Figure 38. Scheme of the oscillating water columns (OWCs) operating system.
The functioning of the oscillating water columns (OWCs) is very similar to that of a wind
turbine, being based on the principle of wave induced air pressurization. The device is set upon
a closed air chamber, which is placed above the water. The passage of waves changes the
water level within the closed housing and the rising and falling water level increases and
decreases the air pressure within the housing introducing a bidirectional air flow. By placing a
turbine on top of this chamber air will pass in and out of it with the changing air pressure
levels. There are two options to separate the bidirectional flow: alternatively, pressure
64
generating valves or, as in this case, a Wells turbine to create suction. The process is described
in Figure 38.
An Oscillating Water Column (OWC) is a wave energy converter consisting of a partially
submerged chamber with an air column over the water column. The work done by the air
column under excitation by the incident waves is used to generate electrical energy through a
power take-off (PTO) device. The air column is under pressure due to the damping from the
PTO device and this pressure is essential for the extraction of wave energy using the OWC. The
relationship between the PTO damping and the hydrodynamic efficiency of the OWC provides
more insight into the wave energy extraction using an OWC.
6.3 Turbine model
In this case, a wells type turbine is considered. The pressure, p (KPa), can be obtained from
the flux, Q (m3/s), by the following expression3:
𝑝 =𝑄|𝑄|
0,078072
(6.1)
The power generated in the OWC, P (Kw) can be obtained from the pressure from the
following expression:
𝑃 = −0,0051 (|𝑝
1000|)
3
+ 0,2815 (|𝑝
1000|)
2
+ 1,1857 |𝑝
1000|
(6.2)
6.4 Model description
The geometry of the model is shown in Figure 39. A cylinder of 6 meters of diameter and 2,5
meters draft has been created. A wave damping zone of 10 meters of draft and starting 7
meters away from the OWC and extended until a diameter of 60 meters has also been created.
3 The expressions to obtain the pressure and the power have been obtained experimentally from the
curve of a Well turbine test.
Figure 39. Isometric view of the computational domain (Length in meters).
65
The mesh size of the OWC is 0,2 meters and 0,5 for the volume near field as shown in the
Figure 40. That results in a mesh of 45849 nodes and 267133 elements.
Figure 40. Mesh scheme.
For this simulation monochromatic waves of 1 meter amplitude and 4 s period have been
considered. The simulation time is 10 seconds.
Amplitude (s) 1
Period (s) 4
Heading (0) 45
Table 5. Wave data. OWC.
This model will be used for both cases, only using SeaFEM and using the communication
interface. For the first one in which only SeaFEM is used the equation to obtain the pressure is
introduced in the P Free Surface section. In the second one Simulink obtains the pressure from
the flux received from SeaFEM. Then the TCL Data is activated.
6.5 Verification case: produced power
To verify that the created model works correctly, firstly the OWC has been simulated
introducing directly the function for obtaining the pressure from the flux in SeaFEM. Then, the
simulation has been carried out again but, in this case, Simulink has calculated the pressure to
send it to SeaFEM. The following graphics show the pressure and power obtained in both tests.
As it can be observed, the results coincide verifying the correct functioning of the simulations.
66
Figure 41. Pressure in the OWC.
Figure 42. Power produced in the OWC.
-800000
-600000
-400000
-200000
0
200000
400000
600000
0 2 4 6 8 10 12
Pre
sure
(kP
a)
Time (s)
SeaFEM
SeaFEM+Simulink
-1600000
-1400000
-1200000
-1000000
-800000
-600000
-400000
-200000
0
200000
0 2 4 6 8 10 12
Po
we
r (k
W)
Time (s)
SeaFEM
SeaFEM+Simulink
67
Chapter 7. Fins effect control algorithm
7.1 Introduction
The intention of this section is to develop and incorporate a simple control element in Simulink that simulates the effect of the fins reducing the roll of the ship. The following sea situations have been considered for that purpose:
- Sea without waves. - Irregular sea.
The decreasing of the roll has been compared for each one of the previous sea situations in the following cases:
- Ship without fins. - Fixed fins. - Active fins.
The fins model used and is also described in this chapter. The verification method followed to prove the correct functioning of the program and the demonstrations can be found in the Appendix F (p. 126).
7.2 Fins model
Fin stabilizers are stability equipment used onboard ships to reduce the roll motion that causes
a decrease of ship's performances and operability. The sea waves produce a perturbation to
the hull, then the stabilizer fins placed on the opposite lateral surfaces of the ship, provide a
torque in contrast to the roll ship (See Figure 43) (Perez & Blanke, 2014).
68
Figure 43. Principles of roll reduction by fin stabilizer.(Kawazoe, Nishikido, & Wada, 1993)
When the water flows around the fins the zones of high and low pressure are created on their
surfaces, thus generating a force perpendicular to the fin surface S. This force can be divided
into two components: the lift, L, directed perpendicular to the horizon line and the drag, D
(Liang, Sun, Shi, & Luan, 2017).
𝐿 =1
2𝑆𝜌𝑉𝑠
2𝐶𝐿(𝛼) (7.1)
𝐷 =1
2𝑆𝜌𝑉𝑠
2𝐶𝐷(𝛼) (7.2)
Lift and drag coefficients can be obtained depending on the attack angle:
𝐶𝐿(𝛼) =𝑑𝐶𝐿
𝑑𝛼=
1.8𝜋𝛼𝐸
1.8 + √𝛼𝐸2 + 4
(7.3)
𝐶𝐷(𝛼) = 𝐶𝐷0 +𝐶𝐿
2(𝛼)
0.9𝜋𝛬 (7.4)
Where CD0=0.0065 and Λ is the ratio of aspect.
69
Figure 44. Localizing active fins on ship hull and stabilizing fin angles. (Rahimuddin, Maimun, & Gani, 2014)(Kula, 2015)
Figure 44 shows the directions of lift and drag forces (Kim & Kim, 2011). The directions of force
and moment due to the fin are determined by the direction of incoming fluid flow to the lifting
surface. Assuming only a forward ship speed, U = (VS, 0, 0), the velocity vector and angle of
incoming flow to the fin, the effective angle of attack αE, can be written as:
𝑉 = (𝑉𝑥 , 𝑉𝑧) (7.5)
and
𝛼𝐸 = 𝛼𝐹 + 𝛼𝑃 (7.6)
𝛼𝑃 = 𝑎𝑟𝑐𝑡𝑎𝑛 (𝑟𝑓𝑤𝑥
𝑉𝑆) (7.7)
Figure 45. Directions of lift force and drag force.(Kim & Kim, 2011)
70
Figure 46. Fin-induced forces and moments.(Lihua, Peng, Songtao, Ming, & Jia, 2018)
Case 1: Ship without fins
This is the simplest case in which no external forces are applied on the ship. For the simulation
the following damping moment has been considered:
𝑀𝑥 = 0.05𝑤𝑋√4𝐾44𝐼𝑥𝑥 (7.8)
To include the effect of physical damping due to the effects of viscosity, the value commonly
used value of 5% of the critical damping has been considered.
Case 2: Fixed fins
Assuming initially that the fin is fixed on the hull and that has been horizontally installed (angle
of the fin, αF= 00), the instantaneous angle of attack of the fin (αE) is the pitch angle (αP).
𝛼𝐸 = 𝛼𝑃 + 𝛼𝐹 (7.9)
𝛼𝐹 = 0 ; 𝛼𝐸 = 𝛼𝑃 (7.10)
Being Vs the velocity of the current in the x-direction, wx the roll angular velocity and yp the
rolling arm (See Figure 46), the vertical velocity induced by the roll is:
𝑉𝑧−𝑓𝑖𝑛 = 𝑤𝑥𝑦𝑝 (7.11)
Thus, the velocity of the fluid respect to a system of reference located in the fin will be (Vs, -
Vz_fin).
𝛼𝐸 = 𝛼𝑃 = arctan (−𝑉𝑧−𝑓𝑖𝑛
𝑉𝑆) = arctan (−
𝑤𝑥𝑦𝑝
𝑉𝑠) (7.12)
In this way, when the ship begins to move in roll, an angle of attack and a relative velocity of
the instantaneous fluid will appear generating a vertical force Fz_fin and a moment that will
dampen the roll.
71
𝑀𝑥 = 𝐹𝑧−𝑠𝑡𝑎𝑟𝑏𝑜𝑎𝑟𝑑𝑦𝑝−𝑠𝑡𝑎𝑟𝑏𝑜𝑎𝑟𝑑 + 𝐹𝑧−𝑝𝑜𝑟𝑡𝑦𝑝−𝑝𝑜𝑟𝑡 (7.13)
The functions previously described have been introduced in the Simulink program as shown in
the Figure 47.
Figure 47. Simulink scheme. Fixed fins.
Case 3: Active fins
In this case, the intention has been to obtain an algorithm able to reduce the roll more that in
the previous case having the 00 fixed fins. An option that has been considered is to create an
algorithm that modifies the angle of the fin depending of the ship rolling velocity and
acceleration. Furthermore, the angle of the fin should not exceed an angle of +-100.
A simple function could be considering that the angle of the fin is proportional to the rolling
angular velocity.
𝛼𝐹 =𝐹𝑤𝑥
Ω𝑥 ; Ω𝑥 =
2𝜋
𝑇𝑟𝑜𝑙𝑙
(7.14)
Where Troll is the fundamental period of the ship and F is a factor to calibrate.
Figure 48 shows the resultant scheme in Simulink once the previous functions are added.
72
Figure 48. Simulink scheme. Active fins.
7.3 Environment and computational domain
The stabilizing fins are installed on a Wigley type hull (see Figure 49) of length L = 100 m and
breadth B = 10 m with a forward speed Vs=6,263 m/s. The vertical center of gravity is located
at ZG=-1.2 m resulting in a natural roll period, Troll=12s (see Figure 51).
Figure 49. Wigley hull model.
An unstructured mesh has been generated. Figure 50 shows the generated mesh that consists
of 128744 nodes and 748333 elements.
73
Figure 50. Wigley hull generated mesh.
The following cases have been carried out for 100s. The wave parameters considered in each
case are described in the following sections.
7.4 Case: Fins effect in a sea without waves
In this case an extinction test with an initial tilt Rx=50rad has been simulated. As mentioned,
no waves have been considered. Figure 51, Figure 52 and Figure 53 show a significant
decreasing in the roll movement, velocity and acceleration, respectively due to the fins effect.
Figure 51. Roll movement. Fins effect in a sea without waves.
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
0 20 40 60 80 100
Ro
ll m
ove
me
nt
(rad
)
Time (s)
Active fins
Without fins
Fixed fins
74
Figure 52. Roll velocity. Fins effect in a sea without waves.
Figure 53. Roll acceleration. Fins effect in a sea without waves.
7.5 Case: Fins effect in irregular sea
In this case, an irregular sea situation has been considered. A Jonswap spectrum has been
selected to define the irregular waves (See Appendix A (p. 81)). The wave data are summarized
in the Table 6.
Wave data
Wave spectrum type Jonswap
Mean wave period (s) 12
Significant wave height (m) 2
Shortest period (s) 5
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
0 20 40 60 80 100
Ro
ll ve
loci
ty (
rad
/s)
Time (s)
Active fins
Without fins
Fixed fins
-0.03
-0.025
-0.02
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
0.02
0.025
0 20 40 60 80 100
Ro
ll ac
cele
rati
on
(ra
d/s
2 )
Time (s)
Active fins
Without fins
Fixed fins
75
Longest period (s) 26
Number of waves periods 15
Mean wave heading (0) 90
Spreading angle (0) 60
Number of waves headings 5
Table 6. Wave data. Fins analysis on irregular sea.
As in the previous section, considered forward speed is Vs=6,263 m/s and the three following
cases have been compared: ship without fins, fixed fins and active fins.
Figure 54 shows the effect of the different fins cases on the roll movement. As expected, the
active fins stabilize the ship having a significant impact on the decreasing of the roll
movement. The roll velocity and acceleration also experiment a decrease due to the fins action
as shown in Figure 55 and Figure 56.
Figure 54. Roll movement. Fins effect in irregular sea.
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0 20 40 60 80 100
Ro
ll M
ove
me
nt
(rad
)
Time (s)
Active Fins
No Fins
Fixed Fins
76
Figure 55. Roll velocity. Fins effect in irregular sea.
Figure 56. Roll acceleration. Fins effect in irregular sea.
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0 20 40 60 80 100
Ro
ll V
elo
city
(ra
d/s
)
Time (s)
Active Fins
No Fins
Fixed Fins
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
0 20 40 60 80 100
Ro
ll A
cce
lera
tio
n (
rad
/s2 )
Time (s)
Active Fins
No Fins
Fixed Fins
77
Chapter 8: Conclusions
The objective of this Master’s thesis was to develop a communication interface between two
programs, Simulink and SeaFEM, to allow the simulation of complex loads adding a control
algorithm. This proposal takes advantage of the facilities that Simulink offers, thanks to the
Instrument Control Toolbox that allows communicating through a TCP/IP protocol, and the TCL
extension included in SeaFEM that brings the possibility of enlarging its functionalities. Thus,
the programs communicate through a TCL code script.
As mentioned during the project, the process would be the following. There is a model created
in SeaFEM and we want to simulate the effect of some loads acting on it. As the loads are
described by a complex function that cannot be introduced directly in SeaFEM they will be
introduced in Simulink that offers this functionality. The data that Simulink needs to solve the
operations come from the internal solver loops of SeaFEM. The loads obtained in Simulink are
sent to SeaFEM that applies them on the model. This process repeats until simulation time is
reached.
For developing the definitive interface several tests have been carried out communicating
firstly the programs with themselves and, later, between them. Some examples to verify the
correct functioning have been presented in this work.
Once it has been possible to transfer data between both programs, the interface has been
applied to simulate two different cases: an oscillating water column (OWC) device and the
stabilizing fins installed on a Wigley type hull. The intention was to verify the correct data
transfer in the first case and the possibility of introducing a control algorithm in the second
case.
The OWC case tried to simulate the effect of a flux through the device turbine obtaining the
applied pressure and the produced power. To verify the functioning it has been tested two
times: introducing the pressure from the flux function directly on SeaFEM and using the
communication interface. The obtained graphics (see Figure 41) show that the simulation
worked as expected.
For the stabilizing fins, three cases have been tested in two different sea conditions making a
total of six situations. The three cases included the ship sailing freely without the fins, the ship
equipped with fixed fins and the ship equipped with active fins using a control algorithm.
These cases have been tested. As it was expected, the fins have a significant impact on the
decrease of the roll movement as shown in Figure 51 and Figure 54 . The results obtained have
been verified introducing a fins effect approximate function directly on SeaFEM.
78
It is possible to consider a fins effect approximate function from the movement equation and the results obtained in the simulation coupling both programs. As it has been described in
detail in Chapter7(p.125), SeaFEM solves the dynamics equation, and evaluates the
moment due to the inertia, damping and restoring loads acting on the ship and Simulink calculates the external loads. From the results with the coupling system, the roll damping constant can be easily obtained as the slope of the curve of roll moment and roll velocity.
In this project, it has been demonstrated the possibility of enlarging the functionalities of a
program by a coupling system. Furthermore, the capability of introducing control algorithms
acting on the external loads allows obtaining more realistic simulations.
79
APPENDICES
80
81
Appendix A: Previous concepts
A.1 Introduction
This annex aims to offer some complementary information for a better understanding of the
simulations carried out in the project. The two different tests that have been simulated in the
project are described in this section: rolling test and extinction test. Additionally, the selected
wave spectrum considered to define the irregular sea is described.
A.2 Rolling tests
Rolling test: The ship model is located in a transversal position respect to the longitudinal
direction of the towing tank. Initially, the ship is in its equilibrium position. After, an external
force is applied on the model allowing the model to oscillate.
On the other hand, the extinction test can be described: The model is located in a transversal
position respect to the longitudinal direction of the towing tank and it is obligated (by an
external force) to reach an initial tilt, Rx. After, the model is left to oscillate freely.
A.3 Wave spectrums
The present status of computer facilities prevents from using certain techniques to obtain
statistical estimates for ocean waves, since the estimated CPU-time makes direct calculations
unrealistic. In addition, there are unsolved physical problems associated with modelling of
breaking waves. In practice, linear theory is used to simulate irregular sea and to obtain
statistical estimates (Faltinsen, 1993). The wave elevation of a long-crested irregular sea
propagating along the positive axis can be written as the sum of a large number of wave
components:
𝜁 = ∑ 𝐴𝑗sin (𝑤𝑗 − 𝑘𝑗𝑥 + 𝜖𝑗)
𝑁
𝑗=1
(A.1)
Here, 𝑨𝒋, 𝒘𝒋and 𝝐𝒋 mean respectively the wave amplitude, circular frequency, wave number
and random phase angle of wave component number j. The random phase angles are
uniformly distributed between 0 and 2π.The wave amplitude can be expressed by a wave
spectrum S (w) (Newman, 1979).
1
2𝐴𝑗
2 = 𝑆(𝑤𝑗)∆𝑤 (A.2)
where ∆𝒘 is a constant difference between successive frequencies.
82
To define the irregular sea, SeaFEM includes the following wave spectra types:
- Pearson Moskowitz spectrum: for open sea conditions the 15th ITTC recommended the
use of this spectrum. It is obtained assuming fully developed sea state (Serván Camas,
2016).
𝑆(𝑤)
𝐻13
2 𝑇1
=0.11
2𝜋(
𝑤𝑇1
2𝜋)
−5
𝑒𝑥𝑝 [−0.44 (𝑤𝑇1
2𝜋)
−4
] (A.3)
Where 𝑯𝟏
𝟑
is the significant wave height defined as the mean of the one third highest
waves and 𝑻𝟏 is mean wave period.
- Jonswap and Jonswap2 spectrum: this spectrum stands for Joint North Sea Wave
Project and it is a peak-enhanced Pierson-Moskovitz spectrum. The 17th ITTC
recommended this spectrum for limited fetch (SeaFEM Theory Manual, n.d.).
155𝐻13
2
𝑇14𝑤5
𝑒𝑥𝑝 (−944
𝑇14𝑤4
) (3.3)𝑌 (A.4)
Where
𝑌 = exp (− (0.191𝑇1 − 1
212𝜎
)
2
)
and
𝜎 = 0.07 𝑓𝑜𝑟 𝑤 ≤ 5.24/ 𝑇1
𝜎 = 0.09 𝑓𝑜𝑟 𝑤 > 5.24/ 𝑇1
- White noise: introduce a number of waves with periods uniformly distributed across
an interval, and with same amplitude and direction. This spectrum is used to carry out
response amplitude operator (RAO) analyses.
83
Appendix B: Simulink blocks
description
B.1 Introduction
In this annex, a detailed description of the Control Instrument Toolbox blocs used for this
project is given (Instrument Control Toolbox 2 User ’s Guide, n.d.).
B.2 TCP/IP Client Send block
Figure 57: Block TCP/IP Client Send.
The TCP/IP Send block (see Figure 57) sends data from the model to remote machines using
the TCP/IP protocol. This data is sent at the end of the simulation or at fixed intervals during a
simulation.
As it is shown in the image, the TCP/IP Send block only has one input port. The size of the input
port is dynamic and inherited from the driving block.
In order to configure the block there are several parameters that the user can modify:
- Remote address: Specify the IP address, name, or the Web server address of the
machine to which send data. This field is empty by default.
- Port: Specify the remote port on the host you need to send the data to. The default
port value is 80. Valid port values are 1 to 65535.
- Verify address and port connectivity: If this button is activated it allows to:
o Check if the specified remote address is correct.
o Establish connection with the specified remote address and port.
84
- Byte order: Specify the instrument's byte order for the data when using binary or
binblock format with more than 8 bits. The options that it offers
are BigEndian or LittleEndian.
- Enable blocking mode: Specify if the user wants to block the simulation while sending
data. This option is selected by default. If this option is not selected the write
operation will not block the simulation.
B.3 TCP/IP Client Receive block
Figure 58: Block TCP/IP Client Receive
This block is used to receive data over TCP/IP from specified remote machine.
The TCP/IP Receive block configures and opens an interface to a specified remote address
using the TCP/IP protocol. The configuration and initialization occur once at the start of the
model's execution. During the model's run time, the block acquires data either in blocking
mode or nonblocking mode.
On the opposite of the TCP/IP Send block, and to complement it, this block has no input ports
and it has either one or two output ports, based on the selection of blocking or nonblocking
mode.
If the blocking mode is selected the block will have one output port corresponding to the data
it receives.
Figure 59: Block TCP/IP Client Receive with Blocking mode activated
If the block is not selected, it will have two output ports, the Data port and the Status port.
Figure 60: Block TCP/IP Client Receive Blocking mode not activated
85
A First In First Out (FIFO) buffer 4receives the data. At every time step, the Data port outputs
the requested values from the buffer. In Nonblocking mode, the Status port indicates if the
block has received new data.
Figure 61. Representation of a FIFO (queue) with enqueue and dequeue operations.
As in the TCP/IP Send block, this block also allows to modify some parameters to configure it.
- Remote address: Enter the IP address, name, or the Web server address of the
machine from which you need to receive data. This field is empty by default.
- Port: Enter the remote port on the remote machine you need to connect to. The
default port value is 80. Valid port values are 1 to 65535.
- Verify address and port connectivity: This option must be activated in order to:
o Check if the specified remote address is correct.
o Establish connection with the specified remote address and port.
- Data size: Specify the output data size, or the number of values that should be read at
every simulation time step. The default size is [1 1].
- Source Data type: Specify the input data type to receive from the block.
- ASCII format string: It defines the format string for the data. This option is only
available ASCII data type is selected.
- Terminator: this option is only available when ASCII data type is selected. It can be
used to set a terminator5 for the data read.
4 FIFO is an acronym for first in, first out, a method for organising and manipulating a data buffer, where
the oldest (first) entry, or 'head' of the queue, is processed first. It is analogous to processing a queue with first-come, first-served (FCFS) behaviour: where the people leave the queue in the order in which they arrive. Figure 12 shows a representation of a FIFO method. 5 The Terminator block can be used to cap blocks whose output ports are not connected to other blocks.
If you run a simulation with blocks having unconnected output ports, Simulink issues warning messages. Using Terminator blocks to cap those blocks avoids warning messages.
86
- Byte order: When using binary or binblock format with more than 8 bits, you can
specify the instrument's byte order for the data. Your options are BigEndian or
LittleEndian.
- Enable blocking mode: this option, selected by default, specifies if the simulation will
be blocked while receiving data. If this option is not selected the read operation will
not block the simulation.
If the blocking mode is enabled, the model will block the simulation while it is waiting for the
requested data to be available. When it is not enabled blocking mode, the simulation runs
continuously. The block has two output ports, Status and Data. The Data port contains the
requested set of data at each time step. The Status port contains 0 or 1 based on whether it
received new data at the given time step. The following diagrams show the difference
between receiving data using blocking mode and nonblocking mode.
B.4 Mux and Demux
Mux block: This block combines inputs with the same data type and complexity into a vector
output. The output mux signal is flat, even if you create the mux signal from other mux signals.
However, you can use multiple Mux blocks to create a mux signal in stages.
A mux signal simplifies the visual appearance of a model by combining two or more signal lines
into one line. Mux signals do not affect simulation or code generation.
Figure 62. Mux block.
Demux: The Demux block extracts the components of an input vector signal and outputs
separate signals. The output signal ports are ordered from top to bottom.
Figure 63. Demux block.
87
Appendix C: Communication interface
development
C.1 Introduction
This annex contains the complete codes and files used for the different communications
between programs.
C.2 TCL to TCL communication
Client code
Sets the channel.
This loop will run until socket is closed.
Asks the user for a message.
Flushes any output buffered for
channelId .
Collects data and saves it in msg.
88
Server code
C.3 Simulink TCL communication
Simulink client configuration
Figure 64. Simulink client configuration.
For each of the blocks, the parameters set by default must be modified.
- TCP/IP Client Receive: The remote address and port must be indicated in the data
reception block. For this example, a port that is known to be available has been
chosen. Since two data are received, it must be indicated as a vector [1 2].
This loop is related to vwait. It
will iterate until vwait condition.
Collects data from the channel
and saves it in clientMsg variable.
Program starts here. Opens the
socket and executes the
procedure Recieve_Data.
Indicates that the while loop will
run forever. It will keep waiting
for the client message.
Configures the channel.
89
The desired format must also be indicated. In this case, double Data Type and
LittleEndian byte order.
The Enable blocking mode option has to be selected.
Figure 65: Block parameters TCP/IP Receive
- TCP/IP Client Send: In the data sending block the Remote address and the Port must
match those previously indicated in the receiving block.
The same Byte order and Timeout must also be maintained. The Enable blocking
mode option has to be activated and the Transfer Delay option deactivated.
Figure 66: Block parameters TCP/IP Send
90
- Data Type Conversion: This block indicates that which format to read. In this case an
int64 format has to be selected.
Figure 67: Block parameters Data Type Conversion
91
TCL server code
Close communication
Channel configuration
vwait waits until
connection is stablished
(value 1 is assigned to
connection).
Calls the procedure proc
accept_client_connection
If connection is stablished value 1 is
assigned to connection otherwise, if it takes
too long to connect, an error message
appears.
Defines the size of the
data that is going to
receive from the channel
Sends data to the
channel
92
Channel definition
Operations
Data type conversion.
Send data to the channel
Get data from the
channel and convert the
data type
End of the communication. Close channel and socket by
calling the procedure proc close_socket
93
C.4 Simulink to SeaFEM Communication
General scheme
94
Simulink client configuration
Next, starting from the explanations of the different blocks that have been given previously, it
will be explained in detail how each one has been configured.
Figure 68: Simulink general scheme
95
TCP/IP Client Receive Block: In this block the Remote Address (127.0.0.1) and the Port (9901)
are defined. A seven component double vector is also defined indicating the Byte order
LittleEndian.
Figure 69: Block Parameters TCP/IP Receive
Demux: This block allows separating the data that arrives in the form of a vector in its seven
components to be able to work with each of them separately.
Figure 70: Block Parameters Demux
96
Data Type Conversion: As it has been done in the TCL script, it is necessary to transform the
value of the flag into a value of type int32.
Figure 71: Block Parameters Data Type Conversion
Mux: Unlike the Demux block, this block allows you to recompose the vector from the
remaining six components to work with them more easily.
If: This block allows entering the condition that imposes the flag value for the program to
perform one or another action. The expression "if" is u1 == 0 and the Elseif expressions are u1
== 1, u1 == 2 and u1 == 3.
Figure 72: Block Parameters If
97
Merge: This block should be added whenever an If block is used to join the conditional results
at the input into a single output signal.
Figure 73: Block Parameters Merge
TCP/IP Client Send Block: The same configuration data as in the TCP / IP Client Receive is
defined in this block.
Figure 74: Block Parameters TCP/IP Send
98
The different actions that Simulink must execute are described below.
ACTION 0 – INITIATE PROBLEM: This action corresponds to the beginning of the program. The
vector composed by the six remaining components enters on the input. A Demux block is used
to split the vector to store the time increment, dt, in the variable dt_. A Mux block is used to
recompose the vector.
Figure 75. Action 0 - Initiate Problem
ACTION 1 – START NEW STEP: Simulink does not perform any task in this action. The data
vector enters on the block by input 1 and exits by output 1.
Figure 76. Action 1 - Start New Step
99
ACTION 2 – Start New Iteration: This action counts the iterations. Iterations are saved on a
Data Store block named “iterations_”. Any changes are made on the data vector. It enters on
the block by input 1 and exits by output 1.
Figure 77. Action 2 - Start New Iteration
ACTION 3 – Finish Iteration: In this action the forces are obtained from the displacements. The
data vector enters in the block on input 1. In the Subsystem block named “OPERATIONS” the
user will have to introduce the operations required to obtain the forces from the
displacements. The resulting vector with the calculated forces exits the block on output 1.
Figure 78. Action 3 - Finish Iteration
ACTION 4 – Finish Time Step: In this action iterations are initialized and time increased. The
time increment, dt, stored in Action 0 is used here to count the time step saved in a data store
named “time_”. Iterations are initialized by saving a value 0 on the “iterations_” data store.
100
Figure 79. Action 4 - Finish Time Step
ACTION 5 – Finish Problem: The Stop Simulation block disconnects Simulink from the channel.
The Stop Simulation block stops the simulation when the input is nonzero, in this case value 1
is assigned to the block.
Figure 80. Action 5 - Finish Problem
TCL server code
101
Close communication
Channel configuration
vwait waits until
connection is stablished
(value 1 is assigned to
connection).
Calls the procedure proc
accept_client_connection
If connection is stablished value 1 is
assigned to connection otherwise, if it takes
too long to connect, an error message
appears.
Defines the size of the
data that is going to
receive from the channel
Sends data to the
channel
102
Channel definition
Functions definition
Functions creation
dt function creation. Get
the value from SeaFEM
Data type
conversion. Send
data to the
channel
Get data from the
channel and convert the
data type
Start Communication
Flag Value assignment
103
Channel and functions
definition
Data type
conversion.
Send data to
the channel
Get data from the
channel and convert the
data type
Flag Value assignment
Channel and functions
definition
Data type
conversion
Send data
to the
channel
Get data from the
channel and convert the
data type
Flag Value assignment
Channel and functions
definition
Flag Value assignement
104
Channel and functions
definition
Data type
conversion.
Send data to
the channel
Get data from the
channel and convert the
data type
Flag Value assignment
Channel and functions
definition
Data type
conversion.
Send data to
the channel
Get data from the
channel and convert the
data type
Flag Value assignment
105
Channel and functions
definition
Data type
conversion.
Send data to
the channel
Communication ending
Flag Value assignment
106
107
Appendix D: OWC codes
D.1 Introduction
This annex contains the complete codes used for the OWC simulation. These codes allow to
obtain the power from the flux through the turbine.
D.2 TCL code
Close communication
Channel configuration
vwait waits until
connection is stablished
(value 1 is assigned to
connection).
Calls the procedure proc
accept_client_connection
If connection is stablished value 1 is
assigned to connection otherwise, if it takes
too long to connect, an error message
appears.
Defines the size of the
data that is going to
receive from the channel
Sends data to the
channel
108
Channel and functions
definitions
Start Communication and
Flag Value assignment
dt function creation. Get
the value from SeaFEM
Functions creation
Data type conversion.
Send data to the channel
Get data from the
channel and convert the
data type
Channel and functions
definition. Flag
assignement.
Function evaluation
Data type conversion.
Send data to the channel
Get data from the
channel and convert the
data type
Apply pressure
Channel definition and
flag assignment.
Data type conversion.
Send to the channel
Get data from the
channel and convert type
109
Channel definition and
flag assignment.
Data type conversion.
Send to the channel
Get data from the
channel and convert type
Channel definition and
flag assignment.
Data type conversion.
Send to the channel
Get data from the
channel and convert type
Channel definition and
flag assignment.
Data type conversion.
Send to the channel
Communication ending
110
D.3 Simulink file description
Figure 81. Simulink general scheme. OWC.
111
Figure 82. Simulink subsystem: Finish iteration. OWC.
Figure 83. Simulink subsystem: Finish iteration. Pressure calculation subsystem. OWC.
112
Figure 84. Simulink subsystem: Finish iteration. Pressure calculation. OWC.
113
Appendix E: Fins effect control
E.1 Introduction
The codes used to simulate the control acting on the stabilizing fin son a Wigley hull are
detailed in this annex.
E.2 TCL code
Close communication
Channel configuration
vwait waits until
connection is stablished
(value 1 is assigned to
connection).
Calls the procedure proc
accept_client_connection
If connection is stablished value 1 is
assigned to connection otherwise, if it takes
too long to connect, an error message
appears.
Defines the size of the
data that is going to
receive from the channel
Sends data to the
channel
114
dt function creation. Get
the value from SeaFEM
Functions creation
Functions evaluation
Channel and functions
definitions
Start Communication and
Flag Value assignment
Variables definition
115
Channel definition and
flag value assignment
Variables definition
Data type
conversion.
Send data to
the channel
Get data
from the
channel
and convert
type
Functions evaluation
116
Data type
conversion.
Send data to
the channel
Get data
from the
channel
and convert
type
Functions definition
Channel definition and
flag value assignment
Variables definition
Functions definition
117
Functions definition
Type
conversion.
Send data
to channel
Get data from
the channel
and convert
type
Apply loads on
SeaFEM
Channel definition and
flag value assignment
Variables definition
118
Functions definition
Type
conversion.
Send data
to channel
Get data from
the channel
and convert
type
Channel definition and
flag value assignment
Variables definition
Functions definition
119
Type
conversion.
Send data
to channel
Get data from
the channel
and convert
type
Channel definition and
flag value assignment
Variables definition
120
Functions definition
Communication ending
Type
conversion.
Send data
to channel
121
E.3 Simulink file description
Figure 85. Simulink general scheme. Active fins installed on a Wigley hull.
122
Figure 86. Start New Iteration. Active fins installed on a Wigley hull.
123
Figure 87. Operations subsystem. Active fins installed on a Wigley hull.
124
125
Appendix F: Fins effect control
verification
In order to verify the correct functioning of the communication between both programs and
the Simulink control element, the three aforementioned cases have been solved introducing
an analogue function as an external force in SeaFEM.
Considering the movement equation for a ship with fins previously described in Chapter 5
(p.57):
𝐼 + 𝐵 + 𝐶𝜃 = 𝑀𝑥 + 𝑀𝐹 (E.1)
the fin moment, MF, can be translated as a damping moment:
𝑀𝐹 = 𝑏𝐹 𝑑𝜃
𝑑𝑡
(E.2)
When the fins are installed on the ship it moves as a damped harmonic oscillator. Thus, the roll
moment, Mx, can be rewritten as a damping moment:
𝑀𝑥 = −𝑐𝑡𝑒 ∗ 𝑤𝑥 (E.3)
Thus, in this case the way to verify that the coupling between programs is correct is to enter
this equation in SeaFEM as an external moment and verify that a similar result is obtained.
In order to be able to introduce the equation in SeaFEM it will be necessary to know the value
of the constant. This value can be obtained as the slope of the Mx-wx curve. Then, once the
calculation of the moment of balance of a ship with fins has been carried out by coupling
Simulink and SeaFEM, the values of angular speed wx and roll moment Mx can be extracted
and represented in a curve as shown in the next Figure 88.
126
Figure 88. General roll moment and angular roll velocity curve.
The following sections describe two verification cases considering two different sea situations:
with waves and without waves. The environment conditions are described in Chapter 7 (p.72).
F.1 Verification case: Sea without waves
A sea situation without waves or currents has been selected to begin the verifications since it
is the simplest scenario. In the following cases a roll extinction test has been simulated by
introducing an initial tilt, Rx = 50.
Case 1: Ship without fins
As previously mentioned in this case a damping external moment has been considered and
introduced in Simulink. Figure 89 shows the rolling movement obtained.
Figure 89. Roll movement. Ship without fins. Sea without waves.
-40000
-20000
0
20000
40000
60000
80000
100000
120000
-0.015 -0.01 -0.005 0 0.005
Mx
(Nm
)
Wx (rad/s)
-0.1
-0.05
0
0.05
0.1
0 10 20 30 40 50 60
Ro
ll m
ove
me
nt
(rad
)
Time (s)
127
Case 2: Fixed Fins
The obtained rolling movement for the ship equipped with fixed fins is shown in Figure 90.
Figure 90. Roll movement. Fixed fins. Sea without waves.
The result obtained has been verified comparing it with the one obtained considering the slope
of the curve of rolling moment and angular velocity shown in Figure 91. The equation
introduced in SeaFEM for the verification is:
𝑴𝒙 = −𝟐. 𝟎𝟒𝟕. 𝟏𝟓𝟒, 𝟑𝟒 𝒘𝒙
Figure 91. Curve Mx-wx. Fixed fins. Sea without waves.
The obtained graphic of rolling movement of Figure 92 shows the same behavior as the
previous graphic obtained coupling the two programs. As shown, due to the fixed fins, the
rolling moment is considerably reduced.
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
0 10 20 30 40 50 60
Ro
ll m
ove
me
nt
(rad
)
Time (s)
-40000
-30000
-20000
-10000
0
10000
20000
30000
40000
50000
-0.03 -0.02 -0.01 0 0.01 0.02
Mx
wx
128
Figure 92. Roll movement. Fixed fins. Sea without waves. Verification.
Case 3: Active Fins
In this case the control algorithm has been tested. Figure 93 shows that the active fins have a
higher impact on the decreasing of the roll movement.
Figure 93. Roll movement. Active fins. Sea without waves.
The result obtained has been verified comparing it with the one obtained considering the slope
of the curve of rolling moment and angular velocity shown in Figure 94. The equation
introduced in SeaFEM for the verification is:
𝑴𝒙 = −𝟕. 𝟗𝟕𝟕. 𝟎𝟒𝟑, 𝟕𝟖 𝒘𝒙
-0.1
-0.05
0
0.05
0.1
0 10 20 30 40 50 60R
oll
mo
vem
en
t (r
ad)
Time (s)
-0.02
0
0.02
0.04
0.06
0.08
0.1
0 10 20 30 40 50 60
Ro
ll m
ove
me
nt
(rad
)
Time (s)
129
Figure 94. Mx-wx curve. Active fins. Sea without waves.
The obtained graphic of rolling movement of figure shows the same behavior as the previous
graphic obtained coupling the two programs.
Figure 95. Roll movement. Active fins. Sea without waves. Verification.
F.2 Verification case: Sea with waves
Following the same procedure of the previous verification case, the three cases have been
tested for the new sea conditions. In this situation a lateral monochromatic wave of 24,5 s of
period and 0,5 m of amplitude has been considered.
Table 7. Waves data. Sea with waves.
Amplitude (m) 0,5
Period (s) 24,5
Heading (0) 90
The situation simulated is a rolling test. For that reason the initial tilt, Rx, is set to 0.
-40000
-20000
0
20000
40000
60000
80000
100000
120000
-0.015 -0.01 -0.005 0 0.005M
x
wx
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
0 10 20 30 40 50 60Ro
ll m
ove
me
nt
(rad
)
Time (s)
130
Case 1: Ship without fins
As previously mentioned in this case a damping external moment has been considered and
introduced in Simulink. Figure 96 shows the rolling movement obtained.
Figure 96. Roll movement. Ship without fins. Sea with waves.
Case 2: Fixed Fins
The obtained rolling movement for the ship equipped with fixed fins is shown in Figure 97.
Figure 97. Roll movement. Fixed fins. Sea with waves.
The result obtained has been verified comparing it with the one obtained considering the slope
of the curve of rolling moment and angular velocity shown in Figure 98. The equation
introduced in SeaFEM for the verification is:
𝑴𝒙 = −𝟐. 𝟎𝟓𝟐. 𝟎𝟗𝟒, 𝟏𝟗𝒘𝒙
-0.1
-0.05
0
0.05
0.1
0.15
0 10 20 30 40 50 60
Ro
ll m
ove
me
nt
(rad
)
Time (s)
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
0 10 20 30 40 50 60
Ro
ll m
ove
me
nt
(rad
)
Time (s)
131
-40000
-20000
0
20000
40000
60000
80000
100000
-0.06 -0.04 -0.02 0 0.02
Mx
(Nm
)
Wx (rad/s)
Figure 98. Mx-wx curve. Active fins. Sea with waves.
The obtained graphic of rolling movement of Figure 99 shows the same behavior as the
previous graphic obtained coupling the two programs. As shown, due to the fixed fins, the
rolling moment is considerably reduced.
Figure 99. Roll movement. Fixed fins. Sea with waves. Verification.
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0 10 20 30 40 50 60
Ro
ll m
ove
me
nt
(rad
)
Time (s)
132
Case 3: Active Fins
In this case the control algorithm has been tested. Figure 100 shows that the active fins have a
higher impact on the decreasing of the roll movement.
Figure 100. Roll movement. Active fins. Sea with waves.
The result obtained has been verified comparing it with the one obtained considering the slope
of the curve of rolling moment and angular velocity shown in Figure 101. The equation
introduced in SeaFEM for the verification is:
𝑴𝒙 = −𝟖. 𝟎𝟎𝟓. 𝟔𝟎𝟕, 𝟐𝟕 𝒘𝒙
Figure 101. Roll movement. Active fins. Sea with waves. Verification.
The obtained graphic of rolling movement of Figure 102 shows the same behavior as the
previous graphic obtained coupling the two programs.
-0.006
-0.004
-0.002
0
0.002
0.004
0.006
0 10 20 30 40 50 60
Ro
ll m
ove
me
nt
(rad
)
Time (s)
-150000
-100000
-50000
0
50000
100000
150000
200000
250000
300000
-0.04 -0.03 -0.02 -0.01 0 0.01 0.02
Mx
(Nm
)
wx (rad/s)
133
Figure 102. Roll movement. Active fins. Sea with waves. Verification.
F.3 Summary
The intention of this section was to verify the correct functioning of the coupling between
SeaFEM and Simulink and the control algorithm of the fins. In order to do that the following
sea situations have been considered:
- Sea without waves.
- Sea with waves.
For each situation three different cases have been simulated:
- Ship without fins.
- Ship with fixed fins.
- Ship with active fins.
To verify that the obtained results are correct other simulations have been carried out
introducing in SeaFEM an analogue fins effect function. As shown in the previous section, the
obtained results with the verification method match with the results obtained coupling
Simulink and SeaFEM.
Furthermore, the following figures show the decreasing in the roll movement due to the fins
effect in each sea situation demonstrating the correct functioning of the program. The active
fins have a major impact on the damping of the roll.
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0 10 20 30 40 50 60R
oll
mo
vem
en
t (r
ad)
Time (s)
134
Figure 103. Roll movement comparison for the three considered cases. Sea without waves.
Figure 104. Roll movement comparison for the three considered cases. Sea with waves.
-0.1
-0.05
0
0.05
0.1
0 20 40 60
Ro
ll m
ove
me
nt
(rad
)
Time (s)
Active fins
Fixed fins
Without fins
-0.1
-0.05
0
0.05
0.1
0 20 40 60
Ro
ll m
ove
me
nt
(rad
)
Time (s)
Active fins
Fixed fins
Without fins
135
References
Faltinsen, O. M. (1993). Sea loads on ships and offshore structures (C. U. Press, ed.). Cambridge.
Instrument Control Toolbox 2 User ’s Guide. (n.d.).
Kawazoe, T., Nishikido, S., & Wada, Y. (1993). Effect of Fin Area and Contorol Methods on Reduction of Rool Motion with Fin Stabilizers. Journal of the Marine Engineering Society in Japan, 28(4), 279–285. https://doi.org/10.5988/jime1966.28.279
Kim, J. H., & Kim, Y. H. (2011). Motion control of a cruise ship by using active stabilizing fins. Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment, 225(4), 311–324. https://doi.org/10.1177/1475090211421268
Kula, K. S. (2015). An Overview of Roll Stabilizers and Systems for Their Control. TransNav, the International Journal on Marine Navigation and Safety of Sea Transportation, 9(3), 405–414. https://doi.org/10.12716/1001.09.03.14
Liang, L., Sun, M., Shi, H., & Luan, T. (2017). Design and analyze a new measuring lift device for fin stabilizers using stiffness matrix of Euler-Bernoulli beam. PLoS ONE, 12(1), 1–22. https://doi.org/10.1371/journal.pone.0168972
Lihua, L., Peng, Z., Songtao, Z., Ming, J., & Jia, Y. (2018). Simulation analysis of fin stabilizer on ship roll control during turning motion. Ocean Engineering, 164(June), 733–748. https://doi.org/10.1016/j.oceaneng.2018.07.015
Newman, J. N. (1979). The Theory of Ship Motions. In Advances in Applied Mechanics (Vol. 18). https://doi.org/10.1016/S0065-2156(08)70268-0
P.G. Howlett, P. J. P. (2006). Advances in Industrial Control. https://doi.org/10.1007/978-3-319-08413-8
Patil, N. S., Chandra Dubey, A., & Anantha Subramanian, V. (2019). Fin based active control for ship roll motion stabilization. MATEC Web of Conferences, 272, 01026. https://doi.org/10.1051/matecconf/201927201026
Perez, T., & Blanke, M. (2014). Control of Ship Roll Motion. Encyclopedia of Systems and Control, 1–8. https://doi.org/10.1007/978-1-4471-5102-9_123-1
Rahimuddin, Maimun, A., & Gani, P. A. (2014). Application of fuzzy logic controller to enhance the semi-SWATH performance in following seas. Jurnal Teknologi (Sciences and Engineering), 69(7), 17–25. https://doi.org/10.11113/jt.v69.3261
SeaFEM Theory Manual. (n.d.).
Serván Camas, B. (2016). A time-domain finite element method for seakeeping and wave resistance problems. (10.20868/UPM.thesis.39794). https://doi.org/10.20868/UPM.thesis.39794
Sysel, M. (2009). TCP/IP OUTPUT FROM THE SIMULINK. 634–637.
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