Simo User`s Manual
Contents
1. The plots might appear with response type numbers The following possibilities exist 1 Wind velocity 2 Wave elevation 2001 516412 01131560 Page 31 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 Wave particle motion at initial position Wave particle motion for distributed hydrodynamic forces Total force Retardation function force convolution integral Stiffness force Linear damping force Quadratic damping force Ist order wave force Wind force Linear current force Quadratic current force 2nd order wave force wave drift force QTF quadratic transfer function force Small body hydrodynamic force Positioning system force Coupling system force Dynamic positioning parameters Specified force External force Thruster force Distributed hydrodynamic force Wave drift damping force wave current interaction Global position from time domain calculations Global acceleration Local position Local velocity Global total position 7 3 2 Statistical analysis Time series statistics Input to the statistical analysis is the time series of the response to be analysed Additional time series for maxima and minima are derived For all three series the four first statistical moments are computed LS m 9 x 7 1 n j 1 The results are presented as average value u standard deviation o and coefficients for skewness and excess y and y u m 7 2 o m mi 7 3 v m3 3mim2t 2m Y2. If the read time series is shorter than the length of the simulation the wave elevation in the last part of the simulation will be set to zero File format ASCII for wave elevation Line 1 Number of samples Line2 Time step Line3 Arbitrary text Line4 Arbitrary text Lines 5 N Time series read in free format arbitrary number of samples on each line Example 2048 Number of samples 50 Time step Text 1 Text 2 20 0000 20 3923 20 7822 21 1672 21 5451 21 9134 2001 516412 01131560 Page 29 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 A complete example from a simulation is given below Should wave time series be read from file N ix Name of wave file File name may be DROP File name Old wave asc New Wave asc Scale factor 1 00000 Time step in model scale is 0 0200 sec Each series consists of 131072 points Wave signal in full scale contains 2048 values different from zero The wave is transformed to ORIGO according to wave direction and coord of the point where the wave is given Transf dist is in FULL scale Deep water is NOT assumed w w g k tanh k d The wave read from file replaces the wav specified on the system input file The wave must be long crested Wave dir is taken from the system input file X and Y coord where wave is given full scale X coord wave 0 00000 y t TD Y coord wave 0 00000 J 20 Wave d
3. Some parameters may have default values The default values are obtained simply by giving a slash instead of the input value The input data are defined by the following input description frames symbolic names of data items description default Dm symbolic names of data items appear in the order they are decoded item is repeated for all items in the heading description 1s used for explaining the parameter format is either LR or A default value may be indicated if relevant note may be used for comments etc 2001 516412 01131560 Page 37 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 The system description file is divided into 5 main data groups SYSTEM DESCRIPTION SIMO Identifies the file type always the first data group HLA COMMUNICATION SPECIFICATION Needed only for real time simulation BODY DATA SPECIFICATION The data group to be repeated for all bodies HYDRODYNAMIC COUPLING DATA The data group to be repeated for each coupling between 2 bodies GENERAL LINE DATA Not to be repeated COUPLING DATA The data group to be repeated for all couplings ENVIRONMENT DATA SPECIFICATION Not to be repeated environmental conditions must be specified together END Indicates end of the file All data within a main data group e g BODY DATA SPECifictation must be given in one sequence However the different data groups within a main data group may be given in an arbitrary sequenc
4. x Hydrostatic stiffness force Linear damping force Quadratic damping force Wind force linear interpolation between directions Linear and quadratic current drag force linear interpolation between directions Average wave drift force The force will be calculated for the instantaneous heading the first and last time step For other steps corrections for instantaneous heading is done utilizing 1 derivatives Small volume hydrodynamic force wave particle velocities are set to zero Coupling element forces Specified forces for t 0 Positioning element forces Thruster forces If a dynamic positioning system is defined the thruster forces are calculated from the thruster allocation algorithm described in the theory manual The thrust demand is where Fai x Gi FE mii F wai Fai Fi F oj Jl 1 2 6 5 3 Ox Positioning error in local coordinate system Gil Position and heading gains in linear controller matrix 2001 516412 01131560 Page 19 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 F vi Static wind force Fwa Static wave drift force F cu Current force Fi Positioning element force Fo Coupling force The equations of motion are stepped the specified number of steps with the modified Euler algorithm At the last step relative position and direction errors are calculated as E max ES Li HL i 1 2 3 5 4 max Eo Lic 1 4 5 6 5 5 Equilibrium position is found
5. 2001 516412 01131560 Page 2 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 4 Prnmtstatic condi sist ideada 18 5 5 Eguilibiumi a O e Sent Saher alate eo tee 18 5 6 Eigenvalue calculation A A ta 20 5 7 Mooring system pretension optimization ooooooccnnocononoconcnonnnonnnconnocono conc cnnncnnnncon cnc nccnnnos 20 5 8 White Initial condition TIC AR 21 5 9 Write file for visualization lis 21 6 USE OF DYNMOD it adi dei eo eau stss eeso siase one Se souas aia aese a ois estase 22 Oo Readanitial Condition files Dd A AA 22 6 2 Set simulation PATA eS 22 6 2 1 Main analysis parameters A A A A da 22 G22 a A A A 23 6 2 3 SIOraS e Parametros 25 6 3 Initialization of time domain simulation A 26 6 3 1 Reading wind time series from file ooooccnnnccinnconocanonanonononononnnocono conc conn ccoo nonnns 27 6 3 2 Reading wave elevation from file s oo A Rave entes 28 6 4 Time domain SHQulatiOflo eos ex beoe ete de 30 6 5 Work array size 11 DY NMOD asinis eet p E Oe reae ete edet ege 30 he USE OF OU TMOD cacicsecsedstaeceasnagececcsansscesssavsneassancgsasvancgeasene evoseebecdsaeeseasasseseetcanncstvsounneunsy 31 FL Defineinputand Output fes A A ai 31 2 Jsst stored dala en ec e de E yl ON 31 7 3 Time series analysis urera eden 0 31 7 3 1 A e NI He e a e 31 7 3 2 Statistical analysis Time series statistics oooooccnnncninccnonconcnoncnconncconocno nacion 32 7 3 3 Spectra ANAL SIS cia 33 TA Snapshot OF bodies A A do
6. 34 5 USE OE S2XMOD scii casei DI ORORSKASNIBERENDES ANNUS USES esras eaea enas sioa atsa ERREUR 35 8 1 Pre series AiO o cet costes Seda cuum ciun entere ore tutes De acto Ri 35 8 2 List modify default settings uiu i ca 35 813 EIU SUCSOT A e es ite een iia ee RSEN REV ENSE 36 O hieu epi car mici lose metuo v nep pda Meme epus ui 36 85 Statistics and plot of Series ood pete e dl a o 36 8 6 EXPORT to one MATLAB Mei as lates 36 8 7 EXPORT to separate ASCII files one MATLAB m file sssssseeeee 36 8 8 EXPORT to DIRECT ACCESS Mle usario eds etat adas 36 9 SYSTEM DESCRIPTION FILE iia iaa 37 9 1 System description file la E US 37 APPENDIX A System description file APPENDIX B MAIS Use of application programs 2001 516412 01131560 Page 3 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 1 INTRODUCTION SIMO is a computer program for simulation of motions and station keeping behaviour of a complex system of floating vessels and suspended loads Essential features are Flexible modelling of multibody systems Non linear time domain simulation of wave frequency as well as low frequency forces Environmental forces due to wind waves and current Passive and active control forces Interactive or batch simulation The user documentation consists of the following parts General description A short description of the most important system functions and features Theory manual A detailed description of
7. aen d des eiu RIT 7 2 4 Error MESSAGES tt 7 3 PROGRAM LAYOUT ient br ER EPOR A QOEM GN RETRO EEUU SEO ERE E RE REAUMT 8 3 1 INPMOD input data manipulation socie oae PY ohne Madama cute 9 3 2 STAMOD initial condition and static equilibrium esee 9 33 DYNMOD dynamic response caleulattQni eiit EE p ee POR Seo tt vi don 10 3 4 OUTMOD oporto das do edes 10 3 5 SZXMOD export OF time Si a AR dat 10 3 6 PLOMOD plotting Ma el ad 10 3 7 SimVis 3D visualization Pro TAM os 10 3 8 Jule SVSECHY aso E E E ETES 11 3 9 R nning SIMO iiie east rire eiu taste a a ana eeu 12 Ay USE OF ANP MOD aio sono serao OFRECE RIO toso eosi si oere S TRE 14 4 1 Body data manipulation A ias 14 4 1 1 Define body type and name e oet tero epe etra re tengas 14 AM Rad A RN 14 4 1 3 Denis body daa da 14 414 Manipulate body data srta ds 14 4 1 5 Status DOL A A A aetatem de det ved e td ii 15 AMO is data Sesaascostes ded seta te tA t dE MUI E Apes 15 41 7 Nte body did dais 15 55 USE OE STAMOD ui Adela 16 5 1 A O nete dui a tends 16 5 2 Read initial condition file redet aite ta 17 3 9 Modify Present SY SECM as un vas vno os tes 17 5 3 1 Select AM di dai 17 2 9 24 SDaitial Positions S A eee he ae tese Res ac ac te as a tue ades 17 5 3 3 Eliminate degrees of freedom A ia 17 53 4 POS SUSICID S eese inire e as old salves hades etude de R EA 17 5 3 5 Restoring TOlCeS osa indan eder e a a a a EA AA 17 A Ds AAA eu ENDE EN eI Ret EE Mu dS 17
8. been written by STAMOD during the present or a previous run may be read If no changes have been made to the system as defined on SYSFIL this is an alternative which is much faster than reading SYSFIL 5 3 Modify Present system The menu for system modification is gt STAMOD modify present system Return Select environment Initial positions Eliminate degrees of freedom Positioning system Restoring force incl environmental forces Dynamic positioning HHHHHHHHHHH Au RWNHO Select option gt 1 Vv 5 3 1 Select environment Several regular and irregular wave conditions current conditions and wind conditions may be defined on SYSFIL or INIFIL The default wave condition will be the present condition If no condition has been selected the first one defined on SYSFIL will be the default Waves current and wind can be removed individually 5 3 2 Initial positions New initial positions for all bodies may be specified Present positions will be default 5 3 3 Eliminate degrees of freedom Elimination of degrees of freedom is implemented by setting the corresponding local acceleration components to zero during time domain simulation DYNMOD and equilibrium iteration STAMOD 5 3 4 Positioning system The initial tension may be changed This is done by moving the anchor position Print of positioning element locations and plot print of line characteristics are available 5 3 5 Restorin
9. environmental conditions can be done A static equilibrium position may be calculated with average environmental forces applied Natural periods and oscillation modes of the system may be calculated The initial conditions is written to the file INIFIL for use by DYNMOD 2001 516412 01131560 Page 9 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 3 3 DYNMOD dynamic response calculation The purpose of the module is to calculate responses in the time domain Before starting time integration of the equation of motion the various simulation parameters must be initialized 3 4 OUTMOD output module The purpose of the module is to read time series files generated in the DYNMOD module generate print and plot of time series and statistical parameters 3 5 S2XMOD export of time series The purpose of the module is to export result from dynamic analysis i e time series to variuos file formats In present verion export to MATLAB m file export to ASCII file and export to DIRECT ACCESS file are available In addition the module provides siple statistics and plot of time series 3 6 PLOMOD plotting module The purpose of the module is to plot results generated by OUTMOD 3 7 SimVis 3D visualization program Stand alone program for 3 dimensional visualization of static and dynamic analysis based on GLView 2001 516412 01131560 Page 10 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 3 8 File
10. is a multiplum of AQ If wave periods are carefully selected the specified wave periods will be obtained The condition for this is that the specified simulation duration is an integer number of wave periods ONA is an integer 6 2 Ao where T is the specified wave period 2001 516412 01131560 Page 26 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 6 3 1 Reading wind time series from file Optionally it is possible to read wind velocity or wind velocity and direction for each body from an ASCII file Read wind series at body id from file N YES Name of wind file File name may be DROP File name Old wind asc New Scaling factor In case one dimensional wind velocity has been specified the input file should contain the time series of wind velocity only The propagation wind direction for the present wind case is used chosen in STAMOD specified on SYSFIL If two dimensional wind velocity the input file must contain series of both wind velocity and wind direction in degrees In this case the read vind time series is transformed to the propagation direction and transverse direction of the present wind case chosen in STAMOD specified on SYSFIL This will not have any influence the results from the simulation It will only have an effect on the stored wind time series stored as components in propagation and transverse directions Both the read wind velocity and time step wi
11. o 7 4 2001 516412 01131560 Page 32 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 Y mi 3m2 4mm3 12 mi m 6 mi 3 o 7 5 For a Gaussian process y and y are zero hence these two parameters describe the deviation from Gaussian distribution An interpretation of these parameters is shown in Figure 7 1 Figure 7 1 Interpretation of skewness and excess coefficients The distribution densities and cumulative distributions are computed based on simple ranking into a set of classes defined by the user in terms of Number of classes Lower range defined by number of standard deviations below mean value Upper range defined by number of standard deviations above mean value The range refers to the initial distribution Thus the distributions of maxima and minima are computed for the same class discretization as the initial distribution No output is presented on PLOFIL 7 3 3 Spectral analysis The spectrum estimate is based on frequency averaging smoothing of hamonic components obtained by FFT The Standard deviation the Average period and the Zero crossing period are calculated When the spectral density is given as a function of the frequency in rad s the defintion of these parameters are Standard deviation sqrt MO Average period T01 2 pi M0 MI Zero crossing period T02 2 pi sqrt M0 M2 MO M1 and M2 are the zero first and second order moment of the spec
12. the theory on which the program is based User s manual All information necessary for correct and efficent use of the program Implementation and testing manual Complete run examples through all modules are described there The manual will be of help to new or unexperienced users Verification manual Results from the verification study 1 1 Program Modules The program is divided into 6 separate modules INPMOD manipulation of input data STAMOD initial condition and static equilibrium DYNMOD dynamic response calculation OUTMOD output module S2XMOD export of time series to various file formats PLOMOD plotting module common with the Riflex program system 2001 516412 01131560 Page 4 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 2 PRINCIPLES FOR USE 2 1 Interactive Communication The program is basically an interactive program but can also be run in batch mode The input from the terminal can be divided into five types Selection among a number of options that are presented on the screen Giving parameters to a command Giving text strings for identification Yes no answers Waiting on user response Common to all types of input is that they allow definition of a macro file they allow a macro file to be executed and they allow temporary switching of control to the operating system The program uses MAIS MArintek Input System for handling the interactive communicat
13. when both e and e are less than 1 Note that initial positions are updated when calculation of equilibrium is selected even 1f equilibrium position is not found It is advised to check the equilibrium position by calculating static forces and printing new initial positions 5 6 Eigenvalue calculation Natural periods and eigen vectors can are calculated for selected modes The calculation is based on a linearized model of the system Mass and stiffness matrices are calculated and the system solved by a standard acobian solver Effect of damping is not included in the analysis The mass matrix 1s built from the virtual mass matrix including both structural and hydrodynamic mass The frequency dependency of the latter is not accounted for in the analysis as asymptotic values are used For bodies of type 1 see appendix A section 2 Body Data Specification this means added mass at infinite frequency while the added mass at zero frequency is used for bodies of type 2 The secant stiffness for the user selected modes is calculated at the initial position The user may choose to specify the secant excursion used in the calculation for each mode The stiffness matrix is made symmetric For each natural period the eigen vectors expresses the relative contribution from each mode Translations are given in the length unit L and rotations in degrees deg In the interpretation of the results it should be kept in mind that damping is not incl
14. All input data must be given in a consistent set of SI units which are defined as a part of the input data set eme Dem CEC w p CO pe em Acceleration Angles are given in degrees deg and coefficients which are multiplied with rotational state variables are given for rotations in radians Angular velocity is given in radians per time unit for instance rad s Thruster speed and rotation are given in revolutions per minute RPM Internally in the program all angles and rotations are converted to radians 2 4 Error Messages An error is reported where it is detected The string to be searched for on the print file is eese ERR Error flags and messages are transferred towards the root of the call tree In interactive mode the user is given control at a high level and can decide whether to continue or terminate the program In batch mode the program is terminated at the top level 2001 516412 01131560 Page 7 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 3 PROGRAM LAYOUT The program system consists of five programs or modules communicating by a file system as shown below INPMOD Read and manipulate system description STAMOD Read system description static analyses define initial condition File system for DYNMOD communi Dynamic analyses generation of time series cation between OUTMOD modules Post processing of time series PLOMOD Plotting A complete dynamic analysis must inclu
15. F Changes the program switch IWAIT to 1 0 resp This switch 1s used internally in the program to check whether press return to continue shall be written on the terminal 2001 516412 01131560 Page 5 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 DISPLAY ON OFF Changes the program switch IDISP to 1 0 respectively This switch is used by the program to enable supress output to the terminal when macro files are executed interactively FILE ifile Changes the program switch IFILE Allowable range is 0 5 This switch is used by the program to change the amount of print to file RESULT iresu Changes the program switch IRESU Allowable range is 0 5 This switch is used by the program to change the amount of information to the terminal STATUS Lists the values of the macro switches The parameter parameter that is currently read shall be read from terminal when a macro file is executed Assume that the user wants to undertake several batch runs To prepare an input file the user first runs the program in demand and logs the terminal input at file FILA MAC This is done by giving the command OPEN FILA MAC This causes the file FILA MAC to be opened All input to the program that is given from terminal will be stored at this file When this first run is finished FILA MAC may be duplicated and modified 1f wanted When the program waits at the same question where recording of macro file started the com
16. MARINTEK Norwegian Marine Technology Research Institute Postal address P O Box 4125 Valentinlyst NO 7450 Trondheim NORWAY Location Marine Technology Centre Otto Nielsens veg 10 Phone 47 7359 5500 MARINTEK REPORT TITLE SIMO User s Manual Version 3 6 Fax 47 7359 5776 AUTHOR S http www marintek sintef no Enterprise No NO 937 357 370 MVA SIMO project team CLIENT S SINTEF FILE CODE CLASSIFICATION CLIENTS REF MTS51 F93 0184 Confidential CLASS THIS PAGE ISBN PROJECT NO NO OF PAGES APPENDICES 516412 38 REFERENCE NO PROJECT MANAGER NAME SIGN VERIFIED BY NAME SIGN 2001 516412 01131560 P Harald Ormberg Halvor Lie REPORT NO DATE APPROVED BY NAME POSITION SIGN 516412 00 04 2007 11 16 Frode Meling Research Director ABSTRACT KEYWORDS ENGLISH NORWEGIAN GROUP 1 Hydrodynamics Hydrodynamikk GROUP 2 Simulation Simulering SELECTED BY AUTHOR SIMO User s Manual MARINTEK V 3 6 November 2007 TABLE OF CONTENTS LL INTRODUCTION ice is ecke npe pesa euo euo pee pe Aa PN Y YHP E eK Ee ERE NNUS Ee HE HT E NUR Aci 4 1 1 uc MT TEPORE 4 2 PRINCIPLES FOR USE uni 5 2 1 Interactive Communication ies deo Ere a EC ERR ERR Pr eG M ERA eai en T pun 5 244 IVIGCEO SV A ety be Seti A boas haven e iden aes 5 2 2 Selection OT execution modern erkein omia adl o RE a a rebel RN RR 6 2 3 Umts aid physical constants eie E o ema ua ecd Ned es d
17. ORT to one MATLAB m file Export one or several time series to MATLAB m file 8 7 EXPORT to separate ASCII files one MATLAB m file Export one or several time series to separate ascii files while information is stored in the MATLAB m file 8 8 EXPORT to DIRECT ACCESS file Export one or several time series to direct access file Information about the file is written to an ascii file 2001 516412 01131560 Page 36 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 9 SYSTEM DESCRIPTION FILE The SYSTEM DESCRIPTION FILE 1s an ASCII file that contains a complete description of the system 9 1 System description file layout The input file is read by the free format reader and decoder FREAD Each set of data card or data card group is identified with a character string consisting of maximum 3 words These are identified by up to maximum four characters in each word Comment lines in the input set are obtained by giving an accent in the fist column Data items in a card image are separated by space Default values of data items are obtained by giving a slash For missing data items the default value is used Continuation of the card image is obtained by amp All numbers given in the input files can be read in free formats both integer and real numbers Data types are specified for each input parameter where I means integer type R means real type A means character or hollerith type
18. Select option 2 Wind forces Three force models are available Calculation of static force due to average wind velocity Force due to total wind velocity Force due to relative wind velocity Interpolation of wind force coefficients between directions may be performed by either linear or spline interpolation Current forces Two force models are available Calculation of static force Force due to relative current velocity Interpolation of current force coefficients between directions may be performed by either linear or spline interpolation The methods to be selected apply for both linear and quadratic current force coefficients 6 2 3 Storage parameters The following results from time domain simulation can be stored on the time series file Wind speed Wind force Wave elevation For short crested sea either each wave component or for resultant wave may be stored Wave particle velocities and accelerations either for each directional wave component or for resultant wave Diffracted wave elevation and wave particle velocities and accelerations 1 order wave force for degrees of freedom where transfer functions have been read Either for each directional wave component or for resultant wave 2 order wave force for degrees of freedom where transfer functions are read If 2 order wave forces are modified due to heading changes the force on the file will be updated and the original value i
19. alternatively different wind time series will be generated for each body Time series of wind force will be calculated for those bodies that have defined wind force coefficients FFT parameters simulation length If waves or dynamic wind responses are included in the simulation time series can be generated by FFT The number of time steps in the pre generated series must be an integer power of 2 For example 2 steps equals 2048 steps Wave generation by summation of harmonic components cosine series in the time domain The time series generated equvidistant frequencies will repeat them selves with a period T 27 0 nin Where A min is the smallest frequency increment For user given number of wave components for wind sea and swell it is important that the number of components is sufficiently high to avoid a repeating wave response time series for the longest duration of the simulated operation that is close to stationary Stochastic amplitudes may be specified to be used for time domain wave response generation This is a conflict with the assumption of ergodic processes and analyses will often require simulations with multiple wave realizations in order to be able to give reliable extreme value estimates Time step The time step for the retardation functions is used as the default time step in the simulation There is a possibility of subdividing each time step into sub steps Sub steps will not be in stored on the time ser
20. de run of the modules STAMOD and DYNMOD Post processing or export of results is done by OUTMOD or alternatively S2XMOD However an efficient data base system simplifies the work during the analysis by storing input data and intermediate results In addition graphic presentation will be possible by use of the interactive plotting program PLOMOD This program communicates with SIMO by a file PLOFIL The layout of the program system is presented in Figure 3 1 Each module will be further detailed in the following 2001 516412 01131560 Page 8 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 External file Cd p M External files SYSFIL L INIFIL NR E DYNMOD TSFFIL 4 L PREFIL 0 4 V NN VISFIL i N r4 i D SENA A OUTMOD S2XMOD a A Y i Sinis 2 PLOFIL Extemal iles MM y PLOMOD Figure 3 1 Layout of the SIMO program system and file communication between modules 3 1 INPMOD input data manipulation The purpose of the module is to provide interfaces to external input data sources for example hydrodynamic programs and to modify the system description file SYSFIL 3 2 STAMOD initial condition and static equilibrium The purpose of the module is to define the initial condition for the dynamic simulation The description of the system to be simulated is read from a file SYSFIL Selection between
21. dratic transfer functions 4 1 7 Write body data A system description file may be generated and updated with the data presently defined 2001 516412 01131560 Page 15 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 5 USE OF STAMOD The main purpose of STAMOD is to read and check the system description from SYSFIL and to write those data to a direct access file INIFIL which will be used in DYNMOD and OUTMOD This file contains a complete system description definition of the environment to be applied and the initial positions for dynamic simulation gt STAMOD main menu Read system description file Read initial condition file Modify present system Print static condition Equilibrium calculation Eigen value calculation Mooring system optimization Write initial condition file Write file for visualisation Terminate 1 0 10 U1 5 WNP 1 O I gt Select option gt 5 1 Read system description file The SYSFIL is an ASCII file containing a complete description of the system to be analysed For a brief describtion of the sys file layout and file syntax see section 8 A detailed description of the file contents is given in Appendix A The SYSFIL is read twice the first time only to find dimensioning parameters for the work array the second time to put all data into the work array If an error occurs messages will be written both on the print file and in some cases a
22. dynamic force with wave particle elocities and accelerations set to zero The force contain contributions from current gravity force and any static soil reaction forces Gravity forces due to time dependend added mass at time zero Gravity and buoyancy force on slender elements and fixed body elements Current drag forces acting on slender eements and fixed body elements Specified forces at time equal to zero External forces i e forces from any special force subroutines linked into the program If a dynamic positioning system is defined thrust demand will be calculated according to equation 5 3 5 5 Equilibrium calculation The following parameters are specified interactively T Typical maximum natural period Ox Position tolerance da Direction tolerance ot Time step From position and direction tolerances the following tolerances for velocities and acceleration are calculated 2001 516412 01131560 Page 18 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 2mT Ox W X d 06a 5 1 OX a OX d o Oa By default critical damping for each degree of freedom can be calculated ci 2M 0 i 1 6 5 2 where M are the diagonal elements of the total mass matrix The equilibrium condition is found by stepping the equations of motion The following force models will be included if they are defined Critical damping force Modified retardation function force F 4 At 5 0
23. e 2001 516412 01131560 Page 38 of 38
24. e following methods exist Average force will be calculated for each time step calculation in the time domain Use initial average force and make corrections in time domain using the derivative of average force calculation by FFT Newman model calculation by FFT or in the time domain cosine series Extend drift force coefficients to full quadratic transfer functions by using the Newman approximation calculation by FFT or in the time domain cosine series Calculation methods for 2 order forces OTF Quadratic transfer functions for both sum and difference frequencies and optionally directional seas may be used as input For difference frequencies the following methods exist Using the frequency diagonal as wave drift force coefficients and apply the Newman model Using the frequency diagonal and expand to off diagonal terms by Newman s approximation Calculation of these forces in the time domain is not yet implemented Wave elevation Normally the resultant wave elevation is stored at the time series file Alternatively time series for each direction may be stored separately Wind velocities Wind velocities will be calculated for the wind propagation direction but also transverse gust speed may be specified 2001 516412 01131560 Page 24 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 Wind velocity I Wind velocity body id I I 1 One dimensional I 2 Two dimensionag I I
25. g forces The horizontal restoring force for translation in any direction or rotation may be specified Output is presented on plots and tables 5 3 6 Dynamic positioning The following data may be modified 2001 516412 01131560 Page 17 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 Reference position and heading including the point on the body to be positioned Start value on bias forces that are not measured If static forces have been calculated the default values will be updated Kalman filter data or PID controller data 5 4 Print static condition Initial positions for all bodies will be written to the terminal standard output and if selected also to the print file Static forces acting on bodies are written to the terminal and optionally to the print file The following forces are presented Average wave drift force calculated for the present heading including wave current interaction if specified Wind force linear interpolation between directions Current drag force based on linear and quadratic current coefficients linear interpolation between directions Munk moment caused current velocity and different magnitude of added mass specified in individual degree of freedom Positioning element forces Thruster forces Coupling element forces Foreces from general line systems Hydrostatic stiffness force Gravity and bouyancy forces also including small volume hydro
26. ies file Care should be used when using a large number of sub steps particularly when retardation functions are specified 6 2 2 Method parameters Possible wave responses The following wave responses may be calculated Wave elevation in origo First order motion 2001 516412 01131560 Page 23 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 Wave particle motion at body initial position for those bodies that have defined small body hydrodynamic forces Wave particle motion for slender structures with distributed hydrodynamic forces 1 order wave forces 1 order diffracted wave kinematics at selected points around large volume bodies Wave drift forces Wave drift damping forces Full 2 order wave forces Ringing forces Wave responses by FFT corrections due to heading changes The following possibilities exist Nocorrection i e responses calculated for initial heading is used throughout the simulation Interpolation in time domain The response is initially calculated for a number of different headings and interpolation between these is preformed in time domain The maximum heading change compared to initial heading must be specified and simulation stops if this is exceeded For wave drift forces only the first and optionally also the second derivative of average drift forces is applied to modify the pre generated forces in time domain Calculation methods for wave drift forces Th
27. il System description file SYSFIL sys chsys dat sys s1 dat Initial condition file INIFIL ini chsys chini sam Print from INPMOD PRIFIL pri chsys lis Print from DYNMOD prd chsys chini lis prd s1 11 lis 2001 516412 01131560 Page 11 of 38 SIMO User s Manual V 3 6 November 2007 MARINTEK 3 9 Running SIMO SIMO is normally started by typing simo at the command line prompt in the operating system The system then typically responds by kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk WELCOME TO SSSSSSSSSS III MMMMM MMMM 00000000 8889888888888 III MMMMM MMMMM 0000000000 sss III MMMMMM MMMMMM 000 O00 sss III MMM MMMMM MMM 000 000 SS8SSSSSSS III MMM MMM MMM 000 000 SSSSSSSSSSS III MMM M MM 000 000 sss III MMM MMM 000 000 sss III MMM MMM 000 000 SSSSSSSSSSS III MMM MMM 0000000000 SSSSSSSSS III MMM MMM 00000000 SIMULATION OF COMPLEX MARINE OPERATIONS kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk Enter system identification gt sysa Enter initial condition identification gt inib I gt SELECTION OF PROGRAM MODULE T I INP SIMO INPMOD I STA SIMO STAMOD T DYN SIMO DYNMOD T OUT SIMO OUTMOD I PLO SIMO RIFLEX PLOMOD i S2X SIMO S2XMOD I I PINP Print postscript inpmod stamod outmod file simo plt I PPLO Print postscript plomod file pscr meta dat I I DEF Redef
28. ine default files for default file names I LIS List identifiers for default file name I I TERM Terminate I Select option gt The user is first asked to specify the system identifier and initial condition identifier They are described in previous sections and are used to transfer default file names between the modules The user has the following options switch between the program modules send print files to printer change default file names terminate SIMO program system If for example the INPMOD module is selected the system will respond with the following kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkx k III I N N PPPP NN N P M M P MMMM O 000 DDDD O D D 2001 516412 01131560 Page 12 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 E I N N N PPPP MMM O O D D fai I N NN P M M O O D D E III N N P M M 000 DDDD x Version 2 Release 2 Module linked at 27 OCT 1994 11 02 kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk System identifier sysa Initial condition identifier inib Use default file names Y The module name version and release number and the link date time the system and initial condition identifiers appears on the screen It is strongly recommended to use default file names File pri sysa lis has been opened as PRINT FILE The module allows test print fr
29. ion This system is described in appendix B Useful features with this system are Numerical values have default values and allowable range Range check can be deactivated by range off Lower case and upper case letters are accepted as input The program will never stop because of wrong input Switch commands print file may be given anywhere User input may be logged on macro file for documentation or later input 2 1 1 Macro System Macro system commands starting with can be used anywhere where the program waits for input The commands must contain enough characters so that they are unique When the user writes HELP the a short description is written at the terminal The following macro commands are available HELP Writes a list of all macro system commands OPEN filename The command opens a macro file for writing All questions and answers until CLOSE is given will be stored on the macro file If the command is given a second time before CLOSE DO filename is stored at the macro file CLOSE The command closes the macro file which 1s opened for writing DO filenamen Input is read from the specified file The file is read n times n may be omitted LIST filename The contents of the file is listed on the terminal SPAWN PAUSE The program is set in a waiting condition A new process is created This means that all operating system commands can be given WAIT ON OF
30. irection 45 00 deg results in a transformation distance of 21 21 m Water depth in FULL scale 100 000 200 Cut off period for HP filter of wave signal 40 0000 a 00 6 4 Time domain simulation The simulation time and the integration method must be specified Clutch on 1 order wave forces is implemented The first and second derivatives of the clutch function are zero in both ends The duration of the clutch function must be specified 6 5 Work array size in DYNMOD The size of the DYNMOD work arrays may be specified using the environment variable SIMO MEM The variables give the size in MB i e 4 times the number of million words The minimum size is 4 MB and the maximum size is 800 MB The default size of the DYNMOD work array is 4 million words e g 16 MB 2001 516412 01131560 Page 30 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 7 USE OF OUTMOD The purpose of OUTMOD is to prepare plots of static system geometry and to analyse and present results from the time domain simulation I gt OUTMOD main menu I I 1 Define input and output files T 2 List stored data T 3 Environmental time series I 4 Force time series T 5 Position time series I 6 Snap shot of bodies I 99 Terminate T I gt Select option 1 gt 7 1 Define input and output files It is possible to use OUTMOD for generation of static geometry only In that case the input files will be the i
31. ll be scaled by the square root of the scaling factor The time step given on the ASCII file may be different from the time step used in the simulation The specified wind time series will be re sampled using the time step applied in the simulation basefd on linear inteprolation Further the velocities will be scaled by the square root of the scaling factor If the read time series 1s shorter than the length of the simulation the wind velocity in the last part of the simulation will be set to zero It is assumed that the reference height for wind velocity coincide with the height for which wind force coeficients are given Further no filtering application of admittance function is done on the read wind times series File format ASCII for one dimensioal wind velocity Line 1 Number of samples Line2 Time step Line3 Arbitrary text Line4 Arbitrary text Lines5 N Time series read in free format arbitrary number of samples on each line Example 2048 Number of samples 50 Time step Text 1 Text 2 20 0000 20 3923 20 7822 21 1672 21 5451 21 9134 2001 516412 01131560 Page 27 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 File format ASCII for two dimensioal wind velocity File head The file head may contain an arbitrary number of comment lines starting with Line 1 Number of samples Line 2 Time step Line 3 Number of columns 2 Time series Line 4 velocity direc
32. lso on the terminal Error messages on the print file are found by searching for the string ERROR from the beginning of the file If a non fatal error is encountered reading of SYSFIL will continue until the maximum number of errors are found If errors are found during the first scan of SYSFIL and the print file does not give any meaningful indications on the problem the amount of ouput to the printfile can be increased by the MAIS command A FILE 5 Symmetry codes Wind force coefficients current force coefficients wave drift force coefficients and transfer functions are given as functions of directions relative to the body In the calculations extrapolation on directions are not allowed In order to avoid problems with program termination due to attempted extrapolation it is advised that both 0 degrees and 360 degrees should be represented in the range of directions on the input file If symmetry codes are used this will automatically be taken care of For example if symmetry code is 2 and the directions 20 degrees and 70 degrees are specified they will be mirrored to 20 20 70 110 160 200 250 290 340 and 380 degrees 2001 516412 01131560 Page 16 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 NB It is strongly advised that values are specified for the symmetry lines For the example above 0 deg and 90 deg should also be included as input 5 2 Read initial condition file An INIFIL that has
33. mands can be repeated by DO FILA 2 2 Selection of execution mode Each SIMO program may be run in two different ways interactive mode and batch mode Selection between interactive and batch mode is done within the modules A symbolic file with name SIMO DEF DAT is searched for at the default directory The file should contain 3 lines with a character variable on each line CHMODE CHSYS CHINI If the file is not found the execution mode will be interactive and both CHSYS and CHINI will be blank Batch mode is selected only if CHMODE has the value gt batch or BATCH CHSYS and CHINI are used for generation of default file names as explained in Section 3 6 Batch mode is useful when several simulations shall be undertaken The necessary input for running the program may prepared with a text editor but it is recommended that the user prepares the input run file by running the program in demand mode and logging the input at a macro file If necessary the macro file can be edited Batch mode and interactive mode are different only in the way they respond to detected errors in the program execution and the amount of output presented at standard output device screen Details about running the program on different computers are found in the implementation and testing manual 2001 516412 01131560 Page 6 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 2 3 Units and physical constants
34. nitial condition file INIFIL and the system geometry file SYSFIL If results from time domain simulation are requested the input files will be PREFIL the time series file TSFIL and the initial condition file INIFIL In this case the names of TSFIL and INIFIL will be read from PREFIL and can not be changed by the user If snapshots or static system geometry are requested SYSFIL must be read as well Note that SYSFIL is used in OUTMOD only to read body geometry data It will be favourable to use a reduced SYSFIL as described in Appendix A Results from OUTMOD will be written to the print file If time series are wanted as output the time series will normally be written This can be avoided by decreasing the print switch FILE Plot information will be written to the plot file PLOFIL It is possible to append more plots to a PLOFIL generated in a previous OUTMOD run Plotting and scaling of plots is done by a separate program PLOMOD 7 2 List stored data A summary of channels stored on TSFIL will be presented on the terminal 7 3 Time series analysis Any part of the time series can be selected for processing Position time series can be derivated twice before processing 7 3 1 Time series Average value standard deviation and extreme values are written to the print file and PLOFIL The time series is written to PLOFIL and may also be written to the print file It is also possible to preview a time series plot in OUTMOD
35. om maximum 10 routines Specify number of routines 0 The following default plotting parameters are used Screen device 72 Plotting device 90 Plot file Simo plt Use default values Y The file name for printed output from the module is displayed Error massages will be written on this file There is an option for output of test print from the different program modules It can be used for debugging purposes in cooperation and on instruction from program system aministrator and normally the number of routines for test print should be set to 0 default value All modules except DYNMOD generate plots These can either be seen on screen or sent to postscript files The default names are simo plt or pscr meta dat PLOMOD These files can be opened in i e Ghostview and then copied directly into 1 e Microsoft Word The following plotting devices are available Screen 72 X11 Windows X terminals or equivalent Plot fil 80 HPGL 90 Postscript 2001 516412 01131560 Page 13 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 4 USE OF INPMOD The purpose of the module is to provide interfaces to external input data sources for example hydrodynamic programs and to modify system description file INPMOD MAIN MENU 1 Body data manipulation 2 Not implemented Coupling data manipulation 3 Environment data manipulation 99 Terminate Select option 4 1 Body data manipula
36. ries generated by SIMO Produce statistics of series Plot series Writes selected series to MATLAB m file format Writes selected series to a direct access file I S2XMOD main menu I I 1 Time series info T 2 List modify default settings I 3 Statistics of series I 4 Plot of series T 5 Statistics and plot of series I 6 EXPORT to one MATLAB m file I 7 EXPORT to separate ASCII files m file I 8 EXPORT to DIRECT ACCESS file E 99 Terminate I I gt Select option 3 8 1 Time series info A summary of channels stored on TSFIL will be presented on the terminal 8 2 List modify default settings List and modify default setting for export of time series statistics and plot Limit for plotting Amount of statistics Minimum maximum mean Minimum maximum mean skewness kurtosis How to specify time series Specified by 1 array number or 2 body number response number and channel Number of time steps to be skipped at start and end of time series Unit on x axis for plotting time or sample number 2001 516412 01131560 Page 35 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 8 3 Statistics of series Gives simple statistics of one or several time series 8 4 Plot of series Present plot of one or several time series 8 5 Statistics and plot of series Present statistics and plot of one or several time series 8 6 EXP
37. rpose of DYNMOD is to perform time domain simulation of the system with initial condition as defined by INIFIL Main analysis parameters method parameters storage parameters and integration parameters must be specified The different options in the main menu must be selected in increasing order I gt DYNMOD main menu I E 1 Read initial condition file T 2 Set simulation parameters I 3 Initialize simulation T 4 Time domain simulation I 99 Terminate un I Select option 1 6 1 Read initial condition file An INIFIL prepared by STAMOD will be read 6 2 Set simulation parameters Default values representing the most common used values are assigned to all parameters Within each group default values can be selected for all parameters Specification can thus be done with a minimum of keystrokes Otherwise default values are obtained by pressing Return during the specification 6 2 1 Main analysis parameters Motion mode for station keeping forces If any of the bodies included in the simulation is of type 2 1 e the motion is separated in HF and LF motions the station keeping forces may be calculated due to LF response or due to the total HF LF response which is the default Wave generation method The time series of wave responses are generated by superposition of harmonic components with uniformly distributed phases by means of pre generation by the Fast Fourier transform FFT or by time domain s
38. s lost Total force Retardation force Hydrostatic stiffness force Linear damping force 2001 516412 01131560 Page 25 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 Quadratic damping force Linear current drag force Quadratic current drag force Small body hydrodynamic force Total force from all elements of a body In addition the total force and the components of each element can be stored Total force from all couplings of a body In addition the total force and components in global and local system can be stored for each coupling element Total force from all thrusters of a body In addition force and direction of individual thrusters can be stored Dynamic positioning estimators Specified forces Global positions Global accelerations Local velocities 6 3 Initialization of time domain simulation Time series of wind speed wave elevation wave particle motion 1st order wave forces and 2nd order wave forces will be generated at the initial positions of the bodies If regular waves are specified these are also generated in the same way as irregular waves The frequencies of the harmonic components are multiples of the frequency increment Ao 27 Ao 6 1 NAE oe where N is the number of time steps and At is the time increment The obtained wave periods will normally be slightly different from the specified ones since the selected wave frequency
39. system When running the SIMO modules different kind of files are needed Each module communicates to terminal or read a macro file and generates output on the print file The system description file SYSFIL contains a description of bodies couplings and environmental data It is a symbolic data file which is read by STAMOD The file is also read by OUTMOD in order to find geometry data for static configuration plots and snapshots The initial condition file INIFIL is generated by STAMOD If only modifications to an already defined initial condition is required STAMOD can also read INIFIL DYNMOD reads INIFIL to fetch the system to be simulated and OUTMOD reads INIFIL to get initial positions and key data The pregenerated data file PREFIL is used for internal storage of simulation parameters in DYNMOD It is also read by OUTMOD to fetch information on the channels that are stored on TSFIL The time series file TSFIL contains all time series It is generated by DYNMOD OUTMOD reads the time series to be processed from TSFIL The plot file PLOFIL is generated by OUTMOD and contains plot information to be read by PLOMOD The default file name system utilizes the system identifier and initial condition identifiers chsys and chini Both contain up to 8 characters At the beginning of each module it is asked if default file names should be used The default file names will be File type File name syntax Example chsys sl chini
40. tion gt INPMOD body data Return Define body type and name Read body data Not implemented Define body data Manipulate body data Status body data Present body data Write body data OU UN HP O E I I E I I I E I I I I Select option 1 4 1 1 Define body type and name Body type and name may be defined 4 1 2 Read body data Body data may be read from a SIMO system description file or results from hydrodynamic programs such as WAMIT MULDIF WADAM or SWIM may be read 4 1 3 Define body data Not implemented in present version 4 1 4 Manipulate body data The following options exist retardation functions may be calculated from added mass and damping added mass and damping may be calculated from retardation functions first order motion transfer functions RAO may be calculated Linear damping 1f defined is then used in addition to potential damping 2001 516412 01131560 Page 14 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 4 1 5 Status body data A list of data groups defined for a body is presented 4 1 6 Present body data The following types of data may be plotted First order wave excitation forces Motion transfer functions RAO Drift force coefficients Added mass damping retardation functions Wind force coefficients Linear current drag coefficients Quadratic current drag coefficients Frequency diagonal of qua
41. tion Line 5 velocity direction Line 3 N i velocity direction Example 2048 Number of samples Comment line 1 N 50 Time step N 2 Format type Head of file Comment line 2 Comment line 3 Last comment line 20 0000 180 000 20 3923 180 500 20 7822 181 000 21 1672 181 500 21 5451 182 000 6 3 2 Reading wave elevation from file Provided that lon crested wave is specified it is possible to read wave elavation time series from an ASCII file Should wave time series be read from fileat body id from file N YES Name of wave file File name may be DROP File name Old wave asc New Scaling factor 1 0000 2001 516412 01131560 Page 28 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 X and Y coord where wave is given full scale X coord wave 0 00000 Y coord wave 0 00000 Water depth in FULL scale 1000 00 Cut off periode for HP filter of wave signal 40 0000 The propagation wave direction for the present sea state is used chosen in STAMOD specified on SYSFIL The read wave elevation will be scaled by the scaling factor while the time step 1s scaled by the square root of the scaling factor The time step given on the ASCII file may be different from the time step used in the simulation The specified wave elevation time series will be re sampled according the time step used in the simulation baseed on linear inteprolation
42. tral density Spectral moments spectrum parameters and spectral values are presented on the print file In addition spectrum values are written to PLOFIL Extreme values are estimated by fitting a Rice distribution to the sample and calculating the expected largest within the time interval to be specified by the user 2001 516412 01131560 Page 33 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 7 4 Snap shot of bodies Both static system geometry and snapshots from dynamic simulation can be generated on PLOFIL Projections into any of the planes defined by the axes of the global coordinate system can be selected In addition 3 dimensional plots can be generated Rotations of the 3 D plots are specified in PLOMOD Wave elevation can be included in the plots In PLOMOD the snap shots can be animated For 3D plots results can be written to files for later visualization by a separate program GLview not a part of the SIMO program system The files generated are ani geo containing the geometry ani txt containing displacements on ascii form The latter should be transformed to binary form by the command vec2one ani txt ani dis 2001 516412 01131560 Page 34 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 8 USE OF S2XMOD The main purpose of S2XMOD is to export time series to other file formats than applied by SIMO DYNMOD The options provided by S2XMOD are Give an overview of all se
43. uded in the analysis Modes that are heavily damped may thereby not be recognized in time domain simulation results Observe also that environmental forces are not included Thus the yaw motion of a turret moored or a single point moored vessel can not be checked by an eigenvalue analysis 5 7 Mooring system pretension optimization By this option it is possible to adjust line lengths or move anchor position in an optimal way in order to counteract average environmental forces The sum of squared differences between pretension and actual tension in each line is minimized 2001 516412 01131560 Page 20 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 5 8 Write initial condition file After all modifications have been made with the system the initial condition must be saved The initial condition file will be read by DYNMOD It can also be read by STAMOD if more modifications are required 5 9 Write file for visualization A file for 3D visualisation by the stand alone program SimVis can be written whenever the system description file has been read successfully This means that the system can be visualized before or after equilibrium condition calculation has been made Visualisation directly after reading the system description file can be advantageus as a preliminar control of the system geometry 2001 516412 01131560 Page 21 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 6 USE OF DYNMOD The pu
44. ummation of the harmonic components Due to these time consuming calculations a combination of pre generated time series and cosine series in the time domain is made possible For such a combination it is also possible to ensure that the same realization of wave components is used for both options for wave response calculation Specification of calculation method for waves I Select method for calculation of waves I I 1 No waves to be calculated I 2 FFT only I 3 FFT and Cosine series combined I 4 Cosine series only I 5 Visualization cosine series I Select option 2 Wind gust generation method 2001 516412 01131560 Page 22 of 38 SIMO User s Manual MARINTEK V 3 6 November 2007 The time series of wind gust are generated either by superposition of harmonic components with uniformly distributed phases by means of pre generation by the Fast Fourier transform FFT or by a time domain state space model driven by white noise Specification of calculation method for wind gust Select method for calculation of wind 1 No wind gust to be calculated LEFT 3 State Space model HHHHH Random seed for waves and wind A seed for generation of random phase angles must be specified With different seed numbers different time series of wind and waves will be generated Itis also possible to read wind and waves from an ASCII file Each body may experience the same wind time series
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