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3D bottom geometry file cannot be read if started with a comment line (Sima/Riflex)

The reading of the 3D bottom geometry file specified by the parameter CHFBOT in Stamod data group "BOTTom GEOMetry FILE" (for IBOT3D = 1) will fail if the first line of the file is a comment line started with the ' sign. The first line of the bottom topography file must be the descriptive text string CHBOTT.

There are no restrictions on comment lines after this line.

The workaround is therefore to move the descriptive string CHBOTT  up as the first line in the file.

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Error message "invalid thread access"

Version: 3.5.0

If the error message "org.exclipse.swt.SWTException: Invalid thread access" occurs in Sima in a pop-up window with many empty error icons (white X in red dot), the reason is probably the following:

There is a bug in Sima ver. 3.5.0., caused by missing mapping from user defined names to short names (8 characters) used by Riflex.

If you use only names having 8 characters or less, the error message will not be given.  It should not affect the results from Simo and Riflex.

The error is fixed in version 3.6.0.

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Error when creating SIMO sys-file

If you have just installed SIMA and you are receiving an error message ("Error when creating SIMO sys-file") when trying to run an analysis, please check the following:

Ensure that SIMO (and RIFLEX if running a coupled analysis) is installed.

Ensure you have the latest version of Application Version Manager installed. You can download the latest version by going to the Software Downloads section on the Customer Portal. After installation (or if you already have the latest version of Application Version Manager installed), open Application Version Manager and click on the Refresh button. This will refresh the application list and ensure that SIMO and RIFLEX are found by SIMA. Start SIMA again and rerun your analysis.

As a sidenote, if you are performing coupled case, you will need to ensure you are running the same version of SIMO and RIFLEX.

  • For Simo version 3.6 they have to be version 4.14. or higher.
  • For Simo version 3.5 they have to be version 4.12. or higher.
  • For Simo version 3.4 they have to be version 4.10. or higher.
  • For Simo version 3.3 they have to be version 4.8 or higher.

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External Wind Turbine Controller in Java

The attached zip file ExternalJavaController.zip contains three files to give you some guidelines on how to set up the wind turbine controller.

  • The file ExternalController.pdf is a guide document on how to set up and use a Java external controller.
  • The file WindTurbineControllerjava.txt should be renamed to WindTurbineControllerjava.jar, as this is Java code.
  • The file ControlInput.txt is the input to the controller.

Please see the attached document ExternalJavaController.

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For diffracted waves, 0-360 degrees must be included if used in a Simo analysis (Sima/DeepC)

If the users want to use diffracted wave in Sima/DeepC (e.g. for time-domain airgap analysis), they need to include the entire direction range, 0 to 360 degrees. 

Symmetry properties cannot be used for diffracted waves.

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How to consider Yaw controller

Yaw controller is available in Sima since version 4.2-00 for both using internal controller and using external controller. The users need to create a Yaw line to emulate the yaw bearing, it must be an extension or part of the tower.

Please see How to consider Yaw controller in Sima for details.

Further references:

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How to define the parking condition

There is no direct option to define the parking condition in Sima. The users could define the parking condition by the external controller file, or through the Wind turbine faults in Dynamic calculation. Shown in the figure below, in Shutdown tab, the blade pitch is controlled by Maximum Pitch Angle, Rate gives the pitch rate. Fault Option should select Total loss of generator torque. For the idling condition, choose No mechanical brake; for the standstill condition, choose Mechanical brake with a proper Linear Torque Damping Coefficient to make sure the rotor will not rotate.

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How to do decay tests

The focus of the decay tests is how to define the initial offset in the dynamic analysis. There are two methods in Sima: one is using Specified force or Specified moment to move the body; the other one is using Static offset increments in Parameter variation to define the offset in Static calculation.

  1. Specified force or Specified moment Apply a Specified force for translation or a Specified moment for rotation on the floater body. The figure below, quoted from the tutorial in Sima example INO WINDMOOR semi 12 MW, shows how a ramp force is applied first, followed by a constant force. After a short duration, the system gets stable, the force is removed. An example can be found in Sima example INO WINDMOOR semi 12 MW.

  1. Static offset increments In Sima, Static offset increments is selected in tab Parameter variation of Static calculation. It will be calculated after the load types defined in the tab Loading sequence. It can be used to define the initial offset in both translation and rotation modes.

To be noted, the supernode for offset should keep fixed during Static calculation, and be released in Dynamic calculation. An example can be found in the attachment ExampleDecayTest.stask.

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How to fix a memory error when running a Sima analysis?

If the memory settings in Sima are set so either Simo or Riflex has no memory left, Sima will not run any analysis.

Especially for coupled analyses, it is important to ensure Riflex has enough memory set. If the SIMO memory is set equal or higher than RIFLEX STAMOD memory or RIFLEX DYNMOD memory, SIMA will not let the user run the analysis and the Run buttons in every condition of the workspace are set to inactive (greyed out). No warnings or error messages are given.

The recommended memory settings (for running large models) are:

RIFLEX STAMOD Memory = 800

RIFLEX DYNMOD Memory = 800

SIMO Memory = 100

The procedure for setting environmental variables is described in the RIFLEX FAQ sections "SIMO & RIFLEX: Riflex and Simo memory setting", or in the attached file.

SIMA should be restarted after setting the environment variables.

Please see the attached document How to set environment variables for Riflex and Simo.

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How to transfer Sima outputs to Wasim

How to transfer Sima outputs to Wasim?

If the users would like to read the Sima outputs into Wasim for a time domain hydrodynamic analysis, they need to select storing the results in Dynamic Calculation – Storage – WASIM export.

The new version Sima v4.2-00 changes the formats of WASIM export compared with previous versions. This change is to align with the updates in Wasim v6.3-10. Now Sima could output the following files in Wasim required formats and store the files in the Dyanmic results folder.

Incoming wave:

  • sima.wave: The incoming wave elevation at global origin.
  • sima.wavecomponents: Export as wave components.

Body motion:

  • sima.motion: Motions (position, velocity and acceleration), 6 DoF.

External force and moments on body:

  • sima.force: The time series of forces and moments, 6 DoF.

There are two kinds of wave files, one is wave elevation time series, the other is described as wave components. Both can be read by Wasim, the user should choose one of them. Details about the file formats can be seen in the Wasim user manual, the commands for Wasim extra parameters can also be found.

  • 2.18.2 Prescribed wave components: New file Format
  • 2.18.4 Prescribed wave elevation
  • 2.19.2 Prescribed motions from Sima      
  • 2.20.1 Prescribed auxiliary forces and moments

SIMA Export files should be defined in Wasim Activity – Execution Directives – Extra parameters.

Regarding the prescribed waves, the user could use the commands for either wave components or wave elevation time series. Two templates can be found in the attachments:

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How to use 3D seabed in a coupled analysis

3D seabed (sea bottom) is allowed only for Riflex analyses.

If the user needs to run a coupled Simo/Riflex analysis with 3D seabed in Sima, she must add a Flat Bottom in the Location folder (in the Navigator) in addition to the Regular 3D Bottom which is created in Riflex.

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How to use Fibre rope model

Fibre rope model is now available in Sima for both Simo task and Riflex task. Fibre rope model is based on the SYROPE model*. In Fibre rope model, there are three different curves: Original curve, Original Working curve and Working curve. Dynamic stiffness coefficients A and B are also required. The data are all obtained from the manufacturer.

See the attached document for more details: How to use Fibre rope model in Sima

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How to visualize models generated by Sesam-GeniE?

Follow the below steps to visualise models generated by Sesam-GeniE:

  • Open a model in GeniE.
  • Choose "File | Save Graphics As" and save file as a ply-file or obj-file.
  • Open Sima, read in a test case.
  • Expand "Model | Bodies" folder. Right click on a body, then choose the "Assign Body Geometry" option and locate the file generated in step 2. Open the file.

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Imported restoring matrix from Wadam G1.SIF file into SIMA (Sima/Wadam)

Imported restoring matrix from Wadam G1.SIF file into SIMA

Importing a Wadam G1.SIF file into SIMA, the imported restoring matrix contains only the geometry contribution of gravity and buoyancy as described in the user manual of Wadam(see below).

Whatever additional restoring components are added in HydroD, e.g. additional restoring matrix, partially filled compartments, anchor elements or TLP elements, the additional restoring components are NOT imported into SIMA.

SIMA users should manually add additional restoring matrix in SIMA if they had additional restoring matrix or partially filled compartments in HydroD. Mooring lines should be added in SIMA modelling in case that anchor elements or TLP elements were included in HydroD.

It is recommended to compare the restoring matrix and the actual restoring coefficients printed in WADAM1.LIS file(ch.2.7)

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No RIFLEX or SIMO runtime found

If you have just installed SIMA and you are receiving an error message ("NativeApps must have 'arch' property set") when trying to run an analysis, please check the following:

Go to Window -> Preferences and check for any messages under SIMO and RIFLEX.

If you see a message "No SIMO runtime found!" and/or "No RIFLEX runtime found!" then please follow the below steps:

  • Ensure you have the latest version of Application Version Manager installed. You can download the latest version by going to the Software Downloads section on the Customer Portal.
  • After installation (or if you already have the latest version of Application Version Manager installed), open Application Version Manager and click on the Refresh button. This will refresh the application list and ensure that SIMO and RIFLEX are found by SIMA.
  • Start SIMA again and rerun your analysis.

As a sidenote, if you are performing coupled case, you will need to ensure you are running the same version of SIMO and RIFLEX.

I.e. for verion 1.0 and 1.6 they will both need to be version 4.0-08 or higher

For Simo version 2.0 they have to be version 4.2-00 or higher.

For Simo version 3.1 they have to be version 4.4-00 or higher.

For Simo version 3.3 they have to be version 4.8-00 or higher.

For Simo version 3.4 they have to be version 4.10.

For Simo version 3.5 they have to be version 4.12.

For Simo version 3.6 they have to be version 4.14.

For Simo version 3.7 they have to be version 4.16.

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Post-processing to obtain acceleration including gravity component

In order to calculate accelerations at any point of a body, one should create a post-processor by using 'Transform point' and 'Differentiation'. On top of that, if one wants to find accelerations including gravitational acceleration, one should add gravity components to the accelerations as shown in the attached document. A Sima post-processor example is attached as well. 

In the example, one can input coordinates of interest in 'Transform point'. Note that the units of two signals connected to 'Add' operator should be the same.

Please see the attached document acceleration.

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Prescribed motion using text file (SIMO)

In SIMO, we can apply prescribed motion from a text file to any bodies. Please see the example procedure below:

  • Change the “Type” to “Prescribed”, change the “Prescribed position” to “Read from file”, and specify the “Position File Name” to point to the file containing the prescribed motion time series. This setup is already completed in the attached stask file.

The format of the file can be found in SIMA documentation “SIMO / Using SIMO in SIMA / Modelling Components / SIMO Body / 2.4.1. Positions Read from File”. (URL: https://sima.sintef.no/doc/4.6.0/simo/sima/context/SIMOBody.html#PositionFromFile)

  • Run the dynamic analysis, and now you can see that the body is moving according to the prescribed time series in the file. (Pitching motion with 10 degrees amplitude)

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Prescribed seismic motion using text file (RIFLEX)

In RIFLEX, we can apply prescribed motion from a text file to any supernodes using the help of a support vessel. Basically, user should do three things to apply prescribed motion:

  • Create a support vessel.
  • Set the supernode’s constraint to “Fixed or prescribed” pointing to the support vessel.
  • Change the dynamic calculation parameter’s support vessel motions.

Please see the example procedure on how to apply a seismic motion to supernodes on the seabed:

  • Download SeismicTLP.stask. and import it into SIMA workspace.
  • See that a support vessel “SupportVessel_Base” is already defined. To add a new support vessel into another model, right click the “Model” folder and select “New → Support Vessel”.

  • Double click any supernodes on the seabed, for example “node12”. Change the “Constraint” to “Fixed or Prescribed” and change the “Support Vessel” to “SupportVessel_Base”. This setup is already completed in the attached stask file for all the supernodes on the seabed.

  • Double click “Model/Calculation Parameters/Dynamic Calculation” to open the dynamic calculation parameters. Go to “Irreg. Analysis” tab and go to “Support Vessel Motions” section. Change the “Irregular motion” to “Forced irregular motions from file” and set the table as below to set which support vessel to apply the prescribed motion to and the motion file parameters. Again, this setup is already completed in the attached stask file.

The format of the file is a space delimited columns of time and 6-DOF motion time series. The column number is set by the user in the above table. Please check the SeismicDisp.txt in the “_resources” folder of the workspace.

  • Run the dynamic analysis, and now you can see that the supernodes on the seabed are moving according to the prescribed time series in the text file.

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Response model curves are available in the 'Plots' workbook

Users may be interested in getting the response curves used in the calculation, i.e. something like figures 4-1 and 4-4 in the DNV-RP-F105.

The response model is presented in the ‘Plots’ sheet with the columns S through V. The curves can reproduce the response model used during the calculations. But the results shown have been multiplied by 10 and 4.

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Time step and cut factor for retardation functions in SIMA

This article explains more about the two input data for retardation functions:

Time step

  • Time step affects the resolution of the retardation functions.
  • Times step also affects the Nyqueist frequency(fnyq=1/2/dt).
  • If time step is too small, fnyq  becomes too larger than the maximum wave frequency defined in HydroD. Then, Sima tries to interpolate in between the fnyq and the maximum wave frequency defined in HydroD, sometimes interpolation could result in poor retardation functions.
  • To avoid such problems,
  • The time step should not be too small(e.g. 0.01 s). The default time step(0.5s) could be ok, and one can decrease down to 0.1 sec.
  • The maximum wave frequency in HydroD should be defined large to show that the potential damping from Wadam can show decreasing tendency.

Cut factor

  • Cut factor determines the length(cut-off length or cut-off period) of retardation functions by comparing the maximum value of retardation functions with the given cut factor.
  • SIMA finds the maximum value of retardation function, Amax = max(abs(R(tau)))
  • SIMA searches the largest tau with abs(R(tau)), that satisfies abs(R(tau)) < Amax /Cut factor
  • Therefore, if the cut factor is larger, the cut-off length will be larger.

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Time step and time increment

“Time step” is how often the forces, velocities, accelerations and new positions of the bodies are computed.

“Time increment” is how often wave elevation, particle velocity, particle acceleration etc., and wind velocity are updated when the time series for waves and wind are generated and stored.

“Time increment” is also how often results for time series are written to file during the simulation.

During the simulation, the wave forces are interpolated in time if the “Time increment” is larger than the “Time step”. “Time increment” should be a multiple of the “Time series”.

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