Riflex

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Different types of motion time series in Sima / Riflex

There are two kinds of motion time series input in Sima / Riflex:

Global positions, Euler sequence Rz-Ry-Rx:

input is the global coordinates of the vessel. The specified rotations are applied in the order z-rotations, y-rotation and finally x-rotation. This order is consistent with SIMO and is suitable for vessels with large yaw motions.

(this corresponds to type POSI in Riflex)

**Global dynamic displacements, Euler sequence Rx-Ry-Rz: **

Input is the vessel displacement relative to the final static position. The specified rotations are applied in the order x-rotations, y-rotation and finally z-rotation. This is consistent with Riflex and is less suitable for large yaw rotations.

(this corresponds to type DYND in Riflex)

The source for vessel motions time series should include information about whether the translations are total coordinates or just the dynamic part and in which order the rotations should be applied.

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Difficulties when running many Riflex analyses from a Windows command ("DOS") window

Users may hvae difficulties when running many Riflex analyses from a Windows command ("DOS") window. It turns out that the problem is due to riflex.bat being called many times with "CALL". This caused the new additions to the PATH variable in each call until PATH was too long and all execution stopped. After updating to 64 bits Java, two folders are added to PATH instead of one in the old 32 bit days. The problem will now occur after fewer analyses.

We therefore recommend calling riflex.bat with "CMD /C"  which will ensure that variables in the calling environment will not be changed.  

We are updating riflex.bat so that PATH is unchanged after it is called.

Improvements

Undo changes to PATH at the end of riflex.bat

When riflex.bat is called with CALL, variables such as PATH will also be changed in the calling environment. Multiple calls to riflex.bat will thus increase the length of the PATH variable, which may lead to errors if it becomes too long.

Calling riflex.bat with "CMD /C" will ensure that variables in the calling environment will not be changed. This is therefore recommended, e.g.:

CMD /C  C:\SINTEF\riflex_simo-4.10.3.BIWR-42-win64\Riflex\bin\riflex.bat i stdin

CMD /C  C:\SINTEF\riflex_simo-4.10.3.BIWR-42-win64\Riflex\bin\riflex.bat s stdin

CMD /C  C:\SINTEF\riflex_simo-4.10.3.BIWR-42-win64\Riflex\bin\riflex.bat d stdin

The PATH variable is now set back to its initial value at the end of riflex.bat.

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Incorrect line stretching for non-linear elasticy (polyeter) lines lying on seabed

For non-linear elasticity  lines lying on the seabed, Mimosa predicts almost zero stretching, which certainly is incorrect.

The reason turns out to be that the non-linear elasticity model is not used for line segments that lie on the seabed. This is a lapse of programming, which we will correct before the next release of Mimosa.

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Modelling a mid-water arch for riser support

In general a mid-water arch like the one in the attached drawing may be modeled in an AR-system in Riflex by modeling the buoy as a pipe and adjusting outer diameter to get correct buoyancy and drag diameter to OD of buoy. Several tethers may be connected to center nodes of pipe, or you may use dummy lines to get correct eccentricity.

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Number of arrays on result files, setting environment variables

Maximum number of arrays on the ifnsta, ifnirr and ifndyn files

The maximum number of arrays on the ifnsta, ifnirr and ifndyn files may be specified using the environment variables RIFLEX_MAXSTA_IFNSTA, RIFLEX_MAXIRR_IFNIRR and RIFLEX_MAXDYN_IFNDYN. The values used are echoed on the _stamod.res or _dynmod.res file.

The minimum size of RIFLEX_MAXSTA_IFNSTA is 2000 and the maximum is 2000000. The default is 20000.

The minimum size of RIFLEX_MAXIRR_IFNIRR is 100 and the maximum is 100000. The default is 2000.

The minimum size of RIFLEX_MAXDYN_IFNDYN is 50000 and the maximum is 2000000. The default is 200000.

The procedure for setting environmental variables is described in the RIFLEX FAQ sections "Setting Environment variables on Windows".

The RIFLEX for Windows utility should be restarted after setting the environment variables.

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Riflex and Simo memory settings

For the case of the memory problems, you must set the environment variable RIFLEX_DYNMOD_MEM to a higher value.

The default is 16, meaning that you have 4 million words available (=16 MB on a 32-bits system). The maximum you can set is 800 (800MB = 200 million words).

You must set the environment variable as a system variable (not a user variable). Please see the attached document for details.

If the above setting still gives you error messages about the memory, please read further down:

In some cases it is SIMO that runs out of memory (even if the error message comes from Riflex). Then you must set the environment variable SIMO_MEM. Its size is defined the same way as RIFLEX_DYNMOD_MEM. Be aware that SIMO_MEM allocates space inside RIFLEX_DYNMOD_MEM, so it cannot be set too large compared to RIFLEX_DYNMOD_MEM.

A typical "max" setting for a system of 2 GB RAM or more will be:

RIFLEX_DYNMOD_MEM = 800 SIMO_MEM = 100

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

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Sloping or inclined seabed in DeepC and Riflex

Specification of an inclined seabed in DeepC is only available for display purpose, i.e. it will not have any impact on the calculation. If you want to run your analysis with a varying water depth you have to manually create the a Riflex seabed file, and then modify Riflex Stamod input file, see the attached example. Instructions is given as comments in the file Read_ExportSystem_bottom_file.js.

Please see the attached document ExportSystem_bottom_file.

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Top Tension Risers (TTR) in DeepC and negative axial tension.

If TTRs (Top Tension Risers) have negative axial tension, i.e. they go into compression, Riflex will fail. Riflex is not capable of handling compressed risers, as this is a  singular numeric solution.

There are two options to avoid this problem:

1: You must reduce the length of the riser to ensure that the axial tension is positive (remember that the weight of the riser will also contribute to compression at the lower end). The length reduction will depend on the weight and axial stiffness.

2: You can model the TTR with two horizontal guide bars to keep the X- and Y-positions of the risers, and provide a spring in the Z-direction to allow flexing in the  Z-direction.

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Unable to locate license file (Simo/Riflex)

When trying to run SIMO or RIFLEX, the license file is not found automatically and a pop up box keeps appearing, prompting the user to enter the location of the license file or license server.

There are several reasons for this error:

  • The user does not have a valid license for SIMO or RIFLEX
  • The environment variable does not point to the correct location. Check the MARINTEK_LICENSE_FILE environment variable.
  • The registry key does not point to the correct location.
  • Check HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\FLEXlm License Manager
  • Check HKEY_CURRENT_USER\Software\FLEXlm License Manager

The value should be C:\Flexlm;2002@localhost 

Note that** C:\Flexlm** is not a valid value as it specifies a file, not the folder. The last \ should be removed.

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