Moordyn coupled with MATLAB

Wind & Water Computer-Aided Engineering Software Tools
1

Dear @Matthew.Hall,

Hope you are doing well. I have some questions regarding MoorDyn module.

  • When i run OpenFast, i notice that fairlead tensions converged to 1% after 24 seconds. However, when i couple MoorDyn with MATLAB, and for the same position of the platform at t=0, the fairlead tensions converged to 1% after 16 seconds. Could you please explain to me why there is this difference in convergence knowing that, i am using the same input file (same parameters) ?

  • Does MoorDyn in OpenFast takes any other parameter than the platform position ? In fact, for the same platform position, OpenFast gives tension in mooring lines different for those given by MoorDyn when coupled with MATLAB. The following figure shows the fairlead tension obtained when coupling MATLAB with MoorDyn:

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The following figure shows the fairlead tension obtained from OpenFast for surge equals 5 m at t=0:

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  • I read in MoorDyn user manual that it is possible to get the net forces on each connection (fairlead) like “con3fX” . I have tried in MATLAB the following command:

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It gives me the following error:

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Could you please tell me how should i write the syntax in MATLAB in order to tell MoorDyn to give me the net forces at each fairlead ?

Best Regards,

Riad

2

Hi Riad,

I can’t give specific answers without knowing which versions of MoorDyn you’re using and what settings you’re using in the input files for each. That being said, differences during the initialization process are not surprising–the different versions do not necessarily have the same capabilities for catenary profiles, and they may also look at different numbers of tensions when assessing convergence. We have mainly focused on ensuring consistent dynamic results when comparing between versions.

I don’t have Matlab and haven’t thought about the Matlab coupling in a while. Your best bet is to look at whatever documentation, comments, and source code pertain to the version you’re using. I believe recent contributions from external developers may have added more support for coupling from Matlab, but I’m not familiar with the details. In general though, you should look at the MoorDyn header file that Matlab is loading, and only try to call functions that are listed in the header file. The error you’re getting makes me think that the function you’re trying to call doesn’t existing in the header file.

Best,
Matt