TMD Parameter Configuration

[WS991106]

Dear @jjonkman，

I want to add a TMD as a passive structural control in the nacelle of a semi-submersible floating wind turbine, considering only the front and rear degrees of freedom, where can I find the optimal values for the TMD's mass, elastic stiffness, damping, and range of motion parameters?

[jjonkman]

Dear @WS991106,

I'm not aware that NREL has developed guidance on designing TMDs for floating offshore wind turbines, but I'm sure you can find general guidance on TMD design in the literature or vibration textbooks. You could also check out the references listed in the online documentation of the Structural Control (StC) submodel of ServoDyn on readthedocs: https://openfast.readthedocs.io/en/main/source/user/servodyn-stc/zrefs.html.

FYI: Given that the StC location is specified relative to the origin of the body you are placing the TMD, if presumably you have selected a nacelle-based StC in ServoDyn (NumNStC = 1), a setting of StC_P_Z = 75 m seems far too high, given that this input is relative to the yaw bearing for a nacelle-based TMD (the input would make more sense if you've selected a tower-based StC, NumTStC = 1 in ServoDyn).

Best regards,

[WS991106]

Dear @jjonkman ，

In the references you provided, TMD-based passive structural control is not specific to semi-submersible turbines, it's basically all about barge and tension leg types. If I want to add TMD to the nacelle of a semi-submersible floating wind turbine, what should StC_P_Z be set to?

[jjonkman]

The StC reference list is not exhaustive, but I'm sure you can find more in the literature.

I would expect StC_P_Z to be no more than a meter or two for a nacelle-based TMD.

Best regards,

[WS991106]

Dear @jjonkman ，

I would like to know how to get the power spectral density of the platform degrees of freedom? Can I get it directly from Mlife or McCrunch?

[jjonkman]

Dear @WS991106,

MCrunch can compute and plot the power spectral density (PSD) of a given time series, but MLife does not.

You can also compute a PSD through a simple script based on FFTs, e.g., see the MATLAB script Jason_PSD.m in the following topic on our forum: https://forums.nrel.gov/t/user-defined-spectrum-from-routine-userwavespctrm-in-hydrodyn/1988.

Best regards,

[WS991106]

Dear @jjonkman ，

How can I download MCrunch please? And where can I find the instructions for using it?

[jjonkman]

Dear @WS991106,

You can find MCrunch here: https://www.nrel.gov/wind/nwtc/mcrunch.

Note, however, that this archive is not currently maintained, given NREL's preference to Python-based post-processors over MATLAB-based post-processors these days.

Best regards,

[WS991106]

Dear @jjonkman ，

My data sampling time is 0.0125s, and there are 40,000 sampling points, what values should I set for df, N, CreatePlot and Binlen in the code above?
The image below shows the parameters I set, but the program reports errors

[jjonkman]

Dear @WS991106,

I agree with your settings of df, N, CreatePlot, and BinLen, but I'm not sure what you error is in English.

Best regards,