Using SubDyn with NREL 5MW Spar OpenFAST model

Wind & Water Computer-Aided Engineering Software Tools
1

Hi all,
I have a query regarding the NREL 5MW Spar OpenFAST model, titled ‘5MW_OC3Spar_DLL_WTurb_WavesIrr’.
I would like to be able to output results from below the still water level (SWL), such the accelerations, displacements and forces at different locations down along the floating spar structure.

From reading some of the guidance notes, I understand that the SubDyn module of OpenFAST can be used to output the local substructure displacements, velocities and accelerations, and so I was hoping to use it for this purpose. However, I do not see any SubDyn.dat file for the ‘5MW_OC3Spar_DLL_WTurb_WavesIrr’ model and have noticed in the .fst file that the CompSub switch is set to 0 by default, meaning SubDyn is not currently used to compute sub-structural dynamics.
I am not entirely sure where the spars properties are currently being inputted into the model. There is a section called ‘Floating Platform’ in the HydroDyn dat file, but even this contains very few of the spars physical properties and instead seems to call up a WAMIT file from the ’5MW_Baseline/HydroData/Spar’ directory. But I assume even this is only used when computing hydrodynamic loads, and not the sub-structural dynamics which I am looking for.

So, I am wondering is SubDyn only available for use with fixed-bottom structures?
Or is there a SubDyn.dat file available for use with this model? If so, could you share it with me. And if not, is there some other way of working around this issue that would allow me to achieve the requested outputs from the spar structure below the water level?
Any guidance would be greatly appreciated.

Thanks as always, and regards,
Stephen Lynch.

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Dear Stephen,

In the OpenFAST model have referenced, the structure of the spar is modeled as a rigid body in ElastoDyn.

As of OpenFAST v2.6.0 and newer, SubDyn can now be enabled to model floating substructures for the purposes of modeling structural flexibility and member-level loads within the floating substructure. However, we have not yet developed a SubDyn input file for the OC3-Hywind spar or any of the floater examples for the NREL 5-MW baseline turbine. This has been posted as a known issue on the OpenFAST github page: github.com/OpenFAST/r-test/issues/39. All of the full-system floating models with substructure flexibility we’ve tested at NREL to-date contain proprietary information that cannot be shared publicly.

Best regards,

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Hi Jason,

That’s understood, thanks for your response.

Kind regards,
Stephen Lynch