Simulating OC3 phase II coupled springs in FAST v7

Dear Satish,

Yes, the joint locations and member (beam) properties of the monopile substructure are set within the SubDyn input file. The SubDyn documentation has not yet been ported to OpenFAST’s online readthedocs documentation, but you find the SubDyn documentation associated with FAST v8 (which should apply to OpenFAST v2.4) on my Google drive: drive.google.com/drive/folders/ … sp=sharing.

Best regards,

Dear Jason,

Thanks for your reply.
Does that mean just changing the joints and member properties (increasing the length below the seabed) will be sufficient for apparent fixity model?

And I see somewhere that we should update the mode shape coefficients in elastodyn, Do we need to do this or I might misinterpreted.

Thanks,
Satish J

Dear Satish,

Yes, your understanding of the apparent fixity model is correct.

If the stiffness of the substructure changes in SubDyn, and if you are modeling the tower in ElastoDyn, then yes, ideally you’d change the mode shapes of the tower in ElastoDyn accordingly. This has been discussed several times on this forum. (Of course, if the stiffness change is small, as it may be for an apparent fixity approach, the impact on the mode shapes may be negligible.)

Best regards,