Dear Jens,
I gather from your question that you are modeling a land-based wind turbine; is that correct? If so, the simplest solution may be to enable the user-specified external platform (ExtPtfm) by setting CompSub = 2 and CompHydro = 0, which is briefly documented here: openfast.readthedocs.io/en/mast … nfast.html.
Best regards,