Hi all,
I’m writing because I’m using NREL’s SOWFA coupled with OpenFAST to simulate via LES a FOWT subject to prescribed sinusoidal surge and sway motions. At this stage I’m more interested in seeing the effect these motions have on the wake dynamics and power performance rather than on the wind turbine structure and aerodynamic loads, although I don’t rule out analyzing them in the future. Furthermore, the characteristics of the substructure or even its mere presence are not of my interest. I’m only interested in having a translation of the whole machine (rotor, nacelle and tower).
Based on the following threads: Regarding Seismic Load by FAST code and https://forums.nrel.gov/t/how-to-input-platform-motions-time-series-and-observe-the-responses/2026, it seems that the Seismic module may be used to specify a platform motion time series independently in all three axes. However, it’s mentioned by @Danupon.Subanapong in the latter that this module cannot be coupled with OpenFAST. Is this true? I’ve read in this thread that @Ricardo.Amaral has used the ExtPtfm module to prescribe such motions (see https://forums.nrel.gov/t/rigid-wind-turbine-with-harmonic-motions/685/13?u=juan.monmeneu). However, it seems that the operation of this module is different.
If I’m not mistaken, one has to perform a time-domain simulation of the isolated substructure using an external program to produce a reduced model. The results of this simulation are written to a file containing the system matrices and the time series of the interface reduced input loads, which are then used by ExtPtfm to perform a simulation in time using this reduced model. Finally, OpenFAST outputs times series of modal loads and displacements at the interface point (correct me if I’m wrong).
What would you recommend I do to prescribe surge and sway motions to the whole structure in OpenFAST without having to perform additional simulations for the substructure?
Thanks in advance
Kind regards,
Juan