Sway Rocking Model

I am studying on the seismic responses of the onshore wind turbine. I am trying to use FAST v.7 to model a gravity foundation wind turbine. I use SR model. I have following questions

  1. According to Seismic Loading for FAST report in 2011, it stated that in FAST v.7 it is assumed that the turbine base does not rotate about any of three axes. So, it means that I need to modify the code in order to create SR model in FAST v.7. Am I right?
  2. I would like to consider higher vibration modes in FAST v.7. How can I do that? I saw that FAST can input the tower mode shape up to the 2nd tower mode shapes.The reason is that I am studying on the effect of the higher tower vibration modes on the shear response at the foundation.
    Best Regards,
    Danupon Subanapong

Dear Danupon,

Your understanding is correct.

The Seismic module of FAST v7 is limited to excitation of the translational surge, sway, and heave modes of the platform/tower base. You’ll need to modify the source code if you wish to add excitation or coupling of the rotational degrees of freedom (DOFs).

The structural module of FAST v7 is limited to two fore-aft and two side-to-side bending mode DOFs of the tower. You would have to modify the source code if you need additional modes or other tower DOFs such as torsion, shear, or axial deformation.

Best regards,

Dear Jason
Thank you so much for your reply