Question about NREL 5MW barge platform dynamics and Tower TMD

Wind & Water Computer-Aided Engineering Software Tools
1

Dear All

I have a question about the interaction between the tower TMD and platform dynamics for NREL 5MW offshore barge wind turbine. I am wondering if the tower TMD (X and Y directions both enabled)motions will influence all the 6 platform DOFs (surge, sway, heave, yaw, pitch, roll) or only influence the platform pitch, roll, yaw and heave? I am not sure if FAST assumes the contact surface between the tower TMD mass and the platform is frictionless. If it is frictionless, I think the TMD mass motions will not influence the surge and sway DOFs if there is no friction between them. The influence caused on platform pitch, roll, yaw, and heave is due to the gravity of the TMD mass, am I right? Thank you!

Best

Xing Wei

2

Dear Xing,

Because the TMDs move horizontally (and a bit vertically if the platform is tilted and/or tower is deflected), I would guess that the TMDs would be most influential to surge, sway, and pitch and roll, and less influential on heave and yaw. The TMDs have influence due to their mass, stiffness, and damping.

Best regards,