I have a question about the vibration of the wind turbine tower. I use Fast 8 and only enable Tower fore-aft displacement DOF and platform pitch DOF and enable the use of TTMD in X direction.
I set the wind to be 0.001m/s and wave condition to be still water. The initial platform pitch angle is set to 0.1 degrees. In my opinion, the TTMD will damp the tower and platform motion so the final position of the tower and barge-platform will be 0. However, I found the final position of the platform is -0.055 degree and the final position of the tower is -0.02m when I set rotor speed to 0 rpm. The final position of the platform is 0.048 degree and the final position of the tower is 0.0036m when I set rotor speed to 12.1 rpm. I am wondering if this is normal? If it is normal, Is there anything wrong about my settings of just because of the FAST model itself?