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!