I am simulating six DOF motion of a semisubmersible FOWT under wind spectrum with mean wind speed 57 m/s, irregular wave and current. The wind turbine is not operating, nacelle yaw is -20 degrees (20 deg clockwise in top view), blades are feathered to 86 degrees.
AeroDyn: WakeMod =0, AfAeroMod=1
ElastoDyn: only six DOF motion enabled
Platform reference point is at COG (0.29 m above SWL)
Below is the list for six DOF, aero forces and hydro forces for measurement (wind+wave+current), OpenFAST (wind+wave+current) and OpenFAST (wind only). I got roll and yaw in opposite signs with measurement. I have trouble to understand how come roll and yaw are negative from OpenFAST given Mx and Mz from aero and hydro are all positive. Is there any other forces that contribute to the six DOF motion?
For my other cases when the wind turbine is in operation, six DOF motion and thrust can be well predicted by OpenFAST, but not for this case, especially for roll and yaw. Any suggestions or comments are greatly appreciated.