Dear Jason,
Thank you very much for the answer and for the article. Your article explained me a lot about pretwist beam and made me find the axis orientation error in my model.
I checked the equation (21) of your article and noticed that it is in the local coordinate. When I transformed the whole equation to the global coordinate, it equals the equation I used (in my last post). The term that adds the influence of the twist on the beam is the second area product of inertia, it was exactly in that term where the error was. So you hit it right when you said that my model was not represented the coupling correctly. Many thanks for your guidance.
Now the only difference between my response and the FAST response is in the tower displacement in the plane of rotation. I am attaching an image with the answers. In the following forum topic (Why do tower top side-to-side deflections have non-zero average? - #4 by Jason.Jonkman) you comment on the application of torque at the top of the tower. I think that this error in the response occurs by the lack of the addition of this torque on the top of the tower. I did not add the rotor torque on my model, I just considered the forces. Am I right in suspecting the lack of torque at the top of the tower? How does FAST add that torque to the tower, considering only the following DOFs (FlapDOF1; EdgeDOF1; TwFADOF1; TwSSDOF1)?
Again, thank you for the great collaboration.
Best Regards
Guilherme Terceiro
