Can the FAST be simplified?

Dear Dr. Jason.

I’m sorry to have troubled you.
Because my knowledge is limited, based on the Kane equation on the whole system modeling process, I simplified a lot。
First, there are only surge, pitch and heave DOF of foundation.
About the blade, I have FlapDOF1, FlapDOF2 and EdgeDOF.
About the tower, I have TwFADOF1, TwFADOF2, TwSSDOF1 and TwSSDOF1.
For the blade speed， I set it to a fixed value such as 1.2671rad/s, also 12.1rpm.
I didn’t have other freedom such as pitch speed or Drivetrain DOF for limited time and limited knowledge.
So can the FAST be simplified to be probably close to my model?

Another problems is that why the TOWER FORE-AFT MODE SHAPES and TOWER SIDE-TO-SIDE MODE SHAPES is different。

Thanks for your help.
Best Regards

Dear Yuanzhao,

I’m not really sure I understand your question, but in FAST you can enable/disable degrees of freedom (DOFs) as you describe.

The tower fore-aft and side-to-side mode shapes are different–even when the tower is a cylindrical steel structure–because the boundary conditions are different in the fore-aft and side-to-side directions…either from the inertia/stiffness of the platform or from the inertia of tower tower-top.

I hope that helps.

Best regards,

Dear Dr. Jason.

Thank you for your help.
I reduced some degrees of freedom and obtain some results.
The hydrodynamic and aerodynamic in FAST are coupled that the motion of floating foundation will influence the aerodynamic load,
and the equations are solved iteratively in time step.
I want to know if the aerodynamic and hydrodynamic can be calculated respectly,
so I can compare the effect of coupling on the results.

Thanks for your help.
Best Regards

Dear Yoanzhao,

I see a few options. You could compare results with and without:

• incident waves enabled in HydroDyn i.e. with waves or with still water
• platform structural DOFs enabled i.e. with a floating platform or with a rigid foundation
• aerodynamic loads i.e. with both wind and wave loads or with only wave loads

I hope that helps.

Best regards,