Verification of 10MW On Shore Linearization with OpenFAST v.2.4.0

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Re: Verification of 10MW On Shore Linearization with OpenFAST v.2.4.0

Postby Jason.Jonkman » Mon Jan 11, 2021 9:51 am

Dear Simone,

OK, thanks for the thorough analysis. Is this a proper summary of your results?:

There are two main concerns:
  • The structural damping of the ED+BD model shows azimuth dependence in the fixed frame of reference (after applying MBC3), particularly for the flapwise mode.
  • The damping obtained after azimuth averaging is not the same as the mean of the azimuthally varying damping.
General observations:
  • ED alone shows the expected behavior.
  • The problems in ED+PD are not influenced by numerical damping (the conclusions are the same with rhoinf = 0 or 1).
  • A precision of "ES17.9E3" is converged (going to a higher precision of "ES20.12E3" does not change the conclusions).
  • The problems are exacerbated when aerodynamics/damping is included.
  • The problems go away when structural damping in BD is eliminated (mu=0).
Because the problem appears to be tied to the structural damping, I would suggest eliminating aerodynamics/aerodynamic damping in further debugging, at least to start.

I would be curious if you see the same azimuth-dependence on damping when linearizing with zero rotational speed (again without aerodynamics/aerodynamic damping).

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
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Re: Verification of 10MW On Shore Linearization with OpenFAST v.2.4.0

Postby Simone.Covre » Tue Jan 12, 2021 4:21 pm

Dear Jason,

Your summary was perfect.

I performed the suggested simulations, in particular I neglected aerodynamics(CompAero=0) and I set RotSpeed=0 rpm, BlPitch(1,2,3)=0 deg, the incoming wind was a steady wind featured by 14 m/s speed. Since RotSpeed=0 rpm I performed 16 different simulation to cover the entire azimuth angles distribution. In BD module both structural and numerical damping were included.

The results are included in the attached .xlsx file and they have same layout of previous files. From the results it is clear that in ED+BD model the damping ratios keep on depending on the azimuth angle and the ones related to azimuth average show same inconsistencies found in previous reply results.

Thanks for your important help.

Simone Covre
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