Question about linearization FAST V7

Good morning,

I have linearized OC4DeepCwind floating wind turbine with FAST V7. Only the pitch platform and GenDof are enabled. I plotted the A matrix coefficients and mean values. I noticed there are some discontinuity. Could you please explain these gaps ?

Attached linearization file without wind disturbance and the two figures with and without disturbance

Thanks in advance,

Best Regards,

NRELOffshrBsline5MW_Floating_SansPerturbation.lin.txt (417 KB)

Dear Salic,

I’m not sure I can speak about specific discontinuities in these matrices, which could be tied to the lack of precision, especially A(3,1), (it looks like you are only outputting 4 digits of precision, which is coarse for linearization output) or to the numerical perturbation technique used to calculate these linearized matrices. In the end, I’m not sure if it matters because normally these matrices are azimuth-averaged anyway.

Please note that it is common to eliminate the generator azimuth state from the linearized model, which would eliminate A(3,2) and A(4,2) from your system. This has been discussed several times on this forum.

I’m also curious with your use of FAST v7 for the OC4-DeepCwind semisubmersible. The hydrodynamics capability of FAST was greatly enhanced in FAST v8 and OpenFAST. I would recommend upgrading to the newest version (OpenFAST v2.5 presently) when modeling this floating offshore wind turbine. I’m also curious if the linearization of this model in OpenFAST would result in the same discontinuities you are referring to.

Bets regards,

Dear Dr. Jonkman,

I am sorry to respond so late to your response I thought I would receive a notification in my emails in case of replies.

I thank you for your answers. I will look at this more precisely.

Regarding the installation of Openfast and its coupling with Matlab\Simulink, it is complicated because it does not work. I have many errors. This is not the subject here and I will try to make do with the documents available on GitHub.

Best regards,


Dear Tom SALIC,

You can set up your account on this forum to receive e-mail notifications in case of replies.

There have been many questions and answers regarding the the MATLAB/Simulink interface on the OpenFAST github issues page. I suggest reviewing the the discussion or posting another question there:

Best regards,