Natural frequency of Wind Turbine With Jacket Support Structure

Hello everyone
There is a question that I hope someone can help doubts, thank you.
I know how to use FAST to get Substructure’s eigenvalue and know how I use BModes to get Tower and Blade eigenvalue, but I’m curious about how to use FAST or any other software from NREL to get the whole wind turbine system (including Jacket, Tower and RNA) of the natural frequency?

Best regards,
Shao-Hua.Yang

Dear Shao-Hua.Yang,

As discussed several times on this forum, while some linearization functionality has been added to FAST v8, it is not yet possible to linearize a model with SubDyn or HydroDyn enabled for offshore systems in order to derive full system natural frequencies. It may be possible to use white-noise wave excitation to derive the natural frequencies you seek.

Best regards,

Dear Jason
Thank you very much for your reply.Please I have another problem.
http://www.nrel.gov/docs/fy13osti/58093.pdf

After I read this paper, I have two questions,
(1)I used FAST to get the Substructure’s eigenvalue, But I take it with the results of the case 1, found that the fourth frequency is not the sameand very different,What is the reason for the difference?

(2)In the paper of case 2, what code is used to calculate the natural frequency of SubDyn’s Full FEM? How can I do it by myself?

Best regards,
Shao-Hua.Yang

Dear Shao-Hua.Yang,

I get the same FEM Eigenvalues you get when running Test21 in the FAST CertTest. I asked Rick Damiani of NREL about this and this is what he said:

I hope that helps.

Best regards,