OC4-Jacket-OWT

Dear Jason,

I am  simulating the offshore wind turbine of Oc4-jacket, I have some questions for the modal analysis, what is the second frequency of the whole system (including the substructure) of Oc4-jacket? If not, can bmodes calculate the second frequency of the whole system?

Looking forward to your reply and thank you for your kindness!

Best regards,
Zhou.Lin

Dear Zhou.Lin,

According to the OC4 Phase I results (nrel.gov/docs/fy12osti/54124.pdf), the second global bending frequency of the tower + jacket of the OC4-jacket is around 1.2 Hz.

BModes can calculate tower natural frequencies, but the jacket must be simplified in BModes as a tower-base boundary condition involving 6x6 mass and stiffness matrices, which can be derived from the SubDyn summary file (hydro_M = MBBt, hydro_K = KBBt, mooring_K = 0).

I hope that helps.

Best regards,