Hello Jason,
I am trying to compare a FAST v7.02 and FAST v8.16. model to ensure they are the same (converted with your matlab functions). Giving turbulent wind (exactly same files) to the two models having the same configurations in the input files, results in differences in the tower base force of ~16% of the tower base force calculated by FAST7, if all components are flexible (except TeetDOF=0). (Same for tower base moment)
Is there any change in the calculation of the tower base moment and force or maybe in the blade moment calculation, that could cause this difference?
I couldn’t really find anything in the ‘ReadMe.pdf’.
Best regards,
Fiona
Dear Fiona,
I would not expect large differences between FAST v7 and FAST v8 unless you’ve enabled functionality that is not available in the other version.
I’m not sure what is causing differences in your case, but I would suggest simplifying the model to debug e.g. by disabling structural DOFs and/or control, and/or simplifying the aerodynamic options.
Best regards,
Dear Jason,
if I have established the following dynamic equations that include the degree-of-freedom responses of the platform, tower, blades, etc. (with these degrees of freedom q defined consistently with OpenFAST),
Can I obtain responses such as the Tower base moment solely from the time histories of these degree-of-freedom responses?
For OpenFAST outputs like TwrBsMxt (tower base roll moment), are these structural loads calculated based on the system’s degree-of-freedom motion responses? If so, could you please explain the calculation procedure?
Thank you again for your reply and help.
Best regards,
Dear @Yingxin.Lv,
Yes, you can calculate the tower-base loads (and other loads) from the states after solving the equations of motion, but the calculation is not straightforward. To calculate the tower-base loads, ElastoDyn uses a load-summation procedure as summarized in the following forum topic: Tower Base loads. The details are explained in the ElastoDyn theory documentation on readthedocs, specifically the FASTLoads.doc document: 4.9. ElastoDyn Users Guide and Theory Manual — OpenFAST v4.1.2 documentation.
This is in contrast to a displacement-based approach, e.g., as discussed in the following forum topic: Root moment of blades verification from mode shape function.
Best regards,
Dear Jason.Jonkman
I would like to thank you for your response. Your insights have clarified my confusion, and I am grateful for your guidance.
Best regards,
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