Hi,
I have looked through the documentation for OpenFAST and BModes but I am still uncertain on the formation of the ElastoDyn tower input file.
In particular, the mode shape polynomials. I am preparing some code to compute these - currently I am only taking the mass and elastic properties of the tower on its own, solving for the eigenvalues and mode shapes, and normalizing according to OpenFAST convention. This process assumes that the effects of the nacelle and platform are included separately by Elastodyn in the equations of motion. Is this true? Or does the RNA and platform mass/inertia need to be included in the formulation of the normalized mode shapes for the tower input file?
Best,
Ian
Dear @Ian.Ammerman,
The tower mode shapes you specify in ElastoDyn should include the effects of the tower-top and tower-base boundary conditions, including the mass/inertia of the RNA at the tower top and whether the substructure is flexible or floating at the tower base.
Best regards,
Dear Jason,
can I assume, that these effects are already included in the default mode shape coefficients in the ElastoDyn_tower input file. I am simulating the 5MW_Land_DLL_WTurb and i am not sure if i have to further adjust these mode shape coefficients for my simulation.
And my second question would be: what kind of normalized mode shapes are these, what are these mode shapes normalized to? The mass or the maximal displacement? I could not find any info about the default mode shape coefficients and would appreciate any help.
Best regards
Zong
Dear @Zong.Linyang,
Yes, the ElastoDyn input file for the 5MW_Land_DLL_WTurb model is set up with proper tower mode shapes. You shouldn’t need to change these unless you change the distributed tower mass, stiffness, or geometry; the mass / inertia of the RNA; and/or the tower-base boundary conditions.
The mode shapes are normalized so that the tip (tower-top) displacement is unity, which is why the mode shape polynomial coefficients must sum to unity.
Best regards,
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