Hi,
I have the data from an original turbine for Tower Mass density, fore-aft and side-side stiffness as well as the tower dimensions. That’s the only data I have.
Is there a way to compute the fore-aft and side-side coefficients from that data.
Best regards,
Karthik
Dear @Karthik.Prakash,
With the data you have, you should be able to compute the cross-sectional mass per unit length and tower fore-aft and side-side bending stiffness (TMassDen, TwFAStif, TwSSStif in the ElastoDyn module of OpenFAST). The only other thing you need to compute the tower mode shapes for ElastoDyn is the tower-top (rotor-nacelle assembly) mass, center of mass, and inertias. For offshore systems, you’d also have to know information about the substructure mass and stiffness.
Best regards,
Many Thanks for the reply @Jason.Jonkman
Is there a way I can calculate or obtain the coefficients for the tower fore-aft and side-side mode shapes with the available data.
Dear @Karthik.Prakash,
Once you obtain the mode shapes of the tower (e.g., using BModes), you could fit a polynomial to the mode shapes to obtain the coefficients (e.g., using ModeShapePolyFitting.xls).
Best regards,
Many Thanks for the response @Jason.Jonkman
I have the tower diameter and thickness as well as the lumped masses, like damper etc.
Is it necessary that those have to be included while making the tower file. Because, while including them and plotting the same, the mass density reduces along the tower length, but with occasionally high spikes due to lumped mass. I am a bit confused whether I should removed the lumped mass or add them as I am not sure if those spikes can affect the solver or calculation.
Best regards,
Karthik
Dear @Karthik.Prakash,
ElastoDyn does not currently support lumped masses placed in the tower, so, to get the correct overall tower mass, you’d have to account for the lumped masses by changing the distributed mass density (TMassDen). This is obviously not ideal, but often works OK.
Alternatively, you could model the tower in SubDyn (by disabling the tower in ElastoDyn and locating the platform reference point at the yaw bearing), which does support lumped masses.
Best regards,
Thanks @Jason.Jonkman
This helps. My plan was to add (sum of all lumped mass/tower height) to base mass density at each tower node.