Damping Tower Motions with user-defined

Wind & Water Computer-Aided Engineering Software Tools
1

Hello all,

is it possible to include a damper in the top part of the tower?
What I have in mind:
It needs to have the nacelle-motions as input, then the damping is calculated with a user-defined function and the damped motions are given back to FAST.
I don’t want to recompile the program and it would be nice when it is possible to use FAST 8.16.
And, unfortunately there is no ADAMS-license available to me.

Best regards,

Simon

2

Dear Simon,

From what you describe, the TMD submodule of the ServoDyn module of FAST v8 should suit your needs. The TMD submodule is a standard feature of FAST v8.16, with documentation available here: nwtc.nrel.gov/TMD.

Best regards,

3

Dear Jason,

yes I saw that there is this module. Is it capable of modeling nonlinear damping and strings? In the default TMD input file I haven’t found an option to include a nonlinear equation.

Thank you for your great help all the time!

Best regards,

Simon

4

Dear Simon,

In the latest release of the TMD submodule in FAST v8.15 and newer, there is an option for a nonlinear spring-force table, among other features (although I don’t think the TMD documentation was updated to reflect that yet). If the exact spring/damper features you’re looking for aren’t available, you’ll have to update the source code accordingly.

Best regards,

5

Dear Jason,

I know that till now the TMD-Modul has to be deactivated for linearization in FAST v8.15 and v8.16,
but when we assume that FAST would be capable to linearize with activated TMD-Modul with TMD_DOF_MODE =2 (Omni-Directional), how would the Eigensolution look like?
Would there be one (because only one more mode is specified) additional mode or two (because the damper acts in a plane) and if only one how could i interpret such an mode?
Are there modes that are Omni-directional?

I hope you understand my questions.

Best regards,

Simon

6

Dear Simon,

The omni-directional TMD includes two structural degrees of freedom, so once FAST linearization with TMD is implemented, the eigensolution would result in two additional modes.

I hope that helps.

Best regards,