ElastoDyn blade and tower structural model

Wind & Water Structural Analysis
1

Dear forum,

within the scope of my masters thesis I am trying to create an openFAST model of my universitys research model scale wind turbine. The turbine has a 60cm tower and a 33cm rotor diameter.
I succesfully implemented all wind turbine parameters into the openFAST model, except for the ElastoDyn structural tower and blade model.
When running the simulation with all DOFs disabled (except the Generator DOF), I am obtaining reasonable results for TSR, cp, cq, ct, rotor/generator speed, etc.
However, as soon as I turn on any blade or tower DOF I am receiving several warnings (see screenshot with FlapDOF1 enabled) and NaNs in my output file. It seems as if my blade displacement would be too large?
I generated the ElastoDyn_Blade and ElastoDyn_Tower files with the QBlade simulation software, in which I modeled the wind turbine prior.

Can you see any mistakes in my ElastoDyn blade and tower (or maybe other) files? Do you have any other hints on how to proceed on debugging or generating my structural blade and tower models?

Please find also attached, all the simulation files.

Kind regards and thanks for any Help!
Jannik
openfast-model-wind-turbine.zip (122 KB)

screenshot.JPG
screenshot.JPG979×887 132 KB

2

Dear Jannik,

I only looked briefly at your input files and output results, but I believe the problem is your time step (DT) is too large for the system frequencies you are resolving. Rules of thumb for selecting the aerodynamic and structural time steps are summarized in the following forum topic: FAST Integrator, step size & precision - #2 by Marshall.Buhl. I haven’t tried to calculate your required structural time step, but for a rotor spinning at 500 rpm (8.33333 Hz), to get 200 azimuth steps per revolution would require a time step of:

DT = 1/(200*8.33333) = 0.0006 s.

Best regards,

3

Dear Jason,

My time step was indeed too large for the high system frequencies, reducing it resolved my issue.

Thanks for your help and quick reply!

Kind regards
Jannik