Higher frequency in tower top response

Wind & Water Structural Analysis
1

Hello everyone,
I am modelling a monopile-based version of the IEA-15MW wind turbine using openfast. I have turned off all the foundation degrees of freedom and the structure is subjected to a range of turbulent wind scenarios with varying mean wind speed, wind shear and turbulence intensity. I have attached the plots for tower-top fore-aft deflection (TwrTpTDxi) and fft of the response. I expected the tower fore-aft deformations to be significantly damped and have a much smoother response, however, the obtained response seems to have significant oscillations at high frequencies.

Is this behaviour expected or could there be some mistake in my simulation setup?

Thanks,
Shubham

TwrTpTDxi_response
TwrTpTDxi_response1680×925 230 KB

TwrTpTDxi_response_fft
TwrTpTDxi_response_fft1680×925 116 KB

2

Dear @Shubham.Baisthakur,

I’m not fully sure what you mean when you say that you “turned off all the foundation degrees of freedom”, but nevertheless, I guess I’m not too surprised by your results. I would expect higher aerodynamic damping with higher mean wind speeds below rated and I would expect higher excitation with higher levels of turbulence (your results have a combination of both).

Best regards,

3

Hello @Jason.Jonkman,
I meant to say I have set all three translation and rotational degrees of freedom to false so that they do not contribute to the tower-top deformation.

Thanks,
Shubham