WECSim Fexc Time-domain Calculation

Wind & Water Computer-Aided Engineering Software Tools
1

Hello All,

From what I understand, WECSim pre-computes the excitation forces during the initialization phase based on the wave elevation. I have been able to successfully reproduce Fexc calculations in the frequency domain by relating the spectra of the wave elevation to the frequency response function (FRF) from WAMIT. But this requires knowledge of future wave inputs. For wave elevation measurements that have to occur during real-time (i.e. sensory data), do you know how I may compute these Fexc forces? I have been having some trouble with the time-domain convolution, and was wondering if I could get any insight into how that may be calculated. Thanks!

Best,

Elaine

2

Dear @Elaine.Liu,

I can’t speak about WECSim specifically, but in general you can solve this issue be a time-shifting method, which in practice would require some estimation of the future wave elevation (e.g., with a nearby buoy and knowledge of wave dispersion relationships). This is summarized in Annex A of our IOWTC 2018 paper where we discuss full-system linearization for floating offshore wind turbines in OpenFAST, including a state-space realization of the wave-excitation loads: https://docs.nrel.gov/docs/fy19osti/71865.pdf.

Best regards,