Undisturbed wave elevation estimation: Correcting for radiation and diffraction effects in measured data near floating wind turbines

A reliable estimation of the undisturbed wave elevation from full-scale measurements is required for model correlation studies for floating offshore structures, but radiation and diffraction effects from the structure itself can decrease the quality of local wave measurements when the floating structure is large compared to the wavelength of the incoming environment. To address this issue, a methodology utilizing a potential flow model is proposed to estimate the undisturbed environmental wave from local measurements in the presence of radiation and diffraction effects from a floating offshore structure. Potential flow theory is a computationally efficient approach for evaluating wave-structure interaction for radiation and diffraction. A scaled model test was performed in a wave tank to test the efficacy of this methodology in three unidirectional irregular wave environments scaled from the design load cases (DLCs) for a barge-type floating offshore wind turbine platform. The experimental campaign enabled the: (1) determination of in which environments radiated and diffracted waves significantly impacted recorded wave elevation, (2) identification of the ideal location to mount wave probes to avoid interference from the structure, and (3) evaluation of the methodology’s ability to determine accurate spectral statistics ($H_s$, $T_p$, shape factor, and total error in the spectrum) and time series wave heights. In an environment where diffraction was significant, the area of total error in the recorded spectrum was reduced by 73 % for the bow probe and by 63 % for the starboard probe. This method will be tested on a field deployed floating offshore wind turbine in the near future.