Undisturbed Wave Elevation Estimation: Correcting Radiated and Diffracted 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 radiated and diffracted effects from the structure itself can decrease the quality of local measurements. 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 radiated and diffracted effects from a floating offshore structure. A scaled model test was performed in a wave tank to test the efficacy of this methodology under design load cases (DLCs) for a barge-type floating offshore wind platform. The experimental campaign enabled the: (1) determination of which environments radiated and diffracted effects 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 correct the wave height time series and associated power spectra. During wave tank testing in an environment where diffraction was significant, the area of total error in the recorded wave spectrum compared to the baseline was reduced by 73% for the bow probe and 63% for the starboard probe. This method is currently planned be tested on the Castine field-scale model testing of VolturnUS Plus in the near future. A similar potential flow based method was then used to identify the ideal mounting locations to place the wave probes for the Castine field-scale model. Potential flow was used to predict the radiated and diffracted response of the model on various sampling locations based on the environmental conditions seen in Castine from the 2014 VolturnUS deployment. The results of these predictions show that placing wave probes outside the direct reflection of waves and the wake of the platform minimizes the diffracted response on the free surface, but that all feasible sampling locations around the platform will still see significant radiated and diffracted effects for typical sea states, and will therefore require the potential flow correction.