OC6 Phase Ib: Validation of the CFD predictions of difference-frequency wave excitation on a FOWT semisubmersible

During the previous OC511 project, state-of-the-art mid-fidelity engineering tools for floating wind systems were found to consistently underpredict nonlinear, low-frequency responses of semisubmersible offshore platforms, leading substantial errors in structural loads because surge and pitch resonance. To examine this underprediction, a coordinated investigation with computational fluid dynamics (CFD) simulations model-basin experiments was carried out. Both investigations involved fixed simplified OC5-DeepCwind bichromatic waves. The wave excitations—especially difference-frequency excitation—on structure from CFD compared experimental measurements validation, uncertainty analyses both results. Further, excitations on each column measured separately experiment, allowing validation results be done per-column basis. Overall, predictions agree measurements, suggesting solutions can used as reference tuning improving engineering-level provide means better understand underprediction at low frequencies.