Wave-Induced Loading Simulation for a Semi-Submersible FOWT Platform Using CFD-SWENSE Coupled Solver

Abstract

Abstract The low-frequency wave-induced loading on semi-submersible floating wind turbines is normally small, but the loading can result in large motions due to resonant responses in surge and pitch. Therefore, one of the most important concerns regarding the numerical simulation of wave-induced loading on floating wind turbines is how to accurately predict the difference-frequency wave-induced loading, especially near the resonance frequencies. The potential flow method based on the Morrison formula cannot consider the fluid viscosity, and thus the numerical accuracy of the prediction of wave-induced loading is generally insufficient, and usually underestimating the highly nonlinear difference-frequency wave loading. Navier-stokes equation based the computational fluid dynamics (CFD) method has shown the merit for improving the numerical prediction of nonlinear wave-induced loading and motions of offshore floating structures, however, the computational cost of the CFD method is too expensive as a higher-fidelity modeling tool, which is not suitable for engineering application at the current stage. This paper aims to establish a CFD-SWENSE (Spectral Wave Explicit Navier-Stokes Equations) coupled solver to solve this problem but maintaining sufficient numerical accuracy. The potential part (the incident waves) is solved with the spectral wave model. The viscous part (the complementary perturbation on the incident waves) is solved with the CFD solver. Based on this potential viscous flow coupled solver, the differential frequency of wave loading of a semi-submersible floating body under the influence of bichromatic waves is investigated. The results show that the computational efficiency of the coupled solver is improved compared with the CFD method, however, the wave-induced loading predicted by the coupled solver is in good agreement with that predicted by the CFD method.