Modelling irregular nonlinear waves: potential flow and volume-of-fluid comparison with experiment

Real ocean wave conditions are irregular and often highly nonlinear, frequently involving wave breaking. As such, numerical methods to recreate these conditions are critical for the de-risking of offshore structures and devices installed in these environments. There are a range of numerical tools available, with varying fidelity and associated computational expense: from potential flow models to two-phase computational fluid dynamics (CFD) simulations able to resolve breaking physics. Here we present comparisons between the fully nonlinear potential flow model OceanWave3D, and the finite volume OpenFOAM solver with volume-of-fluid to capture the air-water interface, for the recreation of irregular wave conditions. A series of eleven well-defined unidirectional irregular conditions, including breaking conditions, are conducted in the FloWave Ocean Energy Research Facility, and equivalent wave generation inputs are provided to both OceanWave3D and OpenFOAM. Statistical and spectral comparisons demonstrate that both models reproduce surface elevations and wave kinematics well, with only OpenFOAM capturing spilling breaking events. OpenFOAM's higher fidelity comes at significantly increased computational cost. The run times are $O$ (mins) for OceanWave3D and $O$ (days) for OpenFOAM and hence it is concluded that the optimal approach depends on the importance of capturing breaking events accurately for the given application, and on the size of domains required.