Energy Dissipation and Nonpotential Effects in Wave Breaking

This paper presents a numerical study of the energy dissipation process in the breaking of focused waves by using a potential flow model and a coupled potential/viscous flow model. An empirical eddy viscosity term is introduced to the fully nonlinear potential (FNP) flow model to account for breaking wave energy dissipation. The FNP model is further coupled with an incompressible two-phase Navier–Stokes (NS) flow solver to generate and propagate focused waves in the domain. Numerical absorbing regions are placed in front of the outlet boundaries to dampen wave reflection. The standalone FNP model and the coupled FNP+NS model are applied to deal with each scenario comparatively. This enables an accurate quantification and comparison of the wave energy loss calculated by the two numerical models. The velocity field is decomposed into the potential component, which is reconstructed from the two-phase calculation of free surface elevation by using the weakly nonlinear wave theory, and the nonpotential rotational component. Detailed analysis of the numerical results shows that (1) wave energy loss is closely related to steepness, (2) mild rotational motion produced by a nonbreaking wave is local in time with a short life span, and (3) strong nonpotential motion triggered by breaking is not local in time but persists in the flow for dozens of or even many more wave periods.