We study processes that occur during impact of a breaking wave on a vertical wall, and the resulting overtopping event, based on numerical simulations using a multiple-fluid Navier-Stokes VOF model (airwater). The latter allows to track high interface deformations during the breaking and impact. Both impact process and overtopping event are studied as a function of the relative distance of the vertical wall from the breaking point (defined as the location where a vertical tangent appears on the free surface). We study hydrodynamic forces and pressure peaks on the vertical wall, with the temporal and spatial discretizations. Expectedly, a finer discretization leads to a better description of the pressure peak on the wall, which can increase the total force applied to the wall by up to a factor 6. Some studies indicated that the critical case, yielding maximum volumetric rate, is for a wall placed at the breaking point. In the application studied here, the maximum overtopped volume of water occurs for a distance to breaking equal to 1.69 times the breaking wave height.
Improving the design of coastal defenses requires in-depth understanding of wave impact and overtopping phenomena. Various time scales are involved in these phenomena, which must be considered in work aimed at achieving such understanding. Many studies, more related to engineering applications, have focused on the larger time scales, by considering the cumulative effects of many waves, for instance on the total overtopping volume. However, individual wave and smaller time scales, must be considered in order to better understand the detailed flow that occurs during individual impact events. In this respect, the experiments of Schmidt et al. (1992) illustrated the effect of breaking point location has on the impact intensity on a vertical wall.
