Breaking wave impacts on coastal protections are simulated using a multi-phase 3D CFD (Computational Fluid Dynamics) software, named neptune cfd, focusing on a particular lay-out composed of a plane sloping bottom and a vertical wall with a recurved parapet on top of it. The goal is to assess the capabilities and performances of the solver to simulate the propagation of regular waves over the variable bathymetry (including shoaling and nonlinear effects), the depth-induced breaking process and the interaction of these breaking waves with the vertical wall. We simulate two experiments involving similar geometry of the seabed and vertical wall, performed at two different scales (1:8 for case A and 1:1 for case B), as described in Ravindar et al. (2021). After a description of the CFD solver and its numerical methods, the model is applied to the simulation of the two cases involving extremely high impact pressure peaks at some places of the wall surface. Numerical results are compared with experimental measurements regarding both free surface elevation and pressure on the wall. In general, a good agreement of the simulations with the measurements is obtained for free surface elevation, including the breaking zone. The time history of pressure variations during wave impacts is correctly reproduced. Although the measured maximum impact pressure peaks exhibit some variability among successive wave impacts, the order of magnitude of these maximum peaks is well predicted for case A. For case B, however, the maximum impact pressures are somewhat underestimated by the current simulations, requiring further tests and improvements. This work is a contribution to the benchmark "Comparative Study on Breaking Waves Interactions with Vertical Wall attached with Recurved Parapet in Small and Large Scale" set up for the ISOPE’2022 conference.
Breaking wave impacts on marine and coastal structures is a question of central interest for many applications as extremely high pressure peaks at the wall can occur depending on the characteristics of the breaking wave and the shape of the jet impacting the wall, the dynamics of air entrapment, and the shape of the wall (see e.g. Oumeraci et al., 1993). Such impact issues are encountered with offshore structures in deep, intermediate or finite water depth (e.g. O&G platforms, monopiles or floating structures supporting offshore wind turbines, coastal or harbor breakwaters, vertical quays and seawalls). Breaking wave impact can also occur in LNG tanks in some particular sloshing conditions (e.g. Ibrahim, 2020). The prediction of the peak values of these breaking impact pressures is challenging. Few methods exist based in particular on the analogy with the slamming effect of a body impacting a free surface at rest (e.g. Ravindar et al., 2019). These breaking waves are usually studied experimentally with model scale tests in wave flumes or basins (e.g. Stagonas et al., 2020; Ravindar and Sriram, 2021). This then raises several issues including taking proper account of scale effects, monitoring the generation of the incident wave(s) to create at model scale the targeted situations, measuring with accuracy the dynamics of the pressure evolution, in particular the impact peak which is often both high in magnitude and very short in duration. Specific subsequent signal processing techniques are then needed to analyze the pressure signal, to separate the quasi-static part from the dynamic one induced by the wave impact, etc.
