Semi-resolved CFD-DEM coupling simulation of wave interaction with submerged permeable breakwaters

Submerged permeable breakwaters are widely used in marine engineering due to their aesthetic and economic advantages. Previous numerical studies have focused on the effect of the breakwaters on wave propagation, with minimal attention paid to wave damage to the breakwaters. In this paper, the non-hydrostatic CFD model is employed to simulate the wave flow and the particle motion is described by the discrete element method (DEM). The CFD-DEM coupling is based on the semi-resolved model, which can theoretically eliminate the limitation on mesh-particle size ratio and make it suitable for simulating the breakwaters composed of polydisperse particles. The hierarchical linked cell method is used to detect the contact between polydisperse particles. The performance of the numerical model is validated by simulating the propagation of a solitary wave over a submerged permeable breakwater using different meshes with mesh-particle size ratios that exceed the limitation of the unresolved model. The results show that the simulated reflected and transmitted waves are in good agreement with the experimental measurements, and that the accuracy of predicting the flow around the breakwater improves as the mesh size is reduced. The validated model is then utilised to simulate Stokes wave interaction with submerged permeable breakwaters composed of polydisperse particles. Analysis of the simulated results elucidates the characteristics of the Stokes wave propagation over the breakwaters and the wave damage to the breakwaters. Moreover, the additional computational effort caused by the semi-resolved model is not significant, especially in the case of a large number of particle collisions.