Experimental study on regular wave breakage and nonlinear characteristics on the terrain of steep coral islands and reefs

The breaking and nonlinearity characteristics of waves on steep coral reef terrain were investigated through wave tank experiments. This study analyzed the variations in nonlinear characteristic parameters (skewness, asymmetry, kurtosis, and Ursell number) of regular waves on steep slope terrain. A steep slope with a slope ratio of 1:3 was employed to simulate the topography of steep coral reefs. Various test conditions using regular waves were examined to observe the wave breakup process on island and reef landscapes. Additionally, a empirical formula that establishes the relationship between skewness, asymmetry, and Ursell number for steep slope terrain was derived. Furthermore, a two-dimensional non-reflecting numerical wave tank based on the smooth particle hydrodynamics (SPH) method was established. This numerical model simulates the propagation and deformation process of waves on steep slope terrain and compares the results with those from physical model tests. The findings indicated that the experiments accurately captured the wave-breaking process. It was observed that the amplitudes of the four nonlinear characteristic parameters all peaked in the breaking section. The water depth significantly influenced skewness and Ursell number while minimally affecting asymmetry. A smaller water depth resulted in more pronounced changes in the parameter amplitudes in the breaking section. Remarkably, the SPH-based numerical simulation agreed well with the physical model test results, thus validating the effectiveness of the proposed methodology.