Design and experimental study on a compact passive wave-absorbing beach using combined perforated plates

Wave reflection at the end of the wave tank undermines the experimental fidelity, especially for the nonlinear, steep waves. We designed a compact passive beach combining three near-surface inclined perforated plates with an array of vertical plates of monotonically decreasing porosity. Based on the theoretical estimate, the first dissipative layer was placed within the depth around 0.3 height of wave tank. In the wave tank of which the length is 6 meters, the width is 0.35 meters and the height is 1.01 meters, a configuration of waves with wave length λ=0.5–1.2 meter and wave steepness H/λ=0.03–0.09 was simulated to evaluate the influence of the porosity, inter-plate spacing and number of layers. The experiments indicated that the optimal layout (3 inclined + 8 vertical plates; total length ≈0.5 λmax) achieved amazing reflection rate RA=0.048–0.085 over the tested range, without sensitivity to the spacing within measurement uncertainty. Compared with single-layer or conventional long beaches, the proposed design approach preserved effective experimental length with high absorption rate under large steepness.