Experimental and numerical investigations on the hydrodynamics of multi-chambered porous breakwaters with a backwall

Abstract

Breakwaters play a vital role in coastal and harbour protection by attenuating incoming waves, with porous types offering unique advantages in energy dissipation and resilience. Owing to the advantages of thin porous barriers, in this study, a breakwater with different thin porous configurations is investigated experimentally and numerically to assess its hydrodynamic performance. A series of experiments is conducted on three porous breakwaters, such as single, dual and triple-chambered designs. The Dual Boundary Element Method (DBEM) effectively models wave scattering by incorporating the quadratic pressure drop boundary condition (QPDC) within the framework of linear wave theory. Further, flow dynamics near porous barriers are analysed using Computational Fluid Dynamics (CFD) simulations, focusing on turbulent kinetic energy (TKE) and velocity vectors. The triple-chambered configuration shows the minimum reflection (K_R = 0.153) at k₀h = 1.53, achieving 38% and 19% greater reflection reduction compared to the single and dual-chambered breakwaters, respectively. This improvement is attributed to enhanced turbulence and vertical flow redirection within the chambers caused by the internal vertical barriers, which promote wave trapping and energy dissipation. A geometric porosity (ε) of 0.3 demonstrates superior energy dissipation, with reflection consistently below 0.125 over the range $k_{0}h=0.8-1.7$, which is a 60% reduction as compared to the 0.2 porosity. Further, the reduced horizontal plate submergence (h₁/h) enhances breakwater performance for longer waves (k₀h < 1.5) without compromising energy dissipation of shorter waves. Overall, the proposed triple-chambered porous breakwater provides multiple advantages for coastal protection when tailored to site-specific wave conditions.