Abstract
We study the interactions between a non-breaking solitary wave and a submerged permeable breakwater experimentally and numerically. The particle image velocimetry (PIV) technique was employed to measure instantaneous free surface displacements and velocity fields in the vicinity of the porous media. The porous media, consisted of uniform glass-made spheres, was mounted on the seafloor. Quantitative mean properties were obtained by ensemble averaging 30 repeated instantaneous measurements. In addition, two different numerical considerations are taken to simulate the experiments. One is to model an idealized volume-averaged porous media using a two-dimensional (2D) volume of fluid (VOF)-type model. This model is based on the Volume-Averaged Reynolds-Averaged Navier–Stokes (VARANS) equations coupled with the non-linear k-ε turbulence closure solver. The other is to model the real porous breakwater constructed by spheres using a three-dimensional (3D) VOF-type model. This model solves 3D incompressible Navier–Stokes equations with Large-eddy-simulation (LES) model. The comparisons were performed between measurements, 2D and 3D numerical results for the time histories of the free surface elevation, instantaneous free surface displacements and corresponding velocity properties around the permeable object. Fairly good agreements were obtained. The verified 3D numerical results were used to trace the trajectories of fluid particle around the porous media to help understand the possible sediment movements in suspended loads. Also, the 2D numerical model is used to estimate the energy reflection, transmission and dissipation using the energy integral method by varying the aspect ratio and the grain size of the permeable obstacle.
Highlights
Submerged permeable breakwaters have been frequently built along the coast to reduce the impacts from waves and currents due to their lower costs than impermeable structures and because they can dissipate more wave energy through viscous dissipation within the porous media
We present the comprehensive measurements of solitary wave propagation over a submerged permeable breakwater using a particle image velocimetry (PIV) system
We use the validated 3D numerical results to trace the trajectories of fluid particle around the permeable breakwater, and the 2D numerical model is employed as a tool to further explore the functional efficiency of the submerged porous media under solitary wave forcing via varying the porosity and the length of the breakwater
Summary
Submerged permeable breakwaters have been frequently built along the coast to reduce the impacts from waves and currents due to their lower costs than impermeable structures and because they can dissipate more wave energy through viscous dissipation within the porous media. The model validation in most existing numerical studies is carried out for the comparisons with free surface motion induced by periodic waves over a porous media.
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