Numerical and Experimental Modelling of Wave Loads on Thin Porous Sheets

Abstract

This work considers the numerical modelling of wave interaction with thin porous structures, based on tests conducted in simplified conditions. Wave flume tests were conducted to measure the wave loads on thin porous sheets extending over the full water column. The porous sheets tested had a range of porosities, hole separation distances and thicknesses. Numerical and analytic models for the wave forces on the porous sheet are formulated under the assumptions of either a linear or quadratic pressure loss across the porous sheet. An iterative boundary element method (BEM) model is formulated to solve the quadratic pressure loss across the porous sheet. It is shown that the assumption of a linear pressure loss at the porous boundary is inadequate to capture the variation in the wave load with both wave frequency and amplitude, but that the quadratic model is in good agreement with the measured forces. The porosity of the sheet is shown to have the dominant effect on the wave loads. The hole separation distance affects the phase of the force on the porous wall, but has only a small effect on the amplitude of the force. The sheet thickness is shown to have a small effect on the amplitude of the force but a significant effect on the phase of the force. The results are of interest for numerical modelling of structures with thin porous boundaries in a wide range of contexts such as breakwaters, aquaculture and offshore structures with porous elements designed to reduce loads.