Optimizing deployment of sponge zone on numerical wave channel

Abstract

In this study, we used the boundary element method to simulate a two‐dimensional wave tank with an absorbing boundary. The absorbing boundary, which consists of a sponge zone, is further divided into an area with a smoothly varied absorption coefficient μ and an area of constant μ. Both solitary, as well as periodic, waves are used in this study. Time histories of surface elevations are measured by a pseudo wave gage. The optimal combination of the absorption coefficient and sponge length to minimize wave reflection is investigated by studying these time series. The efficiency of the absorption zone is demonstrated by the attenuation rate of the wave energy, which for cases can reach a value of 100%. Based upon the present results, it is recommended that in simulating solitary waves, a value of μ 0=0.5 for the absorption coefficient with a sponge length of 15∼25 times the water depth is ideal, whereas a value of μ 0=1.0 in combination with a sponge length 20 times the water depth should be used for periodic waves.