WAVE REFLECTION BY A NUMBER OF THIN POROUS PLATES FIXED IN A SEMI-INFINITELY LONG FLUME

Abstract

The reflection of small-amplitude surface waves by a number of vertical porous plates is investigated . The plates are fixed in a semi-infinitely long channel of constant depth.Analytic solutions in dimensionless closed from are presented for the surface wave profiles in the several regions separated by these plates . And from them the reflection coefficient is obtained . Three cases , one to three porous plates, are evaluated. The results show that for incident waves in the range of 1/20 < water depth/wave length < 1/2 , it is appropriate to maintain the spacing between every two adjoining plates,and between the end wall and its nearst plate at a value of 0.88 times the water depth. As two or three porous plates are used for damping wave , an arrangement would be more effective if the front porous plate has a larger porosity and the back one has a smaller porosity. Several experimental tests for these porous-plate wave absorbers are conducted and the reflection coefficients are measured by using Goda's method. It is found that the theoretical solutions agree fairly well with the experimental results.