ON A HIGHLY EFFECTIVE WAVE ABSORBER

A highly effective wave absorber containing a finite number of porous plates with various porous-effect parameters (G) is investigated. It is shown that the wave reflection by the wave absorber is affected significantly by the spacings between the adjacent porous plates as well as the alignment of these plates. Their relationships are analyzed and a formula for evaluating the reflection coefficient is derived. For incident waves in the range of 1/20 < water depth/wave length < 1/2, it is appropriate to maintain the spacings between the adjacent porous plates, and between the last one and the end wall, at a value of 0.88 times the water depth. In addition, the wave absorber would be more efficient if the porosity magnitudes of plates are arranged in a progressively decreasing order from the front to the back of the wave absorber, especially, if the decreasing amount of the G value along the incident wave direction is decreased. A set of ten sheets of porous plates with the previously mentioned arrangement of spacing and G value could serve as a highly effective wave absorber which gives a reflection coefficient below 0.04 for the wave range of 1/20 < water depth/wave length < 1/2. A number of experimental tests are conducted and the reflection coefficients are measured for several arrangements of the wave absorbers. The theoretical solutions agree fairly well with the experimental results.