WAVE MOTION THROUGH POROUS STRUCTURES

Linear potential theory is applied to the analysis of wave motion thro ugh a two-layer porous structure. For special cases, the characteristi cs of waves in nondissipative, weakly, as well as strongly, dissipativ e media and their relations with the inertial and resistive properties of the media are explored. It is noted that in a nondissipative mediu m, the wave components are either nonpropagative or nondecaying. In a dissipative medium, however, they are always propagative and decaying as well. The reflection, transmission, and dissipation of monochromati c incident waves by a rectangular block, with typical dissipative char acteristics and various thickness as well as submergence of its crest are studied by the method of matched velocity potentials. It is found that there is an optimum thickness for a porous structure beyond which any further increase of the thickness may not lead to an appreciable improvement of its functional performance in reducing the transmission and reflection. It is also discovered that a medium of moderate perme ability may be favorable in the design of a wide-crested breakwater if the wave heights on both front and lee sides of the structure are req uired to be controlled.