DIFFRACTION OF WATER-WAVES BY POROUS BREAKWATERS

Diffraction of water waves by porous breakwaters is studied based on t he linear potential wave theory. The formulation of the problem includ es a newly derived relation for the fluid motion through thin porous s tructures in addition to the conventional governing equation and bound ary conditions for small-amplitude waves in ideal fluids. The porous b oundary condition, indirectly verified by collected experimental data, is obtained by assuming that the flow within the porous medium is gov erned by a convection-neglected and porous-effect-modeled Euler equati on. A vertically two-dimensional problem with long-crested waves propa gating in the normal direction of an infinite porous wall is first sol ved and the solution is compared with available experimental data. The wave diffraction by a semiinfinite porous wall is then studied by the boundary-layer method, in which; the outer approximation is formulate d by virtue of the reduced two-dimensional solution. It-is demonstrate d that neglect of the inertial effect of the porous medium leads to an underestimate of the functional performance of a porous breakwater.