Wave motion over a twin-plate breakwater

Wave reflection and transmission over a horizontal twin-plate structure is investigated analytically based on the linear potential wave theory. The twin-plate system consists of a horizontal single surface plate and a horizontal submerged plate of same dimensions just below the surface plate. The velocity potential in each fluid domain is formulated and the unknown coefficients are determined from the matching conditions using three sets of orthogonal eigenfunctions. The reflection and transmission coefficients are obtained to evaluate the performance of twin-plate system as a breakwater. The effects of relative water depth, relative plate width and relative submergence spacing of the submerged plate below the surface plate are investigated. The performance of the twin-plate breakwater is compared with other available horizontal breakwaters in literature, such as (i) a single surface plate, (ii) a single submerged plate and (iii) a group of submerged plates.