The performance of flexible-membrane wave barriers in oblique incident waves

Abstract

The interaction of oblique incident waves with a tensioned, inextensible, vertical flexible membrane wave barrier hinged at the sea floor is investigated in the context of two-dimensional linear wave-body interaction theory. First, an idealized system (tensioned vertical screen) is considered and analytic solutions are obtained. Second, a more practical system with the membrane tension provided by a buoy is investigated by a boundary integral equation method. For each case, both submerged and surface-piercing systems are considered. A two-domain boundary element program is developed based on a discrete membrane dynamic model and simple-source distribution over the entire fluid boundaries. Since the boundary condition on the membrane is not known in advance, membrane motions and velocity potentials are solved simultaneously. The accuracy and convergence of the developed computer program are checked using the energy-conservation formula. The numerical results are further verified through comparison with analytic solutions when the buoy is infinitely small. Using the developed computer program, the performance of surface-piercing or submerged buoy/membrane wave barriers is tested with various membrane, buoy, and mooring characteristics and wave conditions including oblique wave headings. It is found that the efficiency of a submerged or surface-piercing buoy/ membrane breakwater can be enhanced in oblique waves for certain design conditions. From our numerical examples, it can be concluded that the buoy/membrane wave barrier can function as a very effective breakwater for a variety of incident wave angles if it is properly designed.