Performance of Dual Flexible Membrane Wave Barriers in Oblique Waves

Abstract

The interaction of oblique incident waves with a dual vertical-flexible-membrane wave barrier hinged at the seafloor is investigated in the context of two-dimensional linear wave-body interaction theory. First, analytic solutions for an idealized system without a buoy are obtained as a benchmark result. Second, a more practical system with the membrane tension provided by a buoy at its top is investigated th the three-domain boundary element method (BEM) particularly devised for dual membrane problems. For each case, both submerged and surface-piercing systems were considered. The BEM program is developed based on a discrete membrane dynamic model and simple-source (second-kind modified Bessel function) distribution over the entire fluid boundaries. Because the boundary condition on the membrane is not known in advance, the membrane motions and velocity potentials in each region are solved simultaneously. The accuracy and convergence of the numerical method are checked against the energy-conservation formula and further verified through comparison with analytic solutions in case the size of a buoy is infinitely small. Using the developed computer program, the performance of surface-piercing or submerged dual membrane wave barriers is tested with various system parameters and wave characteristics. It is found that the efficiency of a dual membrane breakwater can be significantly enhanced compared to the single membrane case if it is properly designed. It is also found that the asymmetric system can function better than the symmetric system through desirable tuning.