Resonance and Response of the Submerged Dual Buoy/Porous-Membrane Breakwaters in Oblique Seas

J. Ocean Eng. Technol. 2001;15(2):22-32.

Kee S.T.

Dept. of Civil Eng. Seoul National University of Technology

Keywords: flexible porous membrane, submerged/floating breakwater, wave-flexible structure interaction, mooring lines, oblique waves, boundary element method

Abstract

The numerical investigation of obliquely incident wave interactions with fully submerged dual buoy/porous-membrane floating breakwaters placed in parallel with spacing is studied based on linear potential theory and Darcy's law. The numerical solutions are obtained by using a discrete-membrane dynamic model and second-kind modified Bessel function distribution over the entire boundaries of fluid regions. First, numerical solutions for an idealized dual submerged system without buoys are obtained. Second, a more practical dual submerged system with membrane tension provided by buoys at its tops is investigated by the multi-domain boundary element method particularly devised for dual buoy/porous-membrane problems with gaps. The velocity potentials of wave motion are coupled with porous-membrane deformation, and solved simultaneously since the boundary condition on porous-membrane is not known in advance. The effects of varying permeability on membranes and wave characteristics are discussed for the optimum design parameters of systems previously studied. The inclusion of permeability on membrane eliminates the resonances that aggravate the breakwater performance. The system is highly efficient when waves generated by the buoys and membranes were mutually canceled and its energy at resonance frequency dissipates through fine pores on membranes.