Wave interaction with a concentric bottom-mounted cylinder system with dual porous ring plates

The interaction between linear surface waves and a concentric bottom-mounted cylinder system has been investigated using the eigenfunction expansion approach. This system contains an outer porous cylinder and an inner impermeable cylinder, which are connected by dual porous ring plates. Both cylinders are surface -piercing and rigidly installed on the flat bottom of the ocean, while the porous ring plates are fixed below the free water surface. The analytical solution of the velocity potentials can be obtained by matching the boundary conditions. After obtaining the velocity potentials, the wave force and free surface elevation are computed. The numerical results obtained for limiting cases agreed well with the published results. The results of the study show that reducing the draft, spacing, and permeability of the dual plates all contribute to reduce the horizontal force of the inner cylinder. However, the significance of the lower plate is mainly to cope with the condition where the water surface is lower than the upper plate.