Wave Attenuation by Multiple Outer Porous Barriers in the Presence of an Inner Rigid Cylinder

The wave forces acting on a rigid cylinder are investigated in the presence of multiple outer porous cylindrical barriers by assuming the linear water wave theory. A Bessel series solution is obtained for the boundary value problem by using the methods of eigenfunction expansion and least-squares approximation. Two configurations of outer porous barriers are considered, namely bottom-standing and surface-piercing. As a special case, the effect of fully extended barriers is studied. The wave loads exerted on the cylinders, free surface elevations, and flow distribution around the structures are computed and analyzed for different physical parameters. The present theory is ratified with the result available in the literature for a single fully extended outer porous barrier. The study reveals that the hydrodynamic forces exerted on the inner impermeable cylinder are reduced significantly as the number of outer porous barriers is increased. Thus, multiple outer fully extended or partial porous barriers can be set up to protect the inner rigid cylinder.