Exciting force for a coaxial configuration of a floating porous cylinder and a submerged bottom-mounted rigid cylinder in finite ocean depth

Here, we examine the exciting forces for an arrangement of two coaxial vertical cylinders—a riding porous cylinder and a submerged bottom-mounted solid rigid cylinder. We take up two cases: first we consider a hollow porous cylinder at the top and secondly a solid porous cylinder at the top, and for both the cases, there is a solid rigid cylinder placed at the bottom. The present configuration may be observed as a wave energy device which can tap and transfer ocean wave energy to be used as non-conventional energy. A three-dimensional representation of the problem is developed, based on the familiar method of eigenfunction expansion under the assumption of linear water wave theory. The important porous boundary condition on the porous boundary can be defined by means of Darcy’s law. The matching conditions across the linear interface between the adjacent fluid domains can be obtained through the continuity of pressure and velocity. Subsequently, after solving a system of linear equations, exciting forces and wave run-up for the upper and lower cylinders are calculated through the evaluated velocity potentials. Various numerical experiments show the effect of different parameters, such as porous coefficients, draft ratio, the ratio of radii of the upper and lower cylinders and the water depth on exciting force and wave run-up. It is also shown that higher porosity value of the upper cylinder results in higher energy loss conforming to the wave dissipation by the structure. The obtained results establish that appropriate values of different parameters may be considered in designing practical structures in ocean. Successful validation of the present model carried out with an available established one confirms the efficiency of the present model. The present system may be considered as a wave energy device in other problems where it can tap and transfer ocean wave energy to be used as non-conventional energy.