Wave diffraction from a truncated cylinder with an upper porous sidewall and an inner column

Abstract

An analytical model based on linear potential theory is proposed to predict the three-dimensional wave diffraction from a truncated cylinder with an upper porous sidewall and an inner column in the finite water depth. The velocity potential is analytically derived in the whole fluid domain based on the method of variable separation and eigen-function expansion technique. The continuous conditions of pressure and velocity potential are satisfied on the interface between the adjacent sub-domains. Wave forces are calculated directly from the incident and diffracted potentials. The model is validated in comparison with other published results of wave diffraction from a porous bottom-mounted cylinder and impermeable truncated cylinder, respectively. Then the numerical tests are performed to investigate the effects of the porous coefficient G, the draft ratio h/h1 (h and h1 mean the drafts of the porous part and whole cylinder, respectively), the ratio of the inner and outer radii b/a and the water depth d/h1 (d means the water depth) on the wave forces acting on the structure. It is found that, by introducing an upper porous sidewall, the hydrodynamic loads are improved in comparison with the fully impermeable structure, which may be benefit to enhance the survivability of the relating marine structure.