Hydrodynamic forces due to water wave interaction with a bottom-mounted surface-piercing compound porous cylinder

Abstract

Abstract The interaction of linear water waves with a bottom-mounted surface-piercing compound porous cylinder is investigated theoretically. Only the top ( a ≤ r ≤ b ) of the bottom cylinder and the side-wall of the top cylinder are impermeable. The sea-bed is taken as flat. We use the method of separation of variables to obtain the analytical expressions for corresponding potentials in each flow region. By using matching conditions along the boundaries of two individual successive regions, a system of linear equations for the unknown coefficients is derived and solved. A set of values of hydrodynamic force and wave run-up are obtained for different radii, different drafts and different porosity of the cylinder. It is observed that change in values in radius, draft and porosity have significant effect on the hydrodynamic loads and wave run-up. The behaviour of hydrodynamic load is found to be steady in the lower frequency. However a peculiar behaviour occurs due to the resonance situation in the neighbourhood of a specific frequency. To validate our result, we compare our result with some known results. Comparison is carried out with a compound cylinder, i.e., a totally impermeable cylinder. Good agreement is observed from this comparison. It is observed that certain values of different parameters pertaining to the cylinder and its vicinity, such as porosity, radii, depth etc., may lead to significant reduction of waveload.