Multiple concentric perforated cylindrical walls are newly suggested for the protection of both the internal cylinder and themselves. The porosity parameter is introduced to measure the ability of the perforated wall in dissipating the energy when the fluid passes through it. The 3-dimension linear potential theory based upon the eigenfunction matching method considering the nonlinear boundary conditions is used for the hydrodynamic analysis of the structures. The wave forces on the inner cylinder and protective walls are calculated considering various porosity parameters and radius ratios. The wave elevations at the free surface in the fluid domain for a considered parameter proportion and radius ratio with various numbers of porous walls are further examined. The numerical results are vividly depicted and show that the wave loads on the inner cylinder can be highly reduced by setting one or more porous walls externally. When there is only one perforated wall, whether it is fully or partially perforated at the upper part has little influence in reducing the wave loads on the inner cylinder. In this case, the frequencies where the wave excitation forces approach zero on the outer wall and approach maximum on the inner cylinder are explained by introducing the sloshing problem and further confirmed by the analytical formulas. More numbers of protective walls can better balance the wave elevations and excitation forces on themselves by adjusting the porosity parameter proportions and radius ratios of them.
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