Abstract

Porous structures have been widely studied due to their effectiveness at dissipating the unwanted wave energy. By comparing with the impermeable bodies, both the transmitted and reflected wave heights are relatively reduced, whereas the wave loads on porous structures are decreased. Hence, they become preferable due to their porosity, for applications such as harbor and shore protection (Sollitt & Cross, 1972, 1976; Madsen 1972; Sulisz 1985). At the same time, there is a considerable interest in hydrodynamic interactions between multibody impermeable arrangements due to the diffracted and scattered waves that create the so called trapped-mode phenomenon (Ursell, 1951; Callan et al., 1991). The latter is connected with the wave trapping in the fluid region between adjacent bodies, forming a near-standing wave with much larger amplitude compared to the waves at other wave frequencies, whose energy slowly leaks away to infinity. Maniar & Newman (1997) associated the existence of trapped waves in a channel with near-resonant modes occuring between neighbourhood impermeable bodies with critical spacing. In these modes the diffraction loads are remarkably increased compared to the forces on a body in isolation. The present paper takes a further step dealing with the same problem, enhanced however, with the existence of porous structures in the vicinity of the array. The 3D water-wave diffraction problem by arrays of bottom-seated and surface piercing porous cylinders is formulated and solved, whereas the existence of trapped waves is studied against the porosity parameter.