This paper outlines the numerical and experimental investigation of wave interactions with fully submerged and floating dual buoy/vertical membrane breakwaters. To assess the efficiency of this dual system with non-porous or porous membranes, two-dimensional multi-domain hydro-elastic formulation was carried out in the context of linear wavebody interaction theory and Darcy's law. It is found that transmission and reflection characteristics are sensitive to design parameters of breakwater system; size of buoy, membrane tension and spacing, submergence depth, gaps between seafloor and end of membranes, and mooring type and stiffness. These parameters offer the opportunity to tune the breakwater system, for archiving mutual cancellation to the coming waves, and to reflect incident waves over a wide range of wave frequency. The energy dissipations through fine pores on membranes attenuate the transmitted and reflected waves simultaneously, and reduce dramatically the displacement of buoy and membranes at resonance frequencies.
Flexible and floating membrane breakwater system has desirable characteristics of a quickly deployable, easily re-locatable, sacrificial with less environmental impacts, reusable, and comparably economical system. Thus, it may be an ideal candidate as a portable temporary breakwater for various coastal construction works, demanding sheltered areas or seasonal protection. In this regard, a number of vertical floating buoy/membrane breakwaters have been investigated by Thompson et al. (1992), Kee & Kim (1997), Cho et al. (1997, 1998). Kee et al (2003) extended the work by Kee & Kim (1997) and developed a boundary integral method solution for fully submerged dual buoy/porous-membrane system with gaps between seafloor and membranes structures. System performance was found to be highly dependent on the buoy radius, which is directly related to the membrane stiffness, submergence depth from the free surface to the top of buoy, gaps between seafloor and membranes, asymmetric system with different mooring types.
