Mooring lines connected to floating porous breakwaters

Abstract

An analytical study is conducted to investigate the behavior of a flexible, porous, floating breakwater consisting of a compliant, beam-like porous structure anchored to the sea bed and kept under tension by a small buoyancy chamber at the tip. Additional stiffness is provided by mooring lines. The velocity potentials of the wave motion are coupled with the equation of motion of the breakwater. Analytical solutions in closed forms are obtained for the reflected and transmitted velocity potentials together with the displacement of the breakwater. The free-surface elevation, hydrodynamic force acting on the breakwater, and the overturning moment are determined. The dynamic response of the breakwater in terms of bending moment and shear force are also evaluated. For an impermeable flexible floating breakwater, the agreement between the present solutions and the existing numerical results is fairly good. The results also indicate that, for any finite rigidity breakwater, the transmission coefficient increases as porous effect increases whereas the reflection coefficient decreases. The hydrodynamic force on the breakwater increases as structural rigidity increases and the force decreases as porosity increases. It is found that the reflection coefficient and the hydrodynamic force on the breakwater increase with increases of the mooring line stiffness and angle. It is also found that the role played by the axial force is negligible.