Hydrodynamic performance of floating breakwaters in long wave regime : an experimental study

Hydrodynamic behavior test of long water waves with a floating breakwater is an important mission in some near-reef sea areas. Especially, the performance of the floating breakwater becomes more complicated when its natural periods stay within the range of wave frequencies. In this study, a series of experiments were conducted under long regular wave actions to investigate the hydrodynamic behavior of four slack-moored floating breakwater models, including single box, single porous box, double cylindrical pontoon, double cylindrical pontoon with mesh cage and suspending balls. The experimental results revealed that the wave transmission and wave energy dissipation for four models had multiple turning points near the natural periods of floating structures in long wave regime, while which was not evident for the reflection coefficient. The resonant responses were also observed in the motions and mooring tensions of the four models, which further explained the turning point phenomenon that appeared in transmission and dissipation coefficients. The overall results demonstrated that the porous plates and mesh cage with balls were effective for mitigating the turning point phenomenon due to additional water mass and damping effects, and also held the potential for reducing the motions and mooring forces