A Numerical Study On Twin-Pontoon-Plate Type Floating Breakwater

In recent years, the application of floating breakwaters has been more and more brought to engineering and research people's attention because of their simple structure, inexpensive cost, convenient construction, easy relocation and so on. But at present the results of studies of floating breakwater performance revealed that, in general, the best designs become ineffective on long period wave. So many new floating breakwaters were researched. For instance, pontoon-plate floating breakwater, twin pontoon floating breakwater and so on. This led to the concept of twin-pontoon-plate floating breakwater. In this paper, a generalized mathematical model is present for the study on the hydrodynamic characteristics of twin-pontoon-plate floating breakwater.This paper is a numerical investigation of the hydrodynamic interaction effects between wave and twin-pontoons-plate type floating breakwater in the time-domain, which is obtained by the boundary integral equation method. The catenary theory is utilized to calculate the mooring chain forces. The amplitudes of the body motions are determined according to the motion equations of rigid body. The numerical model is verified by the experimental results.By numerical investigation, the hydrodynamic characteristics of three types of floating breakwater, the pontoon-plate floating breakwater, twin pontoon floating breakwater and twin-pontoon-plate floating breakwater were discussed. The numerical results demonstrate that the twin-pontoon-plate floating breakwater has good ability of dissipating wave with less mooring chain force. Even under the long period wave (the wave period is from 1.1s to 1.55s) action, the transmission coefficient of the twin-pontoon-plate floating breakwater decrease to 0.6.The influences of relative pontoon draught, relative wave height, relative pontoon gap on the hydrodynamics characteristics are investigated. The results indicate that lager relative pontoon draught, relative pontoon gap and smaller relative wave height can decrease the transmission coefficient. And for different pontoon dimensions, it is found that the ratios of pontoon gap in pontoon width gives an optimum transmission coefficient for twin-pontoon-plate floating breakwater. The results demonstrate that larger pontoon draught, relative wave height, relative pontoon gap can decrease movement and mooring chain forces of twin pontoon floating breakwater. In conclusion, twin pontoon floating breakwater has similar feature as pontoon floating breakwater.