The Numerical Simulation On The Hydrodynamic Performance Of The Flexible Multi-Pontoons Breakwater

The thesis studies the hydrodynamic characteristics of a flexible multi-pontoons breakwater numerically by using AQWA based on 3D-diffraction theory.In the first place,the 2D numerical model has been created and verified by the 2D experimental results.The 3D numerical model has then been established to investigate the wave dissipation performance as well as the characteristics of motion response and mooring tension of the multi-pontoons breakwater under oblique waves.Based on the simulation results,the main conclusions can be drawn as:(1)The wave dissipation performance of the flexible multi-pontoons breakwater is less affected by the relative wave height H/D,but more significantly affected by the Angle of the incident waves.Under the action of regular waves with different wave height and period,compared with the wave dissipation performance of 2D-floating breakwater,when the wave incidence angle θ =15°,the wave transmission coefficient increases about 30%;For the wave incidence angle θ =30°,the wave transmission coefficient increases about 60%.When the wave incidence angle θ >45°,as can be seen as floating breakwater is invalid.(2)Among the six degree of motions for the flexible multi-pontoons floating breakwater,sway is the most complicate.The spectra of the seaward mooring tension and sway showed significant dual-peak characteristics,which were not observed in other motion components.(3)The motion responses of flexible multi-pontoons breakwater are more influenced by the wave incidence angle θ.With the wave incidence angle θ increased from 15° to 60°,sway,heave and roll motions decrease to 70%~50%;The pitch motion increases to 150%~175%.The surge and yawing motions with θ variation is not significant.(4)The seaward and leeward mooring tensions were significantly affected by the wave incidence angle θ,but the sideward mooring tension is not like that.Comparing to θ =15°,the mooring tensions under incidence angle θ =60° decrease to 0.6~0.8 and 0.5~0.7 times in seaward and leeward,respectively.For the larger wave height,the sideward mooring tension is larger when θ =30°,can be up to 0.8~1.2 times of the seaward mooring tension.(5)Considering the difference between potential theory and real fluid,as well as the influence of the flexibility of the pontoons and the sloshing of the internal liquid.The corresponding safety coefficient can be obtained according to the calculation results of the 3D numerical model.