Numerical Simulation Study On Hydrodynamic Characteristic Of Pontoon Floating Breakwater

The wave dissipation characteristics of pontoon floating breakwater are significantly different when interacting with wave of different wavelengths.The bigger wave length is,the worse wave dissipation characteristics of pontoon floating break water is.At present the researchs of pontoon floating breakwater have got some achievements,which are obtained by laboratory physical model tests and numerical simulation based on BEM.They mainly focus on the motion response and wave dissipation performance,but seldom study the flow distribution or dynamic pressure.With the development of the computer and CFD(computational fluid dynamics)technology,the numerical wave tank technology has been more and more mature and become the new tool to study the interaction between wave and structures.The numerical wave tank not only saves more time and labor than physical model tests,but also can reduce the scale effect.And more important is that the numerical wave tank based on the N-S equation can simulate the nonlinear problems such as the transformation and breaking of wave,which is of great significance to FSI problems such as the interaction between wave and floating strctures.First,the numerical model based on BEM is established to analyse the law of motion preliminarily at different relative widths(ratio of floating breakwater width W and wave length L),which is the basic of FSI model.Then the RANS k-s turbulence model and the volume of fluid method based on the FLUENT software are used to calculate the gas-liquid two-phase flow.According to the relaxation method and the damping absorber technology.We can realize wave making and no reflection wave tank by UDF function of FLUENT.Results show that the wave tank based on the momentum source term can generate high quality wave and absorb wave transmission,and the most important point is that the reflection and radiation wave of structure can be eliminated successfully.so it can provide a stable wave field for studying the interaction between wave and floating strctures.Combined with the numerical wave tank and 6DOF model and dynamic mesh with full freedom block grids,we establish the FSI model of wave and mooring pontoon floating breakwater.We can analyze the relationship between flow distribution or dynamic water pressure and wave dissipation characteristcs of mooring floating breakwater at different relative widths and put forward a wave transmission coefficient formula.Results show that the established FSI model can reflect the change trend of motion response,and the dynamic water pressure is mainly from the vertical direction,and the motion of floating breakwater is fiercer and the change of vortex is more complex when the wave length is bigger.The wave dissipation method gradually changes from wave reflection and wave interference into turbulent energy dissipation and wave power.The relationship between wave transmision coefficient and relative width is exponential,and the The wave transmision coefficient is low when wave length is short and width of floating breakwater is kept constant,and vice versa.Chamfered corner of pontoon floating breakwater can decrease the wave dissipation coefficient and increase the efficiency of wave dissipation when interacting with the long wave.