Hydrodynamic Analysis Of A Pontoon-Net Floating Breakwater

With the development of ocean engineering technologies,coastal structures are widely applied in offshore regions.Floating breakwater(FB)has the function of defending the waves,absorbing and reflecting the wave energy to achieve the goal of wave elimination.Compared with traditional fixed breakwaters,floating structures are cost-effective,material reducing and water can exchange freely preventing the pollution of sea water.In order to meet the requirement of practical applications for the ocean engineering,FBs’ structures are supposed to be simple,robust,and durable as much as possible.Cylindrical or rectangular cross-sections’ FBs,are more likely to be top priorities for designing.Therefore,in this paper the hydrodynamic performance of this type of floating breakwater is compared numerically and experimentally.In addition,the wave dissipation characteristics of the cylinder-net floating breakwater are described.The main contents are as follows:1.The numerical wave flume is established based on the theory of viscous flow(Navier-Stokes Equations).In order to improve the mesh quality and the computational accuracy during the process of grid generation,the whole fluid domain is discretized by structural grids.Wave generation theory and dissipation theory are separately introduced in the two ends of the numerical flume,besides,mathematical movement model of floating breakwater is built in the middle of this flume.The computational fluid dynamic codes are programmed and incorporated into the software of FLUENT,which realizes the wave interaction with floating structure.2.The Navier-Stokes(N-S)solver combines the double-phase laminar flow and employ the Volume of Fluid(VOF)method to trace fluid-gas dynamic interface.The dynamic layer technology and sub-domain coupling method are integrated into the N-S solver to enhance the controllability of FB,which prevents distortion and deformation of the grid effectively.3.The experiment scheme of floating breakwater is introduced in detail;the main parameters of FB and mooring system are decided based on similarity theory;the wave coefficient is chosen according to the real environmental conditions of the breakwater.Through experiments some results can be obtained,such as motion response of FB,mooring line force and the wave height in the flume.4.Comparing the experimental and computational data,the wave elimination effect and motion response about the rectangular and cylindrical floating breakwater are analyzed when the relative breadth is changed.Analyzing the experimental data,the wave elimination effect and motion response about the cylindrical floating breakwater are analyzed when the number of net is changed.The results reveal that the numerical model can predict the problem about fluid-structure interaction.The natural frequency of the FB has a great impact on the motion response and wave coefficients,which means resonance period has a negative influence on the computational accuracy.The nets can improve the wave elimination effect about the cylindrical floating breakwater and reduce the heave and roll motion responses.