Study On The Method To Reduce Vortex Of Cylindrical Structure With Free Surface

The phenomenon of free surface motion widely exists in ocean,bridge,marine engineering and other fields,such as SPAR platform,marine riser,leg of TLP and so on.These structures are often subjected to the action of strong sea flow load and wind load,which not only cause complex flow separation but also generate the large run-up and depression of free surface,air suction,even result into bubble breaking,and green water.These issues are great challenge for many researchers to explore structure's hydrodynamic characteristics with free surface.For cylindrical structure with free surface,the interaction of motion of two phase flow and the complexity of turbulent vortex is more complex,which makes the simulation and solution more difficult.In this paper,based on the project of the National Natural Science Foundation of China?code:11472087?,the numerical and experimental methods were used to study the suppression of vortex shedding behind cylinder with motion of free surface.Firstly,the experiment was observed to summarize the rules of motion of free surface around the cylinder.Secondly,the modified turbulent model was compiled into the OpenFOAM source to study the numerically predicting method and the accuracy of computational model was verified by comparison and analysis with physical experiments.The comparing results show that the current computational model of two phase turbulence flow is good.On these bases,the hydrodynamic characteristics of flow around the cylinder with free surface were further researched at different Fr numbers.The location and influence of splitter plate were simulated and discussed by detailed on the hydrodynamic characteristics of cylinder,which covers the run-up and depression of free surface,vortex exciting forces,total drag force and so on,then the controlling efficiency of splitter plate was given.The main conclusions are as following:?1?The coefficients of H_max/D and d_cymax/D show that they are linear relationships with Fr²,but slopes are different.?2?Due to the effect of free surface,the three-dimensional distribution characteristics of hydrodynamic coefficients are remarkable,which can't be neglected.The changes of hydrodynamic parameters are severe in the vicinity of the free surface.However,vortex exciting forces tend to be stable values with the increase of water depth.?3?For different Fr numbers,the effect of splitter plate on drag and lift coefficients is the most obvious when the splitter plate is placed at z/D=-3.57.C_R and C_D coefficients are reduced about 20%due to influence of splitter plate,but C_S coefficient is increased a little.The researching results provide available designing reference to reduce vortex induced vibration of slender cylindrical structures.