Numerical Research On Bifurcation Characteristics For VIV Of Low Mass Damping Ratio Cylinder

The low mass damping ratio cylinder is one of the most common structures in ocean engineering.In the design process,there is a mature system to calculate the structural strength,but for the prediction of vortex-induced vibration(affecting fatigue strength),there is still no method to consider both accuracy and efficiency in engineering.The main content of this paper is to study the difference and correlation between two-dimensional and three-dimensional vortex-induced vibration by means of numerical simulation based on OpenFoam,and to revise the amplitude response curve of two-dimensional vortex-induced vibration so as to achieve the accuracy of three-dimensional model.At the same time,the problems of large eddy simulation method and Reynolds averaging method in the calculation of vortex-induced vibration are analyzed and improved respectively,which provides the basis for this study.The main work of this paper is as follows:First,the large eddy simulation method is used to study the three-dimensional effect in vortex induced vibration.Meanwhile,in order to improve the computation speed of the large eddy simulation method,the accuracy and efficiency of large eddy simulation under different parallel computing methods are studied,and the best parallel computing strategy suitable for flow around cylinder is explored.The influence of spanwise mesh number on the accuracy of large eddy simulation is also studied by analyzing the results of numerical models with 1?64 layers.The most suitable grid layer and parallel computing strategy are exploredThen,Reynolds averaged method is used to study the effect of three dimensional effects on the numerical simulation results of two dimensional vortex induced vibration.At the same time,in order to solve the problem that the amplitude of the lock-in phase of the standard SST turbulence model is too small when calculating the vortex-induced vibration of a cylinder with low mass damping ratio,an additional turbulence kinetic energy generation term is added to the specific dissipation rate equation of the SST turbulence equation to obtain a more accurate turbulence model.The response of lift,drag,surface pressure,amplitude and frequency,wake shape and trajectory are analyzed to verify the performance of the improved SST turbulence model in calculating vortex-induced vibration of cylinders with low mass ratio.Finally,the improved SST turbulence model is used to study the relationship between three-dimensional and two-dimensional vortex-induced vibration from the "bifurcation phenomenon" of vortex-induced vibration.Based on the analysis of numerical simulation results of amplitude,frequency,bifurcation diagram and vorticity diagram,the hysteresis phenomenon of vortex-induced vibration and the bifurcation law caused by the disturbance of separation point are studied.According to the obtained law,the "safety factor correction method" is proposed to modify the amplitude response curve of two-dimensional vortex-induced vibration,so that it reaches the accuracy of three dimension modelThe following conclusions can be drawn:combining the improved SST turbulence model and the "safety factor correction method" proposed in this paper,more rapid and accurate prediction of vortex induced vibration response of low mass damping ratio cylinder can be achieved.