Numerical Simulation Of Cvlinder Vortex-induced Vibration Using RANS

Flow around a cylinder is a typical problem in fluid mechanics.The vortex-induced vibration(VIV)of cylinder which occurs frequently in ocean engineering is an important issue involving fluid-structure interaction.Cylinderical structure is widely used in ocean engineering,such as offshore platform piles,marine risers and mooring systems.Riser system is a bridge connecting surface floating platforms and subsea equipment.The growing demand for technology of risers of deep sea is more and more high.Under ocean currents,resonance may occurs,resulting in riser system fatigue damage,which involves more complex flow interference in the fluid-structure interactions.Therefore,considering the fact that cylindrical structure used in offshore oil platform,numerical method is used in this thesis to investigate cylinder vortex-induced vibration(VIV).Firstly,the results of experiments and numerical investigations about flow around a cylinder and vortex-induced vibration(VIV)of cylinder are overviewed.The vortex shedding mechanism,relevant parameters of VIV,the numerical methods and governing equations for fluid-structure interaction are introduced.Secondly,the validity and reliability of the numerical model used are tested by comparing with the experimental results of flow around a single cylinder with Reynolds number 3900.The results show that the numerical results of k-? turbulence model agree better with experimental results than that of k-? turbulence mode.Moreover,the SST k-? turbulence model has obtained even better results.In addition,y(10)value,spatial resolution,the wall function and turbulence intensity of the background also have certain influence on calculation accuracy.Further,in order to obtain more reliable numerical result,the fluid flow around single fixed cylinder under different Reynolds number,two circular cylinders under flow around under the different arrangement,and the VIV of single cylinder under different Reynolds number are investigated.The numerical results agree well with the experimental results.Finally,the vortex-induced vibration of series of circular cylinders under different Reynolds number is investigated.The results show that,at high Reynolds number,the variation of the upstream cylinder horizontal dimensionless amplitude with the change of normalized velocity is similar with that of the single cylinder vortex-induced vibration,The downstream cylinder has a larger lock-in band than that of only single cylinder.When the center spacing ratio is small,the Strouhal number exist in the vortex shedding behind cylinder has two value,but with the increase of normalized velocity,the Strouhal number is near at 0.2.The drag coefficient and wake modes of upstream cylinder and downstream cylinder changes accordingly.Downstream cylindrical lateral movement is not affected by upstream cylinder movement.The results with low Reynolds number is similar to that with high Reynolds number.