Study On Vortex-induced Vibration Of Two Tandem Risers Based On Reynolds Similarity Criterion

A single riser was always taken as the research object when we studied on vortex-induced vibration,but multiple-risers were applied in practical applications.The risers could be easily damaged under the combined effects of the wave and current.Therefore,more and more attentions have been paid on the vortex-induced vibration of multiple-risers.No matter the physical model experiment method or the numerical simulation methods were both based on the gravity similarity criterion at present.Fully dynamic similarity criterion which meet the gravity similarity criterion and the Reynolds similarity criterion at the same time was studied in this paper. The VIV of two tandem risers at high Reynolds was studied in CFX based on this Fully dynamic similarity criterion.The focus of this paper was to research the characteristics of lift/drag force and vortex shedding.It was shown that the lift/drag force and vortex shedding of downstream riser and upstream riser were quite different at different spacing.In addition,the characteristics of lift/drag force with the Reynolds number increasing from5000to400000at same spacing was presented.It was shown that the effect between downstream riser and upstream riser was negligible when the spacing was30times the diameters of the riser.The VIV of two tandem flexisible risers under small reduced velocity considering the fluid-struction interaction was studied in this paper.It can be concluded that the lift force of the rigid risers and flexisible risers varied as10times as much when the distance between two risers was small;The lift/drag force of the rigid risers and flexisible risers was basically the same;The most dangerous situation was observed when the spacing was12times the diameters of the riser.