Sdudy On Vortex-induced Vibration Response Of Two Rough Cylinders In Tandem

Tandem cylinder structures are widely used in ocean engineering(submarine pipelines and risers).Cylinder group structures have attracted more and more attention in ocean engineering.As the simplest type of cylindrical group,the vibration response of double cylinder structures is different from that of isolated cylinders.Scholars at home and abroad have studied the response of single-cylinder smooth structure,single-cylinder rough structure and tandem smooth double-cylinder single-degree-of-freedom structure,but the research on the response of tandem double-cylinder double-degree-of-freedom structure with rough surface is relatively less.In this paper,the flume experiment and numerical simulation are combined.First,the series double cylinders with different center spacing ratios are systematically studied by experiments and the corresponding numerical models are established to simulate them.After verifying the reliability of the numerical algorithm,the large diameter model is established.The series smooth double cylinders and the series rough double cylinders with different center spacing ratios are carried out.Simulation study.The main contents of this paper include:(1)Experiments on the response of tandem double cylinders to vortex-induced vibration in a flume show that when the center spacing ratio is 2.19,in the range of high velocity(10.41<Ur<12.40),due to the small center spacing between the upstream and downstream cylinders,there will be obvious collision phenomenon,which makes the amplitude of upstream and downstream cylinders rise and fall suddenly at high velocity,and when the center spacing ratio become 3.05,the upstream and downstream cylinders are at the junction of collision and non-collision,and the upstream cylinders are stable in both transverse and directional amplitudes.while the downstream cylinders are in the range of intermediate velocity(6.33<Ur<10.41).Due to the influence of the upstream cylinder wake,the unstable upward and downward trend appears;when the center spacing ratio is 4.02 and 4.99,the downstream cylinders are in the range of intermediate velocity.In the range of medium and low velocity(3.39<Ur<10.41),the center spacing is large enough,and the downstream cylinder will hardly affect the upstream cylinder,so the amplitude of the upstream cylinder is almost equal to that of the single cylinder.In addition,the amplitude of the downstream cylinder in both transverse and flow direction is smaller than that of the single cylinder due to the influence of the upstream cylinder wake.(2)The simulation analysis of smooth tandem double cylinders arranged according to different center spacing(L/D=1.5,2,3,4,6)shows that in the range of reduced velocity(7.34<Ur<12.24),the transverse and directional amplitudes of upstream and downstream cylinders increase with the increase of reduced velocity,and the center spacing ratio appears.The smaller the vibration is,the more obvious the galloping phenomenon is.In the case of the center spacing ratio is 1.5,the center spacing between the two cylinders in series is smaller,and the upstream and downstream cylinders C1 and C2 of each vibration series will collide when Ur=6.12-12.24.(3)The simulation analysis of rough tandem double cylinders with different spacing ratios(L/D=2,4,6)shows that the reduction speed is different,and the influence of surface roughness on lift drag coefficient and its frequency is different.The transverse and flow amplitudes corresponding to surface roughness Ks/D=0 increase with the increase of reduction speed,while the transverse and flow amplitudes corresponding to surface roughness Ks/D=0.001,0.005 and 0.01 increase first and then decrease with the increase of reduction speed.The greater the surface roughness,the more obvious the suppression effect of transverse amplitude is.This shows that the three surface roughness have an effect on the transverse flow amplitude of tandem double cylinders.Amplitude has a certain restraint effect;even if the ratio of center spacing between tandem cylinders increases to L/D-6,the transverse and flow amplitudes of upstream and downstream cylinders C1 and C2 still have obvious differences with the increase of surface roughness,indicating that downstream cylinders are in the wake of upstream cylinders,besides the wake vortices of upstream cylinders have influence on their shedding modes,their own roughness will also have a certain degree.Influence.