Effect Of Mass And Damping Ratio On Vibrations Of Square Cylinder In Presence Of Stationary Wake Cylinder

Vortex-induced vibration occurs when air or water flows across blunt devices under certain conditions.Study on vortex-induced vibration in several engineering fields is essential.On the one hand,such research can help to assess the stability of blunt structures such as bridges,offshore platforms and high-rise buildings.On the other hand,they can be used for collecting and converting fluid energy by vibrating devices.At present,a lot of research has been done on flow around single cylinder.Flow around two cylinders requires more attention.This thesis is based on the framework of one fixed square cylinder,which is placed in the downstream,assembled in tandem with another identical cylinder,which is elastic and placed in the upstream,under low Reynolds numbers.A numerical simulation is conducted to study the vibration response and mechanism of the upstream square cylinder at Reynolds number Re=100 and 200.The upstream cylinder vibrates only in the transverse direction.The obtained results are compared with the vibration of a single square cylinder.The dimensionless centre-to-centre spacing of two cylinders L*,referred to as spacing ratio,is taken as 2 and 6.The dimensionless velocity Ur(Ur?1-30)is controlled by altering the natural frequency fn.In the certain Re and L*,the current study analyses the vibration response of the upstream square cylinder,such as the vibration amplitude A*,the vibration frequency fy,the lift coefficient CL,the phase-lag between lift and displacement ?,the Strouhal number St and the vortex structure distribution of the square cylinder vibration flow field.The case with Ur=40 is calculated at Re=100 and L*=2,in order to investigate the pattern of vibration response with changing Ur.In addition,the simulation of the upstream square cylinder with changing Ur(Ur=1-40)at Re=100 and L*=2 is performed with different damping ratios ? and mass ratios m*.The damping ratios Care taken as 0,0.1,0.2 and 0.4.The mass ratios m*are taken as 3,5,10 and 15.The simulation results reveal how the m*and ? affect the vibration response of the upstream square cylinder in terms of vibration amplitude A*and vibration frequency fy.In the meantime,there are three patterns in upstream cylinder vibration responses with varying Ur for different mass-damping ratios m*?.The pattern 1(m*?<0.6):the galloping branch follows the initial branch closely;The pattern 2(0.6?m*<0.75):there is the desynchronization between VIV(Vortex Induced Vibration)and galloping;The pattern 3(m*??0.75):there is no galloping in vibration response.