Numerical Simulation And Mechanism Reasearch Of Vortex-induced Vibration Of A Square Cylinder

The phenomenon of vortex-induced vibration(VIV)is common in nature and engineering field.When viscous fluid passes through unstreamlined structures,such as flexible vegetation,large-span bridges,high-rise buildings,high chimney stacks,as well as marine pipelines,alternate eddy form and shed from the wake of them.Meanwhile periodic force will be loaded on these structures and they will viberate in the direction perpendicular to the flow.The problem of vortex-induced vibration is therefore a fascinating feedback between body motion and vortex motion.Most study on VIV are carried out in tunnel,but few by means of numberical simulation.This paper analysises the vortex-induced vibration of one degree of freedom and two degrees of freedom elastic support cylider by using a fluid-structure-interaction udf program and dynamic mesh method.The main contents are as follows:1.The problem of vortex-induced vibration of one degree of freedom elastic support cylider is first studied in the range of 7.31<U*<15.23.The maxium amplititud obtained from this simulation is compared with the experimental result of Kumar et al.,it shows very well agreement.So it proves the reliability of the fluid-structure-interaction udf program and the simulation method.The phenomenon of 'lock-in','beat','phase switch' have been observed in the simulation.The transverse vibration reduce the intensity of wind load both in transverse direction and in approaching direction.2.Results of previous research indicate that frequency ratio fst*,mass ratio M~*,mass-damping parameter M~*? are important parameters in the problem of VIV.Square cylinders with different mass ratio and mass-damping parameter have been studied in this paper to find the relationship between M~*?M~*and amplititude of vibration.wind load.initiate velocity of 'phase switch'.3.The mechanism of 'phase switch' is also studied in this paper,with the help of flow field analysis.A kind? of diffraction velocity related to vibration is found near the square cylinders,it reduces velocity contrast in transverse direction,and its variation change the initiate velocity of'phase switch'.4.Two degrees of freedom of elastic support cylider is modeled.Resonance properties both in transverse direction and flow direction have been studied.This step try to make sure what degree impact on wind load when cylinder viberate in flow direction.A simple using condtion of using 1-DOF VIV system subsititute 2-DUF VIV system is given in this paper.