Numerical Simulation Of Vortex-induced Vibrations Using PC-Newmark-β-based Fluid-structure Interaction Method

The phenomenon of vortex-induced vibration is often seen in civil engineering structures. When viscous fluid, such as wind and water, flows through flexible structures like long-span bridges, high-rise buildings, tall chimneys, offshore drilling platforms and submarine pipelines, it will cause vortex-induced vibrations of them. If the vortex formation frequency is close enough to the structure’s natural frequency, resonance will happen and the structure will vibrate with large amplitude, thus causing damage to it. So it is very important to conduct study into vortex-induced vibrations.This paper proposes using PC-Newmark-β-based fluid-structure interaction method to conduct numerical simulation into vortex-induced vibrations. This method have an improve on the numerical performance and is much easier to obtain more stable and reliable results, compared with the traditional Newmark-β-based fluid-structure interaction method which needs to make some approximations to the vortex-induced force. The computational fluid dynamics software Fluent is used as the main research tool. And in order to realize the dynamic mesh, User-Defined Functions are written to solve fluid-structure interaction problems concerning two-dimensional problems with two degrees of freedom and three-dimensional problems with multi degrees of freedom, based on PC Newmark-β method. Numerical simulation is performed on vortex-induced vibration of a two-dimensional cylinder at low mass ratio which achieves good results in accord with the experiment results, followed by some detailed analyses of the distinction of the vortex-induced vibration mode between the positive frequency sweep and the negative frequency sweep from several aspects, such as vibration frequency, vortex-induced force, phase, energy transformation and vortex patterns. Then numerical simulation is performed on vortex-induced vibration of a three-dimensional flexible cylinder, obtaining the conclusion that vortex-induced vibration at high modes should be taken into account from the comparison of structural responses of each resonance region, followed by the analyses of the three-dimensional wake vortex patterns of the cylinder and the spatial distribution characteristics of the vortex-induced force discovering that they are closely connected to the vibration modes. Finally numerical simulation is performed on vortex-induced vibration of a two-dimensional twin deck bridge, putting forward some measures of section optimization which can reduce the structural response amplitude of vortex-induced vibration effectively, thus providing very important reference value to the practical engineengs.