CFD Study On Nonlinear Aerodynamic And Vortex-induced Vibration Of Long-span Bridges

The further increase of the span of the long span bridge makes the structural rigidity and damping decrease,the structure is more sensitive to the wind induced vibration,and the nonlinear characteristics of the aerodynamic force are more obvious due to the large movement and the large angle of attack.Vortex-induced vibration(VIV)of the bridge is a kind of wind-induced vibration which is occurring at lower wind speeds.Although the VIV does not lead to the direct destruction of the structure,but its occurrence of low wind speed and the probability of occurrence will have a greater impact on the fatigue performance and driving comfort of the bridge.In this paper,the CFD method was used to study the nonlinear aerodynamic and vortex-induced vibration of the flat steel box girder.The main works of this paper was summarized as follows:(1)The basic control equations of the fluid motion and the common turbulence models of calculation wind engineering were described.This paper also introduced the common space and time discrete scheme and numerical realization of discrete control equations.(2)Taking the Great Belt East Bridge as the engineering background,the numerical method was used to simulate the static flow of the bridge section under different Reynolds numbers.By comparing with the existing studies to verify the reliability of the numerical simulation results.Studing the Reynolds number effect of the section of the Great Belt East Bridge.The CFD flow visualization gived the characteristics of the flow field around the bridge section.(3)The first-order kernel of the nonlinear aerodynamic system of flat box girder section was identified by Volterra series theory and CFD method,then a discrete time aerodynamic model was designed which can reflect the characteristics of the aerodynamic system of flat box girder.The research indicated that the high-order aerodynamic nonlinearity is relative small,and in fact,the flat box girder is a system of weak nonlinearity.(4)Based on the Newmark-? method,the numerical simulation method of structural vortex-induced vibration was established by using FLUENT dynamic grid technique.The complete locking curve of the eighth-order vortex-induced vibration of the Great Belt East Bridge was obtained,and the influencing factors of the vortex-induced vibration were analyzed.The parameters of Scanlan's empirical linear and nonlinear model were identified and the rationality and reliability of the two vortex model were evaluated.