Study On Flutter Of Typical Bridge Section Based On Free Vibration Method

Flutter is a self-excited vibration caused by wind loads on the bridge.It is extremely destructive.The flutter must be strictly prevented in the bridge design stage.The flutter derivatives are important parameters for calculating the critical wind speed of the bridge flutter.Vibration critical wind speed is an important indicator of bridge wind resistance design.Therefore,designers need to identify the flutter derivatives of the bridge during the bridge design stage and the calculate flutter critical wind speed.This paper used the free vibration method to analyze and calculate the flutter of two-dimensional bridge sections through the FLUENT software.The specific content is as follows:First,the ideal plate was replaced by a thin plate as the numerical calculation model to calculate its displacement,velocity and acceleration response under different wind speeds.And then the eight flutter derivatives of the plate were identified and its flutter critical wind speed was searched out.The solution was compared with the theoretical solution and the flutter derivatives and flutter critical wind speed are more consistent with the theoretical solution.The feasibility of the calculation method and UDF program in this paper were verified.Second,The thin flat plate was still as the research object to identify the flutter derivatives and search its flutter wind speed with 3° and 5° wind attack angles.The results were compared with the wind tunnel test results.The influence of the angle of attack of the incoming wind on the aerodynamic stability of the plate is analyzed through the vortex cloud diagram and the streamline diagram.Third,a reduced-scale model of the streamlined flat box girder of the main girder of the Sutong Bridge was established to identify the flutter derivatives of the model at an angle of attack of 0°and forecast the wind speed the flutter critical wind speed of the model.The comparative study of the numerical simulation results of the vibration method further verified the effectiveness of the free vibration method for the flutter numerical simulation analysis on the streamlined box girder whose the aerodynamic shape was similar as the flat-plate section.And then the influence of different wind attack angles on the flutter performance was analyzed.Fourth,a scaled model of the old Tacoma Bridge was established considering its detailed structure,to analyzed its flutter performance.The vortex-induced resonance and "soft flutter" phenomenon were analyzed through its vibration amplitude and frequency.And then the reasons for the aerodynamic instability of the bluff body section were studied through the vorticity cloud diagram and the pressure cloud diagram.Finally,the vibration form of "soft flutter" was analyed.