Study On Nonlinear Aerodynamic Model And Flutter Of Bridge Deck Based On Volterra Series

With the development of science and technology,the innovation of engineering technology and the improvement of theoretical level,more and more large span bridges were designed and constructed during the last decades.Bridge construction has shown a development trend of longer,lighter and more flexible,which leads to the problems of wind-induced vibration of the structures can not be ignored.Flutter is one of the wind-induced vibration problems,which can cause the large divergent vibration of the bridge,leading to the destruction of the bridge structures and resulting in serious consequences.Due to the nonlinear aerodynamic characteristics of main decks of bridges with large amplitude or angle of attack,the flutter critical wind speed calculated by linear flutter analysis theory may underestimate the flutter stability of the actual bridge.With the further increase of bridge span,it is necessary to carry out the research on nonlinear aerodynamic model and flutter stability of bri dge girder section,for laying a foundation for the establishment of nonlinear flutter analysis theory and reasonable evaluation of flutter stability of long-span bridges.This thesis established reduced-order models of nonlinear aerodynamic based on Volterra series for typical main beam sections.Moreover,the flutter stability of bridge deck was calculated with the ROM aerodynamic model proposed in present thesis.The main research work was sunmarized as follows:(1)Firstly,the state-of-the-art in long-span bridges,and the wind effects on bridge structures were reviewed.Then,the achievements and shortcomings of linear self-excited aerodynamic force theory were summarized.Moreover,the domestic and foreign research status of CFD(Computational Fluid Dynamics)numerical simulation method in solving aeroelasticity problems in aviation,bridge and other fields were expounded.Finally,three nonlinear aerodynamic reduced-order models based on CFD method were reviewed.(2)This thesis reviewed the theory of the reduced-order models(ROM)based on Volterra series in nonlinear aerodynamics,and deduced the formulas of a relatively simple method to identify the kernel of Volterra series,namely the impulse response method.Meanwhile,a ROM based on Volterra series in nonlinear aerodynamics was established for a thin plate to study its aerodynamic nonlinear characteristics with large amplitude,which laid the foundation for subsequent research.(3)Taking the main girder section of Great Belt East Bridge(without guardrails,etc.)as an example,a nonlinear aerodynamic ROM of the streamlined main girder section was carried out.By comparing the aerodynamic responses of CFD numerical simulation and reduced-order model based on Volterra series to the large sinusoidal excitation forced motion of Great Belt East Bridge,the practicability and accuracy of the reduced-order model based on Volterra series in nonlinear aerodynamics was proved.The results showed that the aerodynamic characteristics of the streamlined box girder of Great Belt East Bridge in the state of bare beam are weakly nonlinear.Then,taking the original section of Lingdingyang Channel Bridge as an example,this paper established reduced-order model based on Volterra series in nonlinear aerodynamics for the actual streamlined box girder with ancillary facilities such as anti-collision guardrail,etc.By comparing the aerodynamic responses of CFD numerical simulation and reduced-order model based on Volterra series to the large sinusoidal excitation forced motion of Lingdingyang Channel Bridge,the results proved that the nonlinear aerodynamic effect on the streamlined main girder section is improved obviously in large amplitude and high frequency motion,but still weak in low frequency motion after the installation of ancillary facilities such as anti-collision guardrail,etc.(4)Combined with ANSYS Fluent dynamic mesh technology and User-Defined Functions(UDF),the Newmark-β method was used to solve the structural vibration equation,and the fluid-structure interaction simulation of the main beam section was realized to calculate the flutter response characteristics of the main girder sections of Great Belt East Bridge and Lingdingyang Channel Bridge.Then,using the nonlinear aerodynamic reduced-order model based on Volterra series,combined with the Newmark-β method,the flutter response calculation method of the bridge girder was established;The flutter response of the main girder sections of Great Belt East Bridge and Lingdingyang Channel Bridge was calculated.Finally,the accuracy and efficiency of the flutter response characteristic calculation of streamlined girder section using these two methods were compared and analyzed.The results show ed that the nonlinear aerodynamic model based on Volterra series established in this paper can realize the efficient calculation of the fluid-structure interaction of the main beam section,and the calculation accuracy is close to that of the fluid-structure interaction analysis method based on CFD.