Numerical Simulation Of Flutter Of Long Span Bridges Under Wind Load

The fundamental frequency of natural vibration of bridge decreases gradually,the structure will be completely destroyed with the increase of bridge span,the influence of wind load on the stability of bridge is increasingly significant,especially in the C and D areas with complex surface types,the wind-induced flutter of the bridge is easily caused by the skew wind,once the flutter occurs,the whole structure will be completely destroyedAt present,most of the researches on flutter are about wind attack angle,frequency,etc,but little attention is paid to skew wind,especially more than yawed angle of 30.therefore the paper uses the numerical simulation software to build the model of the long-span bridge with four typical working conditions(section shape: blunt,wind tuyere type,inclined web with shoulder and splitter plate)in the two-dimensional and three-dimensional skew wind flow field,according to Scanlan’s flutter theory,the flutter stability of the model at the angle of 0 to 60 is obtained,the simulation results are compared with the theoretical values of Theodorson’s ideal plate and the existing literature result,and the correctness and reliability of the simulation method are verified,finally,the flutter stability of long-span bridges under four working conditions and its main influencing factors are studied,The main research contents and conclusion are as follows:Expounds the background of bridge flutter research at present,and sorts out the basic theories of Computational fluid dynamics.The identification methods of theoretical solution of ideal plate and numerical simulation solution with flutter derivative and the calculation method of flutter critical wind speed.Based on the engineering of EGong Yan river bridge,the first 40 modes are extracted after the three-dimensional model is established.After analyzed the modal factor and dynamic characteristics under the skew wind,the maximum displacement response of torsional vibration will appear.In the two-dimensional simulation flow field,the aerodynamic shape difference of four kinds of girder sections with the same aspect ratio is considered under the yawed angle of 0 to 60.The forced vibration method of different states is used to obtain the flutter Parameters,by analyzing the cloud chart of result and four main girder section geometric shape,the improvement rate of flutter stability increases after 30 yawed angle,and the flutter stability of four main girder sections is inversely related to the initial windward angle,the higher flutter critical wind speed is obtained due to the minimum windward angle of work condition two.In the three-dimensional simulation flow field,four kinds of working conditions of segment model with the same section type and aspect ratio as the two-dimensional girder are established,comparative study of flutter stability with two-dimensional model at 7 yawed angles.The three-dimensional flow field improves the single flow direction,and the calculation result are better than two-dimensional flow field,and flutter stability is still best under work condition two.The numerical simulation method is used to study the flutter stability of four typical sections under the action of yawed wind,it has low cost and high repeatability than the wind tunnel test.The simulation of two-dimensional and three-dimensional skew flow field is carried out at the same time,comparative and analysis of calculation results of four typical working conditions under large yawed angle,the flutter stability of the section of main beam with tuyere or small windward angle is better in the skew flow field.