Flutter Stability Analysis Of Long Span Asymmetric Suspension Bridge Based On CFD Numerical Simulation

With the increasing span of suspension bridge structure,the flutter vibration stability problem is becoming more and more significant.Especially with the vigorous construction of Mountainous Expressway in recent years,asymmetric suspension bridge structure forms are constantly emerging.This kind of structure also has an impact on the flutter stability of longspan suspension bridge structure,and the flutter analysis research of this kind of suspension bridge structure is less.Therefore,in order to better analyze the influence of asymmetric structure on flutter stability of suspension bridge,this paper studies and analyzes the influence of three kinds of asymmetric structure on flutter critical wind speed of suspension bridge.Therefore,this paper takes a long-span suspension bridge with asymmetric supports as the research background,uses CFD numerical simulation to identify the flutter derivatives of the main girder section,and develops the corresponding APDL two parameter three-dimensional flutter analysis program based on the frequency domain full mode method to analyze the influence of different asymmetric structures on the flutter critical wind speed.The main research contents and conclusions are as follows:(1)The basic theory of bridge flutter and CFD numerical simulation method is described.The flutter derivative of ideal flat plate is identified by numerical simulation and compared with the analytical solution of Theodorsen theory.The results show that the overall error of theoretical solution and simulation identification result of ideal flat plate is very small,and the variation trend of flutter derivative with converted wind speed is basically the same,which verifies the numerical model in this paper.The simulation method is feasible and reliable.(2)Based on the separated forced vibration method,the flutter derivatives of the main girder section in the construction stage at 0° and ± 3° wind attack angle and the completed main girder section with auxiliary deck facilities at 0° wind attack angle are identified respectively,and the corresponding two-dimensional flutter critical wind speed is obtained.The results are compared with the test outcoms,which display that the test outcoms are in accordance with the numerical outcoms,and the error is relatively small;The difference sizes among the simulation outcoms and the test outcoms is fewer than 7%.The numerical simulation results also provide the flutter derivative interpolation for the three-dimensional flutter analysis of asymmetric suspension bridges.(3)According to the results of flutter derivatives identified by the previous numerical simulation,the aerodynamic self-excited force is realized in the ANSYS finite element model by using MATRIX27 matrix element.Three kinds of full bridge flutter finite element analysis models with different equal height supports,asymmetric side span main cables and asymmetric side span suspenders are established,and the corresponding two parameter search iterative APDL calculation program is compiled for three-dimensional flutter stability analysis.According to the calculation results,the results show that: the asymmetric structure with unequal height support and asymmetric arrangement of side span suspenders will make the ratio of natural frequency and torsional frequency of suspension bridge smaller,so that the flutter critical wind speed is reduced,and the flutter stability is decreased;the asymmetric structure with unequal side span main cable span almost has no change to the natural vibration characteristics of the structure,and the non symmetric structure within a certain range is stable It is said that the influence of span combination arrangement on flutter stability of suspension bridge is very small,and the influence on flutter stability of suspension structure can be almost ignored.(4)Finally,based on the numerical simulation,the influence of aerodynamic shape parameters optimization on flutter performance of girder section is studied.The results show that the change of height width ratio,inclined web angle and air nozzle angle will not have much influence on flutter derivatives A1* and A3* of girder section,and there will be a maximum flutter coefficient under the premise of avoiding girder section approaching bluff body section.The excellent ratio of width to thickness makes the flutter stability of the main girder structure the best;the critical flutter wind speed of the inclined web angle of the cross section of main girder structure has been improved obviously between 18° and 15°,and the flutter stability is relatively good;the flutter stability performance of the main girder section is relatively good when the angle of the nozzle is relatively small,especially at about 29° for the best effect.