Multi-objective Optimization Of Bridge Wind Barrier Parameters Based On Hybrid Genetic Algorithm

In recent years,traffic accidents on expressways caused by strong winds are frequent,which not only endanger personal safety,but also cause huge losses to economic property.In order to improve the driving safety of vehicles under the action of strong wind,the most commonly used protection measure is to set up the wind barrier on the bridge deck,which has been successfully applied in a large number of practical projects at home and abroad.However,the setting of the wind barrier will change the aerodynamic performance of the vehicle-bridge system.Hence,it is necessary to study the influence of.the wind barrier parameters(height and air permeability)on the vehicle-bridge system and determine the optimal wind barrier parameters.Based on a three-tower double-cable-plane composite beam cable-stayed bridge,wind tunnel tests are carried out to study the influence of the height and air permeability of the wind barrier on the aerodynamic performance and static response of the vehicle-bridge system.Multi-objective optimization about the height and air permeability of wind barrier is realized by applying hybrid genetic algorithm.The influence of the optimal wind barrier parameters on the wind-induced vibration performance of the main girder section is investigated by wind tunnel tests.The main research contents of this thesis are as follows:(1)This thesis briefly introduces the research background and significance,and conventional research methods of wind barrier are expounded.The domestic and foreign research status involving the effect of wind barriers on the aerodynamic performance,wind-induced response and wind barrier parameter optimization of vehicle-bridge system is reviewed.Through the summarization of the shortcomings of the existing research work,the main research content work of the thesis is elicited.(2)Based on a three-tower double-cable plane composite girder cable-stayed bridge,through wind tunnel tests,the aerodynamic coefficients of the van truck under different heights and air permeabilities of the wind barrier are obtained.The influence of wind barrier parameters on vehicle aerodynamic coefficient is analyzed.Based on the vehicle aerodynamic coefficients under different wind barrier parameters,the critical wind speed of the vehicle on the bridge is analyzed by using the vehicle static instability model,which provides an optimization target for the subsequent optimization of the wind barrier parameters.(3)Through wind tunnel tests,the three-component force coefficients of the main girder under different wind barrier heights and air permeabilities are studied.The ANSYS finite element model is established.Then the lateral displacement response of the bridge under the critical wind speed of the static wind instability test is calculated by using the nonlinear static wind stability calculation method,which provides another optimization target for the subsequent optimization of the wind barrier parameters.(4)Based on the genetic algorithm(NSGA-Ⅱ),the height and air permeability of the wind barrier are used as the optimization parameters,and the critical wind speed of the vehicle and the lateral displacement of the main beam are taken as the optimization targets.The Pareto solution set is obtained through multi-objective optimization.Then the relative efficiency value of the Pareto solution set is calculated by adopting a comprehensive evaluation method(super-efficiency CCR-DEA model)to obtain the optimal wind barrier parameters.(5)Through wind tunnel tests,the influence of the optimal wind barrier obtained through multi-objective optimization on the vortex-induced vibration and flutter performance of the main beam is discussed.Meanwhile,the corresponding suppression measures are investigated.