Study On Influence Law And Multi-objective Optimization Of Pantograph’s Aerodynamic Uplift Force

The aerodynamic uplift force of the pantograph is an important part of the pantographcatenary contact force.As the train’s running speed increases,the variation of the pantograph aerodynamic uplift force has a greater impact on the contact force.Meanwhile,the pantograph has two operating conditions including the knuckle-downstream and knuckle-upstream conditions,as the pantograph is longitudinal asymmetry,the aerodynamic uplift forces under the operating conditions of the knuckle-downstream and knuckle-upstream are different,the static uplift forces need to be adjusted when the train changes the running direction.Therefore,optimizing the aerodynamic uplift force of the pantograph and ensuring the consistency of the aerodynamic uplift force under two operating conditions is of great significance to alleviate the fatigue damage of the airbag system and reduce the possibility of pantograph-catenary accidents.This thesis mainly studies the effect of the strips,upper arm,lower arm and baffles on the aerodynamic performance and aerodynamic uplift force of the pantograph using the computational fluid dynamics and multibody system dynamics under the condition of no crosswind.Based on the above variables,a surrogate model of the aerodynamic uplift force of the pantograph is also established,and a genetic algorithm is used to optimize the aerodynamic uplift force with multiple objectives.First of all,the effect of the strip spacing on the aerodynamic uplift force of a high-speed pantograph with double-strip is studied.14 kinds of strip models with different spacings in the range of 0 mm and 900 mm are established,and the aerodynamic characteristics of 300 km/h pantograph with the double-strip are numerically simulated.The results show that the aerodynamic uplift force first increases and then decreases with the increase of the spacing under the knuckle-downstream operating conditions,whereas the aerodynamic uplift force basically increases with the increase of the spacing under the knuckle-upstream operating conditions.In addition,the aerodynamic performances of the pantographs with the single-or double-strip are compared.The aerodynamic uplift forces of the two pantographs under the knuckle-downstream conditions are basically the same,whereas the aerodynamic uplift force of the single-strip pantograph is smaller under the knuckle-upstream conditions.However,the aerodynamic resistance of the strip of the double-strip pantograph is 26% ～ 30% lager than that of the single-strip pantograph,and the far-field aerodynamic noise of the single-strip pantograph is 4 d BA lower than that of the double-strip pantograph.Therefore,the aerodynamic and performance and aeroacoutisc performances of the single-strip pantograph are better.Secondly,the effect of the diameter of the upper and lower arms on the aerodynamic uplift force of the pantograph is studied.7 pantograph models with different diameters of the upper arm and 7 pantograph models with different diameters of the lower arm are established.The aerodynamic characteristics of the pantographs are numerically simulated,and the results show that both the aerodynamic lift force of the upper arm and the aerodynamic uplift of the pantograph increase with the increase of the diameter of the upper arm,and decrease with the increase of the diameter of the lower arm under the knuckle-downstream conditions,however,the diameter of the lower arm has a smaller effect on the aerodynamic uplift force of the pantograph.Morewhile,both the aerodynamic lift force of the upper arm and the aerodynamic uplift of the pantograph decrease with the increase of the diameter of the upper arm,and increase with the increase of the diameter of the lower arm under the knuckle-upstream conditions.Then,the optimization process of installing the baffle to optimize the aerodynamic uplift force of the pantograph is proposed,so that the aerodynamic uplift forces of the pantograph under the two operating conditions are basically equal and satisfy the standard requirements.The aerodynamic uplift forces of the pantograph equipped with a 0° baffle are both positive under the knuckle-downstream and knuckle-upstream operating conditions,but the magnituges are not equal.The aerodynamic characteristics of the independent baffles are numerically simulated,and it is obtained that the aerodynamic lift force of the baffle decreases with the increase of the baffle angle under the knuckle-downstream condition.The aerodynamic lift force of the baffle increases with the increase of the baffle angle under the knuckle-upstream condition,and it is approximately linear.The optimal angle range of the baffle can be estimated by integrating the aerodynamic results of the pantograph and independent baffle,and the optimal baffle can be obtained by the numerical simulating baffles and pantographs within the above angle range.The optimization process of installing the baffle to optimize the aerodynamic uplift force is universal and can be applied to various types of pantographs,which can provide a reference for the pantograph aerodynamic design.Finally,a newly optimization constrained expect improvement infill criterion is proposed based on the traditional constrained expect improvement criterion.The optimization efficiencies of the above criteria are compared using the single objective,multi-objective and constrained multi-objective test functions.The surrogate model is established according to the optimization constrained expect improvement infill criterion,and the diameters of the upper arm,lower arm and the baffle angle are choosen as the design variables.The design space constraint condition is that the diameter of the upper arm is smaller than that of the lower arm.The optimization goals are to minimize the difference in the aerodynamic uplift forces and the aerodynamic resistance of the pantograph under two operating conditions,and one constraint is that the aerodynamic uplift force satisfies the standard.The Pareto solution set of the multiobjective optimization is obtained using a genetic algorithm.The aerodynamic uplift forces of the optimal pantograph under the knuckle-downstream and knuckle-upstream are 36.1 N and39.9 N,respectively,and the pantograph-catenary contact force satisfies the standard considering the static uplift force.Meanwhile,the difference in the aerodynamic uplift forces of the pantograph under two operating conditions is only 3.8 N.