Research On Collision Characteristics Of Medium And Low Speed Maglev Train

Medium and low speed maglev transportation has entered the era of commercial operation in China,and many cities have the intention or plan to open the medium and low speed maglev operation line.At present,there are few researches on the passive safety of medium and low speed maglev trains at home and abroad,so this paper mainly studies its collision response and energy conversion law.Firstly,based on the main structural characteristics of the five-module medium and low speed maglev train consists of three cars,a nonlinear large deformation finite element three-dimensional collision model of the train including the track,the levitation chassis,the car body and the coupler and draft gear is established,using the explicit finite element program LS-DYNA to simulate and analyze the train-level collision.The analysis results show that during the collision process,the maglev vehicle has significant nodding and shaking head movements,which cause the overriding and zigzag lateral buckling of the train separately.The shaking head movement of the vehicle begins to be highlighted after the energy absorbing element of the middle coupler and draft gear reaches the maximum compression stroke,and the positive feedback mechanism of the middle coupler and draft gear promotes this movement and aggravates the lateral buckling of the train.The nodding movement of the vehicle not only causes the train to climb,but also causes a vertical impact between the levitation chassis and the track.The force is an irregular pulse load,and its amplitude reaches several hundred kilonewtons,however,at a low initial collision velocity,the train will not derail;in addition,the nodding movement will also change the direction of the rolling of the levitation chassis.In the longitudinal direction,due to the small capacity of the energy absorbing element,the front structure of the head car has undergone severe collapse deformation,and the survival space of the driver's cab is threatened,but the longitudinal average acceleration of each vehicle meets the requirements.Secondly,in order to improve the collision response,the energy allocation of the medium and low speed maglev train is optimized.According to the simulation analysis of the multi-rigid collision one-dimensional model of trains,it is found that under the premise of ensuring the same designed capacity,the design of force-displacement curve as multi-step with constant gradient or one which has a certain positive slope can make the energy absorbing device absorb more impact kinetic energy compared with a steady force-displacement curve whose force is a constant during a collision.For an energy absorbing device whose load increases linearly with displacement,the magnitude of the slope has an important effect on the energy absorption.A new anti-climbing energy absorbing device consisting of three-section straight-turn tube and anti-climbing teeth is designed with the load-displacement curve under axial compression presenting a two-stage type.The load at each stage is extremely stable without any initial load peak,at the same time,the stroke efficiency is high enough,showing a good deformability and energy absorption capacity.In order to make the designed anti-climbing energy absorbing device meet the requirement that the total energy absorption calculated according to the vehicle end energy absorption formula is not less than 250 kJ and the steady-state impedance is not more than 500 kN,the radial basis function agent model and the genetic algorithm are used to perform multi-objective optimization on the energy absorbing device to find out the suitable design thickness.Then,the simulation calculation of the maglev train after energy optimization design is carried out.The analysis results show that the lateral buckling basically disappears and there is no overriding any more;besides,the energy transmission is stable and orderly,and the vertical load between the levitation chassis and the track is significantly reduced.It is indicated that the installation of anti-climbing energy absorbing device for the head cars and reasonably increasing the energy absorption capacity of the intermediate coupler and draft gears can effectively improve the collision response and the crashworthiness of the train.Finally,the important influence parameters of the collision behavior of medium and low speed maglev train are studied.It is found that the change of friction coefficient between the levitation chassis and the track will change the vertical and lateral motion modes of the maglev vehicle.As the friction coefficient increases,the vertical height difference between the front structures of the active and passive head car increases when they are in contact,resulting in a increased risk of overriding;the friction work is nonlinearly increased significantly,leading to the proportion of the energy absorbed by the plastic deformation of carbody and the energy absorbing element being significantly reduced,contributing to ensure the occupant survival space.The greater the vertical stiffness of the air spring is,the lower the degree of vehicle's nodding movement is.The greater the axial stiffness of the anti-roller beam hanger is,the smaller the roll angle of the left and right modules of the levitation chassis is,which is more conducive to the correct position of the levitation chassis and reducing the risk of collision between the levitation chassis and the magnetic pole surface of the track.