Moving Element Method For High-speed Railway Ballastless Track Dynamic Performance Analyses

In recent years, the gap between limited transport capacity of China Railway and thehuge domestic transport demand of both travelers and goods has become larger and largerwhich urges China Railway to realize leapfrog development within a short period. With theimplementation of the sixth speedup program to the existing railways and the flourishing ofhigh-speed rail service and passenger special lines, it has effectively increased the transportcapacity and efficiency. The rapid development of China Railway has brought remarkableimprovement in speed and optimization of track structures. And now ballastless tracks havebecome a new development trend. The ballastless track system of high-speed railway hasbrought huge social economic benefits on one hand; on the other hand, it has devoted to theincrease of dynamic response of the track structure, and has solved a series of problems suchas vibratory noises, and safety will be ensured even in serious status. Ballastless tracksdifferentiate greatly from ballast tracks, relative domestic theoretical research and experimentis still in its infancy, most of theoretical results have been borrowed from abroad. Therefore,the research on the dynamic features of ballastless track system has its practicality andurgency.Based on numerous theoretical research and analysis, the research on ballastless tracksystem has employed mobile element method, and put forward the corresponding computingmodel of High-speed Train-ballastless tracks-subgrade coupling system, whose computationcombined finite element method and mobile element method. Firstly, this computing modeldiscretizes into two parts (the top and the bottom), the top vehicle element is one vehiclewhich using finite element method and Lagrange equation to calculate mass matrix, dampingmatrix and stiffness matrix of the vehicle element; while the bottom track element is furtherdiscretized into three-dimensional beam element which using mobile element method tocompute mass matrix, damping matrix and stiffness matrix of the track element. Properbottom track length can be selected in computation to couple the vehicle element into trackelement, thus, the total mass matrix, total damping matrix and total stiffness matrix of thewhole model can be completed at once. The model of High-speed Train-ballastless tracks-subgrade coupling system, established by employing mobile element method and finiteelement method, has following merits: first, the constancy of the wheelrail contact point haseliminated the necessity of tracking the contact points of each element; second, the influenceof boundary on computation result will be wiped off, for vehicles can never reach theboundaries; third, this method can be used to study gear changes. Besides, elements ofdifferent sizes can use this model, especially when facing the problem of multiple contactpoints, to improve modeling efficiency. Using Matlab software to program the computing model of High-speed Train-ballastlesstracks-sugared coupling system, and through adjustment of correlation parameters, the resultcan be regarded as simulation computation under the actual conditions. This paper mainlycomputes and analyzes two different operating conditions; they are the dynamic response ofvehicle speed change and the dynamic response of vehicle ballastless track system underirregularity state. In order to get the first-hand material of dynamic response of vehicleballastless track system and to further testify the above model and the correctness of thecomputing theory, the author selects a certain high-speed railway sugared segment for fieldtest, and then compares the test result with simulation computation of the model, the tworesults have approximately matched each other, regardless of some objective factors. Thisresearch has reached the following conclusions:(1) the responses of displacement andacceleration of rails, slabs and concrete-support-layers in ballastless track structures haveclosely related to the running speed of trains. The higher the train’s speed, the bigger thedynamic response value will be, and the fiercer the response will be.(2) The responses ofdisplacement and acceleration of rails, slabs and concrete-support-layers in ballastless trackstructures have close relationship with track irregularity. The worse track irregularity state, thebigger the dynamic response value will be.(3) the dynamic stress of ballastless track haveclosely relative with train speed and irregularity state of tracks, The higher the train’s speed,the bigger contract force; the worse track irregularity, the bigger contract force.(4) Therunning speed of trains and track irregularity state have limited impact on the vibratoryacceleration of vehicle body which is an important index affecting passengers’ ride comfort.This means that the damping capacity of primary suspension and secondary suspension inCRH have functioned well.(5) Present logical Parameter range of Track structure’s sectionsby calculate different parameters.The computing model and the methods in this paper have better correctness andpracticality, but there are some disadvantages as well. At the end of the paper, the author hascome up with several problems in need of solutions based on the conclusions made from theabove analysis.