Development of track geometry inspection equipment for high-speed comprehensive inspection train in China

Purpose–This study aims to analyze the development direction of track geometry inspection equipment for high-speed comprehensive inspection train in China.Design/methodology/approach–The development of track geometry inspection equipment for highspeed comprehensive inspection train in China in the past 20 years can be divided into 3 stages.Track geometry inspection equipment 1.0 is the stage of analog signal.At the stage 1.0,the first priority is to meet the China’s railways basic needs of pre-operation joint debugging,safety assessment and daily dynamic inspection,maintenance and repair after operation.Track geometry inspection equipment 2.0 is the stage of digital signal.At the stage 2.0,it is important to improve stability and reliability of track geometry inspection equipment by upgrading the hardware sensors and improving software architecture.Track geometry inspection equipment 3.0 is the stage of lightweight.At the stage 3.0,miniaturization,low power consumption,self-running and green economy are co-developing on demand.Findings–The ability of track geometry inspection equipment for high-speed comprehensive inspection train will be expanded.The dynamic inspection of track stiffness changes will be studied under loaded and unloaded conditions in response to the track local settlement,track plate detachment and cushion plate failure.The dynamic measurement method of rail surface slope and vertical curve radius will be proposed,to reveal the changes in railway profile parameters of high-speed railways and the relationship between railway profile,track irregularity and subsidence of subgrade and bridges.The 200 m cut-off wavelength of track regularity will be researched to adapt to the operating speed of 400 km/h.Originality/value–The research can provide new connotations and requirements of track geometry inspection equipment for high-speed comprehensive inspection train in the new railway stage.

Influence of span-to-depth ratio on dynamic response of vehicle-turnoutbridge system in high-speed railway

For high-speed railways,the smoothness of the railway line significantly affects the operational speed of trains.When the train passes through the turnout on a long-span bridge,the wheel-rail impacts caused by the turnout structure irregularities,and the instability arising from the bridge's flexural deformation lead to a strong coupling effect in the vehicle-turnout-bridge system.This significantly affects both ride comfort and operational safety.For addressing this issue,the present study considered a long-span continuous rigid-frame bridge as an example and established a train-turnout-bridge coupled dynamic model of high-speed railway.Utilizing a selfdeveloped dynamic simulation program,the study analysed the dynamic response characteristics when the train passes through the turnouts on the bridge.It also investigated the influence of different span-to-depth ratios of the bridge on the vehicle dynamic response when the train passes through the main line and branch line of turnouts and then proposed a span-to-depth ratio limit value for a long-span continuous rigid-frame bridge.The research findings suggest that the changes in the span-to-depth ratio have a relatively minor impact on the train’s operational performance but significantly affect the dynamic characteristics of the bridge structure.Based on the findings and a comprehensive assessment of safety indicators,it is advisable to establish a span-to-depth ratio limit of 1/4500 for a long-span continuous rigid-frame bridge.

Parameters studies for rail wear in high-speed railway turnouts by unreplicated saturated factorial design

Rail wear is one of the main reasons for reducing the service life of high-speed railway turnouts in China. The rail wear characteristics of high-speed railway turnouts are influenced by a large number of input parameters of the complex train-turnout system. To reproduce the actual operation conditions of railway turnouts, random distributions of these inputs need to be considered in rail wear simulation. For a given nominal layout of the high-speed railway turnout, 19 input parameters for rail wear simulation in high-speed railway turnouts are investigated based on orthogonal design of experiment. Three dynamic responses(wheel-rail friction work, normal contact force and size of contact patch) are defined as observed values and the significant factors(direction of passage, axle load, running speed, friction coefficient, and wheel and rail profiles) are determined by two unreplicated saturated factorial design methods, including the half-normal probability plot method and Dong 93 method. As part of the associated rail wear simulation, the influence of the wear models and the local elastic deformation on the rail wear was separately investigated. The calculation results for the wear models are quite different, especially for large creep mode. The local elastic deformation has a large effect on the sliding speed and rail wear and needs to be considered in the rail wear simulation.

Length optimization of straight line connecting turnout on main line in high-speed railway station yard

Taking the development of high-speed railway in China as background, and referring to the dynamic theory and wheel-rail contact mode, dynamic analysis model was established, considering the setting position of straight lines and running conditions of train in high-speed railway station yard. Using the established model, and choosing vehicle lateral acceleration and wheel suspension as the evaluation indexes, dynamic characteristic of vehicle traveling in turnout and adjacent area on main line was analyzed, and effects on travelling safety and stability of train aroused by length variation of straight lines were calculated based on analyzing the damping rules of vibration. The results show that, a certain length of straight lines can alleviate the vibration aroused in turnout and curve(turnout), length of straight lines connecting turnouts in different sections on main line was proposed to meet the demand of traveling stability, and shortening or cancelation of straight line for the scale limitation of station yard has less influence on operation safety of train.

Analysis on the influencing factors of mechanical characteristics of jointless turnout group in ballasted track of high-speed railway

Turnouts are in close proximity to each other in the stations of high-speed railway.The stress and deformation of those turnouts which are laid nearby are influenced mutually and therefore those turnouts should be considered together.On the basis of finite element method,according to No.18 jointless turnout with swing nose frog in the ballasted track of high-speed railway,a finite element calculating model of jointless turnout group coupling the longitudinal,lateral and vertical directions is established.The influencing factors,for instance the number of turnouts,connection form,length of intermediate straight line and ballast bed longitudinal resistance,on the mechanical characteristics of turnout,transverse deformation of switch rail and range of rail temperature for laying turnout are analyzed in this paper.The results show that more turnouts result in more obvious interaction between them when the lengths of intermediate straight line are the same;more significant influence between the turnouts with the connection form of head-to-head is produced compared to that of head-to-end;from the perspective of statics,influence between turnouts could be ignored basically if the intermediate straight line is over 50 m;bigger longitudinal resistance of ballast bed leads to less influence between the turnouts.

Numerical investigation on wheel-turnout rail dynamic interaction excited by wheel diameter difference in high-speed railway

The wheel-rail relationship in turnout is more complicated than that in ordinary track. Profile wear and machining errors of the wheelset cause deviations Of the rolling radius on different wheels. Therefore, wheelsets move to the direction of smaller diameter wheels in search of a new stable state and to change the condition before entering the turnout. Thc main aim of the present work is to examine the wheel-turnout rail dynamic interaction combined with the static contact behaviour. Calculations are performed on a high-speed vehicle CRH2 and the No. 12 turnout of the passenger dedicated line. The wheel-turnout contac! geometric relationship and normal contact behaviour under wheel diameter difference are assessed by the trace principle and finite element method. A high-speed vehicle-turnout coupling dynamic model is established based on SIMPACK software to analyse the wheel-rail dynamic interaction, riding comfort, and wear. Both the wheel diameter amplitudes and distribution patterns are accounted for. The simulation shows that wheel diameter difference can greatly disturb the positions＇ variation of wheel-rail contact points and affect the normal contact behaviour on switch rails by changing the load transition position. The effect of wheel diameter diffierence on wheel-turnout rail dynamic interaction can be divided into three according to its amplitude： when the wheel diameter difference is within 0-1.5 mm, the wheel flange comes into contact with the switch rail in advance, causing a rapidly increased lateral wheel-rail force; when it is within 1.5 2.5 mm, trains are subject to instability under equivalent in-phase wheel diameter difference; when it is larger than 2.5 mm, the continuous flange-switch rail contact helps strengthen the vehicle stability, but increases the wheel-rail wear. It is recommended to control the wheel diameter difference to within 2.5 mm but limit it to 2 mm if it is distributed in-phase.