| In China,rail transit has enjoyed rapid development and formed a large system.While facilitating our everyday travel,its development has set higher requirements for track maintenance support.Rail grinding techniques,as effective and important means to clear rail surface damage,have played an increasingly significant role in the maintenance of public works.The rail grinding vehicle,however,is the double-edged “scalpel” in rail damage treatment—on the one hand,it can effectively improve wheel-rail contact relation and extend the rail service life;on the other hand,it might lead to new damage.The research on the influence of dynamic characteristics of the rail grinder on the grinding quality is relatively complex,and theoretical modeling and numerical simulation involve vehicle engineering,material science,hydromechanics,multi-body dynamics,etc.In previous dynamics models for the rail grinder,both the coupling interaction of pneumatic system-grinding-vehicle dynamic characteristics and the influences of the grinder system dynamics on the rail grinding quality were not taken into account,and the factors influencing the dynamic characteristics of the rail grinder have not been deeply studied yet.Therefore,the research on the dynamic characteristics of the rail grinder and their influences on the grinding quality has very important theoretical significance and engineering value for improving the rail grinding process,guaranteeing the rail grinding quality and reducing rail damages.In this thesis,experiments and numerical simulations on the dynamic characteristics of the rail grinder and their influences on the grinding quality were carried out.The main work and conclusions are as follows:(1)This thesis summarized previous research results and status of the rail grinding technology and rail grinder,described the existing damages on the rail surface,and figured out the influences of dynamic characteristics of the rail grinder on the surface irregularities of ground rails;this thesis clarified the necessities of the dynamic characteristics of the rail grinder to the research on rail grinding quality,and discussed the problems in the current research on rail grinding technology and rail grinder,and future research and development directions.(2)After investigating the ground rails of a domestic high-speed rail line,it was found that there were rail irregularities with a wavelength of about 60 mm on the surface of the ground rails.To identify its cause,the vibration characteristics of the grinder were tested.The natural vibration characteristics of the grinding trolley were figured out by testing the vibration characteristics of the rail grinding trolley using the hammering method;the vibration path of the vehicles and the natural vibration characteristics of the grinder were figured out by testing the vibration of the rail grinder,and the factors influencing the dynamic characteristics of the grinder such as wheel wear and irregularities were tested.The reasons for rail irregularities with a wavelength of 60 mm were analyzed based on natural vibration characteristics of the grinding trolley.(3)The multi-system dynamics model of rail grinder was established.Firstly,a system dynamics model of the rail grinder taking into account the pneumatic system and grinding was built,including the multi-body dynamics model of the rail grinder,the rigid-flexible coupling dynamic model of the grinding trolley,the dynamics model of the pneumatic system,and the dynamic analysis model for rail grinding wheel grinding.The simulation model was verified based on on-site vehicle vibration test and hammering test results.This model was used to simulate and analyze the dynamic characteristics of the rail grinder when the grinding trolley was working or not working.This model can effectively simulate the influences of the grinding between the grinding wheel and the rail on the fluctuation of the pneumatic system;through the rigid-flexible coupling model of the grinding trolley,the influences of grinder vibration on the grinding process were analyzed.(4)Based on the verified system dynamics model of the rail grinder,the influences of the rail grinder suspension parameters,hydraulic system parameters,pneumatic system parameters and typical wheel damages on the grinding quality were calculated and analyzed.The results showed that,when the grinder wheels were out of round,the wavelength irregularities corresponding to wheel out-of-roundness would be caused after rail grinding;the changes in the primary suspension stiffness of steel spring and the core plate of the vehicle would cause the fluctuations in the air pressure of the pneumatic system cylinder,and affect the rail grinding.The influences of primary and secondary suspension stiffness should be considered in designing and maintaining the rail grinder;the wheel diameter difference between left and right wheels after wheel grinding had a certain influence on the grinding amount.Optimization and improvement measures were proposed based on the parameters that significantly affect the grinding quality,and the rationality of the results was verified by simulation calculations.(5)A profile design method based on a multi-objective genetic optimization algorithm was established,and profile fitting was bi-arc fitting.The normal vibration amplitude of the rail grinder was deemed as the optimal solution constraint condition for the profile.To optimize the wear and fatigue indexes under a small grinding amount,the uniformity design idea was adopted in a full reprofiling cycle to ensure that the dynamic performance of the rail profile in the entire wheel reprofiling cycle was not inferior to that in standard wheel-rail matching.The design method of the grinding process is developed against the design of the rail grinding profile,and the maximum interval of grinding motor arrangement is proposed by combining simulation with practical working experience.In the process of power and speed selection,it is necessary to consider the influence of external excitations on the vibrating characteristics of the grinding vehicle such that the sensitive frequency of the grinding vehicle can be avoided by giving priority to different speeds and varying excitation frequencies. |
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