Study On Modelling Of Rotating Flexible Wheelset In Vehicle-track Dynamic System

City development and improvement of people's life have a close relationship with the convenient traffic,and increasing operational speed indeed is an effective way to solve the traffic jam which is a big problem with the development and the improvement.However,operational speed increase is restricted by many factors,because it results in high noise level and severe unevening wear of wheel-rail wear.These are high frequency issues that threaten operational safety and riding comfort.Therefore it is in top need to work on solving them.A thorough coupling vehicle-track dynamic system model is an effective and economic way to effectively solve these problems.It is very important to consider the effect of a high-speed rotating flexible wheelsets in such a model on the behavior of high-speed train and track.This is main purpose of this thesis.This modelling comprises the following three procedures.Firstly,in order to analyze the effect of wheelset axle bending,the wheelset is modelled as an Euler-Bernoulli beam(wheelset axle only).At the two ends of the axle,two wheels are treated as rigid bodies which are fixed on the two ends.It considers the wheelset axle bending deformation in two planes.One is plane parrallel to the track level,and the other is perpendicular to the track level and the longitudinal direction,respectively.The coupling influence of the bending in two planes is neglected.The mode superposition method is used to solve the equations of wheelset motion.The wheels' radial sections are assumed to be perpendicular to the wheelset axle at their connection all the time.This model is used to confirm spatial location of wheel and rail in rolling contact at each instant,which can considers the effect of the wheelset bending on contact geometry parameters of wheel/rail.Secondly,in order to consider the wheelset modes with higher natural frequencies such as wheel umbrella modes and nodal diameter modes,differential equation of the wheelset motion is described with the modal coordinate vector based on the finite element method and modal superposition method.The influence of umbrella modes and nodal diameter modes is analyzed on the rolling contact behavior.In order to consider effect of both wheel web deformation and axle bending,the calculation method of spatial location of wheel/rail in contact needs to be modified again,because that used in the first procedure only can reflect the bending influence.In thought of the common feature of the modes under 5000Hz,the profiles of the wheel rims keep un-deformed or their deformation are quite small and neglected although the wheelset deformation occurring.So,a dummy of rigid wheelset is introduced in the wheelset modelling.If so,the contact issue between a flexible wheelset and a two pair of rails turns into the issue between a dummy of rigid wheelset and two rails.The key of this contact model use is to calculate the motion of the dummy of rigid wheelset.This involves coordinate transformations through using different coordinate systems.Thirdly,wheelset rotation effect is integrated into the second procedure.The derivation of the differential equations of motion of wheelset is in Eulerian coordinate system which does not rotate with the wheelset.The force applied in the fix spatial point on the wheelset can be considered more conveniently in the motion equations to reduce the calculation-time consuming in solving them.The Lagrange equation and modal superposition method are used in the derivation.The difficulty of this model building is how to calculate the matrix coefficients of the motion equation which involves a second derivative.Integrating the three procedures into the vehicle/track dynamic model,the wheel/rail dynamic responses are analyzed in the medium and high frequency ranges.The effect of irregularities of wheel/rail is considered,such as random and harmonic rail irregularities.By analyzing and comparing the dynamic responses(wheel/rail forces,lateral motion of wheel/rail contact points)in time and frequency domains of different wheelset models(rigid,non-rotating and flexible and rotating and flexible),the influence of different resonant modes and high-speed rotation of wheelset on the wheel/rail contact behavior are investigated in detail.