A Transient Dynamic Study Of Friction-Induced Self-Excited Vibrations Of The Railway Wheel-Rail And Pantograph-Catenary Systems

The pantograph-catenary contact pair and the wheel-rail contact pair are two important frictional contact couples in the railway industry. The dynamics performances of the pantograph-catenary system and the wheelset-track system have important influences on the safe operation of high-speed trains. In the past, however, the research on the dynamics of the pantograph-catenary system and the wheel-rail system are mainly focused on those excited by surface irregularities of the contact line, rail and the vibration of the carbody. Seldom attentations ares paid to the self-excited vibration of the pantograpg-catenary sysmtem and the wheel-rail system. Rail corrugation was found a century ago, but it is still difficult to solve. Moreover, the arc charge phenomenon between the pantograph and catenary when trains travel at a low speed is not understood well. New ideas are needed to solve these elusive problems. Self-excited vibrations of the pantograph-catenary system and the wheel-rail system are probably a solution to these elusive problems. Since the interactions between the pantograph and catenary and between the wheel and rail are accompanied with friction, the friction-induced vibration of the pantograph-catenary and the wheel-rail systems most probably takes place. Therefore, studies on friction-induced vibrations of the pantograph-catenary system and the wheel-rail system become important in the aspects of both theory and practice. In the present dissertation, the effect of the friction-induced self-excited vibration on the dynamics performances of the pantograph-catenary system and the wheel-rail system are studied. The main research work involves:(1) A transient dynamic study of the friction-induced vibration of a reciprocating sliding system is performed and its experimental verification is carried out. Firstly, a finite element model of the reciprocating sliding system is established and the occurrence propensity of the friction-induced vibration during reciprocating sliding is predicted using the finite element complex eigenvalue analysis method. Secondly, a dynamic transient analysis of the model is carried out using the ABAQUS software. The result predicted by the complex eigenvalue analysis method is compared with the experimental test result. It is found that these two results have a good agreement in frequency. A comparison between the dynamic transient analysis results and the experimental results is carried out. And it is found that the dynamic transient simulation can accurately predict the frequencies and amplitudes of the unstable vibrations of the friction system. The complex eigenvalue and dynamic transient analysis results demonstrate that when squeal occurred, the normal acceleration and the tangential acceleration have the same vibration frequency. This phenomenon indicates that the motion coupling between the normal vibration and tangential vibration is a main cause resulting in squeal occurrence. Moreover, a parameter sensitivity analysis shows that the normal load, frequency and displacement of reciprocating sliding have important influences on the friction-induced vibration of the metal reciprocating sliding system. The large fluctuation of the normal contact force due to the friction-induced vibration causes a rise of the roughness value of the sliding surfaces and the uneven pit-like material removal. The loading methods have a significantly effect on the squealing vibration. Improving the loading method may suppress the unstable vibration.(2) The effect of the friction-induced vibration on the dynamics performances of a pantograph-catenary system is studied. A dynamic model of a pantograph-catenary system is established. In the model, the motion of the pantograph is coupled with that of the catenary by friction. The stability of the pantograph-catenary system is studied using the finite element complex eigenvalue method and the transient dynamic method. Complex eigenvalue analysis results show that there is a strong propensity of self-excited vibration of the pantograph-catenary system when the friction coefficient is greater than 0.1. The dynamic transient analysis results show that the self-excited vibration of the pantograph-catenary system can affect the contact condition between the pantograph and catenary. If the amplitude of the self-excited vibration is strong enough, the contact may even get lost. A parameter sensitivity analysis shows that the coefficient of friction, static lift force, pan-head suspension spring stiffness, tension of contact wire and the spatial location of the pantograph have important influences on the friction-induced self-excited vibration of the pantograph-catenary system. Bringing the friction coefficient below a certain level and choosing a suitable static lift force can suppress or eliminate the contact loss between the pantograph and catenary.(3) A numerical study of the rail corrugation based on saturated creep force-induced self-excited vibration of a wheelset-track system is carried out. Two dynamic models of a wheelset-track system on a tight curved track and on a straight track are established. Both the transient dynamic and complex eigenvalue analyses are performed to study the self-excited vibration performances of the wheelset-track system. It is assumed that in the models the creep forces between wheels and rails are saturated, that is, approximately equal to the normal forces multiplied by the dynamic coefficients of friction. The simulation results demonstrate that the saturated creep force can induce self-excited vibration of the wheelset-track system. The normal contact force between the wheel and rail fluctuates at the same frequency as the wheel and rail vibrate when the self-excited vibration occurs. Under the same conditions, the frequency of the friction-induced vibration is very close to the measured corrugation frequency from the Beijing metro. This phenomenon indicates that the self-excited vibration of the wheelset-track system may be a main cause of rail corrugation occurrence. The parameter sensitivity analysis shows that the damping of the rail fastener has an important influence on the flutating amplitude of the normal contact force. Increasing the damping of the rail fastener may help to suppress the rail corrugation. The stiffness of rail fastener has a little influence on the fluctuating amplitude of the normal contact force between the wheel and rail.