Study On Related Running Safety Problems For High Speed Trains

The high speed trains in China are characterized by the high operating speed, long opration time and wide operating area. Thereforce, the safety-relevant dynamic problems during the long-term oprations of trains are more significant, e.g., the derailment safety issues in various running environment, hunting stability problems due to the improper wheel-rail matching relations in some particular locations of the track, as well as the braking induced impact and safety for the train to train rescue, etc. Focusing on the relevant dynamic safety prolems appeared in the field tests and line operations, and based on the mechanism analyses, numerical simulations and field tests, the evaluating methods of running safety for high speed trains and their appliacations are intensively studied. The detailed research works are as below:(1) Focusing on the dynamic-relevant safety problems of high speed trains, the safety evaluation methods are studied. Firstly, the dynamic and quasi-static evaluation methods for derailments at home and abroad are detailly investigated. Based on the force analysis for a wheelset, the quasi-static climbing derailement criterion is derived. The union safety domain considering simultaneously the wheelset derailment coefficient and wheel unloading ratio is adopted to evaluate the derailment safety. Different assessing methods for the hunting instability, e.g. the criterion of the limit cycle, methods of the wheel-rail interaction forces and the bogie lateral accelerations, are described. The mechanism of the bogie lateral acceleration alarm is studied based on the rigid motion assumption, and the effects of hunting motion types and measuring loacations on the bogie frame are studied. Aimed at the braking induced impacts for the train to train rescue, the compressed rotational behaviour and the stable mechanism of the coupler are studied. The limit values of operating safeties for the train to train rescue are formulated by the theoretical analyses and testing results.(2) The dynamic model of the vehicle system is developed and the influences of differernt wheel-rail creep models and contact parameters are analysed. According to the dynamic tests on the roller rig, the vechicle system dynamic model is validated through the natural frequency of the suspension system, the bifurcation diagram of the hunting motions and the ride comfort. The dynamic model of the train considering the coupler and draft gear is built, in which the motion degrees of freedom of the coupler, the hysteresis characteristics of the draft gear and the nonlinear boundary limitations are considered. The train and coupler models are verfified by the field test of train to train rescue, on the basis of which the in-trian forces of coupler, buffer displacements, in-train motions and vehicle impacts are compared.(3) An indirect method of wheel-rail force measurement is proposed. Based on the force state, the wheel-rail interaction forces are indentified through the strain of the swing arms, displacements of the primary springs and accelerations of the axle boxes. The specific testing methods for differenct operating scenes are proposed. The verifications of this indirect method for wheel-rail force measurement are carried out based on the dynamic simulations and field test results. Different derailment criteria are compared for typical line conditions, including the dynamic operation, quasi-static curving and cross wind conditions. The safety domain of the wheelset derailement coefficient and wheel unloading ratio is modified and the derailment evaluation is conducted for specific applications.(4) Based on the field dynamic test, roller rig test and numerial simulations, the occurance mechanism and behaviours of the carbody hunting and the bogie hunting are studied. The effects of the suspension parameters and wheel-rail matching on the hunting stability are researched. For the hunting motions with different behaviour forms and bifurcation types, the running safety assessment against instability is studied.(5) The braking induced impact and the compressed coupler rotational behaviour of the train to train rescue is reproduced by the developed train and coupler and draft gear model, in which the inner structures and motion relations of the coupler are detailly considered. For typical train to train resuce scenes, the analyses of the emergency braking, different braking levels and running safeties are conducted. The allowable braking level for the train to train rescue is suggested. The effective measures to improve the running safeties of the coupled train are presented.