The Derailment Safety Of An Alpine Emu Passing By Windbreak Breach In The Bailifeng District

China is a vast country with a complex geographical environment and a variable climate,which leads to some serious fatal effects on the safety of trains,mainly due to strong crosswinds.Based on the windward side derailment phenomena of the first wheel set,the transient computational fluid dynamics(CFD)and the vehicle system dynamics methods were utilized in this study.These methods were validated through full-scale testing,where a high-speed train passed against a windbreak breach on the Lanzhou-Xinjiang line in China.The research focuses on the reproduction of the tested phenomena,understanding of the derailment mechanism on the windward side,prediction of operation safety when a train passes by the breach,and the evaluation of vehicle safety.The main contents are as follows:(1)The train aerodynamic model and the train system dynamic model were developed based on the full-field test.The safety of the high-speed train running at a speed of 120 km/h was investigated when the train passed by a windbreak breach of different lengths whilst subjected to a normal wind speed of 32 m/s.Eight different lengths of breaches were investigated:50,35,25,15,12,10,7 and 2 m.The train aerodynamic model consisted of the outer domain and the sliding domain.The outer domain was comprised of structured hexahedral mesh elements and the sliding domain was comprised of tetrahedral mesh elements.The accuracy of the train aerodynamic model was verified by the grid independence method and compared with the standard train model.(2)The transient aerodynamic loads of the high-speed train were calculated using the Unsteady Reynolds-averaged Navier-Stokes(URANS)model with the sliding mesh technique.The wind force and moment were monitored and applied to the train system dynamic model.The train system dynamic model was validated by using field test data for a breach of 12 m length,which revealed that the equivalent breach of 12 m could reproduce the test phenomena.The flow structure around the train passing by the different windbreak breach was analyzed and therefore,the breach size that could cause the train to derail in crosswinds was determined.(3)The aerodynamic characteristics and dynamic responses of the train head and tail were compared when the train passed by the 12 m breach.By analyzing the flow structures,the reasons behind the different aerodynamic loads on the train head and tail were discussed.Some results obtained-including the wheel-rail force,the derailment coefficient,the overturning coefficient and the movement attitude-indicated that the side force and yawing moment of the train played a key role in the safety of the head and the tail of the train when it passed by a windbreak breach.(4)The train aerodynamics and system dynamics simulations were carried out with different wind speeds: 32 m/s,28 m/s,25 m/s,20 m/s,15 m/s and 10 m/s.The flow structure around the train on the breach was studied and the safety of the train was inspected including the wheel-rail forces,derailment coefficient,overturning coefficient and wheelset motion.The characteristic wind curves(CWC)were obtained based on the derailment coefficient.(5)The root locus method was implemented to study the suspension mode and natural vibration period of the vehicle.A group of scaling factors were applied to change the duration of the wind without changing the amplitude of the wind loads by stretching and compressing the time axle,where this type of crosswinds are referred to as the gust.The impact responses of gusts were explored over different durations in order to obtain the time constraint boundary of the gusts.