Research On Running Safety Of Heavy-haul Railway Vehicle With Partial Load

Off-center loading is defined as the gravity center of loaded car body deviating from the track centerline,which can significantly deteriorate the operational safety of heavy haul vehicle.Therefore,the limit value of off-center loading is curial to the operational safety of rail vehicle.The maximum off-center loading of rail vehicle is usually dependent upon the vehicle type and marshalling type.In recent decades,the heavy haul vehicles of China are booming,characterized by higher speed and increased axle load.However,the old standard for the limit value of off-center loading is still used in the operation right now.Considering the increased loads and operational speed,the off-center loading could pose highly adverse influence on the operating safety of rail vehicle.It is thus desirable to study the limit value of off-center loading considering the complex operating condition.This thesis thus aims at studying the limit values of off-center load of a heavy haul vehicle with an axle load of 30 t.Considering the traction and braking as well as the nonlinearities in the coupler,a one-dimensional longitudinal dynamic model together with a three-dimensional vehicle/track coupled dynamic model were established,so as to investigate the influences of coupler force,operational speed,curve radius,super-elevation and wind loads on the operational safety of heavy haul vehicle in the presence of off-center loading condition.Followings summary the main work and results made in this thesis.(1)The longitudinal impact of long marshalling heavy haul train was studied through simulation of a longitudinal dynamic model of heavy haul train considering different marshalling,operational conditions and track slopes.The results concluded that the increased axle load and the number of cars can significantly increase the longitudinal impact of train,and the maximum impact force of coupler can reach 1200 k N when the vehicle applies the traction or braking in a vertical curve section with a slope of 7.0‰.(2)Regarding to the effects of coupler force on the operational safety of off-center loaded vehicle,the results show that with the increasing of coupler force the derailment ratio and wheel unloading increase when an off-center loaded vehicle negotiates the curve.The influence of compression coupler force is far greater than that of tension coupler force,and the derailment more likely occurs in the braking condition.Due to the longitudinal impact,the derailment coefficient of 30,000-ton heavy-haul train increases by 0.47～1.9 times,and wheel unloading ratio increases by 2.0～2.4 times.Therefore,the determination of safety limit of off-center loading of heavy haul vehicle has to consider the effects of traction and braking.(3)For the effects of curve passing on the operational safety of off-center loaded vehicle,the results suggested that the wheel unloading and the lateral displacement of wheel/rail contact point is much sensitive to the curve radius,and track super-elevation can yield significantly variation in the derailment ratio and the wheel unloading.The decreased track super-elevation of curved track increases the derailment ratio,while the derailment ration decreases for the decreased super-elevation in the S curve.The wheel unloading increases with the decreasing of super-elevation of curved track and S curve.(4)The influence of cross wind on the operating safety of off-center loaded vehicle was also investigated through simulation of proposed coupled vehicle/track dynamic model considering the wind loads,and concluded that the wind speed can significantly affect the wheel unloading comparing with the derailment ratio,lateral displacement of wheel/rail contact point and wheel lift.When the wind speed is greater than 5 m/s,the wheel unloading exceeds the limit of 0.65,and the derailment ratio exceeds the limit of 1 as the wind speed is greater than 30 m/s.Whereas,the lateral displacement of wheel/rail contact point and wheel lift still remain in the safety limit for the wind speed of 30 m/s.Finally,a safety margin of off-center loading of heavy haul train was developed based on four derailment criterions,including derailment coefficient,wheel unloading,lateral displacement of wheel/rail contact point and wheel lift.This safety margin consists of safety area,warning area and derailment area.The results show that the warning boundary determined by the wheel unloading is considered more conservative comparing with other criterions.The boundary of wheel lift and lateral displacement of wheel/rail contact point are much closer to the derailment boundary,and could lead to a smaller safety margin for offcenter loaded vehicle.Considering that the wheel unloading alone could yield too conservative safety limit for off-center loading,other derailment criterions are thus suggested to determine the safety limit of off-center loading together with wheel unloading.This is expected to give rise to a more reasonable safety limit of off-center loading for heavy haul train.