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This paper investigates the influence of wheel eccentricity on vertical vibration of suspended monorail vehicle based on experiment and simulation. Two sets of tests are conducted in the first Chinese suspended monorail, and the tested acceleration is analyzed and exhibited. A multibody dynamic model of the suspended monorail vehicle is established to simulate the vertical vibration of car body excited by wheel eccentricity. The results show that there are three factors which may cause an abnormal vibration considering the track and the vehicle system. The influence of wheel eccentricity on the car body vibration was firstly analyzed. Simulated acceleration of car body has a great accordance with test. The wheel eccentricity could excite the resonance of car body at the speed of 21 km/h, and the vertical acceleration would increase considerably. Decreasing the secondary stiffness can effectively reduce the vertical vibration caused by wheel eccentricity, especially at the resonant speed. In the secondary test, the peak of car body acceleration at speed of 20 km/h is not appearing when only renewing the wheels, and the acceleration is decreasing obviously at the domain frequency. It is further determined that the abnormal vibration is mainly caused by the wheel eccentricity.

Coupler jackknifing has caused a number of derailments, and it is a significant topic that needs in-depth studies. This paper aims to investigate the characteristics of coupler jackknifing and its effects on the dynamic performance of locomotives during braking. A field braking experiment using three eight-axle locomotives was conducted on a tangent track. The experimental results indicated that in-service couplers with a friction arc surface are prone to coupler jackknifing once the compressive force of the coupler exceeds 400 kN. After coupler jackknifing, the coupler angle has a significant positive correlation with the yaw angle of the car body; both coupler jackknifing and coupler angle increase rapidly to maximum values. The contact between the car body and the bogie seriously affects the dynamic performance of the locomotive and causes lateral instability of the locomotive. In particular, the lateral deviation of the coupling couplers generates an eccentric wear on the tail of the coupler. A numerical simulation model is developed to investigate the effect of coupler jackknifing on the running safety of the locomotive. Simulation results show that coupler jackknifing induces an excessive lateral force on the wheelset and increases the risk of derailments and gauge widening. Compared with the existing measures against coupler jackknifing, in this study, an effectively active measure is proposed to improve the stability of the coupler and to prevent possible derailments caused by coupler jackknifing during braking.

The derailments of empty wagons of long freight trains frequently occurred around the world, which caused tremendous losses every year. Aiming at an actual derailment of empty wagons on straight line during dynamic braking, the field investigation was conducted to find the reasons of the accident. According to the investigation results, the large coupler yaw angle and coupler force, the special connection mode by drawbars, as well as the poor conditions of wheel treads and flanges were supposed to be responsible for the accident. The simulaiton model composed of 3 C80-type gondolas, and two RFC-type drawbars is established, the accuracy of which is validated by the field experimental test. When the wheel-rail friction coefficient is set to be 0.7 and the coupler forces are set to be 350 kN with a coupler yaw angle of 7 degrees, the simulation results are consistent with the field investigation results. Simulation results indicate that the coupler yaw angle, coupler force, and wheel-rail friction coefficient have significant influences on the derailment. The increasing coupler yaw angle and coupler force will increase the risk of derailment. For the wagon units adopting the drawbars, the riskiest wagon changes from the middle wagon to the front one as the lateral components of the coupler forces increase. A large wheel-rail friction coefficient can raise the risk of derailment. However, an overlarge friction coefficient will decrease the derailment risk. According to the field investigation and simulation results, the wheel-rail friction coefficients should be limited below 0.5 to ensure the running safety of empty wagons. Besides, the operations of the train should be optimized to avoid large coupler yaw angle and coupler force.

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