The objective of the article is to investigate the vibration characteristic and the long-term service performance of a China Railway High-speed (CRH) train at operation speed of 350 km/h through on-track field tests. The article first introduces the test method and system as well as the field conditions including the main parameters of the test train and track. A CRH electric multiple unit (EMU), called the CRH2C, is chosen for the experiment. A duration test lasting for about 2 months is carried out to acquire the data of vehicle vibration acceleration and the wheel profile wear. Based on the test data, the article presents the vibration behaviours of car body, bogie frame and axle box as well as the lateral hunting stability of the train operating at speed of 350 km/h, and the evolution of the train dynamic performance under long-term operation condition. Results show that the vibration accelerations of vehicle components are in a low level when the train runs on a non-ballasted track at the speed of 350 km/h, indicating that both the ride comfort and the running stability are acceptable. Through wheel re-profiling, it is possible to effectively reduce the vibrations of the axle box, the bogie frame and the car body, and thus the train dynamic performance can be kept in an excellent condition in a long period.

For the long heavy-haul train, the basic principles of the inter-vehicle interaction and train–track dynamic interaction are analysed firstly. Based on the theories of train longitudinal dynamics and vehicle–track coupled dynamics, a three-dimensional (3-D) dynamic model of the heavy-haul train–track coupled system is established through a modularised method. Specifically, this model includes the subsystems such as the train control, the vehicle, the wheel–rail relation and the line geometries. And for the calculation of the wheel–rail interaction force under the driving or braking conditions, the large creep phenomenon that may occur within the wheel–rail contact patch is considered. For the coupler and draft gear system, the coupler forces in three directions and the coupler lateral tilt angles in curves are calculated. Then, according to the characteristics of the long heavy-haul train, an efficient solving method is developed to improve the computational efficiency for such a large system. Some basic principles which should be followed in order to meet the requirement of calculation accuracy are determined. Finally, the 3-D train–track coupled model is verified by comparing the calculated results with the running test results. It is indicated that the proposed dynamic model could simulate the dynamic performance of the heavy-haul train well.

This paper presents a multi-objective optimization approach for a fractional-order control system for electricmagnetic suspension (EMS) type magnetic levitation (maglev) models, aiming to optimize the non-linear magnetic buoyancy control parameters. Firstly, a multi-body dynamics model of an EMS-type maglev vehicle with a fractional-order PID control system is developed. To fulfill the multi-objective requirements and optimize the fractional order parameters, an improved multiobjective optimization algorithm is proposed. The Sperling index and the magnitude of the vertical suspension gap variation are employed as the optimization objectives. Then, the aforementioned multi-objective optimization algorithm is applied to the constructed multi-body dynamics model to perform multiobjective optimization of the control parameters. Finally, the Pareto front solution is calculated and the optimal control parameters are obtained. The results demonstrate that the optimized control parameters can significantly reduce the vertical suspension gap and Sperling index during operation, with the reduction in the vertical suspension gap amplitude and its standard deviation being 10∼73%, and the reduction in the Sperling index being 8∼13%.

High-temperature Superconducting (HTS) maglev trains are vulnerable to the effects of crosswinds when operating at high speeds in open-air conditions, potentially compromising riding comfort and safety. This study established a vehicle dynamic model based on the nonlinear maglev-track relationship and added aerodynamic loads under crosswinds to the train’s simplified load center to address this issue. Using the maximum vibration acceleration limit and the Sperling index, we evaluated the riding comfort of the HTS maglev train under different conditions. Further, the vibration acceleration power spectral density was analyzed to reveal the impact of increasing the train’s operating speed and crosswind speed. The results indicated that the lateral and vertical Sperling index achieved an “excellent” rating, even at crosswind speeds of up to 20.7 m/s when the train was traveling at speeds of up to 600 km/h. However, it was noted that particular attention should be given to the riding comfort in the head car when the speed reaches 600 km/h. Moreover, the influence of the increase in train speed on the vibration frequency domain distribution of the three car bodies and the train’s riding comfort is greater than that of the increase in the crosswind speed. These findings may provide a valuable reference for the future engineering application of the HTS maglev train.

In this paper, a multiobjective optimisation method considering the rail profile at high speed is presented. Based on nonuniform rational B-spline (NURBS) theory, a parameterised model of the rail profile is constructed to determine the variables. The wear index, wheel–rail lateral force and contact stress are selected as the objective function. Based on multibody dynamics theory is applied to establish the vehicle–track coupling dynamic model of the high-speed train CRH380A. An improved NSGA-II algorithm called CN-NSGA-II is proposed in this study. The multi-objective optimisation problem of rail profile is improved by the vehicle–track coupling dynamics model and CN-NSGA-II algorithm. The Pareto front solution is calculated, and the TOPSIS algorithm is used to select the optimal solution and obtain the optimised profile. The analysis of the objective function values of the CN60 profiles and the optimised profile indicate that the maximum wheel–rail lateral force of the left and right wheels of the steering wheelset decreases by 13.3% and 13.71%, the maximum contact stress decreases by 10.35% and 3.21%, and the maximum wear number decreases by 36.09% and 11.4%. The new optimised rail profile can effectively reduce the wheel–rail lateral force, contact stress and wear number in high-speed running conditions.