Kaiyun Wang

Fundamentals of vehicle–track coupled dynamics

This paper presents a framework to investigate the dynamics of overall vehicle–track systems with emphasis on theoretical modelling, numerical simulation and experimental validation. A three-dimensional vehicle–track coupled dynamics model is developed in which a typical railway passenger vehicle is modelled as a 35-degree-of-freedom multi-body system. A traditional ballasted track is modelled as two parallel continuous beams supported by a discrete-elastic foundation of three layers with sleepers and ballasts included. The non-ballasted slab track is modelled as two parallel continuous beams supported by a series of elastic rectangle plates on a viscoelastic foundation. The vehicle subsystem and the track subsystem are coupled through a wheel–rail spatial coupling model that considers rail vibrations in vertical, lateral and torsional directions. Random track irregularities expressed by track spectra are considered as system excitations by means of a time–frequency transformation technique. A fast explicit integration method is applied to solve the large nonlinear equations of motion of the system in the time domain. A computer program named TTISIM is developed to predict the vertical and lateral dynamic responses of the vehicle–track coupled system. The theoretical model is validated by full-scale field experiments, including the speed-up test on the Beijing–Qinhuangdao line and the high-speed running test on the Qinhuangdao–Shenyang line. Differences in the dynamic responses analysed by the vehicle–track coupled dynamics and by the classical vehicle dynamics are ascertained in the case of vehicles passing through curved tracks.

Modelling and experiment of railway ballast vibrations

The vibration of railway ballast is a key factor to cause track geometry change and increase of track maintenance costs. So far the methods for analyzing and testing the vibration of the granular ballast have not been well formed. In this paper, a five-parameter model for analysis of the ballast vibration is established based upon the hypothesis that the load-transmission from a sleeper to the ballast approximately coincides with the cone distribution. The concepts of shear stiffness and shear damping of the ballast are introduced in the model in order to consider the continuity of the interlocking ballast granules. A full-scale field experiment is carried out to measure the ballast acceleration excited by moving trains. Theoretical simulation results agree well with the measured results. Hence the proposed ballast vibration model has been validated.

High-speed train-track-bridge dynamic interactions - Part I: theoretical model and numerical simulation

This paper presents a framework to systematically investigate the high-speed train–track–bridge dynamic interactions, aiming to provide a method for analysing and assessing the running safety and the ride comfort of trains passing through bridges, which are critically important for the design of new high-speed railway bridges. Train–track–bridge interactive mechanism is illustrated. A fundamental model is established for analysing the train–track–bridge dynamic interactions, in which the vehicle subsystem is coupled with the track subsystem through a spatially interacted wheel–rail model; and the track subsystem is coupled with the bridge subsystem by a track–bridge dynamic interaction model. Modelling of each subsystem and each interactive relationship between subsystems are presented. An explicit–implicit integration scheme is adopted to numerically solve the equations of motion of the large non-linear dynamic system in the time domain. Computer simulation software named the train–track–bridge interaction simulation software (TTBSIM) is developed to predict the vertical and lateral dynamic responses of the train–track–bridge coupled system.

Experimental investigation on vibration behaviour of a CRH train at speed of 350 km/h

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.

Lateral Hunting Stability of Railway Vehicles Running on Elastic Track Structures

Considering the viscoelastic property of railway track structure, it is suggested in this paper to include the influence of track dynamics in calculation of lateral stability of railway vehicles running on tracks. A direct numerical method based on the stability of time histories of vehicle components is proposed to ascertain the nonlinear critical hunting speed of railway vehicles. The time histories of the vehicle system are calculated by use of the three-dimensional vehicle-track coupled models, which are capable of taking into account the influence of dynamic properties of track structures on vehicle dynamics. The effect of track system properties such as the rail fastener stiffness and the rail profile on the lateral hunting stability of the vehicle is investigated. Differences of the critical hunting speeds of vehicles on rigid track model and on elastic track model are found out. Generally, the rigid track model overestimates the critical hunting speed by 5―10% for different types of vehicles, which implies that the classical vehicle dynamics predicts higher lateral stability of a vehicle than the vehicle-track coupled dynamics does. This conclusion is of significance to the safety design of railway vehicles and should be taken notice in the design stage. The reason that causes the differences is discussed. A full-scale field experiment was carried out to investigate the hunting behavior of a freight car with three-piece bogies on a straight track. Very obvious hunting motion was observed in the experiment when the unloaded vehicle ran at the speed of 75 km/h, which verified the theoretical calculation results.

Reducing rail side wear on heavy-haul railway curves based on wheel–rail dynamic interaction

This article investigates an optimisation strategy for the design of rail-grinding profiles to be used on heavy-haul railway curves, aiming to reduce the rail side wear on curves. A design methodology of rail asymmetric-grinding profiles is put forward based on the principle of low wheel–rail dynamic interaction. The implementing procedure is illustrated in detail. As a case study, the rail asymmetric-grinding profiles were designed for a curve with 600 m radius on Chinese Shuohuang heavy-haul railway. The characteristics of wheel–rail contact geometry and wheel–rail dynamic interaction were analysed and compared between the original standard rail profiles and the designed rail-grinding profiles. The rails on a test curve were ground according to the designed profiles. Before and after rail grinding, both the wheel–rail dynamics indexes and the rail side wear were measured in the field. The theoretical and experimental results show that the wheel–rail dynamic interaction is clearly improved and the rail side wear is alleviated by 30–40% after rail grinding, which validates the effectiveness of the design methodology of rail asymmetric-grinding profiles on curves.

Lateral interactions of trains and tracks on small-radius curves: simulation and experiment

The lateral dynamic interaction between trains and tracks on small-radius curves is investigated with theoretical method and field experiment in this article. A vehicle–track spatially coupled model and a simulation software are developed to analyze the dynamic performance of vehicles on elastic tracks. A field experiment is carried out to validate the simulation method. Research results show that severe lateral interaction occurs between wheels and rails when a train passes through a small-radius curved track. Under the strong action of the large lateral wheelset force, the rails roll over, obviously, and the rail gauge is enlarged dynamically. In order to raise the train speed and enhance the running safety, a suit of new measures are put forward to strengthen the old wooden sleeper tracks widely used in the curves of the mountain area in Chinese railways. It is shown that the lateral displacements of rails and the dynamic gauge enlargement are decreased by 67% after the small-radius curved track is strengthened, although the lateral wheel/rail forces on the strengthened track are a little larger than those on the original un-strengthened wooden sleeper track.

A locomotive–track coupled vertical dynamics model with gear transmissions

ABSTRACT A gear transmission system is a key element in a locomotive for the transmission of traction or braking forces between the motor and the wheel–rail interface. Its dynamic performance has a direct effect on the operational reliability of the locomotive and its components. This paper proposes a comprehensive locomotive–track coupled vertical dynamics model, in which the locomotive is driven by axle-hung motors. In this coupled dynamics model, the dynamic interactions between the gear transmission system and the other components, e.g. motor and wheelset, are considered based on the detailed analysis of its structural properties and working mechanism. Thus, the mechanical transmission system for power delivery from the motor to the wheelset via gear transmission is coupled with a traditional locomotive–track dynamics system via the wheel–rail contact interface and the gear mesh interface. This developed dynamics model enables investigations of the dynamic performance of the entire dynamics system under the excitations from the wheel–rail contact interface and/or the gear mesh interface. Dynamic interactions are demonstrated by numerical simulations using this dynamics model. The results indicate that both of the excitations from the wheel–rail contact interface and the gear mesh interface have a significant effect on the dynamic responses of the components in this coupled dynamics system.

Establishment and verification of three-dimensional dynamic model for heavy-haul train–track coupled system

ABSTRACT 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.

Study of the Post-Derailment Safety Measures on Low-Speed Derailment Tests

ABSTRACT Prevention of train from derailment is the most important issue for the railway system. Keeping derailed vehicle close to the track centreline is beneficial to minimise the severe consequences associated with derailments. In this paper, the post-derailment safety measures are studied based on low-speed derailment tests. Post-derailment devices can prevent deviation of the train from the rail by catching the rail, and they are mounted under the axle box. Considering the different structures of vehicles, both trailer and motor vehicles are equipped with the safety device and then separately used in low-speed derailment tests. In derailment tests, two kinds of track, namely the CRTS-I slab ballastless track and the CRTS-II bi-block sleeper ballastless track, are adopted to investigate the effect of the track types on the derailment. In addition, the derailment speed and the weight of the derailed vehicle are also taken into account in derailment tests. The test results indicate that the post-derailment movement of the vehicle includes running and bounce. Reducing the derailment speed and increasing the weight of the head of the train are helpful to reduce the possibility for derailments. For the CRTS-I slab ballastless track, the safety device can prevent trailer vehicles from deviating from the track centreline. The gearbox plays an important role in controlling the lateral displacement of motor vehicle after a derailment while the safety device contributes less to keep derailed motor vehicles on the track centreline. The lateral distance between the safety device and rails should be larger than 181.5 mm for protecting the fasteners system. And for the CRTS-II bi-block sleeper ballastless track, it helps to decrease the post-derailment distance due to the longitudinal impacts with sleepers. It can also restrict the lateral movement of derailed vehicle due to the high shoulders. The results suggest that, CRTS-II bi-block sleeper ballastless track should be widely used in derailment prone areas.