Tangent Track Research Articles

Analysis of steering performance of differential coupling wheelset

In order to improve the curving performance of the conventional wheelset in sharp curves and resolve the steering ability problem of the independently rotating wheel in large radius curves and tangent lines, a differential coupling wheelset (DCW) was developed in this work. The DCW was composed of two independently rotating wheels (IRWs) coupled by a clutch-type limited slip differential. The differential contains a static pre-stress clutch, which could lock both sides of IRWs of the DCW to ensure a good steering performance in curves with large radius and tangent track. In contrast, the clutch could unlock the two IRWs of the DCW in a sharp curve to endue it with the characteristic of an IRW, so that the vehicles can go through the tight curve smoothly. To study the dynamic performance of the DCW, a multi-body dynamic model of single bogie with DCWs was established. The self-centering capability, hunting stability, and self-steering performance on a curved track were analyzed and then compared with those of the conventional wheelset and IRW. Finally, the effect of coupling parameters of the DCW on the dynamic performance was investigated.

Electronic differential for tramcar bogies: system development and performance evaluation by means of numerical simulation

The dynamic behaviour of railway vehicles depends on the wheelset configuration, i.e. solid axle wheelset or independently rotating wheels (IRWs). The self-centring behaviour, peculiar of the solid axle wheelset, makes this kind of wheelset very suitable for tangent track running at low speed: the absence of the self-centring mechanism in the IRWs may lead to anomalous wheel/rail wear, reduced vehicle safety and passengers’ discomfort. On the contrary, during negotiation of the sharp curves typical of urban tramways, solid axle wheelsets produce lateral contact forces higher than those of IRWs. This paper illustrates an electronic differential system to be applied to tramcar bogies equipped with wheel-hub motors which allows switching from solid axle in tangent track to IRWs in sharp curve (and vice versa). An electro-mechanical vehicle model is adopted for the design of the control system and for the evaluation of the vehicle dynamic performances.

Condition monitoring at the wheel/rail interface for decision-making support

Many railway assets, such as wheels, suffer from increasing deterioration during operation. Good condition monitoring based on good decision-making techniques can lead to accurate assessment of the current health of the wheels. This, in turn, will improve safety, facilitate maintenance planning and scheduling, and reduce maintenance costs and down-time. In this paper, wheel/rail forces are selected as a parameter (feature) for the condition monitoring of wheel health. Once wheels are properly thresholded, determining their condition can help operators to define maintenance limits for their rolling stock. In addition, if rail forces are used as condition indicators of wheel wear, it is possible to use measurement stations that cost less than ordinary profile stations. These stations are located on ordinary tracks and can provide the condition of wheelsets without causing shutdowns or slowdowns of the railway system and without interfering with railway traffic. The paper uses the iron-ore transport line in northern Sweden as a test scenario to validate the use of wheel/rail forces as indicators of wagon and wheel health. The iron-ore transport line has several monitoring systems, but in this paper only two of these systems will be used. Wheel/rail force measurements are performed on curves to see how the vehicle negotiates the curve, and wheel profile measurements are done on tangent track not far away. The vehicles investigated are iron-ore wagons with an axle load of 30 tonnes and a loaded top speed of 60 km/h. The measurements are non-intrusive, since trains are moving and assets are not damaged during the testing process.

Evaluation of the hunting behaviour of a railway vehicle in a curve

Experimental evidence, as obtained from line tests, shows that, under some circumstances, the level of hunting motion experienced by a railway vehicle negotiating a curve can be higher than for the same vehicle running at the same speed on tangent track. Starting from this experimental observation, this paper aims to propose a physical explanation for the different hunting behaviour of a railway vehicle running in a curve. After presenting the available experimental evidence, a qualitative examination of the phenomenon is provided. A multi-body model of the vehicle running in a curve is defined and validated against line measurements. This model is then used to numerically evaluate the hunting behaviour of the vehicle in a wide range of curve radii relevant for high-speed lines. In this way, the experimental findings are extended to curve radius and cant deficiency values that were not observed in line tests, due to the use of a specific track section and to the range of speeds covered by the tests.

The influence of track geometry irregularities on rolling contact fatigue

Optimised maintenance of railway tracks requires knowledge of how a deteriorated track geometry will affect subsequent damage of the track. In this study the influence on rolling contact fatigue (RCF) is investigated through numerical simulations featuring a freight wagon run on tracks with a single track irregularity or with a track irregularity spectrum generated from a power spectral density. Evaluated RCF impact is correlated to the track geometry to identify intrinsic properties of track geometry and irregularities that promote surface initiated RCF. On tangent track, simulations predict a single lateral irregularity with amplitude of 6mm and length less than 20m to be sufficient to cause RCF. For operations in shallow curves the simulations indicate that the most efficient RCF mitigation measure is to reduce the longwave content of the lateral irregularities. Furthermore, a study of the relation between track irregularity geometries and resulting wheel forces found a fairly weak correlation.

Operating speed pattern optimization of railway vehicles with differential evolution algorithm

The railway transportation system has much advantage in eco-friendliness, punctuality and safety compared to any other transportation system. Most of the railway system administrators have to control and operate under limited resources such as trains and facilities. It is necessary to control traveling time and energy consumption for efficient operation in the railway systems, because the board rate of passenger is inconstant with time variance. It is common that the shorter traveling time causes the greater energy consumption. In this study, a new optimization method considering operation time or energy consumption is proposed by using differential evolution algorithm and some cases are reviewed. The total energy change due to operation time variation are investigated by using the proposed optimization method for tangent and gradient track conditions. Both cases, the total energy decreases exponentially. However, because of gradient the total energy are saturated after a certain time for gradient track.

Coupler jackknifing and derailments of locomotives on tangent track

A number of derailments occurred in recent years due to coupler jackknifing, some of them were reported on tangent tracks where conventionally thought to be the safer sections. This article studied coupler jackknifing behaviour and its implications for locomotive safety on tangent tracks from the experience of China heavy haul. Three types of coupler systems were modelled and simulated regarding coupler jackknifing behaviour. Two typical locomotive derailments occurred on tangent tracks were analysed. From the derailment experience, coupler angle self-lock behaviour was introduced and simulated. An approach to determine coupler angles in the jackknifed position was derived and validated with a self-coded program and SIMPACK. Methods to prevent coupler jackknifing were also evaluated with regard to locomotive stability.

Noise reduction performance of wheel and rail vibration absorbers

The rolling noise reduction effectiveness of wheel and rail vibration absorbers was evaluated at Trimet in Portland, Oregon. Tests included tangent ballast and concrete tie track and curved track slab track with bi-block concrete ties. Under-car noise data were recorded throughout the system with and without wheel vibration absorbers. Results of the rolling noise tests are summarized for various combinations of treated and untreated rails and wheels. The wheel and especially the rail vibration absorbers significantly reduced rail vibration at audio frequencies, but had little effect on wayside rolling noise. Wayside noise at tangent track was slightly higher with rail vibration absorbers than without. However, the “singing rail” noise was eliminated entirely. The “singing rail” vertical vibration transmission spectrum had a pass-band characteristic as expected for periodic supports. The vibration data indicate that above 250 Hz the wheel was the dominant source of noise relative to the rail. A reduction of stick-slip noise was observed over most curves, though results were inconsistent.

Study on Lateral Vibration Offsets of Speed Increased Freight Cars on the Tangent Track

According to the vehicle dynamics theory, the dynamics simulation models of single-vehicle NX70H flat marked loading capacity of 70t with K5 bogies and NX70 flat marked loading capacity of 70t with K6 bogies under certain loading and running conditions were established by SIMPACK, in order to discuss the change rules of the roll angles, the yaw angles, the lateral offsets and the maximum lateral vibration offsets. Based on the statistical analysis of data calculated by SIMPACK, the results of dynamics single-vehicle models of the two wagon types running on Chinese I and III grade railway lines respectively were compared. Simulation results show that the running speed, the line condition and the height distancing the rail surface all have a significant impact on the maximum lateral vibration offset.

Modeling of Railway Vehicles for Virtual Homologation from Dynamic Behavior Perspective

Modeling and simulation in railway vehicle dynamics is a useful tool in the design of rolling stock when choosing the best solutions for vehicle and infrastructure components in assessing possible risks and, more recently, in the certification of railway vehicles from the point of view of dynamic behavior based on virtual approval. This paper presents the discrete-continuous model of two-level suspension passenger car running along a tangent track with random vertical irregularity as the theoretical tool to asses the parameters of the approval criteria: the running behavior and comfort. The equations of motion are solved in frequency-domain using the modal analysis method and then the carbody acceleration and the comfort index are calculated. The results derived from a numerical simulation performed for the virtual homologation of a particular passenger car are presented, and so is the possibility to improve the design of the vehicle suspension, in compliance with the approval criteria.

Application of the trajectory coordinate system and the moving modes method approach to railroad dynamics using Krylov subspaces

This paper presents a procedure that makes use of a particular formulation based on the trajectory coordinate system (TCS) approach, which is specific of ground vehicles, to describe the track deformation by means of a suitable set of mode shapes. The inertia terms of the track elastic displacements are derived using the TCS arc length to couple the system dynamics. The selection of the track modes of deformation is carried out from a finite element model by using Krylov subspaces as the model-order reduction technique. The modes of deformation move along the track fixed to the TCS using the moving modes method (MMM), avoiding the issue concerning the spatial convergence of the load (wheels) on the track and preserving their vertical frequency contents whose accuracy can be chosen beforehand. An unsuspended wheelset with an induced hunting motion moving on flexible and rigid tangent tracks and a vehicle model are simulated using rail defects as excitations sources such that the performance of this procedure using a fully 3D contact algorithm is shown and analyzed.

Electrode feed path planning for multi-axis EDM of integral shrouded impeller

Multi-axis electrical discharge machining is an effective approach for machining integral shrouded blade components. The key is to plan an interference-free and optimized tool electrode feed path while keeping the size of the electrode as large as possible. In this paper, a new electrode feed path planning method called tangent tracking was proposed. The electrode feed path planning can be formulated as a dynamic programming problem which consists of N discrete steps. In each step, the electrode posture optimization can be divided into pre-optimization and re-optimization. By using such a planning method, the electrode can have a smoother feed path and a larger size as compared with traditional methods. The machining tests for an integral shrouded impeller show that the tangent tracking method not only improves the machining efficiency, but also reduces the number of electrodes used.

Optimization of rail profile to reduce wear on curved track

Wear is one of the most important factors affecting the structural life of railways. In urban railways, the curved track results in more wear than tangent track. Furthermore, the wear is frequently detected in a sharply curved track. Wear leads to reduction in the durability of railway as well as increase in the risk of derailment. In a recent study, a rail grinding was suggested to enhance the dynamic performance and extend the fatigue life of rails. This paper deals with an optimum design procedure for asymmetric rail head profile wherein the design profiles of high and low rails are simultaneously determined by minimizing the wear on curved tracks. The procedure employs a genetic-algorithm-based optimization method. The dynamic performances of a train such as lateral force, derailment and vertical force are evaluated using a rail vehicle dynamics program. The optimum design is validated by comparing the initial rail profile with the optimum profile in a full-scale wear test.

Spectral Distribution of Derailment Coefficient in Non-Linear Model of Railway Vehicle–Track System With Random Track Irregularities

Improving the running safety and reducing the risk of derailments are the key objectives in the assessment of the running characteristics of railway vehicles. The present study of the safety against derailment is focused on the effect of wheelset hunting on the derailment coefficient Y/Q and, especially, how it is reflected in the power spectral density (PSD) of Y/Q. The lateral Y and vertical Q forces at the wheel/rail contact are obtained in numerical simulations for a four-axle railway vehicle moving at a constant velocity along a tangent track with random geometrical irregularities. The PSD of Y/Q, calculated as a function of spatial frequency, is found to have a characteristic structure with three peaks for the leading wheelsets and one peak for the trailing wheelsets of the front and rear bogies. The positions of the PSD maxima remain unchanged with increasing ride velocity, while their magnitudes and shapes evolve. One of the PSD peaks occurs for all wheelsets at the same spatial frequency corresponding to the wheelset hunting, while an additional peak at the double hunting frequency is found for the leading wheelsets. Such a peak structure is also found in the PSD of Y/Q determined in simulations with modified parameters of the vehicle primary suspension and for different track sections. The peak at the double hunting frequency is shown, by a detailed analysis of the contact forces, the flange angles and their PSDs, to result from the nonlinear geometry of the wheel/rail contact leading to the second-harmonic term in Y/Q. The emergence of this peak is also closely related to the phase difference between the hunting oscillations of the wheelset lateral displacement and the oscillations of its yaw angle, for which the difference is significantly smaller for the leading wheelset than for the trailing one. Finally, the effect of wheelset hunting is also shown to manifest itself in the strong dependence of the running average of Y/Q, which is used in the railway technical safety standards for the assessment of the safety against derailment (with the Nadal criterion), on the applied window width.

Electrode Feeding Path Searching for 5-Axis EDM of Integral Shrouded Blisks

With a closed shroud on the top of their blades, the so-called integral shrouded blisks gained more and more applications in turbine engines. 5-axis electrical discharge machining (EDM) is regarded as the most effective approach for integral shrouded blisks machining. The tool electrode is shaped and reduced according to the profile of the flow channels to get enough space for electrode feeding. The key of EDM of integral shrouded blisks is to search an interference-free and optimized electrode feeding path. In this paper, a new electrode feeding path searching method called tangent tracking was proposed. Based on the dynamic programming methodology, the electrode feeding path searching process is decomposed into a number of electrode attitude optimization subproblems. Each subproblem can be further divided into two phases: pre-optimization and re-optimization. The purpose of electrode attitude pre-optimization is to make the tangent vector of the electrode centre curve coincide with that of the flow channel centre curve at the flow channels outlet section. If the electrode interferes with the blisk in the pre-optimization, the re-optimization needs to be conducted in order to find an interference-free attitude in the vicinity of the pre-optimized result. The tangent tracking method is validated by an integral shrouded blisk machining experiment.

Running safety of a railway vehicle in the presence of random track irregularities

The paper presents the author�s investigations on dynamics of a railway vehicle, especially the effect of various factors on the running safety. The applied simulation methods used for analysis of running safety are in agreement the technical standards UIC 518 and EN 14363. The numerical simulations are performed for non-linear model of railway vehicle (a passenger car) moving along a tangent track with lateral and vertical geometrical irregularities of random character. The obtained results are used to study how the derailment coefficient is affected by the ride velocity, the parameters of the primary and secondary vehicle suspension, the wear of wheel and rail profiles as well as the track condition. The investigation of running safety is further enhanced by performing the spectral analysis of the dynamical responses of the railway vehicle-track system. It is found that there is a direct relation between the obtained power spectral density (PSD) of the derailment coefficient and the PSD of the lateral and angular wheelset displacements showing the characteristic oscillations due to the wheelset hunting. Finally, the paper presents the results of the statistical analysis of local track geometrical irregularities occurring in the vicinity of the track points where the derailment coefficient attains large values.

Crosswind action on rail vehicles: A methodology for the estimation of the characteristic wind curves

The problem of cross wind for rail vehicles gained, in the last years, an increasing interest within the European railway operators, due to the continuous expansion of the high-speed railway networks. In order to evaluate the aerodynamic performance of a train in terms of safety towards cross wind, the Characteristic Wind Curves (CWCs), have to be defined. In this paper a stochastic approach for the definition of the CWCs is presented. According to this methodology, the wind speed space–time distribution is reproduced through a stochastic process and the algorithm for the definition of the aerodynamic loads acting on the train is set up, which is based on the admittance function. A numerical model for the admittance function is presented and verified by means of comparison with experimental data. The effects of the admittance function and of the stochastic approach in the definition of aerodynamic forces and of the corresponding CWCs are then analysed in terms for a specific case (assigned reference train, flat ground scenario, tangent track running).

Noise and vibration control by rail dampers

MTR Corporation and Wilson Acoustic Limited launched a project to investigate the effect of rail dampers on noise reduction and rail corrugation growth in an operational metro railway at a 300m radius curved track. Corrugation was measured by Corrugation Analysis Trolley (CAT) every month throughout a 6-month grinding cycle. Corrugation of wavelength 50-80mm was observed at the low rail, corresponding to 250-400Hz at train speed of 70km/hr. No corrugation was observed at the high rail. Corrugation growth rate was reduced by 45% after installation of rail dampers. In contrary to rail corrugation models at tangent track which predict exponential growth with time, corrugation growth at the test site is approximately linear. Corrugation at the test site was thought to be the combined effect of low vertical response and high lateral response at 250–400Hz, resulting in periodic fluctuation of normal contact force, minimal normal contact force is accompanied by lateral sliding causing frictional wear. Rail dampers have no apparent effect on the vertical response at anti-resonance 250–400Hz, but significantly reduce the lateral response. Measurement results and literature reviews suggest that using rail dampers to decrease lateral response could reduce growth of short pitched corrugation at sharp curves.

Lateral Stability Analysis of Heavy-Haul Vehicle on Curved Track Based on Wheel/Rail Coupled Dynamics

Being viewed from the standpoint of whole system, the hunting stability of a heavy-haul railway vehicle on a curved track is investigated in this paper. First, a model to simulate dynamic performance of the heavy-haul vehicle on the elastic track is developed. Secondly, the reason of the hunting motion is analyzed, and a bifurcation diagram for the vehicle on the curved track is put forward to simulate the nonlinear critical speed. Results show that the hunting motion of the heavy-haul vehicle will appear due to the larger conicity, the initial lateral shift and the wheelset angle of attack. With the hunting motion appearing, the lateral shift and force of the wheelset are changed sharply and periodically with a wave of circa 3.6 m. There is obvious difference in the bifurcation diagram between on a curved track and on a tangent track. Relative to the centerline of the track, each vehicle body on the curved track has two stable cycles. As for the curved track with a radius of 600 m and a superelevation of 55 mm, the nonlinear critical speed of the heavy-haul vehicle is 76.4 km/h.

Dynamic Response of Railway Bogie Due to Change in Vertical Primary Suspension Stiffness Parameters

A mathematical model of a railway carriage moving on tangent tracks is constructed by deriving the equations of motion concerning the model in which single-point and two-point wheel-rail contact is considered. The presented railway carriage model comprises of carbody and front and rear simple conventional bogie with two leading and trailing wheelets attached to each bogie. The railway carriage is modeled by 31 degrees of freedom which govern vertical displacement, lateral displacement, roll angle and yaw angle dynamic response of wheelset whereas vertical displacement, lateral displacement, roll angle, pitch angle and yaw angle dynamic response of carbody and each of the two bogies. Linear stiffness and damping parameters of longitudinal, lateral and vertical primary and secondary suspensions are provided to the railway carriage model. Combination of linear Kalker's theory and nonlinear Heuristic model is adopted to calculate the creep forces in which introduced at wheel and rail contact patch area. Computer aided-simulation is constructed to solve the governing differential equations of the mathematical model using Runge-Kutta fourth order method. Principle of limit cycle and phase plane approach is applied to realize the stability and to evaluate the concerning critical hunting velocity at which railway carriage starts to hunt. Numerical simulation model is used to study the dynamic responses of a railway carriage bogie subjected to specific parameters of wheel conicity and primary suspension characteristics. A comparison to study the sensitivity of railway carriage bogie to dynamic responses is also presented at different vertical primary suspension stiffness parameters.