Wheel-rail Interaction Research Articles

Severe rail wear detection with rail running band images

AbstractRail wear occurs continuously owing to the rolling contact load of trains and is fundamental for railway operational safety. A point‐based manual rail wear inspection cannot satisfy the increasing demand for rapid, low‐cost, and continuous monitoring. This paper proposes a depth‐plus‐region fusion network for detecting rail wear on a running band, which is a collection of wheel–rail interaction traces. The following steps are involved in the proposed method. (i) A depth map estimated by a modified MiDaS model is utilized as guidance for exploiting the depth information of the running band for rail wear detection. (ii) The running band of a rail is segmented and extracted from images using an improved mask region‐based convolutional neural network that uses the scale and ratio information to perform instance segmentation of the running band images. (iii) A two‐channel attention–fusion network that classifies rail wear is constructed. In this study, we collected real‐world running band images and rail wear‐related data to validate our approach using a high‐accuracy rail‐profile measurement tool. The case‐study results demonstrated that the proposed method can rapidly and accurately detect rail wear under different ambient light conditions. Moreover, the recall rate of severe wear detection was 84.21%.

Nondestructive analysis of rolling contact fatigue cracks using induced scanning thermography.

Rolling contact fatigue (RCF) produced by wheel-rail interaction is now considered to be a critical factor that causes failure. Throughout this work, induced scanning thermography (IST) for detecting RCF defects at different depths is investigated. The original thermal sequences could not utilize the features at the heat dissipation stage; thus, a data reconstruction method, including principal component analysis (PCA) and Tucker factorization, was employed to extract the spatial and time patterns. In addition, detectability was evaluated across a range of speed studies. The Tucker-PCA combination algorithms obtained defects with improved quality, showing a clear boundary over the velocity range of 1-4km/h, which dramatically suppressed background noise. A unique gradient response characteristic in the cooling phase was summarized and utilized through experimental verification in order to recognize defect width.

High-precision distributed detection of rail defects by tracking the acoustic propagation waves.

Nowadays, early defect detection plays a significant role for the railway safety warning. However, the existing methods cannot satisfy the requirements of real-time and high-precision detection. Here, a high-precision, distributed and on-line method for detecting rail defect is proposed and demonstrated. When a train goes through defects, the instantaneous elastic waves will be excited by the wheel-rail interaction, which will further propagate along railway tracks bidirectionally. Through mounting the backscattering enhanced optical fiber on the railway as sensors, the fiber optic distributed acoustic sensing system can record the propagation trace precisely. Further, the acoustic propagation fitting method is applied onto the propagation data to detect and locate defects along the long-distance railway. Especially, the dual-frequency joint-processing algorithm is proposed to improve the location accuracy. The field test proves that multiple defects along the railway can be successfully identified and located with a standard deviation of 0.314m. To the best of our knowledge, this work is the first report of distributed rail defect detection, which will bring a breakthrough for high-precision structural damage detection in the infrastructures such as the railway, pipeline and tunnel.

Random analysis of dynamic wheel–rail interactions in the switch panel of a turnout with geometric tolerances based on the probability density evolution method

During train operation, the geometric tolerance in a turnout can be very random, posing a challenge for traditional deterministic vehicle-turnout coupling studies and for daily maintenance. In light of the above situation, a coupled vehicle-switch panel model with random geometric tolerances is proposed. These tolerances result from the discrepancy in relative height difference of rail tops between the straight switch rail and the curved stock rail, and from the gap between the straight switch rail and the curved stock rail in the closure part. The model takes rail flexibility into consideration. The probability density evolution method (PDEM) is applied to capture the resultant probability density function (PDF) of dynamic wheel–rail interactions. The Monte Carlo method is employed for verification of results obtained from the PDEM. The results show that stronger randomness of the vertical wheel force is induced compared with that of the lateral wheel force. The probabilistic range of the vertical wheel force is found to be around 50 kN on the straight switch rail side. Given the largest maximum mean value of rail displacement, it is found that the part of the straight switch rail with a top width of 40 mm requires significant attention.

Effects of flange wear on dynamic vehicle-turnout interaction

Long-term investigations have revealed incidences of severe flange wheel wear in the field. Slight changes in the profile shape will lead to changes in the geometric relationship between wheel and rail, hence affecting the dynamic wheel-rail interaction. The turnout is an essential piece of track equipment for carrying out train transfer or cross line operation. In turnouts, the rail profile changes throughout the structure, and the wheel load transfers from one rail component to the next, resulting in a complex wheel/rail relationship. This paper investigates the effect of flange wear on the wheel-rail interaction as the vehicle switches into the turnout track in a diverging movement. A coupling model for a high-speed flexible turnout and a multi-rigid vehicle is established, and the dynamic contact trajectories between wheel and rail, the vibration energy of the rail, the lateral wheel-rail force, rail wear, and car body driving stability are analyzed. The results show that the wheel transition position is shifted backward due to the flange wear, and a less sharp impact occurs with a worn flange profile during wheel load transition in the switch panel, which improves lateral wheel-turnout interaction and the rail wear. Worn flange profiles give a large flangeway clearance, which is not conducive to the smooth operation of vehicles in the diverging route of turnouts.

Improved Dynamics Model of Locomotive Traction Motor with Elasticity of Rotor Shaft and Supporting Bearings

The locomotive traction motor is described as a rotor-bearing system coupling the kinetic equations of the traction shaft and its support bearings with the determination of their elastic deformations in this study. Under the effect of excitations induced by the dynamic rotor eccentric distance and time-varying mesh stiffness, the elastic structure deformations of the shaft and support bearings are formulated in the vibration environment of the locomotive. In addition, the nonlinear contact forces between the components of the rolling bearing, the lubricating oil film, and radial clearance are comprehensively considered in this study. The results indicate that the elastic deformations of the shaft and bearings can change the dynamic responses of the traction motor and its support bearings. There are large differences between the ranges of the rotor motion calculated by the rigid and the flexible traction motor models when the intensified wheel-rail interaction is considered. With the increase of the rotor eccentricity, the results underscore the role of the elasticity of traction shaft and support bearings in dynamic researches of the traction motor. The critical value of the initial eccentric distance for the rub-impact phenomenon decreases from 1.23 mm to 1.15 mm considering the flexible effect of the shaft and bearings. This dynamics model of the traction motor can provide more accurate and reasonable simulation results for correlational dynamic researches.

Influence of rail weld irregularity on dynamic stress of bogie frame based on vehicle-track rigid-flexible coupled model

To examine the effects of rail weld irregularity on the dynamic stress of the bogie frame, a numerical model which considers the bogie frame flexibility is established. Field measurements were conducted to validate the reliability of the proposed model and the bogie frame’s modal vibration including the bending deformation of cross beams at 50 Hz can be observed. A comparison between the flexible bogie frame model and the traditional multi-body dynamics model is conducted to investigate the influences of the bogie frame’s flexibility on wheel-rail interactions. Then the numerical model of the rail weld joint is proposed to study the P2 resonance performance and the dynamic stress patterns of the bogie frame. A comparison of influences with different rail weld irregularities and parameter studies are conducted. Then the effects of fastener stiffness on P2 resonance frequencies are discussed. The results show that it is necessary to consider the bogie frame’s flexibility in simulations which will aggravate the wheel-rail vibrations. The short wavelengths in combination with a certain speed could induce the bogie frame’s modal vibration and large track supporting stiffness will threaten the running safety of the vehicle which may also contribute to the formation of wheel out-of-roundness. Besides, the limit values of the rail weld irregularities are discussed to provide a reference for rail surface grinding from different aspects.

Image-based 3D reconstruction for rail profile measurement

The routine inspection of railheads for defects such as wear and surface cracks is a tedious process, which, if not detected, can alter the wheel-rail contact interaction leading to catastrophic events. This study investigates and implements a railhead measurement method using image-based three-dimensional reconstruction, which enables rapid scanning of railheads and production of detail cross-sectional measurements for rail-wheel interface analysis. A complete workflow with a methodology for reconstructing railheads from images and extracting cross-sectional measurements from the reconstructed model is presented. In order to validate the proposed method in the field, a mobile automated system was equipped with an array of cameras specifically spaced to cover the areas of interest on the railhead. The system can automatically transverse along the railhead, acquiring images synchronously. Two case studies in the laboratory environment and the real railway site have been performed to evaluate the performance and accuracy against industry practices. The results show that the proposed method can accurately measure the railhead cross-sectional profile at an root mean square error (RMSE) less than 0.3 mm compared with MiniProf. Furthermore, continuous cross-sectional data and intuitive color information are provided by our method which can help inspectors to locate defects easily and more efficiently.

The influence of the lateral contact point trajectory and the rotation of the monoblock on the impact loads in railway turnouts

A new wheel–rail interaction model for the prediction of turnout impact forces is presented. Although the model is based on the classical “moving irregularity” approach, it is novel in the sense that it accounts for the lateral shift of the wheel–rail contact position during load transfer between the crossing nose and wing rail. This lateral shift increases the mobility of the track due to the rotational response of the monoblock under off-centred excitation. It is shown that the resulting stepwise variation of the wheel and track mobilities upon impact can profoundly influence the impact force time history. It is furthermore shown that these effects are particularly emphasized during the trailing move when the wheel impacts on the off-centred wing rail and much less during the facing move when the impact is absorbed by the crossing nose which is located in the plane of symmetry of the monoblock cross-section. Apart from the stepwise shift upon load transfer the lateral wheel–rail contact point position varies continuously along the longitudinal coordinate of the turnout. Simulations show that these continuous variations have a negligible influence on the impact force time histories and that a simplified model with constant shift gives satisfactory results. A comparison of the calculated crossing nose and wing rail accelerations shows encouraging agreement with field measurements. It is concluded that omission of the rotation leads to an overestimate of the track vibrations. Especially for the trailing move, this overestimate becomes substantial for frequencies above 100Hz.

Long freight trains & long-term rail surface damage – a systems perspective

In this work, the authors present a detailed train-track interaction model of a long freight train operation to predict long-term rail surface damage. In addition to vehicles and track, intermediate maintenance actions in the form of cyclic grinding passes have also been modelled according to European standards to realistically represent the evolving wheel-rail interface. The influence of longitudinal train dynamics in the form of inter-vehicle interactions, traction, braking, gradients, etc is also included in this method to reflect their effect on damage evolution. The authors demonstrate that the novel ‘Train-track interaction’ formulation is more complete and therefore better suited to study long-term rail surface damage as opposed to existing ‘vehicle-track’ formulations since the former brings the system dynamics at play, significantly altering the wheel-rail interaction. A key highlight of this work is that the rail surface damage is expressed in the form of evolving rail profiles over a large tonnage passing and by depicting RCF-affected zones. This framework can be tuned into a digital twin to guide infrastructure managers regarding the condition of rail surface as a function of tonnage passage. This can in turn facilitate predictive maintenance of track depending on traffic and operation.

Random simulation method of track irregularities and its application in vehicle-track dynamic analysis

ABSTRACT Track irregularity holds strong randomicity, evolvability, and large data sets during the long-term operation of a rail line, possessing a significant influence on the dynamic performance of vehicle-track systems. In this work, methods for simulating track random irregularities are developed by combining the track irregularity probability model (TIPM) and the number theory method and by the Karhunen-Loève expansion (KLE). Furthermore, the vehicle-track interaction model considering the interaction between the vehicle, track, and wheel-rail interaction is constructed at a 3-D space, where the multi-rigid-body dynamics, finite method, and wheel-rail contacts are applied to construct matrix-coupled vehicle-track interaction equations. Finally, a unified random vibration analysis framework for the vehicle-track system is presented. From perspectives of the amplitude, power spectral density, and probabilistic distribution, the accuracy and efficiency of TIPM and KLE models in simulating track random irregularities and revealing system dynamics performance are compared and analysed in detail.

A novel machine learning based tangent stiffness calculation method for 3D wheel-rail interaction element

A machine learning (ML) based method is presented in this paper for obtaining tangent stiffness of a complicated three-dimensional wheel-rail interaction element that is able to practically and effectively simulate the complicated dynamic responses of vehicle-track problems. The element tangent stiffness, defined as differentiation of element insisting force to nodal displacement, is important in improving efficiency when Newton’s method is used to solve implicit nonlinear finite element equations. However, deriving and software implementing the tangent stiffness require significant efforts, and calculating the tangent stiffness in each iteration of the Newton method is usually time consuming. On the other hand, ML can directly obtain the implicit mapping between inputs and outputs of complex calculation process with limited programming effort and high computational efficiency, and is potentially a good alternative way to calculate the tangent stiffness of complicated element. In this paper, a feedforward artificial neural network is trained for obtaining the tangent stiffness, while inputs are the displacement and velocity of the element and outputs are the entries of the tangent stiffness matrix. The ML based tangent stiffness are implemented in an open source finite element software framework, OpenSees, and verified by application examples of a wheelset and a light rail vehicle running on straight rigid rail. The accuracy and efficiency are compared between the use of ML based tangent stiffness (MLTS) and the consistent tangent stiffness obtained at different speeds. The results demonstrate the MLTS can ensure the calculation accuracy and significantly improve the calculation efficiency.

Effect of rotor eccentricity on the dynamic performance of a traction motor and its support bearings in a locomotive

Rotor eccentricity is a common fault of traction motors during operation. To ensure the stability and safety of the traction motor, it is essential to analyze the effect of rotor eccentricity on the dynamic performance of the traction motor, particularly the motor bearings. This study focuses on the extraction of the fault vibration features of a locomotive in the presence of rotor eccentricity under complex internal and external excitations from the traction power transmissions and wheel-rail interactions. A spatial locomotive-track coupled dynamics model with an eccentric rotor motor is applied in this study, and the detailed mechanical structures of the traction motor and motor bearings are comprehensively considered. The results indicate that rotor eccentricity can deteriorate the vibration conditions of the traction motor and intensify the interactions between the components of the motor bearings. Due to the effect of the time-varying mesh forces, the variation in the loaded region of the non-driving end bearing is more significant than that of the driving end bearing.

PDEM-based stochastic analysis of a train-track-bridge system using dimension-reduced simulations of turbulent winds and track irregularities

Winds and track irregularities are inherently random in nature, but most of previous work did not fully consider this randomicity in computation of the dynamic response of train-track-bridge system. This study aims to develop an effective framework for stochastic analysis of the wind-train-track-bridge system based on the probability density evolution method. A dimension-reduced simulation scheme is applied since the involved system has high-dimensional random variables. Therefore, the representative samples of turbulent winds and track irregularities can be well expressed with only two random variables. In numerical examples, the accuracy of the framework is verified, and the influences of the mean wind velocity on the random vibration characteristics of the system are investigated. The results show that the dispersion of the lateral displacement of the bridge is larger than the vertical displacement, but both the vertical and lateral accelerations of the bridge have larger dispersions. The existence of lateral wind loads can reduce the dispersion of the lateral wheel–rail interaction forces of the wheel in the leeward direction. Considering the confidence levels of 75%, 85% and 95%, the train can run safely over the bridge in the wind velocity range of 0–25 m/s.

Numerical study of wheel/rail dynamic interactions for high-speed rail vehicles under low adhesion conditions during traction

The evolution of wheel-rail dynamic interaction of a high-speed railway vehicle is essential for the simulation of wheel-rail rolling contact damage under low adhesion conditions. The main objective of this study is to reproduce the dynamic wheel-rail interaction behaviour under various interfacial contaminations by experimental and numerical modelling methodology. Firstly, the wheel-rail adhesion characteristics under different interfacial contaminations were obtained. Subsequently, a simplified numerical methodology was proposed to extract the parameters from the high-speed adhesion tests to modify the simplified theory of Kalker (FASTSIM). The initial slop reduction factor and the slip-velocity-dependent coefficient of friction (COF) were introduced based on the high-speed experimental curves. Furthermore, the modified wheel-rail rolling contact model was incorporated into a longitudinal vehicle-track coupled dynamic model. The wheel-rail dynamic interaction behaviours under different operational conditions were attained. Finally, the wheel-rail wear performances were primarily investigated for typical traction coefficients under wet conditions. Results show that the wheel-rail creep force drops dramatically when the wheel enters the low adhesion zone (LAZ). There is a sudden increase in the creep force when the adhesion recovers. In addition, the wheelsets begin to slide and have severe wear at LAZ when the traction coefficient is larger than 0.1 at high speed.

Floating slab track with inerter enhanced dynamic vibration absorbers

This paper proposes an inerter enhanced dynamic vibration absorber (IDVA) to improve the low-frequency vibration mitigationperformance of the floating slab track (FST). To this aim, the inerter is coupled to a dynamic vibration absorber (DVA) to form the IDVA. Analytical derivations of the FST-IDVA are given. Considering the random property of the wheel-rail interaction, the H2 optimization is performed and closed form solutions for the optimal parameters of the IDVA are obtained. Parametric studies are conducted to evaluate the influences of the inerter on the performances of the FST-IDVA. Numerical simulations are performed to validate the efficiency of the proposed FST-IDVA. Time history analyses of FST, FST-DVA, and FST-IDVA under moving metro vehicle load are computed and compared. When using the FST-DVA, it is found that dynamic responses of the track slab and the force transmitted to the ground are suppressed, but the relative displacement response of the absorber isrelatively large; conversely, when using the FST-IDVA, dynamic responses of the track slab and the force transmitted to the ground are furthersuppressed, more importantly, the relative displacement response of the absorber is mitigated greatly. Overall, the FST-IDVA overperforms the FSTDVA, even the small-mass-ratio absorber is used.

An Effective Tangent Stiffness of Train–Track–Bridge Systems Based on Artificial Neural Network

Dynamic response analysis of a train–track–bridge (TTB) system is a challenging task for researchers and engineers, partially due to the complicated nature of the wheel–rail interaction (WRI). When Newton’s method is used to solve implicit nonlinear finite element equations of a TTB system, consistent tangent stiffness (CTS) is essential to guarantee the quadratic convergence rate. However, the derivation and software implementation of CTS for the WRI element require significant efforts. Artificial neural network (ANN) can directly obtain a potentially good tangent stiffness by a trained relationship between input nodal displacement/velocity and output tangent stiffness. In this paper, the backpropagation neural-network-based tangent stiffness (BPTS) of the WRI element is derived and implemented into a general finite element software, OpenSees, and verified by dynamic response analysis of a high-speed train running on a seven span simply supported beam bridge. The accuracy and efficiency are compared between the use of BPTS and CTS. The results demonstrate that BPTS can not only save the significant efforts of deriving and software implementing CTS but also improve computational efficiency while ensuring good accuracy.

Adaptive simulation and integration method for wheel-rail contact problems in locomotive traction studies

Knowledge of creep forces at wheel-rail interface when high power is applied to the locomotive wheels has been the subject of many recent studies. The common wheel-rail interaction methods are generally divided by two theories – Hertzian and non-Hertzian. The first method uses Hertzian contact for the normal problem and the tangential problem is divided into two algorithms – Polach’s theory and the Simplified theory-based algorithm referred to as Modified Fastsim. Kalker’s original Fastsim-based method shows a better accuracy for these two Hertzian-based algorithms. The second method is based on the non-Hertzian theory, and it uses the Exact theory also developed by Kalker and implemented in the Extended Contact library to calculate forces at the wheel-rail interface. Considering that the second method is more accurate, this paper aims to present an adaptive simulation and integration method (ASIM) which is positioned in the middle between the two common methods and is designed to introduce a transition from the non-Hertzian to Hertzian contact in the normal problem with the application of the Modified Fastsim for the calculation of contact forces at the wheel-rail interface. The proposed method is aimed to be used in vehicle system dynamics studies performed in multibody software packages. A specially developed wheel-rail coupling incorporating geometrical, normal, and tangential modules is integrated into Gensys multibody software and benchmarked with the standard Extended Contact based wheel-rail coupling by means of locomotive traction tests that use a full mechatronic model of a high adhesion locomotive. The computational performance and accuracy of the proposed method are assessed and discussed.

A novel dynamics model of a trailer bogie brake system and its application in stability analysis

The dynamic performance of the trailer bogie brake system is essential for the safe operation of a high-speed train during the braking process. In this work, we developed a novel ten-degree-of-freedom (ten-DOF) dynamics model of a trailer bogie brake system based on dynamic and tribological theories. The non-linear factors including disc-pad non-linear friction and wheel-rail non-linear interactions were considered. The field test results demonstrated that more intense vibrations occur at low vehicle speeds, which is also supported by numerical simulations based on the novel dynamics model. The abnormal vibration is caused by the limit cycle oscillation of the brake unit, and it leads to the instability of the whole system. To further understand the instability of the trailer bogie brake system, the equilibrium points and the linear stability of the system under different braking conditions and suspension parameters were investigated based on the Lyapunov theory. Then, the non-linear vibration response and stability of the trailer bogie brake system affected by the suspension parameters were further calculated by numerical integration methods. The results demonstrated that the mounting stiffness of the brake unit approached 3.4×107N/m and the primary suspension stiffness approached 6.0×105N/m or remained within the range of 10×105-14×105N/m, causing more violent vibrations and increased system instability. A primary suspension damping exceeding 2.4×104N·s/m was conducive to improving system stability.

Numerical investigation on wheel-rail impact contact solutions excited by rail spalling failure

Rail spalling is a typical form of wheel-rail rolling contact fatigue (RCF), and is a difficult problem that has always existed in railways. Once the wheel rolls across the spalling failure area, there will be a violent dynamic wheel-rail interaction. This paper presents an explicit high-speed 3D wheel-rail rolling contact transient explicit finite element model that considers local rail spalling failure. The dynamic wheel-rail interaction under the condition of differentspalling lengths and contact stress states, as well as plastic strain of the rail when the wheel rolls across the rail spalling, are calculated using the theory of transient wheel-rail dynamics. In addition, the time–frequency analysis is carried out to obtain the distribution characteristics of dynamic response signals such as axle box acceleration, rail vibration acceleration and dynamic vertical wheel-rail force in time domain and frequency domain.Furthermore, when the vehicle travels at a high speed, the speed and radius of the wheelhave little influence on the dynamic vertical wheel-rail force, or on the wavelet energy peak and frequency. The effect of the mutual dynamic correlation is small. But the dynamic vertical wheel-rail force, along with wavelet energy peak and frequency, increase in an approximately linear fashion with the impact acceleration of wheelset and the length of spalling failure. These results can be used to guide the dynamic detection of local defects on rails.