Wheel Rail Research Articles

A trailer car dynamics model considering brake rigging of a high-speed train and its application

AbstractBrake systems are essential for the speed regulation or braking of a high-speed train. The vehicle dynamic performance under braking condition is complex and directly affects the reliability and running safety. To reveal the vehicle dynamic behaviour in braking process, a comprehensive trailer car dynamics model (TCDM) considering brake systems is established in this paper. The dynamic interactions between the brake system and the other connected components are achieved using the brake disc–pad frictions, brake suspension systems, and wheel–rail interactions. The force and motion transmission from the brake system to the wheel–rail interface is performed by the proposed TCDM excited by track irregularity. In addition, the validity of TCDM is verified by experimental test results. On this basis, the dynamic behaviour of the coupled system is simulated and discussed. The findings indicate that the braking force significantly affects vehicle dynamic behaviour including the wheel–rail forces, suspension forces, wheelset torsional vibration, etc. The dynamic interactions within the brake system are also significantly affected by the vehicle vibration due to track irregularity. Besides, the developed TCDM can be further employed to the dynamic assessment of such a coupled mechanical system under different braking conditions.

A Physics-Driven Method for Determining Wheel—Rail Contact Area With Gradient-Based Optimization

AbstractIn this paper, a physics-based method to inversely determine wheel—rail contact area in their lifecycle is proposed by introducing a continuous optimization pipeline including filtering and projection procedures. First, the element connectivity parameterization method is introduced to construct continuous objections with discrete contact pairs and formulate the physics-based optimization model. Second, the radius-based filter equation is employed for smoothing the design variables to improve the numerical stability and the differentiable step function is introduced to project smoothed design variables into 0–1 discrete integer space to ensure the solution of the optimization model yields discrete contact pairs. Finally, the method of moving asymptotes is constructed for iteratively updating wheel—rail contact area by analyzing the sensitivity of relaxed optimization formulation with respect to design variables until the algorithm converged. The experimental result shows the effectiveness of the proposed method to inversely determine the wheel—rail contact points in their lifecycle compared to the line tracing method; to the best of our knowledge, it is the first attempt to consider wheel—rail contact area in lifecycle service with both the measured profile and the predicted profile data by gradient-based optimization method.

Influence of wind and rain environment on operational safety of intercity train running on the viaduct

PurposeBased on the aerodynamic loads and dynamic performances of trains, this study aims to investigate the effect of crosswinds and raindrops on intercity trains operating on viaducts to ensure the safe operation of intercity railways in metropolitan areas.Design/methodology/approachAn approach coupled with the Euler multiphase model as well as the standard k-ɛ turbulence model is used to investigate the coupled flow feature surrounding trains and viaducts, including airflow and raindrops, and the numerical results are validated with those of the wind tunnel test. Additionally, the train’s dynamic response and the operating safety region in different crosswind speeds and rainfall is investigated based on train’s aerodynamic loads and the train wheel–rail dynamics simulation.FindingsThe aerodynamic loads of trains at varying running speeds exhibit an increasing trend as the increase of wind speed and rainfall intensity. The motion of raindrop particles demonstrates a significant similarity with the airflow in wind and rain environments, as a result of the dominance of airflow and the supplementary impacts of droplets. As the train’s operating speed ranged between 120 and 200 km/h and within a rainfall range of 20–100 mm/h, the safe operating region of trains decreased by 0.56%–7.03%, compared with the no-rain condition (0 mm/h).Originality/valueThe impact of crosswind speeds and rainfall on the train’s aerodynamic safety is studied, including the flow feature of crosswind and different particle-sized raindrops around the train and viaduct, aerodynamic loads coefficients suffered by the intercity train as well as the operating safety region of intercity trains on the viaduct.

Influence of damping characteristics of mesh–type high damping rail pad on the vehicle–track dynamic performance and rail surface roughness

The rail pad damping is a critical parameter to evaluate its vibration reduction capacity, which has essential research significance. The mesh–type high damping rail pad (MTHDRP) is proposed for the first time in this paper, and the differences in damping performance between MTHDRP and traditional rail pads (PTRP and GRP) are compared and studied. It is concluded that the MTHDRP has the highest damping coefficient than any other rail pads. The dynamics model calculation has discovered that the increase of the rail pad damping coefficient can not only effectively decrease the vibration acceleration, wheel–rail force, and derailment coefficient, but also is beneficial for both vehicle safety and stability and track structure protection. The field test shows that the acceleration of the rail, clip, iron pad, and track bed in the MTHDRP laying section is significantly lower than that in the PTRP laying section, and the rail surface roughness improves significantly after the rail pad is replaced with the MTHDRP for half a year.

Study on rail corrugation on curved tracks on metro ramps

A typical feature of rail corrugation on metro rails is the almost 100% probability that low rails on sharply curved tracks will suffer from corrugation, but both high and low rails on gently curved tracks are less prone to corrugation. On Chongqing Metro Line 10, there is a curved track on an ascending slope, and the high rail of this track suffered from severe corrugation. Shenzhen Metro Line 3 has a curved track on a descending slope, and the low rail of this track was also subjected to corrugation. This article presents a study on the rail corrugation formed on metro ramps. Two vehicle-track coupled dynamic models were employed to judge whether the creep force in the contact patch would be saturated, with results showing that the creep force of the leading wheel on the high rail on the uphill section tends to be saturated, affected by the tractive force. Influenced by the braking force, the creep force on the leading inner wheel on the downhill section is also prone to be saturated. In this study, the formation of corrugation is attributed to the self-excited oscillation generated at the wheel-rail (W-R) interface. Based on this mechanism, a finite element model for predicting the occurrence propensity of the low rail corrugation on the downhill track was developed. The simulation results show that increasing lateral fastener damping is beneficial for suppressing rail corrugation.

Research on polygon suppression of resilient wheels under multiple operating conditions

The polygon effect seriously affects the running stability and safety of the vehicle. In order to suppress the wheel polygon, a dynamic model is established that can calculate the force on the resilient wheel's rim and core. With straight lines, curves, and vertical curves as input excitation, combined with wheel–rail force and acceleration, the suppression effect of the resilient wheel on the polygon is analyzed from the perspective of the time domain, frequency domain, and polygon order. The results show that the resilient wheel can effectively reduce the vertical wheel–rail force and restrain the wheel polygon. After 30 Hz, with the increase in frequency, the suppression effect of the resilient wheel on the polygon becomes increasingly significant. The resilient wheel can sufficiently suppress the polygons generated by 50–150 Hz carriage vibration without affecting the dominant frequency of carriage vibration. This study can provide a new idea for the suppression of wheel polygon.

Transient dynamics of a full wheel rail set passing a weld irregularity at high speed

Compared to tracking the contact force, the monitoring of axle box acceleration (ABA) is an effective way to determine the operation status of a high–speed train passing a weld. In this study, we propose a finite element model for studying the dynamic response of a full wheelset passing weld irregularities at high speed. Simulations provide detailed dynamic information during the pass, such as the peak of the contact force and the history of acceleration. With these simulation results, we propose a standard safety limit for the running speed: a running speed boundary as a function of defect size. Additionally, rail weld defect grinding standards should depend on the running speeds.

Efficient mitigation of railway induced vibrations using seismic metamaterials

The fast growth of railway transport pushed by its sustainability requires all railway stakeholders to work together to minimise any possible drawbacks that might slow down this positive trend. Among these, the induced vibrations generated at the wheel–rail interaction during train passage are the most significant, especially in urban areas where in the form of ground-borne vibrations and/or noise negatively affects the daily life of the residents. In this direction, the innovative concept of seismic metamaterial can enhance the vibration attenuation levels of existing mitigation measures and, at the same time, ensure a straightforward application in the railway environment. This paper uses a combined vehicle/track/soil prediction dynamic model of the T2000 LRV (Light Rail Vehicle) tram operating in Brussels, based on a two-step approach already validated in the past, to analyse the effects that the inclusion of seismic metamaterials within the transmission path has in terms of vibration attenuation. In particular, a four-by-four group of piles is examined with different material proprieties for the inclusions, considering a range of velocities and distances from the track in order to quantify the achievable Insertion Loss (IL) for each configuration depending on the distances and the tram speed, attaining ILs up to 10 [dB]. The study is then extended to other possible arrangements of the group of piles, providing a direct relationship between the repetitiveness of each row of the primitive unit cell of the metamaterial and the gained levels of attenuation, in order to give a base for the costs of this type of mitigation measure. Furthermore, the influence on the attenuation levels of the soil characteristics, is evaluated by considering an ideal uniform underground, extending the IL to 18 [dB] in the case of steel inclusion. Finally, the paper gives insights into the use of metamaterials as mitigation measures for railway-induced vibration in order to understand and evaluate the potential of this novel concept and its benefits.

Ballasted Track Behaviour Induced by Absent Sleeper Support and its Detection Based on a Convolutional Neural Network Using Track Data

With development of the heavy-haul railway, the increased axle load and traction weight bring a significant challenge for the service performance and safety maintenance of the railway track. Conducting defect recognition on concrete sleepers and ballast using big data is vital. This paper focused on the detection of absent sleeper support in a ballasted track with an emphasis on the integration of model-based and data-driven methods. To this end, a mathematical model consisting of the wagon, track and wheel–rail contact subsystems was first established to acquire the necessary raw data for the data-driven method, in which the wagon was regarded as a 47-degree-of-freedom multi-body subsystem, and the track was treated as a multi-layer discrete-elastic support beam subsystem with absent sleeper support. Then, an architectural hierarchy of a three-layer convolutional neural network (TLCNN) was developed, which includes three convolutional layers and two pooling layers, and a method for reconstructing one-dimensional sleeper vertical displacement to a two-dimensional time–space matrix was also proposed. Thirdly, verification was carried out by comparing the simulation and experimental results to illustrate the accuracy and reliability of the mathematical model, and the dynamic behaviour of the track with absent sleeper support was investigated. Lastly, the established TLCNN was used to train the raw data of the sleeper vertical displacement and detect the existence of absent sleeper support. Results show that the integration of model-based and data-driven methods was a reliable and effective approach for the detection of absent sleeper support. The proposed TLCNN can acquire and extract robust characteristics in a noisy environment. To handle more complex recognition tasks and further improve performance, deeper CNN models and larger sample sizes should be preferentially considered in practical applications.

A co-simulation approach for straddle monorail vehicle–bridge interaction subjected to nonlinear excitation

Straddle monorail systems, a lightweight rail transit mode, are being increasingly used for developing infrastructures in medium-sized cities. Vehicle–bridge interaction (VBI) is a critical issue in the design of straddle monorail systems. However, existing straddle monorail VBI studies have not simultaneously considered nonlinear excitations, structural nonlinearities, and bridge alignment defects. Therefore, this study proposes a co-simulation approach that combines MATLAB and ANSYS software packages to analyze the dynamic responses of a straddle monorail VBI system. The equations of motion of the monorail train are formulated following D'Alembert's principle and are solved by self-programming on the MATLAB platform. A finite element model of the bridge is established and solved using the ANSYS programming. The bridge and vehicle subsystems are coupled through global iteration with the exchange of wheel–rail contact forces calculated using MATLAB and bridge responses calculated using ANSYS. The co-simulation approach is validated by the dynamic responses of the monorail train and bridge reported in the relevant literature. To demonstrate further the effectiveness and high efficiency of the proposed approach, the dynamic responses of the VBI system with a monorail train crossing a three-span continuous rigid-frame prestressed concrete-girder bridge are analyzed, and three investigated cases of sole earthquake, sole moving-train, and combined earthquake and moving-train excitations are compared. These results demonstrated that the proposed co-simulation approach can provide an effective tool for nonlinear dynamic responses of straddle monorail VBI systems subjected to nonlinear excitation and other nonlinear-coupled dynamic issues.

Effect of primary suspension and friction wedge maintenance parameters on safety and wear of heavy-haul rail vehicles

Wheel wear is of major interest in railways due to the high cost of wheel reshaping, rail wear, and safety issues in operation. Recent researches employ onboard sensors to evaluate the dynamic behavior of the wagon and determine railway running conditions. However, sensors and computing units are expensive and some maintenance scenarios are impossible to be deliberately generated. In this work, several maintenance parameters for primary suspension, friction wedge, and flange backspacing are evaluated within operational ranges in a Box-Behnken design of experiment (DoE), set in a quadratic surface model. Such a modeling approach uses few experimental points and a significantly small computational cost when compared to a full factorial method, which uses multibody dynamic models on a simulating platform, like Simpack, to determine which parameters are more influential in safety against derailment (Y/Q) and wheel and flange wear (Tγ). The present work evaluates such parameters for heavy-haul gondola rail cars, with meter and broad gauge, running on tangent track and curves, with and without FRA irregularities. The analysis makes it possible to identify non-uniformities in wheel wear and to set different inputs for condition-based maintenance for freight rail wagons. Results show that the primary suspension longitudinal clearance and stiffness affect Y/Q and wear by over 100%, increasing the operational risk and maintenance cost because of wheel wear.

Multiobjective optimisation of rail profile at high speed

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.

A Methodology for Continuous Monitoring of Rail Corrugation on Subway Lines Based on Axlebox Acceleration Measurements

Rail corrugation is a degradation phenomenon that manifests as a quasi-periodic irregularity on the running surface of the rail. It is a critical problem for urban railway lines because it induces ground-borne vibrations transmitted to the buildings near the infrastructure, causing complaints from the inhabitants. A typical treatment to mitigate the rail corrugation problem is the periodic grinding of the rails, performed by dedicated vehicles. The scheduling of rail maintenance is particularly critical because it can be performed only when the service is interrupted. A procedure for the continuous monitoring of rail corrugation is proposed, based on axlebox acceleration measurements. The rail irregularity is estimated from the measured acceleration by means of a frequency domain model of vertical dynamics of the wheel–rail interaction. The results obtained by using two different methods (a state-of-the-art method and a new one) are compared. Finally, the study of the evolution of the power content of the rail irregularity enables the identification of the track sections where corrugation is developing and rail grinding is necessary.

An abnormal carbody swaying of intercity EMU train caused by low wheel–rail equivalent conicity and damping force unloading of yaw damper

AbstractLow-frequency carbody swaying phenomenon often occurs to railway vehicles due to hunting instability, which seriously deteriorates the ride comfort of passengers. This paper investigates low-frequency carbody swaying through experimental analysis and numerical simulation. In the tests, the carbody acceleration, the wheel–rail profiles, and the dynamic characteristics of dampers were measured to understand the characteristics of the abnormal carbody vibration and to find out its primary contributor. Linear and nonlinear numerical simulations on the mechanism and optimization measures were carried out to solve this carbody swaying issue. The results showed that the carbody swaying is the manifest of carbody hunting instability. The low equivalent conicity and the decrease of dynamic damping of the yaw damper are probably the cause of this phenomenon. The optimization measures to increase the equivalent conicity and dynamic damping of the yaw damper were put forward and verified by on-track tests. The results of this study could enrich the knowledge of carbody hunting and provide a reference for solving abnormal carbody vibrations.

The Effect of Various Contaminants on the Surface Tribological Properties of Rail and Wheel Materials: An Experimental Approach

This study reports on the tribological behavior of Indian rail track and wheel materials under different contaminants. A pin-on-disc tribometer was selected for the experimental analysis in ambient conditions (temperature of 24.9 °C and relative humidity of 66%). Sand, mist, leaves, and grease were the contaminants used in this investigation. The railway track was used to make the pin, and the wheel was used to make the disc. The acquired results were analyzed using frictional force and wear depth as a function of time as the variables. These pollutant effects were compared to no-contaminant conditions. It was observed that the sand increased the friction force and wear depth, whereas oil decreased friction and wear. Mist and leaves also reduced friction and wear. The effect of leaves was higher than the mist. The effect of load on various contaminants was also investigated. The results showed that as the load increased, the friction force and wear also increased for all contaminants. The results of this study can help in understanding the wear phenomenon of wheels and rail tracks in different parts of India.

Level-Set-based Wheel–Rail Profile Evolution in Four-Dimensional Continuous Functional Space

Level-Set-based Wheel–Rail Profile Evolution in Four-Dimensional Continuous Functional Space

Dynamic Analysis of the High Speed Train–Track Spatial Nonlinear Coupling System Under Track Irregularity Excitation

Track irregularity is the main factor that affects the safety and comfort of high-speed railway. It is important to study the influence of the track irregularity on the safety service of high speed train–track coupling system. In this paper, a vehicle–track spatial nonlinear coupled system dynamics model is developed with FEM. The model includes vehicle subsystem and track subsystem, which are coupled by wheel–rail interface. The vehicle subsystem is a 31-DOF spatial vehicle model, and the track subsystem is a three-dimensional slab track model composed of the rail, rail pad and track slab. Considering wheel tread profile and rail head profile, the wheel–rail spatial contact geometry relationship is established, and the “Trace method” and the “Minimum distance method” are used to search for wheel–rail contact points. Considering the nonlinear contact between the wheel and the rail, a numerical approach is presented, where the “Trace method” is embedded into the algorithm for solving the vehicle–track nonlinear coupling dynamics equation by cross iteration, realizing searching the wheel–rail contact points and solving the vehicle–track nonlinear coupling equation simultaneously, which greatly improves the efficiency of numerical analysis. As application examples, the dynamic responses of a high speed train–track spatial nonlinear coupled system excited by the track V-shaped local profile irregularity and the track torsional irregularity are analyzed. The results show that the algorithm is effective in solving the vehicle–track spatial nonlinear coupled system dynamics problem, and the track irregularity has significant influence on the dynamic response of vehicle and track structure.

Optimal design of rail level crossings and associated transition zones using adaptive surrogate-assisted optimization

Transition zones such as level crossing and bridge approaches are critical links in railway networks due to higher degradation rates and maintenance needs. In this context, parametric optimization has been applied to improve the design in transition zones; however, it requires a more computationally efficient tool to support repetitive function evaluations, since the involved vehicle–track dynamic simulations are becoming more expensive to evaluate. For this purpose, a surrogate-based simulation methodology is proposed to search for an optimal combination of parameters relevant to the geometry and elasticity of track structures. Specifically, the presented methodology integrates finite element (FE)-based modeling with surrogate-assisted optimization: (1) the FE model is developed to characterize the dynamic behavior of a level crossing under a moving vehicle; (2) the optimization problem is formulated upon this mechanical model by extending the expensive FE simulations to an adaptive surrogate modeling scheme. This integration facilitates efficient exploration of the track design space (thereby reducing the computational cost), and a reasonable balance can be achieved between solution quality and computational effort. The methodology is applied to a Dutch railway case. Results show that compared to a reference design, the optimized design significantly improves performance indicators relevant to wheel–rail contact forces and energy dissipation in the ballast layer. The solution brings great potential in achieving a more desirable vehicle–track interaction and improving the connecting performance between level crossings and transitions. The methodology is applicable to other railway structures and may also contribute to improvements in current track design practices.

In-situ micro-cantilever bending studies of a white etching layer thermally induced on rail wheels

A complex and untraceable mechanical and thermal loading situation in rolling-sliding contacts can lead to the formation of white etching layers (WELs), depicting critical crack initiation sites. For our detailed studies, to obtain a holistic view of the microstructural characteristics and micro-mechanical properties, we prepared a WEL on a decommissioned (after 200,000 km service life) rail wheel by laser surface treatments with a defined energy input. This WEL is predominantly martensitic down to a depth of 30–40 μm, after which a transition to the deformed ferritic-pearlitic microstructure of the hypoeutectoid rail wheel steel is present. The martensitic region is with 6.98 ± 0.68 GPa significantly harder than the transition zone (5.17 ± 0.39 GPa) and the deformed ferritic-pearlitic base material (3.30 ± 0.33 GPa). In-situ V-notched micro-cantilever bending experiments of the martensitic (and thus most brittle) region show crack initiation and propagation – mostly along the boundaries of the martensitic grains – besides a plastic behavior. Applying the elastoplastic fracture mechanics allows to derive the local fracture toughness KIQ, which is 16.4 ± 1.2 MPam1/2 for this martensitic region of the WEL. The results outpoint the application of micro-cantilever bending tests in addition to hardness testing as a promising tool to discuss the relationship of microstructural characteristics with its micro-mechanical properties.

Insulated rail joint (IRJ) contact characterisation-an ultrasonic reflectometry approach for a cross-material interface

Vehicle–track interaction at insulated rail joints (IRJs) plays a significant role in the wear evolvement and damage of the IRJ components. It is, however, challenging to characterise the contact conditions within the region non-destructively and accurately using experimental tools, especially when the IRJ contact involves both wheel–rail and wheel–endpost contact pairs. This study presents an ultrasonic technique to monitor and characterise static IRJ contacts in a non-invasive manner. The proposed ultrasonic reflectometry technique can realise high-resolution visualisation of contact patch and contact pressure distribution for both wheel–rail contact and wheel–endpost contact, by striking a beam of focused ultrasonic signals at the contact interface. Different data post-processing strategies are applied for the two types of contacts and a deconvolution algorithm is applied to rectify the measurements near the rail–endpost boundary. The ultrasonic measurements are verified through finite element simulations and the results show good agreement with each other in terms of both contact area and contact pressure level. It is expected that the proposed ultrasonic approach can be a reliable tool to assist in revealing the contact behaviour of IRJs more profoundly.