Study on the influence of the modelling strategy in the calculation of the worn profile of railway wheels

As changes in the wheel and rail profiles strongly affect vehicle dynamics, running stability and safety, maintenance operations such as wheel turning and rail grinding are necessary. The availability of numerical models for wear prediction can be a huge support to optimize the scheduling of such operations. Thanks to the computational power of modern computer architectures, allowing parallelization and co-simulation, the typical strategy is based on a dynamic module performing the vehicle dynamics simulation, usually developed in commercial multibody (MB) software packages, and on a wear module for the calculation of the worn material. The latter can be implemented in the same MB code or in a separate software, such as Matlab/Simulink, which exchanges data with the MB code. Wear modules rely on wear laws relating the amount of worn material to the normal load and sliding distance or to the energy dissipated at the contact interface. Both types of law can be applied locally, calculating the worn depth in each cell of the discretized contact patch from the contact pressures and sliding speeds, or globally, hence calculating the worn volume or mass starting from the global forces and creepages. In the latter case, the worn material is calculated on the whole contact patch rather than only on the slip zone, and a proper distribution is required to relate the worn depth to the worn volume. The present work aims to further investigate the differences between the two approaches in the computed worn profiles in a specific case study in terms of reference vehicle and track, carrying out the dynamic simulations through the Simpack MB code. The paper is intended to highlight the differences in both the numerical results and computational efforts, comparing the wear computed by a local model with the outputs of the Simpack wear module

Simulation of wheel and rail profile wear: a review of numerical models

The development of numerical models able to compute the wheel and rail profile wear is essential to improve the scheduling of maintenance operations required to restore the original profile shapes. This work surveys the main numerical models in the literature for the evaluation of the uniform wear of wheel and rail profiles. The standard structure of these tools includes a multibody simulation of the wheel-track coupled dynamics and a wear module implementing an experimental wear law. Therefore, the models are classified according to the strategy adopted for the worn profile update, ranging from models performing a single computation to models based on an online communication between the dynamic and wear modules. Nevertheless, the most common strategy nowadays relies on an iteration of dynamic simulations in which the profiles are left unchanged, with co-simulation techniques often adopted to increase the computational performances. Work is still needed to improve the accuracy of the current models. New experimental campaigns should be carried out to obtain refined wear coefficients and models, while strategies for the evaluation of both longitudinal and transversal wear, also considering the effects of tread braking, should be implemented to obtain accurate damage models

Monitoring of railway freight vehicles using onboard systems

Rail freight transport plays a key role in reducing polluting emissions, so major efforts are underway to strengthen the sector. However, this requires an improvement in the performance of the vehicles, and their more efficient use, with an increase of the axle-load and the speed. In relation to these aspects it is important to strengthen the safety of railway transport, by improving the maintenance system and at the same time reducing the vehicle's impact on the line, which can be achieved both by improving the technical characteristics of the vehicles and by reducing the geometric irregularities of the track. The possibility of extending circulation on High Speed lines also to freight vehicles is nowadays of great interest. The improvement of the maintenance level can be achieved by adopting procedures based on the actual condition of the vehicle ("on condition") instead of on the basis of cyclical programming (time or mileage). This requires knowledge of the actual condition of the vehicle and its components, which can be achieved by installing onboard monitoring devices capable of analyzing the behavior of the vehicle in real time. The work illustrates the experimental tests carried out using an innovative monitoring system, installed on board two different types of freight vehicles used for intermodal transport. The tests were performed on different lines: on the historic Gotthard line, and on the new Gotthard high-speed line, including the base tunnel. In this way, it was possible to demonstrate the application of the monitoring system to a rail freight vehicle. Furthermore, the results obtained in terms of accelerations measured on two different types of lines were compared, detecting the different impact of the vehicle on good quality lines compared to lines with significant defects

The influence of resistant force equations and coupling system on long train dynamics simulations

In the simulation of the longitudinal dynamics of long trains, the modeling of the resistant forces and of the coupling system are two essential aspects. The modeling of the resistant forces directly affects the speed reached by each vehicle as well as the in-train forces. A literature review witnesses different laws for the calculation of both ordinary and accidental resistances. One of the objectives of this paper is to evaluate from the numerical point of view the influence of the resistant forces modeling strategy on the simulation outputs, i.e., on the speeds and in-train forces, by comparing different laws for propulsion and curving resistances. For what concerns the connection between the vehicles of the train, it is well known that the connection system is of utmost importance for the safety and running stability of the train. In this paper, the two existing coupling systems, i.e., the European buffer-hook system and the coupler used outside the European continent are first described, both in terms of operation and modelling techniques, and then they are compared on the same simulation scenario. All the simulations are performed on the first scenario of the International benchmark of the longitudinal train dynamic simulators, using the LTDPoliTO code developed by the railway research team from Politecnico di Torino

Study of wheel-rail adhesion during braking maneuvers

The present work aims to better understand the phenomenon of adhesion under degraded conditions during railway braking maneuvers with the aim of optimizing the anti-slip algorithms in order to reduce damage to the profiles of wheels and rails and to minimize the braking distance. The proposed approach is based on the analysis of experimental data acquired during braking tests carried out on track, considering different types of vehicles and different types of contaminants, able to reproduce the typical degraded adhesion conditions occurring during normal operation. The work describes a numerical model that allows to evaluate the dynamics of the vehicle during the braking operation and to correlate the pressures to the brake cylinder, which are related to the braking forces, and the angular velocities measured on the axles of the vehicle, with the adhesion coefficient

Long train dynamic simulation by means of a new in-house code

The need for faster heavy-haul trains with higher axle-loads is responsible for the rise of large in-train forces on wagon connection systems. These forces have a significant impact on longitudinal train dynamics (LTD) from the point of view of performances, running stability and safety during braking and traction operations. Therefore, LTD simulations represent an essential tool to predict in-train forces and to design coupling and braking systems. Long trains are typically modelled as a system of several point masses linked to each other by means of non-linear elements, summarizing the characteristics of the coupling systems. In fact, wagon connection systems present a non-linear force-deflection characteristic, with a hysteresis loop due to the different behaviour in loading and unloading states. The calculation of in train forces is nowadays performed following three main strategies, namely look-up table approaches, mathematical equations based on experimental results and “white-box” models related to physical properties of the connection systems. An International benchmark of LTD simulators was recently proposed to assess the output results obtained by different simulators, following several modelling strategies, in the simulation of the same scenarios. The research group from Politecnico di Torino joined the competition using the multibody commercial software Simpack (ver.9.4). However, inefficiencies appeared because multibody software are usually intended for the simulation of a few vehicles with many degrees of freedom (d.o.fs), rather than many wagons with few d.o.fs each. Therefore, the team developed a new LTD simulator (LTDPoliTO) in MATLAB, totally based on a vector-arithmetic logic. The new simulator can perform both dynamic investigations in time domain and modal analysis in frequency domain. The validation of LTDPoliTO was carried out by performing the four benchmark simulations and a good agreement with the other participants was obtained, in terms of both numerical results and computational speeds

Development and validation of a new code for longitudinal train dynamics simulation

Longitudinal train dynamics have a significant impact on both safety and performance of railway systems. Numerical simulation of long heavy haul trains can thus provide essential information for the development of diagnostic and signaling systems as well as coupling elements and braking systems. Long trains are usually modeled by considering only the longitudinal degree of freedom and by adding extra resistant forces to represent the track curvature and gradients. The prediction of in-train forces represents the most critical aspect in modeling the longitudinal dynamics of long trains made up of several vehicles. In fact, coupling elements have non-linear force-deflection characteristics, with different behavior in loading and unloading states, thus featuring a hysteretic loop. Look-up tables storing data from experimental tests are generally used to model these elements; however, other strategies, such as fitting curves and white-box models are witnessed in the literature. Recently, an international benchmarking of longitudinal train dynamics simulator was established in order to compare the output results obtained by different models with the same input data. The research group from Politecnico di Torino performed the simulations using the multibody software Simpack, but computational inefficiencies and numerical divergences occurred. To overcome these issues, a new dedicated in-house code was developed in the MATLAB environment. The paper focuses on the description of this new code and its validation, which was carried out by performing the simulations according to the benchmark inputs and comparing the results with the outputs from the other participants

Validation of a brake monitoring system using a multi-axle roller-rig

A widespread diffusion of monitoring systems is the key to improving safety and reliability of railway vehicles and to reducing maintenance costs by increasing the lifetime of structural and mechanical components. Several on-board devices have been conceived in recent years to detect faults on critical parts, by monitoring the real-time conditions of wheelsets, bearings, brakes, bogie, carbody, etc. These systems rely on powered sensor nodes, mounted on different parts of the vehicle, which acquire signals of interest and use proper algorithms to detect component faults or train derailments. Roller-rigs represent a good solution to develop and validate new monitoring devices with good repeatability of test conditions. The research group from Politecnico di Torino realized an innovative 1:5 scaled roller-rig, consisting of four wheelsets running on the same pair of rollers, originally used for investigations on wheel-rail adhesion. Then, minor changes were made to simulate and test a braking system monitoring device. Each wheelset is provided with a braking system, consisting of two brake discs and two brake callipers, while the rollers are powered using one AC brushless motor. A freight train pneumatic system is reproduced thanks to three electropneumatic regulators, which simulate the pressure in brake pipe, auxiliary reservoir and brake cylinder. The test bench and the motor drive are managed by an industrial PC using the software LabVIEW, allowing to perform braking operations of a real vehicle. Sensors are installed to measure wheelset speed, calliper temperature and pressures in the braking system. These signals are sent to an electronic control unit, which could be provided with a fault detection logic. The paper deals with the experimental setup of the bench and the preliminary results obtained by laboratory tests, which highlighted that the apparatus can be a reliable tool to develop new monitoring algorithms for train braking systems

Calibration and development of a multi-axis roller bench for monitoring the braking system of a railway vehicle

Summary-The installation of on-board monitoring systems is a fundamental aspect to increase the safety of railway vehicles and to obtain rational and efficient pro-gramming of maintenance interventions. Since the validation of new systems through test runs requires long times and high costs, a possible alternative is to resort to roller-rig systems in real or reduced scale during the early stages of development. The article describes the use of a 1:5 scale multi wheelset roller-rig to test brake system monitoring systems. In particular, the vehicle braking was replicated on the bench by means of a pneumatic system that repro-duces the real one, while the vehicle inertia was simulated by controlling the speed of the rollers in order to consider the real deceleration of the vehicle

Application of low-power energy harvesting solutions in the railway field: a review

In order to ensure safety and reliability of railway transportation the interest in monitoring systems is constantly increasing. These devices include sensors and electronic components, which need electric power supply for their proper working. However not all railway lines and vehicles are provided with electric power, furthermore, it can be complex to provide energy to sensors by cables in some location of the vehicle. The demand of a widespread distributed electrical energy can be fulfilled by energy harvesting techniques from primary sources. This paper analyses the different concepts of energy harvesters proposed in literature for the railway field, both for on board and wayside applications. The harvesters are classified according to the source from which energy is harvested and for each type of harvester advantages and disadvantages are critically discussed. The proposed review highlights the most promising solutions regarding energy harvesting in order to support future researches concerning this topic