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

Design of a test rig for railway Axle-boxes

Abstract Railway axle-boxes are one of the more critical components of the railway vehicle. The axle-box is the housing of the bearings, which support the axle-load of the vehicle, and the confinement of the lubricant required to maintain the performances of the bearings. Therefore, the axle-box is involved both in problems related to vehicle safety, and in problems related to maintenance, becoming an important part of the life cycle cost of the vehicle. To improve safety and reliability of the axle-box, in recent years, diagnostic systems are adopted to detect malfunctions, damage or degradation of the performances of the bearings. This is made both using onboard or wayside monitoring systems, which can be based on vibration or thermal analysis. The effectiveness of these systems rely in the accuracy of the algorithms, that are used to predict the condition status of the bearings. Therefore, it is necessary to be able to validate and tune the algorithms, by means of experimental tests. The tests can be performed on the track, but this implies high variability, costs and the impossibility to experience critical conditions (due to the related risks). The aim of this work is to design an experimental test rig, able to perform tests on railway axle-boxes and to reproduce the real conditions (axle-load, velocity). Several design layout are considered, each one evidencing some benefits and some limitations. The use of the test rig allows to reproduce different failures of the bearings in a safe environment. The repeatability of the tests and the controlled environmental conditions, allow a better setup of the monitoring system being developed

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

a mixed numerical approach to evaluate the dynamic behavior of long trains

Abstract The evaluation of the longitudinal forces exchanged between the wagons composing a long train is very complex due to the large number of d.o.fs to be considered and due to the non linearities introduced by the coupling elements. The most common approach to simulate long trains is the use of simplified wagon models realized considering only the longitudinal d.o.f. In this way the number of d.o.fs used for the full vehicle model is equal or a little greater than the number of the connected cars. The efficiency of this approach, in calculating the in train forces during traction and braking operations, has been demonstrated by several authors in the literature. In particular the long train simulators have been developed with the aim to evaluate the longitudinal forces during the braking operations in order to optimize the braking strategy and the mass distribution along the train. This method is efficient to optimize the train configuration in order to minimize the in train forces, but it does not allow to evaluate the vehicle safety indexes (such as derailment, wheel unload and lateral force) because the wheel-rail contact forces are completely neglected. This work shows a novel approach where the long train numerical model, realized using the Simpack multibody code, is developed considering both simplified wagon models, with few d.o.fs and no contact module, and detailed wagon models, which include several d.o.fs and the algorithm for the contact forces evaluation. In particular this mixed technique allows to evaluate both the longitudinal train dynamic and the behavior of some of the wagons when the train is running on curve. The position of the detailed wagon models along the train combination can be selected by the user in order to evaluate the influence of a particular wagon position on the vehicle safety

EFFETTI DINAMICI DELL’INNALZAMENTO DEL CARICO PER ASSE DI ROTABILI FERROVIARI PER TRASPORTO MERCI

Lo sviluppo di un sistema di trasporto ferroviario merci richiede di minimizzare i tempi di percorrenza e massimizzare la capacità di carico dei convogli. Questo obiettivo può essere raggiunto mediante tre diverse strategie, che possono essere adottate separatamente o in modo congiunto. Le strategie consistono sostanzialmente nell’aumento della capacità di carico del singolo carro, nell’aumento della lunghezza del convoglio e nell’aumento della velocità del veicolo. La possibilità di attuare simultaneamente le tre strategie è possibile solo disponendo di infrastrutture dedicate e utilizzando una progettazione specifica della linea e dei veicoli. Il lavoro illustra gli effetti di un innalzamento del carico per asse, oltre al limite attualmente consentito in Italia, sui principali indicatori utilizzati dalla norma UIC per l’omologazione del materiale rotabile. Le valutazioni sono state effettuate utilizzando un tracciato reale di buona qualità ed un modello numerico di un veicolo di tipo Y25

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

Frenet force analysis in performance evaluation of railroad vehicle systems

A data-driven science approach, based on integrating nonlinear multibody system (MBS) formulations and new geometric concepts, is used in this paper to compare the performance of two widely used railroad bogies: the three-piece bogie and the Y25 bogie. MBS algorithms are used to solve the bogie nonlinear differential/algebraic equations (DAEs) to determine the bogie motion trajectories. To have a better understanding of the bogie dynamic behavior, a distinction is made between the geometry of actual motion trajectories (AMT) and the track geometry. The AMT curves are described using the motion-dependent Frenet-Euler angles, referred to as Frenet bank, curvature, and vertical development angles, which differ from their counterparts used in the description of the track geometry. In particular, the Frenet bank angle defines the super-elevation of the AMT curve osculating plane, referred to as the motion plane, distinguishing this Frenet super-elevation from the fixed-in-time track super-elevation. The paper explains the difference between the lateral track plane force balance used in practice to determine the balance speed and the Frenet force balance which is based on recorded motion trajectories. Computer simulations of bogies travelling on a track, consisting of tangent, spiral, and curve sections are performed with particular attention given to the deviations of the AMT curves from the track centerline. The results obtained in this study demonstrate the dependence of the AMT curve geometry on the wheelset forward motion, highlighting the limitations of tests performed using roller test rigs which do not allow longitudinal wheelset motion

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

SISTEMI DI MONITORAGGIO PER L'INSTALLAZIONE A BORDO DI VEICOLI FERROVIARI

Il lavoro mostra l'attività svolta al Politecnico di Torino per sviluppare sistemi di monitoraggio da installare a bordo di veicoli ferroviari, in grado di misurare ed elaborare i segnali rilevati sulla boccola e sul carrello allo scopo di rilevare malfunzionamenti di diversi componenti critici. Scopo generale del sistema è quello di assicurare una comunicazione di allarme di primo livello in caso di guasto dei componenti, ma è anche in grado di fornire indicazioni relative alle condizioni dei componenti al fine di migliorare la programmazione della manutenzione preventiva. Diverse architetture sono state progettate considerando l'esigenza di ridurre il costo del sistema in modo da consentire la sua applicazione su una grande varietà di veicoli, compresi i veicoli merci. La novità di questo approccio è il fatto che il sistema di acquisizione e diagnostica è stato sviluppato specificamente per l'applicazione ferroviario a partire dal livello di architettura hardware