1,720,999 research outputs found
A Novel Analytical Method to Calculate Wheel-Rail Tangential Forces and Validation on a Scaled Roller-Rig
Full text linkThe study of railway dynamic strongly depends on the estimation of the tangential forces acting between wheel and rail. Simulation of the dynamical behaviour of railway vehicles is often performed using multibody codes, and the calculation of the contact forces must be efficient and accurate, even if the contact problem is strongly nonlinear. Therefore, the contact problem is still of great interest for researchers. This work proposes an analytical and efficient algorithm to calculate wheel-rail tangential forces. The proposed method is compared with the most commonly used algorithms under different conditions. In addition, experimental tests are performed on a scaled prototype on roller-rig to demonstrate that the method can be easily adjusted using experimental results. The benefit of the proposed method is to provide an analytical and fast solution, able to obtain accurate results and to allow corrections based on empirical evidence
Numerical stability of co-simulation approaches to evaluate wheel profile evolution due to wear
No full textWear simulation for railway wheel profiles is a complex problem which requires dynamics simulation of the vehicle on a long track and detailed analyses of the contact forces, which have to adopt non-linear methods to simulate the material behaviour. Since the dynamics of the vehicle and the behaviour of the material evolve differently, it is possible to use different codes to solve the problems. Furthermore, when thousands of kilometres are needed to produce wear, the profile wear is usually virtually amplified using wear multipliers to reduce computing time. This process can produce numerical instability if the multipliers and profile update intervals are not chosen appropriately. In this paper, the Simpack multibody code is used to simulate vehicle dynamics and to calculate the wear removed on a reference track, then the MATLAB code is used to smooth the profile and define the update intervals
Long train dynamic simulation by means of a new in-house code
No full textThe 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
Calibration and development of a multi-axis roller bench for monitoring the braking system of a railway vehicle
No full textSummary-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
Different dynamic track excitations on freight vehicles running on high speed and traditional lines detected with onboard diagnostic systems
No full textThe paper shows the use of a prototype of an onboard monitoring system to compare the dynamic behaviour of freight vehicles on old and new high speed lines, those tests have been performed on traditional freight vehicles during the preliminary tests carried on in the new high speed line running on the Gotthard base tunnel recently built in Switzerland
Study on the influence of the modelling strategy in the calculation of the worn profile of railway wheels
Full text linkAs 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
Application of low-power energy harvesting solutions in the railway field: a review
No full textIn 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
Design and testing of an innovative monitoring system for railway vehicles
No full textIn recent years there has been increased interest in developing a safer and more efficient railway system, as the railway has demonstrated the potential to become the most sustainable mode of transport. In Europe, significant investments have been made in order to increase the speed of both passenger and freight vehicles, but a good efficiency of railway transport can be achieved only if it is possible to ensure a high level of safety and reliability. These requirements can be achieved by adopting onboard diagnostic systems in order to increase the vehicle safety and to improve the strategies for a scheduled and corrective maintenance. This study shows the design and testing of an onboard monitoring system, which can be installed on different types of railway vehicles. The system is able to detect anomalies of the running behavior of vehicles and faults at the component level
Design of a test rig for railway Axle-boxes
No full textRailway 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
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