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

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

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

Characterization of the Channel Constriction Allowing the Access of the Substrate to the Active Site of Yeast Oxidosqualene Cyclase

In oxidosqualene cyclases (OSCs), an enzyme which has been extensively studied as a target for hypocholesterolemic or antifungal drugs, a lipophilic channel connects the surface of the protein with the active site cavity. Active site and channel are separated by a narrow constriction operating as a mobile gate for the substrate passage. In Saccharomyces cerevisiae OSC, two aminoacidic residues of the channel/constriction apparatus, Ala525 and Glu526, were previously showed as critical for maintaining the enzyme functionality. In this work sixteen novel mutants, each bearing a substitution at or around the channel constrictions, were tested for their enzymatic activity. Modelling studies showed that the most functionality-lowering substitutions deeply alter the H-bond network involving the channel/constriction apparatus. A rotation of Tyr239 is proposed as part of the mechanism permitting the access of the substrate to the active site. The inhibition of OSC by squalene was used as a tool for understanding whether the residues under study are involved in a pre-catalytic selection and docking of the substrate oxidosqualene

The use of carboxymethylcellulose for the tartaric stabilization of white wines, in comparison with other oenological additives

The aim of this study was to test the effectiveness of two types of carboxymethylcellulose (CMC), at different doses, for the prevention of tartaric precipitations in two white wines (Pinot Blanc and Chardonnay), in comparison with metatartaric acid and a commercial arabic gum. After the addition of the additives to the wines, the mini-contact test was carried out and the saturation temperature was determined by Ridomi’s method. The determination of the saturation temperature was then repeated on the same trials kept at -4 °C for 10 days. Both kinds of CMC caused a significant decrease in tartaric precipitations induced by the addition of potassium bitartrate (KHT) (mini-contact test), by limiting the growth of the added KHT crystals. Their effectiveness increased with the dose, following a hyperbolic trend. The stabilizing effect of the two kinds of CMC, particularly CMC2 (more viscous), was similar to the one of metatartaric acid. Their use must be considered complementary to the cold treatment (chillproofing).

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

Use of polyaspartates for the tartaric stabilisation of white and red wines and side effects on wine characteristics

Aim: The stabilising efficacy against tartaric precipitations of polyaspartates-based products (PAs), in particular potassium polyaspartate (KPA), was tested with six different wines (three white and three red). Some side effects on wine characteristics (white wine colour stability, wine turbidity and filterability) were also studied. Results and conclusions: All PAs showed good stabilising efficacy against tartaric precipitations according to the cold test. With the same test, the PAs were stable in wine for 1 year of storage, which was the total duration of the study. The dose of 100 mg/L was sufficient to stabilise the tested wines. No differences in filterability were observed in comparison with MTA (metatartaric acid). The hypothesised protective effect against colour browning in white wines was not observed. Significance and impact of the study: The international wine trade requires stable wines. This paper provides information to support wineries in managing the use of KPA, as little information is available to date in the literature on this stabilising additive