Carlos Casanueva

A Lateral Active Suspension for Conventional Railway Bogies

The present paper describes an active centring system for railway vehicles. The proposed solution is based on lateral pneumatic actuators placed between bogie and car body connected to the vertical secondary suspension air springs. The objective of the developed centring system is twofold: the improvement of the curving behaviour of the train and the decrease of the lateral acceleration perceived by the passenger in curve negotiation thanks to the reduction of the ‘souplesse’ coefficient. The system is described in detail in the paper. Results from simulations are included considering a bidimensional model of the vehicle, and a detailed model of the air spring and control valves. The performance in curve negotiation of a vehicle equipped with this system and a conventional one is compared. Specifically, lateral displacements of the secondary suspension, roll angle and lateral accelerations are analysed. The results show noticeable performance improvements in the vehicle curving behaviour. The proposed centring system can be implemented in a conventional bogie without special design requirements; and due to the low air consumption, additional pressurised reservoirs are not required.

Influence of switches and crossings on wheel profile evolution in freight vehicles

Wheel reprofiling costs for freight vehicles are a major issue in Sweden, reducing the profitability of freight traffic operations and therefore hindering the modal shift needed for achieving reduced emissions. In order to understand the damage modes in freight vehicles, uniform wear prediction with Archards wear law has been studied in a two-axle timber transport wagon, and simulation results have been compared to measurements. Challenges of wheel wear prediction in freight wagons are discussed, including the influence of block brakes and switches and crossings. The latter have a major influence on the profile evolution of this case study, so specific simulations are performed and a thorough discussion is carried out.

On integrated wheel and track damage prediction using vehicle-track dynamic simulations

The renewal costs for wheels and rails are a substantial part of the costs for rolling stock operators and infrastructure managers all over the world. The causes for reprofiling or grinding are, in most cases, related to the following: (1) wheel or rail profiles with unacceptable wear, (2) appearance of rolling contact fatigue cracks in the surface, and (3) wheel flats caused by locking wheels during braking. The first two causes are related to the dynamic behavior of the vehicle–track system, and can be predicted using multibody simulations. However, there are several limitations that restrain the usefulness of these prediction techniques, such as simulation time constraints, necessary simplifications, and lack of experimental data that lead to educated assumptions. In this paper, we take the end-user perspective in order to show whether the latest developments in wheel–rail damage prediction can be integrated in a simplified framework, and subsequently used by the different stakeholders for an improved management of the different assets involved in the operation of rail vehicles.

Simple flexible wheelset model for low-frequency instability simulations

As a general rule, the multi-body simulation models used by railway vehicle designers consider the wheelsets to be fully rigid, thus leading to possible errors when calculating the critical speed of the vehicle under study. This article suggests a wheelset model that takes into account wheelset flexibility for the study of dynamic stability. The model is simple to implement, easily parameterised, and can be applied to both conventional and variable gauge wheelsets. The parameters corresponding to wheelset flexibility that most influence the critical speed of high-speed and variable gauge vehicles are also analysed.

Use of Archard’s Wear Law for the Calculation of Uniform Wheel Wear of High Tonnage Freight Vehicles

Wheel profile evolution has a large influence on track and wheelset related maintenance costs. It influences important parameters such as equivalent conicity or contact point positioning, which will affect the dynamic behavior of the vehicle, in both tangent track and curve negotiation. High axle loads in freight wagons may increase both the wheel wear and the damage caused by vehicles with both new and already worn profiles. A common profile in Europe is the S1002 profile, developed for rail inclination 1/40. In Sweden rail inclination is 1/30, so contact conditions might not be optimal. The presented work uses Archard’s wear law to analyze the profile wear evolution in a two axle freight vehicle with Unitruck running gear on the Swedish network. This wear calculation methodology has been successfully used to predict uniform wear in passenger vehicles. First, the vehicle model has been optimized in order to improve the speed of the wear simulations. Experimental measurements of wheel profiles have been performed in order to validate the simulations. The conclusion is that the wear methodology successfully used to predict uniform wheel wear in passenger vehicles cannot be directly applied for the calculation of wheel profile evolution in high tonnage freight vehicles. The influence of block brakes or switches and crossings cannot be dismissed when calculating uniform wheel wear in these cases.Copyright

Wheel life prediction model – an alternative to the FASTSIM algorithm for RCF

ABSTRACT In this article, a wheel life prediction model considering wear and rolling contact fatigue (RCF) is developed and applied to a heavy-haul locomotive. For wear calculations, a methodology based on Archards wear calculation theory is used. The simulated wear depth is compared with profile measurements within 100,000 km. For RCF, a shakedown-based theory is applied locally, using the FaStrip algorithm to estimate the tangential stresses instead of FASTSIM. The differences between the two algorithms on damage prediction models are studied. The running distance between the two reprofiling due to RCF is estimated based on a Wöhler-like relationship developed from laboratory test results from the literature and the Palmgren-Miner rule. The simulated crack locations and their angles are compared with a five-year field study. Calculations to study the effects of electro-dynamic braking, track gauge, harder wheel material and the increase of axle load on the wheel life are also carried out.

New methodology for fast prediction of wheel wear evolution

ABSTRACT In railway applications wear prediction in the wheel–rail interface is a fundamental matter in order to study problems such as wheel lifespan and the evolution of vehicle dynamic characteristic with time. However, one of the principal drawbacks of the existing methodologies for calculating the wear evolution is the computational cost. This paper proposes a new wear prediction methodology with a reduced computational cost. This methodology is based on two main steps: the first one is the substitution of the calculations over the whole network by the calculation of the contact conditions in certain characteristic point from whose result the wheel wear evolution can be inferred. The second one is the substitution of the dynamic calculation (time integration calculations) by the quasi-static calculation (the solution of the quasi-static situation of a vehicle at a certain point which is the same that neglecting the acceleration terms in the dynamic equations). These simplifications allow a significant reduction of computational cost to be obtained while maintaining an acceptable level of accuracy (error order of 5–10%). Several case studies are analysed along the paper with the objective of assessing the proposed methodology. The results obtained in the case studies allow concluding that the proposed methodology is valid for an arbitrary vehicle running through an arbitrary track layout.

Influence of Bearing Flexibility in Rail Vehicle Dynamics

Dynamic multibody models for railway vehicles usually assume that the stiffness of the bearings is much higher than that of the primary suspension, neglecting their effect whatsoever. This assumption might not be entirely valid for high speed vehicles, where the primary suspension is stiffer than other rail vehicles; or for more complex systems such as variable gauge wheelsets, where the whole mechanic system might have a higher than expected flexibility. In this paper, a model to obtain the stiffness of a typical configuration of railway bearings is developed and applied to both a high speed vehicle bearing set and a variable gauge wheelset bearing set. The results show that the reduction of lateral stiffness as a result of bearing flexibility can reach up to 35% of its theoretical value. This massive reduction has a major influence on the prediction of the dynamic behaviour of these vehicles, e.g. critical speed or curving performance.

The Influence of Bearing Flexibility on High Speed Vehicles

Railway multibody models usually ignore the flexibility of the rolling bearings, assuming that it is much smaller than the flexibility of the primary suspension elements. However, this assumption is not necessarily valid for high speed vehicles, which have a much stiffer primary suspension. In this paper a model to obtain the stiffness parameters of a typical configuration of railway bearings is developed and applied to a high speed vehicle bearing system. In this paper a bearing model has been developed, which takes into account the real geometry of the bearings and races for a more precise calculation of the forces transmitted through the different contact patches. It has been demonstrated that the interaction of rollers and races can never be considered as Hertzian contact, as the shape of the contact area goes from ellipsoidal to trapezoidal as the load increases, including a mixed contact shape when only one of the roller end is in contact with the race. Hertzian contact implies a unique type of contact through all the loading cases, with a loss of precision in the areas where it does not behave in this way. The methodology has been applied to a bearing set used in high speed vehicles, with the following results: The stiffness matrix of the bearing set has been obtained. Individual stiffness values are highly dependent on the mounting clearance. A priori, this dependence cannot be neglected for high speed dynamic analyses. The inclusion of bearing stiffness in a high speed vehicle can affect the theoretical values of the primary suspension, i.e. reduce longitudinal stiffness up to 10% or lateral stiffness up to 32%. This effect will decrease the dynamic stability of the vehicle. It can also affect the transmission of the lateral force, displacing the lateral force position closer to the wheelset axis. This effect, which is positive for the dynamic behaviour of the vehicle, is negligible for the stiffness values of the primary suspension and the bearing set of the studied vehicle. Moreover, a polyvalent and adaptable bearing model has been developed that allows the calculation of various characteristics and variables. This model can be further used for other studies that need individual roller characteristics, such as contact geometry or maximum pressures in the races.