1,721,045 research outputs found
The influence of track modelling options on the simulation of rail vehicle dynamics
No full textThis paper investigates the effect of different models for track flexibility on the simulation of railway vehicle running dynamics on tangent and curved track. To this end, a multi-body model of the rail vehicle is defined including track flexibility effects on three levels of detail: a perfectly rigid pair of rails, a sectional track model and a three-dimensional finite element track model. The influence of the track model on the calculation of the nonlinear critical speed is pointed out and it is shown that neglecting the effect of track flexibility results in an overestimation of the critical speed by more than 10%. Vehicle response to stochastic excitation from track irregularity is also investigated, analysing the effect of track flexibility models on the vertical and lateral wheel-rail contact forces. Finally, the effect of the track model on the calculation of dynamic forces produced by wheel out-of-roundness is analysed, showing that peak dynamic loads are very sensitive to the track model used in the simulation
Analysis of the non linear dynamics of a 2–axle freight wagon in curves
No full textThe paper analyses the nonlinear dynamics in curves of 2–axle freight wagons. Both one isolated wagon or an assembly of three wagons are considered. The dependence on both curve radius and vehicle speed is pointed out and it is shown that, considering a single 2–axle freight car, the carbody experiences periodic oscillations with large amplitude (up to 12 mm) at relatively high speed values, which still lie in the operating speed range. The interaction between adjacent vehicles is also investigated, showing that the forces exchanged trough the coupling elements significantly affect the dynamics of the 2–axle freight wagons
Equivalent Models of an Infinite Track for Frequency and Time Domain Analyses
No full textPurpose: Railway track models for the study of train-track interaction are generally based on beam structures on viscoelastic foundations and infinite-length track models are typically used when the track is supposed to be unbounded. However, when non-linear dynamic features or discontinuities of track properties should be considered, it is necessary to perform time domain numerical integration using a finite-length one. This work proposes an approach to develop finite-length models so that the computed results of the frequency and time domain train-track interaction analyses have negligible differences compared to those computed by an infinite-length model, by assigning proper values to the crucial model parameters. Particular attention is paid to obtain equivalent rail responses to stationary and moving point loads. Methods: The track model consists of an Euler–Bernoulli beam supported by a viscoelastic foundation. The beam is formulated by both analytical and Finite Element models. The solution techniques adopted include the exact solution of differential equation, the numerical computation based on the Finite Element model, and the modal superposition approach. Proper values of the beam parameters are firstly determined through frequency domain analysis. Then the parameter values of the beam formulation techniques and solution techniques are determined with time domain analysis. Results and Conclusions: Frequency responses and responses to moving load excitations are computed. The developed finite-length models lead to negligible difference in terms of frequency responses and responses to low-frequency moving loads. For high-frequency moving loads the responses are highly similar. Consequently, the developed finite-length track models are regarded as equivalent to the infinite-length one for both frequency and time domain analyses
Influence of Wheel-Rail Contact Model on the Prediction of Preferential Wavelengths in Rail Corrugation
No full textRail corrugation is among the main issues related to urban railway lines and ap-pears as a quasi-periodic irregularity on the running surface on the rail. A vehicle running on corrugated rails may generate ground-borne vibrations that propagate to buildings in the proximity of the railway line with possible complaints from the inhabitants. For this reason, a mathematical model for the prediction of preferen-tial wavelengths of corrugation formation is a useful tool to support both the de-sign of railway lines and infrastructure managers when the system is in operation. It permits to identify the root causes of the phenomenon and the effectiveness of potential mitigation actions. To this aim, a wheel-rail interaction model is formu-lated in the frequency domain. It is used to study the phenomenon on a sharp curve of a subway network, where corrugation appears on the low rail. In this paper, the effect of the tangential wheel-rail contact model on the evaluation of corrugation wavelengths is investigated. As a general comment, the wheel-rail in-teraction model is able to correctly predict the corrugation formation on the low rail and its wavelength, regardless of the considered force-creepage theory
Analysis of the nonlinear dynamics of a 2-axle freight wagon in curves
Full text linkThis paper deals with the study of the nonlinear dynamic behaviour of 2-axle freight wagons in curves, considering the case of one single wagon (neglecting inter-car coupling forces) and of multiple wagons interacting through the buffers and the couplers. A multi-body model of a single wagon and of a three-car assembly is introduced, paying particular attention to the nonlinear and nonsmooth modelling of the suspensions and of the inter-car coupling elements. Using this model, a numerical analysis of the steady-state solution reached after the negotiation of curve transition is presented and bifurcations are identified for some particular values of the curve radius. For the single car case, it is shown that depending on the curve radius and the vehicle speed the carbody may experience severe periodic oscillations at speeds lying in the operating range of the vehicle. For the car-assembly case, it is shown that the coupling forces exchanged by the wagons significantly affect their dynamics in a curve, reducing the amplitude of vibration
Freight trains dynamics: effect of payload and braking power distribution on coupling forces
No full textCoupling forces, especially buffer forces, play a significant role in affecting running safety of freight trains. The increase in coupling force is due to relative motion between adjacent wagons that depends both on track geometry and on manoeuvre performed. Emergency braking in particular, can strongly excite the longitudinal dynamics of a trainset, usually causing significant solicitations on coupling elements. Additionally, braking while cornering may enhance the effect of the coupling forces on the lateral dynamics of the wagon, decreasing running safety margins. A factor that affects the maximum solicitations on coupling devices during emergency braking is payload distribution compared to brake power distribution along the trainset. This issue is particularly significant in Italian railways where empty wagons may be placed along the trainset between fully laden ones without any particular restriction. This paper presents the results of a research aiming at defining imbalance indexes which can be related to the maximum forces exchanged among wagons through the coupling devices. Indexes can be used as guidelines for identifying critical payload distributions and improve wagons arrangement
Integration of the measure of the primary suspension deflection into a dynamometric wheelset equipped with strain gauge bridges
No full textA fast method for determination of creep forces in non-Hertzian contact of wheel and rail based on a book of tables
Full text linkThe Kalker book of tables for non-Hertzian contact described in a previous work from the authors provides creep forces, but the moment generated in the contact patch is not available. The extended Kalker book of tables for non-Hertzian contact (KBTNH) presented in this paper provides creep forces, as well as the moment. The paper presents the simplified linear theory of rolling contact for a simple double-elliptical contact (SDEC) region used for regularisation of contact patches and, resulting from this theory, the full symmetry relations for creep forces and moment. The parameterisation of variables and structure of the extended book of tables are described. The extended Kalker book of tables of moderate volume has been computed in co-simulation Matlab-CONTACT. The creep forces and moment obtained from KBTNH have been compared to those obtained directly by CONTACT program and FASTSIM algorithm. The comparison shows that KBTNH is in good agreement with CONTACT for a wide range of creepage conditions and shapes of the contact patch, whereas the use of FASTSIM may lead to significant deviations from the reference CONTACT solutions. The presented example of application is a realistic case of a freight wagon curving simulation, where KBTNH has been used to assess the contribution of the moment into the unit frictional work dissipated in contacts of wheels and rails. The high calculation speed and good accuracy of determining creep forces for non-Hertzian wheel–rail contact make the proposed method a suitable tool for multibody system (MBS) simulation programs oriented for rail vehicle dynamics
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