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- Implementation of a non-Hertzian contact model for railway dynamic applicationPublication . Magalhães, Hugo; Marques, Filipe; Liu, Binbin; Antunes, Pedro; Pombo, João; Flores, Paulo; Ambrosio, Jorge; Piotrowski, Jerzy; Bruni, StefanoThe development of wheel–rail contact models is an active topic of railway research with the dual objective of improving the accuracy of multibody simulations and reducing its computational effort. This paper extends the online Hertzian contact model, proposed by Pombo et al. (Veh. Syst. Dyn. 45: 165–189, 2007) to propose a non-Hertzian contact model. The new methodology presented here includes the following steps: (i) search of the points of contact; (ii) identification of the undeformed distance function; (iii) evaluation of the contact patch; (iv) calculation of the normal and tangential contact forces; (v) application of the contact forces in the multibody vehicle model. Among several contact models available in the literature, this non-Hertzian contact approach uses the Kik–Piotrowski model for the normal contact force, while the tangential forces are obtained from the interpolation of the available Kalker Book of Tables for non-Hertzian (KBTNH) contact. With the purpose to demonstrate the proper implementation and selection of parameters that define this new model, several contact analysis and dynamic simulations are performed in which the wheel S1002 and the rail UIC50 are considered. First, the contact analyses that determine the contact condition of different wheel–rail interactions serve to assess the accuracy of the Hertzian and non-Hertzian models with respect to the software of reference CONTACT. Second, the Hertzian and non-Hertzian models are utilised to perform dynamic simulations of a wheelset, a bogie and a vehicle running in tangent and curved tracks. In short, this work provides, not only a complete description of the implementation of a non-Hertzian contact model in a multibody code, but also suggests for the proper selection of the parameters that promote better accuracy and optimal computational efficiency.
- A co-simulation approach to the wheel–rail contact with flexible railway trackPublication . Antunes, Pedro; Magalhães, Hugo; Ambrosio, Jorge; Pombo, João; Neves Costa, JoãoThe standard approach to railway vehicle dynamic analysis includes running the vehicle multibody models in rigid railway tracks. The wheel–rail contact, independently of the rolling contact model used, is either handled online or via lookup tables. This traditional approach disregards the coupling effects between the railway vehicle dynamics and the railway track flexibility. In this work the assumption of rigidity of the railway track is relaxed and a finite element model of the complete track, i.e. rails, pads, sleepers, ballast and infrastructure, is used to represent the track geometry and flexibility. A rail–wheel contact model that evaluates the contact conditions and forces is used online. The dynamics of the railway vehicle is described using a multibody methodology while the track structure is described using a finite element approach. Due to the fact that not only the multibody and the finite element dynamic analysis use different integration algorithms but also because the vehicle and track models are simulated in different, codes a co-simulation procedure is proposed and demonstrated to address the coupled dynamics of the system. This approach allows us to analyze the vehicle dynamics in a flexible track with a general geometry modeled with finite elements, i.e. including curvature, cant, vertical slopes and irregularities, which is another novel contribution. The methodology proposed in this work is demonstrated in an application, in which the railway vehicle–track interaction shows the influence of the vehicle dynamics on the track dynamics and vice versa.
- A new methodology to study the pantograph-catenary dynamics in curved railway tracksPublication . Antunes, Pedro; Ambrosio, Jorge; Pombo, João; Facchinetti, AlanThe pantograph-catenary system is responsible to provide an uninterrupted energy supply to power electric traction railway vehicles. The analysis of the dynamic behaviour of the catenary and pantograph, as well as its interaction, has been the objective of active research to improve energy collection quality. This work proposes an approach for the fully three-dimensional dynamic analysis of pantograph-catenary interaction in general railway tracks including curves. The catenary model and the trajectory of the pantograph base are defined with respect to the track geometry considering the conventional definition used by the rail industry, i.e. the track curvature, cross-level and vertical position. The pantograph is modelled using a multibody formulation being its base motion constrained to follow the generalised trajectory from the railway vehicle roof. The finite element method is used to model the catenary. A co-simulation procedure is set to establish the coupled dynamics of the two systems. In order to demonstrate the methodology, setup models for curved catenaries, analyse modelling implications and highlight applicability, realistic case studies of pantograph-catenary interaction in high-speed rail operations are presented and discussed. In the process, significant differences are found in the dynamic response of the catenary in curved and straight tracks.
- Enhancing pantograph-catenary dynamic performance using an inertance-integrated damping systemPublication . Zhu, Ming; Zhang, Sara Ying; Jiang, Jason Zheng; Macdonald, John; Neild, Simon; Antunes, Pedro; Pombo, João; Cullingford, Stephen; Askill, Matthew; Fielder, StephenFor modern electrical rail systems, the pantograph-catenary dynamic performance is one of the most critical challenges. Too much fluctuation in contact forces leads to either accelerated wear of the contacting components or losses of contact and, consequently, arcing. In this work, inertance-integrated pantograph damping systems are investigated with the objective of reducing the contact force standard deviation. Firstly, a multibody pantograph model is developed with its accuracy compared with experimental data. The model is improved through the calibration of the pantograph head suspension parameters and the introduction of both non-ideal joint and flexibility effects. Using the calibrated model, beneficial inertance-integrated damping systems are identified for the pantograph suspension. The results show that the configuration with one inerter provides the best performance among other candidate layouts and contends a 40% reduction of the maximum standard deviation of the contact force over the whole operating speed range in the numerical modelling scenario analysed. Considering the identified configuration, time-domain analysis and modal analysis are investigated. It has been shown that the achieved improvement is due to the fact that with the beneficial inertance-integrated damping system, the first resonance frequency of the pantograph system coincides with the natural frequency of the catenary system.
- A methodology to study high-speed pantograph-catenary interaction with realistic contact wire irregularitiesPublication . Song, Yang; Antunes, Pedro; Pombo, João; Liu, ZhigangIn high-speed rail operations, the irregularity of the overhead system is a typical disturbance that affects the pantograph-catenary interaction performance. The existing methods, which treat the contact wire irregularities as hard spots, overestimate the negative effect of the irregularities on the contact force, leading to conservative results. In this work, a more accurate methodology aiming to include the effect of contact wire irregularities in the assessment of the pantograph-catenary dynamic performance is proposed. Measured contact wire irregularity data, collected from the Chinese high-speed network, is added to the initial configuration of the catenary model, through a developed Target Configuration Under Dead-loads (TCUD) method. This approach is used here to investigate the effect of the contact wire irregularities on the contact forces. The results indicate that the catenary imperfections have a direct impact on the pantograph-catenary interaction, leading to an increment of the contact forces amplitude, an increase of their standard deviation and an expansion of the contact forces range. A frequency analysis of the results shows that the contact wire irregularity increases the Power Spectral Density (PSD) peaks of the contact force at specific frequencies relevant to the span length and to the dropper spacing.
- A dedicated control design methodology for improved tilting train performancePublication . Magalhães, Hugo; Antunes, Pedro; Pombo, João; Ambrosio, JorgeThe development of detailed multibody models of railway vehicles is essential to address industrial problems through computational tools. The assessment of vehicle dynamic performance is one of the studies that can be performed with a multibody software. But when tilting trains are considered, which comprise active suspension elements, control engineering theories are required to estimate the forces developed by the actuators. Despite its importance, in general the details about the tilting control algorithm are unknown. In this work, a dedicated control design methodology is proposed to estimate the control algorithm of a tilting system in order to assure a proper vehicle performance. For this purpose, a detailed multibody model of a tilting train is used to perform a batch of simulations in order to develop an accurate linear model of the tilting system and to study its performance in realistic operation conditions. Thus, the traditional control techniques can be used to assess the tilting system dynamics and to design the control algorithm so that proper tilting performance is ensured. The control algorithm and the tilting performance are tested on a curved and tangent track with track irregularities. The comfort indexes PCT and RMS are used here to assess the tilting system.
- A novel methodology to automatically include general track flexibility in railway vehicle dynamic analysesPublication . Neves Costa, João; Antunes, Pedro; Magalhães, Hugo; Pombo, João; Ambrosio, JorgeThe interaction between the rolling stock and the infrastructure plays a crucial role in railway vehicle dynamics. The standard approach consists of using a multibody formulation to model the railway vehicles running on simplified tracks. The track model can be rigid, if it comprises only a geometric description of the rail; semi-rigid, if it considers an elastic foundation underneath the rail; or a moving track model, if it comprises a track section underneath each wheelset traveling with the same speed of the vehicle. Despite their computational inexpensiveness, these approaches do not provide a complete representation of track flexibility and disregard coupling effects with the vehicle and among the track components. This work proposes a methodology to automatically generate finite element models of railway tracks comprising its relevant flexible components, i.e., rails, pads, fastening systems, sleepers, and ballast or slab. The finite element mesh is generated based on a parametric description of the track that allows an accurate description of its geometry, including curvature, cross-level, grade, and irregularities. The methodology is demonstrated with a case study in which a track with a complex geometry is loaded with two different approaches. The first approach prescribes moving loads, which is a typical approach used to design or analyze the infrastructure. The second approach applies loads retrieved from the dynamic analysis of a complete vehicle. The results show the benefits of this method and reveal that prescribed loading underestimates the forces resulting from the vehicle dynamics, which is an important issue on curved sections.
- A finite element methodology to model flexible tracks with arbitrary geometry for railway dynamics applicationsPublication . Costa, J. N.; Antunes, Pedro; Magalhães, Hugo; Pombo, João; Ambrósio, J.The dynamic analysis of railway vehicles requires an accurate representation of the vehicle, the track geometry and structure, and their interaction. Generally, flexible track models with curved geometries represent the rails with straight beam elements, which results in a piecewise linear representation of the rails. Consequently, the wheel-rail contact mechanics are not properly captured, and the wheel-rail contact forces present spurious high-frequency oscillations. This work proposes a novel approach to model flexible railway tracks with arbitrary geometries, in which the correct geometry in the wheel-rail contact mechanics is assured by modeling the rails as Timoshenko curved beam elements. This approach improves both the geometric representation of the rails and the accuracy of the wheel-rail contact forces calculation. A realistic operation scenario in which a multibody model of a railway vehicle runs on a flexible track with a curved geometry is used here to demonstrate the novel aspects of this work and then discuss the improvements over the conventional approaches. The results show that the proposed methodology greatly improves the computation of the wheel-rail interaction forces and prevents spurious oscillations from propagating to the vehicle.