F. J. Fuenmayor

PACDIN statement of methods

PAntograph–Catenary Dynamic Interaction (PACDIN) is a code developed by the vehicle technology research centre (CITV) of the Universitat Politècnica de València in collaboration with the railway company Talgo S.L. The model of the catenary is a finite element model using absolute nodal coordinates. It is based on a general formulation that can be applied for analysing a wide range of catenary configurations, including stitch wire, transitions or non-straight path tracks. The formulation is fully non-linear and includes large deformations, dropper slackening and contact interaction. The model is linearised when deformations are small, as in the case of the benchmark dynamic analysis. The results of the PACDIN code show a good agreement with the average results of other benchmark codes.

Influence of the wheel-rail contact instationary process on contact parameters

The rapid convergence of the tangential rolling contact parameters to their stationary values, combined with the high computational cost associated with calculations using instationary models, has meant that stationary models are usually employed in railway dynamics. However, the validity of stationary models when the applied contact conditions are subjected to rapid changes has not been sufficiently investigated. With the objective of deducing the effects of the evolution of the instationary process on the contact parameters, the tangential contact problem is solved for a set of reference conditions. For this purpose a calculation model is adapted, from which it is possible to analyse the evolution of the contact parameters when the forces exerted between rail and wheel are subjected to rapid changes. From the calculations made, situations impossible to simulate by means of stationary theories are obtained according to the frequency of variation in the forces, such as slip zones in the leading edge of the contact area and reverse contact (locally, the traction field is opposite to the direction of the external force transmitted to the contact).

An approach to geometric optimisation of railway catenaries

ABSTRACT The quality of current collection becomes a limiting factor when the aim is to increase the speed of the present railway systems. In this work an attempt is made to improve current collection quality optimising catenary geometry by means of a genetic algorithm (GA). As contact wire height and dropper spacing are thought to be highly influential parameters, they are chosen as the optimisation variables. The results obtained show that a GA can be used to optimise catenary geometry to improve current collection quality measured in terms of the standard deviation of the contact force. Furthermore, it is highlighted that apart from the usual pre-sag, other geometric parameters should also be taken into account when designing railway catenaries.

Stochastic Monte Carlo simulations of the pantograph–catenary dynamic interaction to allow for uncertainties introduced during catenary installation

ABSTRACT The simulation of the pantograph–catenary dynamic interaction is at present mainly based on deterministic approaches. However, any errors made during the catenary stringing process are sources of variability that can affect the dynamic performance of the system. In this paper, we analyse the influence of dropper length, dropper spacing and support height errors on the current collection quality by applying a classic Monte Carlo method to obtain the probability density functions of several output quantities. The effects of installation errors are also studied for a range of train speeds. Finally, the pre-sag that, on average, produces the best behaviour of the system is identified, allowing for the uncertainty in the catenary installation. The results obtained show the convenience to consider variability in pantograph–catenary dynamic simulations.

Crack growth in fretting-fatigue problems using the extended finite element method

The aim of this work is to apply the extended finite element method (X-FEM) to the analysis of crack orientation and propagation in a 2D fretting-fatigue problem. The X-FEM approach features some important advantages in the computational modelling of crack growth problems. The main advantage is that the mesh generation does not need to conform to the geometric discontinuity caused by the crack presence. The discontinuous behavior is introduced via special functions that enrich the classical finite element formulation. In this way, the initial mesh can be used for any further variation in crack length and orientation.

The Use of Bayesian Optimisation Techniques for the Pantograph-Catenary Dynamic Interaction Stochastic Problem

The simulation of the pantograph-catenary dynamic interaction has become an essential tool for the design of the overhead contact line. With the help of an efficient simulation strategy, the geometry of the catenary can be optimised in terms of the current collection quality. This work is a first attempt to obtain robust optimised catenaries in which the uncertainty caused by the installation errors is taken into account in the simulations. The optimisation problem is solved by means of a Bayesian Optimisation algorithm and the stochastic objective function is evaluated via Monte Carlo simulations. The results show, on the one hand, the good performance of the Bayesian Optimisation technique when compared with a Genetic Algorithm, and on the other hand, the coincidence between the deterministic and the robust optimal catenaries.

On the effect of the contact surface definition in the Cartesian grid finite element method

The definition of the surface plays an important role in the solution of contact problems, as the evaluation of the contact force is based on the measure of the gap between the solids. In this work three different methods to define the surface are proposed for the solution of contact problems within the framework of the 3D Cartesian grid finite element method. A stabilized formulation is used to solve the contact problem and details of the kinematic description for each surface definition are provided. The three methods are compared solving some numerical tests involving frictionless contact with finite and small deformations.

Estimación del Error en Elementos Hexaédricos

This paper uses the discretization estimator error Z 2 , proposed Zienckiewz and Zhu, for implementing the refinement by subdivision in hexahedrons elements. Obtaining improved tension field is based on techniques of smoothing tensions by zones, developing three procedures for evaluating the error. The procedures developed in this work were applied to two problems with known solution, in order to evaluate and define the characteristics of each proposed technique. In was observed that in the problem with smooth solution the technique that considers the presence of fictitious nodes and reduced integration could be used. However, in the problem with singularities it is better to consider the nodes with full integration for error estimation.

Sound attenuation of a circular multi-chamber hybrid muffler

The sound attenuation of perforated dissipative circular mufflers including a folded resonator and a short expansion chamber is investigated in detail by means of a two-dimensional axisymmetrical analytical approach based on the mode matching technique. The acoustical properties of the bulk reacting porous material and the perforated screen are taken into account to obtain the governing eigenequation for the wave propagation through the absorbent material and central perforated passage. Once the solution of the transverse eigenproblem is computed in all regions, the muffler transmission loss is determined by matching the acoustic pressure and axial velocity across each geometrical discontinuity. In addition, finite element results and experimental measurements are utilized for validation. The acoustic attenuation performance is examined considering the effect of the internal geometry of the muffler, the properties of the sound absorbent material and the porosity of the perforated pipe. Comparison is also provided with hybrid mufflers of earlier studies. It is shown that the acoustic contribution of the folded resonator is reinforced by the presence of the short expansion chamber, providing a good noise attenuation performance in the low and mid frequency range, whereas the dissipative effects associated with the central chamber suppress the high frequency noise, thus leading to a broadband attenuation of sound energy.