E. Nadal

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.

Mitigation of Railway Wheel Rolling Noise by Using Advanced Optimization Techniques

Rolling noise emitted by railway wheels is a problem that affects human health and limits the expansion of the railway network. This problem is caused by the wheel-rail contact, and it is predominant over the rest of noise sources from the vehicle/track system for the usual speed conditions in urban areas. The minimization of rolling noise through changes on the wheel shape by means of the finite element method is discussed in this work, which focuses on potential shape modifications in existing wheels in the form of an optimal wheel web perforation distribution. Such a modification is a cost-effective solution that can be performed in a relatively short term in already manufactured and operating railway wheels. To this end, two objective functions with different computational costs are studied and analysed with several configurations of a genetic algorithm-based optimizer. Both approaches focus on minimizing rolling noise. Approach 1 is based on the minimization of the area below the sound power vs. frequency curve of the wheel, and thus requires solving the system dynamics. On the other hand, Approach 2 is based on the maximization of the natural frequencies of the wheel in order to shift its resonances out of the excitation range, and therefore it only requires a modal analysis. The acoustic radiation analysis is performed through the computation of the normal surface velocities, using a time-domain approach and including a contact filter applied in the track roughness, considered as excitation. Moreover, the structural requirements for fatigue strength in wheels proposed by the optimizer are ensured according to actual standards. Results using Approach 1 reflect that an optimized distribution of perforations on the web of a railway wheel, can reduce significantly the sound power level in the entire studied frequency domain (0–5 kHz). This is related to the high sensitivity of the acoustic radiation response with the perforation pattern. Such a phenomenon appears to have a higher impact on noise minimization than that associated with the reduction of the radiating surface due to perforations. The high reduction of the radiated sound power is primarily due to the fact that certain wheel vibration modes with high acoustic contribution are shifted out of the excitation range corresponding to the contact force, this effect being observed in the best solution of Approach 1. Less significant sound power reduction is obtained with Approach 2, although its associated computational cost is considerably lower.

3D Topology Optimization with h-adaptive Refinement Using Cartesian Grids Finite Element Method (cgFEM)

Regarding shape optimization of structural components, topology optimization has become one of the most popular methods to achieve significant reductions in mass and volume, while maintaining stiffness. The basic topology optimization algorithm considered in this paper and a heuristic updating scheme are described in Bendsoe [1].

Simulación estructural de espumas de aluminio a partir de imágenes 2D mediante la combinación de técnicas de homogeneización y machine learning

espanolEn la industria actual, el uso de materiales resistentes, rigidos, de bajo peso y con buenas propiedades tanto acusticas como termicas es de gran interes. Entre estos materiales encontramos las espumas de aluminio. Para su uso, es necesario conocer su comportamiento estructural. Para la obtencion de la geometria de una espuma de aluminio se pueden plantear diversas tecnicas, todas ellas basadas en que la informacion inicial proviene de una imagen obtenida mediante una Tomografia Axial Computarizada (TAC). Una posible metodologia, conocida comunmente como segmentacion, consiste en generar un CAD a partir de la imagen y de ahi el modelo de Elementos Finitos (EF). Otra opcion es usar tecnicas como el CellFEM o el cgFEM, donde cierta cantidad de pixeles, que definen las propiedades del material, son embebidos en cada elemento. De entre los diversos metodos que existen para evaluar la matriz de propiedades del material, en este trabajo se propone el uso de tecnicas de homogeneizacion aceleradas mediante tecnicas de machine learning. Dicha tecnica se ha aplicado a problemas reales obteniendo un elevado speed up sin sacrificar la precision. EnglishThe use of resistant, rigid, low-weight materials with good both acoustic and thermal properties is very interesting in today’s industry. Among these materials, one can find aluminium foams, whose mechanical behaviour is necessary for their application. In order to obtain the geometry of an aluminium foam, several techniques can be applied, and all of them are based in the fact that information is initially obtained by a Computed Axial Tomography (CAT). One of these techniques, known as segmentation, involves a CAD being generated from an image in order to build the Finite Element (FE) model. Another option is to use techniques such as CutFEM or cgFEM, in which a certain amount of pixels, which define the properties of the material, are embedded in each element. Among the existing methods for evaluating the material properties matrix, this study proposes the use of homogenization techniques, sped up by the use of machine learning techniques. This method has been applied to real problems obtaining a high speed up, conserving precision.

Diseño de actividades y uso de la coevaluación para fomentar el desarrollo de competencias transversales en ingeniería mecánica y de materiales

En esta comunicacion se presentan las actividades de evaluacion desarrolladas en el marco de un Proyecto de Innovacion y Mejora Educativa, junto con algunos resultados preliminares. El principal objetivo de este proyecto es el diseno de actividades de evaluacion que fuercen a los estudiantes a desarrollar sus competencias transversales, al mismo tiempo que permitan a los profesores evaluar su desempeno en las competencias cientifico-tecnicas. Se emplea un enfoque de evaluacion formativa, de forma que las actividades de evaluacion sean utiles a los estudiantes para mejorar su aprendizaje. Palabras clave: competencias transversales, actividades de evaluacion, coevaluacion