Estudio Dinámico del Sistema Araña-Tela de Araña en condiciones de Resonancia

Se ha estudiado el conjunto araña-tela de araña como un sistema dinámico, con la finalidad de obtener la respuesta de este sistema, cuando es sometido a condiciones de resonancia. La tela de araña es una estructura con una excelente combinación de resistencia, rigidez y tenacidad, óptima para transformar energía cinética en energía disipativa y así capturar a las presas. Sin embargo, hay condiciones ambientales externas que pueden llevar a esta estructura a condiciones de resonancia que podrían dañarla. De manera experimental se pudo comprobar que cuando ello ocurre, la araña es capaz de modificar la tensión de las sedas de la tela de araña, rigidizando la estructura para alejar al sistema de la zona de resonancia. La araña, mediante sus patas, censa la vibración en la tela de araña y actúa cuando las amplitudes aumentan significativamente y se mantienen por un largo periodo, cambiando así la tensión del sistema. Un modelo conceptual dinámico de un grado de libertad es una herramienta eficaz para replicar el comportamiento dinámico del conjunto araña-tela de araña en condiciones de resonanci

Characterization of Dynamic Parameters of a Structure Made Of Spider Silk Dragline

The aim of the research was to determine the dynamic parameters of the structure made of spider silk, addressing the topic from an analytical-experimental perspective. The physical structure made of spider silk is meant to copy an original and natural spider web as a special class of prestressed systems called equitensional structures. A conceptual model was developed, composed of silk threads which reach one each other and a point mass at that intersection, which analytically describes in a roughly way, the dynamic behavior of the structure made by the spiders silk gland producer "Major ampullate" (MA). Using free vibration techniques, two experiments were performed. Comparisons between analytical and experimental values obtained show a great coincidence in relation to the natural frequencies of the system, with minor errors than 2% for the fundamental frequency. Intrinsic damping capacities of the structure and silk's viscosity were also determined. Based on the results, it is concluded that the main function of the spider web is to convert the kinetic energy deformation energy and especially dissipative energy, thanks to the silk's viscoelastic properties

Blind source separation from multi-channel observations with channel-variant spatial resolutions

We propose a Bayesian method for separation and reconstruction of multiple source images from multi-channel observations with different resolutions and sizes. We reconstruct the sources by exploiting each observation channel at its exact resolution and size. The source maps are estimated by sampling the posteriors through a Monte Carlo scheme driven by an adaptive Langevin sampler. We use the t-distribution as prior image model. All the parameters of the posterior distribution are estimated iteratively along the algorithm. We experimented the proposed technique with the simulated astrophysical observations. These data are normally characterized by their channel-variant spatial resolution. Unlike most of the spatial-domain separation methods proposed so far, our strategy allows us to exploit each channel map at its exact resolution and size.The authors would like to thank Anna Bonaldi,(INAF, Padova, Italy) and Bulent Sankur, (Bogazici University, Turkey) for their valuable discussions. The simulated maps are courtesy of the Planck working group on diffuse component separation (WG2.1)

A sparse approach to astronomical point source detection

In this work we introduce a method for the detection of point sources in images based on al l1-norm sparse approximation. The method is inspired on astronomical image analysis but is directly applicable to any kind of images. We introduce a "top-to-bottom" detection algorithm that can greatly reduce the computational burden of detection if the images are sufficiently well-behaved, in the sense that sources are truly sparse and the chances of source overlapping are small. We test our ideas with simulated faint sources embedded in white noise, comparing the results with the matched filter detector for a number of detection thresholds. We show that the sparse detection approach leads to better results in the ROC curve than the matched filter detector. Moreover, with the sparse approach it is possible to provide an objective stopping criterion for the detection algorithm.The authors acknowledge partial financial support from the Spanish Ministry of Education (MEC) under project ESP2004-07067-C03-01 and from the joint CNR-CSIC research project 2008IT0059. MLC acknowledges an EGEE-III postdoctoral contract at IFCA

"Engineering Design" course transformación: From a conceive - design towards a complete CDIO approach

“Engineering Design” is a discipline aimed at improving our understanding about the development processes of novel and successful products, processes and systems in general, and at providing engineers with methodical steps for enhancing such processes. It may well be the engineering discipline more linked to the CDIO approach and to the conceive-design-implement-operate process. The benefits of applying “Engineering Design” principles are better appreciated when facing the development of complex systems. In the field of Mechanical Engineering some of the more complex systems an engineer can develop are advanced mechanical systems and machines. In this study we present the transformation process of an “Engineering Design” course, carried out in parallel to the implementation of the new Master’s Degree in Industrial Engineering at ETSII – TU Madrid. In the old Industrial Engineering plan of studies, implemented in 2000, the “Engineering Design” course was taught in the 5th academic year for Industrial Engineering students specializing in Mechanical Engineering and lasted for one semester. In the new Master’s Degree in Industrial Engineering, which started in 2014-2015, the “Engineering Design” course can be chosen by students from all Industrial Engineering specializations. The new subject lasts for two semesters and it is taught, in the 1st academic year of the Master’s Degree, to students having finished a four-year Bachelor’s Degree in Industrial Technologies. When transforming the course, our first aim was to let students live through a complete CDIO process, as having a two-semester structure gave us additional time for reaching the implementation and operation stages. With the old one-semester structure they could just focus on the conceptual and design phases. With the new approach their experience is more complete but several challenges arise, which are systematically analyzed in the following pages. A comparative study, taking account of the opinions of students and teachers is also presented and helps to support the benefits from complete CDIO experiences. Key aspects, including: student motivation, coordination between teachers, supervision of the projects under a tight schedule, rapid prototyping resources for reaching the implementation and operation stages, among others, are discussed and the more relevant lessons learned and proposals for improvement are put forward. To our knowledge it constitutes the first subject following a complete CDIO cycle in the field of Engineering Design applied to machines engineering in our country

Experimental tests in human-robot collision evaluation and characterization of a new safety index for robot operation

This paper describes an experimental procedure consisting of impact tests that simulate a collision of a human head with an industrial robot with the aim to validate a safety index named as New Index for Robots (NIR) and its outputs. The experiments in this paper are based on lab tests. It is an attempt to characterize the NIR index underlying the main parameters that are involved in crash interaction and to highlight limitations and weakness of suggested impact tests

Models for predicting friction coefficient and parameters with influence in elastohydrodynamic lubrication

This article shows different friction prediction models applicable to lubricants in point contacts under an elastohydrodynamic regime. The types of models used are two variations of the Newtonian theory, the Limiting Shear Stress model and the one based on Carreau's equation. The article sets out the theoretical calculation procedures and the ensuing equations for calculating the friction coefficient. The aims of the article are to study the effect of the parameters with influence on friction and to compare the model's results with those given by an experimental stage performed on a mini traction machine. This test system allows the measurement of friction coefficient in point contacts (ball–disc) under a wide range of variation of parameters such as temperature, slide-roll ratio, lubricant, material, load, or velocity

Cálculo de la resistencia a la fatiga superficial en superficies con lubricación elastohidrodinámica mediante el criterio de Dang Van

Los fenómenos de fatiga superficial en sus diferentes escalas (micropitting, pitting, spalling), aparecen en multitud de elementos mecánicos en contacto lubricado como pueden ser los engranajes o rodamientos o en elementos con contacto seco como son las ruedas de ferrocarril. Los defectos que aparecen en las superficies en contacto debidos a estos fenómenos empeoran las condiciones de funcionamiento, provocando vibraciones, desgaste prematuro y en los casos más extremos el fallo de la máquina. El procedimiento que se sugiere en este artículo se inicia con el cálculo de los parámetros que definen el contacto elastohidrodinámico y que tienen influencia en la resistencia a fatiga del contacto: espesor de película, distribución de presión y coeficiente de fricción. Una vez se tiene la presión y el coeficiente de fricción en la superficie de contacto, se procede al cálculo de las tensiones en el interior del material obteniendo la distribución de tensiones. Conocidas las tensiones en todo punto interior y el proceso de carga completo se aplica el criterio de fatiga de Dang Van y se verifica si existe, o no, probabilidad de fallo por fatiga. El criterio de Dang Van es aplicable para el cálculo de la vida a fatiga para un alto número de ciclos (donde el tiempo de propagación de grieta es despreciable frente al tiempo de iniciación) y se basa en la aproximación a la escala mesoscópica y la existencia de un plano crítico. Una vez descrita la teoría se propondrá una aplicación para el cálculo de tensiones en contactos puntuales y contactos lineales y el análisis de fatiga superficial en engranaje

The Evolution and Development of Mechanical Engineering through large cultural areas

Mechanical Engineering is probably the forerunner of many branches of Engineering and has persistently been their companion up to the present. For this reason, the History of Machines embraces a very broad period of the History of Mankind, and can be studied from many perspectives. This paper attempts to link progress in Mechanical Engineering to the great cultures that have arisen throughout the History of Mankind. This paper begins with the anonymous mechanical developments that appeared in Prehistory and opened up the way to the first civilisations, marked to a large extent, maybe, by Greco-Roman culture in Europe and by China in Asia. After them came the Islamic world, which, in the Middle Ages stimulated society to find new mechanical devices and set the foundations that would lead to the Renaissance. Outstanding in this period was the expansion of Italian, French and German creative and innovative thinking with its “Treatises on Machines”, which, for a short time, coincided with the advance of the Iberian Empire and the development of machinery for the New World. Finally, the Industrial Revolution became the climax of all previous developments and a period of rapid mechanical evolution began that was to be highly interesting from a historical and technological point of view. This was accompanied by a parallel interest in reflecting on and analysing machines, which has led to the appearance of countless “Treatises on Machines”

Improving voltage imbalance in inverter-based islanded microgrids during line-to-line short circuits

Line-to-line short circuits are the transient disturbances that cause the highest currents as well as the largest voltage imbalances in inverter-based microgrids. This paper presents a control scheme for grid-forming inverters in islanded microgrids that limits the current to a safe value during these types of short circuits while providing a lower voltage imbalance compared to state-of-the-art current limiting techniques. This control scheme is based on reducing both the amplitude of the reference voltage with the maximum amplitude of the reference current and the instantaneous reference voltage with only the inductive component of the virtual impedance. The combination of these two control actions provides low voltage imbalance, as the theoretical and experimental studies reveal. This voltage imbalance improvement is the main contribution of this paper and is maintained when the microgrid supplies linear and non-linear loads. In the theoretical study, the paper includes control design guidelines to satisfy static and dynamic specifications. The theoretical predictions are validated by means of experimental results measured in a laboratory microgrid. A practical performance comparison of current limiting techniques based on experimental tests is also reported.This publication is part of the project PID2021-122835OB-C21, financed by MCIN/AEI/10.13039/501000011033 and FEDER “Una manera de hacer Europa”.Postprint (published version