Modelización de contactos termoelastohidrodinámicos

La mejora en la eficiencia energética y la reducción de la tasa de fallos en los contactos lubricados son aspectos que resultan de gran interés en numerosos sectores de la industria, y plantean en estos momentos nuevas dificultades operativas y retos para un futuro próximo. Los avances tecnológicos han incrementado las exigencias técnicas que se requieren a los aceites para cumplir su función al extender sus variables operativas a un mayor espectro de aplicaciones, tanto de condiciones de funcionamiento como a la gran variedad de nuevos materiales constitutivos de los engranajes en los que se tiene que utilizar. Por ello, actualmente se está incentivado el desarrollo de nuevos procedimientos que permitan comprender el comportamiento de este tipo de contactos lubricados, con el fin de lograr mejoras técnicas en su diseño y la correcta selección del aceite. En esta Tesis Doctoral se presenta una metodología de cálculo numérico que permite simular el comportamiento de contactos elastohidrodinámicos (EHD) puntuales, como puede ser el caso de un rodamiento. La resolución de este problema presenta diversas complejidades matemáticas y exige el desarrollo de un elaborado procedimiento de cálculo basado en técnicas multinivel. Para hacer del procedimiento una herramienta válida en un gran número de condiciones de funcionamiento y tipos de lubricantes, se ha tenido en cuenta en el cálculo la posible aparición de comportamientos no-Newtonianos del lubricante y fenómenos de generación y disipación de calor, provocados por el movimiento relativo del fluido y las superficies en contacto. Para la validación del procedimiento, se han contrastado los resultados numéricos obtenidos con nuestro método, con los resultados numéricos y experimentales publicados por otros autores y con valores experimentales propios medidos en un equipo de ensayo de contacto puntual tipo MTM. El desarrollo de este programa ha dotado a la División de Ingeniería de Máquinas de una herramienta que ha permitido, y sobre todo va permitir, evaluar la importancia de cada uno de los parámetros reológicos en los diferentes problemas que va a tener que abordar, evaluación que hasta el momento se realizaba con métodos aproximados que describen la fenomenología con mucha menos precisión. A la hora de emplear nuestro procedimiento numérico para simular situaciones reales, nos hemos encontrado con el obstáculo de que es muy complicado encontrar, en la bibliografía y bases de datos, los parámetros que caracterizan el comportamiento reológico del lubricante en las condiciones de presión, temperatura y grado de cizallamiento habituales en las que se trabaja en este tipo de contactos, y las pocas medidas que existen para estas condiciones de funcionamiento son poco fiables. Por ello como complemento al objetivo principal de esta Tesis hemos desarrollado una metodología para caracterizar los lubricantes en estas condiciones extremas. Dicha metodología está basada en la buena descripción que hace nuestro programa del coeficiente de fricción, lo que nos ha permitido obtener los parámetros reológicos del III lubricante a partir de las medidas experimentales del coeficiente de fricción generado en un equipo MTM lubricado con el lubricante que se desea caracterizar. Madrid, Octubre de 2012 IV Improving energy efficiency and reducing the failure rate in lubricated contacts are issues that are of great interest in many sectors of industry, and right now posed operational difficulties and new challenges for the near future. Technological advances have increased the technical demands required to oils to fulfil its role by extending its operational variables to a wider range of applications, both operating conditions and to the wide variety of new materials which constitute the gear in which must be used. For this reason, has being encouraged currently to develop new procedures to understand the behaviour of this type of lubricated contacts, in order to achieve improvements in design techniques and the correct oil selection. In this Thesis we present a numerical methodology to simulate the puntual elastohydrodynamic contact behaviour (EHD), such as a roller bearing. The resolution of this problem presents various mathematical complexities and requires the development of an elaborate calculation procedure based on multilevel techniques. To make the procedure a valid tool in a wide range of operating conditions and types of lubricants, has been taken into account in calculating the possible occurrence of non-Newtonian behaviour of the lubricant and phenomena of generation and dissipation of heat, caused by the fluid relative motion and contacting surfaces. For the validation of the method, we have compared the numerical results obtained with our method with numerical and experimental results published by other authors also with own experimental values measured on point-contact test equipment MTM. The development of this program has provided the Machines Engineering Division of a tool that has allowed, and especially will allow to evaluate the importance of each of the rheological parameters on the various problems that will have to be addressed, evaluation performed hitherto described methods that phenomenology approximated with much less accuracy. When using our numerical procedure to simulate real situations we have encountered the obstacle that is very difficult to find, in the literature and database, parameters characterizing the rheological behaviour of the lubricant in the usual conditions of pressure, temperature and shear rate in which you work in this type of contact, and the few measures that exist for these operating conditions are unreliable. Thus in addition to the main objective of this thesis, we have developed a methodology to characterize the lubricants in these extreme conditions. This methodology is based on the good description, which makes our program, of the coefficient of friction, that allowed us to obtain the lubricant rheological parameters from experimental measurements of the friction coefficient generated on lubricated MTM equipment with the lubricant to be characterized

Micro-vascular shape-memory polymer actuators with complex geometries obtaines by laser stereolithography

In our work we present the complete development process of geometrically complex microvascular shape-memory polymer actuators. The complex geometries and three-dimensional networks are designed by means of computer aided design resources. Manufacture is accomplished, in a single step, by means of laser stereolithography, directly from the computeraided design files with the three dimensional geometries of the different actuators under development. To our knowledge, laser stereolithography is applied here for the first time to the development of shape memory polymer devices with complex geometries and inner microvasculatures for their activation using a thermal fluid. Final testing of the developed actuators helps to validate the approach and to put forward some present challenges

Evaluation of a Test Dummy for Rehabilitation Platforms

[Resumen] Las terapias de rehabilitación para niños con Parálisis Cerebral han avanzado con la inclusión de los sistemas robóticos. Para iniciar estas terapias es necesario un estudio previo sobre la seguridad y fiabilidad de estos sistemas. En este estudio intervienen métodos de evaluación y ensayos para mejorar estos dispositivos. Así, se puede simular y comprobar si el funcionamiento se corresponde a lo deseado. Por la complejidad de obtener una respuesta realista y, al tratarse de niños, el desarrollo de modelos que imiten la anatomía humana es muy útil. En este contexto, se presenta el diseño y desarrollo de un maniquí pasivo para ensayar plataformas de rehabilitación de la marcha. Este prototipo representa las características antropométricas de un niño de 3 años, con movilidad en el miembro inferior. Con la plataforma de la marcha Discover2Walk se va a simular la caminata del maniquí. Los resultados al comparar el patrón obtenido tienen una desviación media por debajo de 3 cm, capacitando al maniquí como herramienta de ensayos.[Abstract] Rehabilitation therapies for toddlers with Cerebral Palsy have advanced with the incorporation of robotic systems. The initiation of these therapies requires previous studies on the safety and reliability of these systems. These studies involve evaluation and testing methods to improve the devices. This enables to simulate the performance and test whether it corresponds to the desired. Since it is complex to obtain a realistic response and, given that children are involved, the development of models that mimic human anatomy can be very useful. For this purpose, we present the design and development of a passive dummy to test gait rehabilitation platforms. This prototype represents the anthropometric characteristics of a 3-year-old toddler with mobility of the lower limb. The Discover2Walk gait training platform is used to simulate the dummy gait. The results after comparing the obtained pattern, measuring an error of 3%, qualify the dummy as a testing tool.Ministerio de Ciencia e Innovación; PID2019-105110RB-C3

"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

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

Analytical model for predicting friction in line contacts

This paper presents the development of an analytical model for the prediction of the friction coefficient in line contacts under thermal elastohydrodynamic lubrication (TEHL). A new theoretical equation is deduced for determining the friction coefficient, taking into account the rheology of common lubricants under TEHL. This approach also considers the heat generated and its penetration into the bulk of the contacting solids. Therefore, the increase in temperature and ensuing variations in the operating conditions are determined. In order to illustrate the use of the new model and verify its accuracy, an experimental stage is performed in a tribological test rig. The predictions of the proposed model are compared with the results obtained in the test rig and other data reported in the literature for diverse lubricants, showing a good agreement in every case

Seeds of Life in Space (SOLIS): VI. Chemical evolution of sulfuretted species along the outflows driven by the low-mass protostellar binary NGC 1333-IRAS4A

Context. Low-mass protostars drive powerful molecular outflows that can be observed with millimetre and submillimetre telescopes. Various sulfuretted species are known to be bright in shocks and could be used to infer the physical and chemical conditions throughout the observed outflows. Aims. The evolution of sulfur chemistry is studied along the outflows driven by the NGC 1333-IRAS4A protobinary system located in the Perseus cloud to constrain the physical and chemical processes at work in shocks. Methods. We observed various transitions from OCS, CS, SO, and SO2 towards NGC 1333-IRAS4A in the 1.3, 2, and 3 mm bands using the IRAM NOrthern Extended Millimeter Array and we interpreted the observations through the use of the Paris-Durham shock model. Results. The targeted species clearly show different spatial emission along the two outflows driven by IRAS4A. OCS is brighter on small and large scales along the south outflow driven by IRAS4A1, whereas SO2 is detected rather along the outflow driven by IRAS4A2 that is extended along the north east-south west direction. SO is detected at extremely high radial velocity up to + 25 km s-1 relative to the source velocity, clearly allowing us to distinguish the two outflows on small scales. Column density ratio maps estimated from a rotational diagram analysis allowed us to confirm a clear gradient of the OCS/SO2 column density ratio between the IRAS4A1 and IRAS4A2 outflows. Analysis assuming non Local Thermodynamic Equilibrium of four SO2 transitions towards several SiO emission peaks suggests that the observed gas should be associated with densities higher than 105 cm-3 and relatively warm (T > 100 K) temperatures in most cases. Conclusions. The observed chemical differentiation between the two outflows of the IRAS4A system could be explained by a different chemical history. The outflow driven by IRAS4A1 is likely younger and more enriched in species initially formed in interstellar ices, such as OCS, and recently sputtered into the shock gas. In contrast, the longer and likely older outflow triggered by IRAS4A2 is more enriched in species that have a gas phase origin, such as SO2. © ESO 2020.V.T. is grateful to Sylvie Cabrit and Guillaume Pineau des Forêts for stimulating discussions on the chemistry in shocks. The authors acknowledge the CALYPSO consortium for the use of the CALYPSO dataset. This work is based on observations carried out with the IRAM PdBI/NOEMA Interferometer under project numbers V05B and V010 (PI: M.V. Persson), U003 (PI: V. Taquet), and L15AA (PI: C. Ceccarelli and P. Caselli). IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). V.T. acknowledges the financial support from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement n. 664931. This work was supported by (i) the PRIN-INAF 2016 “The Cradle of Life – GENESIS-SKA (General Conditions in Early Planetary Systems for the rise of life with SKA)”, (ii) the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme, for the Project “The Dawn of Organic Chemistry” (DOC), grant agreement No 741002, and (iii) the European MARIE SKŁODOWSKA-CURIE ACTIONS under the European Union’s Horizon 2020 research and innovation programme, for the Project “Astro-Chemistry Origins” (ACO), Grant No 811312. C.F. acknowledges support from the French National Research Agency in the framework of the Investissements d’Avenir program (ANR-15-IDEX-02), through the funding of the “Origin of Life” project of the Université Grenoble-Alpes

Rheological Characterization of Lubrocants Using a Tribometer

This work presents a methodology for predicting the Non-Newtonian behavior of monodisperse lubricants under typical pressure, temperature and shear rate conditions for elastohydrodynamic (EHD) contacts. For its correct application we require some tests using a conventional point contact tribometer and information on the low shear viscosity and density variations with pressure and temperature -these characteristics can be easily found in technical documents or by testing-. Finally, this procedure is validated testing a PAO-6 base oil

Rheological Characterization of Lubrocants Using a Tribometer

This work presents a methodology for predicting the Non-Newtonian behavior of monodisperse lubricants under typical pressure, temperature and shear rate conditions for elastohydrodynamic (EHD) contacts. For its correct application we require some tests using a conventional point contact tribometer and information on the low shear viscosity and density variations with pressure and temperature -these characteristics can be easily found in technical documents or by testing-. Finally, this procedure is validated testing a PAO-6 base oil

Using Smartphones Physical Interfaces in Engineering Education: Experiences in Promoting Student Motivation and Learning

Smartphones are already taking part of the everyday life of more than two and a half billion people. University students are one of the population groups in which smartphone penetration is more intense. Applications for activities organization, voting, translation, information sharing, flashcarding, etc. are already of general use. However, despite the considerable big number of available data acquisition and analysis applications, few learning activities take advantage of the smartphone physical interfacing capabilities (accelerometers, gyroscopes, magnetometer, microphone, camera, flashlight, loudspeaker), which, due to the present computing power of smartphones, are excellent. This leads to infer that smartphones could be a relevant tool for enhancing the teaching-learning process in technical studies. Students attending to engineering careers are an especially adequate target for smartphone aided teaching due to their training in the use of computers and other electronic equipment and their strong previous knowledge in fields as programming or quantitative data management. In this work, the data acquisition capability of smartphones is studied, different teaching-learning activities based on this capability are proposed, and the impact of the introduction of three representative smartphone-based learning activities, as balancing of shafts, evaluation of stick-slip instabilities or machine acoustic power measurement, is analyzed