748 research outputs found
Sort by
Analytical Model of the Current Stress in Active-Bridge Active-Clamp Converter for More Electric Aircraft
Full text linkNowadays, the emergence of electrically supplied actuators and energy storage systems is leading the aeronautic industry to develop aircrafts with more electrical power installed. Therefore, different Power-Electronic Converters (PECs) have been proposed to satisfy the requirements of More Electric Aircraft (MEA) applications. Among them Active-Bridge-Active-Clamp converter is one of the most promising isolated DC/DC PEC topologies. To expand the characterization of this PEC, the analytical model to determine the root mean square and average currents in secondary power devices is presented in this work when working with single-phase shift rectangular modulation. Furthermore, a simulation model is developed in PLECS to validate the analytical model proposed in this work in MEA scenarios. Finally, the simulation model is employed to determine the error caused by dead time and clamp capacitances in the currents that are calculated analytically
Calendar Ageing Model for Li-Ion Batteries Using Transfer Learning Methods
Full text linkGetting accurate lifetime predictions for a particular cell chemistry remains a challenging process, largely dependent on time and cost-intensive experimental battery testing. This paper proposes a transfer learning (TL) method to develop LIB ageing models, which allow for the leveraging of experimental laboratory testing data previously obtained for a different cell technology. The TL method is implemented through Neural Networks models, using LiNiMnCoO2/C laboratory ageing data as a baseline model. The obtained TL model achieves an 1.01% overall error for a broad range of operating conditions, using for retraining only two experimental ageing tests of LiFePO4/C cells
Assessing the statistical validity of momentum-deficit-based measurements in turbulent configurations
Full text linkAn application-agnostic procedure is outlined for checking the validity of momentum-deficit-based drag measurements performed under different turbulent conditions in a wind tunnel. The approach defines a two-step methodology: the first stage characterizes the turbulent flowfield generated downstream a passive grid through a set of statistical parameters. Acceptable values for such parameters are determined by means of two criteria: compliance with the threshold value set by an analysis of the experimental uncertainties, and fulfilment of the isotropic condition for ensuring a well-established turbulent flowfield. Those two prerequisites define a set of turbulent configurations for which the momentum-deficit-based technique applies feasibly.
The second stage of the procedure is configuration-specific, and undertakes drag measurements upon a NACA0021 airfoil subjected to a set of different turbulent configurations. It is shown that performing measurements under invalid turbulent conditions leads to inconsistent drag curves, which serves for defining a validity map based on the testable cases
Design and validation of a questionnaire (LLQ) on facilitating the development of the learning to learn competence in university educators
Full text linkEn el marco del Espacio Europeo de Educación Superior, el profesorado ha de contar con capacidades profesionales para impulsar en el alumnado la competencia aprender a aprender, que hace referencia a la capacidad de autorregulación del propio proceso de aprendizaje. El objetivo del presente trabajo consistió en diseñar y validar un cuestionario para medir los contextos facilitadores de aprendizaje que el profesorado universitario activa para el desarrollo de la competencia aprender a aprender, el CAA. En primer lugar, en base a la revisión teórica y empírica, se definieron 86 ítems. A continuación, se examinaron la validez de contenido (n = 20 expertos), la validez basada en los procesos de respuesta (n = 10 docentes), la validez basada en la estructura interna (n = 415 docentes), la validez concurrente y la validez externa. Los resultados mostraron una adecuada calidad psicométrica, consistencia interna, fiabilidad y bondad de ajuste. La versión final del CAA comprendió 4 dimensiones y 39 ítems. Este instrumento puede ser una herramienta de rápida aplicación, válida y fiable, para conocer el desarrollo de los contextos facilitadores de aprendizaje de la competencia aprender a aprender. Asimismo, puede servir para detectar necesidades de formación profesional en el desarrollo de dicha competencia.Within the European Higher Education Area framework, educa-tors must have acquired professional skills in order to promote the learning to learn competence, which refers to the ability to self-regulate the learning process itself, in their students. The objective of this work was to design and validate a questionnaire, the learning to learn questionnaire (LLQ), to measure the facilitative learning contexts implemented by university educa-tors to develop the learning to learn competence. First, based on a theoret-ical and empirical review, 86 items belonging to 7dimensions were de-fined. Next, content validity (n = 20 experts), validity based on response processes (n= 10 teachers), validity based on internal structure (n = 415 teachers), and concurrent validity were examined. Our results showed suf-ficient psychometric quality, reliability of scores and goodness of fit. The final version of the LLQ consisted of 4 dimensions and 39 items. This in-strument can be considered a valid and reliable tool that can be quickly ap-plied in order to identify the development of facilitative learning contexts in the evolution of the learning to learn competence. Likewise, it can also serve to detect training needs in the development of this competence in university educators
Automatic Web Navigation Problem Detection Based on Client-Side Interaction Data
Full text linkThe current importance of digital competence makes it essential to enable people with disabilities to use digital devices and applications and to automatically adapt site interactions to their needs. Although most of the current adaptable solutions make use of predefined user profiles, automatic detection of user abilities and disabilities is the foundation for building adaptive systems. This work contributes to diminishing the digital divide for people with disabilities by detecting the web navigation problems of users with physical disabilities based on a two-step strategy. The system is based on web user interaction data collected by the RemoTest platform and a complete data mining process applied to the data. First, the device used for interaction is recognized, and then, the problems the user may be having while interacting with the computer are detected. Identification of the device being used and the problems being encountered will allow the most adequate adaptation to be deployed and thus make the navigation more accessible
In-SEM micro-machining reveals the origins of the size effect in the cutting energy
Full text linkHigh-precision metal cutting is increasingly relevant in advanced applications. Such precision normally requires a cutting feed in the micron or even sub-micron dimension scale, which raises questions about applicability of concepts developed in industrial scale machining. To address this challenge, we have developed a device to perform linear cutting with force measurement in the vacuum chamber of an electron microscope, which has been utilised to study the cutting process down to 200 nm of the feed and the tool tip radius. The machining experiments carried out in-operando in SEM have shown that the main classical deformation zones of metal cutting: primary, secondary and tertiary shear zones—were preserved even at sub-micron feeds. In-operando observations and subsequent structural analysis in FIB/SEM revealed a number of microstructural peculiarities, such as: a substantial cutting force related to the development of the primary shear zone; dependence of the ternary shear zone thickness on the underlaying grain crystal orientation. Measurement of the cutting forces at deep submicron feeds and cutting tool apex radii has been exploited to discriminate different sources for the size effect on the cutting energy (dependence of the energy on the feed and tool radius). It was observed that typical industrial values of feed and tool radius imposes a size effect determined primarily by geometrical factors, while in a sub-micrometre feed range the contribution of the strain hardening in the primary share zone becomes relevant
A Multi Camera and Multi Laser Calibration Method for 3D Reconstruction of Revolution Parts
Full text linkThis paper describes a method for calibrating multi camera and multi laser 3D triangulation systems, particularly for those using Scheimpflug adapters. Under this configuration, the focus plane of the camera is located at the laser plane, making it difficult to use traditional calibration methods, such as chessboard pattern-based strategies. Our method uses a conical calibration object whose intersections with the laser planes generate stepped line patterns that can be used to calculate the camera-laser homographies. The calibration object has been designed to calibrate scanners for revolving surfaces, but it can be easily extended to linear setups. The experiments carried out show that the proposed system has a precision of 0.1 mm
Aspects Concerning the Fabrication of Magnetorheological Fluids Containing High Magnetization FeCo Nanoparticles
Full text linkRecently, our collaborative work in the fabrication of a magnetorheological fluid (MRF) containing high magnetization FeCo nanoparticles (NPs, fabricated in our laboratories using the chemical reduction technique; MS = 212 Am2/kg) as magnetic fillers have resulted in a new MRF with superior performance up to 616.7 kA/m. The MRF had a yield stress value of 2729 Pa and good reversibility after a demagnetization process. This value competes with the best ones reported in the most recent literature. Nevertheless, the fabrication process of this type of fluid is not an easy task since there is a strong trend to the aggregation of the FeCo NPs due to the strong magnetic dipolar interaction among them. Thus, now we present the analysis of some aspects concerning the fabrication process of our FeCo NPs containing MRF, mainly the type of surfactant used to cover those NPs (oleic acid or aluminium stearate) and its concentration, and the procedure followed (mechanical and/or ultrasound stirring) to achieve a good dispersion of those magnetic fillers within the fluid
Molinos de viento patentados por Jerónimo de Ayanz y Beaumont en el año 1606: un análisis conceptual desde una perspectiva ingenieril del año 2021
Full text linkEn el presente documento técnico, se realiza un análisis desde un punto de vista ingenieril de los molinos de viento patentados por Jerónimo de Ayanz y Beaumont el siglo XVII. El análisis que se presenta podría denominarse como “análisis conceptual” o “análisis cualitativo”, dado que no se centra en cuantificar ni realizar cálculos numéricos, modelizaciones, mediciones o experimentaciones. Por el contrario, basándose en los conocimientos y experiencias de los autores en las disciplinas de fluido-dinámica, generación de energía mediante aeroturbinas e ingeniería en general, busca realizar un análisis cualitativo de los molinos de viento patentados hace ya más de cuatro siglos por el genio de Gendulain. Por tanto, primeramente se realiza una presentación de los dos molinos de viento a estudiar, esto es, el molino Ayanz de eje vertical y el molino Ayanz de aspas en tornillo. Dichos molinos han salido a la luz recientemente, gracias al trabajo realizado por Nicolás García Tapia, plasmado en el libro “Patentes de invención españolas en el siglo de oro”. Seguidamente, se proporcionan brevemente unos pocos datos históricos para enmarcar en qué contexto Ayanz patenta sus molinos. En tercer lugar, se identifican y exponen los aspectos técnicos relevantes de la inventiva realizada por Ayanz en los molinos de viento propuestos. A continuación, en los siguiente tres apartados, el documento profundiza en el estudio del molino Ayanz de eje vertical. En un primer apartado, se distinguen las similitudes y diferencias entre el molino de Ayanz de eje vertical y un molino de parecidas características que en la actualidad es muy popular, a saber; el molino patentado a principios del siglo XX denominado Savonius. Tras ello, se compara y evalúa el diseño concreto del molino de eje vertical que Ayanz propuso, con las diferentes variantes de molinos de similares características que se estudian y que se emplean en la actualidad. En el último apartado, se muestra lo bien posicionado que se encuentra el molino de Ayanz de eje vertical a día de hoy, para ser empleado en una aplicación tan en boga, como es la de generar energía eléctrica a partir del viento. Finalmente, se ofrecen una serie de conclusiones relevantes del estudio
Estudio comparativo experimental entre MPPT, P&O híbrido y un control basado en lógica difusa para una comparación experiemental de minieólica
No full textThis study focuses on a comparison between different maximum power extraction controls for a small wind turbine application. In this case, a vertical axis wind turbine (VAWT) coupled to a permanent magnet synchronous generator (PMSG) is used. The analysis is performed for variable winds, so that a real small wind turbine application is simulated. An experimental platform and a wind tunnel are used to recreate the different wind profiles. Diverse controls are compared, a "classical" MPPT, a hybrid Perturb & Observe control and a fuzzy control. Artificial intelligence allows the creation of control algorithms that are not bound by the mechanical parameters of the wind turbine, thus avoiding the need to characterize the wind turbine and define the maximum power curve. It is determined that, for almost constant wind profiles, the hybrid Perturb & Observe extracts more energy. However, for the same profile with greater variability, the fuzzy controller extracts more energy