http://hdl.handle.net/2099.1/4489 2013-06-20T03:05:35Z http://hdl.handle.net/2099.1/17660 Title: Estudio de la evolución de la rugosidad en un proceso de pulido de una superficie rectificada Authors: Baró Rius, Oscar Abstract: En el presente trabajo fin de máster se ha estudiado la evolución de la rugosidad superficial de un acero para moldes, que se ha rectificado bajo diferentes condiciones y posteriormente se ha sometido a sucesivos procesos de pulido. Se han realizado diferentes rectificados a unas probetas de acero templado, Wr.12344, material utilizado habitualmente para la fabricación de moldes. Posteriormente, las probetas han sido sometidas a un proceso de pulido con abrasivo de corindón de tamaño 2500 escala Norton. Los datos de rugosidad obtenidos mediante un rugosímetro de contacto han servido para analizar su evolución. Se han estudiado diferentes parámetros de rugosidad, Ra, Rq, Rt, Rk, Rpk, Rvk, Mr1, Mr2, Rku, Rsk, así como las curvas de Abbott-Firestone y las curvas de probabilidad para cada una de las fases del proceso de pulido. Se han propuesto distintos criterios para la determinación del tiempo de pulido: evolución de Ra, evolución de las curvas de Abbot-Firestone o evolución de las curvas de probabilidad. En los tres casos se ha considerado como tiempo de pulido el necesario para que los resultados obtenidos en la dirección longitudinal y transversal coincidan. Además de las pruebas de pulido se han llevado a cabo varios estudios complementarios, tales como: determinación del cut-off óptimo, estudio de la variabilidad entre réplicas de un mismo ensayo, estudio sobre el porcentaje de material idóneo para comparar diferentes curvas de Abbott-Firsetone, así como la sensibilidad de los parámetros de amplitud de rugosidad a una imperfección en la superficie. Los resultados muestran que el parámetro que más influye sobre la topografía superficial obtenida en rectificado es el tamaño de grano de la muela. La rugosidad sigue una evolución exponencial con el tiempo, excepto para el parámetro Rpk que disminuye muy rápido y Rvk que disminuye muy lento. Rku y Rsk son muy sensibles a irregularidades en la superficie. Se recomienda emplear los parámetros de probabilidad en el estudio de piezas fabricadas mediante rectificado y posterior pulido. Entre los criterios estudiados para determinar el tiempo de pulido, es aconsejable utilizar las curvas de Abbott-Firestone o las de probabilidad, considerando como tiempo de pulido el necesario para que los resultados de las medidas longitudinal y transversal coincidan. 2013-03-15T00:00:00Z http://hdl.handle.net/2099.1/14757 Title: Evaluation of the method: Computational modeling of Jominy test with variable thermal properties using finite elements Authors: Caicedo Casas, Juan Manuel Abstract: With the introduction of numerical methods, combined with powerful computational resources, a larger amount of problems of higher complexity could be solved compared to those solved by analytical methods. Analytical solutions, implied at the same time, huge efforts by means of complex mathematical formulation, and solution were restricted to a reduced number of physical problems. Research in numerical methods is being held all around the globe, and an important number of papers in many different areas are being published year after year. The main goal achieved by introducing numerical methods solutions is the possibility this methods gives, in order to obtain a closer-to-reality nonlinear solution, taking into account real geometry, non-independent material’s properties, initial and boundary conditions, and the evolution in time of geometry, material properties and boundary conditions. Jominy test (ASTM A255, SAE J406, ISO 642 / A04-303), is one of those physical test were an analytical solution could not be obtained due the dependence with temperature of material properties as density, specific heat capacity and thermal conduction. In this thesis, two different ways of modeling Jominy test by means of Finite Element Method are presented and compared. The first one is a series of MATLAB! codes, based on finite element theory, where Parabolic First Order Heat Conduction Equation is taken from its continuous time-space domain form, into the discrete time- space domain. In second place, modeling with CAM commercial software ANSYS! is being held, in order to obtain a solution with a proved, well known, CAM software, which allows having trustful results to compare with. Axisymmetric condition is taking into account to reduce the number of axis without losing any accuracy in both, MATLAB! and ANSYS! solutions. An Experimental framework chapter has been added in order to give a better understanding of Jominy test experiment for readers not related to it. It is, indeed, a general overview of the experiment. For a detailed explanation of the procedure it would be necessary for the reader to acquire the ASTM A255 standard of Jominy test, or any equivalent standard (SAE J406, ISO 642/ A04-303). The reader can find technical results from the test in [7], pages 323 and 324. If related with Jominy test, skip chapter one, Experimental Framework, as this introductory chapter is intended, as said before, to readers not related with the experiment in order to establish necessary background for a better understand of the work presented thereafter. Thesis is centered in the numerical results, the main objective is the to be able to conclude if the numerical algorithm implemented in MATLAB! represents indeed the real test, by means of comparing results with simulations made using a high level commercial proved CAM software ANSYS!. A complete and deep explanation of the Theoretical background related with the project is exposed in chapter 2 Theoretical Framework, including, among others, Thermal Parabolic first order equation reigning physical behavior of the specimen submitted to Jominy test, the finite element method applied to the heat-transfer equation, as well as finite difference method used later on in the time-domain. Special care was put into ensure compatibility between both results in order to make the analysis. Enhances have being done in order this comparison could take place and resemble most likely to the real test conditions: A variable mesh, closer to the real thermocouples position, was employed in both programs. In the variable mesh, implicit methods in time were implemented, and an easy to comprehend postprocessor was developed. Motivation for overtaking this thesis lies in observing the correlation in results obtained by own means, compared to those obtained by a trustful source, and this is the most important feature of the thesis. As expected, differences between two solutions are found, but same shape and similar gradient of temperature are obtained, proving the validity of previous results. 2012-03-14T18:01:47Z http://hdl.handle.net/2099.1/10746 Title: Desarrollo de metodología para evaluación mecánica de una junta soldada en "T" Authors: Vieira de Castro, Felipe Abstract: Se realizó el estudio del comportamiento mecánico de una unión soldada en “T” con láminas de acero UNE F1 utilizando electrodos revestidos AWS E-6013 con la finalidad de realizar un aporte en referencia a los procedimientos de cálculo de ésta. Para ello, en primer lugar, se efectuaron cálculos de interés con la finalidad de obtener la resistencia máxima de la junta soldada y la magnitud de los esfuerzos utilizando fórmulas obtenidas de la teoría fundamental de Mecánica de Materiales, lo cual se denomina Método Clásico, considerando cargas estáticas y de fatiga; posteriormente, se hizo una aproximación al cálculo de la junta soldada mediante el Análisis por Elementos Finitos (MEF), también considerando cargas estáticas y de fatiga y, por último, se llevaron a cabo ensayos de tracción y fatiga con probetas soldadas en ángulo. Se hace un estudio comparativo a fin de establecer una metodología actualizada para el cálculo de la junta soldada en cuestión. Se pone de relieve que existen factores utilizados para el cálculo de la vida a fatiga, tanto en el Método Clásico como en el programa basado en MEF utilizado, como por ejemplo el factor de reducción de la vida a fatiga, Kf, que son parámetros de ajuste por ambas metodologías y deben ser obtenidos experimentalmente 2011-01-07T19:10:21Z http://hdl.handle.net/2099.1/10742 Title: Application of reverse engineering concepts to compressed air tank Authors: Gilles, Guedia Guemo Abstract: This study, application of reverse engineering concepts to a compressed air tank, leads us to calculate tank shell in static and fatigue, by using of formulas and software. Furthermore, unsatisfying results from basics formulas of cylindrical and spherical shell, lead us to use standards methods: ASME code and Indian standards to design torispherical head tank. Then obtained results showed that, design a tank with torispherical head by ASME code is more safety than Indian standards. It was proved that, Indian standards is the most economic, because the life consumption of tank is only 3,8 % against 0,73% by ASME code. However, those two methods showed that, the stress in knuckle is superior to admissible strength in case of testing pressure (design pressure), but inferior with maximum operating pressure. This explains the using of ring to reinforce the knuckle in some case. 2011-01-07T18:33:00Z http://hdl.handle.net/2099.1/10589 Title: Practical issue for a new identification method of Hammerstein system Authors: Huy Dang, Bui Abstract: The Hammerstein and Wiener models are nonlinear representations od systems composed by the coupling of a static nonlinearity N and a linear system L in the form N-L (Hammerstein) and L-N (Wiener). Although the forms are very simple, these models still represent many real life processes such as mechanical systems, chemical processes, electrical and electronic systems, etc. The problem of identifying the static nonlinearity and linear system is a tough but interesting and important task, which has attracted a lot of research interest. It has been studied in the available literature either for Hammerstein or Wiener systems, and either in a discrete-time or continuous-time setting. The results of these researches have been useful and widely applied in automatic and control industry. Our project in fact involves in a new technique that was recently proposed [1]. This paper proposed a unified framework for the identification of both systems which are valid for single input single output (SISO) and multi inputs multi outputs (MIMO) systems, and without any particular structure for the static nonlinearity. This algorithm has been proven theoretically but it is necessary for such a verification of its characteristics compared with other existing algorithms. The objective of this project is to discuss some practical aspects of implementation of this algorithm when applied to a simple example Hammerstein model. Then, this model is modified to represent a real life Wind Turbine Model [4]. The identification technique is also modified accordingly, and numerical simulations are carried out to validate this technique. The project is open-ended and the may be further developed with the existence of noise and even some more complicated Hammerstein models. 2010-12-20T17:12:05Z http://hdl.handle.net/2099.1/10569 Title: Design of the manufacturing process of a reduction gear Authors: Tchoudi, William Abstract: The purpose of this project entitled “Design of the manufacturing process of a reduction gear” is to design a manufacturing process in order to produce 20000 units of a reduction gear per year. It is enrolled for a forecast of 5 years. As the product involves public users, therefore it was mandatory to obtain good quality of part. Taking into account today’s highly competitive economic environment, it was also necessary to ensure the economic viability of the project, and thus profitability. For achieving that, different steps have been followed. The first one was the definition of a manufacturing strategy, which consists of deciding, for each part, which kind of operation is done, either internally or externally (outsourcing manufacturing), according to criteria such as surface finish of parts, mechanical properties, and the cost of rough parts. Afterwards, an advanced planning of each cycle phase was prepared. In this second step, the choice of the most convenient process and machine tool, tools, cutting conditions, maximum power of the spindle, machining times and minimal production costs were defined. The cycle and phase sheets were then provided for each machined part with related explaining drawings. In order to avoid waste times, a definition of the workshop organization machine tools and layout was done. Calculation of economical viability has ensured the feasibility and the profitability of the manufacturing process. As a conclusion, a comprehensive manufacturing process has been defined taking into account both quality and economic requirements. 2010-12-16T19:52:33Z http://hdl.handle.net/2099.1/10535 Title: Mechanisms and strategies of power regulation in wind turbines Authors: Dasey, Michael Noel Abstract: The modelling and simulation of wind turbines is becoming more important as the penetration levels of wind turbines are increasing. This means that the effects the various types of wind turbines have on electrical grids and possible ways to control power output quality should be understood in order to facilitate wind energy expansion and to ensure minimal negative effects on local and wider area grids. Chapter 2 provides a literature review of the current research related to constant speed turbines (both passive and active stall) and the variable speed DFIG turbine. Although the latter is not examined further in this thesis, it is mentioned to provide a point of comparison with the constant speed technology. The literature review also enabled to results of previous simulation and the results of this thesis to be successfully validated. The Chapter 3 deals with the constant speed turbine as a steady state simulation. The steady state simulation showed that the chosen turbine characteristic would have a power generation design point of 2MW, and was designed for optimum output at an average wind velocity of 15m/s. The steady state simulations also showed that effect a change in frequency would have on the power output. Comparing the simulations of the passive stall of Chapter 4 and the active stall control of Chapter 5 it was shown that with the addition of pitch control there was still a significant overshoot of design output power of 0.06-0.08p.u, along with a high frequency variation of 0.05p.u. While the pitch actuators were engaged, this did not provide any significant reduction in design point overshoot or turbine behaviour The advantage of the active stall control was explored in Chapter 6, demonstrating the active stall control turbine can be used successfully in providing primary, secondary and high frequency support. A new set point could be reached within the required 10sec, and the output remained relatively steady. Though this power output is of course still reliant, and varies slightly depending on the wind velocity behaviour. 2010-12-15T17:44:17Z http://hdl.handle.net/2099.1/10532 Title: Control of the twin-rotor system Authors: Tien Thinh, Than Abstract: The problem of Multi-Input-Multi-Output (MIMO) control has always been an interesting sub-field within the field of control. Among the systems that require MIMO control, the helicopter stands out as one of the prominent examples. This type of aircraft requires two rotors, rotating in perpendicular planes, therefore can not rely on Single-Input-Single-Output controllers to maneuver in the space. Also, un-manned helicopters have not yet been seen in armies worldwide, this fact gives the task of developing MIMO control systems for helicopters a large room to grow. In order to model the helicopter in laboratorial space, a Twin-Rotor Apparatus has been developed by Feedback company. This apparatus is being studied in Universitat Politècnica de Catalunya, Spain, to provide a good model for teaching and research in the field of MIMO control, with the aim to develop more efficient control methods for the real helicopter. The complete mechanical model for this apparatus has been developed using the software MAPLE. Based on this mechanical model, several control schemes are created to control the apparatus using MATLAB-Simulink. These control schemes are designed to make the Twin-Rotor system go to predetermined points and follow periodical input signals. The task of designing the control schemes requires the author to work on state-space configuration, linearization and experimental works. Mathematical approximation is also applied to get the approximated polynomials for variables relationship. The controllers designed work successfully and make ways for the design of similar controllers using for other MIMO system 2010-12-15T16:39:20Z http://hdl.handle.net/2099.1/10528 Title: Numerical implementation of a new identification tecnique for wiener system Authors: Truong, Do Tho Abstract: Wiener model is a nonlinear representation of systems composed by the coupling of a linear system L and a static nonlinearity N in the form L-N. This model can represent real processes which made it popular in the last decades. The problem of identifying the static nonlinearity and linear system is not a trivial task which has attracted a lot of research interest. In a recent work [I2010], a new methodology for the identification of this system has been proposed. The objective of this thesis is to implement this methodology using numerical simulations. To this end, a real-life Wiener process is taken from the literature. The objective of the study is to program the identification technique of [I2010] using MATLAB/SIMULINK. The inputs are generated by subroutine and the outputs are calculated using the numerical model implemented in MATLAB/SIMULINK. Then, using these input/output data, the unknown static nonlinearity and linear process parameters are determined. The effect of noise on the accuracy of the estimates will also be explored. 2010-12-14T19:14:22Z http://hdl.handle.net/2099.1/10511 Title: Development of testing procedure for welded steel tubes Authors: Hameed, Saqib Abstract: The objective of this study is to perform physical tests on T-joint welded tubes to determine the axial static load behavior and compared them with the analytical and numerical calculations. Three experiments are performed and it is examined that typical collapse modes develop in the section of tube and associated Von-Mises stresses (distortion energy) are compared with the analytical method and numerical simulations. The comparisons with the experimental results are satisfactory. The validated numerical model is used to study the Von-Mises stresses with variation in the leg lengths of weld (2 mm, 3 mm leg lengths). The strength of fillet welded connections is investigated for different leg lengths. The ultimate strength of weld metal is determined by considering the forces acting on the welds. The effect of different leg lengths on the strength of welds is investigated by numerical methods and compared with analytical calculations which show that they are in agreement. The increasing in weld leg length is caused of increasing in weld strength and decreasing in stress progress in weld that cause the increasing in life and strength of the weld which is also in agreement with Iman Hadipour [4]. 2010-12-13T17:56:57Z http://hdl.handle.net/2099.1/10480 Title: Développement d'un nouveau concept de structure pare-chocs Authors: Soares Bravo, Alencar Abstract: Le développement des nouveaux concepts est une manière importante de réussir à ajouter des fonctions et baisser les coûts. Un système flexible de structure pare-chocs peut faciliter l’assemblage des différentes versions de peaux sur le frontal du véhicule SEAT est actuellement en train de développer sa nouvelle génération de structure pare-chocs, il est important que le nouveau format de sustentation du pare-choc soit capable des mêmes performances que la structure précédente utilisée Il est composé pour le guide sous-phare (une pièce qui embrasse et fixe le phare) et le guide fixe (une pièce qui fait l’union des diverses peaux des revêtements). Pour ces pièces il est important de considérer sa longueur et la règle de résistance des matériaux, car elles peuvent se déformer de manière excessive sous des efforts et par conséquent changer la direction du phare. Donc, il faut observer le cahier des charges où sont définies les exigences de l’entreprise pour un minimum de qualité. On utilisera la Convergence Contrôlée pour des processus créatifs, un aspect important de cette méthode est la présentation et la discussion des informations sous la forme d'une matrice. Pour chercher la fonction dont on a discutée précédemment, on propose une nouvelle version du guide fixe afin de régler les problèmes qu’on a rencontrés jusqu’ici. On va dans un premier temps voir si le système proposé est acceptable selon les critères de SEAT. Pour cela on définira des méthodes en utilisant le software Catia V5. Dans annexe I il y a un manuel d’utilisation du module des éléments finis. En utilisant le logiciel Catia V5, on peut facilement obtenir les valeurs des déplacements aux noeuds mais, et si dans le cas d’application d’un moment on désire mesurer la rotation d’une surface, il faut avoir une méthode pour avoir cette mesure qui sera définie pour l’étude. Finalement on a une nouvelle proposition de structure pare-chocs qui permettra d’économiser de l’argent, du temps et des pièces, tout en gardant les mêmes exigences du système précédemment utilisé avec plusieurs avantages pour l’entreprise. 2010-12-10T17:34:59Z http://hdl.handle.net/2099.1/10319 Title: Simulación de un aerogenerador de velocidad variable basado en maquina de inducción doblemente alimentada Authors: Gomes Perini, Luis Agnaldo Abstract: Este proyecto consiste en implementar un modelo de simulación de un aerogenerador de velocidad variable basado en máquina de inducción doblemente alimentada (DFIG), en el free-software de modelado y simulación dinámica SCILAB-SCICOS. Además, se debe conocer y desarrollar las herramientas que permitan simular distintos escenarios y obtener datos y gráficos de la simulación para un mejor estudio del funcionamiento de los aerogeneradores. Para llegar a los objetivos, documentase el modelado del viento, de la turbina, de la transmisión mecánica, del generador, del convertidor, de la red eléctrica y del control utilizado para obtener la máxima potencia y el mejor funcionamiento del aerogenerador. Al final, se hace un análisis comparativo y se estudia los resultados obtenidos, con parámetros que puedan representar una condición real de operación de los aerogeneradores. 2010-11-24T17:46:52Z http://hdl.handle.net/2099.1/8323 Title: Computational study of the smoke propagation in a library Authors: Dolgov, Vitaly Abstract: A firе еmеrgеncy in a univеrsity (Е.T.S.Е.I.B., UPC) library has bееn numеrically studiеd using CFD simulation (Firе Dynamics Simulator) for indoor propagation of hazardous smokе. Thе 3D-CFD simulation was pеrformеd using a modеl of a firе drivеn fluid flow whеrе thе partial dеrivativеs of consеrvation еquations arе approximatеd as finitе diffеrеncеs, and thе solution is discrеtisеd on a thrее-dimеnsional rеctilinеar grid. Thе corе algorithm is an еxplicit prеdictor-corrеctor schеmе that is sеcond ordеr accuratе in spacе and timе. Turbulеncе is trеatеd by mеans of thе Smagorinsky form of Largе Еddy Simulation (LЕS). Radiation hеat transfеr is computеd using a finitе volumе tеchniquе on thе samе grid as thе hydrodynamic flow solvеr. Rеsults dеmonstratе important fеaturеs of thе smokе propagation within thе library еnclosurе as a function of timе, whilе thе еffеct of using thе radiation modеl on thе outputs has bееn studiеd. 2010-01-08T19:52:21Z http://hdl.handle.net/2099.1/8317 Title: Solving the inverse kinematics of an anthropomorphic hand for grasping applications Authors: Caetano Ferreira, Thiago Abstract: The use of anthropomorphic manipulators is a problem faced nowadays in the general industry. When compared to conventional grippers they present two potential advantages: higher grip stability and the possibility to grasp arbitrary shapes. Being in constant development, the robotic grasping with these manipulators still has a large field to be discovered. This work covers all the parts related to the development and implementation of an algorithm able to obtain a valid configuration to an anthropomorphic hand, having 31 degrees of freedom, for grasping applications. The program proposed uses the interactive jacobian method to obtain the solution respecting the constraints. The result obtained shows the importance of defining an initial position to start solving the inverse kinematics. A method proposed in this work to define this position has improved the number of valid solutions from 7 to 58% of the cases, in an average time of 28 seconds. Nevertheless, as future work, the method used can be improved and the fusion of this software with the Kautham platform will lead to a robust system for solving grasping tasks. 2010-01-07T19:27:28Z http://hdl.handle.net/2099.1/8314 Title: CFD study of the gas carry-under in a gas-liquid compact cyclone (GLCC TM) separator using a mixture model Authors: Nkengue Tsobguin, Bienvenue Abstract: A three‐dimensional CFD study of the two‐phase flow field in a Gas‐Liquid Cylindrical Cyclone (GLCC) using the finite volume‐based finite element method is presented. The numerical analysis was made for air‐water mixtures at near atmospheric conditions, while both liquid and gas flow rates were changed. The two‐phase flow behavior is modeled using an Eulerian‐Eulerian approach, considering both phases as an interpenetrating continuum. This method computed the inter‐phase phenomena by including a source term in the momentum equation to consider the drag between the liquid and gas phases. The gas‐liquid flow is modeled using an inhomogeneous mixture model, in order to capture the interfacial effects associated to the general complex interfacial boundaries. Results are compared to experiments and to results from a bi‐modal inhomogeneous particle model. The CFD technique here proposed, demonstrates to satisfactorily reproduce important features not easily depicted in experiments and not computed when using the particle model. Results show phase distributions and velocity profiles inside the GLCC, as well as the computed gas carry‐under for different operating conditions. 2010-01-07T18:35:44Z