967 resultados para Numerical methods
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The analysis of deformation in soils is of paramount importance in geotechnical engineering. For a long time the complex behaviour of natural deposits defied the ingenuity of engineers. The time has come that, with the aid of computers, numerical methods will allow the solution of every problem if the material law can be specified with a certain accuracy. Boundary Techniques (B.E.) have recently exploded in a splendid flowering of methods and applications that compare advantegeously with other well-established procedures like the finite element method (F.E.). Its application to soil mechanics problems (Brebbia 1981) has started and will grow in the future. This paper tries to present a simple formulation to a classical problem. In fact, there is already a large amount of application of B.E. to diffusion problems (Rizzo et al, Shaw, Chang et al, Combescure et al, Wrobel et al, Roures et al, Onishi et al) and very recently the first specific application to consolidation problems has been published by Bnishi et al. Here we develop an alternative formulation to that presented in the last reference. Fundamentally the idea is to introduce a finite difference discretization in the time domain in order to use the fundamental solution of a Helmholtz type equation governing the neutral pressure distribution. Although this procedure seems to have been unappreciated in the previous technical literature it is nevertheless effective and straightforward to implement. Indeed for the special problem in study it is perfectly suited, because a step by step interaction between the elastic and flow problems is needed. It allows also the introduction of non-linear elastic properties and time dependent conditions very easily as will be shown and compares well with performances of other approaches.
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El presente Proyecto de Fin de Carrera supone el propsito conjunto de los alumnos lvaro Morillas y Fernando Sez, y del profesor Vladimir Ulin, de desarrollar una unidad didctica sobre el programa de simulacin para ingeniera Virtual.Lab. La versin sobre la que se ha trabajado para realizar este texto es la 11, publicada en agosto de 2012. Virtual.Lab, del fabricante belga LMS International, es una plataforma software de ingeniera asistida por ordenador, que agrupa en una misma aplicacin varias herramientas complementarias en el diseo de un producto, desde su definicin geomtrica a los anlisis de durabilidad, ruido u optimizacin. No obstante, de entre todas las posibles simulaciones que nos permite el programa, en este proyecto slo se tratan las que estn relacionadas con la acstica. Cabe resaltar que gran parte de los conceptos manejados en Virtual.Lab son compatibles con el programa CATIA V5, ya que ambos programas vienen instalados y funcionan conjuntamente. Por eso, el lector de este proyecto podr transportar sus conocimientos al que es uno de los programas estndar en las industrias aeronutica, naval y automovilstica, entre otras. Antes de este proyecto, otros alumnos de la escuela tambin realizaron proyectos de fin de carrera en el campo de la simulacin computarizada en acstica. Una caracterstica comn a estos trabajos es que era necesario hacer uso de distintos programas para cada una de las etapas de simulacin (como por ejemplo, ANSYS para el modelado y estudio de la vibracin y SYSNOISE para las simulaciones acsticas, adems de otros programas auxiliares para las traducciones de formato). Con Virtual.Lab desaparece esta necesidad y el tiempo empleado se reduce. Debido a que las soluciones por ordenador estn ganando cada vez ms importancia en la industria actual, los responsables de este proyecto consideran la necesidad de formacin de profesionales en esta rama. Para responder a la demanda empresarial de trabajadores cualificados, se espera que en los prximos aos los planes de estudio contengan ms cursos en esta materia. Por tanto la intencin de los autores es que este material sea de utilidad para el aprendizaje y docencia de estas asignaturas en cursos sucesivos. Por todo esto, se justifica la relevancia de este PFC como manual para introducir a los alumnos interesados en iniciarse en un sistema actual, de uso extendido en otras universidades tecnolgicas europeas, y con buenas perspectivas de futuro. En este proyecto se incluyen varios ejemplos ejecutables desde el programa, as como vdeos explicativos que ayudan a mostrar grficamente los procesos de simulacin. Estos archivos se pueden encontrar en el CD adjunto. Abstract This final thesis is a joint project made by the students lvaro Morillas and Fernando Sez, and the professor Vladimir Ulin. The nature of the joint regards the writing of a didactic unit on Virtual.Lab, the simulation software. The software version used in this text is the number 11, released in August 2012. Virtual.Lab, from the Belgian developer LMS International, is a computer-aided engineering software which is used for several related tasks in this field: product design, durability simulation, optimization, etc. However, this project is focused on the acoustical capabilities. It is worthy to highlight that most procedures explained in this text can be used in the software CATIA V5 as well. Both tools come installed together and may be used at the same time. Therefore, the reader of this project will be able to use the acquired knowledge in one of the most relevant softwares for the aerospace, marine and automotive engineering. Previously to the development of this project, this School has conducted projects on this field. These projects regarded the use of ANSYS for modeling and meshing stages as well as the use of SYSNOISE for the final acoustic analysis. Since both systems use different file formats, a third-party translation software was required. This thesis fulfill this pending necessity with Virtual.Lab; the translation software procedure is not necessary anymore and simulations can be done in a more flexible, fast way. Since companies have an increasing usage of numerical methods in the development of their products and services, the authors think that it is important to develop the appropriate method to instruct new professionals in the field. Thus, the aim of this project is to help teachers and students in their process of learning the use of this leading software in acoustical simulations. For all the reasons mentioned above, we consider that this project is relevant for the School and the educational community. Aiming to achieve this objective the author offers example files and video demonstrations with guidance in the CD that accompanies this material. This facilitates the comprehension of the practical tasks and guides the prospect users of the software.
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El objetivo principal de esta tesis es el desarrollo de herramientas numricas basadas en tcnicas de onda completa para el diseo asistido por ordenador (Computer-Aided Design,CAD) de dispositivos de microondas. En este contexto, se desarrolla una herramienta numrica basada en el mtodo de los elementos finitos para el diseo y anlisis de antenas impresas mediante algoritmos de optimizacin. Esta tcnica consiste en dividir el anlisis de una antena en dos partes. Una parte de anlisis 3D que se realiza slo una vez en cada punto de frecuencia de la banda de funcionamiento donde se sustituye una superficie que contiene la metalizacin del parche por puertas artificiales. En una segunda parte se inserta entre las puertas artificiales en la estructura 3D la superficie soportando una metalizacin y se procede un anlisis 2D para caracterizar el comportamiento de la antena. La tcnica propuesta en esta tesis se puede implementar en un algoritmo de optimizacin para definir el perfil de la antena que permite conseguir los objetivos del diseo. Se valida experimentalmente dicha tcnica emplendola en el diseo de antenas impresas de banda ancha para diferentes aplicaciones mediante la optimizacin del perfil de los parches. Tambin, se desarrolla en esta tesis un procedimiento basado en el mtodo de descomposicin de dominio y el mtodo de los elementos finitos para el diseo de dispositivos pasivos de microonda. Se utiliza este procedimiento en particular para el diseo y sintona de filtros de microondas. En la primera etapa de su aplicacin se divide la estructura que se quiere analizar en subdominios aplicando el mtodo de descomposicin de dominio, este proceso permite analizar cada segmento por separado utilizando el mtodo de anlisis adecuado dado que suele haber subdominios que se pueden analizar mediante mtodos analticos por lo que el tiempo de anlisis es ms reducido. Se utilizan mtodos numricos para analizar los subdominios que no se pueden analizar mediante mtodos analticos. En esta tesis, se utiliza el mtodo de los elementos finitos para llevar a cabo el anlisis. Adems de la descomposicin de dominio, se aplica un proceso de barrido en frecuencia para reducir los tiempos del anlisis. Como mtodo de orden reducido se utiliza la tcnica de bases reducidas. Se ha utilizado este procedimiento para disear y sintonizar varios ejemplos de filtros con el fin de comprobar la validez de dicho procedimiento. Los resultados obtenidos demuestran la utilidad de este procedimiento y confirman su rigurosidad, precisin y eficiencia en el diseo de filtros de microondas. ABSTRACT The main objective of this thesis is the development of numerical tools based on full-wave techniques for computer-aided design CAD of microwave devices. In this context, a numerical technique based on the finite element method FEM for the design and analysis of printed antennas using optimization algorithms has been developed. The proposed technique consists in dividing the analysis of the antenna in two stages. In the first stage, the regions of the antenna which do not need to be modified during the CAD process are initially characterized only once from their corresponding matrix transfer function (Generalized Admittance matrix, GAM). The regions which will be modified are defined as artificial ports, precisely the regions which will contain the conducting surfaces of the printed antenna. In a second stage, the contour shape of the conducting surfaces of the printed antenna is iteratively modified in order to achieve a desired electromagnetic performance of the antenna. In this way, a new GAM of the radiating device which takes into account each printed antenna shape is computed after each iteration. The proposed technique can be implemented with a genetic algorithm to achieve the design objectives. This technique is validated experimentally and applied to the design of wideband printed antennas for different applications by optimizing the shape of the radiating device. In addition, a procedure based on the domain decomposition method and the finite element method has been developed for the design of microwave passive devices. In particular, this procedure can be applied to the design and tune of microwave filters. In the first stage of its implementation, the structure to be analyzed is divided into subdomains using the domain decomposition method; this process allows each subdomains can be analyzed separately using suitable analysis method, since there is usually subdomains that can be analyzed by analytical methods so that the time of analysis is reduced. For analyzing the subdomains that cannot be analyzed by analytical methods, we use the numerical methods. In this thesis, the FEM is used to carry out the analysis. Furthermore the decomposition of the domain, a frequency sweep process is applied to reduce analysis times. The reduced order model as the reduced basis technique is used in this procedure. This procedure is applied to the design and tune of several examples of microwave filters in order to check its validity. The obtained results allow concluding the usefulness of this procedure and confirming their thoroughness, accuracy and efficiency for the design of microwave filters.
Resumo:
In this chapter, we are going to describe the main features as well as the basic steps of the Boundary Element Method (BEM) as applied to elastostatic problems and to compare them with other numerical procedures. As we shall show, it is easy to appreciate the adventages of the BEM, but it is also advisable to refrain from a possible unrestrained enthusiasm, as there are also limitations to its usefulness in certain types of problems. The number of these problems, nevertheless, is sufficient to justify the interest and activity that the new procedure has aroused among researchers all over the world. Briefly speaking, the most frequently used version of the BEM as applied to elastostatics works with the fundamental solution, i.e. the singular solution of the governing equations, as an influence function and tries to satisfy the boundary conditions of the problem with the aid of a discretization scheme which consists exclusively of boundary elements. As in other numerical methods, the BEM was developed thanks to the computational possibilities offered by modern computers on totally "classical" basis. That is, the theoretical grounds are based on linear elasticity theory, incorporated long ago into the curricula of most engineering schools. Its delay in gaining popularity is probably due to the enormous momentum with which Finite Element Method (FEM) penetrated the professional and academic media. Nevertheless, the fact that these methods were developed before the BEM has been beneficial because de BEM successfully uses those results and techniques studied in past decades. Some authors even consider the BEM as a particular case of the FEM while others view both methods as special cases of the general weighted residual technique. The first paper usually cited in connection with the BEM as applied to elastostatics is that of Rizzo, even though the works of Jaswon et al., Massonet and Oliveira were published at about the same time, the reason probably being the attractiveness of the "direct" approach over the "indirect" one. The work of Tizzo and the subssequent work of Cruse initiated a fruitful period with applicatons of the direct BEM to problems of elastostacs, elastodynamics, fracture, etc. The next key contribution was that of Lachat and Watson incorporating all the FEM discretization philosophy in what is sometimes called the "second BEM generation". This has no doubt, led directly to the current developments. Among the various researchers who worked on elastostatics by employing the direct BEM, one can additionallly mention Rizzo and Shippy, Cruse et al., Lachat and Watson, Alarcn et al., Brebbia el al, Howell and Doyle, Kuhn and Mhrmann and Patterson and Sheikh, and among those who used the indirect BEM, one can additionally mention Benjumea and Sikarskie, Butterfield, Banerjee et al., Niwa et al., and Altiero and Gavazza. An interesting version of the indirct method, called the Displacement Discontinuity Method (DDM) has been developed by Crounh. A comprehensive study on various special aspects of the elastostatic BEM has been done by Heisse, while review-type articles on the subject have been reported by Watson and Hartmann. At the present time, the method is well established and is being used for the solution of variety of problems in engineering mechanics. Numerous introductory and advanced books have been published as well as research-orientated ones. In this sense, it is worth noting the series of conferences promoted by Brebbia since 1978, wich have provoked a continuous research effort all over the world in relation to the BEM. In the following sections, we shall concentrate on developing the direct BEM as applied to elastostatics.
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The mechanical behavior of granular materials has been traditionally approached through two theoretical and computational frameworks: macromechanics and micromechanics. Macromechanics focuses on continuum based models. In consequence it is assumed that the matter in the granular material is homogeneous and continuously distributed over its volume so that the smallest element cut from the body possesses the same physical properties as the body. In particular, it has some equivalent mechanical properties, represented by complex and non-linear constitutive relationships. Engineering problems are usually solved using computational methods such as FEM or FDM. On the other hand, micromechanics is the analysis of heterogeneous materials on the level of their individual constituents. In granular materials, if the properties of particles are known, a micromechanical approach can lead to a predictive response of the whole heterogeneous material. Two classes of numerical techniques can be differentiated: computational micromechanics, which consists on applying continuum mechanics on each of the phases of a representative volume element and then solving numerically the equations, and atomistic methods (DEM), which consist on applying rigid body dynamics together with interaction potentials to the particles. Statistical mechanics approaches arise between micro and macromechanics. It tries to state which the expected macroscopic properties of a granular system are, by starting from a micromechanical analysis of the features of the particles and the interactions. The main objective of this paper is to introduce this approach.
Resumo:
En esta carta al editor, el profesor D. Enrique Alarcn lvarez comenta el artculo de Thomas J. Rudolphi "An implementation of the Boundary Element Method for zoned media with stress discontinuities" publicado en la revista "International Journal for Numerical Methods in Engineering" Vol. 19, N 1, pags. 115, enero 1983.
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Esta tesis doctoral est encuadrada dentro del marco general de la ingeniera biomdica aplicada al tratamiento de las enfermedades cardiovasculares, enfermedades que provocan alrededor de 1.9 millones (40%) de muertes al ao en la Unin Europea. En este contexto surge el proyecto europeo SCATh-Smart Catheterization, cuyo objetivo principal es mejorar los procedimientos de cateterismo artico introduciendo nuevas tecnologas de planificacin y navegacin quirrgica y minimizando el uso de fluoroscopa. En particular, esta tesis aborda el modelado y diagnstico de aneurismas articos abdominales (AAA) y del trombo intraluminal (TIL), all donde est presente, as como la segmentacin de estas estructuras en imgenes preoperatorias de RM. Los modelos fsicos especficos del paciente, construidos a partir de imgenes mdicas preoperatorias, tienen mltiples usos, que van desde la evaluacin preoperatoria de estructuras anatmicas a la planificacin quirrgica para el guiado de catteres. En el diagnstico y tratamiento de AAA, los modelos fsicos son tiles a la hora de evaluar diversas variables biomecnicas y fisiolgicas de las estructuras vasculares. Existen mltiples tcnicas que requieren de la generacin de modelos fsicos que representen la anatoma vascular. Una de las principales aplicaciones de los modelos fsicos es el anlisis de elementos finitos (FE). Las simulaciones de FE para AAA pueden ser especficas para el paciente y permiten modelar estados de estrs complejos, incluyendo los efectos provocados por el TIL. La aplicacin de mtodos numricos de anlisis tiene como requisito previo la generacin de una malla computacional que representa la geometra de inters mediante un conjunto de elementos polidricos, siendo los hexadricos los que presentan mejores resultados. En las estructuras vasculares, generar mallas hexadricas es un proceso especialmente exigente debido a la compleja anatoma 3D ramificada. La mayora de los AAA se encuentran situados en la bifurcacin de la arteria aorta en las arterias iliacas y es necesario modelar de manera fiel dicha bifurcacin. En el caso de que la sangre se estanque en el aneurisma provocando un TIL, ste forma una estructura adyacente a la pared artica. De este modo, el contorno externo del TIL es el mismo que el contorno interno de la pared, por lo que las mallas resultantes deben reflejar esta particularidad, lo que se denomina como "mallas conformadas". El fin ltimo de este trabajo es modelar las estructuras vasculares de modo que proporcionen nuevas herramientas para un mejor diagnstico clnico, facilitando medidas de riesgo de rotura de la arteria, presin sistlica o diastlica, etc. Por tanto, el primer objetivo de esta tesis es disear un mtodo novedoso y robusto para generar mallas hexadricas tanto de la pared artica como del trombo. Para la identificacin de estas estructuras se utilizan imgenes de resonancia magntica (RM). Deben mantenerse sus propiedades de adyacencia utilizando elementos de alta calidad, prestando especial atencin al modelado de la bifurcacin y a que sean adecuadas para el anlisis de FE. El mtodo tiene en cuenta la evolucin de la lnea central del vaso en el espacio tridimensional y genera la malla directamente a partir de las imgenes segmentadas, sin necesidad de reconstruir superficies triangulares. Con el fin de reducir la intervencin del usuario en el proceso de generacin de las mallas, es tambin objetivo de esta tesis desarrollar un mtodo de segmentacin semiautomtica de las distintas estructuras de inters. Las principales contribuciones de esta tesis doctoral son: 1. El diseo, implementacin y evaluacin de un algoritmo de generacin de mallas hexadricas conformadas de la pared y el TIL a partir de los contornos segmentados en imgenes de RM. Se ha llevado a cabo una evaluacin de calidad que determine su aplicabilidad a mtodos de FE. Los resultados demuestran que el algoritmo desarrollado genera mallas conformadas de alta calidad incluso en la regin de la bifurcacin, que son adecuadas para su uso en mtodos de anlisis de FE. 2. El diseo, implementacin y evaluacin de un mtodo de segmentacin automtico de las estructuras de inters. La luz arterial se segmenta de manera semiautomtica utilizando un software disponible a partir de imgenes de RM con contraste. Los resultados de este proceso sirven de inicializacin para la segmentacin automtica de las caras interna y externa de la pared artica utilizando mtodos basado en modelos de textura y forma a partir de imgenes de RM sin contraste. Los resultados demuestran que el algoritmo desarrollado proporciona segmentaciones fieles de las distintas estructuras de inters. En conclusin, el trabajo realizado en esta tesis doctoral corrobora las hiptesis de investigacin postuladas, y pretende servir como aportacin para futuros avances en la generacin de modelos fsicos de geometras biolgicas. ABSTRACT The frame of this PhD Thesis is the biomedical engineering applied to the treatment of cardiovascular diseases, which cause around 1.9 million deaths per year in the European Union and suppose about 40% of deaths per year. In this context appears the European project SCATh-Smart Catheterization. The main objective of this project is creating a platform which improves the navigation of catheters in aortic catheterization minimizing the use of fluoroscopy. In the framework of this project, the specific field of this PhD Thesis is the diagnosis and modeling of abdominal aortic aneurysm (AAAs) and the intraluminal thrombus (ILT) whenever it is present. Patient-specific physical models built from preoperative imaging are becoming increasingly important in the area of minimally invasive surgery. These models can be employed for different purposes, such as the preoperatory evaluation of anatomic structures or the surgical planning for catheter guidance. In the specific case of AAA diagnosis and treatment, physical models are especially useful for evaluating pressures over vascular structures. There are multiple techniques that require the generation of physical models which represent the target anatomy. Finite element (FE) analysis is one the principal applications for physical models. FE simulations for AAA may be patient-specific and allow modeling biomechanical and physiological variables including those produced by ILT, and also the segmentation of those anatomical structures in preoperative MR images. Applying numeric methods requires the generation of a proper computational mesh. These meshes represent the patient anatomy using a set of polyhedral elements, with hexahedral elements providing better results. In the specific case of vascular structures, generating hexahedral meshes is a challenging task due to the complex 3D branching anatomy. Each patients aneurysm is unique, characterized by its location and shape, and must be accurately represented for subsequent analyses to be meaningful. Most AAAs are located in the region where the aorta bifurcates into the iliac arteries and it is necessary to model this bifurcation precisely and reliably. If blood stagnates in the aneurysm and forms an ILT, it exists as a conforming structure with the aortic wall, i.e. the ILTs outer contour is the same as the walls inner contour. Therefore, resulting meshes must also be conforming. The main objective of this PhD Thesis is designing a novel and robust method for generating conforming hexahedral meshes for the aortic wall and the thrombus. These meshes are built using largely high-quality elements, especially at the bifurcation, that are suitable for FE analysis of tissue stresses. The method accounts for the evolution of the vessels centerline which may develop outside a single plane, and generates the mesh directly from segmented images without the requirement to reconstruct triangular surfaces. In order to reduce the user intervention in the mesh generation process is also a goal of this PhD. Thesis to develop a semiautomatic segmentation method for the structures of interest. The segmentation is performed from magnetic resonance image (MRI) sequences that have tuned to provide high contrast for the arterial tissue against the surrounding soft tissue, so that we determine the required information reliably. The main contributions of this PhD Thesis are: 1. The design, implementation and evaluation of an algorithm for generating hexahedral conforming meshes of the arterial wall and the ILT from the segmented contours. A quality inspection has been applied to the meshes in order to determine their suitability for FE methods. Results show that the developed algorithm generates high quality conforming hexahedral meshes even at the bifurcation region. Thus, these meshes are suitable for FE analysis. 2. The design, implementation and evaluation of a semiautomatic segmentation method for the structures of interest. The lumen is segmented in a semiautomatic way from contrast filled MRI using an available software. The results obtained from this process are used to initialize the automatic segmentation of the internal and external faces of the aortic wall. These segmentations are performed by methods based on texture and shape models from MRI with no contrast. The results show that the algorithm provides faithful segmentations of the structures of interest requiring minimal user intervention. In conclusion, the work undertaken in this PhD. Thesis verifies the investigation hypotheses. It intends to serve as basis for future physical model generation of proper biological anatomies used by numerical methods.
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La ecuacin en derivadas parciales de adveccin difusin con reaccin qumica es la base de los modelos de dispersin de contaminantes en la atmsfera, y los diferentes mtodos numricos empleados para su resolucin han sido objeto de amplios estudios a lo largo de su desarrollo. En esta Tesis se presenta la implementacin de un nuevo mtodo conservativo para la resolucin de la parte advectiva de la ecuacin en derivadas parciales que modela la dispersin de contaminantes dentro del modelo mesoescalar de transporte qumico CHIMERE. Este mtodo est basado en una tcnica de volmenes finitos junto con una interpolacin racional. La ventaja de este mtodo es la conservacin exacta de la masa transportada debido al empleo de la ley de conservacin de masas. Para ello emplea una formulacin de flujo basado en el clculo de la integral ponderada dentro de cada celda definida para la discretizacin del espacio en el mtodo de volmenes finitos. Los resultados numricos obtenidos en las simulaciones realizadas (implementando el modelo conservativo para la adveccin en el modelo CHIMERE) se han comparado con los datos observados de concentracin de contaminantes registrados en la red de estaciones de seguimiento y medicin distribuidas por la Pennsula Ibrica. Los datos estadsticos de medicin del error, la media normalizada y la media absoluta normalizada del error, presentan valores que estn dentro de los rangos propuestos por la EPA para considerar el modelo preciso. Adems, se introduce un nuevo mtodo para resolver la parte advectivadifusiva de la ecuacin en derivadas parciales que modeliza la dispersin de contaminantes en la atmsfera. Se ha empleado un mtodo de diferencias finitas de alto orden para resolver la parte difusiva de la ecuacin de transporte de contaminantes junto con el mtodo racional conservativo para la parte advectiva en una y dos dimensiones. Los resultados obtenidos de la aplicacin del mtodo a diferentes situaciones incluyendo casos acadmicos y reales han sido comparados con la solucin analtica de la ecuacin de adveccin-difusin, demostrando que el nuevo mtodo proporciona un resultado preciso para aproximar la solucin. Por ltimo, se ha desarrollado un modelo completo que contempla los fenmenos advectivo y difusivo con reaccin qumica, usando los mtodos anteriores junto con una tcnica de diferenciacin regresiva (BDF2). Esta tcnica consiste en un mtodo implcito multipaso de diferenciacin regresiva de segundo orden, que nos permite resolver los problemas rgidos tpicos de la qumica atmosfrica, modelizados a travs de sistemas de ecuaciones diferenciales ordinarias. Este mtodo hace uso de la tcnica iterativa Gauss- Seidel para obtener la solucin de la parte implcita de la frmula BDF2. El empleo de la tcnica de Gauss-Seidel en lugar de otras tcnicas comnmente empleadas, como la iteracin por el mtodo de Newton, nos proporciona rapidez de clculo y bajo consumo de memoria, ideal para obtener modelos operativos para la resolucin de la cintica qumica atmosfrica. ABSTRACT Extensive research has been performed to solve the atmospheric chemicaladvection- diffusion equation and different numerical methods have been proposed. This Thesis presents the implementation of an exactly conservative method for the advection equation in the European scale Eulerian chemistry transport model CHIMERE based on a rational interpolation and a finite volume algorithm. The advantage of the method is that the cell-integrated average is predicted via a flux formulation, thus the mass is exactly conserved. Numerical results are compared with a set of observation registered at some monitoring sites in Spain. The mean normalized bias and the mean normalized absolute error present values that are inside the range to consider an accurate model performance. In addition, it has been introduced a new method to solve the advectiondiffusion equation. It is based on a high-order accurate finite difference method to solve de diffusion equation together with a rational interpolation and a finite volume to solve the advection equation in one dimension and two dimensions. Numerical results obtained from solving several problems include academic and real atmospheric problems have been compared with the analytical solution of the advection-diffusion equation, showing that the new method give an efficient algorithm for solving such problems. Finally, a complete model has been developed to solve the atmospheric chemical-advection-diffusion equation, adding the conservative method for the advection equation, the high-order finite difference method for the diffusion equation and a second-order backward differentiation formula (BDF2) to solve the atmospheric chemical kinetics. The BDF2 is an implicit, second order multistep backward differentiation formula used to solve the stiff systems of ordinary differential equations (ODEs) from atmospheric chemistry. The Gauss-Seidel iteration is used for approximately solving the implicitly defined BDF solution, giving a faster tool than the more commonly used iterative modified Newton technique. This method implies low start-up costs and a low memory demand due to the use of Gauss-Seidel iteration.
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This paper deals with the boundary element method (BEM) p-convergence approach applied to three-dimensional problems governed by Laplace's equation. The advantages derived from the boundary discretization and hierarchical interpolation functions are collated in order to minimize human effort in preparation of input data and improve numerical results.
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The 1-diode/2-resistors electric circuit equivalent to a photovoltaic system is analyzed. The equations at particular points of the IV curve are studied considering the maximum number of terms. The maximum power point as a boundary condition is given special attention. A new analytical method is developed based on a reduced amount of information, consisting in the normal manufacturer data. Results indicate that this new method is faster than numerical methods and has similar (or better) accuracy than other existing methods, numerical or analytical.
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Los sistemas de seguimiento mono-cmara han demostrado su notable capacidad para el anlisis de trajectorias de objectos mviles y para monitorizacin de escenas de inters; sin embargo, tanto su robustez como sus posibilidades en cuanto a comprensin semntica de la escena estn fuertemente limitadas por su naturaleza local y monocular, lo que los hace insuficientes para aplicaciones realistas de videovigilancia. El objetivo de esta tesis es la extensin de las posibilidades de los sistemas de seguimiento de objetos mviles para lograr un mayor grado de robustez y comprensin de la escena. La extensin propuesta se divide en dos direcciones separadas. La primera puede considerarse local, ya que est orientada a la mejora y enriquecimiento de las posiciones estimadas para los objetos mviles observados directamente por las cmaras del sistema; dicha extensin se logra mediante el desarrollo de un sistema multi-cmara de seguimiento 3D, capaz de proporcionar consistentemente las posiciones 3D de mltiples objetos a partir de las observaciones capturadas por un conjunto de sensores calibrados y con campos de visin solapados. La segunda extensin puede considerarse global, dado que su objetivo consiste en proporcionar un contexto global para relacionar las observaciones locales realizadas por una cmara con una escena de mucho mayor tamao; para ello se propone un sistema automtico de localizacin de cmaras basado en las trayectorias observadas de varios objetos mviles y en un mapa esquemtico de la escena global monitorizada. Ambas lneas de investigacin se tratan utilizando, como marco comn, tcnicas de estimacin bayesiana: esta eleccin est justificada por la versatilidad y flexibilidad proporcionada por dicho marco estadstico, que permite la combinacin natural de mltiples fuentes de informacin sobre los parmetros a estimar, as como un tratamiento riguroso de la incertidumbre asociada a las mismas mediante la inclusin de modelos de observacin especficamente diseados. Adems, el marco seleccionado abre grandes posibilidades operacionales, puesto que permite la creacin de diferentes mtodos numricos adaptados a las necesidades y caractersticas especficas de distintos problemas tratados. El sistema de seguimiento 3D con mltiples cmaras propuesto est especficamente diseado para permitir descripciones esquemticas de las medidas realizadas individualmente por cada una de las cmaras del sistema: esta eleccin de diseo, por tanto, no asume ningn algoritmo especfico de deteccin o seguimiento 2D en ninguno de los sensores de la red, y hace que el sistema propuesto sea aplicable a redes reales de vigilancia con capacidades limitadas tanto en trminos de procesamiento como de transmision. La combinacin robusta de las observaciones capturadas individualmente por las cmaras, ruidosas, incompletas y probablemente contaminadas por falsas detecciones, se basa en un metodo de asociacin bayesiana basado en geometra y color: los resultados de dicha asociacin permiten el seguimiento 3D de los objetos de la escena mediante el uso de un filtro de partculas. El sistema de fusin de observaciones propuesto tiene, como principales caractersticas, una gran precisin en trminos de localizacin 3D de objetos, y una destacable capacidad de recuperacin tras eventuales errores debidos a un nmero insuficiente de datos de entrada. El sistema automtico de localizacin de cmaras se basa en la observacin de mltiples objetos mviles y un mapa esquemtico de las reas transitables del entorno monitorizado para inferir la posicin absoluta de dicho sensor. Para este propsito, se propone un novedoso marco bayesiano que combina modelos dinmicos inducidos por el mapa en los objetos mviles presentes en la escena con las trayectorias observadas por la cmara, lo que representa un enfoque nunca utilizado en la literatura existente. El sistema de localizacin se divide en dos sub-tareas diferenciadas, debido a que cada una de estas tareas requiere del diseo de algoritmos especficos de muestreo para explotar en profundidad las caractersticas del marco desarrollado: por un lado, anlisis de la ambigedad del caso especficamente tratado y estimacin aproximada de la localizacin de la cmara, y por otro, refinado de la localizacin de la cmara. El sistema completo, diseado y probado para el caso especfico de localizacin de cmaras en entornos de trfico urbano, podra tener aplicacin tambin en otros entornos y sensores de diferentes modalidades tras ciertas adaptaciones. ABSTRACT Mono-camera tracking systems have proved their capabilities for moving object trajectory analysis and scene monitoring, but their robustness and semantic possibilities are strongly limited by their local and monocular nature and are often insufficient for realistic surveillance applications. This thesis is aimed at extending the possibilities of moving object tracking systems to a higher level of scene understanding. The proposed extension comprises two separate directions. The first one is local, since is aimed at enriching the inferred positions of the moving objects within the area of the monitored scene directly covered by the cameras of the system; this task is achieved through the development of a multi-camera system for robust 3D tracking, able to provide 3D tracking information of multiple simultaneous moving objects from the observations reported by a set of calibrated cameras with semi-overlapping fields of view. The second extension is global, as is aimed at providing local observations performed within the field of view of one camera with a global context relating them to a much larger scene; to this end, an automatic camera positioning system relying only on observed object trajectories and a scene map is designed. The two lines of research in this thesis are addressed using Bayesian estimation as a general unifying framework. Its suitability for these two applications is justified by the flexibility and versatility of that stochastic framework, which allows the combination of multiple sources of information about the parameters to estimate in a natural and elegant way, addressing at the same time the uncertainty associated to those sources through the inclusion of models designed to this end. In addition, it opens multiple possibilities for the creation of different numerical methods for achieving satisfactory and efficient practical solutions to each addressed application. The proposed multi-camera 3D tracking method is specifically designed to work on schematic descriptions of the observations performed by each camera of the system: this choice allows the use of unspecific off-the-shelf 2D detection and/or tracking subsystems running independently at each sensor, and makes the proposal suitable for real surveillance networks with moderate computational and transmission capabilities. The robust combination of such noisy, incomplete and possibly unreliable schematic descriptors relies on a Bayesian association method, based on geometry and color, whose results allow the tracking of the targets in the scene with a particle filter. The main features exhibited by the proposal are, first, a remarkable accuracy in terms of target 3D positioning, and second, a great recovery ability after tracking losses due to insufficient input data. The proposed system for visual-based camera self-positioning uses the observations of moving objects and a schematic map of the passable areas of the environment to infer the absolute sensor position. To this end, a new Bayesian framework combining trajectory observations and map-induced dynamic models for moving objects is designed, which represents an approach to camera positioning never addressed before in the literature. This task is divided into two different sub-tasks, setting ambiguity analysis and approximate position estimation, on the one hand, and position refining, on the other, since they require the design of specific sampling algorithms to correctly exploit the discriminative features of the developed framework. This system, designed for camera positioning and demonstrated in urban traffic environments, can also be applied to different environments and sensors of other modalities after certain required adaptations.
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After a short introduction the possibilities and limitations of polynomial simple elements with C1 continuity are discussed with reference to plate bending analysis. A family of this kind of elements is presented.. These elements are applied to simple cases in order to assess their computational efficiency. Finally some conclusions are shown, and future research is also proposed.
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En este estudio se ha realizado el diseo de un receptor de una central de Torre Central de energa solar para generacin directa de vapor, mediante el uso de mtodos numricos, con un perfil de potencia incidente variable longitudinal y transversalmente. Para ello se ha dividido la geometra del receptor segn el mtodo de diferencias finitas, y se ha procedido a resolver las ecuaciones del balance de energa. Una vez resuelto el sistema de ecuaciones se dispone de la distribucin de temperaturas en el receptor y se puede proceder a analizar los resultados as como a calcular otros datos de inters. ABSTRACT In this study it has been made a Central Receiver Solar Thermal Power Plants Receiver design for direct steam production, by using numerical methods, with a variable longitudinally and transversely income solar power profile. With this propose, the receivers geometry has been divided using the finite difference method, and the energy balance equations have been solved. Once the equations system has been solved, the receivers temperature distribution is known, and you can analyze the results as well as calculate other interesting data.
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The solution to the problem of finding the optimum mesh design in the finite element method with the restriction of a given number of degrees of freedom, is an interesting problem, particularly in the applications method. At present, the usual procedures introduce new degrees of freedom (remeshing) in a given mesh in order to obtain a more adequate one, from the point of view of the calculation results (errors uniformity). However, from the solution of the optimum mesh problem with a specific number of degrees of freedom some useful recommendations and criteria for the mesh construction may be drawn. For 1-D problems, namely for the simple truss and beam elements, analytical solutions have been found and they are given in this paper. For the more complex 2-D problems (plane stress and plane strain) numerical methods to obtain the optimum mesh, based on optimization procedures have to be used. The objective function, used in the minimization process, has been the total potential energy. Some examples are presented. Finally some conclusions and hints about the possible new developments of these techniques are also given.
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This paper is devoted to the numerical analysis of bidimensional bonded lap joints. For this purpose, the stress singularities occurring at the intersections of the adherend-adhesive interfaces with the free edges are first investigated and a method for computing both the order and the intensity factor of these singularities is described briefly. After that, a simplified model, in which the adhesive domain is reduced to a line, is derived by using an asymptotic expansion method. Then, assuming that the assembly debonding is produced by a macro-crack propagation in the adhesive, the associated energy release rate is computed. Finally, a homogenization technique is used in order to take into account a preliminary adhesive damage consisting of periodic micro-cracks. Some numerical results are presented.