L’estimation de la charge d’un satellite et du risque de décharge nécessite dans certains cas la prise en compte dans les modèles numériques d’échelles spatiales très différentes. En particulier, les interconnecteurs présents à la surface des générateurs solaires d’un satellite sont susceptibles de modifier son équilibre électrostatique lors de missions spatiales rencontrant un environnement plasma dense. Une modélisation classique de cet effet nécessiterait le maillage d’éléments à des échelles submillimétriques,sur un satellite de plusieurs dizaines de mètres d’envergure, ce qui rendrait la simulation extrêmement onéreuse en temps de calcul. De plus, ces interconnecteurs sont parfois fortement chargés positivement par rapport à l’environnement, ce qui empêche l’application du modèle de Maxwell-Boltzmann classiquement utilisé pour les populations d’électrons. Dans une première partie, nous avons développé une méthode itérative de type Patch adaptée à la résolution du problème non-linéaire de Poisson-Boltzmann pour la simulation du plasma spatial. Cette méthode numérique multigrille permet la simulation de l’impact d’éléments de petite taille à la surface d’un satellite complet. Dans une seconde partie, nous avons développé un schéma correctif permettant d’utiliser le modèle de Maxwell-Boltzmann pour la population d’électrons, malgré la présence de surfaces satellites chargées positivement, en y ajoutant un terme de correction calculé à l’aide de la méthode Particle-in-Cell. Nous avons montré que ce schéma permet, tout en limitant le coût en calculs, de déterminer avec précision les courants collectés par les surfaces du satellites, qu’elles soient chargées négativement ou positivement. / The numerical simulation of spacecraft charging can require to resolve widely different geometrical scales. In particular, solar array interconnects on the surface of solar panels have a major impact ona satellite electrostatic equilibrium. A classical model of this effect would require a mesh refined tosub-millimetre scales, on a spacecraft spanning several dozen metres, which would make the simulation computationally expensive. Moreover, the solar array interconnects can have a large positive potentialrelative to the space plasma, preventing the use of the classical Maxwell-Boltzmann model for theelectrons in the plasma. In a first part, we have developed an iterative patch method to solve thenonlinear Poisson-Boltzmann equation used in plasma simulations. This multigrid numerical scheme allows to resolve the impact of small-scale components on the surface of a complete spacecraft. In asecond part, we have developed a corrective scheme for the Maxwell-Boltzmann model to account for the presence of charged surfaces in the simulation. We have shown that this simple model is able to precisely compute the currents collected by the spacecraft surfaces.

Cette thèse propose différentes méthodes numériques pour simuler les plasmas ou les faisceaux de particules chargées à coût réduit. Le mouvement de particules chargées soumises à un champ électromagnétique est régi par l'équation de Vlasov, couplée aux équations de Maxwell ou de Poisson. Dans la première partie, une méthode multi-fluides est utilisée pour la résolution du système de Vlasov-Poisson 1D. Elle est basée sur la connaissance a priori de la forme prise par la fonction de distribution f. Ce type de méthodes est plutôt adapté aux systèmes restant proches de l'état d'équilibre. La deuxième partie propose de décomposer f en une partie d'équilibre et une perturbation. L'équilibre est résolu par une méthode fluide, la perturbation par une méthode cinétique plus précise. On construit un schéma préservant l'asymptotique pour le système de Vlasov-Poisson-BGK basé sur une telle décomposition. On étudie dans la troisième partie la méthode PIC en géométrie 2D axisymétrique. Un travail basé sur l'analyse isogéométrique est présenté ainsi qu'un code PIC - Galerkin Discontinu parallélisé sur carte graphique. / This thesis presents different numerical methods for the simulation of plasmas or charged particles beams with reduced cost. Movement of charged particles in an electromagnetic field is given by the Vlasov equation, coupled to the Maxwell equations for the electromagnetic field, or to the Poisson equation. In the first part, a multi-fluid method is used for solving the 1D Vlasov-Poisson system. It is based on the a priori knowledge of the shape of f. This kind of methods is rather adapted to systems staying close to the equilibrium. The second part presents the decomposition of f between an equilibrium part and a perturbation. The equilibrium part is solved by a fluid method whereas we use a kinetic method for the perturbation. We construct an asymptotic preserving scheme for the Vlasov-Poisson-BGK system using such a decomposition. The third part deals with the PIC method in 2D axisymmetric geometry. A work based on isogeometric analysis is presented, and then a PIC - Discontinuous Galerkin program computed on graphic card.

Dans ces travaux, nous présentons des méthodes d'optimisation théoriques et numériques pour la conception optimale de circuits magnétiques pour propulseurs à effet Hall. Ces problèmes de conception sont des problèmes inverses très difficiles à résoudre que nous formulons sous forme de problèmes d'optimisation topologique. Les problèmes resultant sont non convexes avec des contraintes aux équations différentielles de Maxwell. Au cours de ces travaux, des approches originales ont été proposées afin de résoudre efficacement ces problèmes d'optimisation topologique. L'approche de densité de matériaux SIMP (Solid Isotropic Material with Penalization) qui est une variante de la méthode d'homogénéisation a été privilégiées. De plus, les travaux de ma thèse ont permis la mise en place de codes d'optimisation dénommé ATOP (Algorithm To Optimize Propulsion) utilisant en parallèle les logiciels de calculs scientifiques Matlab et d'élément finis FEMM (Finite Element Method Magnetics). Dans ATOP, nous utilisant à la fois des algorithmes d'optimisation locale de type descente basés sur une analyse de la sensibilité du problème et des algorithmes d'optimisation globale principalement de type Branch and Bound basés sur l'Arithmétique des Intervals. ATOP permettra d'optimiser à la fois la forme topologique des circuits magnétiques mais aussi le temps et le coût de production de nouvelles génération de propulseurs électriques. / In this work, we present theoretical and numerical optimization method for designing magnetic circuits for Hall effect thrusters. These design problems are very difficult inverse ones that we formulate under the form of topology optimization problems. Then, the obtained problems are non convex subject to Maxwell equations like constraints. Some original approaches have been proposed to solve efficiently these topology optimization problems. These approaches are based on the material density model called SIMP approach (Solid Isotropic Material with Penalization) which is a variante of the homogenization method. The results in my thesis allowed to provide optimization source code named ATOP (Algorithm To Optimize Propulsion) unsung in parallel two scientific computing softwares namely Matlab and FEMM (Finite Element Method Magnetics). In ATOP, we use both local optimization algorithms based on sensitivity analysis of the design problem; and global optimization algorithms mainly of type Branch and Bound based on Interval Arithmetic analysis. ATOP will help to optimize both the topological shape of the magnetic circuits and the time and cost of production (design process) of new generations of electrical thrusters.

Made available in DSpace on 2016-06-02T20:27:38Z (GMT). No. of bitstreams: 1 3466.pdf: 565162 bytes, checksum: 770041f07c68eda588bd0c501dabe93d (MD5) Previous issue date: 2011-02-10 / Financiadora de Estudos e Projetos / In this work we analyze the existence of radially symmetric solutions, positive solutions as well as the existence of ground state solutions for a class of Klein-Gordon-Maxwell equations when the nonlinearity exhibits critical behavior. For the positive and ground state solutions we prove existence results when a potential V is introduced. In order to obtain such results, we use variational methods / Neste trabalho analisamos a existência de soluções radialmente simétricas, soluções positivas, bem como a existência de soluções ground state para uma classe de equações do tipo Klein-Gordon-Maxwell quando a não-linearidade exibe comportamento crítico. Para as soluções positivas e do tipo ground state provamos resultados de existência quando um potencial V é introduzido. A fim de obtermos tais resultados, usamos métodos variacionais.

Submitted by Aelson Maciera (aelsoncm@terra.com.br) on 2017-04-25T19:31:06Z No. of bitstreams: 1 TeseSMP.pdf: 1382232 bytes, checksum: 8758d122cc415ab540988c4f92e38cc8 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-05-02T13:03:01Z (GMT) No. of bitstreams: 1 TeseSMP.pdf: 1382232 bytes, checksum: 8758d122cc415ab540988c4f92e38cc8 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-05-02T13:03:17Z (GMT) No. of bitstreams: 1 TeseSMP.pdf: 1382232 bytes, checksum: 8758d122cc415ab540988c4f92e38cc8 (MD5) / Made available in DSpace on 2017-05-02T13:06:24Z (GMT). No. of bitstreams: 1 TeseSMP.pdf: 1382232 bytes, checksum: 8758d122cc415ab540988c4f92e38cc8 (MD5) Previous issue date: 2015-11-26 / Não recebi financiamento / The main aim of this work is to develop alternative queuing models to M/ G/l, in which arrivals follow a Poisson process, the total number of customers on the system and the total number of service channels are unknown. Our interest is just to observe the service channel that will offer the maximum or minimum service time. Wherefore, the service distributions are obtained from the composition of the Conwav-Maxwell-Poisson distribution truncated at zero, used to model the number of service channels, with the general distribution to the maximum and minimum service time. Thus, we obtain new distributions for service time, which are called Maximum-Conwav-Maxwell-Poisson-general, denoted by MAXCOMPG distribution, and Minimum-Conwav-Maxwell-Poisson-general, denoted by MINCOMPG distribution, consequently, we obtain the queue models M/MAXCOMPG/1 and M/MINCOMPG/ 1, respectively. As general distributions, we use the distributions exponential, Weibull and Birnbaum Saunders, To illustrate the proposed queue models, a simulation study is done and also real data are used. / Este trabalho tem como objetivo apresentar modelos de filas alternativos ao M/G/l, nos quais as chegadas seguem um processo de Poisson, o número total de usuários no sistema e o número total de canais de atendimento são desconhecidos. Neste caso, observamos apenas o canal de serviço que irá oferecer o máximo ou o mínimo tempo de serviço. Para isto, as distribuições de serviço são obtidas a partir da composição da distribuição Conwav-Maxwell-Poisson truncada no ponto zero, usada para modelar o número de canais de atendimento, com uma distribuição geral para o máximo e o mínimo tempos de serviço. Desta forma, surgem novas distribuições de serviço que são denominadas de Máximo-Conwav-Maxwell-Poisson-geral, denotada por distribuição MAXCOMPG, e Mínimo-Conwav-Maxwell-Poisson-geral, denotada por distribuição MINCOMPG, e, assim, obtemos os modelos de fila M MAXCOMPG 1 e M MINCOMPG 1. Como distribuições gerais usamos as distribuições exponencial, Weibull e Birnbaum Saunders, Para ilustrar os modelos de fila propostos um amplo estudo de simulação é feito e dados reais também são utilizados.

Orientador: Luiz Fernando Bovolato / Banca: Sérgio Kurokawa / Banca: Afonso José do Prado / Resumo: Este trabalho analisa a aplicação em linhas de transmissão do método dos elementos de contorno para cálculo de potencial e campo elétrico, com um enfoque em eletrostática. O método dos elementos de contorno baseia-se numa formulação integral que elimina a discretização do domínio, restando apenas o contorno, permitindo o cálculo do potencial e do campo elétrico no contorno e na região estudada. O trabalho configura-se como uma revisão sobre eletrostática, ressaltando as equações de Laplace e Poisson, que serão utilizadas para encontrar as equações integrais do contorno. Há também vários tópicos relacionados ao campo elétrico de linhas de transmissão, bem como, ás normas brasileiras e recomendações internacionais que devem ser utilizadas no projeto de linhas de transmissão. O método dos elementos de contorno utiliza tais equações integrais para encontrar o potencial e o campo no contorno, e após conhecidos o potencial e o campo no contorno, pode-se aplicar o método em todo o domínio, obtendo o potencial e o campo. Para isso, apenas o contorno do domínio de interesse deve ser discretizado, o que trás uma enorme vantagem sobre os métodos que utilizam formulação diferencial. Neste trabalho, serão descritas as principais características do código computacional desenvolvido e suas sub-rotinas mais importantes. Para validar o programa, os resultados serão comparados com aqueles calculados por um procedimento analítico, sendo mostrada a eficiência da discretização do solo. São apresentados os resultados obtidos da análise do campo elétrico gerado por algumas silhuetas de linhas de transmissão. Os valores do campo elétrico gerado por estruturas compactas são comparados com estruturas convencionais e estruturas reduzidas (semi-compactas), também serão comparados os valores do gradiente de potencial na superfície dos condutores e suas capacitâncias equivalentes. / Abstract: This paper analyses the application in transmission lines of the Boundary Element Method (BEM) of the calculation of potential and electric field, with a focus on electrostatic. The Boundary Element Method is based on an integral formulation that eliminates the discretisation of the domain, remaining only the contour, allowing the calculation of the potential and the electric field in the contour and in the region studied. The work is configured as revision on electrostatic, underscoring the equations of Laplace and Poisson, which will be used to find the integral equations of the contour. There are also several topics related to the electric field of transmission lines, as well as to the standards Brazilian and international recommendations to be used in the design of transmission lines. The Boundary Element Method uses such integral equations for finding the potential and electric field in the contour, and after having known the potential and electric field in the contour, the BEM can be applied in the whole domain, and getting the potential and electric field. Therefore, only the contours of the domain of interest should just be discretized, which backward an enormous advantage on the methods that use formulation differential. This paper will describe the main characteristics of computer code developed and their sub-routines more important. To validate the program, the results will be compared with those calculated by an analytic procedure, being shown the efficiency of discretisation of the soil. The results obtained from analysis of the electric field generated by some silhouettes of transmission lines are presented. The values of the electric field generated by compact structures are compared with conventional structures and reduced structures, also will be compared the values of the gradient of potential on the surface of the conductors and their equivalents capacitances. / Mestre

Este trabalho tem como objetivo desenvolver um método numérico para simular escoamentos incompressíveis, isotérmicos, confinados ou com superfícies livres, de fuidos viscoelásticos governados pelos modelos integrais de Maxwell e K-BKZ (Kaye-Bernstein, Kearsley e Zapas). A técnica numérica apresentada é uma extensão do método GENSMAC (Tomé McKee - J. Comp. Phys., (110), pp 171--186, 1994 ) para a solução das equações de conservação, juntamente com as equações constitutivas integrais de Maxwell e K-BKZ. As equações governantes são resolvidas pelo método de diferenças finitas em uma malha deslocada. O tensor de Finger, B_t\'(t) é calculado com base nas idéias do método de campos de deformação (Peters et al. - J. Non-Newtonian Fluid Mech. (89), de maneira que não há a necessidade de seguir a trajetória da partícula de fuido para descrever a história de deformação da partícula. Uma abordagem diferente para a discretização do instante passado é utilizada e o tensor de Finger e o tensor das tensões são calculados utilizando um método de segunda ordem. A validação do método numérico descrito nesse trabalho foi feita utilizando o escoamento em um canal bidimensional e a solução numérica obtida para a velocidade e para as componentes de tensão com o modelo de Maxwell foram comparadas com as respectivas soluções analíticas no estado estacionário, mostrando excelente concordância. Os resultados numéricos para a simulação do escoamento em uma contração planar 4 : 1 mostraram bons resultados, tanto qualitativos quanto quantitativos, quando comparados com os resultados experimentais de Quinzani et al. ( J. Non-Newtonian Fluid Mech. (52), pp 1?36, 1994 ). Além disso, utilizando os modelos Maxwel e K-BKZ, o escoamento em uma contração planar 4 : 1 foi simulado para vários números de Weissenberg e os resultados obtidos estão de acordo com os encontrados na literatura. Resultados numéricos de escoamentos com superfícies livres modelados pelas equações integrais de Maxwell e K-BKZ são apresentados. Em particular, a simulação numérica do jato oscilante para diferentes números de Weissenberg e diferentes números de Reynolds é apresentada. / The aim of this work is to develop a numerical technique for simulating incompressible, isothermal, free surface (also con¯ned) viscoelastic flows of fuids governed by the integral models of Maxwell and K-BKZ (Kaye-Bernstein, Kearsley and Zapas). The numerical technique described herein is an extension of the GENSMAC method (Tome and McKee, J. Comput. Phys., 110, pp. 171-186, 1994) to the solution of the momentuum and mass conservation equations together with the integral constitutive Maxwell and K-BKZ equations. The governing equations are solved by the finite difference method on a staggered grid using a Marker-and-Cell approach. The fluid is represented by marker particles on the fluid surface only. This provides the visualization and location of the fluid free surface so that the free surface stress conditions can be applied. The Finger tensor Bt0(t) is computed using the ideias of the deformation fields method (Peters et al. J. Non-Newtonian Fluid Mech., 89, pp. 209-228, 2001) so that it is not necessary to track a fluid particle in order to calculate its deformation history. However, in this work modifcations to the deformation fields method are introduced: the past time is discretized using a different formula, the Finger tensor Bt0(x; t) is obtained by a second order method and the stress tensor ? (x; t) is computed by a second order quadrature formula. The numerical method presented in this work is validated by simulating the flow of a Maxwell fluid in a two-dimensional channel and the numerical solutions of the velocity and the stress components are compared with the respective analytic solutions providing a good agreement. Further, the flow through a 4:1 planar contraction of a specific fuid studied experimentally by Quinzani et al. (J. Non-Newtonian Fluid Mech., 52, pp. 1-36, 1994) was simulated and the numerical results were compared qualitatively and quantitatively with the experimental results and very good agreement was obtained. The Maxwell and the K-BKZ models were applied to simulate the 4:1 planar contraction problem using various Weissenberg numbers and the numerical results were in agreement with those published in the literature. Finally, numerical results of free surface flows using the Maxwell and K-BKZ integral constitutive equations are presented. In particular, the numerical simulation of jet buckling using several Weissenberg numbers and various Reynolds numbers are presented

Orientador: Hugo Enrique Hernandez Figueroa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-05T08:10:41Z (GMT). No. of bitstreams: 1 Santos_CarlosHenriquedaSilva_M.pdf: 1752834 bytes, checksum: 8ed5b0902bb130762ff802db03187fbb (MD5) Previous issue date: 2005 / Resumo: Esse trabalho tem por objetivo desenvolver soluções computacionais de alto desempenho a um baixo custo, seguindo as propostas incentivadoras do Governo Federal para adoção de software livre. Essas soluções possibilitam simular, de maneira eficiente, os domínios computacionais de médio e grande porte utilizados no eletromagnetismo computacional. Os bons resultados obtidos nesse trabalho mostram a importância e eficiência da computação massivamente paralela utilizando cluster Beowulf para o processamento do método FDTD aplicado em estruturas complexas, porém a um baixo custo financeiro. O desempenho desse sistema ficou comprovado na realização de experimentos para analisar a SAR na cabeça humana e estudar os efeitos de estruturas metamateriais / Abstract: This work has as objective to develop high performance computational solutions to a low cost, following the stimulated proposals of the Federal Government for adoption of free software. They make possible to simulate, in efficient way, the computational domains of middle and high size useful on the computational electromagnetism. The good results gotten in these work showed the importance and efficiency of the massive parallel computation using the Beowulf cluster for the process the FDTD method applied on complex structures, however to a low financial cost. The performance of this system was proved in the realization of experiments to analyze the SAR on the human head and to study the effects of metamarial structures / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Dans une première partie, une nouvelle méthodologie, précise et hautement sensible de caractérisation des paramètres thermiques de liquides par radiométrie photothermique est ici présentée. Deux configurations expérimentales sont proposées. Elles ont été testées et validées avec des matériaux liquides usuels aux paramètres thermiques connus. Par la suite, cette démarche a été utilisée pour l'étude de polymères dispersés dans des cristaux liquides. Les propriétés thermiques dynamiques de chaque échantillon ont été mesurées en fonction de l'amplitude du champ électrique appliqué à une fréquence donnée aussi bien qu'en fonction de la fréquence du champ électrique à une amplitude fixe. Cette étude a montré que les propriétés thermiques étaient sujettes aux effets du champ de dépolarisation aux basses fréquences. La seconde partie de ce manuscrit décrit la nouvelle technique photothermique basée sur l'effet thermoélectrique. Cette technique est utile pour caractériser thermiquement les matériaux thermoélectriques sans avoir à recourir à un capteur extérieur pour mesurer le changement de température. Une étude théorique et expérimentale est présentée. Ces expériences ont été réalisées avec des composites polyaniline/nanotubes de carbone par mesure de la tension générée par l'échantillon thermoélectrique chauffé par un faisceau laser. Des mesures additionnelles à l'aide de la radiométrie infrarouge sur ces mêmes échantillons ont été entreprises et les résultats sont en bon accord avec ceux précédemment trouvés. Enfin, la possibilité d'utiliser les matériaux thermoélectriques comme capteur photothermique au travers d'une cavité résonnante à ondes thermiques est évoquée. / Primarily, newly developed, high sensitive and accurate methods for thermal characterization of liquids using photothermal radiometry are presented. Two experimental configurations are suggested, tested and validated with usual liquid materials. These methods are used to study polymer dispersed liquid crystal samples. Dynamic thermal properties of samples are analysed verses amplitude varying applied electric field with constant frequency as well as versus frequency varying electric field with constant amplitude. Our results clearly show the thermal properties of the samples are prone to depolarizing field effects at the lower frequencies of the applied electric field. The experimental results are modeled against existing theories to predict electric properties of the sample composites. Second part of the manuscript describes the development of a novel photothermal technique based on thermoelectric effect. This technique is particularly useful for thermally characterizing thermoelectric materials without using a separate sensor for measuring induced temperature changes. A theoretical and experimental study is presented. The experiments are done on polyaniline - carbon nanotube composite pellets by measuring Seebeck voltage generated by the samples upon heating by a modulated laser beam. Additional infrared radiometry experiments are done on the same samples and the results are in good agreement with those previously found. Later on, the possibility of photothermoelectric materials to be used as sensors for finding thermal transport properties of materials with a thermal wave resonant cavity is suggested.

Notre étude porte sur des matériaux à effets relativistes importants. L'hamiltonien semi-relativiste, couplé aux équations de Maxwell (EM), permet de déduire les sources de courant et de densité, incluant des termes de second ordre (polarisations de spin et de Darwin). Différents modèles sont développés par expansion des EM. L'étude ab initio montre que (1) le désordre atomique peut produire le ferrimagnétisme (FM) dans GaFeO3 (GFO) multiferroïque, (2) les états 3d Fe des octaèdres déformés ont une levée de dégénérescence tétraédrique (théorie du champ cristallin), (3) la polarisation électrique concorde avec l'expérience, (4) le mécanisme magnétoélectrique (ME) direct est insuffisant pour expliquer le ME observé. Pour Cr2O3, le calcul de l'état massif sous contraintes biaxiales n'explique pas son FM, la taille de l'échantillon ou l'excès d'oxygène pourrait de fait être important. Enfin, nous avons développé le XAS et le XMCD dans le code VASP et calculé ces spectres pour GFO. / We studied the physics of materials where relativistic effects are important. We first coupled the semi-relativistic Hamiltonian with the Maxwell's equations, and derived the current and density sources, which included second-order terms like the spin and Darwin polarizations. Different models were developed, by expanding the Maxwell's equations. We then performed ab initio studies to explain (1) site disorders as the origin of ferrimagnetism in multiferroic GaFeO3 (GFO), (2) crystal-field theory where the Fe 3d states at the deformed octahedra have tetrahedral splittings, (3) the electric polarization as a function of temperature, and (4) the insufficiency of the direct magnetoelectric (ME) mechanism to explain observed ME behavior. For Cr2O3, bulk calculations for different biaxial strains failed to explain its ferromagnetism, indicating that size or excess-O effects might be important. Finally, we implemented XAS and XMCD in VASP and computed these spectra for GFO.