Η ανάπτυξη υπολογιστικών διαδικασιών που είναι σε θέση να προσομοιώσουν και να προβλέψουν με ακρίβεια την μηχανική συμπεριφορά και τις αστοχίες βασικών νανοδομών είναι ο σκοπός της παρούσας διατριβής. Οι υπολογιστικές διαδικασίες αναπτύσσονται βάσει των πεπερασμένων στοιχείων και στη συνέχεια εφαρμόζονται για να παρέχουν αριθμητικά αποτελέσματα σχετικά με την ελαστική, δυναμική και μη γραμμική συμπεριφορά των νανοδομών άνθρακα, όπως του γραφενίου, νιφάδες γραφίτη και νανοσωλήνων άνθρακα. Η μοριακή μηχανική θεωρία παρέχει τα πεδία δύναμης (εκφράσεις διατομικών αλληλεπιδράσεων) που χρησιμοποιούνται ως βάση για το φορμαλισμό πεπερασμένων στοιχείων-ελατηρίων. Η εξιδανικευμένη ατομιστική γεωμετρία των νανοδομών, όπως προκύπτει από την ελαχιστοποίηση της δυναμικής ενέργειας χρησιμοποιείται για να οριστεί η διακριτή γεωμετρία τους και κατ’ επέκταση η γεωμετρία των αντίστοιχων προτύπων πεπερασμένων στοιχείων. Επιπλέον, αναπτύσσονται μεθοδολογίες πεπερασμένων στοιχείων πολυ-κλίμακας για την πρόβλεψη της ελαστικής και μη γραμμικής συμπεριφοράς νανοσύνθετων ενισχυμένων με νανοσωλήνες άνθρακα. Αναπτύσσονται αντιπροσωπευτικά στοιχεία όγκου τα οποία βρίσκονται σε πλήρη συμφωνία με την μικρομηχανική θεωρία. Η ενισχυόμενη φάση, η οποία μπορεί να είναι πολυμερές, μέταλλικό ή ελαστομερές υλικό, αντιμετωπίζεται ως συνεχές μέσο, ενώ η ενίσχυση ως διακριτή δομή. Η διεπιφανειακή ζώνη μεταξύ μήτρας και ενίσχυση προσεγγίζεται με κατάλληλα στοιχεία συνδέσμους και οι ιδιότητες ακαμψίας τους υπολογίζονται με τη χρήση φυσικών υποθέσεων. Σε όλες τις περιπτώσεις, τα αποτελέσματα των προτεινόμενων μεθόδων συγκρίνονται με αντίστοιχες πειραματικές και θεωρητικές προβλέψεις, οι οποίες είναι διαθέσιμες στην διεθνή βιβλιογραφία, αποδεικνύοντας την υψηλή ακρίβεια πρόβλεψης των προτεινόμενων μεθόδων. / The development of computational procedures that are able to accurately simulate and predict the mechanical behaviour and failures of basic nanostructures is the aim of the present thesis. A spring based finite element method is developed and utilized to provide numerical results about the elastic, dynamic and nonlinear behaviour of major carbon allotropes, such as graphene, graphite flakes and carbon nanotubes. The molecular mechanics theory provides the force fields that are used as the base for the spring elements formulation. The optimized atomistic geometry of nanostructures as graphene nanoribbons, graphite flakes, as well as single and multi walled carbon nanotubes as derived by the potential energy minimization is used to be defined their discrete geometry and the corresponding finite element models. Furthermore, multi-scale finite element models are formulated for the prediction of elastic and nonlinear mechanical behavior of carbon nanotube reinforced nanocomposites. Representative volume elements are implemented according to the micromechanical theory. Matrix materials such polymers, metals or rubber are considered as continuum mediums, whereas the reinforcement is modeled as a discrete structure. The interfacial zone between matrix and reinforcement is approached by appropriate elements and their stiffness properties are computed by using physical assumptions. In all cases, the results of the proposed methods are compared with experimental and theoretical ones available in the literature demonstrating the high predicting accuracy of the proposed methods.

La théorie d'homogénéisation élastodynamique des matériaux hétérogènes initiée par J.R. Willis il y a environ une trentaine d'années a récemment reçu une très grande attention. D'après cette théorie qui est mathématiquement exacte, la loi constitutive homogénéisée est non locale en espace et en temps ; le tenseur des contraintes dépend non seulement du tenseur des déformations mais aussi de la vitesse ; la quantité du mouvement dépend à la fois de la vitesse et du tenseur des déformations, faisant apparaître en général une masse anisotrope. Ces propriétés constitutives effectives, qui pourraient être surprenantes d'un point de vue mécanique classique, se révèlent en fait très utiles pour la conception de métamatériaux acoustiques et de capes acoustiques. Ce travail de thèse consiste essentiellement à proposer et développer deux méthodes numériques efficaces pour déterminer les propriétés élastodynamiques effectives des matériaux périodiquement hétérogènes. La première méthode relève de la méthode des éléments finis alors que la deuxième méthode est basée sur la transformée de Fourier rapide. Ces deux méthodes sont d'abord élaborées pour une microstructure périodique 3D quelconque et ensuite implantées pour une microstructure périodique 2D quelconque. Les avantages et les inconvénients de chacune de ces deux méthodes sont comparés et discutés. A l'aide des méthodes numériques élaborées, la théorie de Willis est appliquée au calcul élastodynamique sur un milieu infini hétérogène et celui homogénéisé. Les différents cas d'homogénéisabilité et de non-homogénéisabilité sont discutés / The elastodynamic homogenization theory of heterogeneous materials initiated by J.R. Willis about thirty years ago has recently received considerable attention. According to this theory which is mathematically exact, the homogenized constitutive law is non-local in space and time; the stress tensor depends not only on the strain tensor but also on the velocity; the linear momentum depends on both the velocity and the strain tensor, making appear an anisotropic mass tensor in general. These effective constitutive properties, which may be surprising from a classical mechanical point of view, turn out in fact to be very useful for the design of acoustic metamaterials and acoustic cloaks. The present work is essentially to propose and develop two efficient numerical methods for determining the effective elastodynamic properties of periodically heterogeneous materials. The first method belongs to the finite element method while the second method is based on the fast Fourier transform. These two methods are first developed for any 3D periodic microstructure and then implanted for any 2D periodic microstructure. The advantages and disadvantages of each of these two methods are compared and discussed. Using the elaborated numerical methods, the Willis theory is applied to the elastodynamic computation over the infinite heterogeneous medium and the homogenized one. The various cases of homogeneisability and non-homogeneisability are discussed

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Slip-synchronous permanent magnet generators (SS-PMG) is a recently proposed direct-grid connected direct-drive generator topology for wind power applications. It combines a permanent magnet synchronous generator and a slip permanent magnet generator through a common permanent magnet rotor. In this study the possibility of using an eddy current coupling as the slip permanent magnet generator is investigated. The eddy current coupling has the attractive advantage of completely removing cogging and load torque ripple, which are known problems in the SS-PMG. However, the analytical modelling of the eddy current coupling is complex. Three different topologies are considered for the eddy current coupling. A finite element model is presented for the eddy current coupling. It is shown that 2D finite element methods are inaccurate compared to 3D finite element methods when solving eddy currents in eddy current couplings. In order to test the accuracy of the finite element modelling of a large eddy current coupling a prototype slip rotor is designed to operate with an existing permanent magnet rotor. Two topologies are optimally designed and compared for the slip rotor, using 3D finite element transient simulations. One of the designed topologies is used for the construction of the prototype slip rotor. The manufactured eddy current coupling allows for comparison between the 3D finite element simulations and measured results, which shows an excellent correlation. Based on observations of the 3D finite element simulations an analytical approximation of the eddy current coupling is proposed for low slip frequencies. It is shown that the analytical model is very dependent on the accurate modelling of the eddy current paths in the slip rotor, something that is difficult to determine accurately. An approximation is made, again based on 3D finite element simulations, which allows the accurate modelling of the current paths for different axial lengths. The analytical model is used for rapid design optimisation of both the slip rotor and permanent magnet rotor of the eddy current coupling, for two different eddy current coupling topologies. The optimised eddy current coupling design with the best results is compared to existing slip permanent magnet generator technologies. The eddy current coupling is shown to have the potential to be a feasible alternative to existing slip permanent magnet generator topologies for application in slip-synchronous permanent magnet generators. It has excellent torque versus slip behaviour, and no cogging or load torque ripple. However, the manufacturing and assembly process of the proposed slip rotor has to be improved for the eddy current coupling to be a realistic competitor to the existing slip permanent magnet generator technologies. / AFRIKAANSE OPSOMMING: Die glip-sinkroon permanente magneet generator is ʼn direk-aangedrewe wind generator wat direk aan die krag netwerk gekoppel kan word. Dit kombineer ʼn permanente magneet sinkroon generator en ʼn permanente magneet glip generator deur middel van ʼn gemeenskaplike permanente magneet rotor. In hierdie studie word die moontlike gebruik van ʼn werwelstroom skakel as plaasvervanger vir die permanente magneet glip generator ondersoek. Die werwelstroom skakel het geen vertandings of las draaimoment rimpeling nie, wat bekende probleme vir die glip-sinkroon permanente magneet generator is. Die analitiese modellering van die werwelstroom skakel is egter nie eenvoudig nie. Daar word drie verskillende topologieë oorweeg vir die werwelstroom skakel. ʼn Eindige element model word ontwikkel vir die werwelstroom skakel. Dit word bevind dat 2D eindige element analise onvoldoende is vir die berekening van werwelstrome in die werwelstroom skakel, en gevolglik word 3D eindige element modelle gebruik in hierdie studie. Om die akkuraatheid van die eindige element model te beproef word ʼn prototipe glip rotor optimaal ontwerp deur middel van eindige element analise. Die glip rotor vorm saam met ʼn bestaande permanente magneet rotor ʼn werwelstroom skakel. Vir hierdie ontwerp word twee werwelstroom skakel topologieë gebruik, en met mekaar vergelyk. Die topologie wat beter presteer word gebruik vir die vervaardiging van die glip rotor. ʼn Vergelyking van die gemete waardes van die vervaardigde werwelstroom skakel en die resultate van die 3D eindige element simulasies dui daarop dat die 3D eindige element modellering ʼn baie goeie voorspelling van die werklikheid is. ʼn Analitiese model vir die werwelstroom skakel onder lae glip toestande is ontwikkel deur gebruik te maak van observasies uit die 3D eindige element simulasies. Die analitiese model is baie afhangklik van die modellering van die werwelstrome se stroompaaie, iets wat moeilik is om akkuraat te bepaal. ʼn Benadering word gemaak wat die akkurate modulering van die stroompaaie moontlik maak vir verskillende aksiale lengtes. Die analitiese model word dan gebruik vir vinnige optimering van die werwelstroom skakel se ontwerp vir twee verskillende werwelstroom skakel topologieë. Die geoptimeerde ontwerp wat die beste resultate toon word vergelyk met bestaande permanente magneet glip generators. Dit word gewys dat die werwelstroom skakel die potensiaal het om ʼn uitvoerbare alternatief tot die permanente magneet glip generator te wees, vir gebruik in glip-sinkroon permanente magneet generators. Die werwelstroom skakel toon baie goeie draaimoment teenoor glip gedrag, en het geen vertandings of las draaimoment rimpeling nie. Voordat die werwelstroom generator ʼn realistiese kompeteerder teenoor die bestaande glip-sinkroon tegnologie is, moet daar verbeterde vervaardigings maniere gevind word vir die voorgestelde glip rotor.

[pt] Este trabalho apresenta uma nova abordagem para o balanceamento de seções geológicas baseada em modelagem física e simulação numérica. O objetivo principal é introduzir alguns conceitos da Mecânica do Contínuo no processo de restauração geológica, de forma a considerar as propriedades físicas dos materiais geológicos durante a simulação do movimento de um bloco de rocha sobre uma falha. A estratégia adotada utiliza-se de um algoritmo de Relaxação Dinâmica acoplado ao Método dos Elementos Finitos para resolver sistemas de equações, com condições de contorno específicas para a movimentação do bloco sobre a falha.Foi adotado como ambiente de desenvolvimento um sistema de balanceamento de seções geológicas composto por um conjunto de transformações geométricas comuns na abordagem clássica do problema. O sistema utiliza uma tecnologia de modelagem geométrica baseada em uma estrutura de dados que permite a representação topológica completa de uma subdivisão planar.A simulação numérica do balanceamento de seções geológicas proposta é implementada dentro desse ambiente e integra três módulos distintos: um módulo de pré- processamento no qual os dados requeridos podem ser facilmente gerados, um módulo de análise onde o método de Relaxação Dinâmica foi implementado e, finalmente, um módulo de pósprocessamento em que podem ser visualizados os resultados obtidos da simulação numérica. Considera-se ainda a natureza palinspática do problema de restauração através de uma interface gráfica amigável do ponto de vista do usuário. Neste sentido, foi realizada uma reorganização completa da interface gráfica e das classes de atributos geológicos associados às entidades topológicas (linhas e regiões) da seção geológica. Esta organização teve dois objetivos: o primeiro, implementar um processo gráfico baseado em uma árvore de decisões para o gerenciamento das tarefas do balanceamento, que envolve passos arbitrários de tentativa e erro, e, o segundo, possibilitar a implementação da simulação numérica dentro do processo de balanceamento.As idéias propostas podem ser consideradas como o primeiro passo para o desenvolvimento de um sistema de balanceamento de seções geológicas, cujas medidas de deformação representem de forma mais aproximada o comportamento mecânico das rochas, além de ser mais automatizado, o que sugere futuramente a implementação de um sistema tridimensional, no qual seja menos exigida a interação com o usuário. / [en] This work presents a new approach for the restoration of geological cross-sections that is based on physical modeling and numerical simulation. The main purpose is to introduce Continuum Mechanics concepts into the geological restoration process in order to consider physical properties of the materials during the simulation of the movement of a rock block along a fault. The adopted strategy uses a dynamic relaxation algorithm to solve the equation system that arises from the numerical simulation based on the Finite Element Method, together with some specific boundary conditions to represent the movement of the rock block over the fault.As development environment, a cross-section restoration system was adopted, composed by a group of usual geometric transformations from the classical approach of the problem. This system adopts a geometric modeling technology based on a data structure that is capable of completely representing the topology of a planar subdivision. The proposed numerical simulation is implemented inside this system and integrates with three different modules: a pre-processing module, where the required input data can be easily generated; an analysis module, in which the dynamic relaxation method has been implemented; and a post- processing module, where the results of the numerical simulation can be viewed. The palinspatic nature of the restoration problem is taken into account by means of a user-friendly graphics interface that was specifically designed for the system. The graphics interface and the geological attribute classes were completely re-organized with two purposes. First, to implement a graphical interface based on a decision tree to manage user tasks involved in the restoration process, which includes trial- and-error steps. Second, to provide support for the implementation of numerical simulation in the restoration process.The ideas proposed herein can be considered as a first step towards a complete geological cross-section restoration system in which more consistent deformation measures can be incorporated into the governing equations to better represent the mechanical behavior of the rocks, and is also an expansion of the presented system to a three-dimensional environment, currently under investigation.

Resumo: Neste trabalho é apresentada a modelagem analítica baseada nas equações de Maxwell e a modelagem numérica baseada no Método da Simulação de Cargas (MSC) e no Método dos Elementos Finitos (MEF) empregados no cálculo do campo eletromagnético quase-estático em linhas de transmissão. O método dos elementos finitos consiste numa adaptação do método residual de Galerkin. Ele é atualmente considerado um método matemático para a solução de equações diferenciais parciais, entre as quais se inclui a Equação de Poisson, Equação de Laplace, Equação de Helmholtz, Navier-Stokes, etc. Esse é um método de aproximação de problemas contínuos em domínios fechados onde o contínuo se divide em um número finito de partes, ou elementos, cujo comportamento se especifica mediante um número finito de parâmetros associados a certos pontos característicos denominados nós. Os nós são os pontos de união de cada elemento com seus adjacentes. A solução do sistema completo segue as regras dos problemas discretos. O sistema completo se forma pela associação dos N elementos. As incógnitas do problema deixam de ser funções matemáticas e passam a ser o valor dessas funções nos n nós. O comportamento no interior de cada um dos N elementos passa a ser definido a partir do comportamento dos n nós, mediante adequadas funções de interpolação ou funções de forma. A precisão do método depende da forma do elemento da malha bidimensional, ou seja, se ele é triangular ou quadrilateral, por exemplo. Além disso, a quantidade de pontos de integração e conseqüentemente a base polinomial do elemento finito, podem ser explorados para aumentar a precisão dos resultados. A base do método dos elementos finitos são as funções de mapeamento, e suas derivadas. No método de Galerkin as funções de mapeamento são igualadas às funções de forma originando os elementos... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this research is presented a mathematical modeling based on Maxwell's equations and numerical modeling based on Charge Simulation Method (CSM) and the Finite Element Method (FEM) for calculating the quasi-static electromagnetic field in transmission lines. The finite element method is an adaptation of Galerkin residual method. It's currently considered a mathematical method for solving partial differential equations, among which includes the Poisson equation, Laplace equation, Helmholtz equation, Navier-Stokes, etc. This is an approximation method of continuing problems in closed domains where the continuous is divided into a finite number of parts or elements whose behavior is specified by a finite number of parameters associated with certain characteristic points called nodes. The nodes are union points of each element with its adjacent. The solution of the entire system follows the rules of the discrete problems. The complete system is formed by the association of N elements. The unknowns of the problem, mathematical functions, become the value of these functions on n nodes. The behavior within each of elements N is now defined from the behavior of n nodes, using appropriate interpolation functions or shape functions. The method precision depends on the shape of two-dimensional mesh element, i.e., if it is triangular or quadrilateral. Moreover, the number of integration points and therefore the polynomial finite element basis, can be exploited to increase the accuracy of the results. The basis of the finite element method are the mapping functions and their derivatives. In the Galerkin method the mapping functions are matched to the shape functions form the isoparametric. Finally, from above definitions, simply refer to the tables of numerical integration, showing how the elements are integrated, and use them in the rest of the numerical modeling / Orientador: Luiz Fernando Bovolato / Coorientador: Carlos Alberto Tenório de Carvalho Júnior / Banca: Afonso José do Prado / Banca: Sérgio Kurokawa / Banca: Olivio Carlos Nascimento Souto / Banca: Wander Gonçalves da Silva / Doutor

Orientador: João Antônio Pereira / Resumo: O uso de ferramentas computacionais atualmente está auxiliando o aprimoramento dos processos e procedimentos de análise e simulações em inúmeras áreas do conhecimento humano. A tomografia computadorizada (TC) é uma ferramenta de diagnóstico já consolidada na área médica e atualmente começa a ser utilizada como uma ferramenta para algo ainda mais inovador, a geração de modelos tridimensionais de órgãos ou estruturas ósseas do paciente para uso na criação de biomodelos e fabricação de próteses personalizadas. Biomodelos são cópias físicas das estruturas anatômicas de regiões ou orgãos do corpo humano utilizados para diagnóstico e planejamento cirúrgico. O uso de imagens tomográficas para geração de modelos 3D tem despertado um grande interesse na área médica e de bioengenharia. Além da criação do biomodelo é possível, com o uso das imagens, a geração de modelos computacionais representativos, possibilitando com isso, a realização de diversas simulações e análises biomecânicas da região ou órgão de interesse, visando a fabricação de próteses ou órteses personalizadas. Neste trabalho é apresentada uma metodologia para a geração de modelos matemáticos tridimensionais a partir de tomografias computadorizadas com o objetivo de estudar e analisar um implante personalizado da ATM (Articulação Temporomandibular), solicitado mecanicamente e fabricado em liga de titânio (Ti6Al4V) pelo processo de manufatura aditiva rápida do tipo DMLS (Sinterização Direta de Metais a Laser). Através do m... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The use of computational tools is currently helping to improve the processes and procedures of analysis and simulations in many areas of human knowledge. Computed tomography (CT) is a diagnostic tool already consolidated in the medical field and is now being used as a tool for something even more innovative, the generation of three-dimensional models of organs or bone structures of the patient for use in the creation of biomodels and Manufacture of customized prostheses. Biomodels are physical copies of the anatomical structures of regions or organs of the human body used for diagnosis and surgical planning. The use of tomographic images for generating 3D models has aroused great interest in the medical and bioengineering field. Besides the creation of the biomodel it is possible, through the use of the images, the generation of representative computational models, making possible the accomplishment of several simulations and biomechanical analyzes of the region or organ of interest, aiming at the manufacture of customized prostheses or orthoses. In this work is presented a methodology for the generation of three-dimensional mathematical models from CT scans in order to build, study and analyze a custom implant TMJ (Temporomandibular Joint), requested mechanically and made of titanium alloy (Ti6Al4V) by the prototyping process of type DMLS (Direct Metal Laser Sintering). Through the model created for the TMJ region, computational simulations of stresses and deformations were ... (Complete abstract click electronic access below) / Doutor

Resumo: No presente trabalho desenvolve-se um modelo constitutivo baseado na mecânica do dano contínuo para representar o comportamento de materiais que apresentam diferentes respostas quando solicitados à tração ou à compreensão. obtem-se uma representação constitutiva através da composição de modelos simples e específicos para tratar cada tipo de solicitação. Este modelo combinado é capaz inclusive de lidar com carregamentos alternados (tração e compreensão), envolvendo fechamento e reabertura de fissuras existentes. Para modelar o comportamento em compreensão emprega-se o modelo constitutivo que tem como critério de degradação o segundo invariante do tensor de tensão desviador (critério de Von Mises ou J2). Para simular o aparecimento de fissuras de tração, usa-se o modelo de dano com critério de degradação baseado na energia de deformação da parte positiva do tensor efetivas. A integração dos modelos é feita com base em tensões efetivas associadas a duas escalas distintas (escala grosseira e refinada). O modelo é apto para representar a formação de descontinuidades no campo de deslocamento (descontinuidades fortes) em materiais quase-frágeis. Nesse caso, a região de localização de deformação (zona de processo da fatura) pode ser descrita pelo modelo de dano combinado, com lei de abrandamento de tensões (softening) exponencial, que estabelece dissipação compatível com a energia de fratura. A região contínua pode ser descrita pelo modelo de dano J2, com parâmetros ajustados com base no comportamento não linear à compreensão. Valida-se o modelo proposto mediante testes básicos, focando a capacidade do modelo em representar os principais aspectos do comportamento de materiais quase-frágeis. A aplicabilidade do modelo é demonstrada através do estudo da capacidade de rotação plástica de vigas de concreto armado, confrontando-se os resultados numéricos com os experimentais / Abstract: A combined constitutive model based on the Continuum Damage Mechanics (CDM) is presented to represent the nonlinear behavior of quasi-brittle materials, which present different response when subjected to tension or compreession. The constitutive model is a composition of two simple and specific models designed to treat each type of behavior. The combined model is able to deal with alternating load (tension-compression), involving formation, closure and reopening cracks. To model the compressive behavior, a degradation criterion based on the second invariant of the deviatoric part of the effective stress tensor (Von Miser or J2 criterion) is used. To simulate cracking, a damage model with degradation criterion based on the strain energy associated to the positive part the effective stress tensor is adopted. The combination of the models is made on the basis of the effective stresses associated to two distinct scales (coarse and fine scales) The model is able to represented the formation of discontinuities in the displacement field (strong discontinuities) for quasi-brittle materials. The region of strain localization (fracture process zone) is described by a softening law which establishes dissipation energy compatible with the fracture energy. The continuous region is described by the J2 damage model, with parameters ajusted to describle the compressive nonlinear behavior in compression. Some basic tests are performed to asses the ability of the model to represent the main aspects of the behavior of quasi-brittle materials. The applicability of the model is demonstrated by the study of the plastic rotation capacity of reinforced concrete beams, comparing the numerical responses with the experimental ones / Orientador: Osvaldo Luís Manzoli / Coorientador: André Luís Gamino / Banca: Leonardo José do Nascimento Guimarães / Banca: Edson Antonio Capello Sousa / Mestre

La cavité abdominale présente des organes nobles richement vascularisés qui possèdent une mobilité et une inertie importantes. Au cours des AVP, le niveau élevé d'accélération peut conduire à des arrachements de leurs systèmes d'attaches (dont les vaisseaux sanguins). L'objectif de ce projet est de comprendre comment prendre en compte les interactions et la mobilité des organes abdominaux pour évaluer leur influence sur les mécanismes lésionnels. Pour cela, nous avons tout d'abord caractérisé le comportement du ligament gastro-colique en traction jusqu'à la rupture. Son comportement hyperélastique a été relevé ainsi que sa sensibilité à la vitesse de déformation. Ensuite, nous avons étudié l'avulsion de la rate avec une approche couplant expérimentation et simulation numérique. Cela a permis d'identifier le comportement hyperélastique faiblement non linéaire du ligament pancréatico-splénique. Au travers de l'approche numérique, nous avons pu conclure que la modélisation de la jonction pancréatico-splénique doit s'appuyer sur la modélisation des structures vasculaires, mais doit également intégrer les tissus connectifs et leurs interactions avec les organes adjacents. Enfin nous avons amélioré la modélisation des interactions et de la mobilité des organes dans le modèle préexistant MELBA sur les résultats obtenus précédemment. La cinématique des organes a été évaluée par une étude comparative de la mobilité avec la première version du modèle. Ce modèle ainsi amélioré permet une meilleure représentativité des mécanismes lésionnels de la cavité abdominale en soulignant le rôle prépondérant de leurs systèmes d'attaches lors d'un traumatisme. / The abdominal cavity presents noble and richly vascular organs which have an important mobility and inertia. During road accidents, the high level of acceleration may lead up to tearing of their attachments systems (including blood vessels) and therefore to serious haemorrhages. The target of this project is to understand how to take into account the interactions and the mobility of the abdominal organs in order to be able to assess their influence on the mechanisms of injury. Therefore, we have first of all characterized the performance of the gastro-colic ligament in uniaxial tension until the failure. We noted down its hyper-elastic performance as well as its sensitivity to strain rate. Afterwards, we studied the splenic avulsion with an approach combining experiments and numerical simulation. This has made it possible to identify the slightly nonlinear hyper-elastic performance of the pancreatico-splenic ligament. Through the numerical approach, we could conclude that the modelling of the pancreatico-splenic junction should rely on the modelling of the vascular structures, but should also integrate the connective tissues and their interactions with the adjacent organs. At last we improved the modelling of the interactions and of the organs' mobility in the pre-existing model MELBA upon the results obtained previously. The organs' kinematics was assessed through a comparative study of the mobility with the first version of the model. This model thereby improved allows a better representativeness of the mechanisms of injury of the abdominal cavity by highlighting the important role of their attachments systems during trauma.

[pt] O presente trabalho apresenta a implementação computacional pelo método dos elementos finitos de procedimentos para análise de problemas de escavação e de fluxo permanente bidimensional, não confinado, para solos saturados. Tais procedimentos, particularmente indicados para investigação do comportamento mecânico/hidráulico de barragens de terra, vem completar o trabalho iniciado por Parra (1996) para análise do comportamento de barragens sob carregamentos estático e sísmico. Foram implementadas duas técnicas para simulação de escavações, obtendo-se, em ambas, resultados numéricos praticamente idênticos. O procedimento para análise de fluxo permanente foi baseado na proposição de Bathe e Khoshgoftarr (1979), a qual considera a situação de fluxo não-confinado como problema não linear, porém conservando a configuração original da malha de elementos finitos. Os resultados numéricos obtidos neste trabalho foram detalhadamente comparados com os valores publicados na literatura, numéricos ou analíticos, como forma de assegurar a confiabilidade das implementações computacionais. A previsão do comportamento da barragem de terra Macusani, a ser construída no Peru, foi estudada neste trabalho, nos aspectos referentes às fases de escavação, construção, primeiro enchimento do reservatório e determinação da superficie de infiltração de fluxo permanente. Os resultados assim obtidos podem ser eventualmente úteis no detalhamento do projeto final da obra. / [en] This work presents a computer implementation for finite element analysis of excavation problems and unconfined steady state flow through saturated soils. These computer routines are particularly useful for the study of earth dams and they were written with the aim to pursue the development of a numerical model (Parra, 1996) devised to investigate the behavior of earth dams under static and seismic loading. Two techniques were implemented for excavation simulations, with both yielding the some numerical results. For the unconfined fluid flow problem the technique proposed by Bathe and Khoshgoftaar (1979) was adopted, which recasts the problem in a non-linear form but keeps the same basic finite element mesh. The results computed in this research were compared with other analytical and numerical values published in the literature, in order to ensure, as much as possible, the feasibility and efficiency of the computer implementations. The behavior prediction of the Macusani earth dam, to be built in Peru, was also studied in this research, focusing on several aspects related to its planned construction: the excavation, the construction itself and the first reservoir filling. This results may eventually be useful for the final engineering design of the Macusani dam. / [es] El presente trabajo presenta la implementación computacional de procedimentos para análisis de problemas de excavación y de flujo permanente bidimensional, para suelos saturados utilizando el método de elementos finitos. Tales procedimentos, particularmente indicados para la investigación del comportamiento mecánico/hidráulico de represas, completa el trabajo iniciado por Parra(1996) para análisis del comportamiento de represas bajo sobrecarga estática y sísmica. Se implementaron dos técnicas para simulación de excavaciones, obteniendo, en ambas, resultados numéricos prácticamente idénticos. El procedimento para análisis de flujo permanente tubo como base la propuesta de Bathe y Khoshgoftarr (1979), que considera la situación de flujo no confinado como problema no lineal, pero conservando la configuración original de la malla de elementos finitos. Los resultados numéricos obtenidos em este trabajo fueron detalladamente comparados con los valores publicados en la literatura, numéricos o analíticos, para asegurar la confiabilidad de las implementaciones computacionales. La previsión del comportamiento de la represa de Macusani, que será construida en Perú, fue estudiada en este trabajo, especifícamente los aspectos vinculados a las fases de excavación, construcción y determinación de la superficie de infiltración de flujo permanente. Los resultados obtenidos pueden ser eventualmente útiles en el proyecto final de la obra.

Ce travail de thèse porte sur l'étude des parois de domaines dans des nanofils magnétiques. Nous avons étendu le diagramme de phase des parois de domainesdéjà connu pour des géométries allant des nanobandes aux nanofils. Les différents types de parois et des transitions de phases sont présentés.Nous avons introduit de nouveaux estimateurs s'appuyant sur des grandeurs physiques connues, pour mieux caractériser les configurations magnétiques des parois et prédire leur type en fonction de la géométrie.Pour valider notre approche théorique, nous nous sommes ensuite intéressés à les observer par microscopie.Nous avons choisi le Dichroisme Circulaire Magnétique des rayons X associé à la Microscopie par Emission de PhotoElectrons (XMCD-PEEM). Ce type de microscopie permet d'atteindre une résolution spatiale suffisante pour observer les parois de domaine. Les configurations expérimentales (échantillons et dispositif expérimental) permettent d'avoir accès à la fois à l'aimantation de surface maisaussi à l'ombre du fil projetée sur le substrat. Cette ombre contient l'information sur l'aimantation dans le volume, moyennée le long du chemin desrayons X dans le matériau. Cette configuration donne lieu à des contrastes magnétiques complexes. Nous avons donc développé un modèle permettant de simuler le contraste XMCD à partir de configurations micromagnétiques à l'équilibre. La comparaison entre les contrastes expérimentaux et les contrastes simulés donne lieu à un très bon accord quantitatif.De plus, les paramètres expérimentaux ont été étudiés afin d'obtenir le meilleur contraste réflétant au mieux la configuration micromagnétique de l'échantillon.La suite de ce travail consistera, notamment, à étudier la propagation de la paroi point de Bloch dans les nanofils. / The work performed during my thesis was based on magnetic domain walls in magnetic nanowires. We extended the phase diagram of domain walls already known to a geometry ranging from nanostrips to nanowires. The various types of domain wall and transition phase types are presented. We introduced new estimators based on physical known features, in order to better characterize domain walls magnetic configurations of domain walls and then to predict the type of domain wall according to the geometry.To validate our theoretical approach, we were interested in imaging these domain walls. We chose the X-ray Magnetic Circular Dichroism along with the PhotoEmission Electron Microscopy (XMCD PEEM). This microscopy method enables to reach spatial resolution required to observed domain wall configuration. The experimental conditions (sample and set up) enable to have access both the surface magnetization and also the shadow of the wire projected on to the substrate. This enable caries information about volume magnetization, averaged along the path of the X-ray through the wire. This experimental configuration gives rise to complex contrasts. Thus, we developped a model that enables to simulate the XMCD contrast from steady state micromagnetic configurations. Comparison between experimental and simulated contrasts gives rise to a good quantitative agreement. Moreover, experimental parameters were studied in order to get the best magnetic contrast, reflecting the true magnetic configuration of the sample.For the future, the work consists in the study of the domain wall propagation in nanowires, particularly the propagation of the Bloch point wall.