Apesar de fortes eventos sísmicos serem raros no Brasil, engenheiros estruturais brasileiros são frequentemente envolvidos em tal análise para os países latino-americanos vizinhos. Informações sobre históricos de aceleração sísmica, de natureza aleatória, não estão em geral disponíveis, devido, em parte, à falta de registros. Para contornar tal situação, os códigos de construção indicam o uso de acelerogramas artificiais, mas não fornecem metodologia para sua obtenção. A informação normalizada é o chamado espectro de resposta elástico, que fornece a aceleração de resposta máxima para um sistema linear de um grau de liberdade. Muitas pesquisas estão sendo desenvolvidas a fim de gerar acelerogramas artificiais compatíveis com os espectros de norma. Assim, neste trabalho se apresenta uma proposta para a geração de acelerograma artificial compatível com espectro de resposta regulamentar. Para exemplo de aplicação, é gerado um acelerograma artificial compatível com a Norma Brasileira NBR 15421: 2006 e aplicado à base de um edifício shear building de dez pavimentos e através de integração numérica por diferenças finitas passo-a-passo no domínio do tempo é calculado o deslocamento do último pavimento deste edifício. De forma semelhante, é gerado um acelerograma artificial compatível com a Norma Venezuelana COVENIN 1756: 2001 e aplicado à base de um reservatório d\'água sobre quatro pilares e estudado o seu comportamento elastoplástico perfeito. / Although strong seismic events are rare in Brazil, Brazilian structural engineers are often involved in such an analysis for neighboring Latin American countries. Information on seismic acceleration histories of a random nature is not generally available, due in part to the lack of records. To circumvent such a situation, building codes indicate the use of artificial accelerograms, but do not provide a methodology for obtaining them. The normalized information is the so-called elastic response spectrum, which provides the maximum response acceleration for a linear system of a degree of freedom. Many researches are being developed in order to generate artificial accelerograms compatible with the norm spectra. Thus, this paper presents a proposal for the generation of an artificial accelerogram compatible with a regulatory response spectrum. For an application example, an artificial accelerogram compatible with the Brazilian Standard NBR 15421: 2006 is generated and applied to the base of a ten-story shear building and through numerical integration by finite differences step-by-step in the time domain is calculated the displacement of the last floor of this building. Similarly, an artificial accelerogram is generated that is compatible with the Venezuelan Standard COVENIN 1756: 2001 and applied on the basis of a water reservoir on four pillars and studied its perfect elastoplastic behavior.

In this thesis, the Generalized Finite Difference (GFD) method is applied to analyze the elastoplastic deformation behavior of a long functionally graded (FGM) tube subjected to internal pressure. First, the method is explained in detail by considering the elastic response of a rotating FGM tube. Then, the pressurized tube problem is treated. A long FGM tube with fixed ends (axially constrained ends) is taken into consideration. The two cases in which the modulus of elasticity only and both the modulus of elasticity and the yield limit are graded properties are analyzed. The plastic model here is based on incremental theory of plasticity, Tresca&#039 / s yield criterion and its associated flow rule. The numerical results are compared to those of analytical ones. Furthermore, the elastic response of an FGM tube with free ends is studied considering graded modulus of elasticity and Poisson&#039 / s ratio. The results of these computations are compared to those of Shooting solutions. In the light of analyses and comparisons stated above, the applicability of the GFD method to the solution of similar problems is discussed. It is observed that, in purely elastic deformations the accuracy of the method is sufficient. However, in case of elastic-plastic deformations, the discrepancies between numerical and analytical results may increase in determining plastic displacements. It is also noteworthy that the predictions for tubes with two graded properties, i. e. the modulus of elasticity and the yield limit, turn out to be better than those with one graded property in this regard.

Analytical and numerical models are developed to investigate the effect of orthotropy on the stress distribution in variable thickness solid and annular rotating disks. The plastic treatment is based on Hill&rsquo / s quadratic yield criterion, total deformation theory, and Swift&rsquo / s hardening law. The elastic-plastic stress distributions, residual stresses and radial displacement distributions are obtained after having analysed the cases of rotating solid disk, annular disk with rigid inclusion, annular disk subjected to either internal or external pressure. Thermal loading is also considered for the annular disk with rigid inclusion. Effects of different values of elastic and plastic orthotropy parameters are investigated. It is observed that the elastic orthotropy significantly affects the residual stresses in disks. The most remarkable effect of the plastic orthotropy is observed on the disk with rigid inclusion.

The stress distribution in a rotating solid shaft with temperature dependent yield stress subject to a temperature cycle is investigated. It is presumed that the shaft is in a state of generalized plane strain and obeys Tresca&rsquo / s yield criterion and the flow rule associated with it. By the temperature cycle it is meant that the surface temperature of the shaft is increased to a limiting value, it is held at this temperature for a while, and then slowly decreased at the same rate to the reference temperature. The isothermal shaft is rotated up to around elastic limit rotation speed and then the temperature cycle is applied to the surface of the shaft. Even in an initially purely elastic shaft, two plastic regions with different forms of the yield condition emerge simultaneously at the centre and expand into the elastic region. However, the expansion of the plastic zone ceases soon thereafter, and an unloaded region spreads into the plastic core. It is shown that the stress distribution is altered significantly by the temperature cycle, hence also leading to non-zero residual stresses at stand-still.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 160-166).

Apesar de fortes eventos sísmicos serem raros no Brasil, engenheiros estruturais brasileiros são frequentemente envolvidos em tal análise para os países latino-americanos vizinhos. Informações sobre históricos de aceleração sísmica, de natureza aleatória, não estão em geral disponíveis, devido, em parte, à falta de registros. Para contornar tal situação, os códigos de construção indicam o uso de acelerogramas artificiais, mas não fornecem metodologia para sua obtenção. A informação normalizada é o chamado espectro de resposta elástico, que fornece a aceleração de resposta máxima para um sistema linear de um grau de liberdade. Muitas pesquisas estão sendo desenvolvidas a fim de gerar acelerogramas artificiais compatíveis com os espectros de norma. Assim, neste trabalho se apresenta uma proposta para a geração de acelerograma artificial compatível com espectro de resposta regulamentar. Para exemplo de aplicação, é gerado um acelerograma artificial compatível com a Norma Brasileira NBR 15421: 2006 e aplicado à base de um edifício shear building de dez pavimentos e através de integração numérica por diferenças finitas passo-a-passo no domínio do tempo é calculado o deslocamento do último pavimento deste edifício. De forma semelhante, é gerado um acelerograma artificial compatível com a Norma Venezuelana COVENIN 1756: 2001 e aplicado à base de um reservatório d\'água sobre quatro pilares e estudado o seu comportamento elastoplástico perfeito. / Although strong seismic events are rare in Brazil, Brazilian structural engineers are often involved in such an analysis for neighboring Latin American countries. Information on seismic acceleration histories of a random nature is not generally available, due in part to the lack of records. To circumvent such a situation, building codes indicate the use of artificial accelerograms, but do not provide a methodology for obtaining them. The normalized information is the so-called elastic response spectrum, which provides the maximum response acceleration for a linear system of a degree of freedom. Many researches are being developed in order to generate artificial accelerograms compatible with the norm spectra. Thus, this paper presents a proposal for the generation of an artificial accelerogram compatible with a regulatory response spectrum. For an application example, an artificial accelerogram compatible with the Brazilian Standard NBR 15421: 2006 is generated and applied to the base of a ten-story shear building and through numerical integration by finite differences step-by-step in the time domain is calculated the displacement of the last floor of this building. Similarly, an artificial accelerogram is generated that is compatible with the Venezuelan Standard COVENIN 1756: 2001 and applied on the basis of a water reservoir on four pillars and studied its perfect elastoplastic behavior.

Grâce à leurs bonnes propriétés mécaniques spécifiques, les matériaux cellulaires architecturés présentent un fort intérêt pour répondre aux problématiques du secteur aéronautique. Cependant, la modélisation d'une structure macroscopique incluant un matériau cellulaire nécessite, soit de modéliser complètement l'architecture à l'échelle mésoscopique - ce qui est coûteux en temps de calcul - soit d'utiliser un Milieu Homogène Equivalent (MHE). Ainsi, cette thèse propose de caractériser un matériau cellulaire modèle constitué d'un empilement de tubes, selon un motif carré ou hexagonal, puis d'identifier un modèle phénoménologique rendant compte du comportement mécanique inélastique du matériau. Dans un premier temps, le matériau est caractérisé sous chargements multi-axiaux à l'aide de simulations éléments finis périodiques en petites déformations. Le comportement homogénéisé en petites déformations est ensuite utilisé pour l'identification d'une Loi Homogène Equivalente (LHE) compressible et anisotrope, qui permet la modélisation de structures sandwichs en remplaçant le coeur cellulaire par son MHE. Une comparaison est réalisée entre les réponses mécaniques des simulations de référence complètement maillées et celles utilisant l'approche par MHE, validant ainsi la pertinence de la méthode multi-échelle de modélisation proposée. La caractérisation en grandes déformations des deux types d'empilement est ensuite menée. D'abord, les effets de bords et les instabilités qui gouvernent le comportement macroscopique sont étudiés. Puis, après une étude du volume élémentaire représentatif des empilements, la caractérisation du comportement inélastique par la technique de l'homogénéisation périodique est réalisée. Le comportement adoucissant en compression de l'empilement hexagonal est ainsi étudié. Finalement, une extension des LHE identifiées en petites déformations est proposée pour rendre compte du comportement en compression du matériau observé en grandes déformations. / Cellular materials have excellent specific properties, which make them attractive for aeronautical applications. However, modelling macroscopic structures including a cellular material is either very costly in terms of computational time if the whole mesoscopic structure is considered or a Homogeneous Equivalent Medium (HEM) has to be used. This Ph.D. dissertation presents, the characterisation of a cellular material built from a stacking of tubes with a square or hexagonal based pattern and the identification of a phenomenological model of their inelastic mechanical behaviour. First, the material is characterised for multi-axial loadings through a periodic finite element model in small deformations for each tube stacking pattern. The macroscopic behaviour is then used to identify a compressible anisotropic Homogeneous Equivalent Law (HEL). Within the infinitesimal strain hypothesis, a comparison is carried out between reference full scale models and HEM based ones of sandwich structures with a cellular core, confirming the relevance of the proposed multi-scale method. Then, the mechanical behaviour of each tube stacking is characterised for large deformations in order to study the influence of the boundary size effects and the instabilities in the core on the macroscopic behaviour of sandwich structures. After a study on the representative volume element, the macroscopic inelastic behaviour is characterised through the periodic homogenisation technique, especially the softening observed in compression for the hexagonal pattern. Finally, an extension of the HELs identified in small deformations is proposed to model the behaviour observed in large deformations.

Ce travail vise à accélérer les calculs lors de la simulation numérique du laminage à pas de pèlerin. Pour ce faire, nous nous sommes penchés sur la méthode Multimaillages Multiphysiques Parallèle (MMP) implémentée au sein du code Forge®, et destinée à accélérer les calculs pour des procédés de mise en forme à faible où la déformation est très localisée sur une petite zone du domaine. Dans cette méthode, un maillage localement raffiné dans la zone de déformation et plus grossier sur le reste du domaine est utilisé pour résoudre les équations mécaniques, alors qu'un maillage uniformément raffiné est retenu pour le calcul thermique. Le calcul mécanique étant le plus coûteux, la réduction du nombre de nœuds de son maillage permet d'obtenir des accélérations très importantes. Le maillage de calcul thermique étant uniformément fin, il sert aussi de maillage de stockage pour les champs calculés pour les deux physiques. Pour appliquer la efficacement méthode MMP au laminage à pas de pèlerin, plusieurs aspects importants ont été pris en compte. Tout d'abord la géométrie complexe du tube nécessite le développement d'une technique de déraffinement spéciale afin d'assurer un déraffinement maximal tout en garantissant un maillage convenable pour des calculs. Une technique de déraffinement de maillage utilisant une métrique anisotrope cylindrique a été alors développée. Ensuite, avec la loi de comportement élastoplastique utilisée, des perturbations importantes sont observées sur les contraintes dues aux diffusions numériques engendrées par les différents types de transports des champs P0 (constants du maillage thermique vers le maillage mécanique. Pour y remédier, une approche combinant deux techniques a été développée. La première consiste à effectuer la réactualisation des variables d'état directement sur le maillage mécanique plutôt que sur le maillage thermique et de les transporter ensuite. La deuxième technique est l'utilisation d'un opérateur de transport P0 basé sur un recouvrement super convergent (SPR) et la construction de champs d'ordre supérieur recouvrés. De bonnes accélérations sont alors obtenues sur les cas de laminage à pas de pèlerin étudiés, allant jusqu'à un facteur 6,5 pour la résolution du problème thermomécanique. Les accélérations globales de simulation vont jusqu'à un facteur 3,3 sur un maillage contenant environ 70 000 nœuds en séquentiel. En parallèle les performances chutent légèrement, mais elles restent semblables (2,7). / This work aims at speeding-up the calculations of the numerical simulation of the cold pilgering process. To this end, it is focused on a Parallel Multiphysics Multimesh (MMP) method that bas been implemented in the Forge® code; this method is dedicated to speeding-up the calculations for processes in which the deformation is localized within a small area of the computational domain. A locally refined mesh is used to solve the mechanical equations while a uniformly refined mesh serves as basic mesh to store state variables and is preferred for thermal calculations. The mechanical computations being the most expensive, reducing the number of nodes of its mesh provides high speed-ups. To effectively apply MMP method to cold pilgering process, many important aspects have been taken into account. Firstly the complex geometry of the tube requires the development of a special mesh coarsening technique, in order to ensure a maximum coarsening while guaranteeing a suitable mesh for calculations. A technique using a cylindrical anisotropic metric is then introduced. Afterwards, with the elastoplastic behaviour law used for the considered process, inaccuracies were observed on the stress field. They are mainly due to the numerical diffusion generated by the different transfers operations of P0 variables (constant per element) from the thermal mesh to the mechanical one. To remedy this issue, an approach combining two techniques has been developed. Firstly state variables are directly updated on the mechanical mesh, instead of doing it on the thermal mesh before transferring them on the the mechanical mesh. The second technique consists in using a P0 transfer operator based on super convergent recovery (SPR) technique, which improves the accuracy of the transported field through introduction of higher order recovered fields. High speed-ups are obtained on the studied cold pilgering cases, up to a factor 6,5 for the resolution of the thermomechanical problem, and the global simulation speed-up is up to a factor of 3,2, on a mesh with about 70 000 nodes in sequential calculations. For parallel calculations performances slightly drop but remain quite good.

Lors du forage des puits d'hydrocarbure, une pâte de ciment est coulée dans l'espace annulaire entre le cuvelage en acier et les formations géologiques traversées. Pompée à l'état liquide, cette pâte de ciment fait sa prise le long du puits sous différentes conditions de température et de pression. La gaine de ciment ainsi mise en place a pour principales fonctions de promouvoir l'étanchéité pour protéger le casing contre la corrosion, de fournir le support mécanique pour assurer la stabilité du puits et d'isoler les différents fluides dans les couches traversées. Au cours de sa vie dans le puits, depuis le forage à la complétion et de la production à l'abandon, la gaine de ciment est soumise à différentes sollicitations mécaniques et thermiques qui peuvent l'endommager et altérer ses principales fonctions. La réponse de la pâte de ciment soumis à ces sollicitations dépend non seulement des conditions d'hydratation mais aussi de l'histoire des chargements précédemment appliqués. La prédiction du comportement de la gaine de ciment doit donc se faire à l'aide d'une modélisation numérique qui nécessite une loi de comportement pour la pâte de ciment. Le but de cette thèse est d'établir une loi de comportement de la pâte de ciment en cours d'hydratation pendant le jeune-âge (les 144 premières heures). Pour ce faire, des essais calorimétriques, de mesures de vitesse des ondes et des essais œdométriques ont été réalisés sur une pâte de ciment pétrolier classe G (w/c = 0,44) en cours de prise. Les conditions d'hydratation explorées vont de 7 à 30°C pour les températures et de 0,3 à 45MPa pour les pressions. Les résultats expérimentaux ont montré que les déformations volumiques de la pâte de ciment dues à son hydratation (retrait macroscopique) sont considérablement influencées par la contrainte sous laquelle la pâte de ciment s'hydrate. Plus la contrainte d'hydratation est élevée, plus élevé est le retrait macroscopique à 144 heures. Inversement, les déformations irréversibles dues à un cycle de chargement mécanique à cet âge sont moins importantes pour les contraintes plus élevées. Les résultats ont également montrés qu'au cours de la prise du ciment, il existe un temps critique à partir duquel l'application des cycles de chargement mécanique crée des déformations résiduelles dans la pâte de ciment. Ce temps critique arrive à un degré d'hydratation relativement constant, compris entre 0,18 et 0,20. Le modèle « Boundary Nucleation and Growth » a été utilisé pour étudier la dépendance de ce temps critique à la pression et à la température. Pour la modélisation du retrait macroscopique et de la réponse contrainte – déformation de la pâte de ciment, un modèle élasto-plastique chemo-poro-mécanique couplé, prenant en compte la désaturation du milieu, a été développé. Ce modèle utilise une surface de charge fermée de type Cam-Clay et une loi plastique associée. La loi d'écrouissage dépend des déformations volumiques plastiques et du degré d'hydratation. Les paramètres du modèle ont été évalués pour simuler le retrait macroscopique de la pâte de ciment hydratée sous différentes contraintes et températures. A un degré d'hydratation donnée, le modèle permet également de simuler la réponse contrainte-déformation due à un chargement mécanique / When drilling oil & gas well, cement slurry is pumped between the casing and the rock formation. This cement slurry sets at different conditions of temperature and pressure. The role of this cement sheath is to provide zonal isolation of different fluid along the well, to protect the casing against corrosion and to provide mechanical support. During the life of the well, from drilling to completion, production and P&A (plug and abandonment), the cement sheath is submitted to various mechanical and thermal loading that can potentially damage its properties and alter its performance. The behavior of cement paste submitted to theses solicitations depends both on the hydration condition and the loadings previously applied on the cement paste. The prediction of cement sheath behavior should be done by numerical modeling, which needs a constitutive law for cement paste. The purpose of the present work is to establish a constitutive law of cement paste during its hydration at early age (first 144 hours). The approach is based on combined calorimetric, wave velocities and oedometric tests on an oil-well class G cement paste with water-to-cement ratio equals 0.44. The hydration conditions explored are 7 to 30°C for temperature and 0.3 to 45MPa for pressure. The experimental results showed that the volumetric strain due to cement hydration (macroscopic shrinkage) depends considerably on the hydration pressure. At 144 hours of hydration, the macroscopic shrinkage increases with the hydration pressure increase. But, the residual strain due to application of mechanical cycle at this age is less for cement hydrated under higher pressure. The experimental results revealed that during the hydration there is a critical time after which, the application of mechanical loading can potentially induce residual strain in cement paste. This time is reached at constant hydration degree between 0.18 and 0.20. The Boundary Nucleation and Growth model was used to model the pressure and temperature dependence of this critical time. A coupled elasto-plastic chemo-poro-mechanical model is developed to simulate the macroscopic shrinkage of cement paste hydrated at different conditions of temperature and pressure. A modified Cam-Clay type yield surface with associate flow rule is used. The hardening law depends both on the degree of hydration and on the plastic volumetric strain. At constant degree of hydration, the developed model permits to simulate the stress – strain behavior of cement paste due to the mechanical loading

Le soudage multipasse est mis en œuvre pour recharger des tuyauteries présentant localement des sous-épaisseurs. La simulation numérique facilite le choix des nombreux paramètres de soudage. La réduction des modèles permet d'accélérer ces choix. Dans ce travail, nous nous sommes intéressés aux cas pour lesquelles il est difficile de réaliser intégralement la simulation du soudage, faute de temps ou par manque de moyens de calcul. Ce sont des simulations hors d'atteintes. Or, les prévisions manquantes ne permettent pas la mise en œuvre d'une méthode de décomposition orthogonale aux valeurs propres pour extraire une base réduite de modes empiriques à partir des données produites par simulation numérique. Nous proposons donc soit un modèle directionnel bien adapté au soudage, soit une étape d'extrapolation des données de simulations par décalage spatial des prévisions calculées. Ces deux approches sont complémentaires de la méthode d'hyper-réduction, dans laquelle les équations de bilan sont restreintes à un maillage réduit. Ces méthodes permettent de démarrer une simulation numérique du soudage avec un modèle éléments finis, puis de poursuivre cette simulation par un modèle hyper-réduit. Cela évite d'avoir à réaliser de nombreuses études paramétriques et permet de traiter des simulations qui sont hors d'atteintes. Ce mémoire se termine par un chapitre traitant du cas de rechargement d'un tube, pour lequel EDF a mis en œuvre un essai instrumenté. / Multi-pass welding is used to recharge pipes with local sub-thickness. Numerical simulation facilitates the selection of many welding parameters. Reducing the order of models speeds up these choices. In this work, we were interested in cases where it is difficult to carry out the entire welding simulation due to time constraints or lack of calculation means. These computations are called out of reach simulations. However, the missing forecasts do not allow the implementation of a orthogonal decomposition method to extract a reduced basis of empirical modes from the data produced by numerical simulations. To overcome this difficulty, we propose either a directional model well adapted to welding, or a step of extrapolation of the simulation data by spatial shift of the already calculated forecasts. These two approaches are complementary to the hyper-reduction method, in which the balance equations are restricted to a reduced mesh size. These methods allow to start a numerical simulation of welding with a finite element model, then to continue this simulation with a hyper-reduced model. This avoids the need for numerous preliminary parametric studies and allows simulations that are out of reach. This manuscript ends with a chapter dealing with the case of reloading a tube, for which EDF has carried out an instrumented test.