Orientador: Maria Cecília Amorim Teixeira da Silva / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-17T07:55:36Z (GMT). No. of bitstreams: 1 Pires_SusanadeLima_M.pdf: 919425 bytes, checksum: d13d24300a7bb026a2c9352fd83b1c35 (MD5) Previous issue date: 2006 / Resumo: Este trabalho apresenta um modelo numérico para o estudo de pilares isolados de concreto armado submetidos à flexão normal composta onde as não linearidades física e geométrica são levadas em conta de maneira rigorosa. O procedimento numérico desenvolvido para o cálculo dos deslocamentos é baseado no Método dos Elementos Finitos. Para a inclusão das não linearidades física e geométrica é utilizado o Método de Newton-Raphson Modificado que é um procedimento iterativo para a determinação de raízes de funções não lineares. A relação tensão-deformação do concreto é representada pelo diagrama parábola-retângulo. O aço é considerado um material elastoplástico perfeito. É admitida perfeita aderência entre o concreto e o aço. São desenvolvidos algoritmos para o dimensionamento de pilares e para o estudo da estabilidade do pilar. É desenvolvido um programa de computador utilizando os algoritmos mencionados acima. A eficiência do programa é verificada por meio da comparação com trabalhos experimentais e com o programa comercial CAD/TQS. Os resultados do dimensionamento feito com o programa proposto apresentaram boa concordância com os dados experimentais selecionados. Finalmente é feito um estudo comparativo entre os resultados do dimensionamento de pilares feito pelo programa elaborado, com os resultados obtidos pelas simplificações admitidas pela Norma Brasileira NBR 6118/2003. Esta comparação mostra que, para os exemplos apresentados, a NBR 6118/2003 superestima o dimensionamento de pilares esbeltos realizados através dos métodos simplificados. Para pilares com índice de esbeltez superiores a 90, a norma está certa em impedir o dimensionamento com os métodos simplificados pois podem apresentar resultados contra a segurança. Os efeitos causados pela deformação lenta não foram incluídos neste trabalho / Abstract: This work presents a numerical model for the study of reinforced concrete columns subjected to combined axial load and bending where the geometric and material nonlinearities are rigorously considered. The numerical procedure developed to calculate the displacements is based on the Finite Element Method. An iterative procedure for the determination of roots of nonlinear functions, the Modified Newton-Raphson Method, is used for including nonlinearities. The parabolic-rectangular diagram is adopted as the concrete stress-strain relationship. The steel is considered a perfect elastoplastic material, and a perfect concrete-to-steel bond is admitted. Algorithms are developed for dimensioning and studying the stability of columns. A computer program is developed using the algorithms mentioned above. The efficiency of the program is verified against available experimental data and commercial programs such as CAD/TQS. The values obtained from the program have presented good agreement with experimental data. Finally a comparative study is made among the results of the designed columns with values obtained from Brazilian Code NBR 6118/2003 approaches. This comparison shows that, for the presented examples, NBR 6118/2003 overestimates the slender columns design when using the approaches, and for columns with slenderness index over 90 the code is correct in preventing the design through the simplified methods, for it can lead to unsafe results. The effects caused by the creep are not enclosed in this work / Mestrado / Estruturas / Mestre em Engenharia Civil

La fabrication additive est une famille de procédés permettant de construire des pièces finies, saines, de géométries très complexes, tout en diminuant le temps de développement des pièces, les coûts et les délais vis-à-vis des techniques de fabrication conventionnelles. Le point commun à tous ces procédés est de construire une pièce directement à partir des données CAO définissant sa géométrie sans outillage autre que la machine de fabrication additive.Cette thèse de Doctorat s'inscrit dans le projet de recherche FALAFEL (Fabrication Additive par procédé LAser et Faisceaux d’ÉLectrons) rassemblant les filières aéronautique et procédés laser dans le but de mettre en œuvre, d’améliorer et de valider des procédés de fabrication additive de pièces métalliques, dans des conditions industrielles et sur des composants aéronautiques.L'objectif est de proposer un modèle numérique permettant d’obtenir, dans des temps raisonnables, des informations sur les caractéristiques thermique, métallurgique et mécanique de pièces industrielles en titane Ti-6Al-4V destinées à être fabriquées par deux procédés de fabrication additive : la projection de poudre (Direct Metal Deposition ou DMD) et la fusion laser sélective (Selective Laser Melting ou SLM). / Additive manufacturing processes allow to build finished industrial parts with very complex geometry, while reducing development time and costs compared to conventional manufacturing processes. The main principle of all these processes is to build components directly from a CAD file defining its geometry without requiring any mold nor specific tools.This study is part of the FALAFEL research project focused on additive manufacturing processes by laser and electron beams. It is composed of academic research laboratories and industrial partners from Aeronautics and Laser Processes industries. The main goal of this project is to implement, improve and validate additive manufacturing processes regarding the production of metallic components for Aeronautics. Studies are conducted under industrial conditions.The aim of our thesis is to provide a numerical model to obtain, within a reasonable time, information about the mechanical and metallurgical properties of industrial components made out of titanium Ti-6Al-4V. It is aimed at two additive manufacturing processes: the Direct Metal Deposition (DMD) and the Selective laser melting (SLM).

With the world’s aging power generation network, especially in Europe and the United States, life-extension of steel plant components is increasingly a critical issue, as components are exposed to high temperatures and pressures during their lifetime, potentially resulting in carbide coarsening, making them prone to creep cavitation, possibly leading to component failure. Therefore, in order to evaluate the likelihood of component failure, non-destructive testing and evaluation procedures must be developed to properly assess the level of degradation in power station steels and ensure that end-of-life conditions are not reached. Electromagnetic (EM) inspection techniques have the potential to assess the level of degradation in power station steels through in-situ measurements. This research work introduces and examines a novel approach in the development of an EM sensor system for long term use. Specifically, it focuses on employing the developed EM sensor system technology in the monitoring of microstructural variations in power generation steels (such as boiler tubes) for in-service monitoring and evaluation during maintenance periods. In this work, controlled measurement of the EM properties (differential permeability) of cylindrical samples, machined from power station pipes (P9) and tubes (T22) in different states of degradation were carried out using two different EM sensor systems. Analytical and numerical methods (Finite Elements) were employed to calculate the sensor response to the samples and EM properties inferred by fitting the models to the measured results. The results from a closed magnetic loop sensor system were also considered, where the magnetic hysteresis curves for the steel samples were measured, from which relative incremental permeability values were obtained. It was found that the incremental permeability values measured by this system were connected to the differential permeability values obtained from the induction spectroscopy. Strong correlations have been drawn between microstructural changes (quantified using Vickers hardness measurements) in heat treated samples and EM properties (incremental and differential permeability). Finally, correlations established using the lab-based closed magnetic loop system are transferred to real-world samples, such as grade 91 open pipe / tube specimens. The measurement results verify that the techniques employed for measuring the EM properties of rod samples produce similar results for the open tube samples, demonstrating the viability of application of EM methods for assessment and monitoring of open power station pipes and tubes in-situ.

Dans le présent travail, nous mettons en œuvre un développement numérique d’une méthode de discrétisation mixte MEF/Meshless pour la résolution de problème mécanique fortement non-linéaire. Une attention particulière est attribuée à la construction des fonctions de forme par approximation diffuse. Dans le but de traiter des problèmes de la mécanique des solides en transformations finies, nous développons une méthode numérique dite « mixte » unissant à la fois la méthode numérique Meshless afin de discrétiser les zones à fort gradient de déformation, et la méthode des Eléments Finis (MEF) pour les zones les moins sollicitées. Nous veillons donc à assurer le couplage entre ces deux méthodes de discrétisation à travers la mise en œuvre de techniques spécifiques, notamment pour la continuité du domaine et sa consistance en premier lieu, mais aussi pour le choix de la méthode d’intégration numérique appropriée. Nous testons par la suite la fiabilité et la performance du modèle par la mise en place d’une étude comparative avec un modèle MEF standard conçu pour les mêmes conditions numériques, afin de tester la performance des techniques numériques attribuées au modèle « mixte ». Nous développons, par la suite, un modèle de comportement à travers une description des transformations finies. Nous adoptons ainsi une discrétisation spatiale en éléments «assumed strain», et une discrétisation temporelle adaptées. Pour valider notre modèle « mixte » retenu, nous réalisons une étude comparative avec des exemples simples de calcul non linéaire / In this work, we implement a development of mixed discretization MEF-Meshless for solving strongly nonlinear mechanical problem. Particular attention is given to the construction of the shape functions by diffuse approximation. In order to deal with problems of solid mechanics with large strain, we develop a so-called “mixed” numerical method combining both Meshless to discretize areas of high deformation gradient, and Finite Element Method (MEF) for non-concerned areas. We ensure coupling between both discretization methods through the implementation of specific techniques, including the continuity and consistency of the field and the choice of the appropriate method of numerical integration. We test later the reliability and performance of the model by the introduction of a comparative study with a standard FEM model designed for the same numerical conditions to evaluate numerical techniques attributed to our “mixed” model. We develop, thereafter, a model of behavior through a large strain description. We adopt spatial discretization elements “assumed strain” and a suitable time discretization. To validate our “mixed” model, we perform a comparative study of nonlinear simple calculation examples

The central aim for the research undertaken in this PhD thesis is the development of a model for simulating water droplet movement on a leaf surface and to compare the model behavior with experimental observations. A series of five papers has been presented to explain systematically the way in which this droplet modelling work has been realised. Knowing the path of the droplet on the leaf surface is important for understanding how a droplet of water, pesticide, or nutrient will be absorbed through the leaf surface. An important aspect of the research is the generation of a leaf surface representation that acts as the foundation of the droplet model. Initially a laser scanner is used to capture the surface characteristics for two types of leaves in the form of a large scattered data set. After the identification of the leaf surface boundary, a set of internal points is chosen over which a triangulation of the surface is constructed. We present a novel hybrid approach for leaf surface fitting on this triangulation that combines Clough-Tocher (CT) and radial basis function (RBF) methods to achieve a surface with a continuously turning normal. The accuracy of the hybrid technique is assessed using numerical experimentation. The hybrid CT-RBF method is shown to give good representations of Frangipani and Anthurium leaves. Such leaf models facilitate an understanding of plant development and permit the modelling of the interaction of plants with their environment. The motion of a droplet traversing this virtual leaf surface is affected by various forces including gravity, friction and resistance between the surface and the droplet. The innovation of our model is the use of thin-film theory in the context of droplet movement to determine the thickness of the droplet as it moves on the surface. Experimental verification shows that the droplet model captures reality quite well and produces realistic droplet motion on the leaf surface. Most importantly, we observed that the simulated droplet motion follows the contours of the surface and spreads as a thin film. In the future, the model may be applied to determine the path of a droplet of pesticide along a leaf surface before it falls from or comes to a standstill on the surface. It will also be used to study the paths of many droplets of water or pesticide moving and colliding on the surface.

L’objectif de ce travail de thèse est de proposer la Méthodes des éléments finis de Galerkin discontinus (DGFEM) à la discrétisation des équations compressibles de Navier-Stokes. Plusieurs challenges font l’objet de ce travail. Le premier aspect a consisté à montrer l’ordre de convergence optimal de la méthode DGFEM en utilisant les polynômes d’interpolation d’ordre élevé. Le deuxième aspect concerne l’implémentation de méthodes de ‘‘shock-catpuring’’ comme les limiteurs de pentes et les méthodes de viscosité artificielle pour supprimer les oscillations numériques engendrées par l’ordre élevé (lorsque des polynômes d’interpolation de degré p>0 sont utilisés) dans les écoulements transsoniques et supersoniques. Ensuite nous avons implémenté des estimateurs d’erreur a posteriori et des procédures d ’adaptation de maillages qui permettent d’augmenter la précision de la solution et la vitesse de convergence afin d’obtenir un gain de temps considérable. Finalement, nous avons montré la capacité de la méthode DG à donner des résultats corrects à faibles nombres de Mach. Lorsque le nombre de Mach est petit pour les écoulements compressibles à la limite de l’incompressible, la solution souffre généralement de convergence et de précision. Pour pallier ce problème généralement on procède au préconditionnement qui modifie les équations d’Euler. Dans notre cas, les équations ne sont pas modifiées. Dans ce travail, nous montrons la précision et la robustesse de méthode DG proposée avec un schéma en temps implicite de second ordre et des conditions de bords adéquats. / The aim of this thesis is to deal with compressible Navier-Stokes flows discretized by Discontinuous Galerkin Finite Elements Methods. Several aspects has been considered. One is to show the optimal convergence of the DGFEM method when using high order polynomial. Second is to design shock-capturing methods such as slope limiters and artificial viscosity to suppress numerical oscillation occurring when p>0 schemes are used. Third aspect is to design an a posteriori error estimator for adaptive mesh refinement in order to optimize the mesh in the computational domain. And finally, we want to show the accuracy and the robustness of the DG method implemented when we reach very low mach numbers. Usually when simulating compressible flows at very low mach numbers at the limit of incompressible flows, there occurs many kind of problems such as accuracy and convergence of the solution. To be able to run low Mach number problems, there exists solution like preconditioning. This method usually modifies the Euler. Here the Euler equations are not modified and with a robust time scheme and good boundary conditions imposed one can have efficient and accurate results.