A study of the importance, elements and techniques of architectural contextualism. Contextual architecture is here defined as architecture that creates relationships with its specific site or its broader physical or visual environment. This study posits the comprehensive definition of architectural contextualism on multiple levels: denotatively, connotatively, historically, philosophically, and in its aspects of critical regionalism. American architects adept at the practice of architectural contextualism during the mid-twentieth century offer principles and techniques. These architects are John Carl Warnecke, E. Fay Jones, and George White and others. This research has yielded the systematic, comprehensive definition of contextualism, a set of metrics which can be used as a basis of design and aid in the evaluation of the degree to which a building or set of buildings and their landscape are contextually congruent.

[pt] O efeito da granulometria no comportamento mecânico do lastro tem sido estudado por vários pesquisadores. A revisão destes estudos indicou que uma granulometria mais uniforme que as atualmente usadas pela indústria ferroviária diminuiria a deformação permanente e a degradação do lastro ferroviário. Neste estudo, foi utilizado o equipamento prismoidal triaxial cíclico, projetado e construído na Universidade de Wollongong - Austrália. O deslocamento lateral do lastro ferroviário no campo não está restrito, devido a insuficiente tensão lateral (tensão confinante); por isso a câmera prismoidal triaxial com lados não restritos é uma instalação ideal para a modelagem física das deformações do lastro. Duas granulometrias de lastro foram testadas, sob tensão vertical cíclica máxima de 450 kPa. Uma delas estava de acordo com a granulometria recomendada por Indraratna et al. (2004), para revisão da Norma Australiana AS 2758.7 (1996) e a outra foi preparada em concordância com a norma Brasileira, NBR 5564. Os resultados mostram que a granulometria tem grande influência na deformação permanente e na quebra de lastro ferroviário. Também se apresenta a modelagem de um ensaio de compressão sobre lastro ferroviário utilizando o método dos elementos discretos. Utilizaram-se propriedades típicas de lastro ferroviário tais como peso específico, granulometria, índice de vazios e espessura das camadas. O ensaio virtual compreende a aplicação de uma carga vertical monotônica mediante uma peça de dimensões similares a um dormente, sobre partículas que simulam o lastro colocado numa caixa de dimensões 600 x 800 x 800 mm. São observadas as tensões e velocidades desenvolvidas nas partículas, características difíceis de serem observadas nos ensaios convencionais reais. / [en] The effect of the particle-size-distribution on mechanical behaviour of ballast has been studied by several researchers in the past. The review of these past studies indicated that more uniform gradation than actually used by the railway industry would decrease permanent deformation and degradation of railroad ballast. In this study, the prismoidal cyclic triaxial apparatus designed and built at the University of Wollongong was used. The lateral displacement of railroad ballast in the field is not restricted in the absence of sufficient lateral stress (confining pressure); hence the prismoidal triaxial chamber with unrestrained sides provides an ideal facility for physical modeling of the deformations of ballast. Two different particle size distributions of ballast were tested under cyclic vertical maximum stress of about 450 kPa. One of them was according to PSD recommended by Indraratna et al. (2004) as an improvement to Australian Standard AS 2758.7 (1996) and the other one was prepared in accordance with Brazilian standard NBR 5564. The results showed that gradation had major influence on the permanent deformation and breakage of railroad ballast. Also, it is presented a compression test modelling on railway ballast using the discrete element method. Typical railways ballast properties, such as specific weight, particle-size-distribution, void ratio, layers thickness were used. The virtual test comprises monotonic vertical loading through a piece with similar dimensions to sleeper on particles that simulates ballast inside a 600 x 800 x 800 mm box. Stresses and velocities developed in particles are observed, which are difficult sighting characteristics in real conventional tests.

[pt] Esta pesquisa é motivada, principalmente, por problemas da geomecânica do petróleo como produção de sólidos em poços produtores e dano mecânico de formação. Produção de sólidos é o fenômeno onde partículas sólidas são produzidas juntamente com os fluidos de um reservatório de formação geralmente pouco ou não consolidada, podendo também ocorrer em formações mais resistentes. Dano de formação é o termo usado para identificar a redução da permeabilidade por diversos processos que ocorrem nas formações geológicas, e que reduzem a produtividade e injetividade de poços de sistemas de produção de óleo e gás. Neste trabalho desenvolveu-se uma ferramenta numérica com acoplamento fluidomecânico (mono e bifásico) para ser utilizada em análises destes problemas na microescala (poro e grão). Utilizou-se o método dos elementos discretos (DEM) para a simulação do movimento e interação das partículas sólidas e o método de lattice-Boltzmann (LBM) para a simulação do fluxo nos poros do meio geológico. A principal diferença desta ferramenta numérica em relação a trabalhos anteriores que acoplam o DEM com o LBM (DEM-LBM) está na implementação da formulação do LBM incompressível sugerida por (He e Luo, 1997) permitindo a aplicação de gradientes de pressão sensivelmente maiores do que na formulação convencional, o que é importante para as simulações de produção de sólidos. A ferramenta desenvolvida pode ser vista como um laboratório virtual para testar/verificar leis constitutivas, e que aliada a dados experimentais poderá melhorar o entendimento de mecanismos básicos envolvidos nos processos de dano mecânico de formação e de produção de sólidos. O programa computacional implementado foi verificado através de comparações com soluções analíticas ou resultados publicados na literatura. Simulações relacionadas às aplicações de interesse foram realizadas. / [en] The present research was mainly motivated by petroleum geomechanics problems such as solids production and formation damage. Solids production is related to phenomena whereby solid particles are produced together with fluids from reservoir rocks having little or no consolidation although it is reported that those phenomena have already happened to more resistant materials. Formation damage is the term used in order to identify permeability reduction occurring for various processes and which reduce productivity and injectivity of wells in oil and gas production systems. In the present work, a numerical tool considering fluidmechanical coupling (one and two phase flow) was developed for analyses in the microscale (pores and grains). The DEM (Discrete Element Method) was used for the simulation of motion and interaction of solid particles and the lattice Boltzmann method (LBM) for the simulation of flow inside pores of the geological media. The main difference between the developed tool and the ones developed in previous works that couple DEM with LBM is the introduction of incompressible LBM as suggested by (He e Luo, 1997), one that allows the application of pressure gradients considerably larger than the conventional formulation which is important for the simulation of solids production. The developed tool can be viewed as a virtual laboratory for testing and verification of constitutive laws which together with experimental data may improve the understanding of basic phenomena involved in formation damage and solids production. The numerical implementation was verified through comparisons with analytical solutions and other results from the literature. Simulations related to practical applications were carried out and discussed.

[pt] O método dos elementos discretos (MED), desenvolvido na década de 70, tem despertado, com o aumento da capacidade de processamento e o desenvolvimento de técnicas de computação de alto desempenho, crescente interesse de diversos pesquisadores como ferramenta de estudo de problemas de engenharia. Um campo de estudo de grande apelo é a modelagem de fenômenos associados a materiais granulares, dentre eles a compacta ção de pacotes granulares - como por exemplo em pós metálicos na indústria siderúrgica - , a produção de areia e a produção de material de sustenta ção de fraturas estimuladas hidraulicamente na indústria do petróleo, motivação deste trabalho. A aplicação do método requer em sua primeira etapa a geração da configuração inicial das partículas ou o preenchimento de domínios com as mesmas. Alguns estudos têm se voltado para o desenvolvimento de algoritmos de geração de arranjos densos de partículas. Neste trabalho apresenta-se um algoritmo geométrico de geração de arranjos densos de partículas que correspondam a uma dada curva granulométrica e estejam de acordo com outros parâmetros definidos para o pacote granular. No presente trabalho é dada atenção especial a geração de arranjos bidimensionais de discos para modelar o fenômeno de preenchimento de fraturas em poços estimulados por fraturamento hidráulico. O refluxo desse material com o bombeamento de óleo é uma das principais causas de declínio de produção de petróleo em poços fraturados, além de causar danos ao equipamento. O algoritmo proposto foi implementado em linguagem Java e a otimização dos arranjos segundo a porosidade foi realizada através da aplicação de algoritmos genéticos. Aplicações do algoritmo a alguns arranjos de partículas e ao problema de preenchimento de fraturas são apresentados. / [en] The Discrete Element Method (DEM), developed in the 70’s, has become more a attractive with the increasing computer processing capacity and the development of high-performance computational techniques. This scenario induced growing interest of many researchers as a tool to study engineering problems. A very appealling field of study is the modeling of phenomena associated with granular materials, including the compaction of granular packages, such as metal powders in the steel industry, sand production and proppant flowback in the petroleum industry, which is motivation to this work. The application of the method in its first step requires the generation of the particles’ initial configuration or the filling of domains with them. Some studies have focused on the development of algorithms to generate dense packing of particles. This work presents an algorithm to generate random dense packing of particles that correspond to a given granulometric curve and are consistent with other parameters set for the granular package. In the present work special attention is given to generation of two-dimensional packings of disks to model the phenomenon of fractures filling in wells stimulated by hydraulic fracturing. The proppant flowbak generated by the oil pumping is a leading cause of production decline in fractured wells, besides causing damage to the production equipment. The proposed algorithm was implemented in Java language and the optimization of packings was performed according to the porosity using genetic algorithms. Applications of the algorithm to some packings of particles and the problem of filling of fractures are presented.

Fish farming or Aquaculture is a growing food-producing industry to culture the fish in artificially constructed tanks. A large number of fishes are reared in tanks for 100-150 days and produce food for the population. With increasing population and declining worldwide capture fishery, Aquaculture is perceived as a potential technique to meet the ever-expanding food demand without tarnishing the aquatic food chain. However, problems which are addressed in current systems like human intervention and unused feed material inhibit the production rate. This thesis provides methods and guidelines to resolve the challenges and simplify the mechanical design aspects of storage, transportation, and control of the dispensing process, which ultimately benefits the small-scale producers and entrepreneurs. Storing and distributing the fish feed along the fluid stream involves in considering multi-disciplinary engineering calculations. The fundamental knowledge of fluid mechanics, discrete element properties and mechanical design have been found to be an effective solution for such challenges. The results of this work provide information on designing the fish feeding mechanism incorporating fluid stream particle dispensing and evaluation of components present in the system. The thesis work provides solutions that serve as a starting point for low-cost design, validation and automation of components in a feeding mechanism for aquaculture industries. / Fiskodling eller vattenbruk är en växande livsmedelsproducerande industri för att odla fisk i konstgjorda tankar. Ett stort antal fiskar uppföds i tankar i 100-150 dagar och producerar mat för befolkningen. Med ökande befolkning och minskande världsfångstfiske uppfattas vattenbruk som en potentiell teknik för att möta den ständigt växande efterfrågan på livsmedel utan att skada vattenlevande livsmedelskedjan. Emellertid hämmar problem som tas upp i nuvarande system som mänsklig intervention och oanvänt foderråvara produktions hastigheten. Denna avhandling ger metoder och riktlinjer för att lösa utmaningarna och förenkla de mekaniska designaspekterna av lagring, transport och kontroll av utmatning processen, vilket i slutändan gynnar småskaliga producenter och entreprenörer. Lagring och distribution av fiskfoder längs vätskeflödet innebär att man överväger tvärvetenskapliga tekniska beräkningar. Den grundläggande kunskapen om fluidmekanik, diskreta element egenskaper och mekanisk design har visat sig vara en effektiv lösning för sådana utmaningar. Resultaten av detta arbete ger information om utformningen av fiskmatning mekanismen som innehåller vätskeflöde partikeldosering och utvärdering av komponenter som finns i systemet. Examensarbetet tillhandahåller lösningar som fungerar som utgångspunkt för lågkostnads konstruktion, validering och automatisering av komponenter i en utfodringsmekanism för vattenbruksindustrin.

<p>The main aim of this PhD dissertation is to investigate the inherent and induced anisotropy in granular materials. The study includes both the experimental and theoretical aspects and provides a methodology for characterizing the mechanical response of granular materials that display anisotropy.</p> <p>The content of this thesis is divided into two main parts. The first part is focused on investigating the mechanical properties of materials with inherent anisotropy. In particular, an experimental program designed to investigate the mechanical properties of Ottawa standard sand (C109), with inherent anisotropy that is generated by the initial densification process, is described. The program involves a series of direct shear as well as triaxial axial tests. Its primary objective is to demonstrate that anisotropy may occur in sands that have nearly spherical particles (i.e. are typically considered as isotropic) provided the distribution of pore space has a preferred orientation due to the initial densification process. Following the experimental part, the mathematical formulation based on the Critical Plane Approach (CPA) is presented for describing anisotropic mechanical behavior of the material. The procedure for identification of parameters embedded in the constitutive model is outlined and an extensive numerical analysis is conducted simulating the experimental tests.</p> <p>The second part of this thesis deals with induced anisotropy and its focus is on developing an evolution law for the fabric of particulate materials as a function of continuing deformation. The microstructure descriptors are based on lineal intercept measurements and include the areal porosity and the mean intercept length distribution. The methodology involves performing a series of Discrete Element simulations for a granular assembly under evolving directions of the principal stress/strain and defining a correlation with the evolution of material axes. It is demonstrated that granular materials with spherical particles may become anisotropic due to the initial compaction process and that the induced anisotropy is characterized by the coaxiality between the microstructure and the total strain tensors. The proposed evolution law is incorporated into the constitutive framework for anisotropic materials, as discussed in the first part, and some numerical simulations are conducted. It is demonstrated that the proposed approach can describe, at least in a qualitative manner, several manifestations of induced anisotropy in granular materials.</p> / Doctor of Philosophy (PhD)

[pt] A técnica para estimulação de um campo de petróleo através de fraturamento hidráulico inclui a injeção, com o fluido de fraturamento, de um material para sustentação da abertura da fratura, denominado propante. Uma das dificuldades deste processo é o refluxo do material de sustentação para o interior do poço durante a fase de produção de óleo, ocasionando diversos problemas que podem chegar, em situações extremas, à interrupção definitiva da produção. O controle do fluxo de propante representa, portanto, um grande desafio para a indústria do petróleo. Alguns modelos empíricos - correlação Stimlab, modelo de cunha livre, modelo da velocidade mínima de fluidificação, modelo semi- mecânico - foram desenvolvidos para a previsão desse fenômeno, mas não contemplam todas as variáveis que influenciam no refluxo do material de sustentação da fratura. Uma alternativa aos modelos empíricos é utilizar o método dos elementos discretos para simular computacionalmente a instabilidade do pacote granular. Nesta dissertação busca-se modelar o comportamento do refluxo do propante utilizando uma modelagem 3D da fratura, partículas e fluxo de óleo com auxílio do programa computacional PFC3D baseado no método dos elementos discretos. Os dados das análises (tipos de propante, temperatura, características do fluido e do propante, etc) se referem a 4 cenários principais considerando fraturas sob diversos níveis de tensão e forças de arraste. Foram feitas discussões considerando os resultados numéricos obtidos por análises computacionais bi e tridimensionais, bem como comparações com modelos empíricos de previsão do refluxo do material de sustentação. / [en] The technique for stimulating an oil field through hydraulic fracturing consists of pumping into the oil bore the fracturing fluid mixed with a material to hold the fracture open, called proppant. One of the difficulties in this process is the occurrence of proppant flowback into the well bore during oil production, causing several problems that can result, in critical situations, in a definitive interruption of the oil production. Control of proppant flowback represents a great challenge for the petroleum industry. Some empirical models - Stimlab correlation, propped- free wedge model, minimum fluidization velocity, semi-mechanistic model - were developed for prediction of proppant flowback, yet they do not encompass all variable that play a role in this complex phenomenon. An alternative is to employ the discrete element method in order to computationally simulate the instability of the granular package. The main goal of this thesis is to investigate the proppant flowback phenomenon, through a 3D model of the fracture, particles and flow conditions using the computational program PFC3D, a code based on the discrete element method. The input data (type of proppant, temperature, characteristics of the fluid and proppant, etc.) relate to 4 main scenarios that consider fractures under several levels of stress closure and drag forces. The numerical results computed from 2D and 3D analyses were discussed, as well as comparisons were done with the predictions obtained with empirical methods.

[pt] A proposta deste trabalho é viabilizar e acelerar a simulação de um sistema de grãos implementado inteiramente na GPU, utilizando o Método dos Elementos Discretos (MED). O objetivo de implementar todo o sistema na GPU é evitar o custo de transferência de informações entre a placa gráfica e a CPU. O sistema proposto simula partículas de diferentes diâmetros, com tratamento de colisão entre partículas e entre partículas e o ambiente. Com o Método dos Elementos Discretos são consideradas forças normais e forças tangenciais aplicadas sobre as partículas. Algoritmos paralelos foram desenvolvidos para construção e armazenamento do histórico de forças tangenciais existente em cada contato entre partículas. São comparadas duas propostas de construção de grade regular de células para realizar a detecção de contato. A primeira proposta é muito eficiente para partículas com raio fixo, enquanto que a segunda se mostra com maior escalabilidade para modelos com variação de raio. O sistema é composto por diversos algoritmos executados em threads, responsáveis por cada etapa da simulação. Os resultados da simulação foram validados com o programa comercial PFC3D. O sistema de partículas em GPU consegue ser até 10 vezes mais rápido do que o programa comercial. / [en] The purpose of this work is to make possible and speed up a grain system simulation implemented entirely on GPU, using the Discrete Element Method (DEM). The goal of implementing all the system on GPU is to avoid the cost of data transfer between the graphics hardware and the CPU. The proposed system simulate particles of different diameters, with collision treatment between particles and between particles and the environment. The Discrete Element Method consider normal forces and tangential forces applied on the particles. Parallel algorithms were designed to construct and storage the tangential forces history present in each contact between particles. Two ideas for the construction of the regular grid of cells are proposed and compared to perform the collision detection. The first one is very efficient to particles with fixed radius, while the second one shows more scalability in models with radius variation. The system consists of several algorithms running in threads, responsible for each step of the simulation. The results of the simulation were validated with the commercial program called PFC3D. The GPU particle system can be up to 10 times faster then the commercial program.

É uma verdade incontestável que a fadiga constitui um dos problemas mais críticos em engenharia, especialmente em estruturas formadas por materiais dúcteis. Por essa razão, uma grande quantidade de métodos e estudos tem sido desenvolvida para tratar deste problema. No entanto, no caso de materiais quase frágeis como concreto, rochas cerâmicas e alguns tipos de materiais compostos, o efeito que cargas oscilantes produzem sobre estes materiais é menos conhecido e aparentemente também menos crítico. No presente trabalho, se utiliza uma versão do método dos elementos discretos formado por barras para explorar as possibilidades do mesmo na simulação do efeito de fadiga em materiais quase frágeis. Simulações sobre corpos de prova simples são apresentadas e vários aspectos deste estudo são discutidos, entre eles: influência da escala, influência da aleatoriedade nas propriedades do material simulado e se a lei de crescimento prevista por Paris (1961) se apresenta nas simulações realizadas. Finalmente, nas considerações finais, são salientadas as possibilidades que se abrem ao aplicar o modelo de elementos discretos apresentado no estudo de materiais quase frágeis submetidos à ação de cargas oscilantes. / It is an unquestionable truth that fatigue consists in one of the most critical problems of engineering, especially in ductile material structures. For that reason, a great amount of methods and studies has been developed to deal with this matter. However, when it comes to quasi brittle materials like concrete, ceramic stones and a few kinds of composites, the effect of cyclic loading on these materials is less well known, and apparently also less critical. In this work, a version of the discrete elements method formed by bars is applied to explore the possibilities of its use on simulating the effect of fatigue over quasi brittle materials. Simulations are presented over simple test specimens and several features of this study are discussed, among them: the influence of specimen scale, the influence of random distribution on material properties and if crack growth laws previewed by Paris, (Paris et al., 1961) are verified in the performed simulations. In the final considerations, the possibilities brought by applying the discrete elements method in this study of quasi brittle materials submitted to cyclic loading are highlighted.

Ce travail de thèse concerne la modélisation du béton et des ouvrages en béton soumis à des sollicitations allant du quasi statique à la dynamique rapide, tout en prenant en compte de la présence d'eau libre dans les pores du béton. L'objectif est la mise au point d'un outil prévisionnel de simulation capable de décrire le comportement du béton et des structures en béton, en tenant compte des effets du taux de saturation. Le choix des Éléments Discrets pour cette modélisation est justifié par les phénomènes discontinus qui apparaissent dans le béton, tel que la fissuration, la fragmentation ou l'écaillage. Les Éléments Discrets permettent de reproduire de manière fiable et efficace le comportement discontinu local ainsi que la réponse globale de la structure.La première partie de ce travail concerne la simulation d'essais quasi-statiques sous sollicitations uniaxiales et triaxiales fortement confinées, avec la prise en compte du phénomène de compaction. Les effets de l'eau libre contenue dans les porosités sont pris en compte par l'introduction d'une dépendance entre le taux de saturation en eau et la déformation inélastique. La procédure d’identification des paramètres du modèle est présentée. Enfin, le modèle est validé en reproduisant le comportement quasi-statique du béton par différents essais. La deuxième partie de ce travail est consacrée au comportement dynamique du béton. L'objectif est d'étendre la validation du modèle en simulant des essais d'impacts. Les effets de vitesse sont pris en comptes et des simulations d'impact sur des dalles en béton de différentes épaisseurs sont effectuées. Les résultats obtenus sont en bonne concordance avec les résultats expérimentaux. / This thesis concerns the modeling of concrete and concrete structures subjected to stresses ranging from quasi-static to dynamic loading, taking into account the presence of free water in pores. The objective is the development of a predictive simulation tool capable of describing the behavior of concrete and concrete structures, taking into account the effects of saturation ratio. The choice of discrete elements for modeling is justified by the discontinuous phenomena that appear in the concrete, such as cracking, fragmentation, spalling and scabbing. Discrete Elements can reproduce reliably and efficiently the local discontinuous behavior and the overall response of the structure.The first part of this work concerns the simulation of quasi-static tests under uniaxial and highly confined triaxial loadings, taking into account the compaction phenomenon. The effects of the free water contained in the pores are taken into account by introducing a dependency between the water saturation level and the inelastic deformation. The identification process of the model parameters is presented. Finally, the model is validated by reproducing the quasi-static behavior of concrete in different tests.The second part of this work concerns the dynamic behavior of concrete. The aim is to extend the validation of the model by simulating impact tests on concrete slabs of different thickness. The dynamic effects are taken into account and impact simulations on concrete slabs of different thickness are made. The results are in good agreement with experimental results.