A pressão e o volume não podem ser definidos corretamente em um sistema nãohomogêneo. Neste trabalho, definimos variáveis macroscópicas globais para um gás confinado em uma armadilha harmônica, os quais são análogos à pressão e o volume. Um sistema ultra-frio tem variáveis termodinâmicas naturais como o número de átomos e a temperatura. Introduzimos um novo conjunto de variáveis globais conjugadas para caracterizar o sistema macroscopicamente. Construímos diferentes diagramas de fase para um gás de Bose de 87Rb aprisionado em uma armadilha harmônica em termos dessas novas variáveis globais obtidas a partir das frequências da armadilha e a distribuição da densidade dos átomos. Nós construímos estes diagramas de fase, identificando os principais aspectos relacionados à transição da condensação de Bose-Einstein em um gás aprisionado. Este procedimento pode ser usado para explorar aspectos relacionados com a condensação de Bose-Einstein, tais como a compressão isotérmica relacionados com a transição de fase. Por outro lado, estas novas quantidades termodinâmicas nos permitem estudar a natureza dos fenômenos quânticos como a pressão do ponto zero relacionada ao princípio da incerteza. / The pressure and volume can not be defined correctly on a non-homogeneous system. In this work we define macroscopic variables for a gas confined in an harmonic trap, which are analogous to pressure and volume. An ultra-cold system has natural thermodynamic variables as number of atoms and temperature. We introduce a new set of global conjugate variables to characterize the system macroscopically. We measure different phase diagrams of a 87Rb Bose gas in a harmonic trap in terms of these new global variables obtained from frequencies of trap and the density distribution of atoms. We construct these phase diagrams identifying the main features related to the Bose- Einstein condensation transition in a trapped gas. This procedure can be used to explore different aspects related to Bose-Einstein condensation, such as the isothermal compressibility related with the phase transition characteristics. On the other hand, these new thermodynamic quantities allow us to study the nature of quantum phenomena as the zero-point pressure related to the uncertainty principle.

L'avance technologique a encouragé, au cours de la dernière décennie, la fabrication et l'utilisation de nouveaux matériaux, ayant des propriétés innovantes et un comportement complexe. Leur développement a été conditionné par la nécessité d'augmenter l'efficacité de certains procédés technologiques, dans des domaines importants tels que la médecine, la fabrication de médicaments, de produits cosmétiques, de produits alimentaires, la production d'énergie, le recyclage des matériaux usagés, par exemple par l'industrie des transports dont la construction automobile. Dans le cadre de cette étude, nous nous sommes intéressés au comportement de fluides issus de ces matériaux complexes. En effet, leur développement, leur production et leur utilisation sont conditionnés par la compréhension et la modélisation de leur rhéologie, tant au niveau macroscopique que microscopique, voire même nanométrique. La rhéologie d'un fluide est implicitement déterminée par ses propriétés de viscosité, d'élasticité et de plasticité. Un grand intérêt a toujours été porté au comportement viscoélastique des matériaux, la viscoélasticité d'une matière étant la propriété à manifester simultanément un comportement rhéologique visqueux et élastique, quand elle est soumise à une déformation, en raison de l'application d'une tension. La caractérisation rhéologique d'un liquide suppose la détermination du tenseur de tension supplémentaire, présent dans l'équation de mouvement, provenant de mesures rhéométriques. L'expression de ce tenseur, qui dépend de la déformation et de la vitesse de déformation, s'appelle la relation ou loi constitutive. La détermination du comportement rhéologique des fluides, / This paper was dedicated exclusively to the rheological characterization of simple and complex fluids and a detailed analyze of available rheometric testing procedures. Throughout this thesis the rheological behavior of both simple and complex fluids has been studied and modeled in both shear and the complex motions (shear tests and squeezing tests). By linking conventional experimental test methods with numerical simulations of real flows, this thesis introduces a new concept in rheology: Computational Rheometry. All experimental investigations carried out in this study for the squeezing flows were accompanied by numerical simulations. For the oscillatory squeezing flow the influence of initial film thikness, oscillatory amplitude and frequency, computational time step was investigated by comparison with the theoretical predictions of squeeze force and a Genrealized Reynolds Equation inclued in a finite element code in Fortran. A validity domain was established for the analitical formulation of squeezing force. The constant velocity squeeze flow was investigated also using a quasi-steady approximation of the motion, which brings a significant reduction of the computational time, and a very good correlation with the transient (deformable mesh) approximation and the analytical predictions. The investigation of free surface influence on the distribution of normal force in both constant velocity and oscillatory squeeze flow was analyzed. In the case of constant velocity squeeze flow, the numerical simulations coupled with the free surface evolution and measured normal force during experimental investigations are suggesting the presence of a partial slip during the experimen

Soil compaction under no-tillage system has been causing serious problems to plant growth and to agriculture machines operation due to high soil resistance to tillage. Soil chiseling is a possible solution, however, some aspects regarding permanence in time, effects on soil mechanical properties and relation to draught required by mobilization mechanisms are not clearly known. In this context, the aim of this work was to evaluate the chiseling and compaction effects on soil mechanical properties under no tillage, as well as their effects on force dynamics on mobilization mechanisms. Two studies were carried out. The first was in a clay texture soil, where the temporal effect of chiseling, traffic and their influences in compressibility, shear of soil, mobilized area and draught required by the planter s shaft of no-tillage seeder, were evaluated. The second study was carried out in sandy loam soil, where the compaction influence on soil penetration resistance, mobilized area, volume, specific operational resistance and draught on a chisel plow, were evaluated. In the first study, chiseling had direct influence on shear resistance, pre-consolidation stress, compression coefficient and draught, and its effect lasted for more than 2 years, but less than 4 years. In the second study, soil compaction increased the penetration resistance, draught and microporosity, and decreased the macroporosity and the mobilized area. The specific operational resistance was higher in soils under induced compaction than without it. The chiseling effect was found in upper layer compared to the chiseled one. / A compactação nos solos sob sistema de semeadura direta está causando sérios problemas que, são revertidos à planta e as máquinas agrícolas visualizada pela maior resistência oferecida ao trabalho de implementos de araste. Tem-se como solução o uso da escarificação, porém aspectos sobre o tempo de permanência dos efeitos dessa nas propriedades mecânicas do solo e sua relação com a demanda de esforços em mecanismos mobilizadores não são claramente conhecidos. Neste contexto, o objetivo deste trabalho foi avaliar o efeito da escarificação e da compactação nas propriedades mecânicas do solo sob semeadura direta, bem como o seu efeito na dinâmica dos esforços em mecanismos mobilizadores. Para tal realizaram-se dois estudos, um primeiro em solo de textura argilosa, onde se avaliou o efeito temporal da escarificação, do tráfego e suas influências na compressibilidade, cisalhamento do solo, área mobilizada e demanda de esforços solicitados ao sulcador de semeadora de semeadura direta do tipo facão; e um segundo em solo de textura franco arenosa, onde se verificou a influência da compactação na resistência à penetração, área mobilizada, empolamento, resistência específica operacional e demanda de esforços em haste escarificadora com ponteira estreita. No estudo 1, a escarificação teve influência direta na resistência ao cisalhamento, tensão de pré-consolidação, coeficiente de compressão e na demanda de esforços, sendo que seu efeito perdurou por mais de dois anos e, após 4 anos não se encontrou mais efeito. No estudo 2, a compactação elevou a resistência à penetração, esforço tração e a microporosidade, e gerou redução da macroporosidade e da área mobilizada. A resistência específica operacional foi maior em solo sob compactação induzida do que sem ela. Efeito da escarificação foi encontrado em profundidade superior a escarificada.

Ce travail a pour objectifs d’évaluer le potentiel d'une technique spécifique de caractérisation des propriétés d'écoulement des poudres : le rhéomètre à poudre FT4. L'objectif est de pouvoir mettre en place une analyse complète sur les avantages, les inconvénients et les limites d'utilisation des tests, l'impact de la cohésion des poudres et la répétabilité des mesures. Tout d'abord, des efforts sont faits pour explorer les différences entre la consolidation test de FT4 et le tap-tap. Les résultats indiquent que la consolidation test de FT4 a une bonne répétabilité, mais il peut sous-estimer la compressibilité des poudres. Cette méthode peut être optimisée en améliorant sa procédure d'initialisation pour donner des résultats cohérents en tant que le tap-tap. Deuxièmement, le cisaillement test de FT4 est comparé avec Schulze Ring Shear Tester et Evolution Powder Tester. Cette comparaison indique que le cisaillement test de FT4 peut sous-estimer la cohésion des poudres. Par conséquent, les dimensions des accessoires doivent être optimisées. Enfin, une nouvelle technique de caractérisation a été mise au point. Dans cette méthode, les poudres présentent des mouvements périodiques et la période correspondant peut être liée aux propriétés d'écoulement des poudres. Cette méthode a une très bonne capacité à identifier et à catégorier les propriétés d'écoulement de la poudre dans les conditions de faible contrainte. / This research has been dedicated to evaluate the reliability of the FT4 and to improve the current tests for a better and convenient powder characterization. Firstly, efforts are made to explore the differences between the compaction test provided by the FT4 and the traditional tapped density measurement. Results indicate that the FT4 compaction test has good repetability but it may underestimate powder compressibility. This method can be optimized by improving its initialization procedure to give consistent results as the tapped density measurement. Secondly, the shear tests provided by the FT4 are evaluated by comparing with the methodologies provided by Schulze Ring Shear Tester and Evolution Powder Tester. This comparison indicates that the FT4 shear cell test may underestimate powder strength, especially when a cohesive powder sample is measured, which may cause blockage when using the FT4 method to design a silo. To overcome this shortage, the dimensions of the shear accessories should be optimized. Most importantly, a new characterization technique has been developed. ln this method, powder materials present periodic motions and the cycle time of the periodic flow can be linked to the powder flow properties. This method has very good capability to identify and classify powder flow properties under low stress conditions.

Há poucos estudos sobre a influência da mineralogia no comportamento do solo em relação aos atributos de resistência física. Neste sentido, o estudo tem como hipótese que independentemente do potencial matricial de água no solo a composição mineralógica da fração argila interfere na pressão de préconsolidação, modificando a capacidade de suporte de carga dos solos. Assim, objetivou-se caracterizar a composição mineralógica de classes de solos representativas no Rio Grande do Sul; Determinar parâmetros físico-mecânicos dos solos; E estabelecer correlações entre parâmetros físico-mecânicos com mineralógicos melhorando o entendimento da capacidade de suporte de carga. Para tal, foram selecionados sete solos de duas classes de solos; três Argissolos e quatro Latossolos. As amostras deformadas e indeformadas foram coletadas sob vegetação natural na camada de 10 a 15 cm de profundidade. Na fração TFSA, foram realizadas análises físicas (granulometria e área superficial específica), químicas (carbono orgânico total, teor de óxidos de ferro pedogênicos e óxidos de baixa cristalinidade) e mineralógicas (difratometria de raio x e refletância difusa). Nas amostras indeformadas foram realizadas as análises de permeabilidade ao ar e o ensaio de compressão uniaxial. Os dados foram analisados por correlações de Pearson. Os solos avaliados possuem a caulinita como principal mineral da fração argila, no entanto diferenças com relação aos óxidos de ferro foram encontradas, os quais correlacionaram com a pressão de pré-consolidação. A hematita influenciou positivamente sobre a pressão de pré-consolidação à 100 kPa, assim, dependendo do potencial matricial de água no solo. / There are few studies on the influence of mineralogy on the ground behavior in relation to physical resilience attributes. The is study has hypothesized that regardless of the matric potential of soil water the mineralogical composition of the clay fraction interferes with the pre-consolidation pressure by modifying the soil bearing capacity. Therefore, this study aimed to characterize the mineralogical composition of representative soil classes in Rio Grande do Sul; determine physical-mechanical parameters of the soil; and establish correlations between physico-mechanical parameters mineralogical improving the understanding of the load-bearing capacity. To this end, it was selected seven soils of two soil classes; three Ultisols and four Oxisols. The disturbed and undisturbed samples were collected under natural vegetation in the layer from 10 to 15 cm deep. In TFSA fraction, physical analyzes were performed (particle size and specific surface area), chemical (total organic carbon content of pedogenic iron oxides and low crystallinity oxides) and mineralogical (x ray diffraction and diffuse reflectance). In undisturbed soil samples were carried out air permeability tests and uniaxial compression test. Data were analyzed by Pearson correlations. The evaluated soils have kaolinite as the main mineral of the clay fraction, however differences with respect to iron oxides were found, which correlated with the pressure of pre-consolidation. The hematite had a positive effect on the pre-consolidation pressure of 100 kPa, thus depending on the matric potential of soil water.

Includes bibliographical references / In this thesis, the development of a strongly coupled, partitioned fluid-structure interactions (FSI) solver is outlined. Well established methods are analysed and new methods are proposed to provide robust, accurate and efficient FSI solutions. All the methods introduced and analysed are primarily geared towards the solution of incompressible, transient FSI problems, which facilitate the use of black-box sub-domain field solvers. In the first part of the thesis, radial basis function (RBF) interpolation is introduced for interface information transfer. RBF interpolation requires no grid connectivity information, and therefore presents an elegant means by which to transfer information across a non-matching and non-conforming interface to couple finite element to finite volume based discretisation schemes. The transfer scheme is analysed, with particular emphasis on a comparison between consistent and conservative formulations. The primary aim is to demonstrate that the widely used conservative formulation is a zero order method. Furthermore, while the consistent formulation is not provably conservative, it yields errors well within acceptable levels and converges within the limit of mesh refinement. A newly developed multi-vector update quasi-Newton (MVQN) method for implicit coupling of black-box partitioned solvers is proposed. The new coupling scheme, under certain conditions, can be demonstrated to provide near Newton-like convergence behaviour. The superior convergence properties and robust nature of the MVQN method are shown in comparison to other well-known quasi-Newton coupling schemes, including the least squares reduced order modelling (IBQN-LS) scheme, the classical rank-1 update Broyden's method, and fixed point iterations with dynamic relaxation. Partitioned, incompressible FSI, based on Dirichlet-Neumann domain decomposition solution schemes, cannot be applied to problems where the fluid domain is fully enclosed. A simple example often provided in the literature is that of balloon inflation with a prescribed inflow velocity. In this context, artificial compressibility (AC) will be shown to be a useful method to relax the incompressibility constraint, by including a source term within the fluid continuity equation. The attractiveness of AC stems from the fact that this source term can readily be added to almost any fluid field solver, including most commercial solvers. AC/FSI is however limited in the range of problems it can effectively be applied to. To this end, the combination of the newly developed MVQN method with AC/FSI is proposed. In so doing, the AC modified fluid field solver can continue to be treated as a black-box solver, while the overall robustness and performance are significantly improved. The study concludes with a demonstration of the modularity offered by partitioned FSI solvers. The analysis of the coupled environment is extended to include steady state FSI, FSI with free surfaces and an FSI problem with solid-body contact.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 77-79. / by Ying-Yee Lam. / M.S.

No description available.

No description available.

Subduction is a dynamic and time-dependent process which requires time-dependent models for its study. In addition, due to the very high pressures within the Earth's interior, an evaluation of the role of compressibility in subduction studies should be undertaken. However, most subduction studies have been conducted by using kinematic, steady-state, and/or incompressible mantle convection models; these simplifications may miss important elements of the subduction process. In this dissertation, I evaluate the effects of time-dependence and compressibility on the evolution of subduction by using 2-D Cartesian numerical models. The effect of compressibility on the thermal and flow structures of subduction zones is evaluated by using kinematically prescribed slab and steady-state models. The effect of compressibility is primarily expressed as an additional heat source created by viscous dissipation. The heat results in thinner thermal boundary layer on the subducting slab and increases slab temperatures. With that exception, the effect of compressibility is relatively small compared with, for example, the effect of the mantle rheology on the thermal and flow structures of the mantle wedge. Plate reconstruction models show that the convergence rate and age of the incoming plate to trench vary with time, which poses a problem for steady-state subduction models. Thus, I consider the time-dependent convergence rate and age of the incoming plate in the kinematic-dynamic subduction models in order to understand the localization of high-Mg# andesites in the western Aleutians. The results show that the localization of high-Mg# andesites is a consequence of the time-dependent convergence rate and slab age along the Aleutian arc. The influence of mantle and slab parameters as well as compressibility on the slab dynamics is evaluated by using 2-D dynamic subduction models. The results demonstrate that periodic slab buckling in the mantle results in periodic convergence rate and dip of the subducting slab; time-dependence is a natural expression of subduction. The effect of compressibility on the slab dynamics is not significant. The periodic convergence rate and dip of the subducting slab explain time-dependent seafloor spreading at the mid-ocean ridge, convergence rate of the oceanic plate at trench and arc-normal migration of arc volcanoes. / Ph. D.