A preocupação mundial com a sustentabilidade tem levado as organizações a investigar, cada vez mais, alternativas para melhorar a sua desempenho ambiental e, assim, garantir o desenvolvimento dos seus negócios de forma sustentável. Com o passar dos anos, a literatura tem apresentado diferentes estratégias para apoiar a evolução de empresas ambientalmente conscientes, embora muito pouco tenha se explorado com relação ao potencial para promover a sustentabilidade inerente às práticas de manufatura já existentes. Com o propósito de promover o desenvolvimento de uma cultura de melhoria contínua, lean thinking, ou pensamento enxuto, descreve uma filosofia de trabalho aplicada por muitas empresas de manufatura, a qual foca a eliminação de desperdícios e a aplicação de recursos somente onde há criação de valor para o cliente final. Seguindo essa ideia, o mesmo pensamento de se fazer mais com menos do lean thinking pode ser adaptado para a melhoria dos fluxos que são suporte à produção, isto é materiais, energia e geração de resíduos os quais causam significativo impacto ambiental, contribuindo, assim, para o desenvolvimento de negócios mais sustentáveis. A literatura apresenta diversas evidencias nas quais não só o uso da filosofia lean ajudou na redução de impacto ambiental, mas também exemplos em que a integração dos conceitos de lean e meio ambiente, Lean e Green, é positiva e complementar para redução de resíduos e perdas na produção. Entretanto, não foram encontrados outros estudos com o propósito especifico de utilizar o lean para redução do impacto ambiental na manufatura, incluindo a utilização de um pré-requisito, em termos de nível de desenvolvimento e conhecimento de lean, como requerimento crítico para sua aplicabilidade. O principal objetivo desse projeto é propor um novo modelo, chamado de Lean & Green Business Model (L&GBM). Integrando conceitos de lean e meio ambiente através do desenvolvimento de kaizens em células e em todo fluxo de produção, o modelo desenvolvido tem como principal objetivo a redução do impacto ambiental gerado pelos processos produtivos. O projeto desenvolvido reporta os resultados da aplicação do Modelo Lean e Green em uma corporação multinacional de engenharia, incluindo os resultados do desdobramento do mesmo em diferentes circunstancias: (1) teste piloto em duas células, (2) aplicação do modelo em sete células, (3) aplicação do modelo para células irmãs, (4) aplicação do modelo para fluxo de produção, (5) aplicação do modelo em diferentes ambientes da manufatura. Alguns dos principais resultados identificados até este momento através do desenvolvimento dessa pesquisa incluem: (i) L&GBM é uma boa estratégia de prevenção da poluição, reduzindo de 12 a 35% a aplicação dos fluxos de massa e energia, (ii) L&GBM pode ser usado para reduzir custos, isto é, custos da manufatura de 2 a 8%, (iii), L&GBM adiciona uma nova dimensão ao modelo tradicional de lean, (iv) L&GBM integra completamente os conceitos de lean e sustentabilidade ambiental e (v) L&GBM requer um nível de estabilidade na manufatura para ser aplicado. / Global awareness regarding environmental sustainability has prompted enterprises to investigate different alternatives for improving environmental performance in order to deploy sustainable businesses. There is a growing body of literature proposing different sustainability alternatives for environmentally-conscious firms, although not many have really explored the sustainability side of existent manufacturing strategies. With the purpose of promoting a continuous improvement culture within the business, lean thinking describes a working philosophy applied by many manufacturers, which considers the expenditure of resources for any goal other than the creation of value for the end customer, to be wasteful. Therefore, the same idea of doing more with less from lean thinking can be applied for improving material, energy flows and wastes streams that cause significant environmental impacts, thus supporting the development of a sustainable business. There has been lots of anecdotal evidence that a lean approach can help make the business case for environmental impact reduction and an integrated Lean and Green works for (1) reduction of production waste, (2) reduction of environmental impact but little empirical evidence to substantiate this. The main objective of this project is to propose a new model, which is called Lean & Green Business Model (L&GBM). In this model, environmental sustainability is integrated into pure lean thinking. The model presented in here adopts a Kaizen approach to improve mass and energy flows in manufacturing environments that already possess the necessary deployment level to apply lean thinking. Evidence-based results are first reviewed. It is presented findings to support the need of manufacturing stability as a prerequisite for integrating lean and green at the manufacturing level. The integrated lean and green approach results in (i) a reduction in production waste and (ii) a reduction in environmental impact. The project reports the findings of application of the model in a major engineering international corporation, including the results of the model deployment in several different circumstances: (1) pilot testing in two cells, (2) cell roll out in seven cells, (3) application for sisters’ cells, (4) application for a value stream and (5) application in different manufacturing environments. Some of the research key findings identified include: (i) L&GBM is a good pollution prevention strategy, reducing from 12 to 35% mass and energy flows, (ii) L&GBM can be used to reduce costs, reducing operational manufacturing mass and energy flow costs by 2 to 8%, (iii) L&GBM introduces a new dimension into traditional lean thinking, the environmental concerns, motivating a conceptual transition, (iv) L&GBM fully integrates lean thinking and green thinking, merging the fundamental principles of lean and green thinking (v) L&GBM requires a sufficient level of manufacturing stability and lean deployment prior to its introduction.

O Campo de Miranga, localizado no Compartimento Central da Bacia do Recôncavo, é um importante produtor de óleo e gás. As rochas reservatório portadoras de hidrocarbonetos aqui apresentadas constituem-se de corpos arenosos gerados por fluxos gravitacionais subaquosos intercalados por folhelhos e pertencem a Formação Maracangalha (depositada no Cretáceo Inferior). Com a descrição de 775 m de testemunhos, definiu-se 8 fácies deposicionais e 6 deformacionais para o intervalo estudado. O agrupamento de fácies em conjuntos que apresentam feições estruturais e genéticas similares permitiu a proposição de Associações de Fácies cujas interpretações são: AF1 - lobos turbidíticos distais; AF2 - canais e/ou lobos turbidíticos arenosos; AF3 - franjas de sistemas turbidíticos conglomeráticos; AF4 - deslizamentos ou regiões proximais de escorregamentos; AF5 - porções mais deformadas de corpos de deslizamentos a escorregamentos; AF6 - escorregamentos altamente móveis, plásticos a fluxos de detritos. Foi definido um datum na porção intermediária da formação constituído por uma espessa seção pelítica. Depósitos distais da AF6 dominam a porção basal do intervalo estudado e são sucedidos verticalmente (em direção ao datum) por intercalações entre turbiditos (AF2) e escorregamentos (AF5). Imediatamente acima do datum ocorrem níveis conglomeráticos (AF3) que são sucedidos verticalmente por um domínio onde se intercalam deslizamentos (AF4), escorregamentos (AF5) e turbiditos (AF2), definindose uma grande sucessão progradacional para a Formação Maracangalha na área estudada. O disparo desses fluxos provavelmente associa-se a movimentação de falhas durante estágio sin-rifte responsáveis por intensa sismicidade e remobilização de frentes deltaicas. Um mecanismo auxiliar associa-se ao intenso diapirismo argilocinético. A conectividade lateral rastreada em seções sísmicas é baixa e os melhores reservatórios do campo são os representantes da AF4 e AF2. Por critérios preditivos é possível determinar os intervalos mais propícios para a ocorrência desses corpos. / The Miranga Field, which is located in the Central Compartment of Reconcavo Basin, is an important oil and gas producer. The bearing hydrocarbon reservoirs presented here are composed of sand bodies generated by subaqueous gravity flows inserted between shales, belonging to the Maracangalha Formation (deposited during the Lower Cretaceous). Through the description of 775 m well cores, 8 depositional and 6 deformational facies were defined for the interval studied. These facies were grouped together according to structural and genetic characteristics making it possible to define Facies Associations with the following interpretations: AF1 - distal portions of turbidite lobes; AF2 - channels and/or sandy turbidite lobes; AF3 - borders of conglomeratic turbidite systems; AF4 - slides or proximal parts of slumps; AF5 - distal portions of the slides bodies or slumps; AF6 - highly mobile slumps to debris flows. A datum was chosen in the middle portion of Maracangalha Formation which consists of thick layer of shale. Distal deposits (AF6) dominate the basal portion of interval studied and they are succeeded vertically (toward to the datum) by layers interbedded between turbidites (AF2) and slump deposits (AF5). Immediately above the datum, conglomeratic intervals (AF3) occur and they are succeeded vertically by layers interbedded between slides (AF4), slumps (AF5) and turbidites (AF2), defining a great progradational succession to Maracangalha Formation in the studied area. Trigger mechanisms responsible for the genesis of gravitational flows are probably associated with faults activities during the syn-rift stage which led to intense seismic activity and caused the destabilization of sediments in delta fronts. An alternative cause for triggering may have been intense diapiric shale movements. The lateral connectivity traced in seismic sections is low and the sand bodies that should constitute the best reservoirs in this field belong to AF4 and AF2 categories. It is possible to determine the most favorable intervals for the occurrence of these sand bodies using predictive criteria.

Corrida de detritos é um tipo de movimento que se caracteriza por uma massa fluída bastante densa, constituída por lama, água, rochas e outros detritos, capaz de atingir elevadas velocidades e possuir elevado potencial de destruição. Essas características colocam esse tipo de movimento entre os mais catastróficos desastres naturais, com grande potencial de destruição, principalmente quando ocorre em áreas urbanizadas, onde os prejuízos e perdas podem ser enormes. Como apoio para definição de medidas de prevenção ou mitigação desses desastres, as ferramentas computacionais para modelagem desses movimentos têm se mostrado de grande utilidade, sendo que para isso atualmente existem diferentes abordagens. Nesse sentido, o atual trabalho se baseia na aplicação do software RAMMS em um estudo de caso a fim de verificar a aplicabilidade dessa ferramenta no estudo de casos típicos de corridas de massa em condições brasileiras. Este software, desenvolvido pelo órgão suíço WSL, se baseia no modelo de atrito de Voellmy-Salm, que divide a resistência ao cisalhamento em duas parcelas: atrito seco e atrito turbulento, sendo que para cada uma destas parcelas existe um coeficiente característico, sendo, respectivamente, μ e ξ. Neste trabalho é feita a análise de movimentos de massa que ocorreram no Rio de Janeiro no ano de 1996, nos canais dos rios Quitite e Papagaio, em que foi mobilizado cerca de 130.000m³ de material por cerca 1,5 km. Neste trabalho é feita uma retroanálise desses movimentos através do software RAMMS, de modo a se obter a calibração dos parâmetros de atrito do modelo Voellmy-Salm. Para isso foram realizadas diversas simulações dos movimentos de massa, fazendo-se a comparação dos resultados com os dados dos movimentos reais. As análises realizadas possibilitaram a calibração dos parâmetros de atrito do modelo Voellmy-Salm de modo a reproduzir de maneira satisfatória os movimentos ocorridos. Para o coeficiente de atrito seco (μ), os valores obtidos ficaram entre 0,075 para o material mais fino e 0,25 para o material mais grosseiro. Para o coeficiente de atrito turbulento (ξ) o valor obtido também foi variável de acordo com o trecho, entre 150 e 400 m/s², aproximadamente. Também foi observado que ambos os parâmetros apresentam variação ao longo do trecho da corrida. Esses valores podem vir a servir de base para estudos de novos movimentos em condições similares, através do software RAMMS, auxiliando assim em programas para prevenção ou mitigação das consequências relacionadas às corridas de detritos. / Debris flows is a mass movement characterized as a dense fluid, consisting of mud, water, rocks and other debris, which is able to reach high speeds and to have a high destructive potential. These characteristics classify this type of mass movement among the most catastrophic natural disasters, with great potential for destruction especially when it occurs in urban areas, where losses can be enormous. Computational tools to model these movements have proved to be very useful as support for studies of preventive or mitigation measures for such disasters and there are a number of different approaches currently. The current work is based on the application of RAMMS software in a case study to verify the applicability of this tool on the study of cases under Brazilian conditions. The software was developed by the Swiss agency WSL and is based on the Voellmy-Salm friction model, which divides the shear resistance into two portions: dry friction and turbulent friction, and for each of these portions assumes a characteristic coefficient, μ and ξ, respectively. In this work the analysis of the debris flows that occurred in the Quitite and Papagaio streams, Rio de Janeiro, 1996, which mobilized about 130.000m³ of material for about 1.5 km. Back analysis of these movements were performed using the software RAMMS to obtain calibration parameters for the friction model of Voellmy-Salm. For this purpose, several simulations of mass movements were performed allowing the comparison of the results with data from real movements. These analyzes had allowed the parameters calibration of the Voellmy-Salm friction model which reproduced satisfactorily the movements. For the coefficient of dry friction (μ), the values obtained were between 0.075, for fine material, and 0.25, for coarse material. For the turbulent friction coefficient (ξ) the values were also variable between 150 and 400 m/s, approximately, according to the geometric segment studied. It was also observed that both parameters changed along the stretch. These values may be used as a base for studies of new movements in similar conditions using RAMMS software and can help in prevention or mitigation of debris flows.

abstract: The atomization of a liquid jet by a high speed cross-flowing gas has many applications such as gas turbines and augmentors. The mechanisms by which the liquid jet initially breaks up, however, are not well understood. Experimental studies suggest the dependence of spray properties on operating conditions and nozzle geom- etry. Detailed numerical simulations can offer better understanding of the underlying physical mechanisms that lead to the breakup of the injected liquid jet. In this work, detailed numerical simulation results of turbulent liquid jets injected into turbulent gaseous cross flows for different density ratios is presented. A finite volume, balanced force fractional step flow solver to solve the Navier-Stokes equations is employed and coupled to a Refined Level Set Grid method to follow the phase interface. To enable the simulation of atomization of high density ratio fluids, we ensure discrete consistency between the solution of the conservative momentum equation and the level set based continuity equation by employing the Consistent Rescaled Momentum Transport (CRMT) method. The impact of different inflow jet boundary conditions on different jet properties including jet penetration is analyzed and results are compared to those obtained experimentally by Brown & McDonell(2006). In addition, instability analysis is performed to find the most dominant insta- bility mechanism that causes the liquid jet to breakup. Linear instability analysis is achieved using linear theories for Rayleigh-Taylor and Kelvin- Helmholtz instabilities and non-linear analysis is performed using our flow solver with different inflow jet boundary conditions. / Dissertation/Thesis / Ph.D. Mechanical Engineering 2013

Le contexte général de cette thèse est la simulation numérique de l’injection de carburant dans un moteur à combustion interne, afin d’améliorer son rendement et de limiter la production de polluants. Intrinsèquement, il est possible de simuler l’ensemble de l’écoulement avec les équations classiques de la dynamique des fluides sans avoir recours à des outils de modélisation supplémentaires liés au caractère diphasique. Mais, les tailles des structures générées pendant l’injection (gouttes de diamètre < à 10 μm) conduisent à des temps de calculs prohibitifs pour une application industrielle. C’est pourquoi il est nécessaire d’introduire une modélisation diphasique. C’est dans ce contexte que deux régions sont formellement distinguées: le cœur liquide dense proche de l’injecteur, appelé écoulement à phases séparées, et le spray constitué d’une population de gouttes polydisperse générées après le processus d’atomisation en aval de l’injecteur. Ce travail de thèse étudie les modèles Eulériens pour la description de spray évaporants et polydisperses, en vue d’applications industrielles. Ils représentent une alternative potentielle aux modèles Lagrangiens qui sont majoritairement utilisés en industrie mais présentant des inconvénients majeurs. Ainsi, le modèle multi-fluide est étudié dans un premier temps. Bien que prometteur, deux difficultés sont soulignées: le coût requis pour une description précise de la polydispersion, et son incapacité à décrire les croisements de gouttes (particle trajectory crossing, PTC). La thèse propose des solutions à ces deux limitations. Elles reposent sur des méthodes de moments. Premièrement, le modèle appelé Eulerian Size Multi Size Moment (EMSM) permet de résoudre des sprays évaporants et polydisperses de manière bien plus efficace que le modèle multi-fluide. Des outils mathématiques sont utilisés pour fermer le système d’équations associé au modèle, et combinés à des schémas de types volumes finis appelés schémas cinétiques, afin de préserver la réalisabilité du vecteur de moments, pour le transport et l’évaporation. Une réponse à la seconde limitation est apportée avec le modèle appelé Eulerian Multi Velocity Moment (EMVM) basé sur le transport de moments en vitesse d’ordre élevé. Une distribution bimodale peut être localement reconstruite à partir des moments en utilisant une méthode de quadrature de moments ( QMOM) en une ou plusieurs dimensions d’espace. De la même manière, l’utilisation de schémas cinétiques permet de préserver la réalisabilité du vecteur de moment. De plus, une étude mathématique approfondie de la dynamique du système en une dimension d’espace en révèle toute la complexité et représente une étape indispensable en vue de l’élaboration de schémas de transport d’ordre élevé (supérieur ou égal à 2).Afin de les tester, ces deux modèles ainsi que les outils numériques associés sont implémentés dans MUSES3D, un code académique de simulation numérique directe (DNS) dédié à l’évaluation des modèles de spray. Des résultats de grande qualité démontrent le potentiel des modèles. L’extension du modèle EMSM dans un contexte industriel est ensuite considérée, avec son implémentation dans IFP-C3D, un code résolvant des écoulements réactifs sur des maillages non structurés et mobiles dans un formalisme RANS (Reynolds Averaged Navier Stokes) en présence de sprays. Le formalisme ALE (Arbitrary Lagrangian Eulerian) est utilisé et le modèle EMSM réécrit dans ce formalisme afin de mener des calculs en maillage mobile. De plus, une étude numérique a permis d’étendre les propriétés de précision et de stabilité obtenues en maillage fixe. La robustesse du modèle EMSM est alors démontrée avec succès dans IFP-C3D sur un cas impliquant un mouvement de piston, ainsi que dans le cadre d’une comparaison avec le code MUSES3D. Enfin, des résultats très encourageants prouvent la faisabilité d’un calcul d’injection dans une chambre de combustion d’un spray polydisperse avec le modèle EMSM. / The general context of the PhD is the simulation of fuel injection in an internal combustion engine, in order to improve its thermal and ecological efficiency. This work more generally concerns any industrial device involving a multiphase flow made of liquid fuel injected in a chamber filled with gaz: automotive or aircraft engines, or turbo machines. In and of itself, it is possible to simulate this flow without any modeling. However the small structures created during injection (droplets of diameter until 10 μm or less) lead to a prohibitive computational cost for any industrial application. Therefore modeling is necessary. In this context, two areas are formally distinguished: the dense liquid core close to the injector called separate-phase flow, and the spray made of a polydisperse droplet population (i.e. droplets with different sizes) generated after the atomization processes downstream of the injector. This PhD work investigates Eulerian models for the description of polydisperse evaporating sprays, for industrial computations. They represent a potential alternative to Lagrangian models, widely used at present, yet suffering from major drawbacks. Thus, the Multi-Fluid model is assessed. Although it is very promising, two difficulties are highlighted: its cost for a precise description of polydispersity, and its inability to describe particle trajectory crossing (PTC). Solutions to these two limitations are considered. Both rely on high order moment methods. First, the Eulerian Multi Size Moment (EMSM) proposes a much more efficient resolution of polydisperse evaporating sprays than the Multi-Fluid model does. Mathematical tools are used to close the model and combined with original finite volume kinetic-based schemes in order to preserve the moment-set integrity, for evaporation and advection. An answer to the second limitation is provided with the Eulerian Multi Velocity Moment (EMVM) based on high order velocity moments. A bimodal velocity distribution can be locally reconstructed for the moments using the quadrature method of moments (QMOM), in one or multi-dimensions. Here also, finite volume kinetic-based schemes are studied in order to preserve the moment set integrity. Moreover, a mathematical study of the one-dimensional dynamic system highlights its peculiarity and constitutes a necessary basis for the design of high order numerical schemes. In order to assess them, both the models and their numerical tools are implemented in the MUSES3D code, an academic DNS solver that provides a framework devoted to spray method evaluation. Achievements of the EMSM and the EMVM models are presented. The extension of the EMSM model to an industrial context is then considered, with its implementation in the IFP-C3D code, a 3D unstructured reactive flow solver with spray. In order to perform computations within a moving domain (due to the piston movement) the Arbitrary Lagrangian Eulerian (ALE) formalism is used. A numerical study has been achieved, in order to extent to this formalism the properties of accuracy and stability of the EMSM model, which already induces strong stability condition in an Eulerian approach. The robustness of the EMSM model in the IFP-C3D code has been successfully demonstrated on a case involving a moving piston, and also on a comparison with the MUSES3D code. Moreover, very encouraging results demonstrate the feasibility of the EMSM model for spray injection.

La relaxation thermo-chimique d’écoulements hypersoniques d’azote derrière des chocs forts et pour des détentes en tuyères est étudiée en effectuant des simulations d’écoulements 1D basées sur une cinétique vibrationnelle détaillée. Ces modèles vibrationnels détaillés sont utilisés pour développer des modèles macroscopiques précis et peu coûteux en temps de calcul pour les codes multidimensionels d’écoulements de rentrée. On considère d’abord les couplages hors équilibre entre l’excitation vibrationnelle et les réactions de dissociation / recombinaison. La cinétique vibrationnelle est décrite en utilisant des bases de constantes de réaction vibrationnelles précises de la littérature, complétées par le modèle de l’oscillateur harmoniques forcé. Le rôle prépondérant des processus vibration-translation multiquanta sur la relaxation de la distribution vibrationnelle et les processus de dissociation / recombinaison est mis en évidence derrière les chocs et dans les tuyères. Les distributions vibrationnelles, qui dévient fortement de l’équilibre dans les détentes en tuyères, résultent des processus vibration-translation et de dissociation / recombinaison. Un modèle macroscopique utilisant des groupes de niveaux vibrationnels est développé pour calculer de manière consistante les termes sources de chimie et d’énergie vibrationnelle à partir de la base de constantes de réaction vibrationnelles. Ce modèle reproduit précisément les dynamiques des températures, de la chimie et des distributions vibrationnelles avec un groupe de niveaux derrière un choc et trois groupes de niveaux pour les détentes. Dans un second temps, le modèle détaillé est généralisé aux écoulements d’azote ionisé en adoptant en particulier un modèle détaillé des processus résonants électron-vibration. Derrière les chocs, ces processus contrôlent la dynamique d’ionisation en alimentant les électrons en énergie, jusqu’à ce que les échanges élastiques électron-ion prennent le relais. Il est montré que l’hypothèse couramment utilisée d’équilibre entre les températures des électrons et de vibration conduit à une relaxation trop rapide derrière les chocs. Dans les détentes en tuyère pour lesquelles la concentration en électrons est faible, la température des électrons est contrôlée par les processus électron-vibration. On observe que les électrons sont fortement couplés aux bas niveaux vibrationnels, et que le nombre de niveaux couplés augmente avec la température des électrons. Le couplage de l’écoulement avec le rayonnement, modélisé dans l’approximation des plans tangents, impacte fortement la population du second métastable et de deux états électroniques plus élevés de N. Finalement, le modèle macroscopique est généralisé à l’azote ionisé. Un bon accord avec le modèle détaillé est obtenu avec un groupe de niveaux derrière un choc et trois groupes de niveaux pour les détentes en tuyère. En particulier, le modèle macroscopique proposé décrit plus précisément les échanges électron-vibration que le modèle de Landau-Teller couramment utilisé. / The thermo-chemical relaxation of nitrogen hypersonic flows behind strong shocks and in nozzle expansions is investigated with 1D flow simulations and detailed vibrational kinetics. This work aims at deriving from detailed vibrational models accurate reduced models easy to implement in multidimensional reentry flow codes. First, nonequilibrium couplings between vibrational excitation, dissociation and recombination reactions are considered. Vibrational kinetics is described using accurate vibrational state-to-state rate constant databases of the literature completed with the forced harmonic oscillator model. The key role of multiquanta vibration-translation processes on the relaxation of the vibrational distribution function and the dissociation/recombination processes is put forward behind shocks and in nozzles. The vibrational distributions, which deviate strongly from equilibrium for nozzle expansions, are driven by vibration-translation processes and dissociation/recombination processes. A macroscopic model using groups of vibrational levels is developed to derive consistently the chemical and vibrational energy source terms from the vibrational state-to-state database.This model successfully reproduces the thermal, chemical and vibrational distribution function dynamics predicted by the state-to-state model with one group of levels behind a shock wave, and with three groups of levels in nozzle expansions. In a second step, the detailed vibrational model is extended to ionized nitrogen flows, including in particular a detailed modeling of the resonant electronvibration processes. Behind shocks, these processes control the rate of ionization by feeding energy to the electrons, up until the time when the elastic electron-ion exchanges takes over. It is shown that the widely used assumption of equilibrium between the electron and vibration temperatures predicts a too fast relaxation behind shock waves. In nozzle expansions, it is shown that for low electron concentration, the electron temperature is driven by electronvibration processes. Moreover, it is found that electrons are strongly coupled to low vibrational levels, and that more levels are coupled when the electron temperature increases. Coupling of the flow field with radiation is performed using the tangent slab approximation, and it is shown that the population of a metastable and two higher electronic levels are strongly impacted. Finally, the macroscopic model is extended to ionized nitrogen flows and is successfully applied on shock waves with one group of levels and with three groups of levels in nozzle expansions. In particular, the proposed macroscopic model represents more accurately the electron-vibration coupling than the widely used Landau-Teller model.

Les premières simulations numériques d'écoulements réactifs sur des configurationscomplexes ont été réalisées à l'aide d'approches RANS (Reynolds Averaged Navier Stokes). Ces dernières, bien adaptées aux écoulements de type couches limites attachées et relativement peu coûteuses en temps de calcul, ne donnent accès qu'à des résultats stationnaires qui s'éloignent parfois de la réalité. Pour réaliser des simulations instationnaires d'écoulements, les méthodes de type LES (Large Eddy Simulation) -- plus précises mais plus coûteuses -- sont de plus en plus utilisées. Cependant, ces méthodes sont mal adaptées à la simulation de la dynamique pariétale, car elles nécessitent un effort de maillage souvent prohibitif près de la paroi. Cette thèse est consacrée au développement dans le code CEDRE (code de simulation d'écoulements réactifs complexes de l'Onera) d'une méthode hybride RANS/LES, appelée Delayed Detached Eddy Simulation (DDES), et à son application à des écoulements réactifs massivement décollés. Après une étape de validation sur des couches limites attachées, la DDES a été appliquée à la simulation des écoulements inerte et réactif dans une chambre de combustion en forme de marche descendante (A3C) et comparée aux résultats des approches RANS et LES classiques, ainsi qu'aux résultats expérimentaux. Cette méthode a ensuite permis de réaliser l'étude de la dynamique de l'écoulement réactif décollé dans la tuyère ATAC montée sur le banc cryotechnique MASCOTTE de l'Onera. / The first numerical simulations of reactive flows on complex configurations were performed using RANS (Reynolds Averaged Navier Stokes) approaches. These methods, which are well adapted to attached boundary layer flows and relatively not expensive in computation time, provide only steady results, which may not correctly reproduce reality. For unsteady flow simulations, LES (Large Eddy Simulation) method -- more accurate but more expensive – are increasingly employed. However, these approaches are poorly suited to simulate wall turbulence since they often require a prohibitive meshing effort close to the wall. This PhD thesis is devoted to the development in the CEDRE code (Onera code for the simulation of complex reactive flows) of a hybrid RANS/LES approach, called Delayed Detached Eddy Simulation (DDES) and to its application to massively separated reactive flows. After a step of validation on attached boundary layers, the DDES is applied to the simulation of the inert and reactive flows in a backward facing step combustor (A3C) and compared to the results obtained by RANS and LES approaches, as well as to experimental results. The DDES has then been used to study the dynamics of the separated reactive flow in the ATAC nozzle mounted on the cryotechnic MASCOTTE facility of Onera.

Water is a basic necessity for sustaining life and development of society. Proper management, protection and exploitation of water resources are the challenges imposed by population growth, increasing pressure on the water and land resources by competing usage. A good amount of clean water exists on Earth although it is normally inadequate in supply because of anthropogenic activities such as deforestation and land use change. Like many other catchments that provide economic activities for the community’s livelihood, the Chalimbana river catchment in Zambia has been deforested heavily and most of the local communities believe that deforestation could be the main contributing factor to the drying up of Chalimbana River. The objective of this study was to analyse the impact of deforestation on the stream flow of Chalimbana River Catchment with the help of a conceptual hydrological model, HBV. There was a 24% reduction in the annual average rainfall amounts for the deforested period as compared to the period before deforestation. The Qrec/Qsim ratios had revealed that the annual stream flow generation for the period after deforestation (1987 to 1996) for the Chalimbana River had decreased by about 12% as compared to the period with enough forest cover (1975 to 1985). The ratio of annual Qrec/P had indicated that after a 30% forest loss in Chalimbana catchment, there was a 33% increase in the generation of the stream flow. Based on the results that were obtained, a number of recommendations aiming at improving the catchment management were made.

The goal of this thesis is to study the international portfolio choices of countries in an asymmetric world. In practice, this corresponds to the salient facts of country portfolios and the underlying structural asymmetries between developing and developed countries in a financially integrated world. In the three main chapters of the thesis, frameworks are developed to advance our understanding of the way various country asymmetries contribute to the emergence of these persistent phenomena in international capital markets. The first essay studies the question of why developing countries experience net equity inflows and bond outflows while developed countries experience net equity outflows and bond inflows, the so-called ‘two-way capital flows'. The analysis is based on an open-economy New Keynesian model of endogenous country portfolios with representative agents in each country. The model is so general that it allows one to perform an assessment of the roles of a long list of country asymmetries in determining the pattern of two-way capital flows. While steady-state net country portfolios are zero in the first essay, the second and third essays consider the situations where this is not true. The second essay presents an OLG model of an endowment economy with a country asymmetry in households' patience. Global imbalances in net positions emerge. Gross portfolio positions are obtained as the sum of standard self-hedging and, moreover, the hedging due to external imbalances. The valuation effects of external adjustments between creditor and debtor countries are rationalized. By introducing non-tradable risks, the third essay models a production OLG economy with a country asymmetry in wealth division. Global imbalances in net positions again arise. Gross portfolio positions are composed of self-hedging, hedging of non-tradable income and hedging of external interest payments, which accounts for the reality of asymmetric asset home bias, i.e. although assets are locally biased everywhere, the pattern is more pronounced in creditor countries.

A distribuição do tamanho de bolhas é uma importante característica em sistemas bifásicos. A área interfacial de bolhas está fortemente relacionada às taxas de reações químicas e de transferência de massa em aplicações industriais como colunas de destilação e fermentação, sistemas biológicos, oxidação, hidrogenação, tratamento de água, e em processos naturais, como dinâmicas de aerossóis e transferência de gás oceano-atmosfera. Pontas de provas intrusivas são largamente usadas para determinar a distribuição do tamanho de bolhas em colunas de borbulhamento bifásicas. Embora o tamanho de bolhas não possa ser obtido diretamente pelo uso de uma simples ponta de prova porque estas medem somente comprimentos perfurados em bolhas, é possível relacionar distribuições de cordas à distribuição de tamanho de bolhas usando análises estatísticas. Este trabalho apresenta a implementação de um sistema capaz de medir distribuição de tamanho de bolhas em uma coluna de borbulhamento composta por água e ar através de uma ponta de prova condutiva. Imagens obtidas por uma câmera de vídeo CCD (Charge-Coupled Devices) monocromática são usadas para validar e calibrar o sistema. / The distribution of bubble sizes is a critical feature in two–phase systems. The interfacial area of bubbles is strongly related to chemical reaction and mass transfer rates in industrial applications such as distillation and fermentation columns, biological systems, oxidation, hydrogenation, waste water treatment and in natural processes such as aerosol dynamics and air-sea gas transfer. Intrusive probes are widely used to determine bubble size distribution in two-phase bubble columns. Although bubble size cannot be obtained by a simple probe because it measures only the pierced length of the bubbles, it is possible to relate chord distributions to bubble size distribution by the use of statistical analysis. This work proposes a system implementation which is able to determine bubble size distribution in a water-air bubble column using an intrusive conductance probe. Images obtained by a monochromatic video camera CCD (Charge-Coupled Devices) are used to validate and calibrate the system.