Pour mieux comprendre la combustion en mode stratifié, la propagation de flammes au sein de stratifications de richesse laminaire ou turbulente a été étudiée par des mesures simultanées de richesse et de vitesse effectuées par couplage de la PIV et de la PLIF. L’accent a été mis sur le développement de méthodes permettant d’améliorer la qualité des mesures locales. En particulier, un nouvel algorithme de PIV permettant la mesure locale de la vitesse des gaz frais véritablement à l’entrée de la zone de préchauffage a été développé. Pour améliorer la résolution,les mailles de calcul s’adaptent localement à la topologie de la flamme, pour tenir compte de la forme du front de flamme et de l’expansion des gaz. L’analyse statistique des mesures conditionnée sur la richesse locale a permis de caractériser les propriétés de la flamme soumise à une stratification de richesse dans un écoulement laminaire et turbulent, en particulier en mettant en évidence un effet mémoire. / In order to better understand the stratified combustion, the propagation of flame through stratified mixture field in laminar and turbulent flow conditions has been studied by using combined PIV/PLIF techniques. A great emphasis was placed on developing methods to improve the accuracy of local measurements of flame propagation. In particular, a new PIV approach has beendeveloped to measure the local fresh gas velocity near preheat zone of flame front. To improve the resolution of measurement, the shape of interrogation window has been continuously modified based on the local flame topology and gas expansion effect. Statistical analysis of conditioned local measurements by the local equivalence ratio of flames allows the characterization of theproperties of flame propagation subjected to the mixture stratification in laminar and turbulentflows, especially the highlight of the memory effect.

Microorganisms and drops are ubiquitous in nature: while drops can be found in sneezes, ink-jet printers, oceans etc, microorganisms are present in our stomach, intestine, soil, oceans etc. In most situations they are present in complex conditions: drop spreading on a rigid or soft substrate, drop covered with impurities that act as surfactants, marine microbe approaching a surfactant laden drop in density stratified oceanic waters in the event of an oil spill etc. In this thesis, we extract the physics underlying the influence of two such complicated effects (surfactant redistribution and density-stratification) on the motion of drops and swimming microorganisms when they are in isolation or in the vicinity of each other. This thesis is relevant in understanding the bioremediation of oil spill by marine microbes.<div><br></div><div>We divide this thesis into two themes. In the first theme, we analyze the motion of motile microorganisms near a surfactant-laden interface in homogeneous fluids. We begin by calculating the translational and angular velocities of a swimming microorganism outside a surfactant-laden drop by assuming the surfactant is insoluble, incompressible, and non-diffusing, as such system is relevant in the context of bioremediation of oil spill. We then study the motion of swimming microorganism lying inside a surfactant-laden drop by assuming the surfactant is insoluble, compressible, and has large surface diffusivity. This system is ideal for exploring the nonlinearities associated with the surfactant transport phenomena and is relevant in the context of targeted drug delivery systems wherein one uses synthetic swimmers to transport the drops containing drug. We then analyze the motion of a swimming organism in a liquid film covered with surfactant without making any assumptions about the surfactant and this system is relevant in the case of free-standing films containing swimming organisms as well as in the initial stages of the biofilm formation. In the second theme, we consider a density-stratified background fluid without any surfactants. In this theme, we examine separately a towed drop and a swimming microorganism, and find the drag acting on the drop, drop deformation, and the drift volume induced by the drop as well as the motility of the swimming microorganism.</div>

Stratified two-phase flows were investigated at different test facilities with horizontal test sections in order to provide an experimental database for the development and validation of computational fluid dynamics (CFD) codes. These channels were designed with rectangular cross-sections to enable optimal observation conditions for the application of optical measurement techniques. Consequently, the local flow structure was visualised with a high-speed video camera, delivering data with high-resolution in space and time as needed for CFD code validation. Generic investigations were performed at atmospheric pressure and room temperature in two air/water channels made of acrylic glass. Divers preliminary experiments were conducted with various measuring systems in a test section mounted between two separators. The second test facility, the Horizontal Air/Water Channel (HAWAC), is dedicated to co-current flow investigations. The hydraulic jump as the quasi-stationary discontinuous transition between super- and subcritical flow was studied in this closed channel. Moreover, the instable wave growth leading to slug flow was investigated from the test section inlet. For quantitative analysis of the optical measurements, an algorithm was developed to recognise the stratified interface in the camera frames, allowing statistical treatments for comparison with CFD calculation results. The third test apparatus was installed in the pressure chamber of the TOPFLOW test facility in order to be operated at reactor typical conditions under pressure equilibrium with the vessel atmosphere. The test section representing a flat model of the hot leg of the German Konvoi pressurised water reactor (PWR) scaled at 1:3 is equipped with large glass side walls in the region of the elbow and of the steam generator inlet chamber to allow visual observations. The experiments were conducted with air and water at room temperature and maximum pressures of 3 bar as well as with steam and water at boundary conditions of up to 50 bar and 264°C. Four types of experiments were performed, including generic test cases as well as transient validation cases of typical nuclear reactor safety issues. As an example, the co-current flow experiments simulate the two-phase natural circulation in the primary circuit of a PWR. The probability distribution of the water level measured in the reactor pressure vessel simulator was used to characterise the flow in the hot leg. Moreover, the flooding behaviour in this conduit was investigated with dedicated counter-current flow limitation experiments. A comparison of the flooding characteristics with similar experimental data and correlations available in the literature shows that the channel height is the characteristic length to be used in the Wallis parameter for channels with rectangular cross-sections. Furthermore, for the analysis of steam/water experiments, condensation effects had to be taken into account. Finally, the experimental results confirm that the Wallis similarity is appropriate to scale flooding in the hot leg of a PWR over a large range of pressure and temperature conditions. Not least, different examples of comparison between experiment and simulation demonstrate the possibilities offered by the data to support the development and validation of CFD codes. Besides the comparison of qualitative aspects, it is shown exemplarily how to treat the CFD results in order to enable quantitative comparisons with the experiments.

<p><b>Part I: Micromechanics of dense suspensions</b></p><p>Particulate suspensions are ubiquitous in the industry & nature. Fresh concrete, uncured solid rocket fuel, & biomass slurries are typical industrial applications, while milk & blood are examples of naturally occurring suspensions. These suspensions exhibit many non-Newtonian properties like rate-dependent rheology & normal stresses. Other than volume fraction, particle material, inter-particle interactions determine the rheological behavior of suspension. The average inter-particle gaps between the neighboring particles decrease significantly as the suspension volume fraction approaches the maximum packing fraction in dense suspensions. So, in this regime, the short-ranged non-contact interactions are important. In addition, the particles come into contact due to asperities on their surfaces. The surface asperities are present even in the case of so-called smooth particles, as particles in real suspensions are not perfectly smooth. Hence, contact forces become one of the essential factors to determine the rheology of suspensions.</p><p> </p><p>Part I of this thesis investigates the effects of microscopic inter-particle interactions on the rheological properties of dense suspensions of non-Brownian particles by employing discrete particle simulations. We show that increasing the roughness size results in a rise in the viscosity & normal stress difference in the suspensions. Furthermore, we observe that the jamming volume fraction decreases with the particle roughness. Consequently, for suspensions close to jamming, increasing the asperity size reduces the critical shear rate for shear thickening (ST) transition, resulting in an early onset of discontinuous ST (DST, a sudden jump in the suspension viscosity) in terms of volume fraction, & enhances the strength of the ST effect. These findings are in excellent agreement with the recent experimental measurements & provide a deeper understanding of the experimental findings. Finally, we propose a constitutive model to quantify the effect of the roughness size on the rheology of dense ST suspensions to span the entire phase-plane. Thus, the constitutive model and the experimentally validated numerical framework proposed can guide experiments, where the particle surface roughness is tuned for manipulating the dense suspension rheology according to different applications. </p><p> </p><p>A typical dense non-Brownian particulate suspension exhibits shear thinning (decreasing viscosity) at a low shear rate followed by a Newtonian plateau (constant viscosity) at an intermediate shear rate values which transition to ST (increasing viscosity) beyond a critical shear rate value and finally, undergoes a second shear-thinning transition at an extremely high shear rate values. This part unifies & quantitatively reproduces all the disparate rate-dependent regimes & the corresponding transitions for a dense non-Brownian suspension with increasing shear rate. The inclusion of traditional hydrodynamic interactions, attractive/repulsive DLVO (Derjaguin and Landau, Verwey and Overbeek), contact interactions, & constant friction reproduce the initial thinning as well as the ST transition. However, to quantitatively capture the intermediate Newtonian plateau and the second thinning, an additional interaction of non-DLVO origin & a decreasing coefficient of friction, respectively, are essential; thus, providing the first explanation for the presence these regimes. Expressions utilized for various interactions and friction are determined from experimental measurements, resulting in an excellent quantitative agreement with previous experiments. </p><p><br></p><p><b>Part II: Motion in a stratified fluid</b></p><p>Density variations due to temperature or salinity greatly influence the dynamics of objects like particles, drops, and microorganisms in oceans. Density stratification hampers the vertical flow & substantially affects the sedimentation of an isolated object, the hydrodynamic interactions between a pair, and the collective behavior of suspensions in various ways depending on the relative magnitude of stratification inertia (advection), and viscous (diffusion) effects. This part investigates these effects and elicits the hydrodynamic mechanisms behind some commonly observed fluid-particle transport phenomena in oceans, like aggregation in horizontal layers. The physical understanding can help us better model these phenomena and, hence, predict their geophysical, engineering, ecological, and environmental implications. </p><p><br></p><p>We investigate the self-propulsion of an inertial swimmer in a linear density stratified fluid using the archetypal squirmer model, which self-propels by generating tangential surface waves. We quantify swimming speeds for pushers (propelled from the rear) and pullers (propelled from the front) by direct numerical solution. We find that increasing stratification reduces the swimming speeds of swimmers relative to their speeds in a homogeneous fluid while reducing their swimming efficiency. The increase in the buoyancy force experienced by these squirmers due to the trapping of lighter fluid in their respective recirculatory regions as they move in the heavier fluid is one of the reasons for this reduction. Stratification also stabilizes the flow around a puller, keeping it axisymmetric even at high inertia, thus leading to otherwise absent stability in a homogeneous fluid. On the contrary, a strong stratification leads to instability in the motion of pushers by making the flow around them unsteady 3D, which is otherwise steady axisymmetric in a homogeneous fluid. Data for the mixing efficiency generated by individual squirmers explain the trends observed in the mixing produced by a swarm of squirmers. </p><p><br></p><p>In addition, the ubiquitous vertical density stratification in aquatic environments significantly alters the swimmer interactions affecting their collective motion &consequently ecological and environmental impact. To this end, we numerically investigate the interactions between a pair of model swimming organisms with finite inertia in a linear density stratified fluid. Depending on the squirmer inertia and stratification, we observe that the squirmer interactions can be categorized as i) pullers getting trapped in circular loops, ii) pullers escaping each other with separating angle decreasing with increasing stratification, iii) pushers sticking to each other after the collision and deflecting away from the collision plane, iv) pushers escaping with an angle of separation increasing with stratification. Stratification also increases the contact time for squirmer pairs. The results presented can help understand the mechanisms behind the accumulation of planktonic organisms in horizontal layers in a stratified environment like oceans and lakes. </p><p><br></p><p>Much work has been done to understand the settling dynamics of spherical particles in a homogeneous and stratified fluid. However, the effects of shape anisotropy on the settling dynamics in a stratified fluid are not entirely understood. To this end, we perform numerical simulations for settling oblate and prolate spheroids in a stratified fluid. We find that both the oblate and prolate spheroids reorient to the edge-wise and partially edge-wise orientations, respectively, as they settle in a stratified fluid completely different from the steady-state broad-side on orientation observed in a homogeneous fluid. We observe that reorientation instabilities emerge when the velocity magnitude of the spheroids falls below a particular threshold. We also report the enhancement of the drag on the particle from stratification. The torque due to buoyancy effects tries to orient the spheroid in an edge-wise orientation, while the hydrodynamic torque tries to orient it to a broad-side orientation. The buoyancy torque dominates below the velocity threshold, resulting in reorientation instability.<br></p>

[pt] Modelos analíticos que descrevam o comportamento da pressão são de extrema utilidade na área de avaliação de formações e caracterização de reservatório, pois eles fornecem estimativas sobre diversos parâmetros do reservatório. Este trabalho tem dois objetivos principais: primeiro, estender a solução existente para testes de injetividade e falloff em reservatórios com uma camada e poços horizontais de modo que ela possa ser aplicada também em formações multicamadas com poços horizontais multirramificados. Além disso, este trabalho aplica funções impulso para obter uma formulação alternativa para testes de injetividade em reservatórios estratificados com poços verticais e formações com uma camada e poços horizontais. / [en] Analytical models that describe the pressure behavior are extremely useful for pressure transient analysis and reservoir characterization as they provide estimates of reservoir parameters. This work has two main goals: first, to extend the existing solutions for injectivity/falloff tests in single-layer formations with horizontal wells so that they can be applied to multilayer stratified reservoirs with multilateral horizontal wells. Furthermore, this work applies impulse functions to obtain an alternative formulation for injectivity tests in multilayer commingled formations with vertical wells and single-layer reservoirs with horizontal wells.

[pt] Os sistemas eletromagnéticos de telemetria através de formações geológicas têm sido cada vez mais estudados na última década devido às importantes aplicações de engenharia para a indústria de exploração de óleo e gás. Várias técnicas computacionais puramente numéricas têm sido utilizadas para modelar esses cenários. No entanto, elas exigem um tratamento ardiloso para às bruscas mudanças na condutividade elétrica presente nas formações geológicas. Além disso, o custo computacional necessário para o processo de discretização é muito grande, e as instabilidades em baixas frequências se tornam críticas para problemas em que largas escalas estão envolvidas. Esta pesquisa apresenta uma formulação semianalítica para analisar a propagação dos campos eletromagnéticos em um meio estratificado, dissipativo, e com anisotropia biaxial. A solução proposta emprega uma nova abordagem no domínio espectral onde uma integral baseada na transformada de Hankel é apresentada para modelar a propagação de ondas devido a fontes de corrente do tipo anel com simetria azimutal. O método proposto é empregado para a análise de cenários geofísicos análogos aos do Pré-Sal brasileiro, onde rochas carbonáticas de alta condutividade são predominantes. Além disso, o efeito das formações do pré e pós-sal nos campos eletromagnéticos e sua interação com o tubo metálico que reveste o poço de petróleo é então computado para ambientes isotrópicos e anisotrópicos. É apresentada uma série de resultados de validação que mostram que a técnica proposta é numericamente estável, robusta e computacionalmente eficiente para modelar vários problemas representativos de telemetria sem fio em poços de petróleo. / [en] Electromagnetic telemetry systems through complex geological formations have been increasingly investigated in the last decade due to important engineering applications for the oil and gas industry exploration. Many brute-force computational electromagnetic techniques have been used for modeling this scenario. However, they require a tricky treatment of the large conductivity contrasts present in the soil formations. Also, high-cost computational resources are required for the discretization process and the low-frequency instabilities become critical for such large-scale problems. This research presents a semi-analytic formulation for analyzing the electromagnetic field propagation in a biaxially anisotropic and lossy stratified media. The proposed solution employs a novel spectral domain approach where a Hankel-based integral transform is introduced for modeling wave propagation due to azimuthally symmetric current loop sources. The proposed method is employed for analyzing geophysical scenarios analogous to those of the Brazilian Pre-Salt, where high conductivity carbonate rocks are prevalent. Also, the effect of the pre and post-salt formations on the electromagnetic fields and its interaction with the metallic casing of an oil well is then computed for both isotropic and anisotropic environments. It is presented a series of validation results which show that the proposed technique is numerically stable, robust and computationally efficient for modeling several representative problems of wireless oil well telemetry.

Personality, psychological type and cognitive ability are frequently implied to be underlying causes of differences in reasoning processes, decision-making processes and general success in a job. However, there is a trend towards utilising cognitive and personality measures interchangeably in the context of selection and development, particularly as it pertains to selection based on cognitive ability and cognitive style. The general aim of this research was therefore to investigate the relationship between psychological type, as measured by the Myers-Briggs Type Inventory (MBTI), and cognitive abilities and styles as measured by the Cognitive Process Profile (CPP). Cognitive ability is discussed under the cognitive psychology paradigm. A clarification of concepts associated with cognitive psychology is provided, and the CPP model is introduced as an integrative model encompassing aspects of cognitive ability and cognitive style. Psychological type is discussed under the analytical psychology paradigm, with a focus on personality structure, dynamics and development. This is then integrated into an overview of Jung's theory of personality types and the development of the MBTI. An empirical investigation, utilising Pairwise comparisons and Chi-square statistics was conducted. The results were then integrated to enable a better understanding of the relationship between cognition and personality. Based on this, it was concluded that there is insufficient evidence to suggest that a relationship exists between cognitive styles (as defined by the CPP) and personality (as defined by the MBTI). There were however, sufficient statistically significant findings to suggest that there is some relationship between cognitive processes / competencies and personality. / Industrial and Organisational Psychology / M.A. (Industrial and Organisational Psychology)

This pilot study consists of two parts. The first part investigates the extent to which the domestic electricity consumers intend to use and use energy efficiently using the Theory of Planned Behaviour. The second part investigates the extent to which the Energy @ Home educational intervention changed the domestic electricity consumers’ behaviour. For the first part of the study an advertisement was published and a convenience stratified sample of 61 domestic electricity consumers were selected from the 290 respondents. Data was collected from the domestic electricity consumers via a questionnaire and a telephone response log. The co-relational research design was used to investigate the relationship between the predictor variables the independent variables in the constructs of the Theory of Planned Behaviour. Simple linear regression analysis resulted in F statistic for the predicted behavioural intention was 29.74 with a p value less than 0.0001 which indicates significant statistical evidence of a linear relation between the predictor variables and the independent variables. The r2 of 0.87 implies that data points that fall closely along the best fit line. Therefore the predictor variables were good predictors of the response variable. All the participants that intended to use electricity efficiently confirmed via the telephone that they were using electricity efficiently. In the second part of the study 11 out of the 61 participants were chosen to participate in the Energy @ Home educational intervention and television program. Data was collected via the Energy audit log and the electricity consumption log. The participants intended to save between 2% and 35% of their electricity consumption and the actual electricity consumption savings were between 2% and 30%. / Science and Technology Education / M. Sc. (Mathematics, Physics & Technology Education (Physics Education))

Le climat de la Terre dépend en grande partie des échanges énergétiques entre les masses d’eau chaudes et froides de nos océans. Afin de prédire et de comprendre les variations de notre climat, les modèles numériques globaux de l’océan doivent pouvoir déterminer quelle fraction d'énergie est convertie en mélange irréversible dans un écoulement turbulent et stablement stratifié. Il apparaît que cette fraction est sensible aux paramètres de l’écoulement, ce qui a récemment conduit les océanographes à remettre en question la paramétrisation d'Osborn pour le coefficient de diffusion turbulente kz, qui utilise une efficacité de mélange constante et fixée à ŋ=0,17. Ceci nous a poussé à réaliser au laboratoire de Mécanique des Fluides et d'Acoustique (LMFA) des mesures conjointes de ŋ et kz, afin de mieux comprendre leur inter-dépendance. Cette étude est avant tout expérimentale et se base sur plusieurs dispositifs permettant de quantifier le mélange dans différents types d'écoulement. Trois de ses expériences ont été réalisées au LMFA : une expérience de lock-exchange dans laquelle le mélange est issu du cisaillement à l'interface de deux courants de gravité se déplaçant en sens opposés, une expérience de grille tractée dans un fluide stratifié et une expérience d’injection de stratification dans la grille d’un canal hydraulique. Ce travail a été complété, d'une part par une collaboration sur la plateforme Coriolis du LEGI à Grenoble, permettant d’atteindre de plus grands nombres de Reynolds ; et d'autre part par une campagne de mesure in situ dans le fjord du Saguenay au Canada en collaboration avec l'ISMER, visant à estimer le mélange turbulent conduisant au renouvellement des eaux profondes du fjord, à partir de l'analyse de transects successifs de densité. Dans ces différentes configurations, l'évolution temporelle des profils verticaux de densité ont permis d'analyser la dépendance du coefficient de diffusion turbulente et de l'efficacité de mélange avec les nombres de Reynolds et de Froude. Nos résultats ont permis de quantifier la décroissance de l'efficacité de mélange avec l'augmentation du nombre de Froude dans un écoulement turbulent, ainsi que la sensibilité du coefficient de diffusion turbulente aux nombres de Froude et de Reynolds de flottabilité. L'utilisation de trois dispositifs expérimentaux différents permet de montrer qu'au-delà de ces lois dites universelles, la variabilité propre à chaque géométrie influence fortement les valeurs de l'efficacité de mélange. Ceci est particulièrement mis en lumière dans la configuration de lock-exchange, pour laquelle la valeur limite de ŋ=0.25 prédite par la physique statistique n'est atteinte que dans une configuration fortement tri-dimensionnelle, jusqu'alors peu utilisée dans la littérature. Enfin, toutes les méthodes d'analyse développées pour les expériences de laboratoire ont pu être utilisées pour l'analyse des données in situ, permettant de clore ce travail de thèse sur une étude environnementale. / Our climate partly depends on energy exchange between warm and cold water masses in the ocean's interior. In order to understand and forecast the climate variations, numerical models of the ocean must estimate the amount of energy converted into irreversible mixing in turbulent stably stratified flows. It seems that this quantity depends on the flow parameters. This assertion challenges the famous Osborn model for turbulent diffusivity kz which uses a fixed mixing efficiency of ŋ=0.17. This motivated us to measure separately kz and ŋ in order to obtain a better understanding of their inter-dependencies. The present work is an experimental study based on set-ups which enable to quantify the mixing in different types of flow. Three of those experiments are held in our lab (LMFA) and consist respectively in a lock-exchange experiment where mixing is generated by the shear at the interface of two opposite gravity currents, a stratified towed grid experiment, and a hydraulic channel experiment where the stratification is injected directly by the grid. This study has been complemented with two international collaborations. The first one, on the Coriolis platform (LEGI) consisted in a stratified towed grid experiment in a rotating tank allowing to broaden our parameter spectrum. The second one is a series of in situ measurements led in collaboration with ISMER in the Saguenay fjord (Canada) aiming at measuring density transects over time in order to quantify the turbulent mixing that participates in the renewal of the fjord's deep water. In all of those configurations, dependencies of mixing efficiency and turbulent diffusivity along with the Froude and the Reynolds numbers are extracted from the time evolution of density profiles. In our results, we were able to quantify the decay of the mixing efficiency with the increase of the Froude number. We also highlighted the sensitivity of turbulent diffusivity on the buoyancy Reynolds number. We used three different experimental setups to show that beyond the so called universal turbulence laws, the flow geometry has a huge impact on the mixing efficiency values. This is especially true in the lock-exchange configuration where the asymptotic value of ŋ=0.25, predicted by statistical physics, can only be reached in a set-up which allows 3D flows. Such investigations are still scarce in the literature. Finally, all the data analysis methods developed for the lab experiments were of great help for the analysis of in situ data and thereby enabled us to consider a real-life environnemental flow.

In this work we present the most recent developments in the direction of local fibrations structures of analytic singularities. Using techniques and tools from stratification theory we prove structural theorems in the stratified sense, which will be called singular Milnor tube fibration and Milnor-Hamm sphere fibration. In addition, we present algorithms with the purpose of creating a large number of examples in this new setting and compare our results obtained with the current ones found in the literature. Our results generalize all previous result in both cases: in the classical and in the stratified ones. / Neste trabalho apresentamos os mais recentes desenvolvimentos na direção de estruturas de fibrações locais de singularidades analíticas. Usando técnicas e ferramentas da teoria de estratificação, provamos alguns teoremas estruturais no sentido estratificado, os quais serão chamados fibração singular de Milnor sobre o tubo e fibração de Milnor-Hamm sobre a esfera. Além disso, apresentamos algoritmos com o intuito de criar uma ampla variedade de exemplos e comparamos nossos resultados com os atuais encontrados na literatura. Nossos resultados generalizam todos os previamente existentes tanto no caso clássico, quanto no sentido estratificado.