This doctoral thesis reports analytical and numerical results for the electrostatic response of a dusty plasma to a moving test charge. Two important physical aspects of dusty plasmas, namely grain size distribution and grain charging dynamics were taken into account. In the first case, a dusty plasma in thermal equilibrium and with a distribution of grain sizes is considered. A size distribution is assumed which decreases exponentially with the grain mass for large sizes and gives a simple smooth reduction for small sizes. The electrostatic response to a slowly moving test charge, using a second order approximation is found and the effects of collisions are also investigated. It turns out that for this particular size distribution, there is a remarkably simple result that the resulting effective distribution for the electrostatic response is a kappa (generalized Lorentzian) distribution. In the second case, we present an analytical model for the shielding of a slowly moving test charge in a dusty plasma with dynamical grain charging for cases both with and without the collision effects. The response potential is treated as a power series in test charge velocity. Analytical expressions for the response potential are found up to second order in test charge velocity. The first-order dynamical charging term is shown to be the consequence of the delay in the shielding due to the dynamics of the charging process. It is concluded that the dynamical charging of the grains in a dusty plasma enhances the shielding of a test charge. To clarify the physics, a separate study is made where the charging is approximated by using a time delay. The resulting potential shows the delayed shielding effect explicitly. The terms in the potential that depend on the charging dynamics involve a spatial shift given by the test charge velocity and the charging time. The wake potential of a fast moving test charge in the case of grain charging dynamics was also found. It was observed that the grain charging dynamics leads to a spatial damping and a phase shift in the potential response. Finally, combining these two physical aspects, generalized results for the electrostatic potential were found incorporating the terms from both grain size distribution and grain charging dynamics. The generalized results contain the previous work where these two effects were studied separately and which can now be found as special limiting cases. This kind of work has relevance both in space and astrophysical plasmas. / QC 20100920

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-04-17T12:08:06Z No. of bitstreams: 1 JOSÉ ANTÔNIO LEAL DE FARIAS - DISSERTAÇÃO PPGCC 2014..pdf: 3257698 bytes, checksum: cea41aeb45f4b269f2356f8ecad15069 (MD5) / Made available in DSpace on 2018-04-17T12:08:06Z (GMT). No. of bitstreams: 1 JOSÉ ANTÔNIO LEAL DE FARIAS - DISSERTAÇÃO PPGCC 2014..pdf: 3257698 bytes, checksum: cea41aeb45f4b269f2356f8ecad15069 (MD5) Previous issue date: 2014-08-05 / Recompensas em Crowdsourcing Computação por Humanos é uma abordagem que utiliza seres humanos para obter resultados mais satisfatórios em áreas em que os atuais recursos computacionais não conseguem atender adequadamente. Diversas técnicas e aplicações foram desenvolvidas para suportar essa abordagem e algumas delas utilizam recompensas financeiras como forma de estímulo aos indivíduos, enquanto outras se utilizam de jogos criados especialmente para suportar uma determinada tarefa e ao mesmo tempo como meio para aumentar a participação e o engajamento dos participantes. Este estudo descreve os resultados de um experimento que utilizou jogos comuns, não associados a qualquer tarefa ou atividade específica, criados apenas para entretenimento, como forma de recompensa para esses indivíduos. Nossos resultados mostram que jogos são um meio eficiente de estímulo ao engajamento na execução de Computação por Humanos. / Human Computation is an approach that uses humans to get more satisfactory results in areas where current computational infrastructures cannot meet properly. Several techniques and applications have been developed to support this approach and some of them use financial rewards as a stimulus to individuals, while others make use of games specifically designed to support a particular task and, at the same time, as a means to increase the participation and engagement of his participants. This study describes the results of an experiment that used regular games, not associated with any specific task or activity, created just for entertainment, as a reward for these individuals. Our results show that games are an effective means of stimulating the involvement in the execution of Human Computations.

CAPES / A indústria petrolífera utiliza diversos tipos de bombas conforme a natureza da operação ou a fase do processamento considerada. Entretanto, devido às condições nas quais opera esse tipo de indústria, óleo e gás podem ser produzidos simultaneamente, o que constitui uma questão de escoamento bifásico. A presença de gás em canais de bombas centrífugas prejudica significativamente o seu funcionamento, degradando a capacidade de elevação. As pesquisas relacionadas ao escoamento bifásico em bombas centrífugas centram seus estudos na avaliação da influência de condições operacionais, tais como a fração de vazio, rotação do rotor e pressão de entrada, no desempenho global da bomba. Essa influência, entretanto, é condicionada ao padrão de escoamento bifásico no interior do equipamento. Nesse cenário, o presente trabalho tem como objetivo avaliar o escoamento bifásico nos canais de uma bomba centrífuga mediante o comportamento de uma bolha isolada no meio líquido em rotação. Para isso, foi construída uma bancada experimental no laboratório do NUEM. A carcaça da bomba e o rotor do primeiro estágio originais foram substituídos por outros de material transparente a fim de permitir a visualização das bolhas no interior do canal do rotor. Em particular, pretende-se seguir o movimento de bolhas isoladas nos canais do rotor, como forma de identificar seus caminhos preferenciais, para avaliar suas velocidades ponto a ponto. Além disso, foi desenvolvido um estudo numérico como forma de obter as velocidades do líquido e pressão estática ao longo do canal, utilizando as posições das bolhas obtidas experimentalmente. Um modelo algébrico utilizou os dados numéricos e experimentais para calcular o coeficiente de arrasto e a força de arrasto segundo diferentes condições operacionais. / Electrical Submersible Pump (ESP), are quite common in the oil industry. Due to the nature of the oil production operations, multiphase flow of oil, gas and other fluids are present in reservoirs, pipelines and equipment, including ESP’s. Two-phase flows inside pump diffusers and impellers decrease an ESP’s lift and efficiency. Literature presents a large number of studies about the influence of operational parameters such as void fraction, rotor speed and inlet pressure, on an ESP’s global efficiency. Nevertheless, this influence is strictly related to the two-phase flow pattern. The present study evaluates the two-phase flow inside a pump diffuser and impeller by means of a single bubble flowing through the liquid mass. An experimental apparatus was designed and built at the NUEM facilities. The original pump housing and impeller were replaced by transparent pieces so that bubbles flowing inside the pump could be visualized. The path of the bubbles were followed so as to both define preference paths and to calculate bubbles velocities. Additional CFD analyses provided liquid velocities and static pressure through the pump impeller. An algebraic model fed with numerical and experimental data evaluated the drag coefficient and the drag force according to different experimental conditions.

Les études conduites au cours de ce travail de thèse ont montré que l’optimisation de la position du cycliste sur son vélo était un élément déterminant de la performance. Nos recherches ont porté sur quatre axes principaux : la conception et la validation d’outils de mesure, l’étude de la position aérodynamique, l’étude de la position assise et enfin l’étude de la position danseuse.L’ensemble des résultats obtenus montrent que la capacité de performance du cycliste peut être améliorée en position aérodynamique en augmentant le ratio entre la puissance mécanique (Pméca) et la surface frontale effective (SCx). Le confort représente également un des principaux facteurs de la performance en contre‑la‑montre (CLM) puisqu’il détermine l’aptitude du cycliste à maintenir sa position au cours du temps. Nos travaux montrent une amélioration du confort avec des semelles orthopédiques, chez les cyclistes affectés par une inégalité de longueur des membres inférieurs (ILMI), liée à une réduction des mouvements du bassin. Une correction orthopédique induit également une augmentation du rendement énergétique (+5,7 %). Ainsi, les cyclistes affectés par une ILMI sont recommandés de la compenser avec des semelles orthopédiques individualisées de façon à améliorer leur performance en CLM. Lors d’une étude préliminaire, nous avons également montré la relation entre les mouvements de la tête et le SCx, c’est pourquoi les cyclistes doivent réduire au maximum ces mouvements afin de minimiser leur SCx et ainsi maximiser leur performance. L’évaluation de la position aérodynamique doit être réalisée en conditions réelles de locomotion, que ce soit pour l’évaluation de S ou de SCx. Le développement de nos deux applications est donc un réel atout pour l’évaluation de la traînée aérodynamique (Ra) de manière individualisée dans les prochaines années puisqu’elles rendent le traitement plus accessible aux entraîneurs. Enfin, bien que nous ayons initié une nouvelle méthodologie d’évaluation de la position aérodynamique en associant numérisation 3D et modélisation numérique de la mécanique des fluides, cette méthode serait plutôt recommandée pour l’individualisation de l’équipement.La position assise peut également être optimisée en augmentant l’indice d’efficacité mécanique (IEM) du cycliste, quel que soit le niveau et le sexe. Cette augmentation de l’IEM passe principalement par une diminution de la force résistante (Fres) dans la phase de montée de la pédale. Malgré tout, le cycliste ne doit pas tirer sur la pédale pour générer un couple propulsif car cette stratégie est contre-productive d’un point de vue énergétique. Il serait intéressant d’étendre notre première étude, établie en laboratoire, sur le terrain pour analyser les adaptations biomécaniques du pédalage des cyclistes aux conditions rencontrées sur le terrain. Les différences observées en laboratoire, sur terrain plat et en montée laissent penser que les cyclistes adaptent leur pédalage selon les conditions dans lesquelles ils évoluent.Enfin, les travaux menés sur la position danseuse montrent que les cyclistes augmentent leur coût mécanique (CM) (+4,3 % en laboratoire vs. +19 % sur le terrain) par rapport à la position assise alors que la consommation d’oxygène reste stable entre les deux positions. Ces pertes mécaniques en position danseuse sont principalement dues à l’augmentation du coefficient de roulement (Cr) due aux oscillations latérales du vélo et donc à la torsion des pneus. Puisque les pertes mécaniques sont plus élevées sur le terrain que sur tapis roulant, d’autres facteurs semblent contribuer à cette différence comme la Ra (~10 W), le matériel utilisé par les cyclistes, le Cr de la route et la technique adoptée. Aussi, la position danseuse induit une augmentation du CM pour maintenir la vitesse de déplacement face aux variations de pente en montée. Les cyclistes sont donc fortement recommandés de réduire l’augmentation du CM en position danseuse comparée à la position assise. / The studies conducted during this PhD research showed that optimizing the position of the cyclist on the bicycle is a key factor influencing cycling performance. Our research focused on four main axes: the design and validation of measurement tools, the study of the aerodynamic position, the study of the seated position and the study of the standing position.All the results showed that the performance capacity of cyclists can be improved in aerodynamic position by increasing the ratio between the mechanical power (PO) and the drag area (ACd). Comfort is also a significant factor in time trial (TT) performance as it determines the ability of the cyclist to maintain position over time. Our works show that comfort can be improved via orthopaedic correction in cyclists affected by lower limb length inequality (LLLI) in the TT position, related to a reduction in pelvis movements. The orthopaedic correction also induces an increase in gross efficiency (+5.7%). Thus, this improvement in comfort could increase the PO and/or the amount of time the aerodynamic position can be maintained during a TT. Therefore, cyclists affected by LLLI should compensate LLLI with individualised foot orthotics to improve their TT performance. In a preliminary study, we also showed that there is a relationship between head movements and ACd. Therefore, cyclists should minimise these movements to minimise their ACd and maximise their performance. Aerodynamic position must be evaluated in real cycling locomotion, whether for the evaluation of A or ACd. We have developed two applications that are a real asset for the dynamic evaluation of aerodynamic drag (Ra) as they make the data analysis more accessible to coaches. Finally, although we have initiated a new method to assess ACd in the aerodynamic position by combining 3D scanning and computational fluid dynamics simulation, this method is also recommended for individualisation of cycling equipment.The seated cycling position can also be optimised by increasing the cyclists’ force effectiveness (FE), regardless of practice level or gender. This increase in FE is mainly due to a decrease in resistive force (Fres) during the upstroke phase of pedalling. Nevertheless, the cyclist should not pull on the pedal to generate propulsive torque because this strategy is counterproductive from an energy point of view. It would be interesting to extend our first study, which was set up in a laboratory, to the field to analyse the biomechanical adaptations of cyclists to the real conditions of locomotion. The differences observed in the laboratory, on level ground and over an uphill grade suggest that cyclists adjust their pedalling technique according to the conditions under which they are performing.Finally, studies of the standing cycling position show that cyclists increase their mechanical cost (MC) (+4.3% in the laboratory vs. +19% in the field) compared to the seated position; however, oxygen consumption was similar between the two positions. These mechanical losses (13 W in the laboratory vs. 49 W in the field) in the standing position are mainly due to increased rolling resistance coefficient (Crr), induced by the lateral sways of the bicycle and therefore torsion of the tyres. Because the observed mechanical losses are higher in the field than on the treadmill, other factors could contribute to this difference, such as Ra (~10 W), the equipment used by cyclists, the Crr of the road surface and the technique adopted. Also, the standing position induces an increase in MC to maintain constant speed when faced with uphill slope variations. Cyclists are therefore strongly recommended to reduce the increase of the MC in standing position compared to the seated position. This reduction in mechanical losses can be achieved by decreasing lateral sways and Ra.

En termes d’économie d’énergie, la réduction de trainée revêt un intérêt indéniable. Dans certains cas, ce phénomène obtenu grâce à l’ajout dans le milieu de faibles quantités d’additifs peut atteindre une réduction du frottement à la paroi, en régime turbulent, allant jusqu’à 80% comparé au fluide seul. On le retrouve dans divers domaines d’applications telles quele transport des hydrocarbures et dans les circuits d’eau de chauffage et de refroidissement.Trois systèmes qui ont la capacité de s’autoorganiser en milieux aqueux ou organique ont été étudiés dans le but de vérifier leur possible aptitude à réduire le frottement hydrodynamique.On s’est intéressé à un polysavon (80C12) composé d’un squelette polystyrène auquel sont liées des amines tertiaires portant des chaines alkyles de 12 carbones. Ce composé forme des micelles dans l’eau dont la forme cylindrique a été mise en évidence par diffusion de la lumière et Cryo-MET. L’étude du transfert de masse sur une électrode à disque tournant et les résultats rhéologiques ont mis en évidence le caractère viscoélastique qui est responsable duphénomène de réduction de frottement hydrodynamique recherché.Des études rhéologiques réalisés sur les systèmes lécithine/décane et ionomère/toluène ont permis de mettre en évidence le caractère viscoélastique des associations anisotropes de ces composés. / In terms of energy saving, drag reduction hasan undeniable interest. In some cases drag reduction with additives can reach 80% compared to pure solvent. This phenomenon has applications in many fields suchas transportation of hydrocarbons and cooling and heating systems. Three systems which have the capacity to selforganizein aqueous or organic media have been studied in order to check their possible ability to reduce hydrodynamic friction.We worked on a polysoap (80C12) based on polystyrene skeleton to which tertiary amines bearing alkyls chains of 12 carbons. This compound formsmicelles in water whose cylindrical shape has been demonstrated by light scattering and Cryo-TEM. The studies of the mass transfer on a rotating disk electrode and the rheological results have showed for the 80C12solutions several characteristics attributed to the dragreducing additives.Rheological studies on the systems lecithin/decane and ionomers/toluene, highlight the viscoelastic properties of the anisotropic associations of these compounds.

Le travail réalisé dans le cadre de cette thèse en co-tutelle concerne deux domaines d’étude de l'interaction fluide-structure. Le premier relevant du Génie Minier traite de l'interaction entre une grille mobile au sein d'un sluice et de l'écoulement confiné associé. Le second relevant de l'Hydrodynamique fondamentale porte sur l'interaction d'un cylindre monté sur appuis souples et un écoulement à surface libre en présence de fond. Notre travail contribue à l’étude des écoulements confinés à surface libre par une approche expérimentale. Nous avons couplé des techniques de visualisation par caméra CCD, de mesures de champs de vitesse par PIV et d'efforts hydrodynamiques pour qualifier la dynamique des objets en mouvement dans l'écoulement. Les méthodes et dispositifs expérimentaux sont alors appliqués à l'étude de l'écoulement autour de deux maquettes simplifiées d'un JIG à grille mobile puis à celui du cylindre vibrant sous l'effet de l'écoulement. L’acquisition par PIV suivi des traitements statistique multi-variables par POD nous a permis d'étudier l'évolution des zones de recirculation dans le compartiment ainsi que le champ de vitesse instationnaire. L’étude expérimentale a été complétée par une simulation numérique par ANSYS14.5 pour la maquette de JIG et par un modèle numérique d’oscillation du sillage pour le cylindre. Ces travaux nous ont permis de mettre en évidence une technique simple pour mettre en mouvement, dans un sluice, un filet attaché à un cylindre et d'étudier les effets du confinement sur un cylindre vibrant en présence de surface libre. / The work realized under this co-supervised thesis concerns two study areas of fluid-structure interaction. The first concerned the Mineral Engineering and deals with the interaction between a moving grate in a sluice and the confined flow associated. The second concerns the fundamental Hydrodynamics and deals with the interaction of a cylinder mounted on flexible supports and a free surface flow in presence of plane wall. Our work contributes to the study a confined free surface flow by experimental approach. We coupled techniques of CCD camera visualization, velocity fields measurements by PIV and hydrodynamic forces to qualify the dynamics of structure motion in the flow. Experimental methods and devices are applied to the study the flow around two simplified models of a moving JIG grate and then to study a vibrating cylinder due to flow. Treatments of PIV data acquisitions by multivariable statistical POD enabled us to describe evolution of recirculation zones in the compartment and unsteady velocity field. Experimental study was completed by a numerical simulation of Jig model by using ANSYS14.5 and a numerical wake oscillator model for the case of the cylinder. This work highlighted a simple technique to give motion, in a sluice, a attached net to a cylinder and to study effects of free surface flow confinement on a vibrating cylinder

Ce travail de thèse fait partie intégrante de l’ANR PLAYER (début janvier 2012), projet visant à étendre les simulations d'écoulements gaz-particules à des particules non-sphériques ayant une inertie couvrant une large gamme. Les avancées de cette ANR portent notamment sur la détermination des forces et couples élémentaires sur de tels objets avec la question du nombre de degrés de liberté supplémentaires à prendre en compte, l'impact de la forme et de l’effet d'inertie ainsi que l’influence d’une force extérieure telle que la gravité sur les interactions particule-turbulence. Dans ce cadre, l’objectif de ce travail de thèse est d'étudier finement la dispersion de particules non-sphériques rigides dans un écoulement turbulent à l’échelle mésocospique (il est supposé que les particules sont des points matériels). Pour ce faire, un suivi lagrangien de particules ellipsoïdales couplé à un code de simulation numérique directe d’un écoulement turbulent de canal a été utilisé. Cette méthode nécessite alors une bonne estimation des forces et couples hydrodynamiques agissant sur ce type de particules, ainsi qu’un couplage des équations du mouvement de translation et de rotation. En se basant sur les résultats obtenus par une simulation numérique directe résolue à l’échelle de la particule (Ansys Fluent, body-fitted method), nous avons établi, dans un premier temps, des corrélations pour les coefficients hydrodynamiques (traînée, portance, couple de tangage) dépendant du nombre de Reynolds particulaire, de la forme, et de l'orientation des particules. L’originalité de ce travail réside en la validité de ces corrélations pour des gammes étendues de facteurs de forme (rapport entre la longueur et la largeur de la particule w ∈ [0,2-32] et de Reynolds particulaires Rep ∈ [1-240]. Ces corrélations ainsi que les équations du mouvement de rotation ont été ensuite intégrées dans le code « maison » de simulation numérique directe d’un écoulement turbulent gaz-solide à l’échelle mésocospique. Après avoir validé ce code à travers différents cas tests, nous avons étudié la dispersion de différentes particules ellipsoïdales dans un écoulement de canal turbulent pour un nombre de Reynolds modéré. Trois principaux effets sont à l’étude : l’effet de forme, l'effet d'inertie et l'effet du croisement de trajectoires. / The present work is a part of a program research ANR PLAYER (started from January 2012), the aim of the project is to extend the simulations of gaz-particles flow to the non-spherical particles with a large range of inertia. The main objectives of this project consist, firstly, on the founding of hydrodynamic forces and torques occurring on these non-spherical particles. As results, we focus on the additional degrees of freedom that must be considered, shape effects and effects of inertia. Secondly, we are interested on the study of particle-turbulence interaction and particle-particle interaction. The aim of this Phd thesis consists on the studying of the dispersion of solide non-spherical particles in turbulent channel flow at mesoscopic scale. In order to achieve this work, we considered a one way coupling and we used a technique of Particles Lagrangian Tracking coupled with a Direct Numerical Simulation of the turbulent channel flow (DNS/PLT). This technique requires a well prediction of hydrodynamic forces and torques occurring on each particle. In addition, this technique requires a coupling of translational and rotational motions. Firstly, a Direct Numerical Simulation is used with a body-fitted method in CFD code Ansys-Fluent to simulate flow around ellipsoids. Based on the obtained results, models of correlation for hydrodynamic coeffients (drag, lift and torque) are proposed. The major results of this part is the accuracy models for a large ranges of particles Reynolds number, aspect ratio and orientations. Indeed these models take the particle Reynolds number Rep ∈ [1-240], the shape (aspect ratio w ∈ [0.2-32]) and the orientation of the particle into account. Secondly, these models of correlation as well as translational and rotational motions are implemented in the in-house DNS code. After a rigorous validation of the code using a different test cases, simulations of dispersion of ellipsoidals particles in a tubulent channel flow is performed for a moderate Reynolds number. Three main effects are investigated in this study: shape effect, inertial effect and the “effect of crossing trajectories”.

Vegetation is commonly modelled as emergent arrays of rigid, circular cylinders. However, the drag coefficient (CD) of real stems or trunks is closer to that of cylinders with a square cross-section. In this thesis, vegetation has been idealised as square cylinders in laboratory experiments with a turbulence intensity of the order of 10% which is similar to that of typical river flows. These cylinders may also represent other obstacles such as architectural structures. This research has determined CD of an isolated cylinder and cylinder pairs as a function of position as well as the average drag coefficient (CDv) of larger arrays. A strain gauge was used to measure CD whilst CDv was computed with a momentum balance which was validated by strain gauge measurements for a regularly spaced array. The velocity and turbulence intensity surrounding a pair of cylinders arranged one behind the other with respect to mean flow (in tandem) were also measured with an Acoustic Doppler Velocimeter. The isolated cylinder CD was found to be 2.11 in close agreement with other researchers. Under fixed flow conditions CD for a cylinder in a pair was found to be as low as -0.40 and as high as 3.46 depending on their relative positioning. For arrays, CDv was influenced more by the distribution of cylinders than the flow conditions over the range of conditions tested. Mean values of CDv for each array were found to be between 1.52 and 3.06. This new insight therefore suggests that CDv for vegetation in bulk may actually be much higher than the typical value of 1 which is often assumed to apply in practice. If little other information is available, a crude estimate of CDv = 2 would be reasonable for many practical applications. The validity of a 2D realizable k-epsilon turbulence model for predicting the flow around square cylinders was evaluated. The model was successful in predicting CD for an isolated cylinder. In this regard the model performed as well as Large Eddy Simulations by other authors with a significant increase in computational efficiency. However, the numerical model underestimates CD of downstream cylinders in tandem pairs and overestimates velocities in their wake. This suggests it may be necessary to expand the model to three-dimensions when attempting to simulate the flow around two or more bluff obstacles with sharp edges.

xi, 158 p. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / This study, set in the context of the feminist sex wars, explores the performances of Holly Hughes, Carmelita Tropicana, and Split Britches throughout the 1980s and early 1990s. The purpose of this study is to better understand the implications of a specific style of lesbian comedic performance, found at the WOW Café and defined here as lesbian camp, throughout a contentious era in feminist politics. The motivating questions for this study are: How can a performance inspire an activated spectatorship? How have lesbian comedic performance practices provoked feminist theory and practice? Chapter II defines lesbian camp and attempts to trace a dialogue among lesbian performance critics and academics ruminating over lesbian camp and its existence. It also explores lesbian camp's relationship to drag and butch-femme as well as how lesbian camp functions within specific performances of Holly Hughes, Split Britches, and Carmelita Tropicana. Chapter III argues that it is the very element of lesbian camp that brings forth the potential for an activated spectatorship. It is a chaotic, unstable environment that exposes and disassembles deep-seated fears, ideals, and practices seemingly inherent, although pragmatically constructed, to our communities and cultures throughout the 1980s and early 1990s. It presents a climate of resistance through the disruption of identificatory practices. This, in turn, provokes an activated spectatorship. Chapter IV examines the effects these artists had on the larger stage of the feminist sex wars and culture wars. Holly Hughes, for example, became a national figure, defunded from the National Endowment for the Arts due to her subject of the queer body, then deemed obscene and pornographic. Split Britches were popularized by feminists in the academy not only for their creative techniques but also for their (de)construction of butch-femme coupling. Carmelita Tropicana brought drag to a whole new level with incorporation of male and female drag into her hybrid performances. / Committee in charge: John Schmor, Chairperson, Theater Arts; Sara Freeman, Member, Theater Arts; Theresa May, Member, Theater Arts; Ellen Scott, Outside Member, Sociology

De nombreuses applications industrielles mettent en jeu des fluides complexes qui possèdent souvent un seuil d'écoulement leur permettant de résister à des efforts finis sans s'écouler. Par ailleurs, ces fluides peuvent glisser aux parois lorsque les conditions interfaciales sont favorables. Toutes ces propriétés influencent leurs écoulements autour d'obstacles. Cette thèse se propose de comprendre ces écoulements dans le domaine où les vitesses d'écoulement sont telles que les effets inertiels peuvent être négligés devant les effets visqueux eux-mêmes faibles par rapport aux effets plastiques. Elle analyse l'influence de la vitesse et du glissement sur la force de traînée et les champs cinématiques générés par l'écoulement très lent et en régime permanent d'un fluide à seuil autour d'obstacles aux surfaces adhérentes ou glissantes. Les géométries considérées sont le disque, la sphère, le cône et la plaque plane. Le fluide utilisé a un comportement élasto-viscoplastique pouvant être décrit par les modèles de Herschel-Bulkley et de Hooke. Ce comportement a été caractérisé en volume et en présence de glissement par des mesures rhéométriques. Le nombre adimensionnel clé de l'étude est le nombre d'Oldroyd, ratio entre les effets plastiques et les effets visqueux, compris ici entre 10 et 200. Les mesures de forces de traînée ont montré qu'indépendamment de l'obstacle et des conditions interfaciales, le coefficient de traînée diminue avec le nombre d'Oldroyd et tend vers une valeur asymptotique. Cette valeur montre qu'au-delà d'un certain nombre d'Oldroyd, ce coefficient n'est plus gouverné par la vitesse mais dépend uniquement du seuil et de la surface caractéristique de l'obstacle. Elle permet de calculer un critère de stabilité pour lequel l'objet est maintenu en suspension. Les champs cinématiques déterminés par PIV ont permis de caractériser la forme et l'étendue des zones rigides et cisaillées. Les mesures de forces de traînée et de champs cinématiques ont permis de quantifier la contribution des contraintes normales et tangentielles dans la force de traînée totale. La présence de glissement aux parois de l'obstacle diminue significativement le coefficient de traînée et modifie la morphologie de l'écoulement en réduisant l'étendue des zones cisaillées. Une simulation numérique a été menée dans le cas de la plaque plane avec un modèle élasto-viscoplastique et un code à éléments finis avec points d'intégration Lagrangiens. / Many industrial processes include numerous complex fluids often presenting a yield stress. Those fluids can also slip when interfacial conditions are favorable. All these properties affect their flows around obstacles. This thesis aims to understand such flows in a domain where the flow velocities are so low that inertia effects can be neglected compared to viscous effects which are substantially low compared to plastic effects. It analyzes the influence of the velocity and the slip on the drag force and the kinematic fields of the creeping flow of a yield stress fluid around obstacles either with adhesive or slippery wall. The flow is analyzed in steady regime. The considered geometries are the disc, the sphere, the cone and the flat plate. The fluid used has an elasto-viscoplastic behavior which is modelled by the Herschel-Bulkley and Hooke models. This behavior has been characterized by rheometrical tests performed with adherence and slip conditions. The main non-dimensional number is the Oldroyd number, i.e. the ratio between plastic and viscous effects, which ranges from 10 to 200. The drag forces measurements have shown that regardless of the obstacle and the interfacial conditions, the drag coefficient decreases with the Oldroyd number before tending towards to an asymptotical value. This asymptotical value highlights that for high Oldroyd numbers the drag coefficient is no longer governed by the velocity but depends only on the yield stress and the characteristic section of the obstacle. A stability criterion for which the obstacle is held in suspension has been calculated from it. The kinematic fields determined by PIV have enabled to characterize the shape and the extent of the sheared and static regions. The drag forces and the kinematic fields measurements have enabled to quantify the contribution of the normal and tangential stresses in the total drag force. The wall slip significantly reduces the drag coefficient and also reduces the extent of the sheared zones. A numerical simulation has been performed with an elasto-viscoplastic model by means of a code using finite elements method with Lagrangian integration points in the case of an adhesive flat plane.