The transition from a laminar to a turbulent flow strongly modifies the boundary layer properties.Understanding the mechanisms leading to transition is crucial to reliably predict aerodynamicperformances. For boundary layers subjected to high levels of external disturbances, the naturaltransition due to the amplification of the least stable mode is replaced by an early transition, calledBypass transition. This is the result of non-normal mode interactions that lead to a phenomenon oftransient growth of disturbances. These disturbances are known as Klebanoff modes and take theform of streamwise velocity streaks.This thesis aims at understanding this linear mechanism of transient growth and quantifying itsinfluence on the classical modal amplification of disturbances. This is done by computing theso-called optimal perturbations, i.e. the initial disturbances that undergo maximum amplificationin the boundary layer.These optimal perturbations are first determined for two-dimensional compressible boundary layersdeveloping over curved surfaces. In particular, we show that Klebanoff modes naturally evolvetowards Görtler vortices that occur over concave walls. Three-dimensional boundary layers arethen considered. In such configurations, transient growth provides an initial amplitude to crossflowvortices. Finally, applying the tools developed in this thesis to new flow cases such as swept wingsprovides further understanding of the phenomenon of transient growth for realistic geometries. / Le passage du régime laminaire au régime turbulent s’accompagne d’importantes modifications despropriétés physiques de la couche limite. La détermination précise de la transition est donc crucialedans de nombreux cas pratiques. Lorsque la couche limite se développe dans un environnementextérieur faiblement perturbé, la transition est gouvernée par l’amplification du mode propre le moinsstable. Lorsque l’intensité des perturbations extérieures augmente, des interactions multimodalesentraînent une amplification transitoire des perturbations. Ce phénomène peut conduire à unetransition prématurée, appelée transition Bypass. Les perturbations prennent alors la forme destries longitudinales de vitesse appelées modes de Klebanoff.L’objectif de cette thèse est d’étudier ce mécanisme linéaire de croissance transitoire et soninfluence sur l’amplification modale classique des perturbations. Cela passe par la déterminationdes perturbations les plus amplifiées au sein de la couche limite, appelées perturbations optimales.Ces perturbations optimales sont d’abord calculées pour des couches limites bidimensionnelles etcompressibles se développant sur des surfaces courbes. En particulier, on montre que les modes deKlebanoff évoluent vers les tourbillons de Görtler qui se forment sur des parois concaves. Le cas plusgénéral de couches limites tridimensionnelles est ensuite envisagé. Pour de telles configurations, lacroissance transitoire fournit une amplitude initiale aux instabilités transversales. Enfin, l’applicationdes outils développés dans cette thèse fournit de nouveaux résultats pour des cas d’écoulementsautour de géométries réalistes comme une aile en flèche.

Quantum trajectories are investigated within the complex quantum Hamilton-Jacobi formalism. A unified description is presented for complex quantum trajectories for one-dimensional time-dependent and time-independent problems. Complex quantum trajectories are examined for the free Gaussian wave packet, the coherent state in the harmonic potential, and the the barrier scattering problems. We analyze the variations of the complex-valued kinetic energy, the classical potential, and the quantum potential along the complex quantum trajectories. For one-dimensional time-independent scattering problems, we demonstrate general properties and similar structures of the complex quantum trajectories and the quantum potentials. In addition, it is shown that a quantum vortex forms around a node in the wave function in complex space, and the quantized circulation integral originates from the discontinuity in the real part of the complex action. Although the quantum momentum field displays hyperbolic flow around a node, the corresponding Polya vector field displays circular flow. Moreover, local topologies of the quantum momentum function and the Polya vector field are thoroughly analyzed near a stagnation point or a pole (including circular, hyperbolic, and attractive or repulsive structures). The local structure of the quantum momentum function and the Polya vector field around a stagnation point are related to the first derivative of the quantum momentum function. However, the magnitude of the asymptotic structures for these two fields near a pole depends only on the order of the node in the wave function. Finally, quantum interference is investigated and it leads to the formation of the topological structure of quantum caves in space-time Argand plots. These caves consist of the vortical and stagnation tubes originating from the isosurfaces of the amplitude of the wave function and its first derivative. Complex quantum trajectories display helical wrapping around the stagnation tubes and hyperbolic deflection near the vortical tubes. Moreover, the wrapping time for a specific trajectory is determined by the divergence and vorticity of the quantum momentum field. The lifetime for interference features is determined by the rotational dynamics of the nodal line in the complex plane. Therefore, these results demonstrate that the complex quantum trajectory method provides a novel perspective for analysis and interpretation of quantum phenomena. / text

This work is concerned with stability and receptivity analysis as well as studies on control of the laminar-turbulent transition in boundary-layer flows through direct numerical simulations. Various flow configurations are considered to address flow around straight and swept wings. The aim of this study is to contribute to a better understanding of stability characteristics and different means of transition control of such flows which are of great interest in aeronautical applications. Acoustic receptivity of flow over a finite-thickness flat plate with elliptic leading edge is considered. The objective is to compute receptivity coefficient defined as the relative amplitude of acoustic disturbances and TS wave. The existing results in the literature for this flow case plot a scattered image and are inconclusive. We have approached this problem in both compressible and incompressible frameworks and used high-order numerical methods. Our results have shown that the generally-accepted level of acoustic receptivity coefficient for this flow case is one order of magnitude too high. The continuous increase of computational power has enabled us to perform global stability analysis of three-dimensional boundary layers. A swept flat plate of FSC type boundary layer with surface roughness is considered. The aim is to determine the critical roughness height for which the flow becomes turbulent. Global stability characteristics of this flow have been addressed and sensitivity of such analysis to domain size and numerical parameters have been discussed. The last flow configuration studied here is infinite swept-wing flow. Two numerical set ups are considered which conform to wind-tunnel experiments where passive control of crossflow instabilities is investigated. Robustness of distributed roughness elements in the presence of acoustic waves have been studied. Moreover, ring-type plasma actuators are employed as virtual roughness elements to delay laminar-turbulent transition. / <p>QC 20161124</p>

Pendant la première année le microscope à microSQUID était mis en fonctionnement. On a avancé sur le plan cryogenique (dilution) et électronique (programmation de boucles de régulation et d'une détection synchrone). Les composants étaient testés à température ambiante et on est en train de tout tester à basse température. Une méthode était conçu pour déterminer la longueur de pénétration du champ magnétique dans un supraconducteur avec les données qui pourront être fait avec notre microscope. Ceci va être utilisé pour l'échantillon PrOs4Sb12. Il s'agit de trancher le débat sur la nature multibande de la supraconductivité dans ce composé. En deuxième année le developpement a continué, en particulière le microscope était mis à froid. Des différents problèmes due aux basses températures (mouvement de moteur, thermalisation, câblage) ont été resolues. Ensuite on a avancé sur le plan informatique, notamment le contrôle de differents composants. Pendant le deuxième année quelques images magnétique ont été faites, validant le concept. En troisième année on a commence a mésurer des domaines magnetiques d'un supraconducteur ferromagnetique (UCoGe) en Avril - Aout. On a obtenu des resultats tres interessants. Le même dispositif sera ainsi opérationnel pour l'imagerie de domaines dans des bolomètres supraconducteurs. / Pendant cette thèse un microscope à SQUID et AFM à balayage, l'électronique et les logiciels de contrôle ont été conçus. Pour la calibration des mesures sur un film de niobium (avec des motifs) ont été effectuées, montrant la possibilité de faire des image de la topographie at la distribution du champ magnétique au dessus de l'échantillon simultanément. On présent les premières image dans l'espace réel de la structure de domaines dans le ferro supraconducteur UCoGe, un échantillon basé sur l'uranium (fermion lourd) avec un transition supra à environ 0.5K à la pression ambiante. On montre l'évolution de la transition ferromagnétique en fonction de la température. La microscope a été aussi utilisé pour des mésures sur un couche mince de Rhenium, un supraconducteur conventionel. On a obtenu une estimation pour la force de piégeage de vortex on utilisant l'interaction entre SQUID et vortex. En plus, on a déterminé la longueur de pénétration en fonction de la température.

In this thesis, we numerically investigate quantum turbulence in trapped atomic Bose-Einstein condensates (BECs). We first discuss the appropriate qualitative characterization of turbulence in these systems, showing the limitation of analogies with classical hydrodynamics and turbulence in large superfluid Helium experiments. Due to their lack of available length scales, our investigated systems can only fit the ultraquantum (or Vinen) type of quantum turbulence. Secondly, we propose experimentally feasible schemes for more controlled investigations of turbulence making use of dynamical instability of multicharged vortices as an onset for complex vortex dynamics. In two dimensions, our suggested scheme allows control over vortex polarization in the harmonically trapped system. This setup is then used to study how turbulence decays in such a scenario, through the phenomenological modeling of a vortex-number rate equation. As a consequence, we were able to identify that vortex annihilation in these trapped systems happens through a four-vortex process. For three dimensions, we have first provided a study on the decay of a quadruply-charged vortex, also in a harmonically trapped BEC. Having this setting as a comparison point, we propose a quasi-isotropic turbulent system, starting from a phase-imprinted initial state of two doubly-charged, anti-parallel vortices. The vortex turbulence arisen from such configuration was shown to agree with the Vinen turbulent regime, after we characterized specific features of its decay, such as the energy spectrum [E(k) &#8764; k1] and the time evolution of the vortex-line density [L(t) &#8764; t1]. Although these features have been frequently verified in the context of superfluid Helium turbulence, here this identification was for the first time done for realistic, trapped atomic BECs. / Nesta tese, investigamos numericamente a turbulência quântica em condensados de Bose- Einstein (BECs) aprisionados. Discutimos, inicialmente, a caracterização qualitativa apropriada para estes sistemas, mostrando a limitação de analogias tipicamente feitas com hidrodinâmica clássica e turbulência em grandes sistemas com Hélio superfluido. Devido às suas limitadas escalas espaciais, os sistemas investigados somente podem exibir o tipo de turbulência conhecida como ultra-quântica (ou de Vinen). Em seguida, propomos sistemas experimentalmente factíveis que permitem investigações mais controladas da turbulência, fazendo uso da instabilidade dinâmica de vórtices multi-carregados como ponto de partida para geração de dinâmicas complexas. Em duas dimensões, nossa proposta permite controle sobre a polarização de vórtices em sistemas aprisionados em potencial harmônico. Este arranjo é então utilizado no estudo do decaimento da turbulência nesse contexto, através de um modelo fenomenológico para equação que descreve a taxa de variação do número de vórtices. Como consequência, pudemos verificar que a aniquilação de vórtices dá-se através de um processo que envolve quatro vórtices. Em três dimensões, apresentamos um estudo do decaimento de um vórtice de carga topológica quatro, também em potencial harmônico. Mantendo em mente esse sistema a título de comparação, propomos um cenário turbulento, quase-isotrópico, partindo de um estado inicial formado por dois vórtices duplamente carregados, mas orientados anti-paralelamente. Verificamos que a turbulência decorrente desse arranjo coincide com a regime de Vinen analisando características do seu decaimento, especificamente obtendo o espectro de energia [E(k) &#8764; k1] e evolução temporal da densidade de linhas de vórtices [L(t) &#8764; t1]. Apesar de que essas características são comumente encontradas no contexto de Hélio superfluido, apresentamos pela primeira vez essa identificação no cenário realístico de BEC aprisionados.

A importância da exploração marítima de petróleo, em especial para o Brasil, é indiscutível e risers são estruturas essenciais para essa atividade. Uma melhor compreensão da dinâmica dessas estruturas e dos esforços a que estão submetidas vem resultando de pesquisa constante na área, pesquisa que gera um grande volume de dados, freqüentemente descrevendo fenômenos de difícil compreensão. Este trabalho descreve o desenvolvimento de um ambiente que combina técnicas de realidade virtual (como ambientes 3D, navegação e estereoscopia) e visualização científica (como mapeamento de cores, deformações e glifos) para facilitar a visualização desses dados. O ambiente, batizado como RiserView, permite a montagem de cenas tridimensionais compostas por risers, relevo do solo, superfície marítima, embarcações, bóias e outras estruturas, cada um com sua dinâmica própria. Permite ainda a visualização do escoamento para que a formação de vórtices na vizinhança dos risers e a interação fluido-mecânica resultante possam ser estudadas. O usuário pode controlar parâmetros da visualização de cada elemento e da animação da cena, bem como navegar livremente por ela. Foi desenvolvido também um algoritmo de baixo custo computacional (graças a simplificações possíveis devido à natureza do problema) para detecção e exibição em tempo real de colisões entre risers. O Processo Unificado foi adaptado para servir como metodologia para o projeto e implementação do aplicativo. O uso do VTK (API gráfica e de visualização científica) e do IUP (API para desenvolvimento de interfaces com o usuário) simplificou o desenvolvimento, principalmente para produzir um aplicativo portável para MS-Windows e Linux. Como opções de projeto, a visualização científica e a velocidade na renderização das cenas são privilegiadas, ao invés do realismo e da agilidade na interação com o usuário. As conseqüências dessas escolhas, bem como alternativas, são discutidas no trabalho. O uso do VTK e, através dele, do OpenGL permite que o aplicativo faça uso dos recursos disponíveis em placas gráficas comerciais para aumentar sua performance. Em sua versão atual a tarefa mais custosa para o RiserView é a atualização das posições de risers, principalmente descritos no domínio da freqüência, mas o trabalho discute aprimoramentos relativamente simples para minimizar esse problema. Apesar desses (e de outros) aprimoramentos possíveis, discutidos no trabalho, o ambiente mostra-se bastante adequado à visualização dos risers e de sua dinâmica bem como de fenômenos e elementos a eles associados. / The importance of offshore oil exploration, especially to Brazil, cannot be argued and risers are crucial structures for this activity. A better understanding of the dynamics of these structures and of the efforts to which they are subject has been resulting from constant research in the field, research that generates a large volume of data, often describing phenomena of difficult comprehension. This work describes the development of a software environment that combines elements of virtual reality (3D environments, navigation, stereoscopy) and scientific visualization techniques (such as color mapping, deformations and glyphs) to improve the understanding and visualization of these data. The environment, christened RiserView, allows the composition of tridimensional scenes including risers, the floor and surface of the ocean and ships, buoys and other structures, each with its own dynamics. It also allows the visualization of the flow in the neighborhood of the risers so that vortex shedding and the resulting fluid-mechanic interactions may be studied. The user may control parameters of the scene animation and of the visualization for each of its elements, as well as navigate freely within the scene. An algorithm of low computational cost (thanks to simplifications possible due to the nature of the problem), for the detection and exhibition of collisions between risers in real time, was also developed. The Unified Process was adapted to guide the software's project and implementation. The use of VTK (a scientific visualization and graphics API) and IUP (a user interface development API) simplified the development, especially the effort required to build an application portable to MS-Windows and Linux. As project choices, scientific visualization and the speed in rendering scenes in real time were given higher priority than realism and the agility in the user interaction, respectively. The consequences of these choices, as well as some alternatives, are discussed. The use of VTK and, through it, OpenGL, allows the application to access features available in most commercial graphics cards to increase performance. In its current version, the most costly task for RiserView are the calculations required to update riser positions during animation, especially for risers described in the frequency domain, but the work discusses relatively simple improvements to minimize this problem. Despite these (and other) possible improvements discussed in the work, the application proves quite adequate to the visualization of risers and their dynamics, as well as of associate elements and phenomena.

[pt] A teoria de Bardin, Cooper e Schrieffer (BSC) teve enorme sucesso na explicação das propriedades da maior parte dos materiais supercondutores. Esses materiais, onde a teoria BCS se aplica, são denominados supercondutores convencionais. A observação do aparecimento de supercondutividade não-convencional em diversos materiais reabriu as discussões sobre o fenômeno. Enquanto a transição para fase supercondutora em materiais convencionais envolve apenas a quebra da simetria de calibre, no caso dos materiais não-convencionais, a mesma é caracterizada pela quebra de diversas simetrias adicionais. O mecanismo microscópico da supercondutividade nessas novas classes de materiais ainda é uma questão em aberto. no entanto, muitas propriedades físicas podem ser extraídas apenas de conciderações sobre as simetrias do parâmetro de ordem supercondutor, que está intimamente ligadoá função de onda do par de Cooper. Neste trabalho são analisadas algumas propriedades destes novos supercondutores baseadas em critérios de simetria. Um enfoque especial é dado à classe dos supercondutores não-convencionais onde há uma quebra de simetria de reversão temporal. Para estes materiais são previstas algumas propriedade bem pouco usuais. Quando a estrutura cristalina tiver alta simetria, é possível o surgimento de uma polarização de um spin no condensado. Nestes casos, a magnetização intrínseca pode levar à formação de uma fase espontânea de vórtices. Ocorre também uma forte anisotropia na resposta do supercondutor frente à aplicação de campos magnéticos externos. / [en] The theory of Bardeen, Cooper and Schrieffer (BCS) had great success in explaining most properties of superconducting materials. These materials, where BCS applies, are denominated conventional superconductors. the experimental evidence of unconventional superconductivity in several materials reopened discussions about the phenomenon. While, in conventional materials, the superconducting phase involves only the breaking of gauge symmetry, in the unconventional materials the phase is characterized by several additional broken symmetries. The microscope mechanism of superconductivity in this new classes of materials is still an open question. However, many phisical properties can be understood considering only symmetries of the superconducting order parameter, which is intimately linked to Cooper pair wave function. In this work some properties of these new superconductors are analyzed based symmetry criteria. Special emphasis is given to the class of unconventional superconductors where time- reversal symmetry is broken. For these materials, some unusual properties are predicted. When the crystal structure has high symmetry, the appearence of a spin polarization in the condensate is possible. In these cases, an intrinsic magnetization can lead to the information of a spontanous vortex phase. A strong anisotropic response to an externally applied magnetic field also occurs.

"Optical vortices are ubiquitous features of electromagnetic radiation that are often described as a destructive null in a beam of coherent light. Optical vortices may be created by a variety of different methods, one of which is by the use of a diffractive vortex mask, which is a plate of glass that has been etched in a spiral staircase pattern such that the thickness of the mask varies harmonically in the azimuthal direction. Light passing through the mask gains an azimuthal variation in phase due to the index mismatch between the glass substrate and the surrounding medium and thus an optical vortex is created. There is an implicit assumption that the light is spatially coherent, or in other words, that there is a definite phase relationship between each point in the beam. Optical vortices are not believed to occur in completely incoherent light where the term “phase” no longer holds any meaning. Optical vortices are also poorly understood in partially coherent light where statistics must be used to quantify the phase. The purpose of the research presented in this thesis was to determine how spatial coherence affects the transmission properties of the vortex phase mask. This research enabled us to create a coherence filtering technique based upon the vortex diffractive mask. In this dissertation I will demonstrate the usefulness of this filtering technique in two specific applications. First in the detection of forward-scattered light, where the un-scattered probe beam may blind a detector making detection of the scattered light extremely difficult. Second, in the enhanced resolution of two nearby objects, where the signal from one object may be lost in the glare of a brighter companion. This filtering technique has a wide field of possible applications including the detection of extra-solar planets, the detection of defects in laser optics, and improved methods in optical tomography."

Ce travail de thèse est principalement axé sur le développement d’une nouvelle méthode de manipulation de vortex d’Abrikosov individuels dans les supraconducteurs de type II. Cette méthode, rapide, efficace et précise, est basée sur l’optique en champ lointain et repose sur l’échauffement local du supraconducteur sous l’action d’un faisceau laser focalisé. Elle apporte une excellente alternative aux techniques existantes de manipulation de vortex, toutes basées sur l’utilisation de sondes locales, et donc intrinsèquement lentes et difficiles à mettre en oeuvre dans un environnement cryogénique. La combinaison de cette méthode à une technique d’imagerie magnéto-optique performante permet de déplacer des vortex individuels avec un taux de réussite de 100% et sur de grandes échelles limitées uniquement par le champ de l’objectif de microscope. Les vitesses de manipulation atteintes sont élevées, de l’ordre de 10 mm.s-1, mais encore limitées par l’instrumentation utilisée et loin des limites fondamentales offertes par cette méthode, estimées au km.s-1. La méthode de manipulation optique permet aussi de mesurer la distribution des forces de piégeage de chaque vortex d’un échantillon. En utilisant des puissances de chauffage laser permettant de dépasser localement la température critique, nous avons également pu étudier la pénétration des vortex à l’interface entre une zone normale et une zone supraconductrice.Durant ces travaux, nous avons aussi eu l’opportunité de mettre en évidence, par spectroscopie de molécules uniques, l’effet flexomagnétoélectrique dans un matériau multiferroïque, en employant un supraconducteur de type I comme générateur de champ magnétique inhomogène. Enfin, nous proposons à la fin de ce mémoire un concept de jonction Josephson créée tout optiquement, et dont les propriétés seraient contrôlables en temps réel par laser. / This thesis focuses on the development of a new manipulation technique to handle single Abrikosov vortices in type II superconductors. This fast, efficient and precise method is based on far field optics and rests on the local temperature elevation produced by a focused laser beam. It brings an excellent alternative to the existing techniques which are all based on local probes and thus heavy to implement in a cryogenic environment. The combination of this method with an efficient magneto-optical imaging system allows us to manipulate single vortices with a 100% rate of success on a large scale only limited by the field of view of the microscope objective. Manipulation speeds are high, of the order of 10 mm.s-1, but still limited by our setup and far from the fundamental limits offered by this technique, estimated to the km.s-1. This manipulation technique also allows to measure the pinning force of any single vortex in a superconducting sample. By using a high enough laser power which locally pushes the temperature above the critical temperature, we could also study the vortex penetration at the interface between normal and superconducting areas.In the course of this work, we also evidenced, with single molecule spectroscopy, the flexomagnetoelectric effect in a multiferoic material, by using a type I superconductor as a source of inhomogeneous magnetic field. Finally, we propose at the end of the manuscript the new concept of an optically created Josephson junctions, whose properties could be controlled in real time just with a laser beam.

Le travail présenté dans ce mémoire est une contribution à l'étude numérique des systèmes tourbillonnaires hélicoïdaux qui sont émis dans le sillage des rotors (éoliennes, hélicoptères,...) et de leurs instabilités. Ici, ces écoulements sont localement modélisés par un ensemble de tourbillons à symétrie hélicoïdale. À l'aide d'un code de simulation numérique directe dédié, des solutions de base quasi-stationnaires sont obtenues pour différents systèmes tourbillonnaires. Une caractérisation précise et détaillée de ces solutions est ensuite effectuée : vitesse de rotation, taille et ellipticité du cœur, structure des champs de vitesse et de vorticité... À l'aide d'un algorithme d'Arnoldi couplé à une version linéarisée du code, on détermine les modes dominants d'instabilité ayant la même symétrie que l'écoulement de base, en fonction des paramètres du système: nombre de vortex, pas hélicoïdal, taille de cœur, nombre de Reynolds et présence d'un vortex de moyeu. En dessous d'un certain pas hélicoïdal critique, l'instabilité est dominée par un mode de déplacement global analogue au mode d’appariement d'une allé infinie de points vortex ou d'anneaux tourbillonnaires. En régime non linéaire, ce mode est à l'origine d'une dynamique complexe du système: dépassements, saute-mouton et fusion. On utilise un autre code linéarisé pour déterminer les modes instables qui brisent la symétrie hélicoïdale de l'état de base, caractérisés par une longueur suivant l'axe. À faible nombre d'onde, ces modes induisent localement des rapprochements entre portions de spires voisines. À grand nombre d'onde, on observe un autre type de mode qui déforme les cœurs tourbillonnaires via l'instabilité elliptique. / The work presented in this manuscript is a contribution to the numerical study of helical vortex systems and their instabilities, as encountered in the near wake of rotors (wind turbines, helicopters,~...). In this work, such flows are locally modelled within the framework of helical symmetry. Using a dedicated DNS code, helical quasi-stationary basic state solutions are obtained for several configurations, and accurate tools for their characterisation are developed: angular velocity, core size and ellipticity, structure of the velocity and vorticity fields... An Arnoldi algorithm is then coupled to a linearised version of the code. The dominant instability modes with the same symmetry as the base flow are extracted as a function of the system parameters: number of vortices, helical pitch, core size, Reynolds number, presence of a central hub vortex. Under a critical helical pitch, the instability is dominated by a global displacement mode analogous to the pairing mode of an infinite array of point vortices or vortex rings. In the nonlinear regime, this mode gives rise to complex dynamics: overtaking events, leapfrogging and merging. Another linearised code is then used to extract modes characterised by a wavelength along the helix, which break the helical symmetry of the base flow. At low wavenumbers, these modes induce local displacements of the vortices and bring together portions of neighbouring coils. At large wavenumbers, another type of mode is found, which deforms the vortex cores through the elliptical instability mechanism.