Dernière étape avant l'atomisation d'un volume de liquide, les ligaments sont présents dans de nombreuses applications industrielles, de même que dans le monde qui nous entoure ; leur dynamique demeure mal comprise. L'étirement, qui permet de leur donner naissance, affecte leur évolution et la manière dont ils se fragmentent (ou non). Pour quantifier l'effet de ce dernier, nous avons choisi d'étudier des configurations modèles dans lesquelles plusieurs paramètres peuvent être bien contrôlés. Une configuration de type pont liquide permet notamment de contrôler l'étirement via le déplacement de l'un des supports solides (mors). Lorsque l'étirement imposé est modéré, il est possible de prévoir analytiquement la déviation entre la forme dynamique et la forme d'équilibre correspondante, quelle que soit la loi de déplacement du mors. Cette prédiction montre en particulier qu'un pont liquide étiré peut s'épaissir appréciablement en son centre, suggérant un retardement de la rupture. Elle montre également que l'étirement axial est réparti de manière très inhomogène. Lorsque l'étirement est suffisamment vigoureux, les résultats expérimentaux montrent que le détachement capillaire du ligament peut être significativement hâté. Le temps de rupture est relié à la masse emportée par le mors en mouvement et dépend du protocole d'étirement. Les résultats suggèrent également la possibilité d'obtenir des ligaments démesurément longs et fins sans l'intervention d'effets visqueux. / Liquid ligaments represent the last step before atomization of a liquid volume, and are encountered in a variety of industrial applications, as well as the world around us; yet, there is much to learn about their dynamics and breakup. Stretching is an essential ingredient of ligaments formation, and affect their subsequent dynamics as well as the way they break (or not). In order to quantify its action, we choose model configurations where parameters can be controlled. Liquid bridges, in particular, provide a way to impose stretching by moving one of the solid rod supporting the bridge. When stretching is not too strong, it is possible to predict analytically the shift between the dynamical shape of the bridge and the corresponding static shape, for any given rod displacement. Particularly, this prediction show that the central section of a stretched liquid bridge tend to be thicker, which could delay breakup. It also show that the axial elongation rate is far from being uniform. When stretching is vigorous, experimental results show that the ligament initial breakup can be considerably sped up. Breakup time shows to be linked to the mass taken away by the moving rod and depend on stretching protocol. Finally, results suggest that it is possible to generate infinitely long ligaments without the mediation of viscous effects.

Neste trabalho, a significativa importância dos processos de breakup, fusão incompleta e transferência para o sistema de massa intermediaria 'ANTPOT.6 Li' + 'ANTPOT.59 Co', envolvendo o núcleo estável e fracamente ligado 'ANTPOT.6 Li', é investigada em energias próximas à barreira Coulombiana. Foram realizadas medidas das distribuições angulares das partículas leves nas energias 'E IND.lab' = 18, 22, 26 e 30 MeV, espalhamento elástico nas energias 'E IND.lab' = 12, 18, 22, 26 e 30 MeV e medidas de fusão total (completa+incompleta), por meio do método de espectroscopia 'gama', nas energias 12 MeV < 'E IND.lab' < 26 MeV. As previsões para evaporação do núcleo composto por partículas leves foram baseadas no modelo estatístico, e uma descrição simultânea dos processos de espalhamento elástico, fusão e breakup foi obtida por meio de cálculos de canais acoplados com discretização do contínuo (CDCC). Com base nestes resultados, realizamos a separação das contribuições dos processos de breakup, fusão incompleta e transferência. Por meio de medidas de coincidência entre d e 'alfa', obtivemos as distribuições angulares para o breakup seqüencial do 6Li. Os processos de espalhamento elástico e fusão total do sistema 'ANTPOT.7 Li' + 'ANTPOT.59 Co', e suas descrições sob o formalismo de CDCC também foram estudadas / In the present work, the relative importance of breakup, incomplete fusion and transfer processes is investigated in the vicinity of the Coulomb barrier for the intermediate mass target 6Li + 59Co reaction involving the weakly bound 6Li. Measurements for light particle angular distributions were performed at energies Elab = 18, 22, 26 e 30 MeV,elastic scattering at energies Elab = 12, 18, 22, 26 e 30 MeV and total fusion (complete+incomplete), by the -ray spectroscopy method, at energies 12 MeV < Elab < 26 MeV. The compound nucleus decay by light particles was predicted using the statistical model, and a simultaneous description of scattering, fusion and breakup was obtained by means of continuum discretized coupled-channels calculations (Cdcc). Based on these results, the contribution of non-capture breakup, incomplete fusion and transfer were disentangled. The 6Li sequential breakup cross sections were obtained by means of ´alfa´-d coincidence measurements. The Cdcc descriptions of 7Li + 59Co elastic scattering and fusion processes were also subject of study.

Neste trabalho, a significativa importância dos processos de breakup, fusão incompleta e transferência para o sistema de massa intermediaria 'ANTPOT.6 Li' + 'ANTPOT.59 Co', envolvendo o núcleo estável e fracamente ligado 'ANTPOT.6 Li', é investigada em energias próximas à barreira Coulombiana. Foram realizadas medidas das distribuições angulares das partículas leves nas energias 'E IND.lab' = 18, 22, 26 e 30 MeV, espalhamento elástico nas energias 'E IND.lab' = 12, 18, 22, 26 e 30 MeV e medidas de fusão total (completa+incompleta), por meio do método de espectroscopia 'gama', nas energias 12 MeV < 'E IND.lab' < 26 MeV. As previsões para evaporação do núcleo composto por partículas leves foram baseadas no modelo estatístico, e uma descrição simultânea dos processos de espalhamento elástico, fusão e breakup foi obtida por meio de cálculos de canais acoplados com discretização do contínuo (CDCC). Com base nestes resultados, realizamos a separação das contribuições dos processos de breakup, fusão incompleta e transferência. Por meio de medidas de coincidência entre d e 'alfa', obtivemos as distribuições angulares para o breakup seqüencial do 6Li. Os processos de espalhamento elástico e fusão total do sistema 'ANTPOT.7 Li' + 'ANTPOT.59 Co', e suas descrições sob o formalismo de CDCC também foram estudadas / In the present work, the relative importance of breakup, incomplete fusion and transfer processes is investigated in the vicinity of the Coulomb barrier for the intermediate mass target 6Li + 59Co reaction involving the weakly bound 6Li. Measurements for light particle angular distributions were performed at energies Elab = 18, 22, 26 e 30 MeV,elastic scattering at energies Elab = 12, 18, 22, 26 e 30 MeV and total fusion (complete+incomplete), by the -ray spectroscopy method, at energies 12 MeV < Elab < 26 MeV. The compound nucleus decay by light particles was predicted using the statistical model, and a simultaneous description of scattering, fusion and breakup was obtained by means of continuum discretized coupled-channels calculations (Cdcc). Based on these results, the contribution of non-capture breakup, incomplete fusion and transfer were disentangled. The 6Li sequential breakup cross sections were obtained by means of ´alfa´-d coincidence measurements. The Cdcc descriptions of 7Li + 59Co elastic scattering and fusion processes were also subject of study.

Les écoulements de trains périodiques de gouttes monodisperses confinées dans des microcanaux sont largement utilisés pour diverses applications haut-débits en microfluidique digitale. Pour cela, il est nécessaire de réaliser différentes opérations sur ces gouttes comme les fragmenter, les fusionner ou les trier. Dans ce manuscrit, nous discutons de trois de ces opérations expérimentalement et théoriquement. La première concerne l’encapsulation d’un train de gouttelettes dans des gouttes. Nous étudions la dynamique d’encapsulation et nous présentons une nouvelle méthode d’encapsulation. Par suite, nous investiguons deux modes de fragmentation de gouttes, tous deux influencés par des interactions hydrodynamiques entre gouttes consécutives dans un train. Enfin, nous cherchons à comprendre la sélection du chemin suivi par des gouttes à des bifurcations successives. / Flows of periodic trains of monodisperse drops confined in microchannels are widely used for numerous high-throughput applications in digital microfluidics. The development of such applications requires performing and combining various operations on these drops like breakup, fusion or sorting. In this manuscript, we study experimentally and theoretically three of these operations. We first discuss the encapsulation of a train of droplets inside drops, focusing on the encapsulation dynamics. Also, we present a new way to encapsulate drops to produce double emulsions. We then investigate two ways to break drops against micro-obstacles, both being influenced by hydrodynamics interactions between two consecutives drops in a train. Lastly, we report the investigation of the path selection of drops at successive bifurcations.

Modelling the ice accretion in glaze regime for the supercooled large droplets is one of the most challenging problems in the aircraft icing field. The difficulties are related to the presence of the liquid water film on the surface in the glaze regime and also the phenomena associated with SLD conditions, specifically the splashing and re-impingement. The steady improvement of simulation methods and the increasing demand for highly optimised aircraft performance, make it worthwhile to try to get beyond the current level of modelling accuracy. A semi-empirical method has been presented to characterize the thin water film in the icing problem based on both analytical and experimental approaches. The experiments have been performed at the Cranfield icing facilities. Imaging techniques have been used to observe and measure the features of the thin water film in the different conditions. A series of numerical simulations based on an inviscid VOF model have been performed to characterize the splashing process for different water film to droplet size ratios and impact angles. Based on these numerical simulations and the proposed methods to estimate the thin water film thickness, a framework has been presented to model the effects of the splashing in the icing simulation. These effects are the lost mass from the water film due to the splashing and the re-impingement of the ejected droplets. Finally, a new framework to study the solidification process of the thin water film has been explored. This framework is based on the lattice Boltzmann method and the preliminary results showed the capabilities of the method to model the dynamics, thermodynamics and the solidification of the thin water film.

Modelling the ice accretion in glaze regime for the supercooled large droplets is one of the most challenging problems in the aircraft icing field. The difficulties are related to the presence of the liquid water film on the surface in the glaze regime and also the phenomena associated with SLD conditions, specifically the splashing and re-impingement. The steady improvement of simulation methods and the increasing demand for highly optimised aircraft performance, make it worthwhile to try to get beyond the current level of modelling accuracy. A semi-empirical method has been presented to characterize the thin water film in the icing problem based on both analytical and experimental approaches. The experiments have been performed at the Cranfield icing facilities. Imaging techniques have been used to observe and measure the features of the thin water film in the different conditions. A series of numerical simulations based on an inviscid VOF model have been performed to characterize the splashing process for different water film to droplet size ratios and impact angles. Based on these numerical simulations and the proposed methods to estimate the thin water film thickness, a framework has been presented to model the effects of the splashing in the icing simulation. These effects are the lost mass from the water film due to the splashing and the re-impingement of the ejected droplets. Finally, a new framework to study the solidification process of the thin water film has been explored. This framework is based on the lattice Boltzmann method and the preliminary results showed the capabilities of the method to model the dynamics, thermodynamics and the solidification of the thin water film.

This thesis presents detailed fuel spray investigations relating to an automotive Gasoline Direct Injection (GDI) pressure-swirl injector, employing a combination of numerical and physical analyses. The emphasis is placed on the near-nozzle in recognition that all later flow processes are dominated by this critical region. To enable the technology to maximise its potential, it is essential to further our understanding of the fundamental flow physics that govern the injection process, which remain largely unknown. The complexity of the spray process has led to many avenues of research. Simplified models are particularly suitable for parametric studies, allowing fast computation of some of the most important design parameters, such as nozzle discharge coefficient, cone angle and initial velocity. More complex methods such as Computational Fluid Dynamics (CFD) offer significantly more detail including the temporal and spatial evaluation of the flow field and fuel distribution, but at the cost of often lengthy computational time, and the need to tune models against physical evidence. Unfortunately none are able to describe all aspects of the injection event simultaneously. A considerable body of existing experimental data gathered under atmospheric conditions has been condensed and carefully presented to provide a comprehensive picture of injector operation. This comprises global spray performance data, spray imaging, and droplet velocity and size maps as a function of time after the Start Of Injection (SOl). These serve to provide a means to develop physical models and to correlate model predictions. Particular attention is drawn to the challenges faced by numerical methods to successfully predict the complex spray behaviour. A fundamental computational study employing the Volume Of Fluid (VOF) method describes droplet break-up under controlled conditions. By varying the Weber number of the flow the expected break-up mechanisms are recovered, and the numerics and case set-up tuned to offer a practical balance between the resource burden and solution accuracy. This paved the way to a detailed 3-D transient analysis of the near-nozzle region of a pressure-swirl injector. Computed results clearly identify the consecutive phases of the fuel spray development, from the initial unsteady jet through to the stable, swirling hollow cone formation. Comparison with experimental measurements revealed that the computational approach is able to capture the main qualitative features of the spray process.

No description available.

La coextrusion multinanocouche est un procédé innovant qui permet de combiner deux polymères afin de produire des films composés de couches alternées dont le nombre peut être contrôlé et atteindre plusieurs milliers. Ainsi, les épaisseurs des couches individuelles dans le film peuvent en théorie atteindre quelques nanomètres. Les effets de confinement des chaînes macromoléculaires ainsi que la multiplication des interfaces peuvent alors conduire à des propriétés macroscopiques améliorées, pertinentes dans un contexte industriel (optiques, mécaniques, barrière aux gaz, …). Néanmoins, à ces échelles, des défauts dans la continuité des couches peuvent apparaître pendant la mise en forme et affecter ces propriétés. L’objectif de cette thèse est d’identifier les paramètres clés, procédés et matériaux, et de mieux comprendre les mécanismes à l’origine des instabilités conduisant à ces inhomogénéités de la nanostructure. Dans ce cadre, deux polymères amorphes ont été principalement étudiés, le polyméthacrylate de méthyle (PMMA) et le polystyrène (PS). Des films composés de 65 à plus de 8000 couches alternées, à différents taux d’étirage et compositions massiques, ont été fabriqués dans le but d’étudier la stabilité du procédé à différentes échelles et principalement à l’échelle nanométrique. Les films obtenus ont été caractérisés par microscopie, en particulier la microscopie à force atomique (AFM). Un premier travail a consisté à mettre en place une démarche statistique et quantitative pour caractériser l’épaisseur moyenne des couches obtenues, mais aussi la distribution d’épaisseur et la stabilité des couches. Puis, nous avons cherché à sonder l’effet de différents paramètres procédés et matériaux sur l’homogénéité des structures à l’échelle micronique. En se plaçant ensuite dans des conditions stables à ces échelles, nous avons cherché à faire varier de manière systématique les paramètres procédés pour étudier la stabilité des couches à l’échelle nanométrique. Nous avons mis en évidence l’existence d’une épaisseur critique en dessous de laquelle les couches rompaient, située autour de 10 nm pour le couple PS/PMMA. Lorsque l’épaisseur visée est de l’ordre de la dizaine de nanomètres ou inférieures, le taux de rupture de couches augmente également fortement. Des hypothèses sont faites quant aux causes de ces ruptures et de l’existence de cette épaisseur critique. Nous suggérons que ces ruptures peuvent être provoquées par des perturbations interfaciales (liées à des impuretés et/ou aux fluctuations thermiques) amplifiées par les forces de van der Waals qui deviennent non négligeables pour de faibles épaisseurs de couches (typiquement inférieures à 40 nm) et sont attractives entre deux couches de même nature. Des expériences modèles sont proposées dans la perspective d'une approche quantitative des conditions critiques d'apparition de ces défauts. / Nanolayer coextrusion enables the production of polymeric films composed of up to thousands of alternating layers. The thickness of each layer can in theory be controlled, by monitoring the number of layers, the mass ratio of the polymers, and the draw ratio of the film at the exit die, and can decrease down to several nanometers. It has been shown that such films can display drastically improved macroscopic properties, such as optical, gas barrier, or mechanical, due to confinement and interfacial effects. However, layer beak-up phenomenon occurring at such thicknesses, impacting the resulting properties, has also been reported for many polymer pairs. The goal of this thesis is to investigate the causes for these break-ups and for the instabilities leading to them. Most of this work deals with multilayer films of polymethyl methacrylate (PMMA) and polystyrene (PS), two amorphous polymers which blends were widely studied in the literature. Films with 65 to more than 8000 layers were fabricated by modifying processing and molecular parameters, to determine their impact on the homogeneity of the samples. These films were characterized mainly by using microscopy techniques, and especially atomic force microscopy (AFM), to extract not only the mean layer thickness, but distribution of thicknesses and the ratio of broken layers within the sample. A first necessary step was to develop a reliable statistical and quantitative analysis to obtain such information. Then, a first study focused on the effects of some process and material parameters on the homogeneity of multilayer films with micronic thicknesses. Choosing favourable experimental conditions at these scales, nanolayered films were then fabricated. We showed the existence of a critical layer thickness, below which layer breakup, estimated at around 10 nm for PS/PMMA films. When the targeted thickness is around or below 10 nm, the amount of broken layers increases significantly. We make the hypothesis that the layer breakup phenomenon is due to interfacial instabilities driven by van der Waals forces. The thicknesses of the layers we can reach with this process are so small that dispersive forces between two layers composed of the same polymer cannot be neglected (typically below 100 nm). Model experiments are proposed to quantitatively study the critical conditions of appearance of these layer breakups.

L'inversion conjointe géophysique est la méthode la plus efficace pour imager l'intérieur de la Terre. En intégrant plusieurs techniques géophysiques elle permet de réduire les incertitudes inhérentes à chacune et ainsi améliorer la compréhension de la Terre. Dans cette étude, nous utilisons les techniques des fonctions récepteur (RF) en sismologie, de la magnétotellurique (MT) et de la gravimétrie qui permettent de caractériser respectivement la vitesse des ondes S, la résistivité électrique et la densité du sous-sol.Le but de ce travail de recherche se divise en deux parties: une première, méthodologique, sur le développement d'une nouvelle approche d'inversion conjointe en 3D et une deuxième avec l'application de ces techniques (en approche jointe ou séparée) sur la Divergence Nord Tanzanienne pour mieux comprendre le phénomène de rupture continentale. Pour la partie méthodologie deux approches ont été développées : une entre les données de MT et de gravimétrie avec un calcul original de l'effet gravimétrique de la topographie qui permet de réduire le nombre de mailles tout en gardant une résolution satisfaisante ; et une deuxième méthode entre les données de MT et de RF par une nouvelle approche d'extrapolation des modèles 1D de vitesse en pseudo modèle 3D de vitesse. L'application de ces techniques sur la Tanzanie a permis de mettre en évidence un certain nombre de structures lithosphériques dont deux zones majeures à faible vitesse dans la croûte inférieure et dans le manteau supérieur. Cette dernière semble refléter des interactions entre des structures héritées d'âge protérozoïque et le panache mantellique Africain. / Geophysical joint inversion attempts to reproduce as best as possible the interior of the Earth. By integrating several geophysical techniques the joint inversion reduces the uncertainties of each methods and improves our understanding of the Earth structure. In this study we use the receiver functions (RF), the magnetotelluric (MT) and the gravity methods which enable to charaterize the Swave velocity, the electrical resistivity and the density, respectively. The objective of this research work is divided in two parts; first with the development of a new 3D joint inversion approach and then with the application of these methods (on a joint or separate approach) on the North Tanzanian Divergence to better understand the continental breakup.For the methodologic part two approaches have been developed; one between the MT and gravity data with an original computation of the topographic effect which decreases the number of cells while keeping a satisfaying resolution. And a second method between the MT and RF data where pseudo 3D velocity model are created and combined with the MT models to better takes into account the physical properties of the receiver function. The application of these methods on the Tanzania highlighted several lithospheric structures and particularly two low-velocity areas in the lower crust and the upper mantle. This latter suggests interactions with Proterozoic inherited structures and the African plume material.