In this work we apply the method of hydrodynamic reductions to study the integrability of the class of second order quasilinear equations.

This study aims to examine the throughput of nanoparticles through a Cladophora cellulose based virus removal filter. The effect of Brownian motion and flow velocity on the retention of 5 nm gold nanoparticles, 12.8 nm dextran nanoparticles and 28 nm ΦX174 bacteriophages was examined through MATLAB simulations and filtration experiments. Modeling of Brownian motion at different flow velocities was performed in MATLAB by solving the Langevin equation for particle position and velocity for all three types of particles. The motion of all three particle types was shown to be constrained at local flow velocities of 1∙10-2 m/s or greater. The constraint was greatest for ΦX174 bacteriophages, followed by dextran particles and then gold particles as a result of particle diameter. To verify the effect experimentally, virus removal filters were prepared with a peak pore width of 23 nm. Filtration experiments were performed at different flux values where gold and dextran particles did not exhibit any difference in retention between fluxes. However, a significant amount of gold and dextran particles were removed by the filter despite being smaller than the measured pore size. A decrease in retention with filtrated volume was observed for both particle types. Filtration of ΦX174 bacteriophages exhibited a difference in retention at different fluxes, where all bacteriophages where removed at a higher flux. The results from both simulations and experiments suggest that the retentive mechanism in filtering is more complex than what can be described only by size exclusion sieving, Brownian diffusion and hydrodynamic constraint of particles.

Cell encapsulation is a promising concept in regenerative medicine and stem cell treatment of diseases. Cells encapsulated in hydrogels have shown to yield better therapeutic outcome over cells in suspension. Microfluidic platforms have facilitated the process of cell encapsulation through the controlled mixing of aqueous cell solution and hydrogel with an immiscible liquid to yield a monodispersed population of microcapsules at a high throughput. However, given that the microfluidic process of placing cells in microcapsules is completely random, yielded samples are often riddled with empty microcapsules, raising the need for a post-encapsulation purification step to sort empty microcapsules from cell-laden ones. Sorting of microcapsules can be achieved through several techniques, most desirable of which are electrokinetic such as dielectrophoresis (DEP) and electrophoresis (EP). The advantages of DEP and EP techniques are that they support label-free sorting and yield a high throughput. However to achieve true effective DEP or EP sorting, there is a need to understand how empty microcapsules react to these electrokinetic forces versus occupied microcapsules. This study developed microfluidic devices for characterising the electrokinetic effects on microcapsules using DEP and EP. Results of both characterization techniques showed notable differences in the response of empty microcapsules versus cell-laden ones, reinforcing their potentials for sorting. Furthermore, this study proposed designs for microcapsules sorting devices that leverage EP and DEP.

A MEMS-based micro-electro-discharge machining technique that is enabled by the actuation of micromachined planar electrodes defined on the surfaces of the workpiece is developed that eliminates the need of numerical control machines. First, the planar electrodes actuated by hydrodynamic force is developed. The electrode structures are defined by patterning l8-µm-thick copper foil laminated on the stainless steel workpiece through an intermediate photoresist layer and released by sacrificial etching of the resist layer. The planer electrodes are constructed to be single layer structures without particular features underneath. All the patterning and sacrificial etching steps are performed using dry-film photoresists towards achieving high scalability of the machining technique to large-area applications. A DC voltage of 80-140 V is applied between the electrode and the workpiece through a resistance-capacitance circuit that controls the pulse energy and timing of spark discharges. The parasitic capacitance of the electrode structure is used to form a resistance capacitance circuit for the generation of pulsed spark discharge between the electrode and the workpiece. The suspended electrodes are actuated towards the workpiece using the downflow of dielectric machining fluid, initiating and sustaining the machining process. Micromachining of stainless steel is experimentally demonstrated with the machining voltage of 90V and continuous flow of the fluid at the velocity of 3.4-3.9 m/s, providing removal depth of 20 µm. The experimental results of the electrode actuation match well with the theoretical estimations. Second, the planar electrodes are electrostatically actuated towards workpiece for machining. In addition to the single-layer, this effort uses double-layer structures defined on the bottom surface of the electrode to create custom designed patterns on the workpiece material. The suspended electrode is electrostatically actuated towards the wafer based on the pull-in, resulting in a breakdown, or spark discharge. This instantly lowers the gap voltage, releasing the electrode, and the gap value recovers as the capacitor is charged up through the resistor. Sequential pulses are produced through the self-regulated discharging-charging cycle. Micromachining of the stainless-steel wafer is demonstrated using the electrodes with single-layer and double-layer structures. The experimental results of the dynamic built-capacitance and mechanical behavior of the electrode devices are also analyzed. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

L'objectif de cette thèse est d'étudier l'oscillation collective dans un matériau semi-conducteur (InGaAs) dans le but d'élargir les connaissances théoriques et de proposer de nouvelles configurations et des structures pour la conception de détecteurs ou émetteurs THz innovants et efficaces. Pour ce faire, nous développons un modèle théorique permettant l'étude de l'oscillation collective soumis ou non à une excitation externe (battement optique ou rayonnements THz). Une attention particulière est faite pour prendre en compte des phénomènes physiques importants tels que la mobilité différentielle dynamique négative et les oscillations de Gunn.Cette étude est faite à travers le développement d'un outil de simulation numérique basé sur l'approche HD couplé à un solveur de Poisson unidimensionnel. Le modèle HD décrit le temps de vol et le mécanisme de diffusion par l'énergie et la vitesse de relaxation. En outre, on prend en compte les frottements et leur évolution, la variation de l'énergie, la vitesse, et la masse effective. Par conséquent, le modèle HD permet l'observation des régimes transitoires ainsi que d'effectuer des études de fréquence. L'influence des différents paramètres physiques et technologiques sur les oscillations et résonances collectives des électrons sont évalués. Ensuite, le régime de petits signaux est étudié et la réponse de la diode aux perturbations optiques et électriques harmoniques et non harmoniques est évaluée. L'influence du fort biais appliqué à la diode sur les processus d'émission et de détection est ensuite décrit. / The purpose of this thesis is to obtain theoretical results in order to propose new configurations and structures for the conception of innovant and efficient THz detectors or emitters. For this sake, we develop a theoretical model allowing the study of collective oscillation in a semiconductor materials (we choose InGaAs), submitted or not to an external excitation (that is to optical beating or THz radiations). A particular attention is payed also to important physical phenomena such as negative dynamic differential mobility and Gunn oscillations.This study is made through the development of numerical simulation tool, which is based on the HD approach coupled to a one-dimensional Poisson solver. The HD model describes the free-flight and scattering mechanism through energy and velocity relaxation rates. Also it takes into account frictions and their evolution, the variation of energy, velocity and effective mass. Hence, the HD model allows us observing the transient regimes and performing frequency studies. The influence of the different physical and technological parameters on the electron collective oscillations and resonances are evaluated. Then, small-signal regime is studied and the diode response to harmonic and non-harmonic optical and electrical perturbations is evaluated. The influence of the high bias applied to the diode on emission and detection processes is then described.

L'enjeu principal de cette thèse est de comprendre et prédire les propriétés structurales et rhéologiques de suspensions colloïdales en tenant compte d'éléments complexes tels que (1) les interactions hydrodynamiques (IHs) et/ou (2) des forces extérieures. Nous employons dans cette thèse deux des techniques numériques les plus rapides de la littérature: la dynamique brownienne standard (BD), pour les systèmes où les IHs peuvent être ignorées; et la technique hybride "stochastic rotation dynamics - molecular dynamics" (SRD-MD), pour les systèmes où les IHs doivent être incorporées.Trois systèmes colloïdaux différents ont été étudiés. Le premier est un système de sphères dures soumis à un cisaillement, où le but a été de vérifier que l'introduction des IHs dans la SRD-MD peut correctement reproduire la relation entre la viscosité et la fraction volumique. Les résultats de viscosité sont en accord avec les résultats connus, qu'ils soient analytiques, numériques et expérimentaux. Le second système consiste en une suspension d'alumine, pour laquelle les interactions sont décrites par la théorie DLVO (Derjaguin-Landau-Verwey-Overbeek). Les simulations montrent que le seuil de percolation (phi_c) diminue lorsque la profondeur du puits de potentiel augmente. De plus, nous observons que la prise en compte des IHs tend à former des structures plus allongées également, par rapport aux structures obtenues sans les IHs. Les valeurs de phi_c obtenues dans les simulations sont en bon accord avec celles estimées par le modèle de la contrainte seuil (YODEL) établi par Flatt et Bowen. Le troisième système comporte deux types de colloïdes qui interagissent par un potentiel de Yukawa. Ce système binaire est soumis à l'influence d'un mur attractif. Nous montrons que la présence d'un mur attractif peut altérer la structure cristalline des agrégats à la surface telle qu'une structure de type CsCl qui se forme au lieu de la structure métastable de type NaCl. Finalement, nous avons réalisé une étude préliminaire par SRD-MD de suspensions soumises à un cisaillement oscillant. Nous montrons que lorsque la suspension est soumise au cisaillement oscillant en même temps que l'agrégation se produit, des structures plus compactes se forment. / The main objective of this thesis is to predict and understand the structural and rheological properties of colloidal suspensions when (1) hydrodynamic interactions (HIs) and/or (2) external forces are present. We employ two of the fastest techniques in literature: Brownian dynamics (BD), for systems without HIs; and the hybrid "stochastic rotation dynamics - molecular dynamics" (SRD-MD) for systems with HIs. Three different systems were studied. The first is a system of hard spheres subjected to shear, where the goal was to ensure that SRD-MD can correctly reproduce the viscosity vs. volume fraction relationship. The results are consistent with known analytical, numerical and experimental data. The second system is an alumina suspension described by the DLVO theory (Derjaguin-Landau-Verwey-Overbeek). The simulations show that the percolation threshold (phi_c) decreases as the depth of the potential well increases. Moreover, we note that HIs tend to form more elongated structures compared to the systems without HIs. The phi_c values ​​obtained are in good agreement with those estimated by Flatt and Bowen's yield stress model (YODEL). The third system consists of binary colloids that interact by Yukawa potential and subjected to the influence of an attractive wall. We show that the presence of an attractive wall may alter the crystalline structures such that CsCl crystals are formed instead of the metastable NaCl crystals. Finally, we conducted a preliminary study of suspensions under an oscillating shear. We show that when the aggregation process suspension coincides with the oscillatory motion, more compact structures are formed.

Cette thèse a pour objectif de mieux comprendre les mécanismes physiques qui contrôlent les trajectoires de particules anisotropes dans des écoulements confinés, afin d’en améliorer la prédiction. Nous avons dans un premier temps développé des outils expérimentaux basés sur la microscopie et le traitement d’images afin d’analyser les positions de particules en écoulement confiné dans des microcanaux de section carrée. Ces outils ont ensuite permis l’obtention de résultats originaux sur la migration latérale de particules sphériques dans des écoulements faiblement inertiels. Nous avons montré en particulier que les particules migrent au centre du canal à faible nombre de Reynolds et à proximité du centre de chaque face à Reynolds plus élevé et que ces deux régimes co-existent pour des Reynolds intermédiaires. Parallèlement à leur migration latérale, les particules en écoulement confiné peuvent s’espacer régulièrement sous certaines conditions pour former des trains. Ce travail a donc consisté à mener une étude statistique pour quantifier et localiser la formation des trains. Il a été montré que la formation des trains était contrôlée par la configuration de l’écoulement dans le sillage des particules et que leurs caractéristiques, i.e., le pourcentage de particules en trains et la distance interparticulaire, étaient fonction du nombre de Reynolds particulaire. Enfin, des résultats préliminaires sur le cas d’écoulements bi-disperses ont été obtenus. Pour terminer, les perspectives et développements futurs de ce travail sont dégagés. / This thesis aims to better understand the physical mechanism controlling the trajectories of particles in confined flows in order to improve predictive models. In the first step we have developed experimental tools based on microscopy and image analysis in order to identify the particles positions in confined flows in square section microchannels. These tools have then permitted to obtain original results on the lateral migration of spherical particles in flows at low inertia. In particular we have shown that neutrally buoyant particles in square channels are focused at channel center at low Reynolds number and at four channel faces at high Reynolds, and that there is a co-existence of the two regimes for intermediate Reynolds. In addition to their lateral migration, under certain conditions, particles can also align in the flow direction to form trains of evenly spaced particles. This work has thus been devoted to the statistical study on the quantification and localization of the train formation and configuration. It has been shown that the formation of trains is controlled by the flow configuration in the wake of the particles, and that the train characteristics, i.e., the fraction of particles in trains and the interparticle distance, are functions of the particle Reynolds number. Finally, preliminary results on flows of bidisperse suspensions have been obtained. To conclude, the perspectives and future developments of this work are presented.

To increase profitability for biogas production, new innovative substrates and condition of operations needs to be implemented. At the current state, fats, oils and greases (FOGs) represent a promising substrate even though it brings operational challenges to the anaerobic digestion process. By utilizing hydrodynamic cavitation (HC) as a pre-treatment of the FOGs, the efficiency of FOGs’ co-digestion with wastewater sludge can be significantly improved. Preliminary experiments conducted on oil and water demonstrates that the HC pre-treatment improves the oil solubilisation as well as forms stable oil and water emulsion that last for several hours. The pre-treatment also improved the soluble chemical oxygen demand (COD) of biosludge (BiSl) by up to 115% and the initial degradation rate by up to 35%. In a semi-continues system, this allowed a significant increment in the specific methane yield depending on the organic loading rate (OLR) applied1. With sufficient process optimization, the HC-pre-treatment may prove to be an energy efficient and effective pre-treatment of FOGs.

Le présent travail est une étude sur la modélisation des éoliennes flottantes alliant à la fois des chargements hydrodynamiques et aérodynamiques. L’approche expérimentale a tiré profit de la grande soufflerie de Luminy opérée par le MIO (Institut Océanologique de Méditerranée), unissant une soufflerie de très bonne qualité avec un bassin équipé de systèmes de génération de houle et de courant. Les dimensions de cette installation imposent un travail à échelle très réduite introduisant ainsi les interrogations sur les similitudes à respecter (Reynolds, Froude) et les complexités de maquettage. Ces travaux ont permis de développer des outils numériques avec d’un côté une approche fréquentielle basé sur un code utilisant les éléments finis développé par l’IFP au début des années 70, et de l’autre, une approche temporelle basé sur les formulations de Morison ou de Rainey permettant l’introduction de méthodes avancées de calculs des efforts aérodynamiques. / The present work focuses on the modeling of the hydrodynamic and aerodynamic loads on a floating wind turbine. The experimental approach took advantage of the wind and wave flume in Luminy operated by the MIO (Mediterranean Institute for Oceanography) comprising a wind tunnel with a very high flow quality blowing over a wave tank. The dimensions of the installation impose working at very small scales for which the similitudes (Reynolds, Froude) introduce high modeling complexities. This work allowed the development of numerical tools using one the one hand a frequency domain approach based on a finite element code developped by IFP¨in the early seventies, and in the other hand a time-domain approach based on Morison or Rainey formulation for hydrodynamic loads allowing the introduction of advanced methods for aerodynamic loads computation.

La nageoire caudale des animaux aquatiques peut être modélisée par un foil oscillant qui produit de la poussée. Le sillage moyen d'un tel foil oscillant est un jet de quantité de mouvement nette positive. Il a été proposé que les caractéristiques de stabilité de ces sillages moyens sont liées à l'efficacité de la propulsion des animaux aquatiques. Dans cet étude, nous reprenons cette question en tenant compte à la fois de la poussée et de la traînée exercée sur un corps auto-propulsé lorsqu'il nage. Nous étudions la stabilité d'une famille de sillages ayant une quantité de mouvement nulle, construit comme l'approximation d'Oseen d'un doublet de force se déplaçant à vitesse constante. En effectuant une analyse de stabilité locale, nous montrons d'abord que ces sillages subissent une transition convectif-absolu. En utilisant une approche "time-stepper" et intégrant le système de Navier-Stokes linéarisé, nous étudions la stabilité globale et mettons en évidence des effets non-parallèles de l'écoulement principal, ainsi que le rôle de la région absolument instable dans l'écoulement. Pour compléter le scénario d'instabilité globale, nous abordons l'évolution non linéaire d'une perturbation injectée dans le sillage. Ces résultats sont ensuite discutés dans le contexte de la nage d'un animal aquatique. Selon les résultats de stabilité, les sillages de quantité de mouvement nulle produit par les animaux aquatiques sont généralement stables, tandis que le sillage qui correspondrait à la poussée seule est instable. Il est essentiel de considérer toutes les forces exercées sur un animal auto-propulsé lors de l'examen de la stabilité de son sillage et l'efficacité de sa propulsion. / The caudal fin of swimming animals can be modelled as a thrust-producing flapping foil. When considered alone, such a foil produces on average a jet wake with a positive net momentum. It has been argued that the instability characteristics of these averaged wakes are linked to the propulsion efficiency of swimming animals. Here, we reconsider this question by taking into account both the thrust and the drag exerted on a self-propelled swimming body. To do so, we study the stability of a family of momentumless wakes, constructed as the Oseen approximation of a force doublet moving at constant velocity. By performing a local stability analysis, we first show that these wakes undergo a transition from absolute to convective instability. Then, using the time-stepper approach by integrating the linearised Navier-Stokes system, we investigate the global stability and reveal the influence of a non-parallel base flow as well as the role of the locally absolutely unstable upstream region in the wake. Finally, to complete the global scenario, we address the nonlinear evolution of the wake disturbance. These results are then discussed in the context of aquatic locomotion. According to the present stability results, the momentumless wake of aquatic animals is generally stable, whereas the corresponding thrust part is unstable. It is therefore essential to consider all forces exerted on a self-propelled animal when discussing its wake stability and its propulsion efficiency.