La cascade d’énergie qui a lieu dans les océans, depuis les grandes vers les petites échelles, est capitale pour comprendre leur dynamique et le mélange irréversible associé. Les attracteurs d’ondes internes font partie des mécanismes conduisant potentiellement à une telle cascade. Dans ce manuscrit, nous étudions expérimentalement les attracteurs d’ondes internes, dans une cuve trapézoïdale remplie d’un fluide stratifié linéairement en densité. Dans cette géométrie, les ondes peuvent être focalisées vers un cycle limite : l’attracteur. Nous montrons que la formation de l’attracteur est purement linéaire : des petites échelles sont donc créées grâce à la focalisation des ondes. Les principales caractéristiques de l’attracteur dépendent uniquement de la géométrie trapézoïdale de la cuve. A l’échelle de l’océan, nous montrons que les attracteurs d’ondes internes sont très probablement instables. En effet, ceux-ci sont sujets à une instabilité de résonance triadique, qui transfère de l’énergie depuis l’attracteur vers un couple d’ondes secondaires. Cette instabilité et ses principales caractéristiques sont décrites en fonction de la géométrie du bassin. Pour des expériences de longue durée, l’instabilité produit plusieurs paires d’ondes secondaires, créant une cascade d’instabilités triadiques et transférant l’énergie injectée à grandes échelles vers des échelles plus petites. Nous montrons, pour la première fois de façon expérimentale, de très fortes signatures de turbulence d’ondes internes. Au delà de cet état, la cascade atteint un régime de mélange partiel du fluide stratifié. Cet ultime régime apparait indépendant de la géométrie trapézoïdale du bassin, et donc, universel. Cette thèse est complétée par une étude sur la masse ajoutée et l’amortissement par émission d’ondes d’objets oscillant horizontalement dans un fluide stratifié en densité. Cela a des applications concernant la conversion de l’énergie des marées en ondes internes. / A question of paramount importance in the dynamics of oceans is related to the energy cascade from large to small scales and its contribution to mixing. Internal wave attractors may be one of the possible mechanisms responsible for such a cascade. In this manuscript, we study experimentally internal wave attractors in a trapezoidal test tank filled with linearly stratified fluid. In such a geometry, the waves can form closed loops called attractors. We show that the attractor formation is purely linear: small scales are thus created by wave focusing. The attractor characteristics are found to only depend on the trapezoidal geometry of the tank. At the ocean scale, we show that attractors are very likely to be unstable. Indeed, internal wave attractors are prone to a triadic resonance instability, which transfers energy from the attractor to a pair of secondary waves. This instability and its main characteristics are described as a function of the geometry of the basin. For long-term experiments, the instability produces several pairs of secondary waves, creating a cascade of triadic interactions and transferring energy from large-scale monochromatic input to multi-scale internal-wave motion. We reveal, for the first time, experimental convincing signatures of internal wave turbulence. Beyond this cascade, we have a mixing regime, which appears to be independent of the trapezoidal geometry and, thus, universal. This manuscript is completed by a study on added mass and wave damping coefficient of bodies oscillating horizontally in a stratified fluid, with applications to tidal conversion.

Au travers de leurs instabilités, les ondes internes de gravité, qui se propagent dans les fluides stratifiés, jouent un rôle crucial dans la dynamique océanique. En effet, ces instabilités transfèrent de l'énergie vers les petites échelles et créent ainsi du mélange. Parmi ces mécanismes, nous avons étudié l'instabilité triadique résonante (TRI). Ce processus se caractérise par l'émission à partir d'une onde-mère de deux ondes-filles, dont les fréquences et vecteurs d'onde vérifient avec l'onde-mère des conditions de résonance temporelle et spatiale. Dans le cas où une rotation globale du fluide (cas général en géophysique) s'ajoute à la rotation, celle-ci va changer les propriétés non seulement des ondes internes, on les appellera alors ondes gravito-inertielles, mais aussi de la TRI. L’étude expérimentale sur table tournante de l'instabilité d'un faisceau de forme contrôlée d'onde gravito-inertielle a mis en évidence l’importance de la rotation sur les caractéristiques de la TRI, comme le seuil d'instabilité ou les caractéristiques des ondes secondaires. En outre, ces résultats sont en très bon accord avec un développement asymptotique de cette instabilité qui prend en compte la taille finie du faisceau, paramètre déterminant au laboratoire et dans un contexte océanique. Cet effet est responsable notamment de l'existence d'une latitude critique dans l'océan.Dans un second temps, la réalisation d'un nouveau type de générateur d'onde axisymétrique a permis d'étudier la propagation d'ondes axisymétriques à trois dimensions. Les modes axisymétriques générés par ce nouveau dispositif ont été caractérisés et comparés aux solutions analytiques. Ce dispositif permet également de créer une excitation annulaire localisée qui focalise les ondes internes au centre de la cuve. En changeant la vitesse de groupe de ces ondes, au travers d'une stratification non-linéaire, nous pouvons créer une forte accumulation d'énergie au point de focalisation. En fonction de l'amplitude de l'excitation, on observe la transition entre un état stable vers un état fortement instable. / Through their instabilities, internal gravity waves, which propagate in stratified fluids, play a paramount role in the oceanic dynamics. Indeed, their instabilities transfer energy to small scales and lead to mixing. Among these instabilities, we studied the triadic resonant instability (TRI). This process is characterized by the generation from a primary wave of two secondary internal waves, whose frequencies and wave vectors fulfill the spatial and time resonance conditions. If the fluid is also rotating (which is in generally the case in geophysics), rotation changes not only the properties of internal waves, which, in this case, are named inertia-gravity waves, but also the properties of the TRI. The experimental study on a rotating plateform of the instability of a controlled internal wave beam highlighted the role played by rotation on TRI features, such as the instability threshold or the characteristics of the secondary waves. Moreover, these results are in excellent agreement with an asymptotic development of the instability that takes into account the finite width of the wave beam, key parameter in a laboratory and oceanic context. this effect is responsible for the existence of a critical latitude in the ocean.In a second part of this work, we built a new wave generator, which allowed for the study of tridimensional axisymmetric waves. The axisymmetric modes generated by this new set-up were characterized and compared to analytical solutions. The generator can also produce a localized axisymmetric bump which focalises the wave in the center of the tank. By changing the group velocity of the waves, through a non-linear stratification, we are able to create a large energy build-up at the point of focalisation. Depending on the amplitude of the wave, we observe the transition from a stable state to a strongly unstable one.

L’assemblage couche-par-couche permet de fabriquer des films multimatériaux aux propriétés variées présentant une structure stratifiée. Ce travail décrit les études structurelles des films multicouches de polyélectrolytes à l’aide de mesures de diffusion de neutrons.L’effet du vieillissement des films a été déterminé par réflectométrie des neutrons. Nous avons observé un léger tassement des films après 5 ans et une forte expansion après 15 ans.Nous avons aussi montré que le substrat et l’air en surface ont une influence sur la structure des couches proches des extrémités des films, conduisant à une structure inhomogène perpendiculairement à la surface.Nous avons finalement étudié la conformation des chaînes de polyélectrolytes dans les films multicouches ; nous avons déterminé que les chaînes de PSS dans des films préparés par trempage ont une conformation en pelotes aplaties, contrairement aux chaînes de polyélectrolytes en solution qui présentent une conformation sphérique. / The Layer-by-Layer assembly allows the build-up of multimaterial films with various properties showing a stratified structure. This work describes the structural strudies of multilayer films of polyelectrolytes with neutron scattering measurements.Ageing effect on films was determined by neutron reflectometry. We observed a slight shrink of the films after 5 years and a strong expansion after 15 years.We also showed that the proximity of the substrate and the air at the surface have an influence on the structure of the layers at the extremities of the films, leading to an inhomogeneous structure perpendicularly to the surface.Finally, we studied the conformation of polyelectrolyte chains in the multilayer films ; we determined that PSS chains in dipped films have a flattened coil conformation, whereas the polyelectrolyte chains in solution have a spherical conformation.

The influence of stratification on the structure of turbulent methane/air combustion is investigated using experimental data from laboratory scale burners: a weakly turbulent slot burner, and a higher turbulence co-annular swirl burner. The degree of stratification can be controlled independently of the overall fuel/air flow rate. The resulting measurements of scalar and velocity fields provide detailed test cases for existing and emerging turbulent flame models, covering a range of u'/sL from 1 to 10, turbulence intensities from 5% to 60%, and stratification ratios from 1 to 3. Simultaneous Rayleigh/Raman/CO-LIF measurements of temperature and major species concentrations - CH4, CO2, CO, H2, H2O and O2 - along a line are used to investigate the structure of a series of flames in both the slot and swirl burners. Concurrent cross-planar OH-PLIF allows thermal gradients to be angle corrected to their three-dimensional values. Finally, non-reacting and reacting velocity fields complete the flame database. The behavior of major species concentrations in the slot and swirl burner with respect to temperature is found to agree well on the mean with unstrained premixed laminar flame calculations. Scalar means conditioned on stoichiometry also show good agreement, aside from hydrogen which is enhanced under stratified conditions. Surface density function and scalar dissipation are lower than calculated values in all cases, suggesting that turbulence-induced thickening dominates the effect of increased strain. Metrics commonly used to derive flame surface density (FSD) were investigated. FSD may be determined using a statistical method based on measurements of temperature and its gradient, or a geometric method based on 2D temperature or LIF imaging. A third metric, an extension of the geometric method, is proposed. Good agreement is observed between the three metrics. The current database provides the first detailed high resolution scalar measurements for premixed and stratified flames. The data analysis provides insight into the physics of stratification: for the flames considered, the effects of stratification appear to be surprisingly small compared to those of turbulence, even at significant stratification ratios. The datasets provide a means of validating current and future computational turbulent combustion models.

Avec la révolution récente de la génomique et la médecine stratifiée, le développement de signatures moléculaires devient de plus en plus important pour prédire le pronostic (biomarqueurs pronostiques) ou l’effet d’un traitement (biomarqueurs prédictifs) de chaque patient. Cependant, la grande quantité d’information disponible rend la découverte de faux positifs de plus en plus fréquente dans la recherche biomédicale. La présence de données de grande dimension (nombre de biomarqueurs ≫ taille d’échantillon) soulève de nombreux défis statistiques tels que la non-identifiabilité des modèles, l’instabilité des biomarqueurs sélectionnés ou encore la multiplicité des tests.L’objectif de cette thèse a été de proposer et d’évaluer des méthodes statistiques pour l’identification de ces biomarqueurs et l’élaboration d’une prédiction individuelle des probabilités de survie pour des nouveaux patients à partir d’un modèle de régression de Cox. Pour l’identification de biomarqueurs en présence de données de grande dimension, la régression pénalisée lasso est très largement utilisée. Dans le cas de biomarqueurs pronostiques, une extension empirique de cette pénalisation a été proposée permettant d’être plus restrictif sur le choix du paramètre λ dans le but de sélectionner moins de faux positifs. Pour les biomarqueurs prédictifs, l’intérêt s’est porté sur les interactions entre le traitement et les biomarqueurs dans le contexte d’un essai clinique randomisé. Douze approches permettant de les identifier ont été évaluées telles que le lasso (standard, adaptatif, groupé ou encore ridge+lasso), le boosting, la réduction de dimension des effets propres et un modèle implémentant les effets pronostiques par bras. Enfin, à partir d’un modèle de prédiction pénalisé, différentes stratégies ont été évaluées pour obtenir une prédiction individuelle pour un nouveau patient accompagnée d’un intervalle de confiance, tout en évitant un éventuel surapprentissage du modèle. La performance des approches ont été évaluées au travers d’études de simulation proposant des scénarios nuls et alternatifs. Ces méthodes ont également été illustrées sur différents jeux de données, contenant des données d’expression de gènes dans le cancer du sein. / With the recent revolution in genomics and in stratified medicine, the development of molecular signatures is becoming more and more important for predicting the prognosis (prognostic biomarkers) and the treatment effect (predictive biomarkers) of each patient. However, the large quantity of information has rendered false positives more and more frequent in biomedical research. The high-dimensional space (i.e. number of biomarkers ≫ sample size) leads to several statistical challenges such as the identifiability of the models, the instability of the selected coefficients or the multiple testing issue.The aim of this thesis was to propose and evaluate statistical methods for the identification of these biomarkers and the individual predicted survival probability for new patients, in the context of the Cox regression model. For variable selection in a high-dimensional setting, the lasso penalty is commonly used. In the prognostic setting, an empirical extension of the lasso penalty has been proposed to be more stringent on the estimation of the tuning parameter λ in order to select less false positives. In the predictive setting, focus has been given to the biomarker-by-treatment interactions in the setting of a randomized clinical trial. Twelve approaches have been proposed for selecting these interactions such as lasso (standard, adaptive, grouped or ridge+lasso), boosting, dimension reduction of the main effects and a model incorporating arm-specific biomarker effects. Finally, several strategies were studied to obtain an individual survival prediction with a corresponding confidence interval for a future patient from a penalized regression model, while limiting the potential overfit.The performance of the approaches was evaluated through simulation studies combining null and alternative scenarios. The methods were also illustrated in several data sets containing gene expression data in breast cancer.

In this thesis is presented mathematical model of stratified 2D flow of viscous incopressible fluid and its program realization. Basic equations of fluid flow in Boussinesq approximation were solved by finite volume method on structured nonortogonal grid. Discretization was done by the principle of semi-discretisation. The space derivative was solved by AUSM me- thod with MUSCL velocity reconstruction. The viscid terms were solved through auxiliary grids. During time discretization artificial compressibility method was used in dual time. The resulting system of ODEs is integrated in time by a suitable Runge-Kutta multistage scheme. Numerical experiments were calculated for flow with Reynolds number equals 1000. Further 3 numerical experiments are presented with different boundary conditions. 1

Coherent plane-wave compounding (CPWC) ultrasound is an important modality enabling ultrafast biomedical imaging. To perform CWPC image reconstruction for a stratified (horizontally layered) medium, one needs to know how the speed of sound (SOS) varies with the propagation depth. Incorrect sound speed and layer thickness assumptions can cause focusing errors, degraded spatial resolution and significant geometrical distortions resulting in poor image reconstruction. We aim to determine the speed of sound and thickness values for each horizontal layer to accurately locate the recorded reflection events to their true locations within the medium. Our CPWC image reconstruction process is based on phase-shift migration (PSM) that requires the user to specify the speed of sound and thickness of each layer in advance. Prior to performing phase-shift migration (one layer at a time, starting from the surface), we first estimate the speed of sound values of a given layer using a cosine similarity metric, based on the data obtained by a multi-element transducer array for two different plane-wave emission angles. Then, we use our speed estimate to identify the layer thickness via end-of-layer boundary detection. A low-cost alternative that obtains reconstructed images with fewer phase shifts (i.e., fewer complex multiplications) using a spectral energy threshold is also proposed in this thesis. Our evaluation results, based on the CPWC imaging simulation of a three-layer medium, show that our sound speed and layer thickness estimates are within 4% of their true values (i.e., those used to generate simulated data). We have also confirmed the accuracy of our speed and layer thickness estimation separately, using two experimental datasets representing two special cases. For speed estimation, we used a CPWC imaging dataset for a constant-speed (i.e., single-layer) medium, yielding estimates within 1% of their true values. For layer thickness estimation, we used a monostatic (i.e., single-element) synthetic-aperture (SA) imaging dataset of the three-layer medium, also yielding estimates within 1% of their true values. Our evaluation results for the low-cost alternative showed a 93% reduction in complex multiplications for the three-layer CPWC imaging dataset and 76% for the three-layer monostatic SA imaging dataset, producing images nearly similar to those obtained using the original PSM methods. / Graduate

No description available.

In flows with stable density stratification, a portion of the gravitational potential energy is available for conversion to kinetic energy. The remainder is not and is called “background potential energy”. The partition of potential energy is analogous to the classical division of energy due to motion into its kinetic and internal components. Computing background and available potential energies is important for understanding stratified flows. In many numerical simulations, though, the Boussinesq approximations to the Navier-Stokes equations are employed. These approximations are not consistent with conservation of energy. In this thesis we re-derive the governing equations for a buoyancy driven fluid using Boussinesq approximations. Analytical and stochastic approaches to partitioning potential energy are developed and analyzed in simplified 1-D cases. Finally, ambient and deviatoric potential energies, quantities analogous to background and available potential energy are introduced. Direct Numerical Simulations are used to formulate an energy budget. The actual and surrogate potential energies are compared based on the simulation results.

[pt] Testes de formação são normalmente realizados para determinar as propriedades rochosas do reservatório e os dados obtidos costumam ser interpretados com base no pressuposto que o reservatório é homogêneo na direção vertical e descrito por um modelo uni dimensional. No entanto, muitos reservatórios são compostos por diversas camadas que possuem características diferentes. Os poços de produção nesses reservatórios podem receber óleo de mais de uma camada. Em um sistema de reservatório estratificado, o comportamento da pressão e da temperatura não é necessariamente o mesmo de um sistema em camada única e raramente revela as mesmas propriedades médias de todo o sistema. Prever as características das camadas individuais é importante para descrever adequadamente o reservatório e melhorar o gerenciamento da produção. Este trabalho apresenta um modelo numérico, transiente-térmico para um sistema acoplado poço - reservatório 2D, levando-se em consideração efeitos Joule-Thompson responsáveis pelo aquecimento / resfriamento do fluido, expansão/compressão adiabática, além de efeitos de condução e convecção para o poço e o reservatório em um escoamento monofásico. A análise bidimensional do reservatório permite que se simule zonas de estratificação e barreiras. O modelo permite fluxo através de camadas adjascentes com propriedades de rocha diferentes. Pressão e temperatura a uma certa posição no poço produtor são avaliadas ao longo do tempo. Resultados mostram que a análise do transiente de pressão (PTA) e a análise do transiente de temperatura (TTA) podem ser utilizadas para caracterizar diferentes configurações de um reservatório estratificado. / [en] Well formation tests are usually performed to determine rock properties of a reservoir and the obtained data has often been interpreted based on an assumption that the reservoir is homogeneous in the vertical direction and described by a 1-D model. However, many reservoirs are found to be composed of different number of layers that have different characteristics. Production wells in such reservoirs may receive oil from more than one layer. In stratified reservoir system, the pressure and temperature behavior are not necessarily the same as in single layered system, and rarely reveals the same average properties of the entire system. The prediction of the characteristics of the individual layers is important to describe properly the reservoir and improve production management. This work presents a numerical transient-thermal model for a coupled wellbore/2D-reservoir considering Joule-Thompson heating/cooling, adiabatic fluid expansion/compression, conduction and convection effects for both wellbore and reservoir for a single-phase fluid flow. The two-dimensional reservoir model allows the analysis of stratified zones and barriers. The model allows cross flow between the adjacent layers with different rock properties.Wellbore temperature and pressure at a certain gauge depth are evaluated along the time. Results show how pressure transient analysis (PTA) and temperature transient analysis (TTA) can be used to characterize different configuration of stratified reservoirs.