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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
231

Effet des forces de van der Waals sur la dynamique de l'azote et de l'hydrogène en interaction avec la surface de W(100) / Influence of van der Waals forces in the dynamics of nitrogen and hydrogen in interaction with W(100) surface

Ibargüen becerra, César 28 November 2019 (has links)
Une littérature scientifique nourrie est consacrée aux processus élémentaires hétérogènes se produisant à l’interface gaz-solide en raison de leur rôle clé dans de nombreux domaines. Ainsi, l’interaction d’atomes et de molécules avec les surfaces revêt une importance primordiale dans l’étude de la catalyse hétérogène, la combustion, la corrosion, le stockage de l’hydrogène, l’industrie automobile et pétrolière, les interactions plasma/paroi dans le contexte du réacteur expérimental thermonucléaire (ITER), les technologies du spatial, la chimie atmosphérique et l’astrochimie, pour citer quelques exemples. Lorsqu'un atome ou une molécule entre en collision avec une surface, de nombreux processus élémentaires peuvent avoir lieu. Ils dépendent de nombreux facteurs tels que : l'énergie de collision du projectile, l'angle d'incidence sur la surface, la température de surface, l'état initial le des molécules, le transfert d'énergie entre la surface des projectiles, etc… Tous ces facteurs influencent fortement les mécanismes réactionnels et la dynamique de ces processus. Les expériences de faisceaux moléculaires permettent un contrôle toujours plus précis de l'état initial des réactifs associé à un caractérisation fine des produits de réactions. Cependant, dans la plupart des cas, ces observations expérimentales ne fournissent pas tous les détails qui nous permettent de décrire finement les mécanismes gouvernant les processus élémentaires étudiés. Par conséquent, l'élaboration de modèles théoriques devient essentielle pour en rationaliser la description. L'objectif principal de ce travail de thèse est de proposer une analyse de la dynamique de plusieurs processus élémentaires pouvant se produire sur une surface de W(100) en contact avec de l'hydrogène et de l'azote (diffusion inélastique de N2 et H2, l'adsorption dissociative et non dissociative de H2 et l'adsorption et l'absorption de H et N). Par rapport aux études antérieures, la nouveauté de ce travail réside dans la prise en compte des interactions à longue distance de type van der Waals, qui s’avèrent essentielles lorsqu'on souhaite atteindre un bon accord théorie expérience dans le régime des faibles énergies de collision. Les résultats sont comparés aux données expérimentales disponibles et aux résultats théoriques antérieurs. Des simulations de dynamique moléculaire quasi-classique sont réalisés à l'aide de surfaces d'énergie potentielle (PES) basées sur la théorie de la fonctionnelle de la densité, tenant compte d’interactions non locales, telles que les forces de van der Waals. La dissipation de l’énergie aux vibrations du réseau et aux excitations électroniques est prise en compte au moyen de modèles effectifs. / An important part of scientific literature is devoted to the heterogeneous elementary processes occurring at gas-solid interface due to their great importance and key role in many different domains and applications. Thus, interaction of gas atoms/molecules with surface reactions are of primary importance in the study of: heterogeneous catalysis, combustion of solid fuel and coal gasification, processes of corrosion, hydrogen storage in solid material, automotive and oil industry, plasma-wall interactions in the context of thermonuclear experimental reactor (ITER), atmospheric re-entries technologies and astrochemistry, to name some examples. When an atom or molecule impinges on a surface many different elementary processes can take place, which depends on factors such as: the collision energy of the projectile, the angle of incidence to the surface, the surface temperature, the initial state of the molecules, the transference of energy projectiles-surface, etc. All these factors determines the mechanisms of reaction and the dynamics of the processes. Experimental molecular beams (MB) and other experimental techniques are able to accurately control the initial state of the reactive and characterizing products of gas-surface reactions. However, in most of the case experimental techniques do not provide enough details about the mechanisms through which elementary processes occur. Consequently, theoretical models becomes essential to rationalize the description that in certain cases the experiments do not reach.The main goal of this thesis work is to propose an analyze of the dynamics of several elementary processes occurring on a W(100) surface, such as: the inelastic scattering of N2 and H2, the dissociative and non-dissociative adsorption of of H2 and the adsorption and absorption of H and N. Compared to previous studies, the novelty of this work resides in the taking into account of van der Waals long-distance interactions, which are essential to reach a good agreement between theoretical and experiment results, especially at low collision energy regime. To rationalize the non-adiabatic effects, the energy dissipation to lattice vibrations and electronic excitation are taken in to account by means of GLO and LDFA models respectively.
232

Etude expérimentale et modélisation d'écoulement à surface libre en présence de végétation, et transport sédimentaire associé / Experimental study and modeling of free surface flow in the presence of vegetation, and associated sediment transport

Romdhane, Hela 19 March 2019 (has links)
Les rivières forment un système dynamique complexe soumis à des variations de grande ampleur, en effet les précipitations sont jugées comme la cause fondamentale de ces fluctuations. Au cours du temps, la morphologie des rivières évolue sous l’influence de plusieurs paramètres, en particulier les crues, les ouvrages hydrauliques, le transport sédimentaire. Le développement de la végétation dans le lit de la rivière et sur les berges peut affecter les conditions hydrodynamiques et le comportement des cours d'eau, ainsi l'impact de la végétation est une question cruciale pour la gestion des réseaux d'irrigation et des flux naturels. En réduisant la vitesse, la présence de végétation peut augmenter les dépôts de sédiments et modifier le risque d'inondation du fait des effets combinés de l'augmentation de la rugosité et de la diminution de la zone d'écoulement du chenal principal du fleuve. Ces aspects sont mis en avant par l’application de simulations numériques à des cas réels : cas de la Medjerda et du Canal Medjerda Cap Bon en Tunisie. La végétation est une caractéristique commune des eaux côtières et fluviales naturelles, interagissant à la fois avec le débit d'eau et le transport de sédiments. Cependant, les processus physiques qui régissent ces interactions sont encore mal compris, ce qui rend difficile la prévision du transport des sédiments et de la morpho dynamique. L’enjeu de cette thèse est d’améliorer la connaissance des processus physiques régissant les interactions entre végétation, écoulement et transport sédimentaire. Le but final est de pouvoir améliorer la gestion des hydro-systèmes artificiels ou naturels. Ce travail impliquera deux approches complémentaires d’expériences et de modélisation analytique et numérique. Dans un premier temps, on s’attachera à mieux caractériser les processus physiques d’interaction entre végétation et écoulement. Pour cela des expériences sur différents canaux fourniront l’hydrodynamique au-dessus de végétations modèles. On mettra l’accent sur le développement des méthodes expérimentales spécifiques à l’étude de couche limite au-dessus de macro-rugosités. Ces résultats seront dans un second temps analysés à partir de modèles analytiques qui permettent d’avoir les relations hauteur-débits nécessaires pour la gestion. Les caractéristiques et les performances de plusieurs modèles seront évaluées en regard des différents types de végétations. Dans un troisième temps, des expériences avec des sédiments préciseront l’influence de la végétation sur la modification du transport solide. La réduction des contraintes sur les lits engendre une adaptation nécessaire des lois de transport classique. Un modèle d’ajustement de ces lois sera proposé. / Rivers form a complex dynamic system subject to wide variations, in fact precipitation is considered as the fundamental cause of these fluctuations. Over time, the morphology of rivers evolves under the influence of several parameters, especially floods, hydraulic structures, sediment transport. The development of vegetation in the river bed and on the banks can affect the hydrodynamic conditions and the behavior of a watercourse, so the impact of vegetation on sediment transport is a crucial issue for the management of irrigation networks and natural flows. By reducing velocity, the presence of vegetation can increase sediment deposition and modify the risk of flooding due to the combined effects of increasing roughness and decreasing of flowing area of the river main channel. These aspects are highlighted by the application of numerical simulations to real cases: the case of the Medjerda River and the Channel of Medjerda Cap Bon in Tunisia. Vegetation is a common feature of natural coastal and riverine waters, interacting with both water flow and sediment transport. However, the physical processes governing these interactions are still poorly understood, making it difficult to predict sediment transport and morpho dynamics. The aim of this thesis is to improve the knowledge of the physical processes governing the interactions between vegetation, flow and sediment transport on the one hand, and to select the appropriate model that will be applied in the real case of rivers. The ultimate purpose is to improve the management of artificial or natural hydro-systems. This work will involve two complementary approaches to experiments and analytical and numerical modeling. At first, we will focus on better characterizing the physical processes of interaction between vegetation and flow. For this, experiments on different channels will provide hydrodynamics over model vegetation’s. Emphasis will be placed on the development of experimental methods specific to boundary layer studies over macro-roughness. These results will be analyzed in a second time from analytical models that allow the stage-discharge relationships required for management. The characteristics and performances of several models will be evaluated with regard to different types of vegetation. Thirdly, experiments with sediments will specify the influence of vegetation on the modification of solid transport. The reduction of the constraints on the beds generates a necessary adaptation of the classical transport laws. An adjustment model for these laws will be proposed.
233

COMPLEX FLUIDS IN POROUS MEDIA: PORE-SCALE TO FIELD-SCALE COMPUTATIONS

Soroush Aramideh (8072786) 05 December 2019 (has links)
Understanding flow and transport in porous media is critical as it plays a central role in many biological, natural, and industrial processes. Such processes are not limited to one length or time scale; they occur over a wide span of scales from micron to Kilometers and microseconds to years. While field-scale simulation relies on a continuum description of the flow and transport, one must take into account transport processes occurring on much smaller scales. In doing so, pore-scale modeling is a powerful tool for shedding light on processes at small length and time scales.<br><br>In this work, we look into the multi-phase flow and transport through porous media at two different scales, namely pore- and Darcy scales. First, using direct numerical simulations, we study pore-scale Eulerian and Lagrangian statistics. We study the evolution of Lagrangian velocities for uniform injection of particles and numerically verify their relationship with the Eulerian velocity field. We show that for three porous media velocity, probability distributions change over a range of porosities from an exponential distribution to a Gaussian distribution. We thus model this behavior by using a power-exponential function and show that it can accurately represent the velocity distributions. Finally, using fully resolved velocity field and pore-geometry, we show that despite the randomness in the flow and pore space distributions, their two-point correlation functions decay extremely similarly.<br><br>Next, we extend our previous study to investigate the effect of viscoelastic fluids on particle dispersion, velocity distributions, and flow resistance in porous media. We show that long-term particle dispersion could not be modulated by using viscoelastic fluids in random porous media. However, flow resistance compared to the Newtonian case goes through three distinct regions depending on the strength of fluid elasticity. We also show that when elastic effects are strong, flow thickens and strongly fluctuates even in the absence of inertial forces.<br><br>Next, we focused our attention on flow and transport at the Darcy scale. In particular, we study a tertiary improved oil recovery technique called surfactant-polymer flooding. In this work, which has been done in collaboration with Purdue enhanced oil recovery lab, we aim at modeling coreflood experiments using 1D numerical simulations. To do so, we propose a framework in which various experiments need to be done to quantity surfactant phase behavior, polymer rheology, polymer effects on rock permeability, dispersion, and etc. Then, via a sensitivity study, we further reduce the parameter space of the problem to facilitate the model calibration process. Finally, we propose a multi-stage calibration algorithm in which two critically important parameters, namely peak pressure drop, and cumulative oil recovery factor, are matched with experimental data. To show the predictive capabilities of our framework, we numerically simulate two additional coreflood experiments and show good agreement with experimental data for both of our quantities of interest.<br><br>Lastly, we study the unstable displacement of non-aqueous phase liquids (e.g., oil) via a finite-size injection of surfactant-polymer slug in a 2-D domain with homogeneous and heterogeneous permeability fields. Unstable displacement could be detrimental to surfactant-polymer flood and thus is critically important to design it in a way that a piston-like displacement is achieved for maximum recovery. We study the effects of mobility ratio, finite-size length of surfactant-polymer slug, and heterogeneity on the effectiveness of such process by looking into recovery rate and breakthrough and removal times.
234

Acoustic Streaming in Compressible Turbulent Boundary Layers

Iman Rahbari (8082902) 05 December 2019 (has links)
<div>The growing need to improve the power density of compact thermal systems necessitates developing new techniques to modulate the convective heat transfer efficiently. In the present research, acoustic streaming is evaluated as a potential technology to achieve this objective. Numerical simulations using the linearized and fully non-linear Navier-Stokes equations are employed to characterize the physics underlying this process. The linearized Navier-Stokes equations accurately replicate the low-frequency flow unsteadiness, which is used to find the optimal control parameters. Local and global stability analysis tools were developed to identify the modes with a global and positive heat transfer effect.</div><div><br></div><div>High-fidelity numerical simulations are performed to evaluate the effect of the excitation at selected frequencies, directed by the linear stability analysis, on the heat and momentum transport in the flow. Results indicate that, under favorable conditions, superimposing an acoustic wave, traveling along with the flow, can <i>resonate</i> within the domain and lead to a significant heat transfer enhancement with minimal skin friction losses. Two main flow configurations are considered; at the fixed Reynolds number Re<sub>b</sub>=3000, in the supersonic case, 10.1% heat transfer enhancement is achieved by an 8.4% skin friction increase; however, in the subsonic case, 10% enhancement in heat transfer only caused a 5.3% increase to the skin friction. The deviation between these two quantities suggests a violation of the Reynolds analogy. This study is extended to include a larger Reynolds number, namely Re<sub>b</sub>=6000 at M<sub>b</sub>=0.75 and a similar response is observed. The effect of excitation amplitude and frequency on the resonance, limit-cycle oscillations, heat transfer, and skin friction are also investigated here.</div><div><br></div><div>Applying acoustic waves normal to the flow in the spanwise direction disrupts the near-wall turbulent structures that are primarily responsible for heat and momentum transport near the solid boundary. Direct numerical simulations were employed to investigate this technique in a supersonic channel flow at M<sub>b</sub>=1.5 and Re<sub>b</sub>=3000. The external excitation is applied through a periodic body force in the spanwise direction, mimicking loudspeakers placed on both walls that are operating with a 180<sup>o</sup> phase shift. By keeping the product of forcing amplitude A<sub>f</sub> and pulsation period (<i>T</i>) constant, spanwise velocity perturbations are generated with a similar amplitude at different frequencies. Under this condition, spanwise pulsations at <i>T</i>=20 and <i>T</i>=10 show up to 8% reduction in Nusselt number as well as the skin friction coefficient. Excitation at higher or lower frequencies fails to achieve such high level of modulations in heat and momentum transport processes near the walls.<br> <br>In configurations involving a spatially-developing boundary layer, a computational setup that includes laminar, transitional, and turbulent regions inside the domain is considered and the impact of acoustic excitation on this flow configuration has been characterized. Large-eddy simulations with dynamic Smagorinsky sub-grid scale modeling has been implemented, due to the excessive computational cost of DNS calculations at high-Reynolds numbers. The optimal excitation frequency that resembles the mode chosen for the fully-developed case has been identified via global stability analysis. Fully non-linear simulations of the spatially-developing boundary layer subjected to the excitation at this frequency reveal an interaction between the <i>pulsations</i> and the perturbations originated from the tripping which creates a re-laminarization zone traveling downstream. Such technique can locally enhance or reduce the heat transfer along the walls.<br></div>
235

Stability analysis of channel flow laden with small particles.

Klinkenberg, Joy January 2011 (has links)
This thesis deals with the stability of particle laden flows. Both modal and non-modal linear analyses have been performed on two-way coupled particleladen flows, where particles are considered spherical, solid and either heavy or light. When heavy particles are considered, only Stokes drag is used as interaction term. Light particles cannot be modeled with Stokes drag alone, therefore added mass and fluid acceleration are used as additional interaction forces. The modal analysis investigates the asymptotic behavior of disturbances on a base flow, in this thesis a pressure-driven plane channel flow. A critical Reynolds number is found for particle laden flows: heavy particles increase the critical Reynolds number compared to a clean fluid, when particles are not too small or too large. Neutrally buoyant particles, on the other hand, have no influence on the critical Reynolds number. Non-modal analysis investigates the transient growth of disturbances, before the subsequent exponential behavior takes over. We investigate the kinetic energy growth of a disturbance, which can grow two to three orders of magnitude for clean fluid channel flows. This transient growth is usually the phenomenon that causes transition to turbulence: the energy can grow such that secondary instabilities and turbulence occurs. The total kinetic energy of a flow increases when particles are added to the flow as a function of the particle mass fraction. But instead of only investigating the total energy growth, the non-modal analysis is expanded such that we can differentiate between fluid and particle energy growth. When only the fluid is considered in a particle-laden flow, the transient growth is equal to the transient growth of a clean fluid. Besides thes Stokes drag, added mass and fluid acceleration, this thesis also discusses the influence of the Basset history term. This term is often neglected in stability analyses due to its arguably weak effect, but also due to difficulties in implementation. To implement the term correctly, the history of the particle has to be known. To overcome this and obtain a tractable problem, the square root in the history term is approximated by an exponential. It is found that the history force as a small effect on the transient growth. Finally, Direct numerical simulations are performed for flows with heavy particles to investigate the influence of particles on secondary instabilities. The threshold energy for two routes to turbulence is considered to investigate whether the threshold energy changes when particles are included. We show that particles influence secondary instabilities and particles may delay transition. / QC 20111013
236

Modélisation de l'interaction entre les virus de la grippe et de la rougeole

Bouthillette, François 12 1900 (has links)
Les gens infectés par la rougeole subissent une suppression immunitaire. Ce mémoire porte sur l’influence de cette caractéristique de la rougeole sur un autre pathogène, ici la grippe. Il s’agit donc de modéliser la réponse immunitaire d’une interaction virus-virus, problème d’une grande pertinence durant la pandémie causée par le SRAS-CoV-2 alors que les interactions de celui-ci avec le virus de l’influenza demeurent à déterminer. Nous avons également que la grippe augmente la production d’autres pathogènes. Un modèle de chaque pathogène va être développé et analysé. On cherchera les points fixes, leurs conditions de stabilité et on observera quelques résultats numériques pour constater leurs évolutions dans le temps. Ensuite un modèle suivant l’évolution des deux pathogènes ayant infecté un individu au même moment sera conçu. Dans ce modèle nous inclurons les interactions d’un pathogène l’un sur l’autre pour déterminer théoriquement les effets chez les individus infectés à la fois par la grippe et la rougeole. On pourra par la suite comparer entre les différentes populations lorsqu’il n’y a aucune interaction et avec les différentes interactions entre les deux pathogènes. / People infected with measles experience immune suppression. This work focuses on the influence of this characteristic of measles on another pathogen, here the flu. We also have that the flu will increase the production of other pathogens in a co-infection model. Modeling the immune response to such virus-virus interaction is currently of signficant relevance, given the limited knowledge on SARS-CoV-2/influenza interactions. A model of each pathogen will be developed and analysed. We will look for the fixed points, conditions for their stability and we will observe some numerical results of their evolution over time. Then a model following the evolution of the two pathogens having simultaneously infected an individual will be designed. In this model we will include the interactions of the pathogens on each other to theoretically determine the effects in individuals infected with both influenza and measles. Then we can compare between the different populations when there is no interaction and with the different interactions between the two pathogens.
237

Oscillations torsionnelles magnétohydrodynamiques auto-excitées dans les Jupiters chaudes

Hardy, Raphaël 08 1900 (has links)
Les Jupiters chaudes sont des exoplanètes possédant des caractéristiques uniques. En raison de leur proximité avec leur étoile hôte elles présentent une non-symétrie remarquable. Cette proximité provoquant la rotation synchrone force un côté de la planète à toujours faire face à l'étoile et l'autre à être plongé dans une nuit perpétuelle. Cette géométrie donne lieu à une différence d'allant de 200 K jusqu'à 2000 K entre les deux côtés de la planète, engendrant des écoulements zonaux pouvant atteindre des vitesses de l'ordre du km/s afin de redistribuer la chaleur. Le point chaud, le point le plus chaud de la planète, est un témoin de ces vents intenses. Les observations et les simulations hydrodynamiques montrent que les écoulements zonaux se font d'ouest en est. Cependant, les observations de deux planètes ne se conforment pas aux prédictions. En effet, CoRoT-2 b et HAT-P-7 b montrent des points chauds à l'ouest. L'explication la plus répandue est que le champ magnétique de ces planètes, en interaction avec leur atmosphère partiellement ionisée, peut renverser la direction des écoulements zonaux, si ce champ est assez puissant. Une diffusivité magnétique variable dans l'espace peut générer localement des champs magnétiques lorsque son gradient s'aligne correctement avec le courant électrique. Nous présentons ici un modèle magnétohydrodynamique en une dimension possédant une diffusivité magnétique dépendante de la température dans le plan équatorial dans le contexte de Jupiters chaudes. Les résultats des simulations présentent des oscillations torsionnelles de type alfvéniques reflétant les effets non linéaires dus au couplage des équations aux dérivées partielles de la magnétohydrodynamique et de la température avec la diffusivité magnétique dépendante de la température. Nous explorons un espace des paramètres afin d'établir l'influence de ceux-ci sur les oscillations. Nous avons aussi développé un modèle local afin de dériver des équations analytiques nous permettant de mieux comprendre les résultats observés en plus de comparer les résultats du modèle en une dimension avec ceux du modèle local. Nous finissons par établir que les oscillations générées par notre modèle en une dimension possèdent des périodes équivalentes allant de 225 à 473 jours et des déplacements longitudinaux équivalant à quelques degrés jusqu'à environ 40° pour une planète de la taille de Jupiter. Ces intervalles de périodes et de déplacements sont encourageants, puisque cela signifie que les oscillations pourraient être observées. / Hot Jupiters are exoplanets with unique features. Due to their proximity to their host stars, they show remarkable non-symmetry. This proximity with the star causes tidal locking, meaning one side of the planet is always exposed to intense radiation from its host and the other side is immersed in a perpetual night. This geometry means there is a difference of temperature ranging from 200 K up to 2000 K between the day and night side. This gradient in temperature induces zonal winds that can reach the order of 1 km/s to redistribute heat to the night side. The hot spot is the hottest spot of the planet and is a telltale of these strong winds. Observations and hydrodynamic numerical simulations show that zonal winds on these planets go eastward. However, two recent observations are showing westward winds. These planets are CoRoT-2 b and HAT-P-7 b. The most common explanation to this contradiction is that the magnetic field, which is interacting with the partially ionized atmosphere, can reverse these winds. It was previously shown that a magnetic diffusivity varying in space can locally generate magnetic fields when its gradient aligns correctly with the electric current density. We present here a one-dimensional magnetohydrodynamic model with a temperature-dependent magnetic diffusivity in the equatorial plane in the context of hot Jupiters. The simulations develop growing torsional alfvénic oscillations due to the non-linear coupling of the magnetohydrodynamics and the temperature partial differential equations and the temperature-dependent magnetic diffusivity. We explore the parameter space and study their influence on the oscillations. We have also developed a local model in order to derive analytical equations characterizing these waves and compare its results with the results of the one-dimensional model. We end by calculating the corresponding periods and longitudinal displacement of the one-dimension model oscillations for a Jupiter-sized planet. The periods correspond to an interval from 225 to 473 days and the displacements range from a few degrees up to 40°. This means that the oscillations could be observed with a few orbits.
238

Numerical Methods for Mathematical Models on Warrant Pricing

Londani, Mukhethwa January 2010 (has links)
>Magister Scientiae - MSc / Warrant pricing has become very crucial in the present market scenario. See, for example, M. Hanke and K. Potzelberger, Consistent pricing of warrants and traded options, Review Financial Economics 11(1) (2002) 63-77 where the authors indicate that warrants issuance affects the stock price process of the issuing company. This change in the stock price process leads to subsequent changes in the prices of options written on the issuing company's stocks. Another notable work is W.G. Zhang, W.L. Xiao and C.X. He, Equity warrant pricing model under Fractional Brownian motion and an empirical study, Expert System with Applications 36(2) (2009) 3056-3065 where the authors construct equity warrants pricing model under Fractional Brownian motion and deduce the European options pricing formula with a simple method. We study this paper in details in this mini-thesis. We also study some of the mathematical models on warrant pricing using the Black-Scholes framework. The relationship between the price of the warrants and the price of the call accounts for the dilution effect is also studied mathematically. Finally we do some numerical simulations to derive the value of warrants.
239

Reliability Analysis of Linear Dynamic Systems by Importance Sampling-Separable Monte Carlo Technique

Thapa, Badal January 2020 (has links)
No description available.
240

Physically-based parameterization of heat transport in high-Reynolds-number flows subject to rapid global rotation and density stratification / Fysiskt baserad parameterisering av värmetransport i flöden med hög Reynolds-tal som är föremål för snabb global rotation och densitetsstratifiering

Meunier, Julie January 2021 (has links)
The focus of this thesis is the effect of planetary curvature on the heat transfer efficiencyaccross latitudes in planetary atmospheres and oceans. We investigate both theoreticallyand numerically a physically-based parametrization of baroclinic turbulence inthe Boussinesq Eady model to include variations of the Coriolis parameter with latitude.In this model, a rapidly rotating density-stratified fluid is subjected to a meridional temperaturegradient in thermal wind balance with a uniform vertically sheared zonal flowand the effect of planetary curvature is captured by the parameter β.A normal mode projection of the Eady model with β was inconclusive to properlydescribe meridional heat transfers and the zonal structures usually observed in planetaryflows. However, the DNS solver CORAL allows us to perform 3D high-Reynolds numericalsimulations to seek an extension of the ’vortex-gas’ scaling theory for baroclinic turbulence.Planetary curvature reduces heat transfer between latitudes through the emergenceof coherent zonal structures while the flow remain mainly quasi-geostrophic. The meridionalbuoyancy flux displays the same functional dependence on the control parametersthan for the two-layer model within the framework of quasi-geostrophy.With similar arguments than for the Eady problem, it is shown that in a perturbativefashion for small β, the vertical profiles of meridional buoyancy flux are no longer depthinvariant.The flux decreases at least exponentially with height. The buoyancy transportis shown to be along mean isopycnals, whereas potential vorticity is transported onlyalong instantaneous isopycnals. Overall, the vortex-gas theory and its extension to theβ-plane lead to good predictions for heat transfer in the quasi-geostrophy limit for 3Dflows and weak β. The theory becomes less precise as we increase β. / Fokus för denna avhandling är effekten av planetarisk krökning på värmeöverföringseffektivitetenöver breddgrader i planetariska atmosfärer och hav. Vi undersöker båda teoretisktoch numeriskt en fysiskt baserad parametrisering av baroklinisk turbulens iBoussinesq Eady-modellen för att inkludera variationer av Coriolis-parametern med latitud.I denna modell utsätts en snabbt roterande densitetsskiktad vätska för en meridional temperaturgradient i termisk vindbalans med ett jämnt vertikalt klippt zonflödeoch effekten av planetarisk krökning fångas av parametern β.En normallägesprojektion av Eady-modellen med β var inte övertygande till korrektbeskriv meridionala värmeöverföringar och de zonstrukturer som vanligtvis observeras i planetariskaflöden. DNS-lösaren CORAL tillåter oss dock att utföra 3D high-Reynolds numeriskasimuleringar för att söka en förlängning av skalningsteorin för 'virvelgas' för baroklinisk turbulens.Planetarisk krökning minskar värmeöverföringen mellan breddgrader genom uppkomstenav koherenta zonstrukturer medan flödet förblir huvudsakligen kvasi-geostrofiskt. Meridionalenflytkraftsflöde visar samma funktionella beroende av styrparametrarnaän för tvåskiktsmodellen inom ramen för kvasi-geostrofi.Med liknande argument än för Eady-problemet visas det i ett störandeFör små β är de vertikala profilerna för meridional flytkraft inte längre djupvarianta.Fluxet minskar åtminstone exponentiellt med höjden. Flyttransportenhar visat sig vara längs genomsnittliga isopycnals, medan potentiell vorticitet endast transporteraslängs momentana isopycnals. Sammantaget, vortex-gasteorin och dess utvidgning tillβ-plan leder till goda förutsägelser för värmeöverföring i kvasi-geostrofigränsen för 3Dflyter och svagt β. Teorin blir mindre exakt när vi ökar β.

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