Two new models to calculate the species instantaneous and filtered reaction rates for multi-step, multi-species chemical kinetics mechanisms are developed based on the artificial neural networks (ANN) approach. The proposed methodologies depend on training the ANNs off-line on a thermo-chemical database representative of the actual composition and turbulence level of interest. The thermo-chemical database is constructed by stand-alone linear eddy mixing (LEM) model simulations under both premixed and non-premixed conditions, where the unsteady interaction of turbulence with chemical kinetics is included as a part of the training database. In this approach, the information regarding the actual geometry of interest is not needed within the LEM computations. The developed models are validated extensively on the large eddy simulations (LES) of (i) premixed laminar-flame-vortex-turbulence interaction, (ii) temporally mixing non-premixed flame with extinction-reignition characteristics, and (iii) stagnation point reverse flow combustor, which utilizes exhaust gas re-circulation technique. Results in general are satisfactory, and it is shown that the ANN provides considerable amount of memory saving and speed-up with reasonable and reliable accuracy. The speed-up is strongly affected by the stiffness of the reduced mechanism used for the computations, whereas the memory saving is considerable regardless.

A cause de sa température élevée, le jet propulsif d'un avion de combat est une source de rayonnement infrarouge qui rend l'appareil très vulnérable. Ce rayonnement peut toutefois être réduit en accélérant le mélange du jet avec l'atmosphère. <br />Cette thèse est consacrée à la simulation numérique d'un jet propulsif réaliste contrôlé par des injections radiales et à l'analyse physique des mécanismes d'augmentation de son mélange. <br />Deux types de simulations, RANS et ZDES, ont été réalisés sur la base du modèle de Spalart-Allmaras. Dans le modèle ZDES, une nouvelle longueur caractéristique de maille est formulée et améliore sensiblement la prévision de la région initiale du jet. Globalement, les simulations ZDES restituent fidèlement le champ moyen du jet supersonique sans et avec contrôle, aussi bien les cellules de détente/compression que la diffusion turbulente. <br />L'analyse physique est dédiée à la compréhension d'une part des mécanismes compressibles concentrées au coeur du jet et d'autre part des mécanismes tourbillonnaires périphériques ainsi qu'à l'évaluation de leurs rôles respectifs dans l'augmentation du mélange. Il en ressort que l'augmentation du mélange est exclusivement due aux mécanismes tourbillonnaires. Une étude paramétrique fournit des indications pour concevoir un mélangeur efficace. L'analyse des tourbillons focalisée sur le régime lointain quasi-bidimensionnel souligne leur dynamique moyenne et fait apparaître l'action des fluctuations turbulentes sur leur taux de dégénérescence. Enfin, deux régimes de contrôle sont identifiés et associés aux pénétrations respectivement quasi-stationnaire et intermittente des jets secondaires.

The exact quantification of site water budget is a necessary precondition for successful and sustainable management of forests, agriculture and water resources. In this study the water balance was investigated at the spatial scale of canopies and at different temporal scales with focus on the monthly time scale. The estimation of the individual water balance components was primarily based on micrometeorological measurement methods. Evapotranspiration was assessed by the eddy-covariance (EC) method, while sap flow measurements were used to estimate transpiration. Interception was assessed by a combination of canopy drip, stem flow and precipitation (gross rainfall) measurements and soil moisture measurements were used to estimate the soil water storage. The combination of different measurement methods and the derivation of water balance components that are not directly measurable e.g. seepage and soil evaporation is a very complex task due to different scales of measurement, measurement uncertainties and the superposition of these effects. The quantification of uncertainties is a core point of the present study. The uncertainties were quantified for water balance component as well as for meteorological variables (e.g. wind speed, temperature, global radiation, net radiation and precipitation) that served as input data in water balance models. Furthermore, the influences of uncertainties were investigated in relation to numerical water balance simulations. Here, both the effects of uncertainties in input data and in reference data were analysed and evaluated. The study addresses three main topics. The first topic was the providing of reference data of evapotranspiration by EC measurements. Here, the processing of EC raw-data was of main concern with focus on the correction of the spectral attenuation. Four different methods of spectral correction were tested and compared. The estimated correction coefficients were significantly different between all methods. However, the effects were small to absolute values on half-hourly time scale. In contrast to half-hour data sets, the method had significant influence to estimated monthly totals of evapotranspiration. The second main topic dealt with the comparison of water balances between a spruce (Picea abies) and a beech (Fagus sylvatica) site. Both sites are located in the Tharandter Wald (Germany). Abiotic conditions are very similar at both sites. Thus, the comparison of both sites offered the opportunity to reveal differences in the water balance due to different dominant tree species. The aim was to estimate and to compare all individual components of the water balance by a combination of the above mentioned measurement methods. A major challenge was to overcome problems due different scales of measurements. Significant differences of the water balances between both sites occurred under untypical weather conditions. However, under typical condition the sites showed a similar behaviour. Here, the importance of involved uncertainties deserved special attention. Results showed that differences in the water balance between sites were blurred by uncertainties. The third main topic dealt with the effects of uncertainties on simulations of water balances with numerical models. These analyses were based on data of three sites (Spruce, Grass and Agricultural site). A kind of Monte-Carlo-Simulation (uncertainty model) was used to simulate effects of measurement uncertainties. Furthermore, the effects of model complexity and the effect of uncertainties in reference data on the evaluation of simulation results were investigated. Results showed that complex water balance models like BROOK90 have the ability to describe the general behaviour and tendencies of a water balance. However, satisfying quantitative results were only reached under typical weather conditions. Under untypical weather e.g. droughts or extreme precipitation, the results significantly differed from actual (measured) values. In contrast to complex models, it was demonstrated that simple Black Box Models (e.g. HPTFs) are not suited for water balance simulations for the three sites tested here. / Die genaue Quantifizierung des Standortswasserhaushalts ist eine notwendige Voraussetzung für eine erfolgreiche und nachhaltige Bewirtschaftung von Wäldern, Äckern und Wasserressourcen. In dieser Studie wurde auf der Raumskala des Bestandes und auf verschieden Zeitskalen, jedoch vorrangig auf Monatsebene, die Wasserbilanz untersucht. Die Bestimmung der einzelnen Wasserbilanzkomponenten erfolgte hauptsächlich mit mikrometeorologischen Messmethoden. Die Eddy- Kovarianz- Methode (EC- Methode) wurde benutzt zur Messung der Evapotranspiration, während Xylem- Flussmessungen angewendet wurden, um die Transpiration zu bestimmen. Die Interzeption wurde aus Messungen des Bestandesniederschlags, des Stammablaufs und des Freilandniederschlags abgeleitet. Messungen der Bodenfeuchte dienten zur Abschätzung des Bodenwasservorrats. Die Kombination verschiedener Messmethoden und die Ableitung von nicht direkt messbaren Wasserhaushaltkomponenten (z.B. Versickerung und Bodenverdunstung) ist eine äußerst komplexe Aufgabe durch verschiedenen Messskalen, Messfehler und die Überlagerung dieser Effekte. Die Quantifizierung von Unsicherheiten ist ein Kernpunkt in dieser Studie. Dabei werden sowohl Unsicherheiten in Wasserhaushaltskomponenten als auch in meteorologischen Größen, welche als Eingangsdaten in Wasserbilanzmodellen dienen (z.B. Windgeschwindigkeit, Temperatur, Globalstrahlung, Nettostrahlung und Niederschlag) quantifiziert. Weiterführend wird der Einfluss von Unsicherheiten im Zusammenhang mit numerischen Wasserbilanzsimulationen untersucht. Dabei wird sowohl die Wirkung von Unsicherheiten in Eingangsdaten als auch in Referenzdaten analysiert und bewertet. Die Studie beinhaltet drei Hauptthemen. Das erste Thema widmet sich der Bereitstellung von Referenzdaten der Evapotranspiration mittels EC- Messungen. Dabei waren die Aufbereitung von EC- Rohdaten und insbesondere die Dämpfungskorrektur (Spektralkorrektur) der Schwerpunkt. Vier verschiedene Methoden zur Dämpfungskorrektur wurden getestet und verglichen. Die bestimmten Korrekturkoeffizienten unterschieden sich deutlich zwischen den einzelnen Methoden. Jedoch war der Einfluss auf die Absolutwerte halbstündlicher Datensätze gering. Im Gegensatz dazu hatte die Methode deutlichen Einfluss auf die ermittelten Monatssummen der Evapotranspiration. Das zweite Hauptthema beinhaltet einen Vergleich der Wasserbilanz eines Fichten- (Picea abies) mit der eines Buchenbestands (Fagus sylvatica). Beide Bestände befinden sich im Tharandter Wald (Deutschland). Die abiotischen Faktoren sind an beiden Standorten sehr ähnlich. Somit bietet der Vergleich die Möglichkeit Unterschiede in der Wasserbilanz, die durch unterschiedliche Hauptbaumarten verursacht wurden, zu analysieren. Das Ziel was es, die einzelnen Wasserbilanzkomponenten durch eine Kombination der eingangs genanten Messmethoden zu bestimmen und zu vergleichen. Ein Hauptproblem dabei war die Umgehung der unterschiedlichen Messskalen. Deutliche Unterschiede zwischen den beiden Standorten traten nur unter untypischen Wetterbedingungen auf. Unter typischen Bedingungen zeigten die Bestände jedoch ein ähnliches Verhalten. An dieser Stelle erlangten Messunsicherheiten besondere Bedeutung. So demonstrierten die Ergebnisse, dass Unterschiede in der Wasserbilanz beider Standorte durch Messunsicherheiten verwischt wurden. Das dritte Hauptthema behandelt die Wirkung von Unsicherheiten auf Wasserbilanzsimulationen mittels numerischer Modelle. Die Analysen basierten auf Daten von drei Messstationen (Fichten-, Grasland- und Agrarstandort). Es wurde eine Art Monte-Carlo-Simulation eingesetzt, um die Wirkung von Messunsicherheiten zu simulieren. Ferner wurden auch der Einfluss der Modellkomplexität und die Effekte von Unsicherheiten in Referenzdaten auf die Bewertung von Modellergebnissen untersucht. Die Ergebnisse zeigten, dass komplexe Wasserhaushaltsmodelle wie BROOK90 in der Lage sind, das Verhalten und Tendenzen der Wasserbilanz abzubilden. Jedoch wurden zufriedenstellende quantitative Ergebnisse nur unter üblichen Wetterbedingungen erzielt. Unter untypischen Wetterbedingungen (Dürreperioden, Extremniederschläge) wichen die Ergebnisse deutlich vom tatsächlichen (gemessenen) Wert ab. Im Gegensatz zu komplexen Modellen zeigte sich, dass Black Box Modelle (HPTFs) nicht für Wasserhaushaltssimulation an den drei genannten Messstandorten geeignet sind.

No description available.

A new combustor, referred to as Stagnation Point Reverse Flow (SPRF) combustor has been developed at Georgia Tech to meet increasingly stringent emission regulations. The combustor incorporates a novel design to meet the conflicting requirements of low pollution and high efficiency in both premixed and non-premixed modes. The objective of this thesis is to perform Large Eddy Simulations (LES) on this lab-scale combustor and explain the underlying physics. To achieve this, numerical simulations are performed in both the premixed and non-premixed combustion modes. The velocity field, species field, entrainment characteristics, flame structure, emissions and mixing characteristics are then analyzed. Simulations have been carried out first for a non-reactive case and the flow features in the combustor are analyzed. Next, the simulations have been extended for the premixed reactive case by employing different sub-grid scale combustion chemistry closures - Eddy Break Up (EBU), Artificially Thickened Flame (TF) and Linear Eddy Mixing (LEM) models. Only LEMLES which is an advanced scalar approach is able to accurately predict both the velocity and species field in the combustor. The results from LEM with LES (LEMLES) using a reduced chemical mechanism have been analyzed in the premixed mode. The results showed that mass entrainment occurs along the shear layer in the combustor. The entrained mass carried products into the reactant stream and provided preheating. The product entrainment enhances the reaction rates and stabilizes the flame even at very lean conditions. These products are shown to enter into the flame through local extinction zones present on the flame surface. The flame structure is further analyzed and the combustion mode is found to be primarily in thin reaction zones. The emissions in the combustor are studied using simple global mechanisms for NOx. Computations show extremely low NOx values comparable to the measured emissions. These low emissions are shown to be primarily due to the low temperatures in the combustor. LEMLES computations are also performed with detailed chemistry to capture more accurately the flame structure. The flame in the detailed chemistry case is more sensitive to strain effects and show more extinction zones very near to the injector. LEMLES approach is also used to resolve the combustion mode in the non-premixed case. The studies indicate that mixing of fuel and air close to the injector controls the combustion process. The predictions in the near field are shown to be very sensitive to the inflow conditions. Analysis shows that fuel and air mixing occurs to lean proportions in the combustor before any burning takes place. The flame structure in the non-premixed mode is very similar to the premixed mode. Along with fuel-air mixing, the products also mix with the reactants and provide the preheating effects to stabilize the flame in the downstream region of the combustor.

This dissertation investigates a new design for a magnetostrictive actuator that employs individually controlled coils distributed axially along the magnetostrictive rod. As a quantitative goal, the objective is to show that the multi-coil actuator can operate effectively at frequencies as high as 10,000 Hz with 900 N force and 50 microns of displacement. Conventional, single coil actuators with the same parameters for force and displacement develop significant attenuation in their response at frequencies above the first longitudinal vibration resonance at about 2750 Hz. The goal of the research is to investigate whether multiple coils can effectively increase the frequency range a least four times the range of conventional magnetostrictive actuators. This document derives a new mathematical model of the actuator that represents the spatial distributions of magnetic field and vibration, devises a control design that takes advantage of the multiple inputs to control the displacement of the actuator while consuming minimum electrical power, and describes a prototype multi-coil actuator and experimental system developed to test the idea. The simulations of the multi-coil actuator and control design demonstrate successful transient operation of the actuator over the targeted frequency range with feasible levels of input power and current. Experimental tests of the design, although limited by a computer sampling rate less than 10,000 Hz, are able to validate the predictions of the developed model of the actuator and reproduce the simulated control performance within the constraints of the experimental system.

This thesis aims to explore the potential for using large eddy simulation (LES) as a predictive tool for gas-turbine compressor flows. Compressors present a significant challenge for the Reynolds Averaged Navier-Stokes (RANS) based CFD methods commonly used in industry. RANS models require extensive calibration to experimental data, and thus cannot be used predictively. This thesis explores how LES can offer a more predictive alternative, by exploring the sensitivity of LES to sources of uncertainty. Specifically, the importance of the numerical scheme, the Sub-Grid Scale (SGS) model, and the correct specification of inflow turbulence is examined. The sensitivity of LES to the numerical scheme is explored using the Taylor-Green vortex test case. The numerical smoothing, controlled by a user defined smoothing constant, is found to be important. To avoid tuning the numerical scheme, a locally adaptive smoothing (LAS) scheme is implemented. But, this is found to perform poorly in a forced isotropic turbulence test case, due to the intermittency of the dispersive error. A novel scheme, the LAS with windowing (LASW) scheme, is thus introduced. The LASW scheme is shown to be more suitable for predictive LES, as it does not require tuning to a known solution. The LASW scheme is used to perform LES on a compressor cascade, and results are found to be in close agreement with direct numerical simulations. Complex transition mechanisms, combining characteristics of both natural and bypass modes, are observed on the pressure surface. These mechanisms are found to be sensitive to numerical smoothing, emphasising the importance of the LASW scheme, which returns only the minimum smoothing required to prevent dispersion. On the suction surface, separation induced transition occurs. The flow here is seen to be relatively insensitive to numerical smoothing and the choice of SGS model, as long as the Smagorinsky-Lilly SGS model is not used. These findings are encouraging, as they show that, with the LASW scheme and a suitable SGS model, LES can be used predictively in compressor flows. In order to be predictive, the accurate specification of inflow conditions was shown to be just as important as the numerics. RANS models are shown to over-predict the extent of the three dimensional separation in the endwall - suction surface corner. LES is used to examine the challenges for RANS in this region. The LES shows that it is important to accurately capture the suction surface transition location, with early transition leading to a larger endwall separation. Large scale aperiodic unsteadiness is also observed in the endwall region. Additionally, turbulent anisotropy in the endwall - suction surface corner is found to be important. Adding a non-linear term to the RANS model leads to turbulent stresses that are in better agreement with the LES. This results in a stronger corner vortex which is thought to delay the corner separation. The addition of a corner fillet reduces the importance of anisotropy, thereby reducing the uncertainty in the RANS prediction.

Ce mémoire présente une étude genrée du roman En finir avec Eddy Bellegueule de l´auteur Édouard Louis. L´oeuvre se construit comme un récit autobiographique dans lequel le narrateur décrit la construction de sa propre identité, celle d´un homme homosexuel, dans un environnement provincial enfermé dans des valeurs traditionnelles et patriarcales. En utilisant les outils théoriques offerts par le domaine des études de genre (Gender Studies), nous allons décomposer la notion de masculinité exprimée dans l´oeuvre en nous focalisant sur la signification et les valeurs accordées à la virilité. L’objectif de ce mémoire consiste à dévoiler comment l´image idéalisée de l´homme viril constitue le fondement de l’identité masculine, fonctionnant à la fois comme la pierre angulaire de la domination masculine, mais, également, du processus de marginalisation de l´individu homosexuel. / This thesis presents a gendered study of the novel En finir avec Eddy Bellegueule, [The end of Eddy] by the author Édouard Louis. In his novel the author autobiographically describes not only the development of his own identity, being a homosexual man, but also the rural environment of his childhood, which is defined by the values of the patriarchal system. The goal of this thesis is to reveal how the idealized image of the virile man emerges in the novel and how it constitutes the basis of a gendered role, which is expressed through male domination and the marginalization of the homosexual individual. In our work, we will thus for this purpose, examine the notion of masculinity expressed in the novel by emphasizing the meaning of virility. Using the theoretical tools offered to us by the field of Gender Studies, we will analyze how virility is expressed through the narrative and its creative role as well as its an active part in justifying male dominance in relation to the patriarchal system and to homosexuality.

No description available.

In gas stirred steelmaking ladles, entrainment of slag into metal and vice versa takes place. The slag entrainment has been shown to abruptly increase the mass transfer rates of refining reactions through high temperature and water modeling studies of the past. However such an effect has not been correlated with the degree of entrainment, since the latter has not been quantified in terms of operating parameters like gas injection rate and fluid properties. Much of the past works are limited to finding the critical conditions for onset of entrainment. The difficulty lies in measuring the degree of entrainment in industrial ladles or even in a water model. Mathematical modeling is also challenging due to the complexity of the multiphase phenomena. So in this thesis, a modular mathematical modeling approach is presented wherein the phenomena of slag entrainment into metal is resolved into four aspects, models developed for each and finally integrated to study its role. The individual models are (1) multiphase large eddy simulations to simulate slag entrainment in a narrow domain that receives its boundary conditions from (2) single phase RANS simulation of a full ladle, (3) a Lagrangian particle tracking method to compute the residence times of slag droplets in metal phase and (4) a kinetic model that integrates the above three models to compute mass transfer rate as a function of degree of entrainment. Mass transfer rate predictions comparable to a literature correlation were obtained. This supports the modeling approach and also the assessment of role of various system parameters on entrainment characteristics. In essence, the present work shows a systematic approach to model and study the complex multiphase phenomena. / Thesis / Doctor of Philosophy (PhD) / The entrainment of liquid slag into liquid steel in gas stirred-steelmaking ladles is known to increase the rate of refining drastically. However, there is lack of correlation between degree of entrainment and ladle operating conditions, which this thesis addresses through mathematical modeling.