Student Number: 0420801P Master of Science in Engineering. Faculty of Engineering and the Built Environment / Underground observations at a coal mine indicated failure of the immediate roof above the bords while pillars were observed to be intact. To determine the underlying causes of roof failures, careful observations and photographic recording of occurrences of roof failures have been made. Rock samples of the immediate shale roof were collected for laboratory testing to determine the rock strength and deformation properties. Numerical simulations were carried out to analyse stress and strain distributions and also to attempt to explain the guttering process. Mapping of roof failures showed that these took place mainly towards the centre of the roadways. The roof failures, termed “roof guttering”, were observed to occur violently and with little warning. Occurrence of roof guttering had a negative impact on production. Some panels are abandoned, production times have increased and safety of workers is compromised. The mine authorities initially thought that roof guttering was caused by shear failure of the rock mass. Roof bolts are therefore used as a means of primary support. No improvements have been observed. Increasing the size of pillars has not solved the problem either. It has only increased the amount of coal left in the pillars without any improvements in reducing roof failures. Stress measurement results carried out in 2001 showed that high horizontal stresses exist at the mine. The immediate shale roof was observed to be weak. Laboratory testing showed that the shale rock is transversely isotropic. Numerical modelling results indicated that there are insignificant stress concentrations towards the centre of the roadway using the elastic and transversely isotropic elastic models. Stress concentrations were predicted at the roof-pillar contact area. It is therefore expected that failure should initiate and occur at the roof-pillar contact area. The Mohr-Coulomb and Mohr-Coulomb strain softening models predicted shear failure at the roof-pillar contact area. The two models over predicted the depth and under predicted the width of failures. The extension strain criterion predicted correctly the depth and width of failures although the failures were predicted at the roof-pillar contact area while the observations indicated failure mainly towards the centre of the roads. Initiation of failure was predicted ahead of the coal face at the centre of the road position using the extension strain criterion. Although none of the constitutive behaviours predicted correctly the observed underground failures the extension strain criterion has shown the best agreement. Guttering that occurred at the roof-pillar contact was modelled successfully using the extension strain criterion. The extension strain criterion predicted initiation of failure ahead of the coal face at the road centre position. It is possible that fracture initiation could be taking place in this location ahead of the coal face, and, on blasting the rock that has been fractured falls forming a gutter at the centre of the road.

A dissertação está dividida em duas partes. A primeira trata da eletroquímica fundamental utilizando líquidos iônicos como eletrólito suporte e molécula de estudo. São abordados os fenômenos de estabilidade anódica e catódica, com ênfase no mecanismo de degradação do líquido. Além disso, é apresentado um estudo sobre a oxidação eletrocatalítica de hidrogênio nesse ambiente. Quanto a esse aspecto são abordados aspectos mecanísticos e físico-químicos da reação. Técnicas eletroquímicas, modelagem e simulações numéricas foram utilizadas para investigação e hipotetização dos processos. A segunda parte da dissertação consiste do estudo da interação entre óxidos de platina e alguns compostos orgânicos (ácido fórmico, metanol e etanol). O estudo foi realizado em termos da evolução do potencial de circuito aberto com acompanhamento das espécies reativas através da espectroscopia de infravermelho in situ. Os dados obtidos são analisados sob a luz dos conhecimentos levantados pela área de eletrocatálise e sistemas dinâmicos. Modelagem e simulação do sistema permitiram o entendimento do papel individual das diversas etapas envolvidas sobre o comportamento geral do sistema. / This dissertation is divided on two parts. The first one deals with fundamental electrochemistry employing an ionic liquid as supporting electrolyte and as a subject of study by itself. Phenomena like the anodic and cathodic stability of the liquid, emphasizing its degradation mechanism is presented. It is also shown a study of the electrocatalytic oxidation of hydrogen in this environment. For this case, efforts were made to unravel mechanistic aspects of the reaction, as well as physical chemical features. Electrochemical techniques and numerical simulations were used for investigation and understanding of that system. The second part presents a study of the interaction between platinum oxides and some organic compounds, namely: formic acid, methanol and ethanol. The study was performed under open circuit conditions by following the temporal evolution of the potential and also the concentration of some chemical species by using in situ infrared spectroscopy. Data were analyzed under the guide of knowledge constructed by the fields of electrocatalysis and dynamical systems. Modelling and simulation allowed understanding the individual role of the various participants species on the global behavior of the system.

Foram estudados cinco casos históricos de escorregamentos ocorridos na cidade de Salvador - Bahia, através do levantamento e tratamento dos dados preexistentes. Também foram realizados ensaios complementares através da instrumentação em campo com tensiômetros e ensaios de laboratório. A retroanálise, objetivo central desse trabalho foi realizada a partir das geometrias de cada uma das encostas, antes e após a ruptura resultando na definição dos possíveis parâmetros médios de resistência ao cisalhamento. Secundariamente foram realizadas análises de estabilidade convencional para a avaliação dos fatores de segurança de cada encosta, com os parâmetros de resistência na condição não saturada e saturada. Por fim foram efetuadas simulações numéricas que visavam reproduzir as condições que levaram à ruptura da encosta do Alto do Bom Viver, baseado nos conceitos da mecânica dos solos não saturados. Os resultados mostram que a maioria dos escorregamentos estudados, ocorre no horizonte do solo residual maduro, onde o valor de ângulo de atrito médio é 34º, condizente com as superfícies de rupturas pouco profundas observadas em campo. As análises paramétricas sugerem que o mecanismo de ruptura mais provável esteja relacionado à diminuição da coesão aparente do solo em virtude da diminuição da sucção. / Five historical cases of landslides in the city of Salvador, Bahia, were studied through the survey and treatment of the preexistent data. Complementary experiments were accomplished through the instrumentation field using tensiometers and laboratory testing. The back-analysis, main objective of this research, was accomplished through the geometries of each slope, before and after the rupture, resulting in the definition of the possible medium parameters of resistance to shear. Secondary, analysis of the conventional stability to the evaluation of safety factors of each slope was accomplished, with the parameters of resistance in the unsaturated and saturated condition. At last, numerical simulations were done, aiming at reproducing the conditions which led to the rupture of the slope of Alto do Bom Viver, based on the concepts of mechanics of non saturated soil. The results demonstrated that the majority of the slips studied occur in the horizon of the mature residual soil, where the value of the angle of the medium attrition is of 34 degrees, suitable with the surface of little deep ruptures observed in the field. The parametric analysis suggests that the most probable mechanism of rupture is related to the decrease of the apparent cohesion of the soil due to the decrease of suction.

Nesta tese de doutorado apresentamos um estudo sobre o comportamento de diversos sistemas irrevers?veis, caracterizados pela existencia de estados absorventes, atraves de abordagens distintas. Utilizamos aproximacoes de campo medio dinamico, simulacoes numericas usuais, mudanca de ensemble e expanso em serie. Alem disso, mostramos numa parte deste trabalho que a abordagem proposta para o estudo de sistemas irrevers?veis no ensemble em que o numero de part?culas e constante tambem pode ser estendida para sistemas em equil´?brio termodinamico, descrito pela distribuicao de probabilidades de Gibbs. Finalmente mostramos problemas em aberto para trabalhos futuros. / In this PHD thesis, we have presented a study about several nonequilibrium systems with absorbing states by means of different approaches, such as mean-field analysis, usual numerical simulations, analysis in another ensemble and perturbative series expansions. In a specific part of this thesis, we have shown that the approach proposed here for describing nonequilibrium systems in the constant particle number ensemble can also be used to caracterize equilibrium systems, described by Gibbs probability distribution. Finally, we have shown open problems for future researchs.

Ce travail a pour objectif de montrer la capacité des simulations numériques à modéliser les phénomènes aux interfaces solides et liquides. Dans le travail sur les interfaces solides, la méthode GCMC a été utilisée pour simuler l'isotherme d'adsorption de !'acétaldéhyde sur la glace dans les conditions de la haute troposphère, puis l'adsorption de composés organiques bi-fonctionnalisés sur la glace a été caractérisée par dynamique moléculaire avec pour objectif d'interpréter des résl1ltats expérimentaux de la littérature. Une partie de ce travail a été consacrée à la circulation du diagramme de phase (p,T) d'aérosols organiques (acide oxalique et malonique) clans les conditions troposphériques afin d'étudier la capacité de ces aérosols à jouer le rôle de noyaux de condensation pour les particules de glace. Le travail sur les interfaces liquides a concerné tout d'abord l'adsorption compétitive de polymères et de smfactants à la surface de l'eau. Il s'appuie sur une description très précise, par simulation, de la structure et de la dynamique de la surface des systèmes considérés. La deuxième partie des travaux sur les interfaces liquides s'est intéressée à la caractérisation du transfert d'ions à travers une interface liquide/liquide par le biais du calcul des variations de l'énergie libre du système au cours du transfc1i. Afin d'obtenir une description très rigoureuse des détails des processus mis enjeu, une méthode spécifique a été développée dans cette thèse pour calculer le profil d'énergie libre en tenant compte directement du caractère très dynamique de l'interface. / This work aims to demonstrate the ability of numerical simulations to mode] solid · and liquid interfaces. In the work on the solid interfaces, the GCMC method was used to sin:rnlatc the ads011Jtion isotherrn of acetaldehyde on ice under the conditions of the ·upper tropospherc and the molecular dynamics method was usecl to characterize the adsorption of difünctionalized organic compounds on ice, aiming at interpreting experimental results. Part of this work was devotcd to the simulation of the phase diagrarn (p, T) of organic aerosols (oxalic acid and malonic) in tropospberic conditions to study the ability of aerosols to act as condensation nuclei for icc particlcs. The work: on liquid interfaces concerned firstly the competitive adsorption of polymcrs and surfactants at the water surface. It is based on a very precise desc1iption, by mnncrical simulation, of the structure émd dynamics cif the surface of the considered systems. The second pari of the work on liquid interfaces bas focused on the characterization of ion transfer across a liquid/liquid interface through the calculations of the free energy variations of the system during the transfo·. To obtain a rigorous desc1iptio11 of the details of the corresponding processes, a specific method was developed in this thesis to calculate the free energy profile while taking into account tbe dynamics of the interface.

Ce travail de thèse porte sur une catégorie de matériaux actifs dénommés Elastomères Magnéto-Rhéologiques (EMR). Ces derniers sont composés de particules micrométriques et magnétisables imprégnées dans une matrice élastomère isolante. Il est possible de modifier les propriétés mécaniques de tels matériaux en les soumettant à un champ magnétique externe. Avec pour objectif d’aboutir à une caractérisation couplée (magnéto-mécanique) du comportement des EMRs en grandes déformations et en présence de champs magnétiques élevés, ce travail propose une approche à la fois expérimentale, théorique et numérique.La première partie de ce travail s’intéresse à des aspects expérimentaux où l’influence de la microstructure (isotrope et transverse isotrope) et l’influence de la fraction volumique de particules sont étudiées. Un échantillon dédié est développé afin d’obtenir simultanément des champs mécaniques et magnétiques les plus homogènes possibles dans celui-ci lors d’une caractérisation couplée. La question de l’adhésion interfaciale entre les particules de fer doux et la matrice en silicone est également traitée et il est montré qu’un traitement chimique des particules est nécessaire afin d’éviter toute décohésion avec la matrice lorsque le matériau est soumis à un champ magnétique externe. Avant d’analyser les données obtenues, le dispositif expérimental permettant d’obtenir de manière simultanée une mesure du champ de déformation en trois dimensions et une mesure des champs magnétiques internes, est décrit. Malgré l’ensemble des difficultés expérimentales en grande partie dûes à des phénomènes d’instabilité qui sont omniprésents chez les EMRs, de nombreuses données sont collectées et serviront à la calibration des lois de comportement.La seconde partie de cette thèse couvre la modélisation couplée magnéto-mécanique des EMRs en s’appuyant sur le cadre théorique général des solides magnéto-élastiques proposé par Kankanala, Triantafyllidis et Danas (2004, 2012, 2014). En particulier, la méthode énergétique (qui s’appuie sur l’utilisation d’une fonction d’énergie libre) est préférée et des formulations variationnelles équivalentes (qui diffèrent entre elles simplement par le choix de la variable magnétique indépendante utilisée pour décrire le problème : B, H ou M) sont proposées et implémentées dans des codes numériques 3D s’appuyant sur la méthode des éléments finis. Ces outils numériques sont combinés à la méthode de minimisation des moindres carrés afin d’obtenir l’ensemble des paramètres matériaux du modèle de comportement des EMRs. L’utilisation de simulations numériques est nécessaire car une approche purement analytique ne permettrait pas de modéliser « l’effet de forme » observé expérimentalement. En effet, il est primordial de modéliser ce dernier car dans le cas contraire les paramètres identifiés dépendraient de la forme de l’échantillon expérimental et ne décriraient pas uniquement le matériau.La troisième partie de cette étude décrit en détail l’implémentation numérique des différentes formulations variationnelles proposées précédemment. Dans chacun des cas, il est prouvé que l’utilisation d’éléments isoparamétriques est bien adaptée. De nombreuses difficultés numériques ont été observées dans le cas des formulations variationnelles utilisant le champ de déplacement et le potentiel vecteur magnétique comme variables indépendantes. L’ensemble de ces difficultés (comme par exemple la minimisation de l’énergie potentielle sous la contrainte imposée par la jauge de Coulomb) est surmonté dans ce travail. Avant de décrire les différents problèmes tests utilisés pour s’assurer de la validité et de la précision des codes numériques, les différentes étapes nécessaires à la simulation d’un problème aux limites sont expliquées. Plus précisément, les questions liées aux spécificités des conditions aux limites à appliquer sur le potentiel vecteur magnétique ou encore aux conditions de symétries, sont traitées. / In this thesis, we study a class of “active materials” called Magnetorheological elastomers (MRE) which are ferromagnetic impregnated rubbers whose mechanical properties are altered by the application of external magnetic fields. With the purpose of characterizing the behavior of MREs up to large strains and high magnetic fields, this work brings a completely novel experimental, theoretical and numerical approach.The first part of this study focuses on an experimental investigation of MRE where multiple microstructures (isotropic and transversely isotropic materials) and multiple particles’ volume fraction are tested. A special sample geometry is designed in order to increase the uniformity of internal magnetic and mechanical fields measured during coupled-field experiments. The interfacial adhesion between the iron fillers and the silicone matrix is investigated and we show that when specimens are subjected to external magnetic fields, a silane primer treatment of the particles is needed to prevent debonding at the interface particle/matrix. Then, we present the magneto-mechanical testing setup that allows simultaneous 3D mechanical and magnetic measurements before discussing the results. Even if is found that instabilities are ubiquitous in MREs, lots of useful data are collected and will be used to compute the parameters proposed in the material model.The second part of the thesis is dedicated to the modeling of isotropic MREs. The continuum description proposed by Kankanala, Triantafyllidis and Danas (2004, 2012, 2014) to derive constitutive laws that account for finite strains is used and, in particular, the energetic approach (that requires an energy density function) is chosen. Multiple equivalent variational formulation alternatives (based on different choices of the independent magnetic variable used in the energy function: B, H or M) are given and implemented into 3D finite element (FEM) codes. Based on the use of FEM simulation in combination with least square optimization methods, the previously collected experimental data are fitted and all three energy functions ψB , ψH and ψM are computed. The obtained material model proves to have excellent predictive capabilities when compared to other experiments not used in the fitting process. The use of numerical tools is necessary to make sure that the calculated material parameters are not influenced by the shape of experimental specimens.The last part of this work details the numerical implementation of the different variational formulations. For each one of them, it is found that isoparametric elements are well suited to simulate coupled magneto-mechanical boundary value problems. We show that special care is needed when implementing variational formulations using the displacement vector and the magnetic vector potential as independent variables. Indeed, ensuring the uniqueness of the vector potential requires to numerically enforce the Coulomb gauge, which leads to numerical complications that are addressed in this thesis. Before describing the different patch tests that have been considered to validate the numerical codes, we show which are the valid boundary conditions for the magnetic vector potential and how to use the symmetry properties of a given boundary value problem to reduce its complexity and the computational resources needed to solve it.

Les moteurs-fusées hybrides combinent les technologies des deux autres catégories de moteurs à propulsionchimique, et associent un combustible et un oxydant stockés respectivement sous phase solide et liquide.Cette architecture offre un certain nombre d’avantages, comme par exemple des coûts plus faibleset une architecture simplifiée par rapport à la propulsion bi-liquide; la possibilité de réaliser de multiplesextinctions et ré-allumages et une bonne impulsion spécifique théorique par rapport à la propulsion solide,et enfin une sécurité de mise en œuvre accrue et un impact environnemental faible vis-à-vis de ces deuxautres modes de propulsion. Comme toutes les chambres de combustion, celles des moteurs hybrides peuvent subir des oscillations de pression sous certaines conditions de fonctionnement. Ces instabilités se traduisent par des fluctuationsde poussée qui peuvent dégrader la structure d’un lanceur ou d’un satellite. Des phénomènes diverspeuvent être à l’origine des fluctuations de pression observées dans les moteurs hybrides.L’objectif de la thèse est de proposer une modélisation des instabilités d’origine hydrodynamique quiapparaissent dans les moteurs hybrides. Une exploitation nouvelle de la base de données disponible àl’ONERA a servi de support pour la modélisation, ainsi que des simulations numériques instationnaires 2Det 3D réalisées à l’aide du code CFD CEDRE. Les instabilités sont provoquées par la formation périodiquede structures tourbillonnaires dans la chambre de combustion, qui génèrent des fluctuations de pressionlors de leur passage dans le col de la tuyère. L’originalité du modèle, basé sur la théorie classique degénération tourbillonnaire dans une cavité, consiste à prendre en compte les variations géométriques dela chambre de combustion au cours des tirs. Ces variations ont un effet sur la vitesse de l’écoulement, surla zone de recirculation dans la post-chambre, ainsi que sur les tourbillons eux-mêmes. Enfin, plusieursnouveaux essais du moteur hybride HYCOM ont été effectués et confrontés au modèle développé dans lecadre de la thèse. / Hybrid rocket motors combine solid and bi-liquid chemical propulsion technologies and associate asolid fuel and a liquid oxidizer in its classical configuration. This architecture offers several advantagesover liquid propulsion such as lower costs and a simplified architecture. The possibility of performingmultiple extinctions and re-ignitions and a good theoretical specific impulse is also an improvement inregard to solid propulsion. Hybrid engines also have improved safety and a lower environmental impactthan other chemical propulsion systems. As in all combustion chambers, hybrid engines suffer from pressure oscillations under specific operating conditions. These instabilities provoke thrust fluctuations that can damage the launcher and payloads.Various phenomena can induce the pressure oscillations observed in hybrid rocket engines.The objective of this thesis is to propose a model of hydrodynamics instabilities that appear in hybridengines. A new exploitation of the database available at ONERA, and unsteady 2D and 3D numericalsimulations were used for the modeling. The instabilities are provoked by the periodic formation ofvortices in the combustion chamber that generate pressure fluctuations when passing through the nozzlethroat. The originality of the model, which is based on the classical theory of vortices generation ina cavity, consists in taking into account the geometrical variations of the combustion chamber duringoperation. These variations have an effect on the flow velocity, on the recirculation area in the postchamberand on the vortices. Finally, several new firing tests of the hybrid engine HYCOM have beenperformed and compared to the model developed in this thesis.

L’évolution chimique des phases les plus diffuses aux plus denses du milieu interstellaireest un processus continu : la composition chimique du milieu interstellairedans une phase dépend de sa composition dans sa phase antérieure.Les études, qui s’intéressent à la chimie du milieu dense et froid ainsi qu’à l’évolutionde sa composition au cours du temps, font de fortes hypothèses sur son évolutiondepuis le milieu diffus.L’objectif de ma thèse a donc été de suivre l’évolution de la chimie de la matièreinterstellaire du milieu diffus jusqu’à la formation des nuages denses.J’ai pour cela utilisé un modèle de chimie gaz-grain dépendant du temps que j’aisignificativement contribué à améliorer pour la partie chimie de surface. J’ai dansun premier temps suivi une approche "classique" (c.-à-d. : semblable aux études préexistantes)de la modélisation des régions froides. Cela m’a permis d’étudier en détailles processus physiques et chimiques à l’origine de la complexité moléculaire dans lesnuages denses et froids et de comparer les prédictions du modèle avec les études existantes.Dans une deuxième partie, j’ai appliqué ce modèle pour suivre l’évolution de lacomposition chimique du milieu interstellaire au cours du processus de formation desnuages moléculaires à partir du milieu diffus. Pour cette étude, j’ai utilisé les résultatsd’une simulation hydrodynamique à l’échelle galactique. Cela m’a permis de montrerque l’histoire de l’évolution des conditions physiques dans les phases antérieures à laformation des nuages moléculaires peut avoir un impact significatif sur la compositionchimique de ces derniers. / The chemical evolution from the most diffuse parts of the interstellar medium tothe formation of dense clouds is a continuous process : the chemical composition inone phase depends on the chemical composition in the previous one.However, most studies of the time dependent chemistry in the cold and dense interstellarmedium make strong assumptions on the transition between diffuse and densemedium.The goal of my thesis was to study the chemical evolution of the interstellar mediumfrom the most diffuse parts to the formation of dense clouds in a continuousway.To do so, I used a time dependent gas-grain model that I significantly contributedto improve for the treatment of the surface chemistry. In a first part, I followed a "classical"approach (i.e. : similar to most of the pre-existing studies) to model cold denseclouds. This allowed me to study in details the physical and the chemical mechanismsresponsible for the chemical complexity of dense clouds and to compare the modelpredictions with the existing literature. In a second part, I applied this model to followthe evolution of the chemical composition during the formation process of denseclouds from the diffuse medium. I used results from an hydrodynamical simulation ofthe interstellar medium at galactic scales. This study allowed me to show that the pastphysical history of each particles that form the dense clouds have a significant impacton their chemical composition.

<p> Stars are born in turbulent molecular clouds that fragment and collapse under the influence of their own gravity, forming a cluster of hundred or more stars. The star formation process is controlled by the interplay between supersonic turbulence and gravity. In this work, the properties of stellar clusters created by numerical simulations of gravoturbulent fragmentation are compared to those from observations. This includes the analysis of properties of individual protostars as well as statistical properties of the entire cluster. </p> <p> It is demonstrated that protostellar mass accretion is a highly dynamical and time-variant process. The peak accretion rate is reached shortly after the formation of the protostellar core. It is about one order of magnitude higher than the constant accretion rate predicted by the collapse of a classical singular isothermal sphere, in agreement with the observations. </p> <p> For a more reasonable comparison, the model accretion rates are converted to the observables bolometric temperature, bolometric luminosity, and envelope mass. The accretion rates from the simulations are used as input for an evolutionary scheme. The resulting distribution in the T_bol-L_bol-M_env parameter space is then compared to observational data by means of a 3D Kolmogorov-Smirnov test. The highest probability found that the distributions of model tracks and observational data points are drawn from the same population is 70%. </p> <p> The ratios of objects belonging to different evolutionary classes in observed star-forming clusters are compared to the temporal evolution of the gravoturbulent models in order to estimate the evolutionary stage of a cluster. While it is difficult to estimate absolute ages, the realtive numbers of young stars reveal the evolutionary status of a cluster with respect to other clusters. The sequence shows Serpens as the youngest and IC 348 as the most evolved of the investigated clusters. </p> <p> Finally the structures of young star clusters are investigated by applying different statistical methods like the normalised mean correlation length and the minimum spanning tree technique and by a newly defined measure for the cluster elongation. The clustering parameters of the model clusters correspond in many cases well to those from observed ones. The temporal evolution of the clustering parameters shows that the star cluster builds up from several subclusters and evolves to a more centrally concentrated cluster, while the cluster expands slower than new stars are formed. </p> / <p>Sterne entstehen im Inneren von turbulenten Molekülwolken, die unter dem Einfluss ihrer eigenen Gravitation fragmentieren und kollabieren. So entsteht ein Sternhaufen aus hundert oder mehr Objekten. Der Sternentstehungsprozess wird durch das Wechselspiel von Überschallturbulenz und Gravitation reguliert. In dieser Arbeit werden verschiedene Eigenschaften solcher Sternhaufen, die mit Hilfe von numerischen Simulationen modelliert wurden, untersucht und mit Beobachtungsdaten verglichen. Dabei handelt es sich sowohl um Eigenschaften einzelner Protosterne, als auch um statistische Parameter des Sternhaufens als Ganzes.</p> <p>Es wird gezeigt, dass die Massenakkretion von Protosternen ein höchst dynamischer und zeitabhängiger Prozess ist. Die maximale Akkretionsrate wird kurz nach der Bildung des Protosterns erreicht, bevor sie annähernd exponentiell abfällt. Sie ist, in Übereinstimmung mit Beobachtungen, etwa um eine Größenordnung höher als die konstante Rate in den klassischen Modellen.</p> <p>Um die Akkretionsraten der Modelle zuverlässiger vergleichen zu können, werden sie mit Hilfe eines Evolutionsschemas in besser beobachtbare Parameter wie bolometrische Temperatur und Leuchtkraft sowie Hüllenmasse umgewandelt. Die dreidimensionale Verteilung dieser Parameter wird anschließend mittels eines Kolmogorov-Smirnov-Tests mit Beobachtungsdaten verglichen.</p> <p>Die relative Anzahl junger Sterne in verschiedenen Entwicklungsstadien wird mit der zeitlichen Entwicklung der Modelle verglichen, um so den Entwicklungsstand des Sternhaufens abschätzen zu können. Während eine genaue Altersbestimmung schwierig ist, kann der Entwicklungsstand eines Haufens relativ zu anderen gut ermittelt werden. Von den untersuchten Objekten stellt sich Serpens als der jüngste und IC 348 als der am weitesten entwickelte Sternhaufen heraus.</p> <p>Zuletzt werden die Strukturen von jungen Sternhaufen an Hand verschiedener statistischer Methoden und eines neuen Maßes für die Elongation eines Haufens untersucht. Auch hier zeigen die Parameter der Modelle eine gute Übereinstimmung mit solchen von beobachteten Objekten, insbesondere, wenn beide eine ähnliche Elongation aufweisen. Die zeitliche Entwicklung der Parameter zeigt, dass sich ein Sternhaufen aus mehreren kleineren Gruppen bildet, die zusammenwachsen und einen zum Zentrum hin konzentrierten Haufen bilden. Dabei werden neue Sterne schneller gebildet als sich der Sternhaufen ausdehnt.</p>

A turbulent two-phase flow model using kinetic theory of granularflows for the particle phase is developed and implmented in afinite element code. The model can be used for engineeringapplications. However, in this thesis it is used to investigateturbulent gas-particle flows through numerical simulations.  The feedback from the particles on the turbulence and the meanflow of the gas in a vertical channel flow is studied. In particular,the influence of the particle response time, particle volumefraction and particle diameter on the preferential concentration ofthe particles near the walls, caused by the turbophoretic effect isexplored. The study shows that when particle feedback is includedthe accumulation of particles near the walls decreases. It is also foundthat even at low volume fractions particles can have a significant impacton the turbulence and the mean flow of the gas. The effect of particles on a developing turbulent vertical upward pipeflow is also studied. The development length is found to substantiallyincrease compared to an unladen flow. To understand what governs thedevelopment length a simple estimation was derived, showing that itincreases with decreasing particle diameters in accordance with themodel simulations. A model for the fluctuating particle velocity in turbulentgas-particle flow is derived using a set of stochastic differentialequations taking into account particle-particle collisions. Themodel shows that the particle fluctuating velocity increases whenparticle-particle collisions become more important and that increasingparticle response times reduces the fluctuating velocity. The modelcan also be used for an expansion of the deterministic model for theparticle kinetic energy. / QC20100726