Le Capital-Investissement et plus particulièrement les opérations de LBO, occupent une place importante dans l'économie mondiale et française. Ce travail de recherche a pour objet l'analyse de l'impact des leviers organisationnels et de gouvernance sur la performance opérationnelle et la rentabilité des entreprises françaises sous LBO. Nous présentons ainsi, en premier lieu, dans les deux premiers chapitres de cette thèse, une revue complète de la littérature, ainsi que le modèle théorique de l'impact des leviers organisationnels et de gouvernance sur la performance opérationnelle et la rentabilité des entreprises sous LBO en privilégiant une approche actionnariale de la gouvernance.Ensuite, dans le cadre des troisième et quatrième chapitres de cette thèse, nous examinons de façon empirique, d'une part, l'impact de la mise en place des opérations de LBO sur la performance opérationnelle des entreprises françaises, et, d'autre part, les effets des leviers organisationnels et de gouvernance sur la rentabilité des entreprises françaises sous LBO.Nos résultats confirment en partie les résultats anglo-saxons concernant l'impact positif des opérations de LBO sur la performance de la société cible, ils sont obtenus en effectuant une double analyse comparative : la première en comparant l'évolution de la performance avant et après la mise en place du LBO, et la deuxième en effectuant une comparaison par rapport à un groupe de contrôle composé d'entreprises aux caractéristiques comparables mais qui n'ont pas fait l'objet d'un LBO.Enfin, nous proposons un modèle explicatif des effets des leviers organisationnels et de gouvernance sur la rentabilité des entreprises sous LBO. / Private Equity, especially Leverage Buyout activity (LBO), is now an important concern in the world economy and also in France. This kind of investment is an important alternative to capital market.The main purpose of this thesis is to examine the effects of corporate governance and organizational mechanisms on the performance of French firms leveraged buyout.We presented in the first part of this thesis, the first and second chapter of it, the history of the emergence of these investments in the world and especially in France, and an overview of the literature on private equity and leveraged buyouts, focusing on our theoretical framework which is based on corporate governance theories, especially on agency theory and financial performance.Moreover, we discussed the literature about the relation between operating performance, corporate governance and Leverage Buyout. As part of this thesis and in the third and fourth chapters, we proposed an empirical study of the impact of LBO on operating performance.This research also proposes a new approach to the relationship governance-performance by a financial modelling of the relation between corporate governance and performance in the case of leveraged buyout firms in France.This thesis is a contribution to the Leverage Buyout and Private Equity literature from a theoretical and empirical point of view. It also has implications for the managers of private firms.

L'objectif de la thèse est d'améliorer la compréhension des processus hydrologiques lors des événements de crues éclair. Se basant sur un modèle existant (MARINE), l'étude se concentre sur les processus internes au sol. Une étape préliminaire permet, à partir de l'analyse des données, de confirmer l'activité du socle rocheux durant les crues éclair. Une analyse structurelle de MARINE est réalisée, afin de connaître la sensibilité des flux de subsurface aux choix structurels. Une nouvelle modélisation, plus robuste et intégrant explicitement une représentation des roches altérées, est mise en place. Supposant des chemins préférentiels à l'interface sol/roche, le modèle donne une bonne reproduction des bassins sédimentaires. Sur les bassins granitiques, il sous-estime les récessions et, en conséquence, les éventuels seconds pics de crue, montrant la nécessité de représenter des flux significatifs sur ces bassins, y compris dans la zone altérée. / The purpose of this thesis is to improve the knowledge of hydrological processes during flash flood events using rainfall-runoff modelling. The project focuses on hydrological processes occurring into soil and subsoil horizons. A preliminary data analysis corroborates the activity of the weathered bedrock during flash floods. The hydrological response, simulated by the MARINE model, is then investigated to detect the sensitivity of subsurface flow processes to model assumptions. It leads to several modifications of the model structure in order to make it more robust. Moreover a two-layered soil column is implemented to explicitly integrate the activity of the weathered bedrock into the model. Assuming preferential path flows at the soil-bedrock interface, the model performs well on sedimentary watersheds, but underestimate recession curves and second flood peaks on granitic ones, showing the need to simulate as well significantcontribution from the weathered bedrock.

This thesis deals with the development of a new adaptive algorithm for three-dimensional fluid flows based on a residual error estimator. The residual, known as the R –parameter has been successfully extended to three dimensions using a novel approach for arbitrary grid topologies. The computation of the residual error estimator in three dimensions is based on a least-squares based reconstruction and the order of accuracy of the latter is critical in obtaining a consistent estimate of the error. The R –parameter can become inconsistent on three–dimensional meshes depending on the grid quality. A Zero Mean Polynomial(ZMP) which is k–exact, and which preserves the mean has been used in this thesis to overcome the problem. It is demonstrated that the ZMP approach leads to a more accurate estimation of solution derivatives as opposed to the conventional polynomial based least-squares method. The ZMP approach is employed to compute the R –parameter which is the n used to derive the criteria for refinement and derefinement. Studies on three different complex test problems involving inviscid, laminar and turbulent flows demonstrate that the new adaptive algorithm is capable of detecting the sources of error efficiently and lead to accurate results independent of the grid topology.

Le système turbiditique du Var présente la particularité d’être fréquemment parcouru par des écoulements gravitaires. Cela en fait un endroit privilégié pour étudier simultanément les facteurs déclenchant des courants de turbidité, leurs caractéristiques hydrodynamiques, leur contenu particulaire et les dépôts associés. Dans le cadre du projet Européen HERMES (6ème Programme Cadre), nous avons acquis pendant 2 ans dans le canyon du Var et dans la vallée turbiditique (1) des séries temporelles dans la colonne d’eau (30 m et 400 m au dessus du fond) sur la vitesse des courants, la température et le flux particulaire, et (2) des prélèvements répétés par carottage du sédiment de surface (...) / In the framework of the HERMES European project, this study aims to characterize the sedimentary processes acting in the Var turbiditic system, their impact on the morphology, and their evolution through time and space. This work uses data acquired along the system, including interface cores, acoustic data, and measurement in the water column (temperature, particulate fluxes, speed and direction of the currents) thanks to mooring lines. The Var turbiditic system is under the influences of the Northern Current and of the Var river by a direct connection. Sedimentary processes are related to gravity-driven currents, oceanic currents which remobilizes sediments and hemipelagic decantation. Gravity-driven processes are dominant and are responsible of 80% of the mean annual sedimentary transport in the system, at the scale of two years (2005-2007). They are characterized by a mean speed of 100 to 600 mm.s-1 and a mean particulate flux of 10 to more than 400 g.m-2.j-1. The combination of the river discharge data and our in-situ measures allows to discriminate the mechanism responsible of their triggering: mass-wasting or river floods. Hyperpycnal turbidity currents, generated by the plunging of the turbid plume are observed for flood extended to the whole hydrographic system, with a river discharge of more than 306 m.s-1 at the river mouth (...)

External gear machines (EGMs) are used in a variety of industries ranging from fluid power machinery to fluid handling systems and fuel injection applications. Energy efficiency requirements and new trends in hydraulic technology necessitate the development of novel EGMs optimized for efficiency and reliability in all of these applications. A crucial piece in the novel EGM development process is a numerical model that can simulate the operation of EGM and predict its volumetric and hydro-mechanical performance.<div><br></div><div>The EGM simulation models developed in the past have focused mostly on the challenges related to the modeling of the theoretical behavior and elementary fluid dynamics, and determining appropriate modeling schemes. Key aspects related to the flow and geometry are either considered in a simplified manner or not considered at all. In particular, the current simulation models assume the fluid to be Newtonian and the leakage flows to be laminar. However, EGMs working in fluid handling applications operate with non-Newtonian fluids. Further, in fuel injection applications, due to low fluid viscosity and high operating speed, the internal leakage flows may not remain laminar.</div><div><br></div><div>With respect to the geometric aspects, the gears in EGMs are prone to manufacturing errors that are not accounted by any simulation model. In addition, there is no method available in the literature for accurately modeling the leakage flows through curve-constricted geometries in EGMs. Further, the goal of current simulation tools is related to the prediction of the volumetric performance of EGMs. However, an equally important characteristic, hydro-mechanical performance, is often ignored. Finally, the energy flow during EGM operation can result in the variation of the fluid temperature. Thus, the isothermal assumption of current simulation tools is another major limitation.</div><div><br></div><div>The work presented in this dissertation is focused on developing numerical methodologies for the modeling of EGMs that addresses all the aforementioned limitations of the current models. In this work, techniques for evaluating non-Newtonian internal flows in EGMs is developed to permit an accurate modelling of EGMs working with non-Newtonian fluids. For fuel injection EGMs, flow regime at the tooth tips of the gears is investigated and it is shown that the flow becomes turbulent for such EGMs. A methodology for modeling this turbulent flow is proposed and its impact on the performance of EGMs is described. To include gear manufacturing errors in the simulation model, numerical techniques are developed for modeling the effects of two common gear manufacturing errors: conicity and concentricity. These two errors are shown to have an opposite impact on the volumetric efficiency of the EGM. For the evaluation of flows through curve-constricted leakage paths in EGMs, a novel flow model is developed in this work that is applicable for a wide range of geometry and flow conditions. Modeling of the hydro-mechanical efficiency of EGMs is accomplished by developing methodologies for the evaluation of torque losses at key interfaces. Finally, to account for the thermal effects in EGMs, a thermal model is developed to predict the temperature distribution in the EGM and its impact on the EGM performance.</div><div><br></div><div><div>To validate the numerical methodologies developed in this work, several experiments are conducted on commercial gear pumps as well as on a custom apparatus designed and manufactured in the course of this research work. The results from the experiments are found to match those obtained from the simulations which indicates the validity of the methodologies developed in this work. </div><div><br></div><div>These numerical methodologies are based on the lumped parameter approach to allow the coupling with mechanical models for gear micromotion and permit fast computations so that the model can be used in optimization algorithms to develop energy efficient and reliable EGMs.</div><div><br></div><div>The methodologies described in the dissertation are useful for accurate analysis of a variety of EGMs working with different types of fluids and at wide range of operating conditions. This capability will be valuable for pump designers in developing novel better performing EGM designs optimized for various applications.</div><div><br></div></div>

Au cours de l’utilisation de certains systèmes propulsifs, tels que les moteurs fusées cryotechniques ou les moteurs Diesel, le point de fonctionnement peut varier sur une large plage de pressions. Ces variations de pression peuvent conduire à un changement de régime thermodynamique si la pression critique du fluide est franchie, l’injection initialement diphasique devenant alors transcritique. Ce changement modifie la topologie de l’écoulement, ainsi que la dynamique du mélange, ce qui impacte le comportement de la flamme. L’objectif de cette thèse est de développer une méthodologie originale capable de traiter au sein du même solveur des écoulements sous-critiques ainsi que supercritiques. Pour cela, une extension du solveur AVBP-RG aux écoulements diphasiques sous-critiques est proposée, basée sur des modèles d’interface diffuse. Les développements nécessaires à l’intégration de ces modèles dans le cadre du solveur aux éléments finis sont effectués. Des simulations numériques multidimensionnelles sont ensuite proposées de manière à confronter le modèle à des données exprérimentales, vis-à-vis desquelles un bon accord est observé. Cesrésultats offrent des perspectives encourageantes vers de futures améliorations du modèle et des applications à des configurations industrielles complexes. / In various industrial combustion devices, such as liquid rocket engines at ignition or Diesel engines during the compression stage, the operating point varies over a wide range of pressures. These pressure variations can lead to a change of thermodynamic regime when the critical pressure is exceeded, switching from two-phase injection to transcritical injection. This change modifies the topology of the flow and the mixing, thereby impacting the flame dynamics. The objective of the present Ph.D thesis is to develop an original methodology able to address both subcritical and supercritical flows within the same solver. To achieve this, an extension of the real gas solver AVBP-RG to subcritical two-phase flows is provided, based on diffuse interface models. The required developments for the integration of such models into the finite-element framework of the solver are provided. Multidimensional numerical simulations are led in order to confront the model with experimental data, with which good agreement is observed. These results offer encouraging perspectives regarding further enhancements of the model and applications to complex industrial cases.

In our ever evolving society security becomes more and more important as a lot of our lives move online. Performing security analysis of IT-systems is a cumbersome process requiring extensive domain knowledge and tailored analysis per system. Research shows that manual tasks are error prone. In this thesis we have implemented an automation of performing security analysis of integration flows, building on an earlier project between KTH and SAP. To perform the analysis Common Vulnerability and Exposure-records containing information about vulnerabilities are connected to relevant parts of the system utilizing Meta Attack Language. The vulnerabilities are weighted according to their impact and then attack simulations are performed in the program SecuriCAD. Automating the input for the attack simulations removes an earlier manual task. Utilizing coreLang which is an implementation of MAL that is generally applicable means that the automated process can be used to perform analysis on integration flows in general. Domain knowledge is still needed to configure the automated process. More work can be done in the future to continue automating further tasks in the process. More work can also be done on visualizing security analysis to make the results more available to a general audience / I dagens ständigt expanderande värld som snabbt utvecklas blir säkerhet allt viktigare allteftersom mer av våra liv flyttar in på Internet. Att utföra säkerhetsanalyser av IT-system är en omständlig process som kräver extensiv kunskap om domänen och ofta skräddarsydda lösningar per system. Forskning visar att manuella arbetsuppgifter leder till fler fel än automatiserade processer. I det här examensarbetet har vi implementerat automatisering av säkerhetsanalyser baserade på integrationsflöden. Examensarbetet bygger vidare på ett tidigare projekt mellan KTH och SAP. För att utföra analysen används sårbarheter dokumenterade genom Common Vulnerability and Exposure. Dessa sårbarheter kopplas till relevanta delar av systemet genom användning av Meta Attack Language. Sårbarheterna är viktade i relation till deras påverkan och attacksimuleringar utförs sedan i verktyget SecuriCAD. Automatiseringen av indata i denna process eliminerar en tidigare manuell arbetsuppgift. Användandet av coreLang vilket är en generellt applicerbar implementation av MAL betyder att den automatiserade processen kan appliceras på generalistiska integrationsflöden. Kunskap om domänden behövs fortfarande för att konfigurera den automatiserade processen. I framtiden kan processen utvecklas genom att automatisera andra delar i processen av en säkerhetsanalys. Mer jobb kan även göras för att utveckla visualiseringen av analyserna för att tillgängliggöra resultaten för en bredare publik.

<p>Many practical fluid flows involve liquid-particle systems and so there is a need to better understand the mechanism of particle deposition, adhesion, and agglomeration in suspensions, especially in complex geometries with moving boundaries and free surfaces. In this thesis, the nature of the particle-solid interactions and particle-fluid interactions is studied where the above complexities are present, taking into account particle collision, colloidal, and hydrodynamic forces, and two way coupling between the fluid flow and particles. The research is motivated by the industrial examples of: flow of dross particles near the sink roll surface in a galvanizing bath (moving surface), and the flow of particles in slot coating dies (free and moving surfaces). Particle motion and agglomeration play important roles in the example systems chosen for this fundamental 3-D study. Numerical studies of flow of dispersed suspensions makes it possible to understand the effects of flow conditions, particle characteristics, and flow geometry specifications that lead to agglomeration of particles in complex systems, especially where experimental studies are difficult to perform. Often the effects of these conditions are discovered due to process or product failures, rather than through insight into the processing steps.</p> <p>The modeling methodology used in this work is that micron sized spherical particles are tracked in the fluid phase by solution of Newton`s second law of motion for each particle. Fluid phase applies hydrodynamic forces on particles (drag, lift). Body forces, (soft sphere) particle-particle collisions and particle-wall collisions are considered. Particle concentrations are in the dilute regime between 0.01-5%vol. Flow of particles with the fluid phase is a fully coupled formulation in systems with particle concentrations > 1%vol.</p> <p>The thesis is organized around three example problems taken from industry that pose challenging modeling issues. The first involves particle collisions with a moving wall (dross particles in a zinc bath). The second problem includes particle-particle and particle-wall collisions in a turning flow geometry. The third problem, particle dispersion flows in a slot coating die, has the most complexity and includes particle-particle, particle-wall and free surfaces.</p> <p>Dross particle build up on the sink roll inside the zinc bath is an industrial problem that causes significant down time, and where an experimental study of the molten zinc in a bath running at C is difficult to perform. With the aid of computational fluid dynamics, turbulent flow of molten zinc in galvanizing bath is simulated, compared with previous cold model experiments, and coupled with the motion of dross particles around the sink roll. The presence of fixed position hardware and moving sink roll and guide rolls in a bath with dimensions in the orders of meters, and micron sized (20-100 ) dross particles makes this case a complex study. Drag, buoyancy, lift force and soft sphere nonlinear collision is considered in solution of Newton`s law of motion for each particle. Turbulent flow is simulated using a standard model. Simulations show regions on the sink roll where particles are dragged toward the surface of sink roll and have long residence times. These regions have been reported to experience large particle build-ups in the hot-dip galvanizing process.</p> <p>In another study, formation and breakage of agglomerates in a turning flow is studied. Neutrally buoyant particles with concentration of 5%vol are tracked in a fully coupled flow. Particles form agglomerates at the corner, where drag and lift force from the fluid breaks a number of agglomerates. The presence of a moving wall in the turning flow shifts the suspended particle formations toward the inside of channel. Location of particles agglomerates shifts toward the free surface with the presence of free surface at the turning flow.</p> <p>Motion of micron sized spherical particles with 1-4%vol through a slot die coating system is elucidated in a separate study. The system is complex with presence of moving web and free surface. Discrete element method (DEM) for motion of dispersed phase and volume of fluid (VOF) method for solution of continuous phase are integrated in a simulation study. Particles are 2-4 and the flow dimensions of the system are in the order of 100 . Particles experience collision, colloidal and hydrodynamic forces. Coupling between flow of particles and fluid phase is conducted. The results of this study show particle positions on the coating film can be predefined and depends on their initial positions within the feed slot. Particles agglomerate in recirculating regions of the coating gap and follow the streamlines of flow on the moving web. Regions in the coating gap where particles have high residence times (inside the die and near the feed slot edges) have particle agglomerations in the slot die coating system.</p> / Doctor of Philosophy (PhD)

<p dir="ltr">Results from the Flow Boiling and Condensation Experiment (FBCE), which collected the first flow boiling and condensation data in long-duration, steady microgravity through experiments performed onboard the International Space Station (ISS), are presented. Prior to the ISS experiments, a new correlation for flow boiling critical heat flux (CHF) is developed from data obtained in Earth gravity at different orientations and short durations of microgravity onboard parabolic flight. The new correlation accounts for the influence of gravity in the direction of the flow, impacting vapor removal from the channel, and perpendicular to the heated walls, affecting bubble detachment from the walls, on flow boiling CHF. Novel flow boiling experiments in long-duration microgravity were performed with one or two opposite walls heated using the Flow Boiling Module (FBM), which simultaneously captures heat transfer data and high speed images of flow patterns. The unique microgravity CHF results are presented, and parametric trends are correlated to variations in flow patterns. The results are divided into subcooled and saturated inlet conditions and applicable correlations are assessed. The newly proposed correlation outperforms is the best preforming for the entire database, validating its use in microgravity. Visual observations leading up to CHF justify use of the Interfacial Lift-off model, which predicts CHF with good accuracy for all operating conditions. The data obtained onboard the ISS is consolidated with the prelaunch database to develop highly accurate artificial neural networks (ANNs) for flow boiling heat transfer and CHF in microgravity. The ANNs are developed using a systematic approach that enables the prediction of physical trends. Instabilities observed during subcooled flow boiling are further investigated in dedicated experiments performed at an elevated data capture rate of 30 Hz and extended image capture period up to 28 s. Criteria was proposed to demarcate the stable and unstable operating conditions, and a new correlation to predict the onset of flow instability is proposed. Lastly, microgravity flow condensation heat transfer experiments were conducted onboard the ISS, yielding the first flow condensation data in stable microgravity. Trends in the data are discussed and the two-phase mixture Reynolds number is found to be strongly correlated to local heat transfer coefficient. A separated flow model for annular flow is found to accurately predict trends in average heat transfer coefficient, but underpredicts the microgravity database.</p>

<p dir="ltr">The kinetic-based lattice Boltzmann method (LBM) is a specialized computational fluid dynamics (CFD) technique that resolves intricate flow phenomena at the mesoscale level. The LBM is particularly suited for large-scale parallel computing on Graphic Processing Units (GPU) and simulating multi-phase flows. By incorporating a volume fraction parameter, LBM becomes a volumetric lattice Boltzmann method (VLBM), leading to advantages such as easy handling of complex geometries with/without movement. These capabilities render VLBM an effective tool for modeling various complex flows. In this study, we investigated the computational modeling of complex flows using VLBM, focusing particularly on pulsatile flows, the transition to turbulent flows, and pore-scale porous media flows. Furthermore, a new discrete dynamical system (DDS) is derived and validated for potential integration into large eddy simulations (LES) aimed at enhancing modeling for turbulent and pulsatile flows. Pulsatile flows are prevalent in nature, engineering, and the human body. Understanding these flows is crucial in research areas such as biomedical engineering and cardiovascular studies. However, the characteristics of oscillatory, variability in Reynolds number (Re), and shear stress bring difficulties in the numerical modeling of pulsatile flows. To analyze and understand the shear stress variability in pulsatile flows, we first developed a unique computational method using VLBM to quantify four-dimensional (4-D) wall stresses in image-based pulsatile flows. The method is validated against analytical solutions and experimental data, showing good agreement. Additionally, an application study is presented for the non-invasive quantification of 4-D hemodynamics in human carotid and vertebral arteries. Secondly, the transition to turbulent flows is studied as it plays an important role in the understanding of pulsatile flows since the flow can shift from laminar to transient and then to turbulent within a single flow cycle. We conducted direct numerical simulations (DNS) using VLBM in a three-dimensional (3-D) pipe and investigated the flow at Re ranging from 226 to 14066 in the Lagrangian description. Results demonstrate good agreement with analytical solutions for laminar flows and with open data for turbulent flows. Key observations include the disappearance of parabolic velocity profiles when Re>2300, the fluctuation of turbulent kinetic energy (TKE) between laminar and turbulent states within the range 2300</p>