Correntes de densidade são fluxos gravitacionais gerados pela diferença de densidade entre dois fluidos. Correntes de turbidez fazem parte de uma sub-classificação das correntes de densidade, na qual o fluido mais denso tem, na sua composição, partículas em suspensão. Muitos trabalhos numéricos já estudaram a dinâmica das correntes de turbidez, mas, nenhum dos encontrados aplicou mudanças de relevo concomitantes com a simulação, causadas pela sedimentação das próprias partículas da corrente e nem alterou o relevo após a passagem de cada evento em um domínio tridimensional. O presente trabalho pretende analisar a alteração no relevo de fundo causada por uma corrente de turbidez. No código Incompact3d, as equações de Navier-Stokes, Continuidade e Transporte e Difusão são resolvidas em uma malha cartesiana tridimensional. A condição inicial adotada é a de Lock-Exchange. As simulações realizadas utilizaram Simulação Numérica Direta (DNS). O código utiliza um esquema compacto centrado de sexta ordem, em diferenças finitas, para o esquema espacial, e Adams-Bashfort de terceira ordem para o esquema temporal. A validação do código foi realizada comparando-se com trabalhos experimental e numéricos. A análise das diferentes proporções granulométricas mostrou que quanto maior é a quantidade de material grosso na condição inicial, maior será seu depósito para um dado tempo. Em consequência, mais relevante se torna a consideração da alteração do relevo de fundo. Além disso, quanto maior o fator de compactação do sedimento, maior será o erro de não considerar a atualização de fundo. Os resultados também apontaram que os erros médios ao não considerar a atualização do fundo são da ordem de 4% da massa de depósito em 20 tempos adimensionais, para os parâmetros utilizados. Ao se propagar uma corrente de turbidez sobre o depósito de outra, os erros se mostram menores. / Gravity currents are gravitational fluxes triggered by density di erence between two fluids. A sub-classification of those are turbidity currents, in which the denser fluid is composed by the lighter fluid plus suspended particles. Many papers had shown turbidity currents dynamics, although none of the papers found had applied changes in the simulated topography due to deposit during the own simulation, neither they had altered a 3D domain topography after each flux, applying the changes caused by the previous current. The present dissertation aims to analyse the turbidity current dynamics alteration caused by the influence of its own deposit, altering the topography during the very simulation. The analysis is conducted in a polidispersed turbidity current. The Incompact3d code solves Navier-Stokes, continuity and transport-di usion equation, in a tridimensional cartesian mesh. Lock-exchange was chosen to be the initial condition. Direct Numerical Simulations (DNS) are performed. Sixth order compact finite-di erence schemes are used on the spatial domain, while third order Adams-Bashfort is applied for the temporal evaluation. Comparisons with numerical and experimental papers were performed for code verification. Results showed the coarser the particles on the starting lock-exchange, the higher its deposit is, and the more the terrain will be altered. Nevertheless, the bigger the compacting factor, the bigger the error of not considering bathymetry alteration. Results also point that the average errors of not considering the update are in order of 4% on the mass deposit, after 20 dimensionless times, for the used parameters. When a current propagates over the deposit of a previous one, these errors are smaller.

Un code de résolution des équations de Navier-Stokes pour un fluide incompressible a été développé en utilisant une approche mixte spectral/différences finies, compatible avec une mise en oeuvre dans un environnement massivement parallèle. On procède, grâce à ce nouvel outil, à des simulations directes de la turbulence dans une configuration où l'agitation est synthétisée à l'aide d'un forçage aléatoire. La production de turbulence est confinée dans une couche centrale du domaine et s'auto-diffuse en direction d'une surface libre ou d'une paroi adhérente. Dans cette configuration on obtient un état statistiquement stationnaire où le cisaillement moyen, généralement à l'origine de la production de la turbulence, est nul. Ces conditions permettent de mieux comprendre l'origine du transfert intercomposantes, caractéristique de la partie lente du terme de corrélation pression-déformation dans les équations-bilan des tensions de Reynolds. L'accent est mis sur l'analyse de ce transfert lorsqu'il s'effectue sous l'influence de l'effet de blocage au voisinage d'une surface. Les résultats obtenus permettront de mieux appréhender la modélisation des termes de corrélation pression-déformation au voisinage d'une paroi dans les modèles de fermeture au second ordre. / A Navier-Stokes solver for incompressible flow has been developed using a mixed spectral/finite-difference approach, while being compatible with a massively parallel environment. We use it to perform direct numerical simulations in a situation where the turbulent agitation is synthesized under the action of a random forcing. The turbulence production is confined in a central layer and self-diffuses towards a free-slip or no-slip surface. With this set-up, we obtain a statistical steady state in which the mean shear, usually associated with the turbulence production, is zero. These conditions allow a better understanding of the intercomponent energy transfer, induced by the slow part of the pressure-strain correlation in the Reynolds tensor budget. We focus on this transfer when it occurs in combination with the blocking effect, in the vicinity of the surface. The results will help to model the pressure-strain correlation in a second- order-closure context.

Hypertext markup language 5 (HTML5), a new standard for HTML, enriched with additional features is expected to override all the basic underlying overhead needed by other applications. By the advent of new extension, HTML5, the web’s basic language is transplanted from a simple page layout into rich web application development language. Furthermore, with the release of HTML5, traditional browsing is expected to change and modify accordingly and on the other hand the potential users will have an alternative rather than sticking in platform and OS dependent native applications. This thesis deals with the readiness assessment of HTML5 with regard to different smart phones- Android and Windows. In order to visualize the fact, we analyzed different constraints like DNS lookup time, page loading time, memory and CPU consumption associated with two applications-Flash and HTML5 running right through the smart phones. Furthermore, the comparative analysis is performed in different network scenarios- Wi-Fi and 3G and user experience is estimated based on network parameters. From the experiments and observations taken, we found that android phones provide better support for HTML5 web applications than windows mobile devices. Also, the HTML5 applications loading time is limited by the browser rendering time rather that the content loading time from the network and is also dependent on hardware configuration of device used.

NinetechGruppen AB is an IT service providing company with about 30 employees, primarily based in Karlstad, Sweden. The company began to have problems with their DNS administration because the number of administrated domains had grown too large. A single employee was responsible for all the administration, and text editors were used for modifying the DNS configuration files directly on the name servers. This was an error prone process which also easily led to inconsistencies between the documentation and the real world. NinetechGruppen AB decided to solve the administrative problems by incorporating a DNS administration system, either by using an existing product or by developing a new sys-tem internally. This thesis describes the process of simplifying the DNS administration procedures of NinetechGruppen AB. Initially, an investigation was conducted where existing DNS administration tools were sought for, and evaluated against the requirements the company had on the new system. The system was going to have a web administration interface, which was to be developed in ASP.NET 2.0 with C# as programming language. The administration interface had to run on Windows, use SQL Server 2005 as backend database server, and base access control on Active Directory. Further, the system had to be able of integrating customer handling with the domain administration, and any changes to the system information had to follow the Informa-tion Technology Infrastructure Library change management process. The name servers were running the popular name server software BIND and ran on two different Linux distributions – Red Hat Linux 9 and SUSE Linux 10.0. The investigation concluded that no existing system satisfied the requirements; hence a new system was to be developed, streamlined for the use at NinetechGruppen AB. A requirement specification and a functional description was created and used as the basis for the development. The finalized system satisfies all necessary requirements to some extent, and most of them are fully satisfied.

Covert Channels have existed for more than twenty years now. Although they did not receive a special attention in their early years, they are being more and more studied nowadays. This work focuses on network covert channels and it attempts to give an overview on their basics to later analyse several existing implementations which may compromise the security perimeter of a corporate network. The features under study are the bandwidth provided by the channel and the ease of detection. The studied tools have turned out to be in most cases unreliable and easy to detect with current detection techniques and the bandwidth provided is usually moderate but they might pose a threat if not taken into consideration.

The search for clean and efficient combustors is motivated by the increasingly stringent emissions regulations. New gas turbine engines are designed to operate under lean conditions with inhomogeneous reactants to ensure cleanliness and stability of the combustion. This ushers in a new mode of combustion, called the inhomogeneous reactants premixed combustion. The present study investigates the effects of inhomogeneous reactants on premixed combustion, specifically on the interactions of an initially planar flame with field of inhomogeneous reactants. Unsteady and unstrained laminar methane-air flames are studied in one- and two-dimensional simulations to investigate the effects of normally and tangentially (to the flame surface) stratified reactants. A three-dimensional DNS of turbulent inhomogeneous reactants premixed combustion is performed to extend the investigation into turbulent flames. The methaneair combustion is represented by a complex chemical reaction mechanism with 18 species and 68 steps. The flame surface density (FSD) and displacement speed S_d have been used as the framework to analyse the inhomogeneous reactants premixed flame. The flames are characterised by an isosurface of reaction progress variable. The unsteady flames are compared to the steady laminar unstrained reference case. An equivalence ratio dip is observed in all simulations and it can serve as a marker for the premixed flame. The dip is attributed to the preferential diffusion of carbon- and hydrogen- containing species. Hysteresis of S_d is observed in the unsteady and unstrained laminar flames that propagate into normally stratified reactants. Stoichiometric flames propagating into lean mixture have a larger S_d than lean flames propagating into stoichiometric mixtures. The cross-dissipation term contribution to S_d is small (~~10%) but its contribution to the hysteresis of S_d is not (~~50%). Differential propagation of the flame surface is observed in the laminar flame that propagates into tangentially stratified reactants. Stretch on the flame surface is induced by the differential propagation, which in turn increases the flame surface area.

Worldwide demand for energy is increasing rapidly, partly driven by dramatic economic growth in developing countries. This growth has sparked concerns over the finite availability of fossil fuels and the impact of their combustion on climate change. Consequently, many recent research efforts have been devoted to the development of renewable fuels and sustainable energy systems. Interest in liquid biofuels, such as ethanol, has been particularly high because these fuels fit into the conventional infrastructure for the transportation sector. Ethanol is a renewable fuel produced through the anaerobic fermentation of sugars obtained from biomass. However, the relatively high energy demand of its production process is a major factor limiting the usefulness of ethanol as a fuel. Due to the dilute nature of the fermentation product stream and the presence of the ethanol-water azeotrope, the separation processes currently used to recover anhydrous ethanol are particularly inefficient. In fact, the ethanol separation processes account for a large fraction of the total process energy demand. In the conventional ethanol separation process, ethanol is recovered using several distillation steps combined with a dehydration process. In this dissertation, a new hybrid pervaporation-distillation system, named Membrane Dephlegmation, was proposed and investigated for use in ethanol recovery. In this process, countercurrent vapour-liquid contacting is carried out on the surface of a pervaporation membrane, leading to a combination of distillation and pervaporation effects. It was intended that this new process would lead to improved economics and energy efficiency for the entire ethanol production process. The Membrane Dephlegmation process was investigated using both numerical and experimental techniques. Multiphase Computational Fluid Dynamics (CFD) was used to study vapour-liquid contacting behaviour in narrow channels and to estimate heat and mass transfer rates. Results from the CFD studies were incorporated into a simplified design model and the Membrane Dephlegmation process was studied numerically. The results indicated that the Membrane Dephlegmation process was more efficient than simple distillation and that the ethanol-water azeotrope could be broken. Subsequently, a pilot-scale experimental system was constructed using commercially available, hydrophilic NaA zeolite membranes. Results obtained from the experimental system confirmed the accuracy of the simulations.

The main object of this thesis was to design a computer network for small and medium companies which will be made among others from network server providing simple network control. The next task was to provide internet connection to subscribers of local area network, their security and access to common services. There had been discussed the choice of distribution of Linux operation system with regarding to demanded services, stability and long lasting operation in theoretical part. One part of the work is a theoretic preliminary to separate services, to the purpose of their using and to their weaknesses. The practical part deals with an installation and configuration of Debian operating system, launching the base services and the setting of selected monitoring programs.

The work deals with the measurement of electrical quantities, distribution of data across the Ethernet network into the Internet and intelligent selection of the required values to be transmitted and stored on a central node. The work describes the communication protocols in scale that is necessary for implementation, discussed the requirements for computational resources and microcontroller control is proposed by flowcharts. Attached are source codes in C programming language for microcontroller and PHP scripts for storing and presenting data on Web server.

La méso-combustion est le régime de combustion où la taille caractéristique du domaine est juste supérieure à la distance de coincement de la flamme , typiquement de l'ordre du centimètre. La difficile réalisation de systèmes de combustion fonctionnant en ce régime de flamme particulier suscite l'intérêt : il devient alors possible de tirer parti de la haute densité énergétique des hydrocarbures pour concevoir des systèmes de production d'énergie plus compacts. Nous nous intéressons à la réalisation de calculs DNS compressibles d'une chambre de combustion cubique de 8 x 10 x 8 mm3. Ce travail présente autant la mise en œuvre des calcules, en particulier la problématique de la condition frontière mur, que les résultats obtenus. Ces derniers nous permettent d'analyser la phénoménologie complexe de cet écoulement réactif confiné et serviront de base à des modélisations futures. / Meso-combustion can be defined as the combustion regime where the involved lenghts scales are close but slightly larger than the quenching distance of the flame, tipically smaller than a cm. By taking advantage of the high energetic density of liquid hydrocarbons, it would become possible to build small-sized combustion-based long-lived lighter electrical power systems. However combsution phenomena at these meso-scales have their own shortcomings. Indeed, by decreasing the system size, the usual phenomenological balance betwenne chemical reactions, mixing, turbulence and heat transfer is changed. In the present work, we focus on the DNS calculation of a cubic meso-combsution chamber of 8 x 10 x 8 mm3. This works presents the implementation of the numerical strategy used, with a specific attention to the no-slip wall compressible boundary condition. We then present an analysis of this particular reactive flow. The results are useful for future modeling of such a combustor.