• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 6
  • 5
  • 2
  • 1
  • 1
  • Tagged with
  • 16
  • 7
  • 7
  • 7
  • 6
  • 6
  • 6
  • 6
  • 6
  • 6
  • 6
  • 6
  • 5
  • 5
  • 4
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

A local extrapolation method for hyperbolic conservation laws: the ENO and Goodman-LeVeque underlying schemes and sufficient conditions for TVD property

Adongo, Donald Omedo January 1900 (has links)
Doctor of Philosophy / Department of Mathematics / Marianne Korten / Charles N. Moore / We start with linear single variable conservation laws and examine the conditions under which a local extrapolation method (LEM) with upwinding underlying scheme is total variation diminishing TVD. The results are then extended to non-linear conservation laws. For this later case, we restrict ourselves to convex flux functions f, whose derivatives are positive, that is, fœ A0 and fœ A0. We next show that the Goodman-LeVeque flux satisfies the conditions for the LEM to be applied to it. We make heavy use of the CFL conditions, the geometric properties of convex functions apart from the martingle type properties of functions which are increasing, continuous, and differentiable.
2

TV digital regional : a transição de modelos tecnológicos e seus aspectos regulatórios e de inovação

Jackie Cardoso Sodero Toledo 05 June 2014 (has links)
A televisão regional se encontra num momento crucial em sua história, desafiada enquanto meio de comunicação de massa a adotar novo padrão tecnológico e imprimir profundas mudanças em sua cadeia produtiva, migrando do padrão analógico para um novo padrão digital, de alta definição, capaz de interagir e de permitir a portabilidade de seus conteúdos. O objetivo central da pesquisa é analisar o período de transição dos modelos de transmissão analógica para digital de TV aberta no âmbito da televisão regional. Trata-se, portanto, de uma abordagem sob a ótica da regulação do setor e da gestão da inovação, a partir dos conceitos que norteiam os processos de transição tecnológica. Como foco regional, a pesquisa buscou esclarecer como as emissoras do Vale do Paraíba Paulista realizaram a gestão da inovação digital e cumpriram as exigências regulatórias para o setor no período de transição entre tais tecnologias. Quanto à metodologia aplicada, a pesquisa, de natureza descritiva e exploratória, teve o enfoque na adoção da pesquisa bibliográfica como fonte secundária; a seguir, foi conduzida por um método de documentação direta, através de levantamento de dados e da aplicação da técnica da pesquisa de campo, de modo a identificar a percepção das redes de televisão regional das condições de cada entidade para este período de mudanças. Como resultado, a partir da segmentação das emissoras em semi-locais e localmente comprometidas, evidenciou-se o impacto da TV digital terrestre como uma inovação radical e aberta, que trouxe como consequência a necessidade de mudanças internas nas corporações, a adequação de suas realidades e de seu corpo técnico, a participação das universidades e centros de pesquisa no processo de transição e, também, a necessidade de cumprir as exigências regulatórias do setor sem comprometer economicamente as emissoras neste período. E, por fim, a percepção homogênea das emissoras centrou-se na percepção dos usuários e destinatários finais como fator central para o sucesso da implantação da TV digital aberta no Brasil. / The regional TV is at a crucial moment in its history.It is being challenged as a mean of mass communication to adopt a new technological pattern and impose deep changes in its productive chain, flocking from the analogic pattern to a new high-definition digital one, which is capable of interacting and allowing the portability of its contents. The main goal of this research is to analyse the transition period from the analogical transmission models to the digital broadcast TV in the framework of the regional TV. It therefore constitutes an approach under the vision of the sector regulation and management of innovation, which goes from the concepts that surround the technological transition. As a regional focus, this research aims to clarify how the broadcasters from Vale do Paraíba carry out their digital innovation management and fulfill its sector regulatory requirements during the transition period between such technologies. Thus, it is important to analyse the Brazilian State role on the determination of industrial policies innovation (IP) and foster the implementation period of the Brazilian System of Terrestrial Digital TV (SBTVD-T). Regarding the applied methodology, the research was developed from a deductive method, that is descriptive and exploratory in nature,focussing on the adoption of a bibliographical research as a secondary source and then, conducted by a direct documentation method, through the data collection and the field research technique, as so to identify the perception of the regional wired TV networks and its general conditions for each entity throughout this period of changes. With the adoption of interviews and treatment of qualitative data, the adapting conditions of these regional TV broadcasters into those technological changes were discussed, in order to meet the regulatory demands as well as dispose the innovative advances in the sector.
3

Modélisation de la purification de l'aluminium liquide par procédé de flottation en cuve agitée / Modelisation of liquid aluminium purification by flotation in stirred reactor

Mirgaux, Olivier 17 December 2007 (has links)
L’élimination des inclusions indésirables par flottation en cuve agitée est un procédé largement utilisé dans l’industrie de l’aluminium. Ce procédé consiste en l’injection de gaz au sein de la cuve par le biais d’un rotor ; les bulles ainsi formées captent, lors de leur ascension dans le métal liquide, les inclusions et les drainent en surface où elles sont éliminées mécaniquement.Dans le but de prédire l’évolution numérale de la population d’inclusions dans la cuve de flottation au cours du temps, un modèle 2D a été développé. Afin de rendre compte du transport convectif des inclusions au sein de l’écoulement diphasique métal liquide – bulles, des phénomènes de décantation, d’agglomération et de flottation, ce modèle couple la Mécanique des Fluides Numérique et la technique des Bilans de Population. Une attention particulière a été portée aux modèles d’agglomération et de flottation pour qu’ils soient applicables sur une grande plage de conditions de turbulence.Les simulations numériques réalisées, nous ont notamment permis de mettre en évidence l’importance de veiller à une bonne répartition des bulles dans la cuve, en particulier dans les zones de forte turbulence. En parallèle de ce travail de modélisation, une analyse de la littérature et des travaux expérimentaux sur métal liquide ont été réalisés, afin de mieux comprendre le rôle du chlore dans le procédé de flottation. Un effet de seuil a ainsi pu être mis en évidence : une certaine quantité de chlore injectée dans le métal est nécessaire pour que la flottation devienne efficace. La compréhension du rôle du chlore reste cependant partielle, mais des pistes de recherche prometteuses ont put être identifiées / Inclusions removal by flotation in mechanically agitated vessels is widely used in liquid aluminium treatments. This process consists of gas injection in a molten aluminium reactor using an impeller. Inclusions are attached to the bubbles while rising into the liquid bulk and released in the froth at the vessel surface.With the aim of both a better understanding of the physical processes acting during flotation and the optimization of the refining process, a 2D mathematical modelling of the flotation tank was set up. Transport phenomena, sedimentation, agglomeration and flotation of inclusions were considered here. The model couples Population Balance with convective transport of the inclusions, in the multiphase flow field. Simulations showed that a good dispersion of the bubbles into the tank, especially in the high turbulence zones, is essential for an efficient process. This situation was achieved with a strong agitation. Gas flow affected the process efficiency weakly.Theoretical and experimental studies on chlorine effects were done. It was noticed that a critical amount of chlorine into the melt is required for the flotation to be efficient. Complete understanding of chlorine role is not achieved yet, but promising ideas for future research have been exhibited
4

Méthodes particulaires avec remaillage : analyse numérique nouveaux schémas et applications pour la simulation d'équations de transport / Particle methods with remeshing : numerical analysis, new schemes and applications for the simulation of transport equations

Magni, Adrien 12 July 2011 (has links)
Les méthodes particulaires sont des méthodes numériques adaptées à la résolution d'équations de conservation. Leur principe consiste à introduire des particules ``numériques'' conservant localement l'inconnue sur un petit volume, puis à les transporter le long de leur trajectoire. Lorsqu'un terme source est présent dans les équations, l'évolution de la solution le long des caractéristiques est prise en compte par une intéraction entre les particules. Ces méthodes possèdent de bonnes propriétés de conservation et ne sont pas soumises aux conditions habituelles de CFL qui peuvent être contraignantes pour les méthodes Eulériennes. Cependant, une contrainte de recouvrement entre les particules doit être satisfaite pour vérifier des propriétés de convergence de la méthode. Pour satisfaire cette condition de recouvrement, un remaillage périodique des particules est souvent utilisé. Elle consiste à recréer régulièrement de nouvelles particules uniformément réparties, à partir de celles ayant été advectées à l'itération précédente. Quand cette étape de remaillage est effectuée à chaque pas de temps, l'analyse numérique de ces méthodes particulaires remaillées nécessite d'être reconsidérée, ce qui représente l'objectif de ces travaux de thèse. Pour mener à bien cette analyse, nous nous basons sur une analogie entre méthodes particulaires avec remaillage et schémas de grille. Nous montrons que pour des grands pas de temps les schémas numériques obtenus souffrent d'une perte de précision. Nous proposons des méthodes de correction, assurant la consistance des schémas en tout point de grille, le pas de temps étant contraint par une condition sur le gradient du champ de vitesse. Cette méthode est construite en dimension un. Des techniques de limitation sont aussi introduites de manière à remailler les particules sans créer d'oscillations en présence de fortes variations de la solution. Enfin, ces méthodes sont généralisées aux dimensions plus grandes que un en s'inspirant du principe de splitting d'opérateurs. Les applications numériques présentées dans cette thèse concernent la résolution de l'équation de transport sous forme conservative en dimension un à trois, dans des régimes linéaires ou non-linéaires. / Particle methods are numerical methods designed to solve advection dominated conservation equations. Their principle is to introduce ``numerical'' particles that concentrate the unknown locally on a small volume, and to transport them along their trajectories. These methods have good conservation properties and are not subject to the usual CFL conditions that can be binding for the Eulerian methods. However, an overlap condition must be satisfied between the particles to ensure convergence properties of the method. To satisfy this condition, a periodic remeshing of the particles is often used. New particles uniformly distributed are created on a regular mesh. When this remeshing step is performed at every time step, numerical analysis of particle methods needs to be revisited. This is the purpose of this thesis. To carry out this analysis, we rely on an analogy between remeshed particle methods and grid schemes. We show that for large time step the numerical schemes have a loss of accuracy. We propose correction methods wich ensure consistency at any grid point, provided the time step satisfies a condition based on the gradient of the velocity field. Limitation techniques are also introduced to remesh particles without creating any oscillations in the presence of strong variations of the solution. Finally, these methods are generalized to dimensions greater than one. Numerical example on various transport equations are given to illustrate the benefit of the proposed algorithms.
5

Construction de méthodes de volumes finis tridimensionnelles sans solveur de Riemann pour les systèmes hyperboliques non-linéaires

St-Cyr, Amik January 2002 (has links)
Thèse diffusée initialement dans le cadre d'un projet pilote des Presses de l'Université de Montréal/Centre d'édition numérique UdeM (1997-2008) avec l'autorisation de l'auteur.
6

Méthodes particulaires avec remaillage : analyse numérique nouveaux schémas et applications pour la simulation d'équations de transport

Magni, Adrien 12 July 2011 (has links) (PDF)
Les méthodes particulaires sont des méthodes numériques adaptées à la résolution d'équations de conservation. Leur principe consiste à introduire des particules ''numériques'' conservant localement l'inconnue sur un petit volume, puis à les transporter le long de leur trajectoire. Lorsqu'un terme source est présent dans les équations, l'évolution de la solution le long des caractéristiques est prise en compte par une intéraction entre les particules. Ces méthodes possèdent de bonnes propriétés de conservation et ne sont pas soumises aux conditions habituelles de CFL qui peuvent être contraignantes pour les méthodes Eulériennes. Cependant, une contrainte de recouvrement entre les particules doit être satisfaite pour vérifier des propriétés de convergence de la méthode. Pour satisfaire cette condition de recouvrement, un remaillage périodique des particules est souvent utilisé. Elle consiste à recréer régulièrement de nouvelles particules uniformément réparties, à partir de celles ayant été advectées à l'itération précédente. Quand cette étape de remaillage est effectuée à chaque pas de temps, l'analyse numérique de ces méthodes particulaires remaillées nécessite d'être reconsidérée, ce qui représente l'objectif de ces travaux de thèse. Pour mener à bien cette analyse, nous nous basons sur une analogie entre méthodes particulaires avec remaillage et schémas de grille. Nous montrons que pour des grands pas de temps les schémas numériques obtenus souffrent d'une perte de précision. Nous proposons des méthodes de correction, assurant la consistance des schémas en tout point de grille, le pas de temps étant contraint par une condition sur le gradient du champ de vitesse. Cette méthode est construite en dimension un. Des techniques de limitation sont aussi introduites de manière à remailler les particules sans créer d'oscillations en présence de fortes variations de la solution. Enfin, ces méthodes sont généralisées aux dimensions plus grandes que un en s'inspirant du principe de splitting d'opérateurs. Les applications numériques présentées dans cette thèse concernent la résolution de l'équation de transport sous forme conservative en dimension un à trois, dans des régimes linéaires ou non-linéaires.
7

Construction de méthodes de volumes finis tridimensionnelles sans solveur de Riemann pour les systèmes hyperboliques non-linéaires

St-Cyr, Amik January 2002 (has links)
Thèse diffusée initialement dans le cadre d'un projet pilote des Presses de l'Université de Montréal/Centre d'édition numérique UdeM (1997-2008) avec l'autorisation de l'auteur.
8

Um esquema upwind polinomial por partes para problemas em mecânica dos fluidos / A piecewise polynomial upwind scheme for problems in fluid mechanics

Sartori, Patrícia 20 April 2011 (has links)
Este trabalho de pesquisa é dedicado ao desenvolvimento, análise e implementação de um novo esquema upwind de alta resolução (denominada PFDPUS) para a aproximação de termos convectivos em leis de conservação e problemas relacionados em mecânica dos fluídos. Usando variáveis normalizadas de Leonard, o equema PFDPUS é baseado em uma função polinomial por partes que satisfaz os critérios de estabilidade CBC e TVD. O desempenho do esquema PEDPUS é investigado na solução das equações de advecção de escalares, Burgers, Euler e MHD. O novo esquema é então aplicado para simular escoamentos incompressíveis envolvendo superfícies livres móveis. Para tanto, o esquema PFDPUS é implementado dentro do software CLAWPACK para problemas compressíveis, e no código Freeflow para poblemas incompressíveis. Os resultados numéricos são comparados com dados experimentais, numéricos e analíticos / This work is dedicated to the development, analysis and implementation of a new high-resolution upwind scheme (called PFDPUS) for approximation of convective terms in conservation laws and related fluid mechanics problems. By using the normalized variables of Leonard, the PFDPUS scheme is based on a piecewise polynomical function that satisfies the CBC and TVD stability criteria. The performance of the PFDPUS scheme is assessed by solving advection of scalars, Burgers, Euler and MHD equations. Then the new scheme is applied to simulate incompressible flows involving moving free surfaces. The PFDPUS scheme is implemented into the CLAWPACK software for compressible problems, and in the Freeflow code for incompressible problems. The numerical results are compared with experimental, numerical and analytical data
9

Um esquema upwind polinomial por partes para problemas em mecânica dos fluidos / A piecewise polynomial upwind scheme for problems in fluid mechanics

Patrícia Sartori 20 April 2011 (has links)
Este trabalho de pesquisa é dedicado ao desenvolvimento, análise e implementação de um novo esquema upwind de alta resolução (denominada PFDPUS) para a aproximação de termos convectivos em leis de conservação e problemas relacionados em mecânica dos fluídos. Usando variáveis normalizadas de Leonard, o equema PFDPUS é baseado em uma função polinomial por partes que satisfaz os critérios de estabilidade CBC e TVD. O desempenho do esquema PEDPUS é investigado na solução das equações de advecção de escalares, Burgers, Euler e MHD. O novo esquema é então aplicado para simular escoamentos incompressíveis envolvendo superfícies livres móveis. Para tanto, o esquema PFDPUS é implementado dentro do software CLAWPACK para problemas compressíveis, e no código Freeflow para poblemas incompressíveis. Os resultados numéricos são comparados com dados experimentais, numéricos e analíticos / This work is dedicated to the development, analysis and implementation of a new high-resolution upwind scheme (called PFDPUS) for approximation of convective terms in conservation laws and related fluid mechanics problems. By using the normalized variables of Leonard, the PFDPUS scheme is based on a piecewise polynomical function that satisfies the CBC and TVD stability criteria. The performance of the PFDPUS scheme is assessed by solving advection of scalars, Burgers, Euler and MHD equations. Then the new scheme is applied to simulate incompressible flows involving moving free surfaces. The PFDPUS scheme is implemented into the CLAWPACK software for compressible problems, and in the Freeflow code for incompressible problems. The numerical results are compared with experimental, numerical and analytical data
10

Interatividade e perspectivas no telejornalismo da TV digital

Pereira, Lívia Cirne de Azevêdo 19 February 2010 (has links)
Made available in DSpace on 2015-05-07T14:46:48Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3391922 bytes, checksum: 512cad9880f5f6b2ceae9aa114c11bb6 (MD5) Previous issue date: 2010-02-19 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In Brazil, the TV news had its origins in 1950, in a simple struture, without many audiovisual resources. However, as time goes by, transformations get introduced in the production of TV journalism, proved principally by the following characteristics: the use of the videotape, the emission of contents at a distance, the diffusion in colors, the beginning of the TV by subscription, the appearing of the Internet. Such innovations ensure the advent of the new technologies for a proper television, as a result, the development of the TV journalism, pushing it to revise its concepts and paradigms. An example that certificates this issue is the fact that the TV news show the need of the establishment of new formats, making available the spectator participation, based on the interactive assumption of the cyberspace, encouraging potential of content, where is valued the Internet user autonomy. In the meantime, could be said that this participation still find limitations in the analog technology, what push us to mention that to have the dialogue between the transmitter and the audience, this has to cover the other coexisting medias. In this context, the Brazilian digital TV had its origins, one media with a resolution superior than the one of the conventional TV and that allow the simultaneous emission of more information and interactive services, been these principals differentials, enabling to the users experiences more ―actuating‖, revealing inclusive, the unidirectional nature of the television. In this type of TV, the digital TV journalism, already operating in many countries, is multimedia, interactive and multidimensional. Because so, this dissertation proposal intent to produce reflections about the journalism to be disseminated by this new TV, recently even in Brazil, pointing the perspectives of development of interactive platforms. / No Brasil, o telejornal teve origem em 1950, em uma estrutura simples, sem muitos recursos audiovisuais. Contudo, ao longo dos anos, incidiram-se transformações na produção dos telejornais, evidenciadas principalmente pelas seguintes características: o uso do videotape, a emissão de conteúdos a distância, a difusão em cores, o início da televisão por assinatura, o surgimento da Internet. Tais inovações asseguram que o advento das novas tecnologias para televisão propicia, em consequência, o desenvolvimento do telejornalismo, forçando-o a rever seus respectivos conceitos e paradigmas. Um exemplo que atesta esta questão é o fato dos telejornais revelarem a necessidade de estabelecerem novos formatos, disponibilizando a participação dos telespectadores, baseados nos pressupostos interativos do ciberespaço, potencial fomentador de conteúdo, onde se valoriza a autonomia do internauta. Entretanto, cabe ressaltar que essa participação ainda encontra limitações na própria tecnologia analógica, o que significa mencionar que para haver o diálogo entre emissora e audiência, esta tem que recorrer às outras diversas mídias coexistentes. Neste contexto, tem origem a TV digital brasileira, uma mídia com resolução superior a da TV convencional e que permite a emissão simultânea de mais informações e serviços interativos, sendo estes os principais diferenciais, por permitirem aos usuários experiências muito mais atuantes, desvelando-se, inclusive, do caráter unidirecional da televisão. Neste tipo de TV, o telejornalismo digital, já em operação em variados países, é multimídia, interativo e multilinear. Assim sendo, esta proposta de dissertação intenta produzir reflexões acerca do jornalismo a ser veiculado por esta nova TV, ainda recente no Brasil, apontando as perspectivas de desenvolvimento de plataformas interativas.

Page generated in 0.4724 seconds