No description available.

Yes / The flow in the main channel of a meandering compound channel does not occur in the ridge direction because of the effect of the upstream floodplain flows. This study proposes a model for estimating the flow direction in the depth-averaged two-dimensional domain (depth-averaged flow angles) between the entrance and the apex sections. Detailed velocity measurements were performed in the region between the meander entrance section and apex section in a large-scale meandering compound channel. The vertical size of the secondary current cell is highly related to the depth-averaged flow angle; thus, the means of the local flow angles above the secondary current cell and within the cell are separately discussed. The experimental measurements indicate that the mean local flow angle above the cell is equal to the section angle, whereas the mean local flow angle within the cell is equal to zero. The proposed model is validated using published data from five sources. Good agreement is obtained between the predictions and measurements, indicating that the proposed model can accurately estimate the depth-averaged flow direction in the meandering compound channels. Finally, the limitations and application ranges of the model are discussed. / National Key Research and Development Program of China (No. 2016YFC0402302), the National Natural Science Foundation of China (Nos. 51539007 and 51609160)

Les systèmes de télécommunications requièrent de plus en plus l’utilisation des composants passifs hyperfréquences. La commercialisation de ces composants nécessite la miniaturisation de leurs tailles, l’augmentation de leurs performances et la réduction de leurs coûts. Parmi ces composants passifs, nous citons le coupleur directionnel qui est un quadripôle destiné à répartir la puissance sur deux ports de sortie, le quatrième port reste isolé. Les travaux relatés dans ce manuscrit ont pour objectifs la conception et la réalisation d’un coupleur à accès coplanaires obtenu à partir d’un résonateur auquel nous avons appliqué des lignes de couplage. Un modèle équivalent approché a été mis en évidence par un logiciel de simulation circuit. Une étude paramétrique a été réalisée à l’aide d’un logiciel électromagnétique 3D pour fixer une règle de conception qui permet un dimensionnement convenable du composant pour un intervalle de fréquences prédéfinies. Un fonctionnement bi-bandes a été exploité pour chaque raccordement de la fréquence. Une deuxième structure de couplage a été déduite en reliant directement les lignes couplées sur le résonateur. Une étude paramétrique ainsi qu’une règle de conception ont mis en évidence un fonctionnement de coupleur mono-bande de cette structure à des fréquences prédéfinies. Une troisième structure qui fonctionne en coupleur a été exploitée en remplaçant le filtre résonateur par deux circuits en méandres. Ce nouveau coupleur à méandres présente des bandes passantes assez larges ainsi qu’un fonctionnement possible en bi-bandes. Ces coupleurs mis en œuvre peuvent assurer un couplage de l’ordre de 3 ; 6 ; 8 et 10 dB et d’un déphasage entre les deux ports de sortie de 180° pour les deux premières structures et de 90° pour le coupleur à méandres. Plusieurs séries de prototypes sont ensuite fabriquées à partir des structures optimisées en simulation. Les caractérisations hyperfréquences de ces composants montrent la performance des dispositifs réalisés / Telecommunications systems require more use of passive microwave components. The commercialization of these components requires the miniaturization of their size, increasing their performance and the reduction of their costs. Among these passive components we cited the directional coupler which is designated to spread the power between two outputs, the fourth port being isolated. The ambition of this work is to study and fabricate a coupler with coplanar access obtained from a resonator where we applied coupling lines. An equivalent approximate model was obtained using circuit simulation software. A parametric study was made using 3D electromagnetic software to fix a design rule that allows a suitable design for the component in a predefined frequency range. Dual-band operation has been exploited for each frequency. A second coupling structure was deduced by directly connecting the coupled lines to the resonator. A parametric study and a design rule have shown the operation of this structure as a single band coupler at predefined frequencies. A third structure which operates like a coupler has been exploited by replacing the resonator filter by two meandering circuits. This new meandering coupler presents a wide bandwidth and a possible operating in dual-band. These implemented couplers provided a coupling factor of 3, 6, 8 and 10 dB and a phase shift between the two output ports of 180° for the two first structures and a 90° phase shifter for the meandering coupler. Several sets of prototypes are then made. The microwave characterizations show the performance of the fabricated device

Na presente pesquisa investiga-se a geomorfologia da planície fluvial do rio Pinheiros entre os bairros de Pinheiros, Butantã e Cidade Jardim, na cidade de São Paulo. Para tal, propõe-se uma carta geomorfológica de detalhe deste setor da planície na escala de 1:20.000, confeccionada a partir de pesquisa arquivística prévia e, principalmente, de fotografias aéreas e de mapas antigos. A análise da carta e a sua correlação com informações sedimentológicas e estratigráficas encontradas, principalmente, em recentes relatórios de engenharia para a construção do Metrô de São Paulo, permitem a caracterização do sistema fluvial deste setor do rio Pinheiros, bem como de parte da morfodinâmica atuante no sistema antes da perturbação antrópica de alto impacto decorrente da urbanização que ali se instalou a partir da década de 1930. A pesquisa permitiu também a interpretação de uma provável sequência de eventos geomorfológicos atuantes no setor estudado durante o Pleistoceno Superior e o Holoceno. Parâmetros morfométricos tais como índice de sinuosidade de canais e paleocanais e largura da planície no trecho estudado evidenciaram aspectos da influência da estrutura geológica em sua evolução. O reconhecimento de sistemas geomorfológicos em seu estágio préperturbação antrópica é essencial para a compreensão dos processos atuais, principalmente em meios intensamente modificados como as áreas urbanas. A pesquisa apresenta então este tipo de reconhecimento, colaborando assim na compreensão dos processos antecedentes às grandes rupturas que se instalam no sistema a partir das ações antrópicas na superfície. / This research investigates the geomorphology of part of Pinheiros River fluvial plain in São Paulo city. This study main result is a detailed geomorphologic map - 1:20,000 - that used ancient aerial photographs and maps obtained from formal archival surveys. The descriptions of floodplain units were associated to stratigraphic and sedimentologic data obtained from recent engineering projects reports of São Paulo underground (such as subway). This association allows the understanding of part of Pinheiros River fluvial system and morphodynamic before urbanization. The research also allowed offering a sequence of geomorphological events related to the floodplain and channel systems over the Holocene. Morphometric parameters, such as width and sinuosity index of channels and paleo-channels of floodplain meandering system, appear as an evidence of the structural influence in geomorphological evolution of this system. The recognition of geomorphologic systems in pre-disturbance stage is essential for understanding the current processes, mainly in environments greatly modified by human actions, such as urban areas. This research presents this kind of recognition and contributes to the understanding of processes in the system before human actions in the surface.

This experimental study analyses the dynamics of concentration fluctuations in a passive plume emitted by a point source within the turbulent boundary layer. We aim to extend the popular study of Fackrell and Robins (1982) about concentration fluctuations and fluxes from point sources by including third and fourth moments of concentration. We also further inquire into the influence of source conditions, such as the source size, source elevation and emission velocity, on higher order concentration moments. The data set is completed by a detailed description of the velocity statistics within the TBL, with exhaustive information on both the temporal and spatial structure of the flow. The experimental data-set has been used to test two different modeling ap- proaches: an analytical meandering plume model (in one and in three dimen- sions) and a Lagrangian stochastic micro-mixing model.

Na presente pesquisa investiga-se a geomorfologia da planície fluvial do rio Pinheiros entre os bairros de Pinheiros, Butantã e Cidade Jardim, na cidade de São Paulo. Para tal, propõe-se uma carta geomorfológica de detalhe deste setor da planície na escala de 1:20.000, confeccionada a partir de pesquisa arquivística prévia e, principalmente, de fotografias aéreas e de mapas antigos. A análise da carta e a sua correlação com informações sedimentológicas e estratigráficas encontradas, principalmente, em recentes relatórios de engenharia para a construção do Metrô de São Paulo, permitem a caracterização do sistema fluvial deste setor do rio Pinheiros, bem como de parte da morfodinâmica atuante no sistema antes da perturbação antrópica de alto impacto decorrente da urbanização que ali se instalou a partir da década de 1930. A pesquisa permitiu também a interpretação de uma provável sequência de eventos geomorfológicos atuantes no setor estudado durante o Pleistoceno Superior e o Holoceno. Parâmetros morfométricos tais como índice de sinuosidade de canais e paleocanais e largura da planície no trecho estudado evidenciaram aspectos da influência da estrutura geológica em sua evolução. O reconhecimento de sistemas geomorfológicos em seu estágio préperturbação antrópica é essencial para a compreensão dos processos atuais, principalmente em meios intensamente modificados como as áreas urbanas. A pesquisa apresenta então este tipo de reconhecimento, colaborando assim na compreensão dos processos antecedentes às grandes rupturas que se instalam no sistema a partir das ações antrópicas na superfície. / This research investigates the geomorphology of part of Pinheiros River fluvial plain in São Paulo city. This study main result is a detailed geomorphologic map - 1:20,000 - that used ancient aerial photographs and maps obtained from formal archival surveys. The descriptions of floodplain units were associated to stratigraphic and sedimentologic data obtained from recent engineering projects reports of São Paulo underground (such as subway). This association allows the understanding of part of Pinheiros River fluvial system and morphodynamic before urbanization. The research also allowed offering a sequence of geomorphological events related to the floodplain and channel systems over the Holocene. Morphometric parameters, such as width and sinuosity index of channels and paleo-channels of floodplain meandering system, appear as an evidence of the structural influence in geomorphological evolution of this system. The recognition of geomorphologic systems in pre-disturbance stage is essential for understanding the current processes, mainly in environments greatly modified by human actions, such as urban areas. This research presents this kind of recognition and contributes to the understanding of processes in the system before human actions in the surface.

Made available in DSpace on 2014-08-20T14:25:46Z (GMT). No. of bitstreams: 1 dissertacao_marieli_sallet.pdf: 231023 bytes, checksum: f445526b62fbfcde40fb1bc5ca90923a (MD5) Previous issue date: 2007-02-23 / Currently, the search for analytical solutions for the dispersion problems is one of the main research subjects in the pollutant dispersion modeling. These solutions become important due to the intention to obtain dispersion models that generate reliable results in a small computational time, which are of great interest for regulatory air quality applications. Lagrangian particle models are an important and effective tool to simulate the atmospheric dispersion of airborne pollutants. These models are based on the Langevin equation, which is derived from the hypothesis that the velocity is given by the combination between a deterministic term and a stochastic term. In this work is presented a new Lagrangian particle model to simulate the pollutant dispersion in low wind speed conditions. During low wind speed, the diffusion of a pollutant in the planetary boundary layer (PBL) is indefinite and it has been observed that the plume is subject to a great deal of horizontal undulations, which are called plume meandering. The method proposed leads to a stochastic integral equation whose solution has been obtained through the Method of Successive Approximations or Picard s Iteration Method. The integral equation is written in terms of the real and imaginary parts of the complex function before performing the multiplication of the integrating factor, expressed by the Euler formula, inside and outside of the integral solution. To take account the meandering effect, the Frenkiel s Eulerian autocorrelation functions for low wind conditions is included naturally in the model. The new approach has been evaluated through the comparison with experimental data and other different dispersion models. Particularly, the results obtained by the model agree very well with the experimental data, indicating the model represents the dispersion process correctly in low wind speed conditions. It is also possible to verify that the new model results are better than ones obtained by the other models. The analytical feature of the technique and the natural inclusion of the Frenkiel s Eulerian autocorrelation function become the model more accurate than other models. / Atualmente, a busca por soluções analíticas para os problemas de dispersão é um dos principais assuntos de pesquisa na modelagem da dispersão de poluentes. Estas soluções tornam-se importantes devido à intenção de obter modelos de dispersão que geram resultados confiáveis em um tempo computacional pequeno, que são de grande interesse para aplicações no controle da qualidade do ar. Modelos de partícula Lagrangeano são uma ferramenta importante e eficaz para simular a dispersão atmosférica de poluentes do ar. Esses modelos são baseados na equação de Langevin, que é derivada da hipótese que a velocidade é dada por uma combinação entre um termo determinístico e um termo estocástico. Neste trabalho é apresentado um novo modelo de partícula Lagrangeano para simular a dispersão de poluentes em condições de velocidade de vento fraco. Durante a velocidade de vento fraco, a difusão de um poluente na Camada Limite Planetária (CLP) é indefinida e tem sido observado que a pluma está sujeita a grandes ondulações horizontais, que são chamadas meandro do vento. O método proposto leva a uma equação integral estocástica cuja solução é obtida através do Método das Aproximações Sucessivas ou Método Iterativo de Picard. A equação integral é escrita em termos das partes real e imaginária da função complexa antes de realizar a multiplicação do fator integrante, expresso pela fórmula de Euler, dentro e fora da solução integral. Para considerar o efeito do meandro, as funções de autocorrelação Euleriana de Frenkiel para condições de vento fraco são incluídas naturalmente no modelo. A nova aproximação foi avaliada através da comparação com dados experimentais e outros diferentes modelos de dispersão. Particularmente, os resultados obtidos pelo modelo concordam muito bem com os dados experimentais, indicando que o modelo representa o processo de dispersão corretamente em condições de velocidade de vento fraco. Também é possível verificar que os resultados do novo modelo são melhores do que os obtidos pelos outros modelos. A característica analítica da técnica e a inclusão natural da função de autocorrelação Euleriana de Frenkiel tornam o modelo mais exato que os outros modelos.

Laboratory experiments concerning stage-discharge, flow resistance, bedforms, sediment transport and flow structures have been carried out in a meandering channel with simulated non-vegetated and vegetated floodplains for overbank flow. The effect of placing solid blocks in different arrangements as a model of rigid, unsubmerged floodplain vegetation on a floodplain adjacent to a meandering channel is considered. The aim was to investigate how density and arrangements of floodplain vegetation influence stage-discharge, flow resistance, sediment transport and flow behaviours. Stage-discharge curves, Manning's n and drag force FD are determined over 165 test runs. The results from the laboratory model tests show that the placing of solid blocks along some part of the bend sections has a significant effect on stage-discharge characteristics. The change in stage-discharge by the blocks is compared using different arrangements, including the non-vegetated floodplains case. The experimental results show that the presence of energy losses due to momentum exchange between the main channel and the floodplain as well as the different densities of the blocks on a floodplain induce additional flow resistance to the main channel flow, particularly for shallow overbank flows. In general, the results show that the density and arrangement of blocks on the floodplains are very important for stage-discharge determination and, in some cases, for sediment transport rates, especially for a mobile main channel. Also, the correction parameter, a is introduced in order to understand the effects of blocks and bedforms on the force balance equation. By applied the correction factor c; a stagedischarge rating curve can be estimated when the avalue is calibrated well. Telemac 2D and 3D were applied to predict mean velocity, secondary flow and turbulent kinetic energy. Telemac computations for non-vegetated and vegetated floodplain cases in a meandering channel generally give reasonably good predictions when compared with the measured data for both velocity and boundary shear stress in the main channel. Detailed analyses of the. predicted flow variables were therefore carried out in order to understand mean flow mechanisms and secondary flow structures in compound meandering channels. The non-vegetated and two different cases of vegetated floodplain for different relative depths were considered. For the arrangement on a non-vegetated floodplain shows how the shearing of the main channel flow as the floodplain flow plunges into and over the main channel influences the mean and turbulent flow structures, particularly in the cross-over region. While applying vegetated floodplain along a cross-over section confirmed that the minimum/reduction shearing of the main channel flow by the floodplain flow plunging into and over the main channel is observed from the cross-sectional distributions of the streamwise velocity (U), lateral velocity (V), and secondary flow vectors. In addition to that, the vegetated floödplain along the apex bend region shows a small velocity gradient within the bend apex region. However, strong secondary flow in the cross-over section suggested that the flow interaction was quite similar to the non vegetation case in the cross-over section region.

Les réacteurs-échangeurs à plaques (HEX) sont une technologie clé en intensification des procédés. Cependant, la plupart des recherches existantes portant sur ce type d'équipement ont été réalisées dans le cas d’écoulements monophasiques. Pour les réactions gaz-liquide, peu d'études ont été conduites. Cette thèse a pour objectif d’étudier localement le transfert de matière gaz-liquide autour de bulles de Taylor en écoulement dans des canaux millimétriques droits et ondulés par une méthode dite colorimétrique. Ceci constitue une étape préliminaire indispensable avant la mise en œuvre de systèmes réactifs diphasiques. Il a d’abord déterminé si une possible accélération du transfert de matière gaz-liquide pouvait avoir lieu en présence de la réaction chimique utilisée. La deuxième phase de ce travail s’est focalisée sur l'étape de formation des bulles de Taylor dans un microréacteur. Ensuite, l'hydrodynamique gaz-liquide a été caractérisée et les effets des coudes sur le mécanisme de transfert de masse ont été étudiés localement dans un canal carré millimétrique ondulé. Enfin, une comparaison rigoureuse a pu être effectuée entre les différentes géométries de canaux (ondulé et droit). Elle a permis de montrer comment et pourquoi une géométrie ondulé permet d’intensifier le transfert de masse gaz-liquide (notamment en terme d’efficacité de transfert). L’ensemble de ces résultats ont conduit à la formulation une loi d'échelle, exprimée en termes de nombres de Sherwood, de Graetz et de Péclet, capable de décrire l'évolution du transfert de matière gaz-liquide en fonction de la position axiale dans le canal et des conditions opératoires mises en œuvre. / Compact Heat-EXchanger reactors (HEX) are an important part of process intensification technology. However, most of the existed research dealing with such type of equipment has been focused on the application of one-phase reactive flows. For gas-liquid reactions, few investigations have been out carried. This thesis aims at locally studying gas-liquid mass transfer around Taylor bubbles flowing in straight and meandering millimetric channels using a colorimetric method; this is a preliminary step essential before implementing two-phase reactive systems. Firstly, the occurrence of a possible enhancement of the gas-liquid mass transfer by the chemical reaction involved was investigated. Secondly, the gas-liquid mass transfer occurring in Taylor flows right after the bubble formation stage in a microreactor was studied. Thirdly, the gas-liquid hydrodynamics were characterized and the effects of bends on the mass transfer mechanism were locally investigated in a millimetric meandering channel. At last, a rigorous comparison could be made between the meandering and straight channels. It showed how and why the meandering geometry leads to intensify gas-liquid mass transfer. All these findings enabled to formulate a scaling law, expressed in terms of Sherwood, Graetz and Péclet numbers, able to describe the evolution of gas-liquid mass transfer as a function of axial position and operating conditions.

Le phénomène connu sous l'appellation "méandrement" (ou meandering) désigne les variations aléatoires de la trajectoire du sillage aérodynamique d'une éolienne. Ce phénomène est responsable de contraintes mécaniques particulières sur les éoliennes positionnées dans le sillage d'autres éoliennes et joue donc rôle dans la conception et dans la prévision de production des parcs éoliens.Ce travail propose d'étudier le méandrement par des moyens expérimentaux et numériques. La problématique est traitée en deux parties, la première portant sur la modélisation de l'écoulement de couche limite atmosphérique, avec une attention particulière portée à la modélisation des grandes échelles de la turbulence atmosphérique. La seconde partie porte sur l'étude du sillage d'un disque actuateur soumis à un écoulement atmosphérique. Chacune de ces parties comporte un volet expérimental et un volet numérique. La modélisation numérique instationnaire de l'écoulement atmosphérique fait intervenir une technique de génération stochastique de champs de vitesse turbulente avec évolution temporelle, spécialement développée au cours de la présente thèse et à laquelle un chapitre spécifique est dédié.L'un des principaux résultats est que le méandrement du sillage est fortement corrélé avec les grandes échelles de la turbulence atmosphérique. / The phenomenon known as meandering describes the unsteady trajectory variations of the wake of a wind turbine. This phenomenon is responsible for specific mechanical stresses on turbines positioned in the wake of other turbines. As such, this phenomenon must be accounted for in the design and operation of wind turbine plants.This work uses numerical fluid simulation and wind tunnel testing in order to study the meandering of the wake of a wind turbine. The subject is discussed in two parts. The first part discusses the modeling of the atmospheric boundary layer, with a focus on the large scales of the atmospheric turbulence. The second part is a study of the behavior of the wake of an actuator disc model in atmospheric wind conditions.Both parts include experimental and numerical work. The numerical simulation of the atmospheric boundary layer involves the generation of synthetic turbulent velocity time series by mean of a stochastic technique developed during this thesis, to which a chapter is dedicated.One of the main results of this work is that the meandering is highly correlated with the large scales of the atmospheric turbulence.