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This thesis concerns the computation of bed adjustments of equilibrium in alluvial meandering streams. It is assumed that the channel centerlines follow sine-generated curves, the banks are rigid, and the steady-state flow is turbulent and sub-critical. The flow width is assumed to remain constant in the streamwise direction, and the flow width-to-depth ratio is large (>=15, say). The bed material is cohesionless and homogeneous. The purpose of the thesis is to develop and test a numerical model for the computation of bed development, given the aforementioned idealized conditions. The model comprises: 1- an initial bed topography generator, to generate the bed at time t = 0 of the calculations; 2- the vertically-averaged hydrodynamic model of Zhang (2007) to calculate the flow fields; and 3- a sediment transport model to relate the bed deformation to the flow. Both the initial bed topography generator (expression of the deformed bed surface) and the numerical sediment transport model based on the sediment transport continuity equation are original and developed entirely by the author. The resulting model is computationally very efficient. In contrast to previous works on the theoretical determination of bed deformation, the beds at the beginning of the calculations may represent any stage of the development process, and not necessarily the initial flat bed. The bed deformation was tested for several test cases, devised on the basis of laboratory runs available in the literature. These include Run ME-2 by Hasegawa (1983) in a 30-degree-channel, Run 3 by Binns (2006) in a 70-degree-channel and the run by Termini (1996) in a 110-degree-channel. The erosion/deposition patterns of the computed equilibrium bed topographies were found to be in reasonable agreement with their measured counterparts. However, as evidenced by the difference plots included in this thesis, in detail there are substantial differences between the computed and measured equilibrium beds, especially in the regions near the banks. As a by-product of the present thesis, the functions representing the parameters required by the hydrodynamic model of Zhang (2007) were also evaluated. In particular, the present results suggest that the coefficient Alpha-q appearing in the expression of the local friction factor (used in the flow model of Zhang 2007) depends on the flow width-to-depth ratio and bed roughness to a much larger extent than previously thought. Considering this, a generalization of the expression of Alpha-q due to El-Tahawy (2004) (and adopted by Zhang 2007 in her model) is proposed. Future work should be carried out to address the application of the present model to real river conditions, including generalizations to irregular meandering plan shapes, unsteady-state flows and non-homogenous bed materials. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2008-12-19 21:32:06.645

The present research focuses on the development and computer implementation of a novel threedimensional, anisotropic turbulence model not only capable of handling complex geometries but also the turbulence driven secondary currents. The model equations comprise advanced algebraic Reynolds stress models in conjunction with Reynolds Averaged Navier-Stokes equations. In order to tackle the complex geometry of compound meandering channels, the body-fitted orthogonal coordinate system is used. The finite volume method with collocated arrangement of variables is used for discretization of the governing equations. Pressurevelocity coupling is achieved by the standard iterative SIMPLE algorithm. A central differencing scheme and upwind differencing scheme are implemented for approximation of diffusive and convective fluxes on the control volume faces respectively. A set of algebraic equations, derived after discretization, are solved with help of Stones implicit matrix solver. The model is validated against standard benchmarks on simple and compound straight channels. For the case of compound meandering channels with varying sinuosity and floodplain height, the model results are compared with the published experimental data. It is found that the present method is able to predict the mean velocity distribution, pressure and secondary flow circulations with reasonably good accuracy. In terms of engineering applications, the model is also tested to understand the importance of turbulence driven secondary currents in slightly curved channel. The development of this unique model has opened many avenues of future research such as flood risk management, the effects of trees near the bank on the flow mechanisms and prediction of pollutant transport.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this study is propose a new mathematical expression to describe the observed meandering autocorrelation functions in low-wind speed. The analysis utilizes a large number of the data to show that the new proposed theoretical function reproduces the experimental behavior of the fit curves, well as the negative lobes that characterizing the autocorrelation function for meandering condition. Furthermore, the good agreement of the measured autocorrelation curves with the proposed algebraic autocorrelation function allows to calculate the magnitudes of the meandering period and of the loop parameter. In adition, the parameters founded in this study can be used to simulate the dispersion of contaminant during low wind episodes. The results agree with the values presented and discussed in the literature. / O presente estudo propõe uma nova expressão matemática para descrever as funções de autocorrelação observadas sob condições de meandro do vento horizontal. A análise utiliza um grande número de dados para demonstrar que a função proposta reproduz o comportamento da curva experimental, bem como os lóbulos negativo que caracterizam a função de autocorrelação para a situação de meandro. Além disso, a boa concordância entre as curvas de autocorrelação observadas e a nova função de autocorrelação algébrica, proposta neste trabalho, permitiu realizar o cálculo de grandezas físicas como o parâmetro de oscilação e o período de meandro. Um resultado adicional, foi empregar os valores médios encontrados para os parâmetros do meandro na simulação da dispersão de contaminante durante episódios de vento fraco. Os resultados encontrados estão de acordo com os valores apresentados e discutidos na literatura.

Les systèmes turbiditiques chenalisés permettent le transfert de sédiments depuis le plateau continental vers le domaine marin profond de la même façon que les cours d’eau sur les continents. Les dépôts sédimentaires turbiditiques forment parmi les plus grands réservoirs d’hydrocarbures actuellement exploités. MINES ParisTech développe depuis une vingtaine d’années Flumy, un modèle numérique simulant l’évolution d’un système fluviatile méandriforme pour la simulation de réservoirs. L’approche proposée dans ce travail est de transposer Flumy aux systèmes sous-marins profitant de l’analogie entre ces environnements. La géomorphologie des systèmes chenalisés méandriformes fluviatiles et sous-marins est d'abord comparé à titre de données naturelles, et des expériences en laboratoire mettent en évidence les différences dans les écoulements aériens et sous-aquatiques. L'intégration dans Flumy de ces résultats permet de reproduire l'architecture stratigraphique des réservoirs turbiditiques. / Channelized turbidite systems act as sediment transfer routes through the submarine realm similarly to rivers on the continents. The turbidite sedimentary deposits create among the biggest hydrocarbon reservoirs currently produced. MINES ParisTech has developed in the last twenty years Flumy, a numerical model that simulates the evolution of a meandering fluvial system to simulate reservoirs. In this work, we propose to transpose Flumy to submarine systems taking advantage of the analogy between these environments. Using natural data, the geomorphology of channelized meandering fluvial and submarine systems is compared, and laboratory experiments highlight the differences in terms of aerial and subaqueous flow behavior. The integration of the results of these studies allows Flumy to accurately simulate the stratigraphic architecture of channelized turbidite reservoirs.

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Yes / For overbank flows in meandering channels, the flow direction along a meander varies and is affected by floodplain vegetation. This study proposes a model for predicting the depth-averaged two-dimensional flow direction (depth-averaged flow angle) along a meander in smooth and vegetated meandering compound channels. Laboratory experiments were performed in smooth and vegetated channels. Measurements show that the height of the secondary current cell in the main channel is increased by dense floodplain vegetation comparing with that in a non-vegetated channel. A method of determining the height of the cell is proposed. At the middle section between the apex and exit sections, where the secondary current cell is absent, the depth-averaged flow angle is independent of the height of the cell. Beyond the middle section, a new secondary current cell is formed, and the flow angle is highly dependent on the height of the cell. The proposed model is thoroughly verified using the flume experimental and field observed data. Good agreement is obtained between predictions and measurements, indicating that the proposed model is capable of accurately predicting the depth-averaged flow angle along a meander in smooth and vegetated meandering compound channels. / National Key Research and Development Program of China (No. 2016YFC0402302), and the National Natural Science Foundation of China (Nos. 51709022, 51609160 and 51539007)

京都大学 / 新制・課程博士 / 博士(工学) / 甲第25253号 / 工博第5212号 / 新制||工||1994(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 川池 健司, 教授 山上 路生, 准教授 米山 望 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Cette étude, menée principalement par des moyens expérimentaux, analyse la dynamique des fluctuations de concentration produites au sein d’un panache d’un scalaire passif émis par une source ponctuelle dans une couche limite turbulente. En étendant le travail de Fackrell and Robins (1982) sur les fluctuations de concentration, on décrit l’évolution des quatre premiers moments de la concentration et on étudie l’influence des conditions à la source (telles que la taille et la hauteur de la source et la vitesse de sortie) sur les moments mêmes. L’étude est complétée par une description détaillée des statistiques du champ de vitesse dans la couche limite, comprenant des informations sur la structure spatiale et temporelle de la turbulence. Cette base de données expérimentale a été utilisée pour valider deux différentes approches à la modélisation de la dispersion: un modèle analytique de meandering et un modèle Lagrangien stochastique avec un schéma de micro mélange. / 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.

By examining halokinetics and channel evolution in a deep-water system, we investigate how submarine channel morphology is affected by changing seascape linked to diapirism. The study area is located in Mississippi Canyon, Gulf of Mexico (GOM), situated directly off the continental slope in a prominent salt dome region. Interactions of salt domes with submarine channels in the GOM are poorly documented. Utilizing 3D seismic data and seismic geomorphology techniques, a long-lived Plio-Pleistocene submarine channel system has been investigated to develop a relationship between variable phases of salt movement and plan-form morphology of preserved channels. We suggest that halokinetics acts as a driver for topographic-channel evolution in the study area. We show how submarine channel morphology can be directly controlled by halokinetics, where salt movement can act as a structural control on both location and morphology of meandering channel complexes. Channels are able to move towards an equilibrium state only when holokinetics decreases.