Thèses : « Shear stress bed »

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Su, Yan. « An annular fluidized-bed experiment for inter-granular shear stress ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0008/MQ31257.pdf.

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Yang, Qingjun (Judy Qingjun). « Estimation of the bed shear stress in vegetated and bare channels ». Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99580.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 69-77).
The shear stress at the bed of a channel influences important benthic processes such as sediment transport. Several methods exist to estimate the bed shear stress in bare channels without vegetation, but most of these are not appropriate for vegetated channels due to the impact of vegetation on the velocity profile and turbulence production. This study proposes a new model to estimate the bed shear stress in both vegetated and bare channels with smooth beds. The model, which is supported by measurements, indicates that for both bare and vegetated channels with smooth beds, within a viscous sub-layer at the bed, the viscous stress decreases linearly with increasing distance from the bed, resulting in a parabolic velocity profile at the bed. For bare channels, the model describes the velocity profile in the overlap region of the Law of the Wall. For emergent canopies of sufficient density (frontal area per unit canopy volume a >/= 4.3m⁻¹ ), the thickness of the linear-stress layer is set by the stem diameter, leading to a simple estimate for bed shear stress.
by Qingjun (Judy) Yang.
S.M.

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Yaeger, Mary A. « MEAN FLOW AND TURBULENCE AROUND TWO SERIES OF EXPERIMENTAL DIKES ». Thesis, The University of Arizona, 2009. http://hdl.handle.net/10150/193453.

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Scour around various structures obstructing flow in an open channel is a common problem; therefore a better understanding of how turbulent flow affects sediment transport is needed. Additionally, is it the mean flow or the turbulence properties that are more important in contributing to bed shear stress? To this end, an experimental study was conducted in a fixed-bed flume containing a series of dikes. Turbulence intensities and Reynold's stresses were calculated from 3-D velocity measurements gathered with a microADV. Results showed that the maximum shear stress was nearly 12-20 times that of the approach flow, while maximum turbulence intensities were about 3-5 times those of the incoming flow. Highest magnitudes of both were seen at the tip of the second dike in the three-dike series. The mean velocity appeared to have no relation to the formation of scour near the tips of the dikes but the turbulence intensities did.

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Emerson, Samuel D. « The role of bed shear stress in sediment sorting patterns in a reconstructed, gravel bed river ». Thesis, San Jose State University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10128515.

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The role of bed shear stress in bed surface grain size sorting was investigated on a reconstructed reach of the Merced River in the Central Valley of California. Pebble count data were collected at the inside, middle, and outside of ten bends in April 2015 and compared to data from pebble counts conducted in previous years. Output from a previously developed 2D flow model (FaSTMECH) was compared to critical shear stresses calculated from median grain-size data. Comparison of pebble count results from 2002 through 2015 showed that there was no temporally consistent pattern of coarsening or fining along the study reach; however, the bed surface coarsened between 2002 and 2015. Pebble count data from April 2015 revealed a distinct spatial distribution of grain sizes with a larger median grain size (D₅₀) at the outside of bends and a smaller D₅₀ at the inside of bends. Regression analyses performed on pebble count data from point bars revealed statistically significant downstream changes in surface grain size on two of the seven bars. Analysis of shear stress data showed a weak relationship between the modeled bed shear stress (τ_b) and the calculated critical shear stress (τ_cr). The weak relationship between τ_b and τ_cr indicated that bed shear stress was not solely responsible for the grain size sorting in the study reach. It is likely that the observed grain size sorting patterns resulted from helical secondary flows at the bends.

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Sarra, Angela M. « Particle-wall shear stress measurements within the standpipe of a circulating fluidized bed ». Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=2078.

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Thesis (M.S.)--West Virginia University, 2001.
Title from document title page. Document formatted into pages; contains xi, 137 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 136-137).

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Perret, Emeline. « Transport of moderately sorted gravels at low bed shear stress : impact of bed arrangement and fine sediment infiltration ». Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1223/document.

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Le but de cette thèse est de comprendre la dynamique des graviers au sein des rivières alpines à faible contrainte en utilisant des expériences en laboratoire. Ces rivières sont souvent composées d’une large gamme de sédiments, allant des argiles aux galets. Ces différentes classes sédimentaires peuvent interagir entre elles, ce qui peut rendre difficile l’estimation du transport solide. Des expériences en laboratoire ont été conduites en écoulements instationnaires dans un canal de 18m de long et 1m de large. Deux types de lits ont été étudiés : lits unimodaux et bimodaux. Une attention particulière a été portée sur la réalisation des lits de graviers dans notre canal. Ils ont été créés dans le but d’approcher au mieux la configuration des lits de rivières alpines, c’est-à-dire avec différents arrangements et degrés de colmatage du lit par des sédiments fins. Les lits unimodaux sont composés de graviers peu triés avec divers arrangements de surface. Les lits bimodaux sont composés d’une matrice de graviers peu triés dans laquelle des sédiments fins se sont infiltrés (sables ou limons). Les processus régissant le transport de graviers ont été mis en avant. Le transport de graviers est impacté par l’arrangement du lit, la concentration de sédiments fins dans la couche de charriage, et par le changement de propriétés du lit due à la présence de sédiments fins (cohésion, perméabilité du lit). Plus le lit est arrangé, plus le transport est difficile. Plus la couche de charriage est concentrée en sédiments fins, plus le transport est facile. La forme des sédiments fins est aussi un facteur important pouvant modifier le transport des graviers. La présence de sédiments fins cohésifs dans la matrice peut considérablement réduire le taux de graviers transportés. Un modèle conceptuel a été développé pour résumer les différents processus contrôlant le transport de graviers. Il décrit le comportement des graviers dans les différentes configurations étudiées. L’outil proposé peut aider à comprendre, estimer et interpréter le transport de graviers. Il a été appliqué et discuté sur un cas de terrain sur la rivière de l’Arc. Basé sur ce modèle, nous avons proposé une nouvelle analyse dimensionnelle pour la construction d’un modèle de prédiction de transport solide prenant en compte des paramètres décrivant l’arrangement du lit, les propriétés géotechniques du lit et la présence de sédiments fins
This PhD thesis aims to understand gravel dynamics in Alpine rivers at low bed shear stress using laboratory experiments. Alpine river beds are often poorly sorted and composed of sediments ranging from clay to pebble. To understand interactions between these classes is an issue for predicting bedload rate. Laboratory experiments were performed in a 18m long and 1m wide flume, under unsteady flows. Two types of bed were investigated: unimodal and bimodal beds. A particular attention was paid to the bed construction, which was conducted in order to obtain a nature-like bed 12with different bed arrangements and degrees of clogging. Unimodal beds were made of moderately sorted gravels with different bed surface arrangements. Bimodal beds were made of moderately sorted gravels in which fine sediments (sand or silt) were infiltrated. Gravel rate was found to be impacted by the bed arrangement degree, the fine sediment concentration within the bedload layer and the changes in bed properties due to fine sediment presence (bed cohesion, bed permeability). The more packed the bed is; the more difficult it is to move gravels. The more concentrated in fine sediment the bedload layer is; the easier the transport of gravels is. The shape of fine sediments can also be an important factor for modifying the gravel rate. The presence of cohesive fine sediments within the bed matrix reduces significantly the gravel rate. A conceptual model was developed to recap the different processes controlling gravel transport. It provides a phenomenological description of the overall bed responses to a hydrograph. This tool is designed to help understanding, estimating or interpreting gravel transport in Alpine rivers. The conceptual model was discussed and applied to a field case made on the Arc River. Using the model, we also suggest a new dimensionless analysis for the construction of a bedload predicting model involving parameters describing bed arrangement, bed properties and fine sediment presence

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Thompson, Charlotte E. L. « The role of the solid-transmitted bed shear stress of mobile granular material on cohesive bed erosion by unidirectional flow ». Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398824.

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Sime, Louise C. « Reach-scale spatial variation of grain-size, shear stress, and bedload transport in gravel-bed rivers ». Thesis, University of Sheffield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401128.

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Valentine, Kendall. « Characterization of the bed, critical boundary shear stress, roughness, and bedload transport in the Connecticut River Estuary ». Thesis, Boston College, 2015. http://hdl.handle.net/2345/bc-ir:104550.

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Thesis advisor: Gail C. Kineke
This study characterizes the bed of the Connecticut River estuary in terms of grain size and bedforms, and relates these to river discharge, tidal currents, and sediment transport. Over four field excursions, sediment cores were collected, in addition to bathymetry surveys, and water column measurements. A three-dimensional circulation and sediment transport model calculated boundary shear stress over the same time. The bed of the estuary is composed mostly of sand, with small amounts of fine sediments. Deposition of fine sediments is limited by the landward extent of the salt intrusion. Large bedforms are oriented seaward. The critical shear stress for the median grain size is exceeded each tidal cycle. Bedload transport is dominantly seaward during high discharge conditions, but varies during low discharge. Bathymetry surveys from previous studies and this study show consistent bedform fields over 25 years. Bedforms observed in the field reflect typical conditions rather than extreme events
Thesis (MS) — Boston College, 2015
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Earth and Environmental Sciences

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Mayoral, Helen. « Particle Size, Critical Shear Stress, and Benthic Invertebrate Distribution and Abundance in a Gravel-bed River of the Southern Appalachians ». Digital Archive @ GSU, 2011. http://digitalarchive.gsu.edu/geosciences_theses/31.

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To determine the relationship between the abundance and density of benthic invertebrates, and the critical shear stress of individual grain sizes, a reach along Smith Creek, was divided into ten 2m x 2m quadrants. Within each quadrant, five randomly selected clasts for each grain size ranging from 2.26 to 25.6 cm were cleaned for benthic invertebrates. Wolman pebble counts for each quadrant were also conducted and used to determine the critical Shields stress per grain size fraction from the model given by Wiberg and Smith (1987) that explicitly accounts for particle hiding/sheltering effects in mixed-bed rivers. Particle entrainment values were then compared with estimated bankfull Shields stress values to determine sediment transport potential during bankfull flow. Invertebrate abundance was strongly positively correlated with critical Shields stress up to the 18.0 cm grain size, indicating a preference for certain grain sizes; while density was positively correlated with all grain sizes present.

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Genovese, Marco. « Analisi sperimentale e misura diretta dello sforzo taglianti di fondo di correnti in canale a pelo libero ». Doctoral thesis, Universita degli studi di Salerno, 2015. http://hdl.handle.net/10556/1976.

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2013 - 2014
The manuscript presents the study that led to the design, implementation and testing of an innovative system for the direct measurement, in the laboratory, of the bed shear stress of flows in open channel. The related analysis has been intended at exploring the possibility of providing a new tool to survey research, especially in the context of the erosion of the bed during the events known as debris flow. In facts, the shear stress between the debris flow and the ground over which it propagates, is now recognized as one of the key parrrameters that affect the most dynamic local and global motion (Iverson 2010). However, experimental resarch has not sufficiently investigated this aspect. The electromechanical system presented in this work earned, therefore, the purpose to make a contribution to this survey... [edited by Author]
XIII n.s.

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Bouckaert, Frederick. « Characterization of microhabitat flow regimes in streams and rivers on the basis of near-bed velocity, shear stress and turbulence intensity measured with an Acoustic Doppler Velocimeter (ADV) ». Thesis, Bouckaert, Frederick (1995) Characterization of microhabitat flow regimes in streams and rivers on the basis of near-bed velocity, shear stress and turbulence intensity measured with an Acoustic Doppler Velocimeter (ADV). Honours thesis, Murdoch University, 1995. https://researchrepository.murdoch.edu.au/id/eprint/63073/.

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Near-bed flow regimes in streams and rivers remain a poorly researched topic, despite its importance for the distribution of benthic invertebrates. The poor characterization of macroinvertebrate microhabitat severely constrains the further understanding of instream flow requirements to protect the ecological integrity of streams and rivers, and may be responsible for the wide confidence intervals often associated with macroinvertebrate sampling. Traditionally, benthic habitats have been characterized by depth, substratum and mean velocity (measured at 0.4 of the depth from the bed) despite evidence that these parameters are insufficient to describe microflow regimes. Some researchers have introduced more complex hydraulic variables to characterize flow regimes. Yet many of those variables cannot be measured directly, and the inferred values are not sufficiently accurate to describe microflow in ·quantitative terms. The difficulties involved in measuring velocities close to the streambed have now been overcome by the development of an Acoustic Doppler Velocimeter (ADV) which enables the real-time three dimensional measurement of velocities within centimeters of the bed. The resolution of 25 Hz also enables the calculation of turbulence statistics, so that shear stress and turbulence intensity can be obtained at a spatial resolution small enough to quantify flow regimes within 5 mm from the bed. The objective of this study was to investigate the hypothesis that differences in the distribution of benthic macroinvertebrates in stream and rivers are partially or wholly related to differences in benthic flow regimes. To this aim, an ADV was used in an artificial stream channel to examine the effects of different (homogeneous) substrata on near-bed flow regimes under conditions of constant depth and mean velocity. Near-bed flow regimes were characterized by velocity, shear stress and turbulence intensity. Macroinvertebrate distributions were examined upstream and downstream of isolated roughness elements in a riffle of a stream section, and related to microflow characteristics obtained with the ADV. Under conditions of constant depth and velocity, homogeneous substrata of varying roughness resulted in significantly different microflow regimes. In the field, the distribution of benthic invertebrates contrasted significantly between upstream and downstream sampling sites, despite the absence of statistically significant differences in microflow regimes at those locations. It is suggested that the indirect effects of flow may sometimes be more important than the direct 'flow exposure' effects with regard to macroinvertebrate community composition. The ADV has enabled a quantitative characterization of microflow regimes, including the description of turbulent flow conditions. This will enable further research into tolerance ranges of microflow regimes for benthic invertebrates and may offer the possibility to investigate critical values for shear stress and turbulence intensity. The quantification of microflow regime will enable a more accurate definition of macroinvertebrate (micro )habitats. This knowledge will find applications in many other areas of limnological research and in the management of streams and rivers.

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Dornelas, Breno Almeida. « Análise experimental da tensão de cisalhamento mínima para suspensão de partículas em um leito horizontal ». Universidade Federal do Espírito Santo, 2009. http://repositorio.ufes.br/handle/10/6248.

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Made available in DSpace on 2016-12-23T14:08:13Z (GMT). No. of bitstreams: 1 Breno Almeida Dornelas - parte 1.pdf: 376911 bytes, checksum: b45e88c007da3db1f74fa38428506e5c (MD5) Previous issue date: 2009-12-22
A remoção eficiente de cascalhos ainda é um desafio na perfuração de poços para produção de óleo e gás. O ponto crítico corresponde ao estágio horizontal da perfuração que intrinsecamente tende a formar um leito de partículas sedimentadas na parte inferior do poço em perfuração. A erosão desse leito de cascalhos oriundos do solo perfurado depende principalmente da tensão de cisalhamento promovida pelo escoamento do fluido de perfuração. Utilizando uma bancada experimental, composta de sistema para circulação de fluidos, caixa de cascalhos, unidade de bombeio e equipamentos de medição, investiga-se a tensão de cisalhamento mínima necessária para a erosão de um leito em função das propriedades do fluido e das partículas do leito. A área de observação consiste de uma caixa abaixo da linha de escoamento, para partículas calibradas de areia, em um duto de acrílico. Para as medições iniciam-se as bombas com baixa rotação e são feitos incrementos de freqüência. A cada patamar de freqüência são capturadas imagens de partículas carreadas pelo escoamento, registrando a vazão estabelecida. Com a análise do processamento das imagens define-se o momento em que o carreamento das partículas deixa de ser aleatório e esporádico e começa a ser permanente. A tensão de cisalhamento é determinada pela Correlação PKN (de Prandtl, von Kármán e Nikuradse) a partir da vazão mínima necessária para o arraste. Os resultados são obtidos para o escoamento de água e de solução águaglicerina
The efficient hole cleaning is still a challenge in the wellbore drilling for production of oil and gas. The critical point is the horizontal drilling that inherently tends to produce a bed of sediment particles at the bottom of the well. The erosion of this cuttings bed depends mainly on the shear stress promoted by the flow of drilling fluid. The shear stress required to drag cuttings bed is investigate according to the fluid and particles properties, using an experimental assembly, composed of a loop for circulation of fluids, of a particle box, of a pump system, camera and measuring equipment. The area of observation consists of a box below the line of flow, for calibrated sand particles, in an acrylic duct. The test starts with the pumps in low frequency and are made the increments. At each level of frequency are captured images of particles carried and it is records the established flow rate. The erosion criteria is defined when the drag particle no longer be random and sporadic, and begins to be permanent. The shear stress is determined by the PKN correlation (by Prandtl, von Kármán, and Nikuradse) from the minimum flow rate necessary to start the erosion process. Results were obtained for the flow of water; and of water and glycerin solution

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Ghoma, Mohamed I. « The Effect of Wall Jet Flow on Local Scour Hole ». Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5501.

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This thesis reports on investigations carried out to study of the effect of horizontal wall jets on rough, fixed and mobile beds in open channel flow. Experimental tests were carried out, using fixed and mobile sediment beds. Computer simulation models for the flow within the jet and resulting sediment transport were developed and their results analysed in this study. In the experimental phase, tests were carried out with both fixed and mobile sediment beds. The shape of the water surface, numerous point velocity measurements and measurements of the evolving scour hole shape were made. Detailed descriptions of the turbulent flow field over a fixed rough bed and for scour holes at equilibrium were obtained for a range of initial jet conditions. Fully turbulent, multiphase flow was modelled using the Fluent Computational Fluid Dynamics software. This was used to analyze the flow caused by a jet in a rectangle open-channel with a rough bed, and also the flow pattern in a channel with a local scour hole. The volume of fluid (VOF) multiphase method and K- model was used to model the fluid flow in both cases. The model predictions of velocity and shear stress were compared against experimental observations. The experimental data was used to develop new empirical relationships to describe the pattern of boundary shear stress caused by a wall jet over fixed beds and in equilibrium scour holes. These relationships were linked with existing bed-load transport rate models in order to predict the temporal evolution of scour holes. An analytical model describing the relationship between the wall jet flow and the development of a local scour hole shape was reported and its predictions compared with experimental data.

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Ghoma, Mohamed Ibrahem. « The effect of wall jet flow on local scour hole ». Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5501.

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This thesis reports on investigations carried out to study of the effect of horizontal wall jets on rough, fixed and mobile beds in open channel flow. Experimental tests were carried out, using fixed and mobile sediment beds. Computer simulation models for the flow within the jet and resulting sediment transport were developed and their results analysed in this study. In the experimental phase, tests were carried out with both fixed and mobile sediment beds. The shape of the water surface, numerous point velocity measurements and measurements of the evolving scour hole shape were made. Detailed descriptions of the turbulent flow field over a fixed rough bed and for scour holes at equilibrium were obtained for a range of initial jet conditions. Fully turbulent, multiphase flow was modelled using the Fluent Computational Fluid Dynamics software. This was used to analyze the flow caused by a jet in a rectangle open-channel with a rough bed, and also the flow pattern in a channel with a local scour hole. The volume of fluid (VOF) multiphase method and K- model was used to model the fluid flow in both cases. The model predictions of velocity and shear stress were compared against experimental observations. The experimental data was used to develop new empirical relationships to describe the pattern of boundary shear stress caused by a wall jet over fixed beds and in equilibrium scour holes. These relationships were linked with existing bed-load transport rate models in order to predict the temporal evolution of scour holes. An analytical model describing the relationship between the wall jet flow and the development of a local scour hole shape was reported and its predictions compared with experimental data.

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Louis, Stephen. « Continuer à irriguer quand les lacs-réservoirs de barrage souffrent de taux de sédimentation sévères - Recommandations d'amélioration de la gestion du principal canal d'irrigation alimenté par l'ouvrage répartiteur de Canneau (Haïti) ». Doctoral thesis, Universite Libre de Bruxelles, 2019. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/288808.

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L’État haïtien, pour faire face à l’insécurité alimentaire que connaît sa population (à croissance rapide et à faible revenu), s’appuie particulièrement sur la Vallée du département de l’Artibonite qui constitue depuis toujours le véritable grenier agricole du pays, en fournissant, à elle seule, plus de 80% de la production rizicole nationale. Cette production agricole assure non seulement les besoins alimentaires de la population locale, mais également ceux particuliers des départements voisins (Ouest, Nord et Centre).L’irrigation de cette vaste plaine agricole (32400 ha de terres agricoles irrigables) est garantie, à plus de 75%, par le réseau d’irrigation établi en rive Gauche de l'ouvrage-partiteur de Canneau, alimenté par un Canal principal (CMRG) ayant un débit nominal de 40 m3/s.Néanmoins, ce Partiteur, source d’approvisionnement exclusive du CMRG, est lui-même régulé par le Barrage-réservoir de Péligre qui se trouve à 70 km plus en amont sur le fleuve de l’Artibonite. En termes hydrauliques, nos travaux ont d'abord examiné la situation du réservoir de Péligre. Alors qu'au moment de la construction il était initialement prévu d’y stocker 607 Mm3, il ne reste plus aujourd'hui qu'à peine 40% de cette capacité utile, en raison des dépôts sédimentaires qui se sont constitués année après année derrière le barrage.Cette sédimentation spectaculaire (due à l’érosion des bassins versants amont fort dégradés), combinée aux déficits pluviométriques, provoque en période d’étiage une rareté d’eau, des lâchers insuffisants et donc des déficits en eau utile envoyée en amont de ce Partiteur de Canneau. Cela impacte significativement le réseau d’irrigation aval, dont le CMRG. Nos travaux ont montré que la situation est d'autant plus critique que les débits eux-mêmes, en amont comme en aval du Partiteur, sont en fait très mal connus et devraient faire l'objet d'approches méthodologiques plus rigoureuses que celles déployées sur site actuellement.Aussi, face à ces constats, de nouvelles règles de distribution de l’eau s’imposent, pour continuer à irriguer et espérer obtenir un rendement agricole acceptable (souhaitable).Notre travail s'est ainsi donné pour objectif de contribuer à la mise en place des nouvelles règles de gestion de l’eau (répartition) au sein du réseau d’irrigation alimenté par le CMRG, pour continuer à fournir l’eau à l’irrigant en quantité acceptable (et connue). Cette amélioration de gestion a été envisagée à la fois en amont et en aval de ce réseau d’irrigation, particulièrement en ses différents nœuds-clés (Canal principal et Canal secondaire).La démarche méthodologique adoptée pour relever ce défi majeur s’appuie notamment sur un système d’information hydro-morpho-sédimentaire actualisé et de qualité. Il s’agit d’une base de données, riche en observations de hauteurs d’eau (lues aux stations limnimétriques), vitesses de surface au flotteur, champs de vitesse explorés au moyen d’un courantomètre et en données bathymétriques et granulométriques des tronçons des canaux étudiés, appréciées respectivement au moyen d’un GPS différentiel et du tamisage à sec.Les résultats fort encourageants obtenus permettent d'acquérir une meilleure compréhension du système et une amélioration particulière du réseau d’irrigation en rive gauche du Partiteur de Canneau. En s’appuyant sur les historiques de sédimentation du Lac-réservoir de Péligre (de 1960 à 2016), nous présentons un document de synthèse sur la sédimentation du Lac-réservoir de Péligre. Ce document met notamment en exergue le taux de sédimentation sévère de ce dernier (5.47 Mm3/an), qui continue d’augmenter encore aujourd’hui, ainsi que les conséquences de celui-ci sur les débits turbinés et la disponibilité de l’eau en amont du Partiteur de Canneau.Nous mettons également en évidence les formes irrégulières (Lit-non prismatique) des tronçons des canaux étudiés, via une vue axonométrique des profils en travers (issus de l’étude bathymétrique) des canaux d’irrigation en terre battue étudiés. Puis, nous présentons de manière détaillée le caractère très hétérogène des dépôts sédimentaires de ces derniers, à partir d’une analyse des représentations en Log-Probit des résultats du tamisage, construites au moyen du logiciel GrandPlots.En nous appuyant sur les mesures expérimentales des contraintes de Reynolds et des profils instantanés de vitesse (pris à intervalle de 64 ms), tirés de la base de données EPFL, nous avons montré qu’il faut absolument travailler dans les 18% inférieurs de la colonne d’eau (z/h<0.18) et en mode déficitaire, dans un écoulement turbulent comme celui-là, pour extraire de façon représentative et pertinente une pente expérimentale u*/, comme indicateur de u*.À l’issue d’un examen détaillé de la distribution verticale de la vitesse au canal secondaire FNE, nous validons un DMLWL (Dip-Modified-log-wake-law) à la fois en amont et en aval du réseau. Nous montrons que ceci permet de modéliser le Dip-phenomenon observé systématiquement au sein des profils explorés in situ. Nous proposons une relation entre le coefficient d’inégale répartition de la vitesse à la verticale αv (de Prony) et l’aspect ratio (W/h) pour tout le réseau d’irrigation étudié ;ceci afin d’obtenir une vitesse débitante (Ū), simplement à partir d’une prise de vitesse au flotteur, dans l’axe central d’écoulement.À partir des débits quantifiés à la section de référence du CMRG, via l’équation de continuité (Q=AŪ), nous fournissons un Abaque, diagramme à 3 entrées (débit (Qp), charge amont (H0) et ouverture de vanne (hv)), permettant aux vanniers de connaitre les débits au pont de fer correspondant aux différentes ouvertures de vanne et celui pour lequel le trop-plein (retour des eaux excédentaires vers le fleuve de l’Artibonite) commence à fonctionner.À l’égard des opérateurs locaux et gestionnaires du système, nous mettons enfin à disposition, des méthodes/outils simples et efficaces leur permettant de quantifier finement le débit au Canal principal en amont ainsi qu’au canal secondaire en aval, simplement à partir d’une mesure de hauteur d’eau (h) et de vitesse de surface au flotteur (Us).
Doctorat en Sciences agronomiques et ingénierie biologique
info:eu-repo/semantics/nonPublished

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Galeta, Martin. « Zanášení vývarů dnovými splaveninami ». Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2018. http://www.nusl.cz/ntk/nusl-371904.

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The main goal of this study is to define the technique to be used to assess the aggradation (by bed load) and degradation (of sediments) of the recessed as well as non-recessed stilling basins of rectangular cross section; when the hydraulic jump occurs in the stilling basin where the submergence coefficient equals 1,05. It consists of two parts, theoretical and experimental. The theoretical part summarizes the related theory on a hydraulic jump, design of a stilling basin, an incipient motion of sediment, an assessment of silting and scouring of the stilling basin. The second part, the actual experiment, led to the determination of the critical values essential for the assessment. For the evaluation, the nondimensional shear stress and the densimetric Froude number were used.

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18

Chassagneux, François-Xavier. « Etude expérimentale des processus hydro-sédimentaires sous le déferlement de vagues irrégulières ». Thesis, Grenoble, 2011. http://www.theses.fr/2011GRENI011.

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Cette thèse présente une simulation, en canal à houle, des processus naturels hydrodynamiques etde transport sédimentaire de la zone de déferlement bathymétrique. L’analyse spatio-temporelle dela structure moyenne et instantanée de l’écoulement repose sur un jeu de mesures hauterésolutions.On effectue une étude des processus de couche limite et de l’impact des processus desurface libre sur le fond sédimentaire.Un profil de plage en forme de terrasse est engendré par le déferlement de séries de vagues irrégulières(JONSWAP) sur un fond mobile constitué de sédiments de faible densité (_ _ 1.19). Dans cesconditions, la mesure acoustique (ADVP) de profils de vitesse, de concentration et de flux de sédimentsest synchronisée à des séquences d’images vidéo et à des mesures de hauteurs de vagues.Une analyse de l’évolution des quantités moyennes hydrodynamiques et de transport solide est réaliséedans la zone de déferlement. Une analyse à l’échelle intra-vague aborde la structure del’écoulement sous le déferlement de vagues irrégulières. Enfin, on s’attache à une comparaison de lacontrainte au fond sous une vague déferlée calculée par des modèles physiques, à celle obtenue parmesures directes
This thesis presents a wave channel simulation of the hydrodynamic and sediment transportprocesses in the wave breaking region. The spatio-temporal analysis of the mean and instantaneousflow structure relies on a full set of high resolution data. The study focuses on processes related tothe wave boundary layer and to the impact of surface breaking on the mobile bed.A terraced beach profile is generated by the breaking of irregular wave sequences (JONSWAP) on amobile bed constituted of low density sediments (_ _ 1.19). In these conditions, the acoustic measurementof velocity profiles, concentration profiles and sediment flux profiles are synchronised withsequences of video images and wave heights. An analysis of the evolution of mean hydrodynamicand sediment transport quantities is undertaken across the entire wave breaking zone. An intra-waveanalysis on the flow structure below irregular breaking waves is carried out. Finally, bed shear stressbelow a breaking wave predicted by different physical models and direct measurements, are comparedand discussed

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19

Desombre, Jonathan. « Modélisation vof de l’écoulement de jet de rive en surface et dans une plage perméable ». Thesis, Pau, 2012. http://www.theses.fr/2012PAUU3038/document.

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Cette thèse propose une modélisation numérique 2D des écoulements en zone de jet de rive avec un code Volume-Of-Fluid. Dans un premier temps, le détail de la structure interne de l’écoulement de jet de rive généré par l’effondrement d’un front d’onde turbulent sur une plage imperméable lisse est étudié. Le modèle numérique est ensuite étendu à la simulation des écoulements en milieu poreux internes à la plage. L’utilisation d’une unique équation de quantité de mouvement (VARANS) et de la méthode 1-fluide, permet de résoudre simultanément les écoulements de l’eau et de l’air à la surface et dans une plage perméable. Ce modèle a été confronté à une série de cas tests analytiques et à de récentes mesures expérimentales. Les résultats numériques montrent l’aptitude du modèle VOF-VARANS à reproduire les écoulements en zone de jet de rive sur une plage imperméable fixe
A 2D numerical modeling of flows in the swash zone is proposed using a Volume-Of- Fluid code. The detailed flow structure of a bore-driven swash event over an impermeable beach is first studied. The numerical model is then developed to account for porous media flow within the beach. The unique VARANS momentum equation and 1-fluid method used allow to solve simultaneously both surface and subsurface flows of air and water phases in the swash zone. This model is validated against a series of analytical tests cases and confronted to recent experimental measurements. The numerical results highlight the ability of the VOF-VARANS model to reproduce swash flows over and within a permeable beach

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20

Jeffcoate, Penelope. « Experimental and computational modelling of 3-D flow and bed shear stresses downstream from a multiple duct tidal barrage ». Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/experimental-and-computational-modelling-of-3d-flow-and-bed-shear-stresses-downstream-from-a-multiple-duct-tidal-barrage(13b4b1d2-d144-4510-bc46-50a25739e41c).html.

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The near-field depth-varying velocities and resulting bed stresses downstream from a tidal barrage have not previously been studied. The flow through and downstream of a row of seven open draft tubes in a barrage has been investigated through laboratory experiment in a wide flume, 3-D RANS CFD simulation and 2-D depth-averaged computation. When there is no turbine representation and hence negligible swirl in the draft tubes, agreement between the experiments and 3-D modelling is shown to be good, including the prediction of an asymmetric Coandă effect. With the addition of bulb bodies and vanes creating swirl in the draft tubes the velocity profiles are changed, with increased swirl directly downstream from the draft tubes and throughout the entire flume cross-section further from the barrage. The addition of rotors did not significantly alter the flow field patterns, for the stator/rotor combinations presented here. 3-D CFD could not accurately predict the velocity profiles resulting from the swirl in the ducts. The experiments and 3-D model shows that bed shear stress can be magnified markedly near the barrage particularly where the jets become attached to the bed. At full-scale this would result in a fully mobile bed with sand of typical grain size 1mm. One aim was to determine the distance downstream where depth-averaged modelling gives reasonable prediction and this is shown to occur around 20 tube diameters (20D) downstream of the barrage. Upstream of this, the depth-averaged modelling inaccurately predicts water level and bed shear as well as the 3-D flow field. The addition of swirl cannot be modelled using 2-D modelling, but by 20D downstream there is minimal velocity variation transversely and throughout the depth, indicating depth-averaged modelling would be applicable from this distance.

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21

Chaloupka, Martin. « Vliv účinků poddolování na volbu typu nosné konstrukce mostu v km 332,420 trati Dětmarovice - Č. Těšín ». Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2012. http://www.nusl.cz/ntk/nusl-225534.

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The aim of the master’s thesis was t odevelop alternative solutions supporting steel structure of the railway bridge on the undermined area. The range of single fields were chosen based on the location of existing substructures. Reducing the width of bridge openings were not allowed. Based on the geodetic survey plans were drawn up clear of the current state. On the basis of specifications for developing a detailed process was chosen variant Gerber’s beam reinforced with an arch in mean field. For this variant was performed structural analysis of the main parts of the main structure of the bridge, which was calculated with the effects of undermining. For variant Gerber’s beam were made clear drawings and drawing details of the selected steel bridge construction (new state). Further, detailed analysis of selected structural detail was made. Specifically, connecting rod to the main beam, which was designed optimal shape and thickness of the joints plate with a suitable radius of the firing to avoid plastification of the material in this area. Variant of the continuous beam without joints was prepared to. It has been observed, what is the effect of undermining on the stress in the construction of the bridge - was confronted with the effects on Gerber’s beam. To reduce stress in the construction of the bridge and compliance of ultimate state of applicability of the main beam has been designed bearing adjustment and after considering several options its implementation too. The economic comparison between the two variants was conducted. The assembling procedure was designed for both types of bridge structures. In the technical report we can read about due to the intention of building a new bridge and further we can find there other important technical information. In conclusion of the master’s thesis there has been recommended for the construction specific variant – from the perspective of an investor, and from the static aspect-view of the designer.

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22

Guan-ShiunHuang et 黃冠勳. « Measurement of bed shear stress in swash zone ». Thesis, 2012. http://ndltd.ncl.edu.tw/handle/51390792805358396838.

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碩士
國立成功大學
水利及海洋工程學系碩博士班
100
The hydrodynamics in swash zone has been an important subject for scientist and engineers due to its importance and complexity. Direct measurements of bed shear in the swash zone are presented. The data were obtained using a shear plate in laboratory swash zone. Data were obtained across the swash zone. The ﬂow velocities through the full swash cycle were obtained through measured velocity data. The measured stresses and measured ﬂow velocities were subsequently used to back-calculate instantaneous local skin friction coefﬁcients using the quadratic drag law. The experiments were conducted in a wave flume in Tainan Hydraulics Laboratory. The measurements indicate strong temporal and spatial variation in bed shear stress throughout the swash cycle, and a clear distinction between the uprush and backwash phase. For a single swash event, the maximum uprush bed shear stresses occur in the lower swash zone, within the range 0.05〈x/H 〈0.08.

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23

Chien-yehHo et 何建業. « Numerical simulation of bed shear stress in swash zone ». Thesis, 2013. http://ndltd.ncl.edu.tw/handle/19167847707032824333.

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碩士
國立成功大學
水利及海洋工程學系碩博士班
101
In this study, the dynamic process of solitary wave propagating from shore to swash zone is investigated numerically by using a 2-D Reynolds Averaged Navier-Stokes (RANS) solver. The turbulence field is described by using a non-linear k-ε turbulence closure model and the free surface configuration is tracked by the Volume Of Fluid (VOF) method. To validate the numerical model, the results were compared with theoretical solution and existing experimental data. The result of the validation shows good agreement. Besides, the numerical model is applied to investigate the horizontal velocity, bottom shear stress, turbulence kinetic energy (TKE) and boundary layer in the swash zone of the different bed roughness and bed slopes. The results show that the maximum velocity, bottom shear stress and turbulence kinetic energy exerted by uprush, and the maximum bottom shear stress and turbulence kinetic energy increase with the bed roughness and bed slope increase. The maximum velocity decreases as the bed roughness increase, but increases with the bed slope increases. The boundary layer vanishes during flow reversal and then grows during the backwash, and becomes depth limited at the end of the swash cycle. From the analysis of the velocity and turbulence field, the boundary layer flow was observed obviously as the bed roughness increases. When the bed slope increases the solitary wave in the form of spilling breaker to surging breaker.

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24

蔡立宏. « Bed shear stress and friction factor under random waves ». Thesis, 1991. http://ndltd.ncl.edu.tw/handle/86757898070163624253.

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25

Gao, Yu-feng, et 高郁峰. « Characteristics of bed shear stress in the coastal waters ». Thesis, 2012. http://ndltd.ncl.edu.tw/handle/18700815191142394144.

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碩士
國立中山大學
海洋生物科技暨資源學系研究所
100
A 3-axis acoustic Doppler Velocimeter (ADV) with high sampling rate was used to measure the bed shear stress and turbulence under wave-current interaction conditions in this study. Experimental sites include laboratory tank, Love River in Kaohsiung and Howan coastal waters in Pingtung. Bed shear stress is estimated primarily by the inertial dissipation method, also by the turbulent kinetic energy method and eddy correlation method. Results of the laboratory experiments indicate that the bed shear stress increases as both the flow speed and wave height increase, and the flow speed is a more important factor. Field experiments can be divided into several types. The first type is under slow flows and calm waves. Love River is a typical condition of this type with turbid waters and a low flow speed. During the experimental period the ADV correlations reach 90% or more. Because the river flow is quite small, no significant bed shear stress is produced and u* is mostly less than 1 cm/s. As a result the deposition effect is much larger than erosion, thus a very thick layer of mud is formed on the riverbed. The observations in Howan in April 2010 also reveal the condition of slow flows and small waves, and the bed shear stress is also quite small. Due to the factors of clean coastal waters and weak turbulence in this season, the quality of ADV signals is poor. The second type is under large flows and small waves, as shown from the observations of Howan in April 2011, during which the maximum speed reached 25 cm/s and wave heights less than 20 cm. In this experiment the shear stress is large, the u* are mostly greater than 0.8 cm/s and the value of the drag coefficient is 0.0021; the ADV signals have good quality and the inertial sub-range is well defined. The third type is under weak flows and large waves. The observations of Howan in July 2011 show significant rainfall and maximum wave heights of 90 cm. In this case the u* are mostly centered around 1 cm/s. The acoustic backscatter intensity is positively correlated with the turbidity and wave height. Sizable bed shear stress induced by the orbital velocity of waves contributes a significant part to the total bed shear stress.

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26

Zen, Lin Yio, et 林佑任. « Variation of bed shear stress during flood flow in compound channel ». Thesis, 1995. http://ndltd.ncl.edu.tw/handle/78613031566244408272.

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27

Jing-Hua, Lin, et 林敬樺. « Application of Slip Velocity Boundary Condition to EstimateWaves induced Bed Velocity and Bed Shear Stress ». Thesis, 2013. http://ndltd.ncl.edu.tw/handle/67232313706557911343.

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博士
國立中山大學
海洋環境及工程學系研究所
101
In the present study, a new and simple method for determining the slip velocity (also called the bed velocity) on the solid-fluid interface in the wave boundary layer is proposed. Based on experimental and numerical results, when waves travel over a rigid permeable seabed, a nonzero slip velocity exists at the solid-fluid interface. The defect of a small slip velocity has been found to occur in previous studies and is usually encountered in fluid-porous layer problems. In the wave-rigid permeable seabed problem, the slip effect depends on the properties of the seabed. The slip velocity boundary condition (SVBC) is one specification of the slip conditions and is usually applied to explain the slip phenomenon in a fluid-porous layer problem. However, the traditional SVBC or the slip velocity is only considered in a single flow, and the application of SVBC in harmonic motion is still an open problem that necessitates a simple formula for determining the slip velocity in realistic cases. The Stokes’ second problem and the slip length model (SLM) are applied to derive a new slip velocity and a slip factor in this paper. Both the permeability and the roughness of the seabed are chosen as the characteristic length of slip motion. The analytical solution shows that the new slip velocity depends on the wave period and the pressure gradient, and the slip factor is related to the wave Reynolds number, the permeability, and the roughness of the seabed. The resultant slip velocity shows good agreement with the experimental results. Using the slip factor to determine the bed shear stress in the laminar/turbulent-rough regimes is the second part in this study. A simple relationship is developed to theoretically estimate the wave friction factor in various flow regimes in the porous media based on the slip factor formula. The theoretical formula shows that the wave friction factor varies inversely with the relative bed roughness,A/ks , over a rough bed and that it can be conveniently determined if wave conditions and sediment parameters are known without using a specific regression formula deduced from experiments. A laboratory experiment that directly measures the wave-driven bed shear stress dominant in the turbulent regime with a permeable bed is used to examine the newly-derived relationship. In the laminar regime, the comparison demonstrates that the theoretical results determined by the proposed formula are in good agreement with existing measurements. In the turbulent-rough regime, the influence of eddy viscosity is considered in the present model and the zero-equation model is used to estimate an average eddy viscosity. The theoretical wave friction factor is reasonably close to the experimental measurement, and considerably better than that obtained by other existing regressions. It is also found that the wave friction factor in the small zone can be described by the present model, with comparisons showing that the slip factor theory can be extended to estimate the wave friction factor in the turbulent-rough regime. Additionally, the proposed relationship is demonstrated to be effectively used in an alternate rough bed. Experimental results further indicate that the wave friction factor in porous medium is affected by the permeability of the sediment. Based on many comparisons with previous results, it is concluded that the method provided by the present study can be applied for determining the slip velocity and bed shear stress and setting up the parameter in the real case and numerical model.

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28

Lai, Tai-Zon, et 賴泰榮. « Shear Stress Distribution on Channel Bed of a Scour Hole by Free Overfall ». Thesis, 1996. http://ndltd.ncl.edu.tw/handle/91549615834655806231.

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碩士
國立中興大學
土木工程學系
84
AbstractThe main objective of this study was to investigate the variations of the distribution of shear stress along the scour hole downstream of a weir during the evolution of the scour hole.The shapes of the scour hole were selected based on the results of the local scour testswith standard sand. An electromagnetic current was used to measure the flow field in theplunge pool. Based on the analysis of the laboratory dada, it was found that in general the scour holecan be described with two straight lines and one curve or semi-circle. An exponentialfunction was used to describe the dimensionless maximum scour depth. Expressionsfor the unit erosion rate and area factor were also developed. These function and expressionwere proved by other investigators.Both the energy and momentum correction factors, trere were found to increase from the toe of the weir. Their values remained in the same order of magnitude along the first straight lineof the scour hole. The values of both increased for one to three order of magnitude alongthe curved portion of the hole due to the free overfall jet impact. The values decreased tobe around 1 along the second straight line due to the dissipation of energy. The relationshipof alpha and bata was also satisfied along the second straight line of the scour hole.The shear stress was found to decrease in the downstream direction of the scour hole forboth the results of strain transducter and strain gages. These results were probably dueto the fact that the energy dissipated in the downstream direction. For a given distragethe value of the shear stress decreased with time, and eventually approached the criticalshear stress of the sand particle.

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29

Lo, Rou-Yu, et 羅若瑜. « Microscopic simulations of rock abrasion induced by bed shear stress and particle saltation ». Thesis, 2011. http://ndltd.ncl.edu.tw/handle/23195502689070111755.

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碩士
國立交通大學
土木工程學系
99
River discharge in Taiwan varies a lot during flooding season; this situation often results in unstable river channel. The intensive erosion of bedrock during flood may also endanger the stability of cross-river structures, especially for cases of river bed composed of soft rocks. This study makes use of numerical simulation as “virtual erosion test” to explore the mechanisms of rock erosion. In the simulation, rock material is modeled as a granular assemblage with inter-particle bonding; the erosion process is simulated as particles’ release due to de-bonding. Virtual rock specimen are subjected to boundary loads from either bed shear stress or saltating particle to simulates physical erosion experiments. The purpose of this thesis is to investigate the important factors that may control the erodibility of soft rock subjected to bed shear stress and particle saltation; also, the dissipated energy and bonding failure associated with the occurrence of rock erosion are studied. For erosion due to bed shear stress, simulated results show that the number of de-bonded particles raises as the bed shear stress increases. It is found the shear stress required for the initiation of a de-bonded particle in fresh soft rock material is significantly higher than the typical in-situ bed shear stress that may occur in a flood. It appears clear water current alone may hardly erode a fresh rock material. However, it is common to see the degradation or weathering of soft rock exposed to the periodical variation of water level (i.e., subjected to drying-wetting cycles). These weakening processes are likely to cause the rock material become more erodible. Saltating abrasion can be a consequence of impacts of gravels traveling along with water flow; the impact results in the local failure and causes abrasion of river-bed rock material. The major factors affecting the erodibility and erosion rate are examined through a series of virtual erosion tests. Simulated results show that more de-bonded particles may occur for a condition with higher impact speed, higher impact angle, larger gravel size, higher Young’s modulus, or lower rock strength. Besides, a good correlation relationship between the number of de-bonded particles and the accumulated dissipated energy is notable.

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30

Cantrell, William. « Method of Evaluation for Stream Bed Shear Stress and Sediment Transport Capacity in Urbanizing Watershed : Implications for Stream Restoration ». 2009. http://trace.tennessee.edu/utk_gradthes/27.

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In the field of stream restoration, use of a one-dimensional flow model with typical Manning’s n values for an open channel greatly over-predicts bed shear values. This, in turn, incorrectly predicts the size of the mobile fraction on the bed and if used in a bedload transport function over-predicts mass movement of the bed material. This study identified 12 sites for which watershed and reach characteristics were compiled, and bedload sampling was performed. This information was used to produce an empirical relationship between reach pebble count data and an effective Manning’s n value that can be used to produce accurate bed-shear values in a one-dimensional flow model. With this tool, simple field activities can provide sufficient information to allow a stream restoration practitioner to accurately predict bed shear values. Relationships between watershed characteristics and reach scale bed characteristics, and bed depositional patchiness and sediment supply were also explored. It was found that Wolman Pebble Count data can be used to predict an effective Manning’s n value with sufficient accuracy, while watershed characteristics were not adequate to predict reach scale bed characteristics and bed depositional patchiness was valuable as a threshold indicator but not as a predictive variable.

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31

Cantrell, William R. « Method of evaluation for stream bed shear stress and sediment transport capacity in urbanizing watershed implications for stream restoration / ». 2009. http://trace.tennessee.edu/utk_gradthes/27.

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32

Chen, Xingnian. « Numerical Study of Abutment Scour in Cohesive Soils ». 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2008-12-225.

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This research is part of the extension of the SRICOS-EFA method for predicting the maximum scour depth history around the bridge abutment. The basic objective is to establish the equation for predicting the maximum bed shear stress around the abutment at the initial condition of scouring. CHEN3D (Computerized Hydraulic ENgineering program for 3D flow) program is utilized to perform numerical simulations and predict bed shear stress before scouring. The Chimera technique incorporated in CHEN3D makes the program capable of simulating all kinds of complex geometry and moving boundary. CHEN3D program has been proven to be an accurate method to predict flow field and boundary shear stress in many fields and used in bridge scour study in cohesive soils for more than ten years. The maximum bed shear stress around abutment in open rectangular channel is studied numerically and the equation is proposed. Reynolds number is the dominant parameter, and the parametric studies have been performed based on the dimensional analysis. The influence of channel contraction ratio, abutment aspect ratio, water depth, abutment shape, and skew angle has been investigated, and the corresponding correction This research is part of the extension of the SRICOS-EFA method for predicting the maximum scour depth history around the bridge abutment. The basic objective is to establish the equation for predicting the maximum bed shear stress around the abutment at the initial condition of scouring. CHEN3D (Computerized Hydraulic ENgineering program for 3D flow) program is utilized to perform numerical simulations and predict bed shear stress before scouring. The Chimera technique incorporated in CHEN3D makes the program capable of simulating all kinds of complex geometry and moving boundary. CHEN3D program has been proven to be an accurate method to predict flow field and boundary shear stress in many fields and used in bridge scour study in cohesive soils for more than ten years. The maximum bed shear stress around abutment in open rectangular channel is studied numerically and the equation is proposed. Reynolds number is the dominant parameter, and the parametric studies have been performed based on the dimensional analysis. The influence of channel contraction ratio, abutment aspect ratio, water depth, abutment shape, and skew angle has been investigated, and the corresponding correction factors have been proposed. The study of the compound channel configuration is conducted further to extend the application of the proposed equation. Numerical simulations of overtopping flow in straight rectangular channel, straight compound channel and channel bend have been conducted. The bridge deck is found to be able to change the flow distribution and the bed shear stress will increase significantly once overtopping. The influence of the channel bend curvature, abutment location in the channel bend, and the abutment shape is also investigated. The corresponding variation of the bed shear stress has been concluded. The scour models, including the erosion rate function, roughness effect, and the turbulence kinetic energy, have been proposed and incorporated into the CHEN3D program. One flume test case in NCHRP 24-15(2) has been simulated to determine the parameters for the roughness and the turbulence kinetic energy. The prediction of the maximum scour depth history with the proposed model is in good agreement with the measurement for most cases. The influence of overtopping flow on the abutment scour development is also studied and the corresponding correction factor is proposed.

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33

Tait, Simon J., J. Heald, I. K. McEwan, M. Soressen, G. Cunningham, B. Willetts et D. Goring. « Probabilistic modelling of bed-load composition ». 2009. http://hdl.handle.net/10454/2850.

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No
This paper proposes that the changes which occur in composition of the bed load during the transport of mixed-grain-size sediments are largely controlled by the distributions of critical entrainment shear stress for the various size fractions. This hypothesis is examined for a unimodal sediment mixture by calculating these distributions with a discrete particle model and using them in a probabilistic calculation of bed-load composition. The estimates of bed-load composition compare favorably with observations of fractional transport rates made in a laboratory flume for the same sediment, suggesting that the hypothesis is reasonable. The analysis provides additional insight, in terms of grain mechanics, into the processes that determine bed-load composition. These insights strongly suggest that better prediction methods will result from taking account of the variation of threshold within size fractions, something that most previous studies have neglected.

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34

Lai, Chin-Chun, et 賴志鈞. « Measurement and analysis of downstream flow and shear stress induced by a submerged vane in a fixed bed channel ». Thesis, 2009. http://ndltd.ncl.edu.tw/handle/39396142096396618671.

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碩士
國立宜蘭大學
土木工程學系碩士班
97
Submerged vane system is a technique for river bank protection. By inducing a wake vortex downstream, the secondary vortex in the channel bend responsible for the erosion of the concave bank is reduced and the foundation of the bank is strengthened. Due to the viscous and turbulent dissipation of the fluid flow, the strength of the vane-induced near bed transverse shear stress gradually decreases both in the transverse and stream-wise direction. Using a 3D Acoustic Doppler Velocimeter, this study measured the near bed transverse velocity induced by vanes with various dimensions. The vane-induced transverse bed shear stress is then calculated by utilizing a formula deriued by previous researchers. The results show that the strength of the wake vortex at 10 water-depths downstream of the vane drops down to half of the strength at 1 water-depths downstream. The performance of the vanes with 25° to the flow is better than those with 15°. In the cases studied, the optimal vane-height is with in the range of 0.52~0.8 water-depths and the optimal vane-length is 1.6 water-depths. The selection of the vane-dimension thus relies up on the purpose of the vane.

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35

Glasbergen, Kenneth. « The Effect of Coarse Gravel on Cohesive Sediment Entrapment in an Annular Flume ». Thesis, 2014. http://hdl.handle.net/10012/8288.

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The amount and type of cohesive sediment found in gravel river beds can have important implications for the health of aquatic biota, surface/groundwater interactions and water quality. Due to landscape disturbances in the Elbow River watershed, increased sediment fluxes have negatively impacted fish habitat, water quality and water supply to the City of Calgary. However, little is known about the source of cohesive sediment and its interaction with gravel deposits in the Elbow River. This research was designed to: 1) quantify the transport properties (critical shear stress for erosion, deposition, porosity, settling velocity, density) of cohesive sediment and 2) evaluate the potential for coarse gravel to entrap cohesive sediment in the Elbow River. A 5m annular flume was used to conduct erosion and deposition experiments using plane and coarse bed conditions. The critical shear stress for deposition and erosion of the Elbow River cohesive sediments was 0.115Pa and 0.212Pa, respectively. The settling velocity of the cohesive sediment had an inverse relationship between floc size and settling velocity for larger flocs, due to a decrease in floc density with increased size. Cohesive sediment moved from the water column into the gravel bed via the coupling of surface and pore water flow. Once in the gravel bed, cohesive sediments were not mobilized from the bed because the shear produced by the flume was less than the critical shear to mobilize the gravel bed. Using a model developed by Krishnappan and Engel (2006), an entrapment coefficient of 0.2 was determined for the gravel bed. Entrapment coefficients were plotted against substrate size, porosity and hydraulic conductivity, demonstrating a relationship between entrapment coefficient and these variables. It was estimated that 864kg of cohesive sediment is stored in the upper 0.08m of a partially submerged point bar in the Elbow River. Accordingly, when flow conditions are sufficient to mobilize the gravel bed and disturb the amour layer, cohesive materials may be entrained and transported into the Glenmore Reservoir, where it will reduce reservoir capacity and may pose treatment challenges to the drinking water supply.

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Antony, S. J., M. Al-Sharabi, Nejat Rahmanian et T. Barakat. « Shear stress distribution within narrowly constrained structured grains and granulated powder beds ». 2015. http://hdl.handle.net/10454/7544.

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An experimental study is presented here to understand the stress transmission characteristics under different geometrical arrangements of particulates inside a narrow chamber subjected to axial compression loading. The multi-grain systems considered here are face-centred, simple cubic and poly-dispersed structures, as well as inclusions embedded inside seeded, unseeded and cohesive powder bed of Durcal (calcium carbonate). The distribution of the maximum shear stress, direction of the major principal stress and shear stress concentration factor were obtained using photo stress analysis tomography (PSAT). The results show that the maximum shear stress distribution in the simple cubic structure is chain-like and self-repetitive, i.e., a single grain behaviour is representative of the whole system. This is not the case in the case of other granular packing. In the case of the inclusion surrounded by powder media, the maximum shear stress distribution in the inclusion occurs through ring-like structures, which are different from those observed in the structured granular packing. This tendency increases for an increase in the cohesivity of the surrounding particulates. In the granular systems, the direction of the major principal stress is mostly orthogonal to the direction of loading except in some particles in the random granular packing. In the case of inclusion surrounded by Durcal particulates, the directional of the major principal stress acts along the direction of the axial loading except in the ring region where this tends to be oblique to the direction of axial loading. Estimates of the shear stress concentration factor (k) show that, k tends to be independent of the structural arrangement of granular packing at higher load levels. In the case of inclusion surrounded by powder bed, k for the seeded granulated particulate bed is mostly independent of the external load levels. In the case of unseeded particulate (granulated) bed, a fluctuation in k is observed with the loading level. This suggests that the seeded granules could distribute stresses in a stable manner without much change in the nature of shear stress-transmitting fabric of the particulate contacts under external loading. An increase in the cohesion of particulate bed results in more plastic deformation as shown by the differential shear stress concentration factor. The results reported in this study show the usefulness of optical stress analysis to shed some scientific lights on unravelling some of the complexities of particulate systems under different structural arrangements of grains and surrounding conditions of the inclusions in particulate media.

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Thèses sur le sujet « Shear stress bed »

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