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1
Lovick, Jonathon. "Horizontal, oil-water flows in the dual continuous flow regime." Thesis, University College London (University of London), 2004. http://discovery.ucl.ac.uk/1383486/.
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The research presented in this thesis is concerned with the flow behaviour of two-phase, liquid-liquid, oil-water flow through horizontal pipes. The test liquids used were oil (density 828kg/rn3, viscosity 6x iO 3 Pa s) and water, with experiments carried out in a purpose built test facility with a stainless steel pipe (internal dia. 38mm, length 8m). Visual observation of the flow was possible at low mixture velocities through a lm transparent pipe at the end of the test section. At higher mixture velocities local probes were used for flow pattern identification. These local probes were a conductivity probe for identifying the continuous phase, and a high frequency impedance probe for measuring local phase distribution. A dual sensor impedance probe was also developed for measuring local drop velocity and also the drop chord length distributions. Pressure gradient was also measured using a differential pressure transducer, and in-situ phase fractions were obtained using Quick Closing Valves. Experimental results show that the dual continuous flow regime, where both phases retain their continuity while there is mixing at the interface, dominates at all input oil fractions at low mixture velocities and intermediate oil fractions at high mixture velocities. In general the pressure drop of the two-phase mixture is lower than that of single phase oil. At higher mixture velocities a minimum in pressure gradient appeared at high oil fractions perhaps as a combination of the drag reduction phenomenon and the relative fraction of the oil and water layers in the pipe. At the highest mixture velocity this minimum was at the boundary of fully dispersed oil continuous flow with dual continuous flow. Velocity ratios are shown to increase with increasing oil fraction at low mixture velocities, with this trend reversing at high mixture velocities. These trends in the pressure gradient and velocity ratio can be explained using the phase distribution diagrams, with the interfacial curvature greatly affecting velocity ratio. Local chord length data shows that, in general, drop sizes decrease with increasing distance from the interface and that oil drops tend to be slightly larger than water drops. Mixture velocity did not significantly affect the drop size of either phase in dual continuous flow. A modified version of the two-fluid model was suggested for dual continuous flow that treats the upper and lower layers as dispersions and uses experimental entrainment to calculate their properties. Better predictions were obtained when friction factors that accounted for the drag reduction phenomenon were used to calculate wall shear stresses.
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Watson, Martin James. "Flow regime transitions and associated phenomena." Thesis, Imperial College London, 1999. http://hdl.handle.net/10044/1/8790.
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Rashid, Bilal. "Simplifying reservoir models by flow regime." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/11104.
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This study focuses on the interaction between geological heterogeneity and the reservoir processes which govern fluid flow in porous media. We have developed and tested a measure of heterogeneity which uses the coefficient of variation of the vorticity of the flow field to quantify the impact of geological uncertainty on oil recovery. We go on to explore the vorticity formulation of the equations of motion in porous media as a basis for understanding reservoir dynamics, particularly in the presence of heterogeneity and density differences. We derive dimensionless numbers to quantify the relative importance of viscosity and density differences, molecular diffusion, dispersion, and permeability heterogeneity on reservoir flow behaviour. This approach is used to develop an objective measure of the impact of permeability heterogeneity on reservoir performance, which we have compared with traditional heterogeneity indices and shown how it may be used for realistic 2D and 3D geological models. We have used our heterogeneity index, and the dimensionless numbers to analyse the impact of heterogeneity, buoyancy effects, mobility ratio and dispersion on breakthrough time and recovery for first contact miscible gas injection processes using geologically realistic reservoir models. We find that the new heterogeneity number, in conjunction with these dimensionless numbers, provides meaningful results for real non-linear reservoir flows. We present phase diagrams which show how reservoir performance depends on mobility ratio, viscous-gravity ratio, and heterogeneity. We have proposed that the phase diagram, and a comparison of these dimensionless numbers can be used to identify the key factors which control recovery, thus assisting the engineer in determining appropriate enhanced oil recovery (EOR) techniques, without resort to detailed flow simulation. This will enable a quick, and more robust, evaluation of the impact of geological uncertainty in the field.
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Nema, Gaurav. "Flow regime transitions during condensation in microchannels." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22592.
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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008.Committee Chair: Garimella, Srinivas; Committee Member: Ghiaasiaan, Seyed Mostafa; Committee Member: Mistree, Farrokh.
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Kamram, Muhammad. "Analysis of Various Complex Flows of Micropolar Fluids in the Slip Flow Regime." Thesis, Curtin University, 2018. http://hdl.handle.net/20.500.11937/70737.
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Four mathematical models have been developed to study the slip flow of micropolar fluids over a stretching/shrinking sheet under the influence of slip and the Newtonian heating conditions at the boundary. The optimal homotopy analysis method is applied for the solutions of these models. The results obtained from this study are useful in liquid crystals, polymeric suspensions, polishing artificial heart valves and internal cavities.
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SARE, ALEXANDRE REIS. "ANALYSIS OF FLOW REGIME IN CURUÁ-UNA DAM, PARÁ." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2003. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=3749@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORA análise das condições de fluxo na barragem de Curuá-Una (Pará) tem como objetivo avaliar a viabilidade geotécnica quanto à elevação do nível de operação do reservatório. A Usina de Curuá-Una (operada pela REDE Celpa) é responsável pelo abastecimento elétrico de Santarém. No entanto, nos horários de grande consumo, a produção de energia tem se mostrado insuficiente. O alteamento do reservatório de Curuá-Una é uma alternativa para o aumento de geração energética. Curuá-Una destaca-se por ser fundada em terreno arenoso, solução poucas vezes utilizada no mundo. A barragem de terra é do tipo zonada, com altura máxima de 26m e comprimento de 600m. Os parâmetros geotécnicos necessários para as análises do presente trabalho foram obtidos em ensaios de laboratório, em informações referentes à construção e em dados de instrumentação durante a operação da barragem. As análises numéricas foram realizadas com o programa FLOW3D. A retroanálise do regime de fluxo, feita com base na piezometria, possibilitou a estimativa das permeabilidades dos diversos materiais. A partir destes dados foi possível simular as poropressões associadas a diferentes níveis do reservatório. Foram definidos três níveis de alerta (normal, atenção e emergência) referentes à segurança da barragem. As análises indicam que a barragem opera atualmente dentro do nível normal e que um alteamento de 1,5m do reservatório não afeta a condição de segurança. O aumento das subpressões na base da barragem foi também avaliado, com os resultados mostrando um incremento máximo de 5 por cento.
The analysis of flow conditions in Curuá-Una Dam, State of Pará, has the objective of evaluating the geotechnical feasibility of raising the operation level of the reservoir. Curuá-Una Power Plant, operated by REDE Celpa, is responsible for the electric supply of Santarém city. However, in periods of peak consumption, the energy production has been insufficient. Raising of Curuá-Una reservoir is an attractive alternative for increasing energy production. Curuá-Una Dam is distinguished for being constructed on sandy alluvial soil, which is a solution rarely used in the world. The earth dam is zoned, with maximum height of 26m and crest length of 600m. The geotechnical parameters were obtained from laboratory tests, field instrumentation data and construction reports. The numerical analyses were carried out with FLOW3D program. A back-analysis of flow behavior was performed for evaluating permeability parameters, taking into account results from piezometers installed in the dam and in the foundation materials. These parameters were used to predict pore pressures associated to different reservoir levels. Three levels of alert conditions (normal, attention and emergency) referring to the safety of the dam have been defined. The analyses indicated that the dam is operating within normal levels and a 1.5m rising of the reservoir shall not affect dams safety. The uplift pressures, due to different reservoir levels, have also been evaluated, with results showing a maximum increment of 5 percent.
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Mohapatra, Chinmoy Krushna. "Computational Study of Internal Two Phase Flow in Effervescent Atomizer in Annular Flow Regime." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470741568.
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O'Donnell, Brynn Marie. "The Flow Regime of Function: Influence of flow changes on biogeochemical processes in streams." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/101660.
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Streams are ecosystems organized by disturbance. One of the most frequent disturbances within a stream is elevated flow. Elevated flow can both stimulate ecosystem processes and impede them. Consequently, flow plays a critical role in shifting the dominant stream function between biological transformation and physical transportation of materials. To garner further insight into the complex interactions of stream function and flow, I assessed the influence of elevated flow and flow disturbances on stream metabolism. To do so, I analyzed five years of dissolved oxygen data from an urban- and agriculturallyinfluenced stream to estimate metabolism. Stream metabolism is estimated from the production (gross primary production; GPP) and consumption (ecosystem respiration; ER) of dissolved oxygen. With these data, I evaluated how low and elevated flows differentially impact water quality (e.g., turbidity, conductivity) and metabolism using segmented metabolism- and concentration- discharge analyses. I found that GPP declined at varying rates across discharge, and ER decreased at lower flows but became constant at higher flows. Net ecosystem production (NEP; = GPP - ER) reflected the divergence of GPP and ER and was unchanging at lower flows, but declined at higher discharge. These C-Q patterns can consequently influence or be influenced by changes in metabolism. I coupled metabolism-Q and C-Q trends to examine linked flow-induced changes to physicochemical parameters and metabolism. Parameters related to metabolism (e.g., turbidity and GPP, pH and NEP) frequently followed coupled trends. To investigate metabolic recovery dynamics (i.e., resistance and resilience) following flow disturbances, I analyzed metabolic responses to 15 isolated flow events and identified the antecedent conditions or disturbance characteristics that most contributed to recovery dynamics. ER was both more resistant and resilient than GPP. GPP took longer to recover (1 to >9 days, mean = 2.5) than ER (1 to 2 days, mean = 1.1). ER resistance was strongly correlated with the intensity of the flow event, whereas GPP was not, suggesting that GPP responds similarly to flow disturbances, regardless of the magnitude of flow event. Flow may be the most frequent disturbance experienced by streams. However, streams are exposed to a multitude of other disturbances; here I also highlight how anthropogenic alterations to streams – namely, burying a stream underground – can change biogeochemical function. This thesis proposes novel frameworks to explore the nexus of flow, anthropogenic disturbances, and stream function, and thereby to further our understanding of the complex relationship between streams and disturbances.Master of Science
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Alvarez, Martinez José Manuel. "Foam-flow behavior in porous media : effects of flow regime and porous-medium heterogeneity /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Chen, Li-Kwen. "Unsteady flow and heat transfer in periodic complex geometries for the transitional flow regime." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2008. http://scholarsmine.mst.edu/thesis/pdf/Chen_09007dcc804bed71.pdf.
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Thesis (Ph. D.)--Missouri University of Science and Technology, 2008.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed May 12, 2008) Includes bibliographical references.
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Alssayh, Muammer Ali Ahmed. "Slug Velocity Measurement and Flow Regime Recognition Using Acoustic Emission Technology." Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/8399.
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Slug velocity measurement and flow regime recognition using acoustic emission technology are presented. Two non-intrusive and three intrusive methods were employed to detect the slug regime and measure its velocity using AE sensors. For the non-intrusive methods, AE sensors were placed directly on the exterior of the steel pipe section of the test rig with and without clamps. The intrusive method involved using different waveguide configurations with the AE sensors flush with the inner wall of the pipe.
The experimental study presented investigated the application of Acoustic Emission (AE) technology for detecting slug velocity in addition to differentiating flow regime in two-phase (gas/liquid) flow in horizontal pipes. It is concluded that the slug velocity can be determined with acoustic emission (AE) sensors. The results were compared to slug velocities measured using high speed camera (HSC) and Ultrasound Transit Time (UST) techniques with good agreement between the three techniques at low gas void fraction (GVF). However, at high GVF (up to 95%) where the UST technique has limitations in application, the AE and HSC offered a good agreement. Flow regimes were also differentiated by using a combination of AE technology and Kolmogorov–Smirnov test technique. Stratified, slug and bubble regimes were recognised differentiated.
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Rawes, W. "The application of signal analysis techniques based on chaos theory to flow regime identification." Thesis, Cranfield University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245497.
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O'Gorman, William Thomas. "Development of a directional flow probe for the hypersonic regime." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq29370.pdf.
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Terry, Stephen D. "On Flame Stability In The Hysteresis Regime In Co-Flow." NCSU, 2005. http://www.lib.ncsu.edu/theses/available/etd-04182005-093850/.
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This study documents experiments performed on lifted turbulent diffusion flames in the hysteresis regime with air co-flow. Undiluted methane, ethylene, and propane were used as fuels and two nozzle sizes were used. The results confirm the non-linearity of the lift-off height with nozzle velocity, showing a previously undocumented region where lifted flame height increases as fuel velocity is decreased and that reattachment nozzle velocity varies linearly with co-flow. Using jet relations from Tieszen, the local excess jet velocity was computed and found to vary linearly for flames lifted well above the nozzle. The effect of co-flow was captured using an effective local excess jet velocity, similar to the effective nozzle jet velocity proposed by Montgomery used in conjunction with the results of Khalghatgi. Local excess jet velocities at the reattachment point were also compared for varying co-flow and found to be consistent between co-flow cases. This threshold velocity was found to vary with the inverse of the laminar burning velocity of the fuel squared. Relations for reattachment nozzle velocity and flame lift-off height at reattachment were also determined. The results extend the work of Khalghatgi into the hysteresis regime and complement the work of Gollahalli in determining the mechanisms that support flame stability in the hysteresis regime. Any comprehensive theory for flame stability will have to explain some of the unexpected results seen in the hysteresis regime and incorporate the findings of this study.
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Triplett, Kimberly Ann. "Two-phase flow regime maps and pressure drop in microchannels." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/16867.
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Kuidjo, Kuidjo Emmanuel Vianney. "Towards a predictive model to reproduce flow regime transitions in gas-liquid flows with Neptune CFD : from a dispersed to a separated regime." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0456.
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Dans les réacteurs nucléaires, divers régimes d’écoulement gaz-liquide peuvent apparaître avec des transitions entre eux. La modélisation de ces transitions dans les codes CFD 3D requière le traitement d’interfaces déformables de différentes tailles, la prise en compte d’interactions par coalescence et fragmentation ainsi que le développement de lois de fermeture indépendantes du régime. Ce travail vise la modélisation et la simulation de l’hydrodynamique des écoulements gaz-liquide adiabatiques grâce à un modèle bi-fluide à trois champs dans Neptune CFD. Dans une première étape, un modèle avec un champ liquide continu et deux champs de gaz dispersés représentant petites et grandes bulles est utilisé pour simuler des écoulements cap et churn avec un taux de vide jusqu’à 0.5 et une emphase est mise sur la prédiction de l’aire interfaciale. Dans une seconde étape, le deuxième champ dispersé est remplacé par un champ hybride continu/dispersé représentant les grandes bulles et les régions continues de gaz. Le modèle est validé sur plusieurs régimes d’écoulements en tuyaux de large diamètre et dans des canaux rectangulaires confinésIn nuclear reactors, several regimes of gas-liquid flows may occur with some transitions between them. The main challenges associated with simulating these transitions in 3D CFD codes are associated with deformable interfaces of different sizes, accounting for coalescence and breakup interactions between gas structures and developing flow regime independent closure relations. This work aims at modelling and simulating the hydrodynamics of adiabatic gas-liquid flows thanks to a three-field two-fluid model in Neptune CFD. In a first step, a model with one continuous liquid field and two dispersed gas fields for small and large bubbles is used to simulate cap and churn flows with a void fraction up to 0.5 and a focus is put on the interfacial area prediction. In a second step, the second dispersed field is replaced by a hybrid continuous/dispersed field representing both large bubbles and continuous gas regions. The model is validated on several flow regimes in large diameter pipes and in confined rectangular channels
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Martins, João Pedro Fernandes Farinha de Oliveira. "Avaliação ecohidrológica de caudais modificados e de caudais ecológicos em troços de rios modificados." Master's thesis, ISA/UTL, 2012. http://hdl.handle.net/10400.5/5373.
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Mestrado em Gestão e Conservação de Recursos Naturais - Instituto Superior de AgronomiaThis study aimed to improve our understanding of the ecohydrological characteristics of environmental and modified flows in Portuguese rivers considered Heavily Modified Water Bodies (HMWB), using the Indicators of Hydrologic Alteration (IAH) method. For a given set of "heavily modified river sections", this study did the characterization and analysis of present flow regimes observed, natural flow regimes, and ecological flow requirements simulated by the method of INAG, DSP (2002). Based on Indicators of Hydrologic Change, the determination of the deviations from natural regimes was performed for the present hydrological regimes: both modified and ecological. The analysis of indicators of hydrologic alteration, based on ecohydrologic assumptions that guide the definition of environmental flow regimes, allowed to develop proposals for environment mitigation, whose effectiveness should be evaluated in the context of monitoring the ecological quality of HMWB sections in order to achieve the environmental objectives set out in national and European legislation on water resources the Water Frame Directive WFD (Directive 2000/60/EC) transposed to the Portuguese legislation by the Water Law - Law n.º 58/2005, 29 December 2005
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Doup, Benjamin. "Methodology Development of a Gas-Liquid Dynamic Flow Regime Transition Model." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1409031809.
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Pierre, Sylvain. "Aerodynamics of wings with leading-edge flow separation in supersonic regime." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60716.
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Analytical methods solving for the separated flow over delta wings have been based on the slender-body theory, which applies for wing geometries of small aspect ratio. The slender-body solutions are independent of the Mach number, and therefore, for supersonic flow, cannot appropriately take into account the directional propagation of disturbances. The slender-body model is attractively simple of the pressure distribution and lift prediction, but in the supersonic regime it can lead to large errors when the wing geometry is not very slender with respect to the Mach cone.In the treatment of attached flow over arbitrary wing-body combinations in supersonic flow regime, the method of Velocity Singularities based on conical motion provides a more accurate alternative over slender-body theory by considering the appropriate boundary condition of flow disturbances outside the wings.
This thesis presents an extension of the method of Velocity Singularities for the analysis of the separated flow over thin delta wings.
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伍智榮 and Chi-wing Ng. "Interactions of vortices from two circular cylinders in bistable flow regime." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B3123608X.
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Hamedi, Amirmasoud. "Advanced Characterization of Hydraulic Structures for Flow Regime Control: Experimental Developement." FIU Digital Commons, 2017. http://digitalcommons.fiu.edu/etd/3369.
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A good understanding of flow in a number of hydraulic structures, such as energy dissipators, among others, is needed to effectively control upstream and downstream flow conditions, for instance, high water depth and velocity to ensure, scouring, flow stability and control scouring, which is thus crucial to ensuring safe acceptable operation. Although some previous research exists on minimizing scouring and flow fluctuations after hydraulic structures, none of this research can fully resolve all issues of concern. In this research, three types of structures were studied, as follows: a) a vertical gate; b) a vertical gate with an expansion; and c) a vertical gate with a contraction. A Stability Concept was introduced and defined to characterize the conditions downstream of gated structures. When established criteria for stability are met, erosion is prevented. This research then investigated and evaluated two methods to classify the flow downstream of a gated vii structure to easily determine stability. The two classification methods are: the Flow Stability Factor and the Flow Stability Number. The Flow Stability Factor, which is developed based on the Fuzzy Concept, is defined in the range of 0 to 1; the maximum value is one and indicates that the flow is completely stable; and the minimum value is zero and indicates that the flow is completely unstable. The Flow Stability Number is defined as the ratio of total energy at two channel sections with a maximum value of one, and it allows flow conditions to be classified for various hydraulic structures; the number is dimensionless and quantitatively defines the flow stability downstream of a hydraulic structure under critical and subcritical flow conditions herein studied, also allowing for an estimate of the downstream stable condition for operation of a hydraulic structure. This research also implemented an Artificial Neural Network to determine the optimal gate opening that ensures a downstream stable condition. A post-processing method (regression-based) was also introduced to reduce the differences in the amount of the gate openings between experimental results and artificial intelligence estimates. The results indicate that the differences were reduced approximately 2% when the post-processing method was implemented on the Artificial Neural Network estimates. This method provides reasonable results when few data values are available and the Artificial Neural Network cannot be well trained. Experiments were conducted in two laboratories, for two different scales, to investigate any possible scale effect. Results indicate, for instance, that the case of the vertical gate with an expansion performs better in producing a downstream stable condition than the other two studied structures. Moreover, it was found that smaller changes caused by expansions and contractions on the channel width show better performance in ensuring a viii downstream stable condition in the cases of a vertical gate with an expansion and a vertical gate with a contraction over a wide range of structures. Moreover, upstream flow depths in the gate with expansion are higher than in the cases of a gate and a gate with a contraction, suggesting that it may be more appropriate for agriculture applications. This research also applied Game Theory and the Nash Equilibrium Concept in selecting the best choice among various structures, under different flow expectations. In addition, the accuracy of the Flow Stability Factor and the Flow Stability number were compared. This showed that the Flow Stability Factor and the Flow Stability number had good agreement in stable conditions. Hence, the Flow Stability Factor can then be used instead of the Flow Stability number to define stable conditions, as a visual method that does not need any measurement. Importantly, a Fuzzy-based Efficiency Index, a method based on an image processing technique, was also innovatively tested to estimate the hydraulic efficiency of the hydraulic structures. The method was tested and validated using laboratory data with an average agreement of 96.45%, and then demonstrated for prototype case situations in Florida and California. These cases yielded overall efficiencies of 96% and 97.87% in Spillway Park, FL and Oroville Dam, CA, respectively. Statistical assessment was also done on the image, determining an Efficiency Index. Specifically, an image histogram was extracted from the grayscale image, then the mean and standard deviation of the histogram was used to calculate the Index. The method uses the darkness and whiteness of the image to estimate the Efficiency Index; it is easy to use, quick, low cost, and trustworthy.
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Carlin, Mattia. "The response of river bar topography to the hydrological flow regime." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/312573.
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Alternate bars are large-scale bedforms characterised by an ordered sequence of scour zones and depositional diagonal fronts alternating along channel banks, which are typical of straight channelized rivers. Due to their high relief and migration properties, they represent a problem in river management, because they affect navigation, increase the flooding risk and interact with instream structures. For this reason, in the last decades many studies took the challenge of defining suitable criteria able to describe their morphometric properties.
Theoretical, experimental and numerical works have clearly demonstrated that bar occurrence is a threshold process governed by the width-to-depth ratio of the channel, β. If this parameter exceeds a critical threshold, βcr, an instability mechanism amplifies the riverbed perturbations occurring due to the effect of the turbulent flow on the cohesionless riverbed, leading to the spontaneous growth of finite amplitude bars. Under steady flow conditions, alternate bars achieve an equilibrium configuration, whose amplitude value is related to the difference β-βcr.
Much less information is available to describe bar characteristics under variable flow conditions, when the width-to-depth ratio changes in time and the amplitude of bars evolves depending on the duration and the shape of the hydrograph. The effect of a single idealized flood on bar amplitude evolution was successfully described by the weakly nonlinear model of Tubino (1991), which was able to capture the trajectory of bar amplitude during different stages of the flood. Supported by experimental results, he found that the response of bars crucially depends on the ratio between the flood duration and the bar-growth timescale. Nevertheless, the effect of a complex flow regime, characterised by a sequence of flow events, is to a large extent unexplored. Specifically, (i) the definition of a criterion to predict the average response of alternate bars in a river reach subject to an hydrological flow regime and (ii) the quantification of bar amplitude evolution due to a complex flow regime are still to a large extent unexplored.
The goals of this work are: (i) to investigate the dependence of bar properties to variable discharge conditions; (ii) to analyse the effect of flow unsteadiness in terms of duration and sequencing of flood events and derive the main hydrological characteristics that primarily control the average response of bar amplitude; (iii) to determine the long-term bar geometry and define the "bar-forming'' discharge, which is the theoretical discharge that if maintained indefinitely would produce the same long-term bar response as the natural hydrograph; (iv) to analyse the effect that a sequence of flood events composing a complex flow series has on the evolution of bar amplitude.
To pursue these purposes, we adopted a methodology primary based on theoretical models, then supported and validated through the analysis of laboratory experiments and field data. The methodology and the key results for the different parts of this thesis can be summarized as follows:
1. First, the response of bar topography to different flow stages has been investigated both theoretically and through the analysis of experimental data, observing the dependence of alternate bars to peculiar threshold conditions. The validity of weakly nonlinear model of Colombini et al. (1987), originally defined in the neighborhood of the critical condition βcr, has been extended taking into account the emersion of bars for low flows.
2. Subsequently, the average response of bars to idealized flow series has been analysed, exploring their dependence on the duration and sequencing of flood events. The probability density function has been found to be the essential hydrological information of the flow series required to determine the long-term response of bar amplitude, while the integral scale of flow sequence is a suitable metric to quantify the unsteadiness of a flow regime.
3. Then, an innovative approach has been introduced to define an occurrence criterion for alternate bars in straightened river reaches that accounts for the hydrological regime, and to determine the average bar state, with the corresponding "bar-forming'' discharge. The key novelty with respect to the classical methods adopted so far to predict the long-term equilibrium channel geometry is that in this case the morphodynamical work acted on river bars by relatively low-flow stages enhancing their formation can be reversed by high-flow stages that suppress them. Therefore, both the occurrence criterion and the average state are found from a balance between the cumulative effects of bar-forming and bar-suppressing events.
4. Finally, the weakly nonlinear model of Colombini et al. (1987), originally defined to predict the evolution of bars under steady flow conditions, has been extended to reproduce a natural flow series by considering the basic flow varying in time. This approach allows us to (i) statistically investigate the effect of flood magnitude and duration on the variations of bar amplitude and (ii) to simulate the morphological response of a river to alterations of the hydrological regime.
The long-term analysis of bar amplitude, as such as its evolution subject to the hydrological flow regime, have been applied to four different study cases, each of them characterised by a distinctive average bar response: two reaches of the Alpine Rhine River, upstream and downstream the confluence of the River Ill (Switzerland), respectively, the Adige River near Trento (Italy) and the Isère River near Montmèlian (France). The theoretical model is able to capture both qualitatively and quantitatively the observed bed response. Specifically, it predicts the occurrence of high-relief bars for the upstream reach of the Alpine Rhine River and for the Isère River, while a plane configuration is predicted for the Adige River. Also the intermediate response of the downstream reach of the Alpine Rhine River is reproduced, showing a predominant flat bed morphology with sporadic low-relief bars.
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Ng, Chi-wing. "Interactions of vortices from two circular cylinders in bistable flow regime /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B18037379.
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Silva, Rui Pedro Guerreiro Duarte Rivaes da. "Exploring riparian vegetation interactions with flow regime and fluvial processes for an improved river management and conservation." Doctoral thesis, ISA/UL, 2018. http://hdl.handle.net/10400.5/17516.
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Osho, Adeyemi Joseph. "Effects of pipe orientation on sand transportation." Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/8409.
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Sand transport in hilly terrain geometry is different and complex to understand compared to horizontal pipeline, due to the influence of the geometry that greatly affect multiphase flow and sand behaviour at the dip. The overall aim of this research work is to use experimental method to investigate the effects of multiphase flow behaviour on sand transport in a dip configuration. Experimental work was carried out to understand the complex dynamic mechanisms that exist during sand multiphase flow using 2” inch dip test facility with different inclination angles of ±24° and ±12° configurations. In order determine the multiphase flow parameters and sand flow regimes, extensive data were collected and analysed from continuous local measurement of instantaneous liquid hold up and sand hold up using conductivity rings. Significant observations were made during this study from which several conclusions were made. In the air–water test, three slug behaviours were observed at the dip: complete stratified flow downhill with slug initiation at dip; stratified flow (with energetic ripple) downhill with slug initiation and slug growth upward dip; and aerated slug downhill and slug growth at the dip. These behaviours are different from published work on this subject with low angle of inclination. The data analysis revealed that the two types of slug initiation mechanisms (wave growth and wave coalescence) observed are geometry specifics. The slug translational velocities (at the dip and uphill section) were used as criterion to determine the flow condition for each slug initiation mechanism at the dip. Significant observations were made during this study from which several conclusions were made. In the air–water test, three slug behaviours were observed at the dip: complete stratified flow downhill with slug initiation at dip; stratified flow (with energetic ripple) downhill with slug initiation and slug growth upward dip; and aerated slug downhill and slug growth at the dip. These behaviours are different from published work on this subject with low angle of inclination. The data analysis revealed that the two types of slug initiation mechanisms (wave growth and wave coalescence) observed are geometry specifics. The slug translational velocities (at the dip and uphill section) were used as criterion to determine the flow condition for each slug initiation mechanism at the dip. Five sand-water flow regimes (full suspension, streak, saltation, sand dune, and sand bed) were established by physical observation and data analysis. It was also observed that sand streaks were denser towards the central line of pipe bottom in the downhill pipe than that in uphill pipe. At downhill pipe section, there were sand gathering toward the central line of the pipe bottom. The characteristics of sand transportation at the dip section were found slightly different from downhill and uphill pipe for higher sand concentrations. When dense streak occurred at the downhill, the sand particles become dispersed at the dip. The minimum transport conditions (MTC) were determined at different sand concentration. The sand minimum transport condition in the dip section was found to be slightly lower than those in the downhill and uphill section. The minimum transport condition for a single phase water flow for the 24˚ dip. test section was slightly higher (with difference of about 0.1m/s) than that of the 12˚ at the downward and upward of the dip section at low sand concentration. In addition, local sand measurements using conductivity time series results at the downhill and uphill section showed the influence of sand concentration and flow condition on sand flow patterns. The air-water-sand results showed that sand deposits occurred in uphill section after sand transport at the downhill and dip sections. This was due to different flow regimes exhibited at the different pipe sections. The stratified (wavy) flow was the dominant flow in downhill pipe; therefore sand was observed transporting within the liquid film as thin streak for most of test conditions. The slug initiation at the dip section was observed to be a major factor that influences the sand behaviour. Sand particles in the slug unit (at the dip and uphill of the pipe) were observed to be entrained in the slug body once slug is initiated, thereby changing the force vector generating turbulence flow at the front of slug body. Once the sand particles entered the film zone of the slug unit, they immediately stopped moving forward due to the film velocity significantly lower than the slug body coupled with gravity effect. . Sand particles were found to be falling back while travelling with the water film at some conditions, until they were picked up by the next slug body. The results of this work provide a better understanding to the study of multiphase flow for pipeline design and most especially sand behaviour at the dip. The sand dune regime is identified distinctively using conductivity ring technique which would assist in determining the operating conditions that allow sand dune formation. The knowledge of flow condition at full suspension of sand is an important parameter to determine the erosion rate over the life span of the pipeline. Also, the quantity of sand bed and flow condition of sand settling at the dip is useful information for production chemist in order to determine the effectiveness of corrosion inhibitor at the bottom of the pipe. In conclusion, sand transport characteristics and MTC were strongly dependent on the gas-liquid flow regime and pipe geometry; and cannot be generalised on the superficial liquid and gas velocities of the transport fluid.
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Magnini, Mirco <1982>. "CFD modeling of two-phase boiling flows in the slug flow regime with an interface capturing technique." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4437/.
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The objective of this thesis was to improve the commercial CFD software Ansys Fluent to obtain a tool able to perform accurate simulations of flow boiling in the slug flow regime. The achievement of a reliable numerical framework allows a better understanding of the bubble and flow dynamics induced by the evaporation and makes possible the prediction of the wall heat transfer trends.
In order to save computational time, the flow is modeled with an axisymmetrical formulation. Vapor and liquid phases are treated as incompressible and in laminar flow. By means of a single fluid approach, the flow equations are written as for a single phase flow, but discontinuities at the interface and interfacial effects need to be accounted for and discretized properly. Ansys Fluent provides a Volume Of Fluid technique to advect the interface and to map the discontinuous fluid properties throughout the flow domain. The interfacial effects are dominant in the boiling slug flow and the accuracy of their estimation is fundamental for the reliability of the solver. Self-implemented functions, developed ad-hoc, are introduced within the numerical code to compute the surface tension force and the rates of mass and energy exchange at the interface related to the evaporation. Several validation benchmarks assess the better performances of the improved software.
Various adiabatic configurations are simulated in order to test the capability of the numerical framework in modeling actual flows and the comparison with experimental results is very positive. The simulation of a single evaporating bubble underlines the dominant effect on the global heat transfer rate of the local transient heat convection in the liquid after the bubble transit. The simulation of multiple evaporating bubbles flowing in sequence shows that their mutual influence can strongly enhance the heat transfer coefficient, up to twice the single phase flow value.Questa tesi si è posta l'obiettivo di migliorare il codice commerciale CFD Ansys Fluent, per ottenere un solutore in grado di compiere simulazioni accurate di flussi in ebollizione nel regime slug flow. Un codice numerico affidabile permette una miglior comprensione della dinamica della bolla causata dall'evaporazione, rendendo possibile la stima dello scambio termico alla parete. Per limitare il costo computazionale delle simulazioni, il problema è modellato con una formulazione assialsimmetrica. Le fasi liquido e vapore sono incomprimibili ed in moto laminare. Attraverso un approccio di tipo single fluid, le equazioni che governano il moto sono scritte come per un flusso a fase singola, tuttavia discontinuità ed effetti di interfaccia vanno introdotti e discretizzati propriamente. Fluent dispone di una tecnica di tipo Volume-of-Fluid per l'avvezione dell'interfaccia e per mappare le discontinue proprietà del fluido su tutto il dominio. Nello slug flow gli effetti di interfaccia sono dominanti, di conseguenza l'accuratezza con cui essi sono calcolati è fondamentale per la veridicità del solutore. A tale scopo, sono state introdotte nel codice numerico delle funzioni esterne, sviluppate appositamente per il calcolo della tensione superficiale e dello scambio di massa ed energia all'interfaccia come conseguenza dell'evaporazione. Le migliori prestazioni del codice modificato rispetto a quello originale sono dimostrate attraverso numerosi casi test. Per provare la validità del nuovo codice numerico nella riproduzione di reali configurazioni di flusso, sono stati simulati diversi flussi adiabatici ed il confronto con i risultati sperimentali è molto positivo. La simulazione dell'evaporazione di una bolla singola evidenzia che la convezione transitoria nel liquido, successivamente al passaggio della bolla, ha un effetto dominante sul coefficiente di scambio termico globale. La simulazione di bolle multiple che evaporano in sequenza mostra che la loro influenza reciproca migliora notevolmente il coefficiente di scambio, fino a due volte il valore a fase singola.
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Chen, Min. "Neural net-aided criterion of flow regime transition in trickle bed reactors." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0017/MQ38047.pdf.
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Xia, Qingfeng. "Enhancement of liquids mixing using active pulsation in the laminar flow regime." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/enhancement-of-liquids-mixing-using-active-pulsation-in-the-laminar-flow-regime(bcb5ff26-11c4-4301-bdc1-9cae46f46580).html.
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Both the need for mixing highly viscous liquids more effectively and the advance of micro-scale applications urge the development of technologies for liquid mixing at low Reynolds numbers. However, currently engineering designs which offer effective jet mixing without structural and operational complexity are still lacking. In this project, the method of enhancing liquid mixing using active pulsation in the laminar flow regime is explored experimentally. This work started by improving the inline pulsation mechanism in an existing confined jet configuration whereby the fluid from a primary planar jet and two surrounding secondary planar jets are pulsated by active fluid injection control via solenoid valves in the out-of-phase mode. The influence of Reynolds number, pulsation modes, frequency, duty cycle on mixing is then investigated using PLIF and PIV experimental techniques. A combination of different mixing mechanisms is found to be at play, including sequential segmentation, shearing and stretching, vortex entrainment and breakup. At a given net flow Reynolds number, an optimal frequency exists which scales approximately with a Strouhal number (Str=fh/Uj) about 1. This optimal frequency reflects the compromise of the vorticity strength and segmentation length. Furthermore, a lower duty cycle is found to produce a better mixing due to a resultant higher instantaneous Reynolds number in the jet flow. Overall, the improvement of the rig has resulted in an excellent mixing being achieved at a net flow Reynolds number of 166 which is at least order of magnitude lower than in the original rig. In order to achieve fast laminar mixing at even lower Reynolds numbers, the active pulsation mechanism using lateral synthetic jet pairs is designed and tested at a net flow Reynolds number ranging from 2 to 166 at which a good mixing is achieved. The influence of actuation frequency and amplitude, and different jet configuration is evaluated using PLIF and PIV experimental techniques. At the mediate to high Reynolds numbers tested in this study, the interaction and subsequent breakup of vortices play a dominant role in provoking mixing. In contrast, at the lower end of Reynolds numbers the strength of vortex rollup is weakened significantly and as a result folding and shearing of sequential segments provide the main mechanism for mixing. Therefore it is essential to use multiple lateral synthetic jet pairs to achieve good mixing in both mixing channel and synthetic jet cavity at this Reynolds number. It is found that an increase in both the actuation magnitude and frequency improves mixing, thereby the velocity ratio represents the relative strength of the pulsation velocity to the mean flow velocity is crucial for mixing enhancement. In order to identify actuation conditions for good mixing, a regression fit is conducted for the correlation between the dimensionless parameters, net flow Reynolds number Ren, stroke length L and Strouhal number Str. Over the tested range of the net flow Reynolds number from 2 to 83, the relationship of parameters is found and the velocity ratio at least above 2.0. Suggested by the comparatively small exponent, net flow Reynolds number is less influential than stroke length and Strouhal number. The success in obtaining excellent mixing using lateral synthetic jet pairs at low Reynolds numbers in the present work has opened up a promising prospect of their applications in various scenarios, including mixing of highly viscous liquids at macro-scale and micro-mixing.
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Souza, Manuela Santin de. "Fluxo de caixa por regime de competência." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/12/12136/tde-29112006-165812/.
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A Demonstração do Fluxo de Caixa (DFC) é uma peça contábil elaborada sob o regime de caixa. Essa característica torna difícil sua comparação com outras demonstrações elaboradas à luz do regime de competência. Neste trabalho, desenvolve-se um novo modelo, consoante os estudos desenvolvidos por Dechow e Dichev (2002) nos Estados Unidos: a Demonstração do Fluxo de Caixa elaborada pelo regime de competência. Essa nova peça contábil tem como função promover um elo entre a DFC tradicional e as demais demonstrações contábeis, principalmente com a Demonstração do Resultado do Exercício (DRE). Tem-se, como referencial teórico deste estudo, a exploração dos conceitos de regime de caixa e competência, a discussão dos principais aspectos da DFC e da DRE, e a referência aos estudos empíricos que já foram realizados sobre o assunto. Em seguida, foi desenvolvido o modelo em que os fluxos de caixa são segregados conforme sua competência, ilustrando-se com um exemplo hipotético. Para o teste empírico, selecionou-se, através do banco de dados Economática, empresas brasileiras do período de 1995 a 2005. A análise de regressão múltipla com dados em painel foi utilizada como ferramenta estatística. Como resultado deste trabalho, os testes estatísticos confirmaram as hipóteses inicialmente desenvolvidas, concluindo-se que o fluxo de caixa operacional elaborado à luz do regime de competência fornece informações mais precisas sobre os "accruals" e provê uma melhor comparação com as demais demonstrações contábeis quando comparado ao fluxo de caixa por regime de caixa.The Cash Flow Statement (CFS) is a financial statement prepared under the cash basis accounting. This characteristic grows difficult its comparison with other financial statements that are prepared under de accrual basis accounting. In this study, it was developed a new model, according the studies done by Dechow and Dichev (2002) in the United States of America: the Cash Flow Statement under the accrual basis accounting. This new financial statement has the role of link the traditional CFS and the other statements, mainly the Income Statement. The theory of this study is based in the concepts of cash and accrual basis accounting, in the discussion of the principal aspects of the CFS and Income Statement and the reference of the empiric researches realized about this subject. Following, a model was developed taking account of the cash flows divided into the accrual period and an example was built. For the empiric test, we selected, through the Economatica data base, Brazilian companies to the period of 1995 until 2005. The multiple regression analysis with panel data has been utilized as a statistic instrument. As a result of this study, the statistics tests sustained the hypothesis developed in the initial part of the study, concluding that the operational cash flow under the accrual basis accounting provide precise information about the accruals and supply a better comparison with the other financial statements when faced to the cash flow under the cash basis accounting.
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McLaughlin, Fraser. "Using regional flow regime classes to identify flow anomalies in a set of Canadian rivers regulated by dams." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123105.
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It is well established that a river's natural flow regime is a key determinant of ecological integrity and that dam regulated-flow releases can in some cases be detrimental to biotic communities (e.g. Poff and Zimmerman, 2010). Regional flow classes, groups of rivers that share similar natural flow regimes (called 'river types' by Poff and Zimmerman (2010)) and to which regional fish communities are adapted, have been proposed (e.g. Poff, 1996; Poff and Zimmerman, 2010; McManamay et al., 2012a) as units of analysis to identify significant damming related flow alteration. Specifically, the natural range of flow behaviour within regional classes can be used to identify the most anomalous flow features in rivers regulated by dams. Through ordination analysis, 5 flow regime clusters were identified based on 70 ecologically important flow indices. These clusters are distinct classes of regional flow regimes for 96 unregulated rivers in proximity to 16 regulated sites chosen as NSERC HydroNet sites in Eastern and Western Canada. The distinguishing characteristics of natural flow regimes within each flow class are explored through visualization in principal component space. The 16 regulated HydroNet sites were assigned to these flow classes through discriminate function analysis based on shared geographic location and watershed characteristics. Anomalous flow features in the regulated rivers are identified and characterized in terms of type and strength by identification of flow indices that are significantly different from observed natural variability in the relevant regional class. We also discuss the potential biological implications of the dominant flow anomalies in this set of rivers regulated by hydro dams.Selon le paradigme du 'Natural Flow Regime', le régime hydrologique naturel (ou régime de débits) d'une rivière est un déterminant clé de son intégrité écologique. L'altération significative de ce régime par un barrage hydroélectrique peut en effet négativement affecter les communautés biotiques d'un écosystème lotique (Poff and Zimmerman, 2010). Récemment, des auteurs influents (e.g. Poff, 1996; McManamay et al., 2012a) ont ainsi proposé qu'afin d'identifier les altérations du régime naturel les plus significatives causés par la régulation par barrage, on utilise un point de référence régional (les 'river type') (Poff and Zimmerman, 2010) constitué de la variabilité présente dans un sous-ensemble de rivières non-régulées coulant dans la région du site régulé, rivières qui partagent naturellement certaines caractéristiques de régime hydrologique (et auxquelles la faune aquatique régionale est adaptée). A cet effet, une analyse d'ordination a été effectuée sur les régimes naturels de débit de 96 rivières non régulées situées à proximité des 16 sites sur rivières régulées par barrage choisis pour étude dans le projet HydroNet, et ce dans deux régions distinctes, l'une dans l'ouest et la seconde dans l'est canadien. Cette ordination, effectuée à partir de 70 métriques de débit reconnus pour leur pertinence écologique, distingue 5 sous-ensembles régionaux de régimes naturels assez distincts (5 'flow classes', sensu McManamay et al., (2012a)) réparties à travers les régions à l'étude. Les caractéristiques contrastantes des régimes de chacune de ces 5 sous-ensembles sont présentées et discutées. Par la suite, une analyse par fonction discriminante permet d'assigner les 16 sites régulés à l'étude à une ou l'autre de ces 5 classes, comme point de comparaison naturel. Cette analyse nous permet par la suite de repérer et de décrire les divers aspects des régimes de débits aux sites régulés qui sont clairement 'hors normes' par rapport à ce qui est observé dans le sous-ensemble régional de référence. Nous discutons brièvement par la suite de certains effets possibles de ces anomalies particulières sur les populations de poisson dans ces écosystèmes.
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Emamzadeh, Mohammad. "Modelling of annular two-phase flow in horizontal and vertical pipes including the transition from the stratified flow regime." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9970.
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The thesis presents a general one-dimensional mathematical model to simulate two-phase, gas-liquid, annular flow in horizontal as well as vertical pipes, and to mechanistically predict the transition from stratified to annular flow in horizontal pipes. The method is based on the transient one-dimensional two-fluid model whereby the two phases are considered as (i) liquid layer and (ii) a mixture of the gas and liquid droplets in which the droplet concentration in the mixture is considered as a flow variable. The model entails the introduction of a scalar transport equation for the conservation of mass of liquid droplets accounting for liquid transfer to and from the film liquid layer. The interface curvature is modelled by a double circle geometric configuration incorporating a new empirical relation for the specification of wetted angle. The droplet exchange rate between the liquid film and gas core is modelled by employing droplet entrainment and deposition rates derived from modifications of models existing in the literature. Using the new model the droplet entrained fraction (E), which is defined as the ratio of the droplet mass flow rate to the total liquid mass flow rate, is computed and validated against different experimental data for both horizontal and vertical pipes. The predictions show good agreement with most of the measurements, being within 30% of the data. This is a significant development since, unlike all other exist- ing models, both horizontal and vertical annular flows can be predicted well with the same model. Moreover, the transition point from the stratified to the annular regimes in horizontal flow can also be predicted and the transition points compare very well with the usual regime boundaries found in existing flow regime maps.
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Vila, Martínez Núria. "Effects of flow regime on the fish communities of the lower Ebro River." Doctoral thesis, Universitat Rovira i Virgili, 2018. http://hdl.handle.net/10803/664726.
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Els ecosistemes aquàtics presenten una estreta connexió entre forces físiques i processos ecològics. Als rius, aquesta interacció física-ecologia és dirigida pel cabal, un dels factors principals que determinen la integritat biològica. La combinació de grans alteracions hidrològiques degudes a la regulació per preses i una creixent presència d’espècies al·lòctones, posa en perill les comunitats de peixos autòctons a la Península Ibèrica. L’objectiu d’aquesta tesi és explorar les relacions entre el règim hidrològic i les comunitats de peixos del tram baix de l’Ebre per mitjà de l’anàlisi de dades de campanyes de pesca elèctrica realitzades durant més de 10 anys. Enfocàrem aquest objectiu des de tres punts de vista diferents: Al capítol 1 s’avaluaren les relacions entre les abundàncies de cada espècie i el règim hidrològic, mentre que als capítols 2 i 3, l’objecte d’estudi foren índexs de qualitat biològica basats en peixos i l’espectre de mides de la comunitat íctica, respectivament. Per descriure el règim hidrològic, férem servir un conjunt de variables calculades a partir de series diàries i horàries de cabals facilitades per la Confederació Hidrogràfica de l’Ebre (CHE). Els resultats mostraren la importància del cabal en determinar la composició íctica a nivell d’espècie, comunitat i estructura de mides. Aquests coneixements poden ser de gran utilitat pel desenvolupament d’eines de restauració ecològica i la conservació d’espècies de peixos, especialment en el context actual de creixents pressions sobre els ecosistemes d’aigua dolça (escalfament global, consum d’aigua i espècies invasores, entre d’altres).En los ecosistemas acuáticos se observa una estrecha relación entre fuerzas físicas y procesos ecológicos. En los ríos, esta interacción física-ecología está dirigida por el caudal, uno de los factores clave que determinan la integridad biológica. La combinación de grandes alteraciones hidrológicas debidas a la regulación por presas y una creciente presencia de especies introducidas, pone en peligro las comunidades piscícolas nativas de la Península Ibérica. El objetivo de esta tesis es explorar las relaciones entre el régimen hidrológico y las comunidades de peces del tramo bajo del Río Ebro mediante el análisis de datos de campañas de pesca eléctrica realizadas durante más de 10 años. Enfocamos este objetivo desde tres puntos de vista diferentes: En el Capítulo 1 se evaluaron las relaciones entre las abundancias de cada especie y el régimen hidrológico, mientras que en los capítulos 2 y 3, el objeto de estudio fueron índices de calidad biológica basados en peces y el espectro de tamaños de la comunidad ictiológica respectivamente. Para describir el régimen hidrológico, utilizamos un conjunto de variables calculadas a partir de series de caudal diarias y horarias facilitadas por la Confederación Hidrográfica del Ebro (CHE). Los resultados mostraron la importancia del caudal en la determinación de la composición ictiológica a nivel de especie, comunidad y estructura de tamaños. Estos conocimientos pueden ser de gran utilidad para el desarrollo de herramientas de restauración ecológica y conservación de especies de peces, especialmente en el contexto actual de crecientes presiones sobre los ecosistemas de agua dulce (calentamiento global, consumo de agua y especies invasoras, entre otras).
Aquatic ecosystems are characterized by a strong coupling between physical forcing and ecological processes. In rivers, this physics-ecology interaction is driven by flow, one of the main factors determining biological integrity. The combination of high flow alterations due to dam regulation and an increasing presence of alien species is endangering native fish communities in the Iberian Peninsula. The aim of this thesis is to explore the relationships between flow regime and fish communities in the lower Ebro River by analysing data from electrofishing campaigns collected during more than 10 years. We addressed this objective through three different approaches: On Chapter 1, the relationships between single species abundances and hydrological regime were evaluated while in Chapter 2 and 3 the objects of study were fish-based biological quality indices and size spectrum of fish community, respectively. To describe flow regime, we used a set of hydrological variables calculated from daily and hourly flow data series provided by the Ebro Basin Water authority (Confederación Hidrográfica del Ebro). The results showed the importance of flow in shaping fish composition at species, community and size structure levels. This knowledge may prove useful for the development of ecological restoration tools and fish species conservation, especially in a context of increasing pressures over freshwater ecosystems (global warming, water consumption and invasive species, among others).
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Stout, Jacob B. "Trout Habitat in an Altered Gravel-Bed River with an Augmented Flow Regime." DigitalCommons@USU, 2019. https://digitalcommons.usu.edu/etd/7589.
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The Diamond Fork River, and it’s tributary Sixth Water Creek, has been highly altered in terms of shape, function, and ecologicaly due to large, trans-basin flows additions to the system for irrigation starting in the early 1900s. Flows were exceptionally large for 80 years, after which they were reduced in 2004. Larger than natural flows during the low flow season were then added to the river in an effort to improve ecosystem health and recreational fishing opportunities. Since the prescription additional flow during low flow seasons, the river channel has undergone further change, most noticeably in the form of narrowing. With the channel change that has occurred over the past decade, it has been suggested that the additional flows, which augment baseflows, are too large and that key habitat elements, particularly pools, are lacking throughout the river.
We evaluated trout habitat throughout the altered reaches of the Diamond Fork River and Sixth Water Creek which are still subject to flow additions. We used a model to estimate the number of fish a reach can support at a given flow in order to evaluate which flow produces the highest quality trout habitat. We found that the current summer baseflows of 80 cfs for the lower Diamond Fork and 32 cfs for Sixth Water Creek are less than desirable and that flows less than 40 cfs for the lower Diamond Fork and flows between 20 cfs and 30 cfs for Sixth Water Creek would increase the quality of trout habitat.
We also evaluated the size and number of pools throughout the system and identified that pools are generally lacking both in size and number relative to standard requirements for trout success. We documented that as the channel narrowed, the number of pools/deep water disappeared. The lack of sediment and the limited number of flows capable of moving sediment were identified as key causes of the channel simplification and loss of pool habitat. Crucial components of future pool formation and maintenance are i) active sediment availability and ii) frequent sediment mobilizing flows. If the baseflow regime were to be lowered, we predict that the channel would narrow, which would increase the effectiveness of floods, increase mobility of sediment, and overall increase pool habitat. This research, as part of a larger, interdisciplinary project, lays the foundation for proposing new flows for the Diamond Fork River that targets ecological goals identified by stakeholders as well as providing information for future habitat restoration projects.
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Wilkens, Robert Joseph. "Prediction of the flow regime transitions in high pressure, large diameter, inclined multiphase piplines." Ohio : Ohio University, 1997. http://www.ohiolink.edu/etd/view.cgi?ohiou1175023280.
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周浩賢 and Ho-yin Paul Chow. "Prediction of fluctuation in groundwater flow regime at the pos selim landslide in response to rainfall using a numerical modellingapproach." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40722302.
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Torabi, Haghighi A. (Ali). "Analysis of lake and river flow regime alteration to assess impacts of hydraulic structures." Doctoral thesis, Oulun yliopisto, 2014. http://urn.fi/urn:isbn:9789526206684.
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Abstract A key challenge in Integrated Water Resources Management (IWRM) is determination of environmental flow (EF). This is relevant in all water use scenarios and river regulation work. Water use and management alter water availability for ecosystems and the timing and distribution of runoff. Increased water consumption and allocation of water to different types of consumption impose pressures on aquatic ecosystems, affecting their status and ability to deliver important services, well–known examples being the Aral Sea in Asia and Lake Chad in Africa. This thesis presents new methods to determine the impacts of hydraulic structures on the flow regime of lakes and rivers. Methods to quantify different characteristics of flow in a non–dimensionless way are also presented. These tools allow more environment–based regulation of flow regimes. By using three main flow characteristics of river regime (magnitude, timing and intra–annual), three impact factors, MIF (magnitude impact factor), TIF (timing impact factor) and VIF (variation impact factor), were developed. Combining these impact factors produced a new river impact (RI) index to assess the impacts of hydraulic structure using monthly flow data. Based on RI variations, a classification was developed rating impacts along a scale from ‘Low’ to ‘Drastic’. The importance of climate patterns and river flow regime in controlling lake levels was examined. The lake simulation results were compared using a new index, Degree of Lake Wetness (DLW) and lake response time to changes in hydrology or climate was evaluated. Environmental flow allocation and optimisation of annual EF distribution are critical for ecosystem health. Flow release from reservoirs can be partly supplemented or compensated for by natural runoff from downstream (residual) catchment areas. In a new hydrological approach, optimal intra–annual flow regime for EF can be estimated while considering water inflow from the downstream residual sub-catchment. This thesis provides methods and indices to help quantify river and lake regimes, better understand the possible impacts of changes and manage these impacts optimally. This knowledge is crucial for decision making about EF regimes and achieving water release patterns from dams and hydropower that minimise the hydrological, morphological and biological impactsTiivistelmä Integroidun vesivarojen suunnittelun ja hallinnan (IWRM) yhtenä haasteena on ympäristövirtaaman määrittäminen valuma–alue-tasolla. Tämä on tärkeää arvioitaessa säännöstelyn ja vesirakentamisen ympäristövaikutuksia. Vedenkäyttö ja hallinta muuttavat veden saatavuutta jokiekosysteemissä ja virtaaman vuosittaista ajoittumista sekä jakautumista eri kuukausien välillä. Vesivarojen lisääntyvä käyttö eri tarkoituksiin voi vaikuttaa vesiekosysteemeihin ja niiden tuottamiin ekosysteemipalveluihin. Aral–järvi Aasiassa ja Chad–järvi Afrikassa ovat hyviä esimerkkejä veden liiallisesta käytöstä ja ympäristönäkökulman huomiotta jättämisestä. Väitöstyön keskeisin tavoite oli kehittää menetelmiä, joilla voidaan arvioida miten vesirakentaminen vaikuttaa jokien virtaamiin ja järvien vedenpintoihin. Jotta vesistövaikutuksia voidaan yleistää, menetelmät kehitettiin dimensiottomiksi. Nämä menetelmät luovat perustan ympäristöystävällisemmällä vesistöjen virtaamien säännöstelylle. Käyttäen kuukausittaista keskivirtaamaa ja kolmea tyypillisintä virtaamaluokkaa (suuruus, ajoittuminen ja vuodenaikainen vaihtelu), määritettiin uusi yhdistetty jokivaikutusindeksi (RI). Tämän indeksin avulla voitiin lopulta arvioida vesirakentamisen vaikutusta. Perustuen RI-indeksiin, usean joen vesirakentamisen vaikutuksia arvioitiin luokittelemalla vaikutukset vähäisiksi tai merkittäviksi. Työssä tarkasteltiin ilmaston vaihtelun ja jokien virtaamaolosuhteiden vaikutusta järvien vedenpintoihin. Järvisimuloinnin tuloksia verrattiin puolestaan käyttäen indeksiä, joka kuvaa järvessä tapahtuvia muutoksia suhteessa hydrologisiin ja ilmastollisiin olosuhteisiin. Väitöskirja käsittelee myös ympäristövirtaamien (EF) keskeisiä kysymyksiä: vedenkäytön jakautumista ja vuosittaisen virtaaman optimointia ympäristövirtaaman näkökulmasta. Työssä käytetään uutta hydrologista lähestymistapaa arvioimaan ympäristövirtaaman optimoitua kausivirtaamavaihtelua. Tässä lähestymistavassa vesivarastoaltaista lähtevää virtaamaa voidaan osittain täydentää tai kompensoida alapuoliselta valuma–alueelta tulevalla virtaamalla. Väitöstyön tulokset lisäävät ymmärrystä vesivarojen kestävästä käytöstä. Lisäksi työssä kehitetyillä menetelmillä voidaan määrittää ja optimoida jokien ja järvien virtaamaolosuhteita erilaisissa tilanteissa. Väitöstyö tarjoaa uusia käytäntöjä päätöksentekoon liittyen ympäristövirtaamaolosuhteisiin ja -jakaumiin vesivoima- ja vedenkäyttökysymyksissä ottaen huomioon hydrologiset, morfologiset ja biologiset rajoitteet
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Tchowa, Medjiade Willy Baudelaire [Verfasser], and Adrian [Akademischer Betreuer] Schumpe. "Flow Regime Identification in a Bubble Column / Willy Baudelaire Tchowa Medjiade ; Betreuer: Adrian Schumpe." Braunschweig : Technische Universität Braunschweig, 2016. http://d-nb.info/1175818895/34.
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Wilkens, Robert Joseph. "Prediction of the flow regime transitions in high pressure, large diameter, inclined multiphase pipelines." Ohio University / OhioLINK, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1175023280.
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Bennett, Micah. "EFFECTS OF FLOW REGIME ON FISHES AND FISHERIES: FROM LIFE HISTORIES TO ECOSYSTEM SERVICES." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/dissertations/1148.
Full textAbstract:
Stream flow in freshwaters is considered a “master variable” influencing processes and traits from individual organisms to ecosystems. Due to this strong linkage, anthropogenic modification of flow regimes in freshwater ecosystems worldwide continues to have major impacts on populations, species, communities, and ecosystems and the many services they provide to humans. My dissertation investigated the impacts of flow regime and its variability on three levels of biological organization: populations, communities and ecosystems. The approach highlights links among evolutionary, community, and ecosystem ecology, while also testing basic models and demonstrating applied significance in freshwater conservation. At the population level, I evaluated the generality of the trilateral life history model (TLHM) for fishes - a trait-environment model well-studied at the assemblage level – finding that the TLHM adequately described major trade-offs in traits among populations in all species. Some TLHM flow-based predictions were confirmed, with periodic traits (high fecundity) favored at sites with greater flow seasonality and lower flow variability in two species, and equilibrium traits (large eggs) in more stable flow conditions in two species. However, relationships contradicting the TLHM were also found. In Chapter 3, I evaluated the effects of geographic location, scale, and sampling gear on agree with TLHM predictions using a fish community dataset from Louisiana. Generally, fewer than half of significant relationships supported TLHM predictions. These results suggest that, due to collinearity of hydrologic variables, effects of sampling gear, and scale of analysis, applying and operationalizing the predictions of the TLHM in terms of hydrology may not be straightforward. here is a continued need to match high-quality biological data with hydrologic data while also developing hydrologic modeling and datasets of correlated environmental variables at finer scales to match the grain of most biological sampling. Trait-environment models that are well-supported at multiple levels of biological organization could improve understanding of the impacts of environmental change on populations and communities and the valuable ecosystem services that they support. Chapters 4 and 5 focus on ecosystem services and how they are related to each other and influenced by flow regime in a large river-floodplain ecosystem – the Atchafalaya River in Louisiana. I first developed a model of denitrification in the Atchafalaya River. Denitrification rates ranged from 5,394 kg N y-1 (3.07 kg N km-2 y-1) in 1988 to 17,420 kg N y-1 (9.92 kg N km-2 y-1) in 1981, and rates were consistently higher in fall compared to spring. Total nitrate (NO3−) denitrified in the basin was negligible compared to total NO3− entering the GOM. If all N denitrified in the basin instead entered the Gulf, the hypoxic zone was predicted to increase only 5.07 km2 (0.06%). This negligible effect on N dynamics in the GOM agrees with other mass balance and isotopic studies in the region. Denitrification is only one of many ecosystem services provided by river-floodplain ecosystems. Because of the overriding influence of flow regime on river systems, an understanding of flow-ecology relationships in rivers is necessary to assess potential impacts of management decisions. However, translating complex flow-ecology relationships into stakeholder-relevant information remains a struggle. The concept of ecosystem services provides a bridge between flow-ecology relationships and stakeholder-relevant data. Flow-ecology relationships were used to explore complementary and trade-off relationships among 12 ecosystem services and related variables in the Atchafalaya River Basin, Louisiana. Results from Indicators of Hydrologic Alteration were reduced to four management-relevant hydrologic variables using principal components analysis. Multiple linear regression was used to determine flow-ecology relationships and Pearson correlation coefficients, along with regression results, were used to determine complementary and trade-off relationships among ecosystem services and related variables that were induced by flow. Seven ecosystem service variables had significant flow-ecology relationships for at least one hydrologic metric. There was a single complementary relationship mediated by flow and there were three such trade-off relationships; however, other trade-off and complementary relationships were not related to flow. These results give insight into potential conflicts among stakeholders, can reduce the dimensions of management decisions, and provide initial hypotheses for experimental flow modifications.
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Chow, Ho-yin Paul. "Prediction of fluctuation in groundwater flow regime at the pos selim landslide in response to rainfall using a numerical modelling approach." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B40722302.
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Inyiama, Fidelis Chidozie. "Active control of hydrodynamic slug flow." Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/7996.
Full textAbstract:
Multiphase flow is associated with concurrent flow of more than one phase (gas-liquid, liquid-solid, or gas-liquid-solid) in a conduit. The simultaneous flow of these phases in a flow line, may initiate a slug flow in the pipeline. Hydrodynamic slug flow is an alternate or irregular flow with surges of liquid slug and gas pocket. This occurs when the velocity difference between the gas flow rate and liquid flow rate is high enough resulting in an unstable hydrodynamic behaviour usually caused by the Kelvin-Helmholtz instability.
Active feedback control technology, though found effective for the control of severe slugs, has not been studied for hydrodynamic slug mitigation in the literature. This work extends active feedback control application for mitigating hydrodynamic slug problem to enhance oil production and recovery.
Active feedback Proportional-Integral (PI) control strategy based on measurement of pressure at the riser base as controlled variable with topside choking as manipulated variable was investigated through Olga simulation in this project. A control system that uses the topside choke valve to keep the pressure at the riser base at or below the average pressure in the riser slug cycle has been implemented. This has been found to prevent liquid accumulation or blockage of the flow line.
OLGA (olga is a commercial software widely tested and used in oil and gas industries) has been used to assess the capability of active feedback control strategy for hydrodynamic slug control and has been found to give useful results and most interestingly the increase in oil production and recovery. The riser slugging was suppressed and the choke valve opening was improved from 5% to 12.65% using riser base pressure as controlled variable and topside choke valve as the manipulated variable for the manual choking when compared to the automatic choking in a stabilised operation, representing an improvement of 7.65% in the valve opening. Secondly, implementing active control at open-loop condition reduced the riser base pressure from 15.3881bara to 13.4016bara.
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Vancko, Robert M. "Effect of a drag reducing agent on pressure drop and flow regime transitions in multiphase horizontal low pressure pipelines." Ohio : Ohio University, 1997. http://www.ohiolink.edu/etd/view.cgi?ohiou1184354301.
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Laneryd, Carl-Johan Tor. "Studies on slow gas flows in the near-continuum regime." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/49141.
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学位授与大学：京都大学 ; 取得学位: 博士(工学) ; 学位授与年月日: 2007-09-25 ; 学位の種類: 新制・課程博士 ; 学位記番号: 工博第2860号 ; 請求記号: 新制/工/1420 ; 整理番号: 25545Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第13389号
工博第2860号
新制||工||1420(附属図書館)
25545
UT51-2007-Q790
京都大学大学院工学研究科航空宇宙工学専攻
(主査)教授 青木 一生, 教授 稲室 隆二, 教授 斧 髙一
学位規則第4条第1項該当
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Jamieson, Nicholas Peter. "Experimental sensitivity analysis and control of thermoacoustic systems in the linear regime." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275891.
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Thermoacoustic instability is one of the most significant problems faced in the design of some combustion systems. Thermoacoustic oscillations arise due to feedback between acoustic waves and unsteady heat release rate when the fluctuating heat release rate is sufficiently in phase with the unsteady pressure. The primary aim of designers is to design linearly stable thermoacoustic systems in which these dangerous oscillations do not arise. In thermoacoustics, adjoint-based sensitivity analysis has shown promise at predicting the parameters which have the most influence on the linear growth and decay rates as well as oscillation frequency observed during periods of linear growth and decay. Therefore, adjoint-based methods could prove to be a valuable tool for developing optimal passive control solutions. This thesis aims to develop novel experimental sensitivity analysis techniques and provide a first comparison with the predictions of adjoint-based sensitivity analysis. In this thesis experimental sensitivity analysis is performed on (i) a vertical electrically-driven Rijke tube, and (ii) a vertical flame-driven Rijke tube. On the electrically-driven Rijke tube, the feedback sensitivity is studied by investigating the shift in linear growth and decay rates and oscillation frequency observed during periods of linear growth and decay due to the introduction of a variety of passive control devices. On the flame-driven Rijke tube, the base-state sensitivity is studied by investigating how the linear growth and decay rates as well as oscillation frequency during periods of linear growth and decay change as the convective time delay of the flame is modified. Adjoint-based sensitivity analysis gives the shift in linear growth and decay rate and the oscillation frequency when parameters are changed. This thesis provides experimental measurements of the same quantities, for comparison with the numerical sensitivity analysis, opening up new avenues for the development, implementation and validation of optimal passive control strategies for more complex thermoacoustic systems.
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Tjäder, Jessica. "Flödesvariatonens påverkan på artrikedomen inom strandvegetationen : - Hur påverkas artrikedomen längs tre sel i Juktån av ett reglerat flöde?" Thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-172231.
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In this study I investigate how the biodiversity of vascular plants differs between three slow flowing parts of the stream Juktån in northern Sweden where hydropower has impacted the flow regime and thus the conditions for riparian vegetation. The hypothesis was that species richness would increase with the distance from the hydropower plant due to increasing naturalness of the flow regime. Species richness was investigated since it is a fundamental and important function for the maintenance and quality of ecosystems (Naiman and Décamps 1997). Juktån, where data for the study was collected, receives a static minimum flow of barely 12 % of the yearly natural medium flow released from the hydropower station into the channel (Wisaeus 2014). The minimum flow follows the variation set by the hydropower which deviates from natural seasonal flow variation, which is essential for the germination, growth, and reproduction of many plant species (Poff et al. 1997). The investigation includes a comparison between species richness and richness of 4 functional groups among the three study locations. In addition, analysis of the relationship between environmental variables such as position on the riparian zone (height) and substrate composition were performed. Sikselet that was the slow flowing reach closest to the hydropower station had the highest species richness while Bredselet further downstream had the lowest species richness with Långselet having intermediate species richness. One reason for the pattern in species richness could be that seeds get trapped in weirs located between Sikselet and Långselet. In that case, reintroducing a natural flow regime may not suffice to increase species richness.
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Domínguez, Lucía García 1988. "Efeito da vazão nas curvas de permeabilidade relativa em regime transiente." [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265757.
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Orientador: Rosângela Barros Zanoni Lopes MorenoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociências
Made available in DSpace on 2018-08-28T12:56:20Z (GMT). No. of bitstreams: 1 Dominguez_LuciaGarcia_M.pdf: 8169227 bytes, checksum: 3b6d0e210f4dc8a2db3d9f8b9f93f6c0 (MD5) Previous issue date: 2015
Resumo: A capacidade de armazenamento de hidrocarbonetos no reservatório depende do tipo de rocha e da estrutura dos poros. Uma das propriedades rocha-fluido mais estudadas é a permeabilidade relativa, ou seja, a medida da resistência ao escoamento que um fluido apresenta na presença de outro. A permeabilidade relativa é essencial para a avaliação dos processos de recuperação de hidrocarbonetos e previsão do escoamento multifásico de fluidos através do reservatório. A permeabilidade relativa depende de outros parâmetros que têm sido estudados por especialistas durante os últimos anos, como saturação dos fluidos, molhabilidade, tensão interfacial, estrutura porosa, temperatura, heterogeneidades e vazão de deslocamento. Em relação ao efeito da vazão de deslocamento na permeabilidade relativa, muitas pesquisas têm sido realizadas sem conseguir um acordo. Por tanto, a principal motivação deste estudo é a falta de conformidade na literatura. O foco do trabalho é encontrar se existe dependência da permeabilidade relativa com a vazão e avaliar este efeito em óleos de diferentes viscosidades. Foram realizados quinze testes de deslocamento em regime transiente a temperatura e vazão constantes. Os experimentos de laboratório foram executados com três plugues, cortados a partir de uma amostra única de rocha carbonática e saturados com três óleos de viscosidades diferentes, respetivamente. Foram utilizadas três vazões diferentes para cada amostra, que correspondem aos valores mínimo, máximo e intermediário de acordo o critério de dos Santos et al (1997) que visa balancear as forças viscosas, capilares e gravitacionais. Estas vazões foram variadas começando pela maior e diminuindo até a menor e posteriormente revertendo o ciclo, para observar se a sequência seguida influencia nos resultados. A análise dos resultados foi realizada mediante o método de Johnson-Bossler-Naumann para calcular as permeabilidades relativas ao óleo e à água. Sob as condições dos testes realizados, observou-se que as saturações e permeabilidades dos pontos terminais bem como as curvas de permeabilidade relativa, dependem da vazão. Além disso, pode-se observar que as variações foram diferentes dependendo da viscosidade do óleo utilizado. Deste modo, o óleo de menor viscosidade sempre se comportou de modo contrário ao de maior viscosidade e a mistura dos outros dois teve um comportamento intermediário. Este comportamento tem sido atribuído, nos óleos mais viscosos, a um aumento no ângulo de contato e consequente diminuição do número capilar em resposta à vazão mais elevada. Já nos óleos menos viscosos, a vazão não altera significativamente o ângulo de contato e, portanto, o número capilar aumenta com a vazão. Estas diferenças na variação do número capilar, dependendo do óleo utilizado, podem gerar as tendências diferentes nos resultados e explicar o desacordo na literatura
Abstract: The storability of hydrocarbons in the reservoir is dependent upon the rock formation and the pore structures. One of the main important rock-fluid property is the relative permeability, a measure of the flow resistance of one fluid in the presence of another one into the rock. Relative permeability depends on other parameters which have been studied by researchers during the years like fluid properties and saturation, wettability, interfacial tension, porous structure, temperature, heterogeneity and flow rate. Many researchers have focused on flow rate influence in relative permeability curves without obtaining agreement. Therefore, the main motivation for this study is the lack of conformity in the literature. The focus of the work is to find whether there is dependence of relative permeability with the flow and evaluate this effect in oils of different viscosities. Fifteen transient displacement tests were performed at constant temperature and flow rate. The laboratory experiments were performed with three plugs, cut from a single sample of carbonate rock and saturated with three fluids of different viscosities, respectively. Three different flow rates were used for each sample, corresponding to the minimum, maximum and intermediate according to dos Santos et al criterion (1997) which aims to balance the viscous, capillary and gravitational forces. These flow rates were varied starting with the largest and decreasing to the smallest, and subsequently reversing the cycle, to see if the next sequence influences the results. Experimental results were analyzed using JBN method (Johnson-Bossler-Naumann) to calculate oil and water relative permeability curves. Under the studied circumstances, it was observed that the end point saturations and permeabilities and the relative permeability curves depend on the flow rate. Moreover, variations were different depending on the viscosity of the oil used. Thus, the lower viscosity oil will always behave in a contrary manner to the higher viscosity and the mixture of the other two had an intermediate performance. This behavior has been attributed, for more viscous oils, to an increment in contact angle and thus diminution in the capillary number in response to the higher flow. Nevertheless in lower viscous oils, the flow rate does not alter significantly the contact angle and thus the capillary number increases with flow rate. These differences in the variation of the capillary number depending on the oil used may generate the differences on the results trends and explain the disagreement in the literature
Mestrado
Reservatórios e Gestão
Mestra em Ciências e Engenharia de Petróleo
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Benyamina, Mohamed. "Etude des courants d'ecoulement dans un tube rugueux en regime laminaire." Poitiers, 1988. http://www.theses.fr/1988POIT2288.
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Determination theorique des lignes de courant au voisinage immediat des asperites; simulation experimentale sur un modele plan de grandes dimensions. Definition des zones de la couche diffuse entrainees par l'ecoulement et modelisation de la charge convectee dans un tube rugueux
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Ghrist, Melissa Renee. "Zero gravity two-phase flow regime transition modeling compared with data and relap5-3d predictions." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2353.
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Olsson, Linda. "Effect of design and dosing regime on the treatment performance of vertical flow constructed wetlands." Thesis, Linköpings universitet, Ekologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-69689.
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Vertical flow constructed wetlands (VF CWs) are becoming increasingly popular for onsite wastewater treatment due to their high oxygen transfer capacity and high nitrification rates. However, there are still some question marks regarding (1) how the treatment performance of VF CWs is affected by design and operational parameters, and (2) the treatment processes happening inside the wetland bed as the wastewater percolates through. In this study, we investigated the effects of filter media (coarse sand or fine gravel), dosing regime (hourly with 4 mm or bi-hourly with 8 mm) and plant presence (with or without Phragmites australis) on the treatment performance and concentration depth profiles of pollutant removal in six pilot-scale VF CWs treating primary treated domestic wastewater. Grab samples of wastewater were collected every 2-3 weeks during 5 months and analyzed for organic matter, suspended solids, nitrogen and E. coli. We found that sand beds performed better than gravel beds for removal of all pollutants except total nitrogen, although for long term operation gravel may be less susceptible to clogging. The overall treatment performance was not affected by different dosing regimes, but the concentration depth profiles showed that smaller and more frequent doses led to more pollutant removal in the upper part of the beds. The presence of plants was moderately important for the removal of ammonium, but had no effect on other pollutants.
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Al-lababidi, Salem. "Multiphase flow measurement in the slug regime using ultrasonic measurement techniques and slug closure model." Thesis, Cranfield University, 2006. http://hdl.handle.net/1826/4166.
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Multiphase flow in the oil and gas industry covers a wide range of flows. Thus, over the
last decade, the investigation, development and use of multiphase flow metering system
have been a major focus for the industry worldwide. However, these meters do not
perform well in slug flow conditions.
The present work involves experimental investigations of multiphase flow measurement
under slug flow conditions. A two-phase gas/liquid facility was designed and
constructed at Cranfield University. It consisted of a 0.05 m diameter 25 m long
horizontal pipeline with the necessary instrumentation.
An ultrasonic multiphase metering concept has been proposed and investigated. The
concept was based on the combination of non-invasive and non-intrusive ultrasonic
sensors and a slug closure model. The slug closure model was based on the "slug unit"
model to infer the gas and liquid phase volumetric flowrates.
The slug characteristics obtained by non-invasive and non-intrusive ultrasonic
techniques were inputs to slug closure model which calculates the factors KI
(Liquid),
K2
(Liquid),
K3
(Gas) and K4
(Gas).
These factors are function of the slip ratio in the slug body,
flow profile (CO), drift velocity (Vd), liquid holdup and gas void fraction in slug body,
slug length, film length, and the total length of the slug unit. Based on ultrasonic sensor
measurements, the slug translational velocity was estimated and the slug closure model
then calculates the gas and liquid phase volumetric flowrates.
Air water slug flow data were gathered and processed for a range of superficial
velocities VSL=0.3 to 1.03 ms'1 and VsG=0.6 to 3.01 ms'1. The overall goal of a 5%
relative error metering for both phases was not achieved for the conditions tested. The
liquid phase percentage errors were from
-63.6% to 45.4% while the gas phase
percentage errors were from 42% to -14.6%.
Key words: slug flow, slug characteristics, slug closure model, non-invasive ultrasonic,
non-intrusive ultrasonic, clamp-on transit time ultrasonic flowmeter.