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Costigan, G. "Flow pattern transitions in vertical gas - liquid flows." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361925.
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Yato, Hiroki. "Flow pattern transition in curvilinear shear flows of viscoelastic fluids." 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/131910.
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Valota, Luca. "Microgravity flow pattern identification using void fraction signals." Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969.1/2248.
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Knowledge of the two-phase flow state is fundamental for two-phase flow system design and operation. In traditional two-phase flow studies, the flow regime refers to the physical location of the gas and liquid in a conduit. Flow configuration is important for engineering correlations of heat and mass transfer, pressure drop, and wall shear. However, it is somewhat subjective since it is mostly defined by experimental observation, resulting in an approximate and equivocal definition. Thus, there is need for a better, objective flow regime identification. The void fraction is a key parameter in monitoring the operating state of a two-phase system and several tools have been developed in order to measure it. The purpose of this study is to use the void fraction and other parameters of the system to achieve a model for flow pattern identification. Recently, an experimental program using the Foster-Miller two-phase flow test bed and Creare Inc. capacitance void fraction sensors was conducted in the microgravity environment of the NASA KC-135 aircraft. Several data types were taken for each phase, such as flow rate, superficial velocity, density and transient void fraction at 100Hz. Several analytical approaches were pursued, including a statistical approach of the fluctuation of the void fraction, Martinelli analysis, and Drift Flux analysis, in order to reach a model for flow pattern identification in microgravity conditions. Several parameters were found to be good flow pattern identifiers such as the statistical moments variance and skewness, Signal -to- noise ratio (SNR), Half Height Value (HHV) and Linear Area Difference (LAD). Moreover, relevant conclusions were achieved using the Martinelli parameter and the Drift Flux model in microgravity conditions. These results were compared with the basic literature.
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Meng, Ziyuan. "Two-Bit Pattern Analysis For Quantitative Information Flow." FIU Digital Commons, 2014. http://digitalcommons.fiu.edu/etd/1326.
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Protecting confidential information from improper disclosure is a fundamental security goal. While encryption and access control are important tools for ensuring confidentiality, they cannot prevent an authorized system from leaking confidential information to its publicly observable outputs, whether inadvertently or maliciously. Hence, secure information flow aims to provide end-to-end control of information flow. Unfortunately, the traditionally-adopted policy of noninterference, which forbids all improper leakage, is often too restrictive. Theories of quantitative information flow address this issue by quantifying the amount of confidential information leaked by a system, with the goal of showing that it is intuitively “small” enough to be tolerated. Given such a theory, it is crucial to develop automated techniques for calculating the leakage in a system.
This dissertation is concerned with program analysis for calculating the maximum leakage, or capacity, of confidential information in the context of deterministic systems and under three proposed entropy measures of information leakage: Shannon entropy leakage, min-entropy leakage, and g-leakage. In this context, it turns out that calculating the maximum leakage of a program reduces to counting the number of possible outputs that it can produce.
The new approach introduced in this dissertation is to determine two-bit patterns, the relationships among pairs of bits in the output; for instance we might determine that two bits must be unequal. By counting the number of solutions to the two-bit patterns, we obtain an upper bound on the number of possible outputs. Hence, the maximum leakage can be bounded. We first describe a straightforward computation of the two-bit patterns using an automated prover. We then show a more efficient implementation that uses an implication graph to represent the two- bit patterns. It efficiently constructs the graph through the use of an automated prover, random executions, STP counterexamples, and deductive closure. The effectiveness of our techniques, both in terms of efficiency and accuracy, is shown through a number of case studies found in recent literature.
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Ng, Yin Heung Pauline. "Flow pattern analysis for magnetic resonance velocity imaging." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416781.
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Sharma, Sanjeev. "Spray drier simulation and air flow pattern studies." Thesis, Aston University, 1990. http://publications.aston.ac.uk/10224/.
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The literature pertaining to the key stages of spray drying has been reviewed in the context of the mathematical modelling of drier performance. A critical review is also presented of previous spray drying models. A new mathematical model has been developed for prediction of spray drier performance. This is applicable to slurries of rigid, porous crust-forming materials to predict trajectories and drying profiles for droplets with a distribution of sizes sprayed from a centrifugal pressure nozzle. The model has been validated by comparing model predictions to experimental data from a pilot-scale counter-current drier and from a full-scale co-current drier. For the latter, the computed product moisture content was within 2%, and the computed air exit temperature within 10oC of experimental data. Air flow patterns have been investigated in a 1.2m diameter transparent countercurrent spray tower by flow visualisation. Smoke was introduced into various zones within the tower to trace the direction, and gauge the intensity, of the air flow. By means of a set of variable-angle air inlet nozzles, a variety of air entry configurations was investigated. The existence of a core of high rotational and axial velocity channelling up the axis of the tower was confirmed. The stability of flow within the core was found to be strongly dependent upon the air entry arrangement. A probe was developed for the measurement of air temperature and humidity profiles. This was employed for studying evaporation of pure water drops in a 1.2m diameter pilot-scale counter-current drier. A rapid approach to the exit air properties was detected within a 1m distance from the air entry ports. Measured radial profiles were found to be virtually flat but, from the axial profiles, the existence of plug-flow, well-mixed-flow and some degree of air short-circuiting can be inferred. The model and conclusions should assist in the improved design and optimum operation of industrial spray driers.
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Aven, Matthew. "Daily Traffic Flow Pattern Recognition by Spectral Clustering." Scholarship @ Claremont, 2017. http://scholarship.claremont.edu/cmc_theses/1597.
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This paper explores the potential applications of existing spectral clustering algorithms to real life problems through experiments on existing road traffic data. The analysis begins with an overview of previous unsupervised machine learning techniques and constructs an effective spectral clustering algorithm that demonstrates the analytical power of the method. The paper focuses on the spectral embedding method’s ability to project non-linearly separable, high dimensional data into a more manageable space that allows for accurate clustering. The key step in this method involves solving a normalized eigenvector problem in order to construct an optimal representation of the original data.
While this step greatly enhances our ability to analyze the relationships between data points and identify the natural clusters within the original dataset, it is difficult to comprehend the eigenvalue representation of the data in terms of the original input variables. The later sections of this paper will explore how the careful framing of questions with respect to available data can help researchers extract tangible decision driving results from real world data through spectral clustering analysis.
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HUALLPACHOQUE, ROBERTO CARLOS CHUCUYA. "NUMERICAL ANALYSIS OF FLOW PATTERN IN HORIZONTAL TWO-PHASE SLUG FLOW STATISTICALLY PERMANENT." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2010. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=17309@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR<br>O escoamento bifásico no regime de golfadas é um padrão de escoamento que requer esforço em sua caracterização e modelagem, devido às características marcantes da distribuição espacial das fases, que gera intermitência ao escoamento. Este escoamento ocorre na presença de uma grande faixa de vazões de gás e líquido, em tubulações de diâmetro médio e pequeno, com variação periódica da densidade, fração de vazio e pressões na seção transversal da tubulação. No presente trabalho estuda-se numericamente o regime de golfadas ao longo de tubulações horizontais utilizando-se o Modelo de Dois Fluidos. Uma análise detalhada das estatísticas do escoamento é realizada com a caracterização dos principais parâmetros de uma golfada, como comprimento, velocidade da frente e cauda e freqüência de passagem das golfadas ao longo da tubulação. Os dados obtidos das simulações são analisados através de histogramas de distribuição assim como de funções densidade de probabilidade (PDF) das variáveis hidrodinâmicas, destacando-se o caráter estocástico do escoamento no padrão de golfadas. Adicionalmente, comparações com dados de trabalhos experimentais da literatura foram realizadas com concordância muito boa.<br>Slug flow is a two-phase flow pattern that requires large effort in its characterization and modeling, due to special characteristics of the phase’s spatial distribution, which causes flow intermittency. This flow occurs in a wide range of gas and liquid flow rates in pipes of medium and small diameters, with periodic variation of density, void fraction and pressures in pipe-cross-section. This work presents a numerical study of the slug regime through horizontal pipes using the Two-Fluid Model. A detailed statistical analysis of the flow was carried out with characterization of main slug parameters, such as slug length, front and tail velocities and slug frequency along the pipeline. The numerical results were analyzed through distribution histograms as well as probability density function (PDF) of the hydrodynamic variables, showing the stochastic characteristic of slug flow pattern. Further, comparisons with experimental data from the literature were performed, showing very good agreement.
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Akbarzadeh, Masoud S. M. Massachusetts Institute of Technology. "Designing performative surfaces : computational interpretation of flow pattern drawings." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/72802.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Architecture, 2012.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 70).<br>Introduction: In spring 2011, while I was working on my thesis in architectural Design degree, I came across with an interesting problem in design: a parametric river. I realized that it is not possible to control the river parameters without understanding the geometry of the surface of terrain. in other words, the shape of the terrain or topography may change the shape of the river down the hills. I started to look up more examples in geoscience and geomorphology to find out more about this topic. I came across drainage patterns which vary based on the shape of the terrain in different parts of the world [Howard 1967]. As a designer, the first thought passed through my mind was: "is it possible to design a terrain using drainage patterns?" There must be a way to derive the landscape geometry from the one of the river!" Later on, through searching related topics in geoscience, I realized that this topic has interested researchers from 1858 and there is a quite enormous body of research on that in geo-computation and geography and computer science. I made this topic as the main goal of present thesis to explore the design possibility of such representation in architecture and connecting the world of design with hydrological and geological characteristics of the land. Recently the design proposals tend to become more engaged in sustainability aspects, more recently in energy generation. Therefore, many designers now seek approaches to integrate architectural ideas with interdisciplinary subjects to tackle the different aspects of energy constrains and sustainability issues. There is a recently developed area of research among architects which tries to define the design through the lenses of energy production. This field has received more attention in landscape design and planning strategies. Among all energy generating methods such as wind and solar, there are no many examples of addressing the design through hydropower energy generation which is the main basis of investigation in current study. In order to explain the goals of the thesis it is important to clarify the objectives of this study in a simple question: Is it possible to construct complex geometry of the surface of the terrain using drainage analysis? Or is it possible to embed required information of 3-dimensional space into 2-dimensional drawing. In that case, designers can design complex geometries using simple plan drawings which might result in more function-oriented design.<br>by Masoud Akbarzadeh.<br>S.M.
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Cheng, Hong. "The bubble to slug flow pattern transition in vertical columns." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339664.
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Eck, Thomas. "Measurement of vibrational energy flow using electronic speckle pattern interferometry." Thesis, Loughborough University, 2007. https://dspace.lboro.ac.uk/2134/35529.
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Vibrational energy flow (VEF) analysis (VEFA) is used to attain vibrational energy flow information within a vibrating structure of interest. Two essential pieces of information are provided, the direction of the energy flow as well as the magnitude of the energy flow. Once this information is available, vibration may be manipulated in order to suppress undesired vibrational phenomena. The measurement of VEF is an important part in providing VEF information from real structures. In the past the measurement of VEF was restricted to single point measurements only. However, recent developments in advanced laser measurement techniques, such as electronic speckle pattern interferometry (ESPI), have gained interest in applying these measurement techniques to the measurement of VEF.
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Achuthanandam, Ramasubramaniam Kam Moshe Hrebien Leonid. "Identifying regions of difference in flow cytometric data /." Philadelphia, Pa. : Drexel University, 2005. http://dspace.library.drexel.edu/handle/1860/730.
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George, Martin Selby. "Multi-resolution motion analysis using optical flow techniques." Thesis, University of Warwick, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365231.
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Wisby, C. "Real-time digital imaging techniques for flow visualization." Thesis, University of Surrey, 1989. http://epubs.surrey.ac.uk/848586/.
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A real-time digital imaging technique has been applied to smoke flow visualized turbulent flows to provide statistical data concerning bluff body wakes. The 'digital imaging technique' has been successfully applied to the wake of a two-dimensional flat plate, circular cylinder and a jet in a crossflow configuration. A detailed study of the two-dimensional flat plate model involved comparative hot-wire and pressure measurements combined with data from previously published experimental investigations. The results obtained included, intermittency measurements, vortex shedding spectral analyses (autocorrelations), spatial correlations, wake interface statistics and turbulence data. In the majority of cases, the digital imaging technique was found to provide excellent quantitative detail whilst also offering some unique wake interface statistics. The experiments conducted on the circular cylinder model revealed details of secondary vortex shedding and their base-bleed dependence, whilst the jet in a crossflow configuration enabled the imaging technique to be applied to a complex, three-dimensional flow model. The resulting iso-intermittency contour map was produced expediently, and within an experimental period far shorter than could be expected for single-location probe measurements. In addition to the above-outlined quantitative technique, real-time digital imaging was also applied more qualitatively to the study of dynamic stall on an aerofoil and to the enhancement of high-speed vapour-screen visualizations, both techniques offering the possibility for enhanced quantitative flow studies in future investigations. Finally, true-colour video digitisation has been exploited in a preliminary study of the quantification of global surface shear stress values using liquid crystal technology. Although in its infancy, the realisation of an experimental procedure along such lines would be of immense benefit to experimental aerodynamic research.
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Khan, Rab N. "The use of flow control devices to improve the flow pattern and throughput of sieve trays." Thesis, Aston University, 1998. http://publications.aston.ac.uk/9599/.
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Compared to packings trays are more cost effective column internals because they create a large interfacial area for mass transfer by the interaction of the vapour on the liquid. The tray supports a mass of froth or spray which on most trays (including the most widely used sieve trays) is not in any way controlled. The two important results of the gas/liquid interaction are the tray efficiency and the tray throughput or capacity. After many years of practical experience, both may be predicted by empirical correlations, despite the lack of understanding. It is known that the tray efficiency is in part determined by the liquid flow pattern and the throughput by the liquid froth height which in turn depends on the liquid hold-up and vapour velocity. This thesis describes experimental work on sieve trays in an air-water simulator, 2.44 m in diameter. The liquid flow pattern, for flow rates similar to those used in commercial scale distillation, was observed experimentally by direct observation; by water-cooling, to simulate mass transfer; use of potassium permanganate dye to observe areas of longer residence time; and by height of clear liquid measurements across the tray and in the downcomer using manometers. This work presents experiments designed to evaluate flow control devices proposed to improve the gas liquid interaction and hence improve the tray efficiency and throughput. These are (a) the use of intermediate weirs to redirect liquid to the sides of the tray so as to remove slow moving/stagnant liquid and (b) the use of vapour-directing slots designed to use the vapour to cause liquid to be directed towards the outlet weir thus reducing the liquid hold-up at a given rate i.e. increased throughput. This method also has the advantage of removing slow moving/stagnant liquid.
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Quinn, John R. Hrebien Leonid. "Development of a pattern recognition approach for analyzing flow cytometric data /." Philadelphia, Pa. : Drexel University, 2006. http://dspace.library.drexel.edu/handle/1860%20/843.
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Gehmlich, Michael Grant. "Flow pattern effects on aerosol size distributions of dry powder inhalers." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0013/MQ60122.pdf.
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Yórquez-Ramírez, María Isabel. "Gas flow pattern in the freeboard above a bubbling fluidised bed." Thesis, University of Edinburgh, 1999. http://hdl.handle.net/1842/11963.
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At present, a thermal cracking process is being developed at pilot plant scale at BP's research facilities in Scotland. The process converts a mixture of waste plastic into a hydrocarbon intermediate, which can be used for petrochemical or refinery processes. A problem of the process is the formation and growth of small amount of fibrous carbon in the freeboard space of the fluidized bed, used as the main reactor. The fibres are believed to form on active metallic sites, detach and grow in the recirculating areas in the freeboard. This can be tolerated but there are economic advantages in their reduction. The aim is to characterise the hydrodynamics of the flow in the freeboard to understand and control the growth of the fibres. A cold model of the fluidised bed used in the pilot plant have been constructed, following scaling laws that allow similar hydrodynamics behaviour of the two beds. Particle Image Velocimetry, PIV, a full-field non-intrusive optical velocity measurement technique is used to analyse the gas pattern in the freeboard. Due to the complexity of the flow and the limitations of the technique PIV was implemented using image shifting. The gas flow in the freeboard of a fluidised bed is strongly dependent on bubble eruption at the bed surface. Here, the gas flow above an erupting bubble has been studied by the injection of single bubbles in an incipiently fluidised bed. Gas velocity vector maps of the vertical central plane above the bed surface, i.e. a plane parallel to the direction of the overall flow, have been determined using image shifting. A mechanism has been proposed to describe the process of single bubble eruption.
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Hossen, Md Shakhawat. "Freight Flow, Pattern and Variable Magnitudes: Ins and Outs of Midwest." University of Toledo / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1501889816604518.
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Paluszny, Rodriguez Adriana. "Numerical simulation of fracture pattern development and implications for fluid flow." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/4438.
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Simulations are instrumental to understanding flow through discrete fracture geometric representations that capture the large-scale permeability structure of fractured porous media. The contribution of this thesis is threefold: an efficient finite-element finite-volume discretisation of the advection/diffusion flow equations, a geomechanical fracture propagation algorithm to create fractured rock analogues, and a study of the effect of growth on hydraulic conductivity. We describe an iterative geomechanics-based finite-element model to simulate quasi-static crack propagation in a linear elastic matrix from an initial set of random flaws. The cornerstones are a failure and propagation criterion as well as a geometric kernel for dynamic shape housekeeping and automatic remeshing. Two-dimensional patterns exhibit connectivity, spacing, and density distributions reproducing en echelon crack linkage, tip hooking, and polygonal shrinkage forms. Differential stresses at the boundaries yield fracture curving. A stress field study shows that curvature can be suppressed by layer interaction effects. Our method is appropriate to model layered media where interaction with neighbouring layers does not dominate deformation. Geomechanically generated fracture patterns are the input to single-phase flow simulations through fractures and matrix. Thus, results are applicable to fractured porous media in addition to crystalline rocks. Stress state and deformation history control emergent local fracture apertures. Results depend on the number of initial flaws, their initial random distribution, and the permeability of the matrix. Straightpath fracture pattern simplifications yield a lower effective permeability in comparison to their curved counterparts. Fixed apertures overestimate the conductivity of the rock by up to six orders of magnitude. Local sample percolation effects are representative of the entire model flow behaviour for geomechanical apertures. Effective permeability in fracture dataset subregions are higher than the overall conductivity of the system. The presented methodology captures emerging patterns due to evolving geometric and flow properties essential to the realistic simulation of subsurface processes.
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Kombo, Rainah. "Qualitative analysis of flow patterns : two-phase flow condensation at low mass fluxes and different inclination angles." Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/61303.
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A great deal of work has been conducted on in-tube condensation in horizontal and vertical smooth tubes. The available literature points to mechanisms governing two-phase condensation heat transfer coefficients and pressure drops, which are directly linked to the local flow pattern for both horizontal and inclined configurations. However, the work has been limited to flow pattern observations, heat transfer, pressure drops and void fractions for both horizontal and inclined tubes at high mass fluxes. No work has been conducted on the analysis of the observed flow patterns and the effect of temperature difference between the average wall temperature and average saturation temperature for different inclination angles at mass fluxes of 100 kg/m2.s and below. The purpose of this study is to carry out a qualitative analysis of flow patterns, and show the effect of temperature difference on the heat transfer coefficient for inclination angles from +90° (upward flow) to -90° (downward flow) at mass fluxes below 100 kg/m2.s. An experimental set-up provided the measurements for the two-phase condensation of R-143a in a smooth tube with an inside diameter of 8.38 mm and a length of 1.5 m. The mass fluxes were 25 kg/m2.s to 100 kg/m2.s, the saturation temperature was 40 °C and the mean qualities were 0.1 to 0.9. A high-speed camera was used to visually analyse and determine the flow patterns for both the inlet and the outlet of the test section. Through the results, eight flow patterns were observed: stratified-wavy, stratified, wavy, wavy-churn, intermittent, churn, annular and wavy-annular. The maximum heat transfer was observed for downward flow between inclination angles of -15° and -30°. The Thome-Hajal flow pattern map correctly predicted horizontal flow patterns, but failed to predict most of the inclined flow patterns. Various flow pattern transitions were identified and proposed for all the investigated inclination angles in this study. Finally, the heat transfer coefficient was found to be dependent on quality, mass flux, temperature difference and inclination angle.<br>Dissertation (MSc)--University of Pretoria, 2016.<br>Mechanical and Aeronautical Engineering<br>MSc<br>Unrestricted
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Ali, Shazia Farman. "Two-phase flow in a large diameter vertical riser." Thesis, Cranfield University, 2009. http://hdl.handle.net/1826/4476.
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The rapid depletion of hydrocarbon fields around the world has led the industry to search for these resources in ever increasing water depths. In this context, the large diameter (D > 100mm) vertical riser has become a subject of great interest.
In this research work, a major investigation was undertaken to determine the two phase flow hydrodynamics in a 254mm vertical riser. Two types of experiments were performed for range of air-water superficial velocities. The first experimental campaign addresses the issue of the two gas injector’s performances (conventional vs. novel design gas injector) in the large diameter vertical riser. The experimental results show that the novel design gas injector should be the preferential choice.
The second set of the experimental work investigates the two phase flow hydrodynamics in the vertical riser in detail. The two phase flow patterns and their transitions were identified by combination of visual observations and statistical features. Based on the results, the experimental flow regime map was developed and compared with the existing vertical upflow regime maps/models. None of the flow regime transition models adequately predicted the flow regimes transitions in large diameter vertical risers as a whole. In this regard, the Taitel et al. (1980) bubble to slug flow transition model has been modified for large diameter vertical upflow conditions, based on the physical mechanism observed. The general trends of modified criteria agreed well with the current and other large diameter experimental results.
The effect of upstream conditions on the vertical riser flow behaviour was also investigated in detail by two different inlet configurations (i) near riser base injection and (ii) upstream flowline injection. It was found that no significant differences exist in flow behaviour at low air-water superficial velocities for both the inlet configuration, at high air-water superficial velocities, the intermittent flow behavior in flowline influences the riser flow pattern characteristics and thereby controls the riser dynamics. It is found that liquid slugs from the flowline naturally dissipate to some extent in the riser as a consequence of compression of succeeding bubble that rapidly expands and break through the liquid slug preceding it when it enters the riser. The experimental work corroborates the general consensus that slug flow does not exist in large diameter vertical upflow condition.
Experimental data has been further compared to increase the confidence on the existing two phase flow knowledge on large diameter vertical riser: (a) by comparing with other experimental studies on large diameter vertical upflow in which generally, a good agreement was found, (b) by assessing the predictive capability of void fraction correlations/pressure gradient methods. The important implication of this assessment is that the mechanistic approach based on specific flow regime in determining the void fraction and pressure gradient is more successful than conventional empirical based approaches. The assessment also proposes a proposed set a of flow regime specific correlations that recommends void fraction correlations based on their performances in the individual flow regimes.
Finally, a numerical model to study the hydrodynamic behaviour in the large diameter horizontal flowline-vertical riser system is developed using multiphase flow simulator OLGA. The simulated results show satisfactory agreement for the stable flows while discrepancies were noted for highly intermittent flows. The real time boundary application was partially successful in qualitatively reproducing the trends. The discrepancies between the predicted results and experimental data are likely to be related to the incorrect closure relations used based on incorrect flow regimes predictions. The existence of the multiple roots in the OLGA code is also reported for the first time.
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Holt, Adrian John. "Two-phase pressure drop and void fraction in narrow channels." Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.480644.
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DALL'OLIO, Stefano. "Boiling of the R134a inside a glass minichannel : a new approach of flow pattern characterization based on flow visualization." Doctoral thesis, Università degli studi di Bergamo, 2009. http://hdl.handle.net/10446/84.
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Hallgren, Line. "Effect of swriling blade on flow pattern in nozzle for up-hill teeming." Licentiate thesis, KTH, Materials Science and Engineering, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4269.
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<p>The fluid flow in the mold during up-hill teeming is of great importance for the quality of the cast ingot and therefore the quality of the final steel products. At the early stage of the filling of an up-hill teeming mold, liquid steel enters, with high velocity, from the runner into the mold and the turbulence on the meniscus could lead to entrainment of mold flux. The entrained mold flux might subsequently end up as defects in the final product. It is therefore very important to get a mild and stable inlet flow in the entrance region of the mold. It has been acknowledged recently that swirling motion induced using a helix shaped swirl blade, in the submerged entry nozzle is remarkably effective to control the fluid flow pattern in both the slab and billet type continuous casting molds. This result in increased productivity and quality of the produced steel. Due to the result with continuous casting there is reason to investigate the swirling effect for up-hill teeming, a casting method with similar problem with turbulence.</p><p>With this thesis we will study the effect of swirling flow generated through a swirl blade inserted into the entry nozzle, as a new method of reducing the deformation of the rising surface and the unevenness of the flow during filling of the up-hill teeming mold. The swirling blade has two features: (1) to generate a swirling flow in the entrance nozzle and (2) to suppress the uneven flow, generated/developed after flowing through the elbow. The effect of the use of a helix shaped swirl blade was studied using both numerical calculations and physical modelling. Water modelling was used to assert the effect of the swirling blade on rectifying of tangential and axial velocities in the filling tube for the up-hill teeming and also to verify the results from the numerical calculations. The effect of swirl in combination with diverged nozzle was also investigated in a similar way, i. e. with water model trials and numerical calculations.</p>
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Hallgren, Line. "Effect of swirling blade on flow pattern in nozzle for up-hill teeming." Licentiate thesis, Stockholm : Department of Materials Science and Engineering, Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4269.
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Gai, Huawen. "Ultrasonic techniques for flow imaging : front-end transducers, image reconstruction algorithms and system design." Thesis, University of Manchester, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387579.
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Manathunga, Kalpani. "Technology support for scalable and dynamic collaborative learning: a pyramid flow pattern approach." Doctoral thesis, Universitat Pompeu Fabra, 2017. http://hdl.handle.net/10803/456041.
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Collaborative Learning is the pedagogical approach that considers social interactions as key means to trigger rich learning processes. Collaborative Learning Flow Patterns define best practices to orchestrate collaborative learning activity flow mechanisms (i.e., group formation, roles or resources allocation, phase change). Flow patterns have been experimented and evaluated as effective in small scale settings for decades. Directly applying these pedagogical methods to large learning scenarios is challenging due to the burden that scale represents in the orchestration load or the difficulty of keeping a dynamic meaningful progression when flexible changes are required in a large classroom or in a MOOC. Some attempts have shown positive results, but research around scalable collaborative learning approaches, models and technologies for large classes is scattered. This dissertation conducts a systematic literature review of collaborative learning applications on large classes and analyses the social learning potential of diverse technology-supported spaces in massive courses. Then the dissertation focuses the study on how collaborative learning could address key challenges (i.e., scalability and dynamism) identified in large collaborative learning contexts. Consequently, the thesis proposes a Pyramid flow pattern instantiation, composed of a model with a set of algorithmic rules for flow creation, flow control and flow awareness as well as a PyramidApp authoring and enactment system implementing the model. Experimentation across diverse learning contexts shows that, on one hand, the contributions support meaningful scalable and dynamic collaborative learning and on the other hand, learners and educators perceive the experiences as engaging, with learning values and effective from the perspective of orchestration.<br>El aprendizaje colaborativo es el enfoque pedagógico que considera las interacciones sociales como un medio clave para desencadenar procesos de aprendizaje ricos. Los patrones de flujo de aprendizaje colaborativo definen buenas prácticas para orquestar mecanismos de flujo en actividades de aprendizaje colaborativo (es decir, la formación de grupos, la asignación de roles o recursos, los cambios de fase). Los patrones de flujo han sido probados y evaluados como efectivos en entornos de pequeña escala durante décadas. La aplicación de estos métodos pedagógicos en grandes escenarios de aprendizaje supone un reto debido a la carga que representa la escala en la orquestación, así como a la dificultad de mantener una progresión dinámica con sentido pedagógico cuando se requieren cambios flexibles en un aula grande o en un MOOC. Existen algunos intentos interesantes, pero la investigación en torno a enfoques de aprendizaje colaborativo escalables, y modelos y tecnologías para entornos educativos con muchos estudiantes está dispersa. Esta tesis lleva a cabo una revisión sistemática de la literatura sobre aplicaciones de aprendizaje colaborativo con muchos estudiantes y analiza el potencial de aprendizaje social de diversos espacios apoyados por la tecnología en este tipo de contextos. A continuación, la tesis se centra en el estudio de cómo el aprendizaje colaborativo podría abordar desafíos clave identificados en contextos de aprendizaje colaborativo con un gran número de estudiantes (es decir, la escalabilidad y el dinamismo). En consecuencia, la tesis propone una instanciación del patrón de flujo Pirámide, compuesto de un modelo con un conjunto de reglas algorítmicas para la creación, el control y la conciencia del flujo de aprendizaje, así como un
sistema de creación e implementación del modelo. La experimentación realizada en distintos contextos de aprendizaje demuestra que, por un lado, las contribuciones apoyan un aprendizaje colaborativo escalable y dinámico, y que, por otro lado, los estudiantes y los educadores perciben las experiencias como amenas, con valor para el aprendizaje y efectivas desde la perspectiva de la orquestación.
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Han, Yanjie. "Two-phase flow pattern identification from fluctuating signals of pressure and void fraction." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0020/MQ48853.pdf.
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Davis, Shanon Marie. "Heat-Flux Measurements for a Realistic Cooling Hole Pattern and Different Flow Conditions." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1315013452.
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Castellano, Gabriela. "Investigation and application of a complex wavelet transform algorithm for the estimation of optical flow." Thesis, King's College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391765.
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Bai, Haitong. "A Study of the Swirling Flow Pattern when Using TurboSwirl in the Casting Process." Doctoral thesis, KTH, Tillämpad processmetallurgi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-196806.
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The use of a swirling flow can provide a more uniform velocity distribution and a calmer filling condition according to previous studies of both ingot and continuous casting processes of steel. However, the existing swirling flow generation methods developed in last decades all have some limitations. Recently, a new swirling flow generator, the TurboSwirl device, was proposed. In this work, the convergent nozzle was studied with different angles. The maximum wall shear stress can be reduced by changing the convergent angle between 40º and 60º to obtain a higher swirl intensity. Also, a lower maximum axial velocity can be obtained with a smaller convergent angle. Furthermore, the maximum axial velocity and wall shear stress can also be affected by moving the location of the vertical runner. A water model experiment was carried out to verify the simulation results of the effect of the convergent angle on the swirling flow pattern. The shape of the air-core vortex in the water model experiment could only be accurately simulated by using the Reynolds Stress Model (RSM). The simulation results were also validated by the measured radial velocity in the vertical runner by the ultrasonic velocity profiler (UVP). The TurboSwirl was reversed and connected to a traditional SEN to generate the swirling flow. The periodic characteristic of the swirling flow and asymmetry flow pattern were observed in both the simulated and measured results. The detached eddy simulation (DES) turbulence model was used to catch the time-dependent flow pattern and the predicted results agree well with measured axial and tangential velocities. This new design of the SEN with the reverse TurboSwirl could provide an almost equivalent strength of the swirling flow generated by an electromagnetic swirling flow generator. It can also reduce the downward axial velocities in the center of the SEN outlet and obtain a calmer meniscus and internal flow in the mold.<br>Tidigare studier visar att ett roterande flöde kan ge en mer likformig hastighetsfördelning och en lugnare fyllning i både göt- och stränggjutning av stål. De befintliga metoderna för att generera ett roterande flöde har vissa begränsningar. En ny metod för att generera det roterande flödet, en så kallad TurboSwirl, föreslogs nyligen. I detta arbete undersöktes ett konvergent munstycke med olika vinklar för att se hur detta påverkade det roterande flödet som genererades i anordningen. Resultaten visar att skjuvspänningen i systemet kan reduceras genom att ändra munstyckets vinkel mellan 40º till 60º. En lägre maximal axiell hastighet kan också uppnås med en mindre konvergent vinkel på munstycket. Det är även möjligt att påverka den maximala axiella hastigheten och skjuvspänningen i systemet genom att förflytta den vertikala kanalen i anordningen. Vattenmodellexperiment har utförts för att validera simuleringsresultaten. Det kraftigt roterande flödet kunde endast beskrivas väl av Reynolds Stress Model (RSM). Validering utfördes också genom att mäta den radiella hastigheten i den vertikala kanalen med en Ultrasonic Velocity Profiler (UVP). TurboSwirl-anordningen vändes och kopplades till gjutröret för att generera det roterande flödet. Detta studerades både med numeriska modeller och med vattenmodellering. Ett periodiskt asymmetriskt roterande flöde observerades både i numeriska modellerna och i vattenmodellerna. För att modellera detta periodiska flöde så användes detached eddy simulation (DES) modellen. Resultaten då denna modell användes stämmer väl med de experimentella mätningarna. Denna nya design med TurboSwirl kan uppnå liknande styrka på det roterande flödet som när elektromagnetisk omrörning användes. Det resulterande roterande flödet leder till en lägre axiell hastighet i gjutröret samt en lugnare yta och ett lugnare flöde i kokillen.<br><p>QC 20161123</p>
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Duran, Tibo. "Summary of Laboratory Multiphase Flow Studies in 2” Diameter Pipe at the University of Dayton and Comparison to OLGA Predictions." University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1430004871.
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Bhattarai, Pawan Kumar. "Study on River Dyke Breach Characteristics by Overtopping Flow." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/202685.
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Sancet, Aitor. "Study of heat transfer and flow pattern in a multiphase fuel oil circular tank." Thesis, University of Gävle, University of Gävle, Department of Technology and Built Environment, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-4926.
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<p>This is a thesis work proposed by Sweco System in order to carry out a study related to the heating system of a circular fuel oil storage tank or cistern. The study tank is a 23m diameter and 18m height with a storage capacity of around 7500m3 of Eo5 heavy fuel oil. The content ought to be at a minimum storage temperature of 50ºC so that the fuel oil is fluid enough and operation labors can be adequately performed. In fact, these types of heavy fuel oils have fairly high viscosities at lower temperatures and the heating and pumping system can be compromised at temperatures below the pour point. For this purpose a heating system is installed to maintain the fluid warm. So far the system was operated by an oil burner but there are plans to its replacement by a District Heating-heat exchanger combo. Thereby, tank heating needs, flow and thermal patterns and heat transfer within it are principally studied.</p><p> </p><p>Tank boundaries are studied and their thermal resistances are calculated in order to dimension heat supply capacity. The study implies Finite Elements (Comsol Multiphysics) and Finite Volume (Fluent) analysis to work out some stationary heat transfer by conduction cases on some parts and thermal bridges present on these boundaries. Afterwards both cooling and heating processes of the fuel oil are studied using several strategies: basic models and Computational Fluid Dynamics (CFD). CFD work with Fluent is focused on optimizing inlet and outlet topologies. Understanding the cooling process is sought as well; Fluent CFD transient models are simulated in this way as well. Additionally the effect of filling levels is taken into account leading to a multiphase (fuel oil and air) flow cases where especially heating coupling of both phases is analyzed.</p><p> </p><p>Results show that maximum heat supply needs are around 80kW when the tank temperature is around 60ºC and 70kW when it is around 50ºC. Expectedly the main characteristic of the flow turns out to be the buoyancy driven convective pattern. K-ε turbulence viscous models are applied to both heating and cooling processes showing thermal stratification, especially at the bottom of the tank. Hotter fluid above follows very complex flow patterns. During the heating processes models used predict fairly well mixed and homogenous temperature distribution regardless small stratification at the bottom of the tank. In this way no concrete inlet-outlet configuration shows clear advantages over the rest. Due to the insulation of the tank, low thermal conductivity of the fluid and vast amount of mass present in the tank, the cooling process is slow (fluid average temperature drops around 5.7 ºC from 60ºC in 15 days when the tank is full and ambient temperature is considered to be at -20ºC) and lies somewhere in the middle between the solid rigid and perfect mixture cooling processes. However, due to stratification some parts of the fluid reach minimum admissible temperatures much faster than average temperature does. On the other hand, as expected, air phase acts as an additional thermal resistance; anyhow the cooling process is still faster for lower filling levels than the full one.</p><br><p>El presente proyecto fue propuesto por Sweco Systems para llevar a cabo un estudio relacionado con el sistema de calefacción de una cisterna o tanque de almacenamiento de fuel oil circular. Dicho tanque tiene 23 m de diámetro y 18 m de altura con una capacidad de almacenamiento de alrededor de 7500 m<sup>3</sup> de Eo5 fuel oil pesado. El contenido mantenerse a una temperatura mínima de 50 ºC de manera que el fuel oil es suficientemente fluido para que las labores de operación puedan ser ejecutadas adecuadamente. De hecho, estos tipos de fuel oil pesado tienen altas viscosidades a bajas temperaturas y, por tanto, tanto los sistemas de calefacción y como el de bombeo pueden verse comprometidosr a temperaturas por debajo del pour point. Con este fin un sistema de calefacción es instalado para mantener el fluido suficientemente caliente. Hasta el momento, el sistema era operado por un quemador de fuel, sin embargo, hay planes que éste sea sustituido por un combo intercambiador de calor-District Heating. Por lo tanto, principalmente son estudiadas las necesidades de calefacción así como los flujos térmicos y fluidos.</p><p>Se estudian las fronteras del tanque, y sus respectivas resistencias térmicas son calculadas con el fin de dimensionar la capacidad necesaria de suministro de calor. El estudio implica Elementos Finitos (Comsol Multiphysics) y Volúmenes Finitos (Fluent) para elaborar análisis estacionarios de transferencia de calor por conducción en algunos casos. Existen puentes térmicos en las paredes y su importancia es también anallizada. Posteriormente se estudian tanto los procesos de calentamiento y enfriamiento del fuel oil utilizando diversas estrategias: modelos básicos y Dinámica de Fluidos Computacional (CFD). El trabajo con CFD se centra en la optimización de topologías de entradas y salidas del sistema. También es solicitado entender el proceso de enfriamiento; En este sentido, se simulan modelos CFD transitorios de Fluent. Además, el efecto de los niveles de llenado se tiene en cuenta dando lugar a estudios de flujo multifase (fuel oil y aire), haciendo hincapié en el análisis de acoplamiento de transferencia de calor entre las dos fases.</p><p>Los resultados muestran que las necesidades de calefacción máximas son de alrededor de 80kW cuando la temperatura del tanque es de alrededor de 60 º C y 70kW cuando está alrededor de 50 ºC. Como era de esperar, la principal característica de este tipo de flujos es la convección natural resultante de las fuerzas de flotabilidad. Se aplican modelos turbulentos k-ε a los procesos de calentamiento y enfriamiento, mostrando estratificación térmica, sobre todo en la parte inferior de la cisterna. El líquido más caliente que se sitúa encima muestra complejos patrones de flujo. Durante los procesos de calentamiento, los modelos utilizados predicen un buen mezclado y distribución homogénea de la temperatura independientemente de esta pequeña estratificación en la parte inferior de la cisterna. De esta manera, ninguna concreta configuración de entradas-salidas simuladas muestra claras ventajas sobre el resto. Debido al aislamiento de la cisterna, la baja conductividad térmica del fluido y la gran cantidad de masa presente en el tanque el proceso de enfriamiento es lento (la temperatura media del fluido desciende 5.7 º C desde 60 º C en 15 días cuando el tanque está lleno y la temperatura ambiente es de -20 º C) y se encuentra en algún lugar en medio de los procesos de enfriamiento del sólido rígido y perfecta mezcla. Sin embargo, debido a la estratificación, algunas partes el líquido alcanzan la temperatura mínima admisible mucho más rápido que la media de temperatura. Por otra parte, como se esperaba, la fase de aire actúa como una resistencia térmica adicional, de todos modos, el proceso de enfriamiento es aún más rápido para niveles de llenado más bajos que el lleno.</p>
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Guo, Zhenyu 1963. "Time-frequency representation and pattern recognition of doppler blood flow signal for stenosis classification." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41252.
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The objective of this thesis is to characterize the time-frequency representation (TFR) of the Doppler blood flow signal in order to improve the detection and quantification of arterial stenoses. First of all, we studied the statistical behavior of the Doppler blood flow signal and found that the signal is Gaussian and inherently nonstationary. However, the usual assumption of stationarity during a short time interval ($ leq$10 ms) is acceptable. The signal was then modeled as a complex autoregressive (AR) process to provide directional information about the blood flow. It was shown that the TFR based on AR modeling is less sensitive to window length and sampling frequency than the spectrogram. In order to obtain a more precise Doppler TFR, a new distribution based on a Bessel kernel was proposed. This Bessel distribution can suppress the cross-terms effectively and has many desirable properties with high resolution in time and frequency. A numerical alias-free implementation of this distribution was also developed.<br>A realistic model of the Doppler blood flow signal of the femoral artery was proposed and used to simulate signals for comparing five TFR techniques: the short-time Fourier transform, AR modeling, the Bessel distribution, the Choi-Williams distribution, and the Choi-Williams Reduced Interference Distribution. The results showed that the Bessel distribution is the best, but the Choi-Williams distribution and AR modeling are also good techniques to compute Doppler TFRs. The short-time Fourier transform, AR modeling, and the Bessel distribution were then applied to clinical data to derive diagnostic features for a pattern recognition system to assess lower limb arterial stenoses in 37 patients. A total of 379 arterial segments were classified into three stenotic classes. The results were in agreement with those based on computer-simulated signals, and confirmed that the Bessel distribution and AR modeling improve the Doppler spectral estimates and thus provide better classification of arterial stenosis.
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Ashfaque, Khandaker. "Effect of hydrological flow pattern on groundwater arsenic concentration in Bangladesh by Khandaker Ashfaque." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42218.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2007.<br>Includes bibliographical references.<br>Widespread arsenic contamination of groundwater has become a major concern in Bangladesh since the water supply, particularly in rural areas, is heavily dependent on groundwater. However, relative to the extent of research on biogeochemical processes of arsenic mobilization, very little work has been conducted to understand the complex transient dynamics of groundwater flow, and the transport of arsenic and other solutes that control its mobility in the area. A detailed three-dimensional hydrological model of our study area in Munshiganj indicates that: (1) the shallow aquifer acts primarily as a conduit for flow from ponds and rice fields to irrigation wells and rivers; (2) most inflow to the aquifer occurs during the dry season, and monsoon contributes relatively little to the inflow since the aquifer storage is small; (3) since the increase in irrigation pumping and pond construction have changed the groundwater flow dynamics, arsenic concentrations are unlikely to be at steady-state. These observations are consistent with those from the lumped-parameter model. Analysis of various fluxes from the three-dimensional groundwater model also reveals that ponds provide the largest source of recharge to the aquifer, and hence, is a potential source of dissolved arsenic to the subsurface. Accordingly, a "Pond Hypothesis" has been developed suggesting that arsenic mobilization in Bangladesh aquifer is deriving from reductive dissolution of various arsenic bearing oxides (the widely accepted mechanism for arsenic mobilization in Bangladesh) deposited at the pond bottoms. The process of reductive dissolution occurs in the presence of organic matter and under reducing environment, when residing microbes respire on oxygen from oxide-minerals (e.g. Fe and Mn oxides) to process the organic matter for growth, and subsequently causes release of arsenic associated with the oxide-minerals to the aqueous phase.<br>(cont.) Afterwards, at the end of flooding season, the dissolved arsenic along with mixture of various dissolved solutes from pond bottoms enters the aquifer and is driven towards the well screen both vertically due to overlying recharge and horizontally due to increased pumping. Extensive small-scale pump tests and one large-scale extended pumping experiment carried out at our study area in Munshiganj indicates that the aquifer is anisotropic in nature creating flow convergence at the depth of irrigation well screen. Results from a three-dimensional hydrological model suggests that groundwater irrigation has changed the flow dynamics in the area - not only by reducing the residence and travel times, but also carrying solutes to particular depth from different sources and locations. Model simulations carried out for three different scenarios - 'Current Stage' (if the current flow condition continues), 'Ancient Stage' (before the advent of habitation and irrigation practices), and 'Inception Stage' (the beginning of irrigation and creation of ponds) - indicates that in general, the rice field water dominates at the shallowest depth while pond water dominates at the depth of irrigation well, and the contribution from river water increases with depth. Analysis of the average groundwater age distribution indicates that younger age dominates at shallower depths. More importantly, the age values at the monitoring locations can be explained by the relative contribution of recharge water from different sources. Furthermore, modeling results indicate that the groundwater age at 30m depth in Bejgoan Field Site is about 24-60 years old, which is consistent with the tritium age measurement at the same depth. The stable water isotope values in our study area shows a similar profile to the dissolved arsenic concentration, and their peak concentrations coincidence with the depth of irrigation well.<br>(cont.) Furthermore, comparison of calculated and measured isotopic values at the Bejgoan Field Site indicates that the calculated values are within the range of measured values, and thereby, confers that the observed isotopic profile results from the mixing of water from various recharge sources. More importantly, the lighter water at the depth of peak arsenic concentration can only be derived from lighter pond water recharge in November, whereas recharge from river and rainfall mainly occurs after March when those waters are actually heavier. Finally, observation of two distinct peaks in the dissolved arsenic concentration profile from a recently installed cluster beside a highly recharging pond provides a direct evidence supporting the "Pond Hypothesis". While the peak concentration at 30-40m depth corresponds to the characteristic regional hump observed in our study area, the second peak at a shallower depth (20m) has been explained as the local arsenic plume originating from the nearby pond bottom.<br>Ph.D.
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Sunday, Nsidibe. "Numerical Investigation of Multiphase Flow in Horizontal and Inclined Flowlines." Electronic Thesis or Diss., Bourges, INSA Centre Val de Loire, 2023. http://www.theses.fr/2023ISAB0005.
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Alors que la quête d'hydrocarbures s'approche des nouvelles frontières dans un environnement sous-marin difficile et hostile. Le coût énorme de la gestion des problèmes d'assurance de l'écoulement dans les puits sous-marins, les conduites d'écoulement et les colonnes montantes, en particulier dans les applications en eaux profondes, a nécessité une approche proactive pour prévenir le risque d'apparition de ces problèmes. Pour s'assurer que le transport des hydrocarbures est économique et efficace depuis la tête de puits sous-marine jusqu'aux unités de traitement, un système de gestion de la chaleur pour l'assurance de l'écoulement est pertinent dans la conception et la planification d'un système de transport des fluides. Par conséquent, l'avancement des nouvelles technologies pour répondre aux besoins croissants en explorant l'environnement sous-marin hostile et technologiquement difficile est d'une grande importance. Les chiffres de l'étude ont montré la nécessité d'une recherche scientifique dans le domaine du chauffage actif.Ce travail se poursuit à ce stade. Il étudie et étend un modèle biphasé tridimensionnel concernant différents aspects. Pour ce faire, le solveur biphasique interFoam du code source OpenFoam est utilisé. Pour commencer, les propriétés hydrodynamiques de différents modèles dans les lignes d'écoulement sont étudiées en analysant un écoulement diphasique tridimensionnel de gaz et de liquide dans une ligne d'écoulement horizontale. InterFoam, un solveur diphasique transitoire, a d'abord été modifié pour mettre en œuvre le modèle k-ε à faible nombre de Reynolds (LRN) dans le code OpenFOAM. Ce modèle de turbulence LRN k-ε est utilisé pour résoudre les phénomènes de turbulence dans les mélanges de gaz et de liquide. L'écoulement diphasique est calculé en utilisant le solveur développé basé sur l'approche Volume de fluide (VOF). Les résultats des modèles d'écoulement à différentes vitesses superficielles du gaz et du liquide sont validés par les données expérimentales de la littérature. Ensuite, trois modèles Navier-Stokes moyennés par Reynolds (RANS) ont été utilisés pour les calculs : LRN k-ε, standard k-ε, et le modèle Shear Stress Transport k-omega (SST k-ω). Les résultats numériques générés sont comparés aux données expérimentales obtenues et aux modèles mécanistes.En outre, la structure de l'écoulement huile-eau rapportée dans la littérature est complètement différente de celle de l'écoulement gaz-pétrole et cette distinction est attribuée au faible effet de flottabilité et à la grande capacité de transfert de quantité de mouvement dans les écoulements huile-eau. Pour découvrir les caractéristiques de l'écoulement huile-eau, un modèle mathématique 3D de l'écoulement newtonien huile-eau dans des conditions non isothermes est établi pour explorer les mécanismes complexes du transport diphasique huile-eau et du transfert de chaleur dans la ligne d'écoulement horizontale et inclinée. Dans ce travail, un modèle d'écoulement diphasique non isotherme est d'abord modifié, puis implémenté dans le solveur InterFoam en introduisant l'équation d'énergie à l'aide d'OpenFOAM®. Les modèles d'écoulement et les coefficients de transfert de chaleur locaux (HTC) pour l'écoulement diphasique huile-eau à différentes inclinaisons des lignes d'écoulement (0°, +4°, +7°) sont validés par les résultats de la littérature expérimentale et les erreurs relatives sont également comparées. Le modèle a également été utilisé pour vérifier l'effet de la coupe d'eau d'entrée et de l'inclinaison des lignes d'écoulement sur les régimes d'écoulement, et les résultats ont été validés dans la littérature avec un niveau de précision élevé. Une analyse de sensibilité globale est ensuite menée pour déterminer l'effet des différents paramètres sur les performances des systèmes d'hydrocarbures diphasiques produits pour un transport efficace des fluides sous-marins<br>As the quest for hydrocarbon approaches the next frontiers in a challenging and hostile subsea environment. The enormous cost of handling the challenges of flow assurance in subsea wells, flowlines, and risers, especially in deepwater applications, has necessitated a proactive approach to prevent their risk of occurrence. To ensure that the transportation of the hydrocarbon is economical and efficient from the subsea wellhead to the processing units, a flow assurance heat management system is relevant in the design and planning of a fluid transport system. Therefore, the advancement of new technologies to serve the increasing need by exploring the technologically challenging and hostile subsea environment is of great significance. The figures from the study showed the need for scientific research in the field of active heating.This work continues at this point. It investigates and extends a three-dimensional two-phase model regarding different aspects. For this purpose, the two-phase solver interFoam in the OpenFoam source code is employed. To begin with, the hydrodynamic properties of different models in flowlines are investigated by analyzing a 3-D two-phase gas and liquid flow in a horizontal flowline. InterFoam a transient two-phase solver was first modified to implement the Low Reynolds Number (LRN) k-ε model in the OpenFOAM code. This LRN k-ε turbulence model is utilized to resolve the turbulence phenomena within the gas and liquid mixtures. The two-phase flow is calculated by using the developed solver based on the Volume of Fluid (VOF) approach. Results of the flow patterns at different superficial gas and liquid velocities are validated by the experimental data in the literature. Afterward, Three Reynolds-Averaged Navier-Stokes (RANS) models were used for computations: LRN k-ε, standard k-ε, and the Shear Stress Transport k-omega (SST k-ω) models. Generated numerical results are compared with obtainable experimental data and mechanistic models.Furthermore, the oil-water flow structure reported in the literature is completely different from that of gas-oil flow and this distinction is attributed to the small buoyancy effect and large momentum transfer capacity in the oil-water flows. To find the features of the oil-water flow, a 3D mathematical model of oil-water Newtonian flow under non-isothermal conditions is established to explore the complex mechanisms of the two-phase oil-water transportation and heat transfer in the horizontal and inclined flowline. In this work, a non-isothermal two-phase flow model is first modified and then implemented in the InterFoam solver by introducing the energy equation using OpenFOAM®. The LRN k-ε turbulence model is utilized to resolve the turbulence phenomena within the oil and water mixtures. The flow patterns and the local heat transfer coefficients (HTC) for two-phase oil-water flow at different flowlines inclinations (0°, +4°, +7°) are validated by the experimental literature results and the relative errors are also compared. The model was also employed to ascertain the effect of input water cut and flowline inclinations on the flow regimes, and the results were validated in the literature with a high accuracy level. Global sensitivity analysis is then conducted to determine the effect of the different parameters on the performance of the produced two-phase hydrocarbon systems for effective subsea fluid transportation.Thereafter, HTC and flow patterns for oil-water flows at a flowline inclination ranging from -10° to +10° can be predicted by the model
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Jeyaraj, Jesudoss Asirvatham. "Numerical Modeling of Concrete Flow in Drilled Shaft." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7528.
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Drilled shafts are cylindrical, cast-in-place concrete deep foundation elements. Their construction involves drilled excavation of soil or rock using large diameter augers, and placement of the necessary reinforcing steel in the excavation followed by concreting. Where a high water table is encountered, drilling slurry is used to support the excavation walls and concreting is tremie-placed. Even though the history of drilled shaft construction goes back to the 1950s, the occurrence of anomalies persists in the form of soil inclusions, reduction in shaft cross-sectional area and exposure of reinforcement. One of the main reasons for the anomalies is attributed to the kinematics of concrete flowing radially from within the reinforcing cage to the surrounding annulus/concrete cover region. In view of this radial component of concrete flow and thus radially flowing interfaces between the concrete and slurry, the region outside the cage is more likely to contain veins of poorly cemented or high water-cement ratio material. These veins contain trapped slurry, which oftentimes consists of bentonite, jeapordizing the integrity of the shafts.
This research program focuses on the numerical evaluation of self-consolidating concrete (SCC) for drilled shaft application by taking into account realistic non-Newtonian concrete flow properties and the shaft structural blockages. For this objective, a 3-D computational fluid dynamics (CFD) model of the concrete flow in the shaft excavation is developed in ANSYS-Fluent. As a precursor to 3-D modeling, 2-D CFD modeling is carried out using COMSOL Multiphysics. In both 2-D and 3-D models, the Volume of Fluid method is used for computing the motion of the interface between the concrete and the drilling slurry. The models predict the flow patterns and volume fraction of concrete and slurry. The results are encouraging as the flow pattern from the simulation shows both horizontal and vertical creases in the concrete cover region. Moreover the flow pattern shows the concrete head differential developed between the inside and the outside the reinforcement cage. Further, the 3-D model is evaluated by studying the influence of the size of drilled shaft and arrangement of the bars and the results obtained are realistic.
With this 3-D model developed as a tool, the simulation of SCC and the normal standard concrete (NC) flow in drilled shaft concreting are studied in terms of creases and concrete head differential encountered in the flow. From the simulation, it is observed that in the flow pattern of SCC, the creases are very few compared to the one obtained from the flow pattern of NC. Moreover, the concrete head differential in the flow pattern of SCC is much less, than the head differential obtained from the flow pattern of NC flow. In the case of SCC, the head differential encountered about one inch. In the case of NC, the concrete head differential is 4-inch when the vertical rebars are spaced at 7-inch apart and 10-inch when the rebars are placed at 3.5-inch apart. Based on this numerical evaluation of SCC flow in the drilled shaft excavation, it is concluded that the performance of SCC is better than the performance of NC in filling the cover annular region of drilled shafts.
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Alm, Max-Bernhard. "Flow pattern analysis of a Surface Flow Constructed Wetland : Treating surface runoff and landfill leachate water from the Löt waste management site." Thesis, KTH, Hållbar utveckling, miljövetenskap och teknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-285896.
Full textAbstract:
The waste management and recycling company, Söderhalls Renhållningsverk (SÖRAB) have constructed a surface flow wetland in order to treat surface runoff from the waste management site, Löt. The contaminated water passes several treatment steps until it reaches the wetland and a subsequent soil infiltration step. It is suspected that the flow path of the water through the wetland is short-circuited which may result in a reduced treatment efficiency. The current discharge concentrations of the chemical compounds tested for do not exceed the allowed discharge limits. However, it is of interest to keep the discharge concentrations as low as possible to protect sensitive areas and water bodies downstream. The aim of the thesis was therefore to investigate the flow pattern of the wetland and suggest measures which potentially could improve the treatment efficiency. The flow pattern was modelled numerically in a Physio-Mathematical model developed by Wörman and Kjellin (2020). The current flow pattern was modelled, followed by several simulation runs where the controlling factors of the flow were changed one by one. The validity of the modelling result is uncertain and should therefore be confirmed or rejected by conducting a tracer test prior to implementing any changes in the wetland design. The modelling results indicate the presence of a main flow path passing through the narrower section of the permeable embankment (intersecting the northern and southern part of the wetland, see Fig. 3). The results further indicate that the permeable embankment, the bottom topography and the vegetation distribution were the three major factors controlling the flow pattern within the wetland. Recommended improvements would therefore be to first conduct a tracer test to make sure that any changes implemented are based on the true current flow pattern. The embankment and the vegetation distribution seem to be the main causes of non-idealities in the flow but at the same time probably also have positive effects on the treatment efficiency (since they provide filtration and surface areas where microorganisms can attach to perform their treatment). One solution to reduce the non- idealities in the flow could therefore be to adjust the embankment to be equally wide and deep across the wetland. Furthermore, the bottom topography around the embankment could be adjusted so that the shift in bottom elevation is equal around it. This would probably aid in hindering the development of preferential flow paths through the embankment. Finally, the vegetation distribution could be made uniform. (It should also be noted that a uniform vegetation distribution would require adjustment of the water depth to be below 1,5 m to allow an equal establishment of vegetation).<br>Avfallshanterings- och återvinningsföretaget Söderhalls Renhållningsverk AB (SÖRAB) har anlagt en våtmark vid Löts avfallsanläggning, ca 35 km norr om Stockholm. Våtmarken utgör det näst sista reningssteget i reningsprocessen av lak- och processvatten från avfallsanläggningen. Riktvärdena för utsläppshalterna överskrids inte men det är önskvärt för SÖRAB att åstadkomma så låga utsläppsvärden som möjligt för att minimera påverkan på känsliga områden och vattendrag nedströms. SÖRAB misstänker dock att preferentiella flödesvägar kan förekomma där vattnet passerar alltför fort genom våtmarken. Detta resulterar ofta i en lägre reningseffektivitet då föroreningarna som är lösta i vattnet får en kortare kontakttid med de naturliga reningsmekanismerna som förekommer i våtmarken. Syftet med det här arbetet var därför att undersöka strömningen i våtmarken och identifiera vattnets flödesvägar med hjälp av en numerisk modell utvecklad av Wörman och Kjellin (2020). Strömningen i våtmarker styrs av en energigradient där flödet går från en punkt i ett vattendrag med högt energiinnehåll till en punkt med lågt energiinnehåll. Enligt principen om energins bevarande omvandlas energin mellan kinetisk, potentiell, tryckenergi och värmeenergi. Ändringen i energiinnehåll beror i sin tur på verkan av externa krafter (gravitationskraften, hydrostatiska tryckkrafter, friktionskrafter, kontraktions- och expansionskrafter och skjuvkrafter från vind. Dessa krafter verkar vid förändringar i bottentopografin, vattendjupet, ytmotståndet (vid våtmarkens botten och väggar), våtmarkens geometri samt där vattenytan är exponerad för vind. Dessa faktorer orsakar utvecklandet av skjuvkrafter i flödet som i sin tur orsakar utvecklandet av hastighetsprofiler och omblandning. Bildandet av hastighetsprofiler och omblandning av vattnet gör att olika vätskeelement eller föroreningar stannar i våtmarken olika lång tid då de rör sig olika fort. För att åstadkomma en så hög reningsgrad som möjligt är det därför önskvärt att hela våtmarkens volym nyttjas till samma grad och att samtliga vätskeelement rör sig med samma hastighet genom våtmarken vilket även kallas för en ideal flödesregim (där ingen omblandning i flödesriktningen förekommer). Då utvecklandet av skjuvkrafter i flödet utgör den grundläggande orsaken till avvikelser från en ideal flödesregim är det önskvärt att minimera dessa. De styrande faktorerna som orsakade utvecklandet av skjuvkrafter i flödet var som nämndes ovan: variationer i våtmarkens bottentopografi och vattendjup, våtmarkens geometri (som kan orsaka isolerade vattenvolymer), ytmotståndet (som bl.a. beror på distributionen av vegetation), vind, samt in- och utflödeshastigeter. Våtmarken undersöktes genom inmätning och lodning som sedan låg till grund för en konceptuell modell av systemet. Den konceptuella modellen utgjorde sedan en grund för att modellera våtmarken numeriskt. I den konceptuella modellen ingick identifiering och definition av systemgränser samt randvillkor, att definiera bottentopografin samt att dela in våtmarken i delområden med homogent flödesmotstånd. Systemgränser och randvillkor identifierades baserat på en vattenbalans. Med hjälp av vattenbalansen kunde relevanta komponenter att inkludera som randvillkor identifieras. Randvillkorens värden bestämdes genom mätningar av den hydrauliska potentialen med hjälp av en GNSS-mottagare (där GNSS står för Global Navigation Satellite System och mottagaren nyttjar satelliter för att bestämma höjd och position i en geografisk punkt) samt från erhållna mätvärden från SÖRAB av in- och utflöden som pumpas in och ut ur våtmarken. Då bottentopografin var okänd bestämdes den genom att vattendjupet mättes, interpolerades och subtraherades från en referensnivå. Vattendjupet mättes genom lodning och mätpunkterna interpolerades sedan i det geografiska informationsverktyget ArcMap för att erhålla ett heltäckande lager av mätvärden över vattendjupet. Därefter kunde vattendjupet subtraheras från vattenytans medelhöjd över havet vilket var 38,1 m och ett heltäckande lager över bottentopografin kunde erhållas. Flödesmotståndet beräknades enligt ekvation 16 (se avsnitt 2.1.) och våtmarken delades in i homogena delområden baserat på förekomsten av vegetation och om strömningen skedde genom ett poröst medium eller öppet vatten. Den numeriska modelleringen genomfördes genom att först modellera den nuvarande strömningen med och utan ett rör som går genom den genomsläppliga vallen. Därefter ändrades de styrande faktorerna för flödet en i taget för att kunna utvärdera vilken effekt varje faktor hade på strömningen i våtmarken för att åstadkomma en ideal flödesregim. Följande simuleringar genomfördes: (1) Bottentopografin gjordes jämn med ett vattendjup på 0,5 respektive 1,0 m, (2) inloppszonen gjordes längre för att undvika skapandet av isolerade vattenvolymer längs ytterkanterna, (3) vegetationens distribution gjordes homogen, (4) den genomsläppliga vallen justerades. Pålitligheten i resultatet från den numeriska modelleringen är osäker. Därför skulle ett spårämnesförsök behöva genomföras för att undersöka huruvida resultatet från modelleringen är tillförlitligt eller inte. Enligt modelleringsresultatet förekom en tydlig flödesväg som passerade genom den smalare delen av vallen. Modelleringen indikerade vidare att de kontrollerande faktorerna som styrde flödet i våtmarken framförallt utgjordes av distributionen av vegetation samt den genomsläppliga vallen tillsammans med omgivande bottentopografi. Det rekommenderas därför att modelleringsresultatets validitet först undersöks med ett spårämnesförsök innan några åtgärder vidtas. Möjliga förbättringsåtgärder som skulle kunna införas därefter för att sträva mot ett idealt flöde skulle kunna vara att justera den genomsläppliga vallen till att ha en lika stor tjocklek och ett lika stort djup överallt samt att justera bottentopografin runt vallen så att den förändras lika mycket runt vallen. Detta för att skapa förutsättningar för att undvika preferentiella flödesvägar genom den. En jämn fördelning av vegetation (och justering av vattendjupet till att understiga 1,5 m som tillåter kolonisering av växter) att störningar i flödet minimeras.
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Arubi, Isaac Marcus Tesi. "Multiphase flow measurement using gamma-based techniques." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/8347.
Full textAbstract:
The oil and gas industry need for high performing and low cost multiphase meters is ever more justified given the rapid depletion of conventional oil reserves. This has led oil companies to develop smaller/marginal fields and reservoirs in remote locations and deep offshore, thereby placing great demands for compact and more cost effective soluti8ons of on-line continuous multiphase flow measurement. The pattern recognition approach for clamp-on multiphase measurement employed in this research study provides one means for meeting this need. Cont/d.
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Tan, Zhe. "Some Aspects of Improving Initial Filling Conditions and Steel Cleanliness by Flow Pattern Control Using a Swirling Flow in the Uphill Teeming Process." Doctoral thesis, KTH, Tillämpad processmetallurgi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-117718.
Full textAbstract:
The flow pattern has widely been recognized to have an impact on the exogenous non-metallic inclusion generation in the gating system and mold flux entrapment in the uphill teeming process. Thus, a well-controlled flow pattern during the teeming process can improve the quality of ingots and further increase the yield during steel production. The current study focused on investigating and optimizing the flow pattern of steel in the gating system and molds to improve steel cleanliness during the initial filling moment. A mathematical model considering a trumpet was initially compared to a reduced model only considering part of the runner channel. Thereafter, the influence of swirl blades implemented at the bottom of the vertical runner on the improvement of initial filling conditions in the molds was investigated in a model considering the entire mold system including a trumpet. The effects of a swirl blade orientation on a swirling flow were further discussed. The simulation results, when utilizing swirl blades, were also verified by plant trials performed at Scana Steel. In addition, a new novel swirling flow generation component, TurboSwirl, was studied in a model considering the entire mold system including a trumpet. The model was based on modifications of the refractory geometry at the elbow of the runners near the mold without the usage of an inserted flow control device in the gating system. Owing to its great potential for improving the flow pattern of steel during the initial filling moment, the effect of TurboSwirl on steel cleanliness was also studied. The results showed that the initial filling conditions during the uphill teeming process can be improved by using a swirl blade or a TurboSwirl in the gating system. This makes it possible to further decrease the initial position of mold powder bags. In addition, it reduces the possibilities of exogenous non-metallic inclusion generation in the gating system as well as mold flux entrapment in the mold during the uphill teeming process. However, the utilization of swirl blades created a considerable amount of droplets when steel entered the molds during the first couple of seconds, which also was verified by the plant trials. The introduction of TurboSwirl showed a greater potential than a swirl blade due to a more evenly distributed swirling flow. The DPM model adopted in the simulations revealed that the TurboSwirl can improve steel cleanliness by increasing the non-metallic inclusion collision rate both with respect to Stokes and turbulent collisions.<br><p>QC 20130204</p>
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Misra, Rajul. "Toward a comprehensive representation and analysis framework for non-worker activity-travel pattern modeling /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Baranski, Jacek. "Physical and numerical modelling of flow pattern and combustion process in pulverized fuel fired boiler." Licentiate thesis, KTH, Materials Science and Engineering, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1533.
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<p>This licentiate thesis describes development of modellingtools, experimental physical modelling and numerical modellingto simulate real combustion processes for advanced industrialutility boiler before and after retrofit.</p><p>The work presents extended study about formation,destruction and control of pollutants, especially NOx, whichoccur during combustion process.</p><p>The main aim of this work is to improve mixing process incombustion chamber. To do this, the optimization of placementand direction of additional air and fuel nozzles, the physicalmodelling technique is used. By using that method, it ispossible to obtain qualitative information about processes,which occur in the real boiler. The numerical simulationsverify the results from physical modelling, because duringmathematical modelling quantitative informations about flow andmixing patterns, temperature field, species concentration areobtained.</p><p>Two 3D cases, before and after retrofit, of pulverized fuelfired boiler at 125 MW output thermal power are simulated. Theunstructured mesh technique is also used to discretize theboiler. The number of grid was 427 656 before retrofit and 513362 after retrofit. The comparisons of results of numericalsimulation before and after retrofit are presented. The resultsfrom physical modelling and numerical simulation are alsoshown.</p><p>Results present that nozzles of additional air and fuel givea considerably better mixing process, uniform temperature fieldand CO2 mass fraction. The whole combustion chamber worksalmost as a "well stirred reactor", while upper part of boilerworks as a "plug flow reactor".</p><p>Differences between from measured of temperatures andpredicted temperatures are not too big, the maximum differenceis about 100 K. It seems, that calculated temperatures showgood agreement with measurement data.</p><p>The results illuminate the potential of physical andnumerical modelling methods as promising tools to deal with thecomplicated combustion processes, even for practicalapplication in the industry.</p><p><b>Keywords:</b>air staging, fuel staging, boiler, furnace,computational fluid dynamics, numerical simulation, pollutants,physical modeling, pulverized fuel combustion.</p>
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Klasa, Marc. "On the interaction between the synoptic-scale eddies and the Pacific North American flow pattern." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=68192.
Full textAbstract:
The barotropic interaction in the upper troposphere between the synoptic-scale eddies and the Pacific/North American (PNA) pattern is investigated. The study uses NMC data for the years 1965-89 and examines separately the positive and negative phases of the monthly mean PNA anomalies. Northern Hemisphere maps of the eddy kinetic energy, the barotropic conversion between the eddies and the monthly mean flow and the eddy vorticity forcing are presented for both PNA phases. The eddy vorticity forcing of the PNA anomalies by the eddies is presented in terms of monthly mean geopotential tendencies.<br>It is found that the geopotential tendencies generated by the synoptic-scale eddies are spatially in phase with the PNA anomalies at the 250 hPa level. The characteristic time scale of the forcing in winter is about 6 to 10 days. The strongest anomaly in the eddy forcing is collocated with the largest amplitude PNA centre over the northern Pacific.<br>During periods of strong PNA patterns, the synoptic-scale eddy kinetic energy and its transfer into the monthly mean flow is most important in the mean jet exits. The maxima in eddy activity and kinetic energy transfer for the positive PNA phase are situated over the eastern Pacific and are significantly greater than the corresponding maxima for the negative phase, which are located over the central Pacific.
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Lu, Hung-Fu, and 盧鴻復. "The flow pattern off northeast Taiwan." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/06933076569185295010.
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Chen, Yong-Wen, and 陳泳彣. "Two-phase flow distribution and flow pattern in compact parallel flow heat exchangers." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/45276169781307167218.
Full textAbstract:
碩士<br>國立雲林科技大學<br>機械工程系碩士班<br>99<br>In this experiment, mixed liquid-gas two-phase fluid flows into the compact
parallel flow heat exchanger test section.The two-phase flow is mixed flowing into the horizontal header and distributed to the nine branch vertical parallel small tubes (d = 3 mm).The two phase flow regimes distributed in the horizontal header and the nine vertical parallel small tubes and header were shoot by the high-speed camera to observe the two-phase flow patterns, and then to make the flow regime map from the measured data of air and water flow rates in each tubes.
The experiment data taken at three different total mass flux G = 98、192、288 kg/m2s and two qualities, x = 0.01 and x = 0.005, however, x = 0.03 is added for G = 98 data. In addition, there has an intrusion depth (h = 8mm) of the parallel tubes into the horizontal header in order to increase the entrance resistance and flow turbulence for improving the two-phase flow distribution in the nine parallel tubes. However, the results for the 8 mm intrusion did not make liquid-gas two-phase flow evenly distributed in the nine vertical branch tubes than the tests with non intrusion depth.
Experimental results show that the mixed gas-liquid two-phase flow into the horizontal header formed into gas, mixing and liquid regions which are located at the front, middle and rear sections, respectively, in the header. When the mass flux is increased, mixing region almost filled the whole header, the liquid-gas flow rate is closer and distributed more evenly in each parallel vertical tube. For the tests with non intrusion depth h = 0 mm, the observed flow patterns in the nine branch vertical parallel small tubes are similar with MASHIMA’s flow regime map for small vertical tubes ( d = 2, 4 mm).
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Lin, Ta-Li, and 林達禮. "Flow Pattern of Gas-Liquid Two Phase Flow in Inclined Tube." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/44868020095597050241.
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碩士<br>淡江大學<br>化學工程學系<br>88<br>The influence of inclination angle on the flow behavior in an inclined gas-liquid two-phase flow system was investigated based on various operating parameters (ratio of gas to liquid flow rate and diameter of tube). The experiments were carried out in an acrylic tube by using dextran T500 aqueous solution as the tested solution.
Experimental results show that the size of tube diameter affects the shape and size of the gas bubble but it doesn’t affect significantly on the bubble frequency. The ratio of gas to liquid flow rate can influence the shape and frequency of the bubble. And the inclination angle affects all these flow behaviors(shape, size and frequency of the bubble). For the tube with 6 mm diameter and under 50~55 inclination angle has a longer bubble size, this phenomenon can explain the enhancement of permeate flux by tilting membrane in gas-liquid two-phase ultrafiltration system.
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YUAN, SHIEH JENG, and 謝政原. "Simulation of Flow Pattern within a CVD Reactor." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/76047598435875633574.
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碩士<br>國立臺灣大學<br>化學工程研究所<br>81<br>A three-dimensional simulation program employing finite element
method is established successfully to study the flow
phenomenon within a horizontal Chemical Vapor Deposition (CVD)
reactor. The flow system under consideration is non-isothermal,
and Boussinesq approximation is adopted to incorporate the
thermal effect. Three-dimensional vortices are discovered with
the program, which is a breakthrough comparing with the
conventional two-dimensional approach. The 3-D vortices can be
further decomposed the transverse rolls and the longitudinal
rolls. The critical parameter for the onset of the vortex is
found to be (Gr/Re**k), which agrees well with the reports in
the literature. The effect of various reactor wall temperature
distributions on this vortex flow phenomenon is analysed. The
influence of the tilted angle of the susceptor is studied also.
All the results indicate that the simulation approach of this
study is reliable and can be used extensively for the purpose
of reactor design.
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Cordeiro, Susana Cristina Oliveira. "Doppler flow pattern in patients with aortic coarctation." Master's thesis, 2015. http://hdl.handle.net/10451/20369.
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Tese de mestrado em Bioestatística, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2015<br>A coartação da aorta (CoAo) é uma cardiopatia congénita caracterizada pelo estreitamento de um segmento da aorta torácica ou abdominal, mais frequentemente localizada no istmo aórtico. O Doppler codificado a cor e o Doppler espectral são ferramentas utilizadas no ecocardiograma transtorácico de rotina que permitem a avaliação do fluxo sanguíneo na aorta descendente. Em pessoas sem cardiopatia, o padrão de fluxo Doppler na aorta descendente apresenta uma velocidade máxima inferior a 2 metros por segundo e o fluxo ocorre apenas em sístole. Em doentes com CoAo, o padrão de fluxo Doppler apresenta um aumento da velocidade de fluxo sanguínea na aorta descendente e, em alguns casos, exibe uma persistência de fluxo em diástole, denominada extensão diastólica.
A gravidade da doença tem sido avaliada de forma invasiva, semi-invasiva ou com técnicas mais complexas, estudando a relação entre o diâmetro da CoAo e o diâmetro da aorta ao nível do diafragma (CoAo/DAo). No estudo de Carvalho et al. (1990), que utilizou a variável CoAo/DAo calculada por angiografia como referência padrão de gravidade da doença, o estudo por Doppler demonstrou ser mais eficaz em avaliar a gravidade da CoAo quando as quantificações Doppler sistólicas e diastólicas foram consideradas em conjunto. No estudo de Tan et al. (2005), utilizando a variável CoAo/DAo obtida por ressonância magnética e estudos Doppler antes e após implantação de stent, a velocidade de fluxo Doppler diastólica na onda T permitiu prever a gravidade da CoAo. Apesar da relação entre quantificações diastólicas do padrão de fluxo Doppler e a gravidade da CoAo ter sido descrita anteriormente, estudos prévios não utilizaram os gradientes invasivos.
Inicialmente pensou-se que a persistência de fluxo em diástole na aorta descendente de doentes com CoAo dependia apenas da gravidade da CoAo. Estudos prévios in-vitro (Tacy et al., 1999) e com modelos computacionais (DeGroff et al., 2003) sugeriram que a rigidez arterial deve ser considerada na avaliação de doentes com CoAo, visto que a extensão diastólica aumenta quando a rigidez arterial diminui. Assim, é objetivo desta dissertação descrever a relação entre o padrão de fluxo Doppler da CoAo, os gradientes invasivos da CoAo e a rigidez arterial, num grupo selecionado de doentes, utilizando modelos de regressão.
Cinquenta estudos foram obtidos em 31 doentes (14 mulheres, 21.5±15.5 anos de idade). Em 19 doentes, foram realizadas avaliações antes e após intervenção percutânea (dilatação com balão e/ou implantação de stent). Nos 50 estudos obtidos, 12 foram apenas de diagnóstico, 19 foram prévios à intervenção percutânea e 19 foram obtidos após a intervenção percutânea. Foram medidos os gradientes sistólicos invasivos (Sgrad) no cateterismo cardíaco. Por ecocardiograma transtorácico foram avaliados vários parâmetros de Doppler obtidos na altura do procedimento invasivo, que incluíram o gradiente de Doppler corrigido (Dgrad), a velocidade diastólica no final da onda T (DVT), a velocidade em telediástole (DVQ), os tempos de hemipressão sistólicos e diastólicos (SHPTc e DHPTc) e a velocidade runoff (VRc – tempo para a velocidade decrescer do seu valor máximo até 33%). VRc, SHPTc e DHPTc foram corrigidos com a fórmula de Bazett para normalizar as medições de tempos para diferentes valores de frequência cardíaca. A rigidez arterial foi estimada através da medição da velocidade da onda de pulso (PWV - pulse wave velocity) entre as artérias carótida e radial direita, por tonometria.
Através de regressão linear simples, Sgrad apresentou relação com Dgrad, DVT, DVQ, SHPTc, DHPTc e VRc (p<0.01). O modelo de regressão linear múltipla foi obtido, resultando na formula Sgrad=−4.61+0.75×Dgrad+0.06×DHPTc. Apesar de Dgrad ter como objetivo estiar o valor que Sgrad por ecocardiografia, o modelo de regressão linear múltipla demonstrou que as variáveis que devem ser utilizadas para prever Sgrad são Dgrad e DHPTc. Este modelo apresentou um melhor ajustamento aos dados comparando com o modelo que inclui apenas a variável Dgrad (R2 = 0.77 incluindo Dgrad e DHPTc versus R2 = 0.74 incluindo apenas Dgrad), demonstrando que DHPTc resolve parte da imprecisão de Dgrad em prever Sgrad.
Foi criada uma variável binária Sign onde Sign = 0 se Sgrad apresentasse valores inferiores a 20 mmHg e Sign = 1 se Sgrad apresentasse valores iguais ou superiores a 20 mmHg. O modelo de regressão logística múltipla foi obtido, resultando na formula 𝐿𝑛(𝑝𝑆𝑖𝑔𝑛1−𝑝𝑆𝑖𝑔𝑛)=−4.70+0.12×Dgrad+0.06×DHPTc−0.0008×Dgrad×DHTPc. Porque a consequência de uma CoAo não tratada tem um impacto significativo na saúde do doente, foi escolhido o cutoff de 0.34 para 𝐿𝑛(𝑝𝑆𝑖𝑔𝑛1−𝑝𝑆𝑖𝑔𝑛) que resultou em 96% de sensibilidade e 74% de especificidade para este modelo, ou seja apenas 4% de falsos negativos e 26% de falsos positivos. Para os doentes identificados como falsos positivos no modelo de regressão logística proposto, a consequência é apenas a realização de um cateterismo de diagnóstico que tem baixa probabilidade de complicações.
Os estudos prévios que demonstraram o efeito da rigidez arterial no padrão de fluxo Doppler simularam esse efeito para CoAo com o mesmo grau de severidade. Posto isto, foi estudada a relação de PWV com as restantes variáveis na amostra inteira e em grupos selecionados de doentes. Como esperado, não foi encontrada relação significativa entre PWV e as restantes variáveis nos 28 doentes em que foi obtida medição de PWV (em 22 doentes não foi obtida medição de PWV). Através de análise gráfica, o grupo com Sgrad inferior a 30 mmHg foi selecionado (19 doentes). Para avaliar a relação entre PWV e DHPTc neste grupo, foi obtida uma nova variável DTail com DTail = 0 se DHPTc fosse também igual a zero e DTail = 1 se DHPTc apresentasse valores superiores a zero. Neste grupo com Sgrad inferior a 30 mmHg, verificou-se uma correlação negativa entre DTail e PWV através do modelo de regressão logística com a formula 𝐿𝑛(𝑝𝐷𝑇𝑎𝑖𝑙1−𝑝𝐷𝑇𝑎𝑖𝑙)=6.69−0.94×PWV, com p=0.05 para o teste da razão de verosimilhanças. Este modelo prevê que para cada redução de 1 metro por segundo da PWV, existe uma probabilidade 2.57 vezes maior para DTail = 1, no grupo de doentes com Sgrad inferior a 30 mmHg. Este achado é concordante com os estudos prévios in-vitro e com modelos computacionais. Uma artéria com menor rigidez aumenta de diâmetro quando a onda de pulso a atravessa e depois regressa ao diâmetro basal. Na presença de CoAo, este retorno ao diâmetro basal no início da diástole pode ser o responsável pelo fluxo sanguíneo tardio que resulta na extensão diastólica. Por outro lado, uma artéria com maior rigidez não sofre o aumento de diâmetro fisiológico quando a onda de pulso a atravessa. Assim, a ausência de extensão diastólica em doentes com CoAo significativa pode ser devido a uma rigidez arterial aumentada. A relação significativa entre PWV e DTail sugere que a rigidez arterial reduzida pode contribuir para persistência de fluxo em diástole, sobretudo em doentes com CoAo ligeira ou moderada. Em doentes com CoAo grave, o obstáculo significativo parece induzir per se a presença de extensão diastólica, seja o PWV baixo ou elevado.
Em suma, Dgrad e DHPTc são variáveis obtidas por Doppler espectral no ecocardiograma que podem ser utilizadas para prever o gradiente invasivo da CoAo, Sgrad. Em doentes com CoAo ligeira a moderada, a rigidez arterial parece influenciar o valor de DHPTc visto valores mais elevados de DHPTc serem mais prováveis em doentes com menor rigidez arterial. Estes resultados foram obtidos pela aplicação de modelos de regressão que permitiram construir fórmulas matemáticas que podem ser utilizadas ao estudar os doentes com CoAo.<br>Patients with coarctation of the aorta (CoAo) often show a Doppler flow pattern with diastolic flow in the descending aorta. The effect of arterial stiffness on CoAo flow pattern was described in-vitro and with computer models. Study of Doppler flow patterns may provide helpful data to support the decision of CoAo treatment.
Fifty studies were obtained in 31 patients (14 women, 21.5±15.5 years of age). In 19 patients, studies were performed before and after intervention. Systolic invasive gradients were measured (Sgrad). Doppler parameters measured at the time of invasive evaluation, included Doppler corrected gradient (Dgrad), diastolic velocity at end of T wave (DVT), end diastolic velocity (DVQ), systolic and diastolic half pressure times (SHPTc and DHPTc) and velocity runoff (VRc). Arterial stiffness was assessed by measuring pulsed wave velocity (PWV) between right carotid and radial arteries.
With simple regression models, Sgrad showed correlation with Dgrad, DVT, DVQ, SHPTc, DHPTc and VRc (p<0.01). The best multiple linear regression model provided the formula Sgrad=−4.61+0.75×Dgrad+0.06×DHPTc (R2=0.77). A binary variable named Sign were Sign=0 if Sgrad<20 mmHg and Sign=1 if Sgrad≥20 mmHg was created. The best multiple logistic regression model provided the formula 𝐿𝑛(𝑝𝑆𝑖𝑔𝑛1−𝑝𝑆𝑖𝑔𝑛)=−4.70+0.12×Dgrad+0.06×DHPTc−0.0008×Dgrad×DHTPc. A cutoff value of 0.34 for 𝐿𝑛(𝑝𝑆𝑖𝑔𝑛1−𝑝𝑆𝑖𝑔𝑛) resulted in a sensibility of 96% and specificity of 74% for this model.
A variable named DTail was obtained with DTail=0 if DHPTc=0 and DTail=1 if DHPTc>0. In the group with Sgrad below 30mmHg, a negative correlation was found between DTail and PWV (p=0.05) suggesting that low aortic stiffness may contribute to persistent diastolic flow in the descending aorta.
Doppler systolic and diastolic parameters correlated well with severity of CoAo. In mild to moderate CoAo, Doppler diastolic flow in the descending aorta was more likely in patients with lower arterial stiffness.