Rozprawy doktorskie: „Fluid mechanics”

1

Wylie, Jonathan James. "Geological fluid mechanics". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627211.

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Hildyard, M. L. "The fluid mechanics of filters". Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233871.

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Goode, Peter Allan. "Momentum transfer across fluid-fluid interfaces in porous media". Thesis, Heriot-Watt University, 1991. http://hdl.handle.net/10399/847.

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Coffey, Christopher J. "The fluid mechanics of emptying boxes". Thesis, Imperial College London, 2006. http://hdl.handle.net/10044/1/11978.

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Connick, Owen. "The fluid mechanics of hybrid ventilation". Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/39347.

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A low-energy ventilation system is often incorporated as one of the major energy saving measures in sustainable building design. These systems often employ a hybrid strategy in which mechanical equipment, governed by a computer controlled building management system, is used to assist or manage a naturally-driven airflow - the latter occurring due to the density difference between warm air inside and cooler air outside the room. Hybrid ventilation flows are poorly understood and the principal aim of the research was to enhance our understanding of the fluid mechanics through complementary theoretical and experimental modelling. The research begins by comparing solely natural and solely mechanical ventilation of a room. The hybrid ventilation of a room is then considered under the combined effect of naturally occurring and mechanically imposed pressure differences, in which a mechanical fan imposes a fixed airflow rate through one vent, thereby altering the natural pressure distribution. Simplified theoretical models, to describe the ventilation airflow rate through a room and the resulting mean air temperature, were developed for solely natural ventila- tion, solely mechanical ventilation and, finally, hybrid ventilation. At each stage the theoretical model was compared with results from small-scale experiments, and good agreement was demonstrated. From the theoretical investigation, the neutral pressure level emerged as a key pa- rameter in determining the characteristics of the ventilation airflow. Moreover, it was found that the airflow rate through an open vent can be controlled remotely by managing the position of the neutral pressure level, and that this can be achieved by varying the magnitude of the mechanically imposed airflow rate. Experimental investigations revealed that, as the neutral pressure level approached the plane of a vent, quasi-steady pulsing flows and bi-directional or exchange flows were observed. The complicated fluid dynamics involved in these flows provides inspiration for significant future work.

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PAULINO, RIVANIA HERMOGENES. "USING MULTIGRID TECHNIQUES ON FLUID MECHANICS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1997. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=19462@1.

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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
Este trabalho trata da solução numérica das equações de Navier-Stokes, na forma vorticidade-função corrente, via método das Diferenças Finitas e técnicas de aceleração baseadas no uso de malhas múltiplas. Embora outras opções tenham sido consideradas, a que melhor funcionou tratou o problema de forma não acoplada: a solução da equação de vorticidade foi obtida pela uso desta aceleração e a solução da equação de função corrente, uma equação puramente elíptica, foi resolvida via método das relaxações sucessivas. O código desenvolvido foi aplicado a diversos problemas, inclusive ao problema da cavidade com tampa móvel, em diversos números de Reynolds, típico no teste de simuladores em Dinâmica dos Fluidos. Foram testados um método clássico (armazenamento da correção) e o método FAZ (Full Approximation Storage). Os resultados obtidos mostram claramente os ganhos computacionais obtidos na formulação escolhida. Expressando em percentual, valores com 80 por cento de ganho foram obtidos se comparados os resultados do método multigrid com o método iterativo básico utilizado (S.O.R.), indicando o potencial do uso desta técnica para problemas mais complexo incluindo aqueles em coordenadas generalizadas.
This works deals with the numerical solution of the Navier-Stokes equations, written in the stream function-vorticity form, by the finite difference method and acceleration techniques using multiple meshes. Although other solution schemes have been investigated, best results were obtained by treating the problem in a non-coupled form: the solution for the vorticity equation was obtained by the multigrid method and the solution of the streamfunction equation, which is purely elliptic, was solved by the S.O.R. (Successive over relaxation method). The computer code was applied to several problems, including the wall driven problem considering a wide range of Reynolds numbers, which is a typical benchmark problem for testing fluid-dynamic simulations. The classical method (storage of the correction) and the methos FAS (Full Approximation Storage) have been tested. The results obtained clearly show that a very efficient computational scheme has been achieved with the multigrid method. For example, when comparing this method with the basic S.O.R. method, relative gains in the order of 80 per cent have been obtained. This indicates that the present technique has potential use in more complicated fluid dynamics problems including those involving generalized coordinates.

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Heimerdinger, Daniel John. "Fluid mechanics in a magnetoplasmadynamic thruster". Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/34030.

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Lea, Patrick D. "Fluid Structure Interaction with Applications in Structural Failure". Thesis, Northwestern University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3605735.

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Methods for modeling structural failure with applications for fluid structure interaction (FSI) are developed in this work. Fracture as structural failure is modeled in this work by both the extended finite element method (XFEM) and element deletion. Both of these methods are used in simulations coupled with fluids modeled by computational fluid dynamics (CFD). The methods presented here allow the fluid to pass through the fractured areas of the structure without any prior knowledge of where fracture will occur. Fracture modeled by XFEM is compared to an experimental result as well as a test problem for two phase coupling. The element deletion results are compared with an XFEM test problem, showing the differences and similarities between the two methods.

A new method for modeling fracture is also proposed in this work. The new method combines XFEM and element deletion to provide a robust implementation of fracture modeling. This method integrates well into legacy codes that currently have element deletion functionality. The implementation allows for application by a wide variety of users that are familiar with element deletion in current analysis tools. The combined method can also be used in conjunction with the work done on fracture coupled with fluids, discussed in this work.

Structural failure via buckling is also examined in an FSI framework. A new algorithm is produced to allow for structural subcycling during the collapse of a pipe subjected to a hydrostatic load. The responses of both the structure and the fluid are compared to a non-subcycling case to determine the accuracy of the new algorithm.

Overall this work looks at multiple forms of structural failure induced by fluids modeled by CFD. The work extends what is currently possible in FSI simulations.

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Woods, Andrew W. "Geophysical fluid flows". Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306472.

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Bocchi, Edoardo. "Compressible-incompressible transitions in fluid mechanics : waves-structures interaction and rotating fluids". Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0279/document.

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Ce manuscrit porte sur les transitions compressible-incompressible dans les équations aux dérivées partielles de la mécanique des fluides. On s'intéresse à deux problèmes : les structures flottantes et les fluides en rotation. Dans le premier problème, l'introduction d'un objet flottant dans les vagues induit une contrainte sur le fluide et les équations gouvernant le mouvement acquièrent une structure compressible-incompressible. Dans le deuxième problème, le mouvement de fluides géophysiques compressibles est influencé par la rotation de la Terre. L'étude de la limite à rotation rapide montre que le champ vectoriel de vitesse tend vers une configuration horizontale et incompressible.Les structures flottantes constituent un exemple particulier d'interaction fluide-structure, où un solide partiellement immergé flotte à la surface du fluide. Ce problème mathématique modélise le mouvement de convertisseurs d'énergie marine. En particulier, on s'intéresse aux bouées pilonnantes, installées proche de la côte où les modèles asymptotiques en eaux peu profondes sont valables. On étudie les équations de Saint-Venant axisymétriques en dimension deux avec un objet flottant à murs verticaux se déplaçant seulement verticalement. Les hypothèses sur le solide permettent de supprimer le problème à bord libre associé avec la ligne de contact entre l'air, le fluide et le solide. Les équations pour le fluide dans le domaine extérieur au solide sont donc écrites comme un problème au bord quasi-linéaire hyperbolique. Celui-ci est couplé avec une EDO non-linéaire du second ordre qui est dérivée de l'équation de Newton pour le mouvement libre du solide. On montre le caractère bien posé localement en temps du système couplé lorsque que les données initiales satisfont des conditions de compatibilité afin de générer des solutions régulières.Ensuite on considère une configuration particulière: le retour à l'équilibre. Il s'agit de considérer un solide partiellement immergé dans un fluide initialement au repos et de le laisser retourner à sa position d'équilibre. Pour cela, on utilise un modèle hydrodynamique différent, où les équations sont linearisées dans le domaine extérieur, tandis que les effets non-linéaires sont considérés en dessous du solide. Le mouvement du solide est décrit par une équation intégro-différentielle non-linéaire du second ordre qui justifie rigoureusement l'équation de Cummins, utilisée par les ingénieurs pour les mouvements des objets flottants. L'équation que l'on dérive améliore l'approche linéaire de Cummins en tenant compte des effets non-linéaires. On montre l'existence et l'unicité globale de la solution pour des données petites en utilisant la conservation de l'énergie du système fluide-structure.Dans la deuxième partie du manuscrit, on étudie les fluides en rotation rapide. Ce problème mathématique modélise le mouvement des flots géophysiques à grandes échelles influencés par la rotation de la Terre. Le mouvement est aussi affecté par la gravité, ce qui donne lieu à une stratification de la densité dans les fluides compressibles. La rotation génère de l'anisotropie dans les flots visqueux et la viscosité turbulente verticale tend vers zéro dans la limite à rotation rapide. Notre interêt porte sur ce problème de limite singulière en tenant compte des effets gravitationnels et compressibles. On étudie les équations de Navier-Stokes-Coriolis anisotropes compressibles avec force gravitationnelle dans la bande infinie horizontale avec une condition au bord de non glissement. Celle-ci et la force de Coriolis donnent lieu à l'apparition des couches d'Ekman proche du bord. Dans ce travail on considère des données initiales bien préparées. On montre un résultat de stabilité des solutions faibles globales pour des lois de pression particulières. La dynamique limite est décrite par une équation quasi-géostrophique visqueuse en dimension deux avec un terme d'amortissement qui tient compte des couches limites
This manuscript deals with compressible-incompressible transitions arising in partial differential equations of fluid mechanics. We investigate two problems: floating structures and rotating fluids. In the first problem, the introduction of a floating object into water waves enforces a constraint on the fluid and the governing equations turn out to have a compressible-incompressible structure. In the second problem, the motion of geophysical compressible fluids is affected by the Earth's rotation and the study of the high rotation limit shows that the velocity vector field tends to be horizontal and with an incompressibility constraint.Floating structures are a particular example of fluid-structure interaction, in which a partially immersed solid is floating at the fluid surface. This mathematical problem models the motion of wave energy converters in sea water. In particular, we focus on heaving buoys, usually implemented in the near-shore zone, where the shallow water asymptotic models describe accurately the motion of waves. We study the two-dimensional nonlinear shallow water equations in the axisymmetric configuration in the presence of a floating object with vertical side-walls moving only vertically. The assumptions on the solid permit to avoid the free boundary problem associated with the moving contact line between the air, the water and the solid. Hence, in the domain exterior to the solid the fluid equations can be written as an hyperbolic quasilinear initial boundary value problem. This couples with a nonlinear second order ODE derived from Newton's law for the free solid motion. Local in time well-posedness of the coupled system is shown provided some compatibility conditions are satisfied by the initial data in order to generate smooth solutions.Afterwards, we address a particular configuration of this fluid-structure interaction: the return to equilibrium. It consists in releasing a partially immersed solid body into a fluid initially at rest and letting it evolve towards its equilibrium position. A different hydrodynamical model is used. In the exterior domain the equations are linearized but the nonlinear effects are taken into account under the solid. The equation for the solid motion becomes a nonlinear second order integro-differential equation which rigorously justifies the Cummins equation, assumed by engineers to govern the motion of floating objects. Moreover, the equation derived improves the linear approach of Cummins by taking into account the nonlinear effects. The global existence and uniqueness of the solution is shown for small data using the conservation of the energy of the fluid-structure system.In the second part of the manuscript, highly rotating fluids are studied. This mathematical problem models the motion of geophysical flows at large scales affected by the Earth's rotation, such as massive oceanic and atmospheric currents. The motion is also influenced by the gravity, which causes a stratification of the density in compressible fluids. The rotation generates anisotropy in viscous flows and the vertical turbulent viscosity tends to zero in the high rotation limit. Our interest lies in this singular limit problem taking into account gravitational and compressible effects. We study the compressible anisotropic Navier-Stokes-Coriolis equations with gravitational force in the horizontal infinite slab with no-slip boundary condition. Both this condition and the Coriolis force cause the apparition of Ekman layers near the boundary. They are taken into account in the analysis by adding corrector terms which decay in the interior of the domain. In this work well-prepared initial data are considered. A stability result of global weak solutions is shown for power-type pressure laws. The limit dynamics is described by a two-dimensional viscous quasi-geostrophic equation with a damping term that accounts for the boundary layers

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Sakatani, Yuho. "Relativistic viscoelastic fluid mechanics and the entropic formulation of continuum mechanics". 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157762.

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Brereton, Clive. "Fluid mechanics of high velocity fluidised beds". Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/28629.

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This thesis project studied a number of aspects relating to the fluid, mechanics of circulating fluidised beds. Studies of the macrostructure of a 9.3 m high x .15 m dia. riser showed a strong dependence of one important macroscopic descriptor, the density profile, upon the geometry of the gas/solids exit and the location of the solids return. It was found that abrupt exits promoted inertial solids separation from the conveying gas which generated strong internal circulation patterns and high slip velocities. Microstructural studies, in support of the macrostructural investigation, and using a needle capacitance probe, showed how the radial density profile develops with height causing a gradual density decay. The structure, characterised by an "intermittency index," was strongly radially non-uniform at all locations in the lower regions of the column with pronounced aggregation or clustering at the highest densities. However, the cluster-like structures present at the base rapidly gave way to a more dilute core-annular type flow slightly further up the column. This radially non-uniform structure was used to explain a number of macroscopic phenomena. These included the effects of exit type, solids return location, secondary air addition and gas mixing. The results of the various studies, drawn together, allow fast fluidisation to be defined tentatively with respect to its relationships to choking, pneumatic transport, and other fluidisation regimes. Separate studies were performed to examine gas mixing and the transition to turbulent fluidisation. The gas residence time distribution was found to be substantially different from plug flow and could be characterised crudely by a two-zone model. The turbulent transition was found to be gradual, but nonetheless a transition, although a developed turbulent zone did not exist until well beyond transport conditions.
Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate

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Lister, John Ronald. "Density-driven flows in geological fluid mechanics". Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328831.

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Archer, Andrew John. "Statistical mechanics of soft core fluid mixtures". Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288269.

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FOINY, DAMIEN. "COUPLED SYSTEMS IN MECHANICS: FLUID STRUCTURE INTERACTIONS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=32283@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
As interações fluido-estrutura são muito comuns na engenharia mecânica e civil porque muitas estruturas, como pontes, plataformas de petróleo, linhas de transmissão ou turbinas eólicas, estão diretamente em contato com um fluido, que pode ser o ar, no caso de vento, ou água, que irá perturbar a estrutura através de ondas. Um papel importante do engenheiro é prevenir a falha da estrutura devido às instabilidades criadas pelas interações fluidoestrutura. Este trabalho apresentará em primeiro lugar todos os conceitos básicos necessários para o estudo de problemas de interação fluido-estrutura. Assim, é realizada uma análise dimensional visando classificar os problemas de fluido-estrutura. A classificação é baseada na velocidade reduzida, e algumas conclusões sobre as conseqüências das interações fluido-estrutura podem ser feitas em termos de estabilidade ou, o que é mais interessante, de instabilidade. De fato, usando modelos simplificados, pode-se mostrar instabilidades estáticas e dinâmicas, induzidas por fluxo, que podem ser críticas para a estrutura. As partes finais do trabalho apresentarão uma estrutura não-linear específica, uma ponte suspensa. Primeiro, a formulação de um modelo simplificado unidimensional é explicada e, em seguida, através de uma discretização por elementos finitos, é realizado um estudo dinâmico. Além disso, algumas conclusões são apresentadas sobre a dinâmica das pontes suspensas. A última parte deste trabalho apresenta um método que foi uma importante fonte de publicação para nós, o método de decomposição regular.
Fluid-structure interactions are very common in mechanical and civil engineering because many structures, as bridges, offshore risers, transmission lines or wind turbines are directly in contact with a fluid, which can be air, which will be source of wind, or water, which will perturb the structure through waves. An important role of the engineer is to prevent structure failure due to instabilities created by the fluid-structure interactions. This work will first present all the basic concepts needed for the study of fluid-structure interaction problems. Thus, a dimensional analysis of those problems is performed and also all the equations governing such cases are presented. Then, thanks to the dimensional analysis made, a classification of problems, namely based on the reduced velocity, can be done and some conclusions concerning the consequences of the fluid-structure interactions can be drawn in terms of stability or, which is more interesting, instability. Indeed, using simplified models one can show static and dynamic flow-induced instabilities that may be critical for the structure. The final parts of the work will present a specific non-linear structure, a suspension bridge. First the formulation of a simplified one-dimensional model is explained and then, through a finite element discretization, a dynamical study is performed. Also, some conclusions are made concerning the dynamic of suspension bridges. The last part of this work presents a method that was an important source of publication for us, the Smooth Decomposition method.

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Smith, Andrew. "The fluid mechanics of embryonic nodal cilia". Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4626/.

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Symmetry breaking of the left-right body axis is a crucial step in development for many vertebrate species. In many this is initiated with a directional cilia-driven fluid flow in the organising structure. This work focuses on the mouse and the zebrafish organising structures, the node and Kupffer's vesicle, wherein cilia perform a tilted rotation producing an asymmetric flow. Using singularities of Stokes flow, slender body theory and the boundary integral equation, a computational model of flow in the mouse node for a range of cilia configurations simulating developmental stages is developed and run on the University of Birmingham's cluster, BlueBEAR. The results show the emergence of a directional flow as the cilia tilt increases. To model the Kupffer's vesicle the regularised boundary integral equation is used with a mesh representation of the entire domain to investigate potential cilia mechanisms that produce the observed flow as there is not a consensus. The results show that a combination of the experimental observations could be a sufficient mechanism. This model is expanded using observations of cilia with two rotation frequencies which are incorporated by allowing such cilia to ‘wobble’. This wobble accentuates the asymmetric flow in wildtype embryos and diminishes it in mutant embryos. All of these results agree well with experiment suggesting that vertebrates develop a combination of rotation mechanisms in their organising structures before an appropriate symmetry breaking flow is established.

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Pegler, Samuel Santeri. "The fluid mechanics of ice-shelf buttressing". Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608122.

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Jarvis, Richard Allan. "Crystallization and melting in geological fluid mechanics". Thesis, University of Cambridge, 1991. https://www.repository.cam.ac.uk/handle/1810/275236.

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Vella, Dominic Joseph Robert. "The fluid mechanics of floating and sinking". Thesis, University of Cambridge, 2007. https://www.repository.cam.ac.uk/handle/1810/221845.

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This thesis is concerned with the fluid mechanics of floating and sinking. More specifically, the majority of this thesis considers the role played by surface tension in allowing dense objects to float. We first derive the conditions under which objects can float at an interface between two fluids. We obtain the conditions on density and size for various objects to float and show that being 'super-hydrophobic' does not generally help small, dense objects to float. Super-hydrophobicity does, however, dramatically reduce the energy required to remove an object from the interface. We then show that two floating objects can sink if they come into close proximity with one another. We extend this to show that a raft consisting of many interfacial objects can become arbitrarily large without sinking, providing that its density is below a critical value. Above this critical value, there is a threshold size at which sinking occurs. We then consider the surface tension dominated impact of an object onto a liquid-gas interface. We determine a similarity solution, valid shortly after impact, for the shape of the interface and study the asymptotic properties of the capillary waves generated by impact. We also show how the interfacial deformation slows down the impacting body. We use a boundary integral simulation to study the motion at later times and determine the conditions under which the object either sinks or is trapped by the surface. We find that for an object of a given weight there is a threshold impact speed above which it sinks. We study the waterlogging of a floating porous body as a model for the waterlogging of the pumice 'rafts' that often form on bodies of open water after a volcanic eruption. We study the inflow of water that is driven by capillary suction and hydrostatic pressure imbalances, and determine the time taken for this inflow to cause the object to sink. Finally, we study the effects of a natural slope on the spreading of carbon dioxide sequestered into aquifers. We use laboratory models and numerical techniques to study the spreading of the resulting gravity current. Initially the current spreads axisymmetrically, while at later times it spreads predominantly along any slope in the overlying cap rock. We show that in industrial settings the time scale over which this asymmetry develops is typically a few years. This effect may have important practical implications since the current propagates faster in the asymmetric state.

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Omnès, Florian. "Geometry optimization applied to incompressible fluid mechanics". Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS278.

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Cette thèse de mathématiques appliquées est consacrée à la modélisation et à l'exploration de techniques numériques d'optimisation de la forme d'objets au contact de fluides. Le premier chapitre est consacré à un algorithme d'optimisation géométrique mis en œuvre dans le logiciel optiflow, dans le cas où le bord à optimiser est associé à des conditions de non-glissement. L'implémentation est mise en ligne et accompagnée d'une notice d'utilisation. Il est ainsi possible de l'utiliser pour des applications de la vie réelle, par exemple pour l'optimisation de la géométrie d'un pipeline, de conduits de climatisation, etc. Dans le second chapitre, nous décrivons une façon de modéliser l'écoulement fluide à travers une aquaporine. Après avoir précisé et motivé le modèle fluide, nous prouvons l'existence d'une forme optimale pour le critère d'énergie dissipée par le fluide. Les conditions de bord de glissement partiel font apparaître des difficultés dans le calcul de sensibilité, nous présentons un traitement numérique spécifique pour y remédier. Enfin, plusieurs exemples numériques sont présentés et commentés
This applied mathematics thesis is dedicated to the modelling and exploration of numerical geometry optimization techniques. The first chapter is dedicated to a geometry optimization algorithm implemented in optiflow, in the case where the boundary to optimize is associated to no-slip conditions. The implementation is online and comes with a manual. It is therefore possible to use it for real-life applications such as pipeline or air conditioning, etc. In the second chapter, I describe a way to model fluid flow through an aquaporine. After making the fluid model precise, the existence of an optimal shape for the dissipated energy criterion is proven. Partial boundary conditions make appear difficulties in the sensitivity analysis of the optimization problem. A specific numerical treatment is presented to overcome this difficulty. Finally, several numerical examples are presented and commented

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Hatoum, Hoda. "Fluid Mechanics of Transcatheter Aortic Valve Replacement". The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1541781379381912.

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Santavicca, Jeffery W. "Fluid mechanics tutorials in GKS supported FORTRAN". Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-09122009-040300/.

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Rathgen, Helmut. "Superhydrophobic surfaces from fluid mechanics to optics". Göttingen Sierke, 2008. http://d-nb.info/991741188/04.

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Ryan, Barry James Saffman P. G. "Lie-Poisson integrators in Hamiltonian fluid mechanics /". Diss., Pasadena, Calif. : California Institute of Technology, 1993. http://resolver.caltech.edu/CaltechETD:etd-10242005-152235.

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MAHMUD, MD READUL. "Fluid Mechanics in Innovative Food Processing Technology". Doctoral thesis, Politecnico di Torino, 2016. http://hdl.handle.net/11583/2641365.

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Generally, food industries employ traditional technologies and bulk devices for mixing, aeration, oxidation, emulsification and encapsulation. These processes are characterized by high energy consumption and result in high cost product, with limited diversity and usually with non-competitive quality. Moreover, the byproduct is also high. In recent years immense efforts have been dedicated to overcome these issues and major advances in food engineering have come from transfer and adaptation of knowledge from related fields such as chemical and mechanical engineering. It is well known that the majority of elements contribute to transport properties, physical and rheological behavior, texture and sensorial traits of foods are in micro-level. In this context invention at microscopic level is of critical importance to improve the existing foods quality while targeting also the development of new products. Therefore, microfluidics has a significant role in future design, preparation and characterization of food micro-structure. The diminutive scale of the flow channels in microfluidic systems increases the surface to volume ratio and is therefore advantageous for many applications. Furthermore, high quality food products can be manufactured by means of innovative microfluidic technology characterized by less energy consumption and a continuous process in substitution to the problematic batch one. To meet these challenges, this work is focused on main two tasks: (i) efficient micromixing, and (ii) production of microbubbles and microdroplets. Firstly, two novel 3D split and recombine (SAR) micromixers are designed on an extensive collection of established knowledge. Mixing characteristics of two species were elucidated via experimental and numerical studies associated with microchannels at various inlet flow-rate ratios for a wide range of Reynolds numbers (1-100); at the same time, results are compared with two well-known micromixers. It was found that performances of the mixers are significantly affected by their design, inlet flow-rate ratios and Reynolds numbers. The proposed micromixers show better efficiency (more than 90%) in all examined range of Reynolds numbers than the well-known basic mixers at each desired region; the required pressure-drop is also significantly less than that of the previous mixers. Furthermore, numerical residence time distribution (RTD) was also explored, which successfully predicts the experimental results. In a word, the presented new micromixers have advantages of high efficiency, low pressure-drop, simple fabrication, easy integration and ease for mass production. Secondly, four micro-devices are designed for the mono-dispersed droplets and bubbles generation. Two different experimental setups were used to create water droplet in silicone oil (W/O) and air bubble in silicone oil (A/O) for continuous flow rate from 10 ml/h to 230 ml/h. The mean size of droplet and bubble as well as frequency of generation can be controlled by dispersed and continuous flow rate. Besides, squeezing and dripping flow regimes are observed inside the four devices over a broad range of Capillary numbers: 0.01~0.18. Among the examined four devices, T-1 and T-2 provide smaller droplet (100 µm) and higher production rate. Furthermore, negative pressure setup provides more robust bubble generation but positive pressure yields better production rate. In addition, droplet and bubble diameter is about four times less than the microchannel dimension, therefore small droplet and bubble can be generated spending less energy. In summary, the investigation in this dissertation reflects that both SAR micromixers and micro-devices are very efficient and can be applied to meet the growing demands of food industries. The first part of the thesis, chapters 1 to 5, addresses state of art, design, experimental technique and results of micromixers. The second part, chapters 6 to 9, presents background, construction of devices, tests and results related to the production of microdroplets and microbubbles. Finally, chapter 10 summaries the whole presented work.

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26

Gart, Sean William. "Interfacial fluid dynamics inspired by natural systems". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/64459.

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Many natural systems interact with the interface between air and liquids on a daily basis. Plants like the lotus that have self-cleaning leaf surfaces and animals that intake fluids in a variety of ways are all examples of these systems. Plants and animals exploit interfacial fluid dynamics in a variety of ways to survive in numerous harsh environments. In this thesis, five studies, inspired by natural interactions with interfaces are presented. The first study explores the influence of surface wettability in the dynamics of beams struck by water droplets. This study is inspired by raindrop-leaf interaction in nature. We characterize beam behavior after impact using a simple ODE and also find that a hydrophobic cantilever experiences reduced average torque over time than a cantilever with a hydrophilic surface. In the second study we investigate the fluid dynamics of how dogs lap water with their tongue. Dogs lap because they have incomplete cheeks and cannot suck. When lapping, a dog's tongue pulls a liquid column from the bath, suggesting that the hydrodynamics of column formation are critical to understanding how dogs drink. We measured lapping in nineteen dogs and used the results to generate a physical model of the tongue's interaction with the air-fluid interface. These experiments help to explain how dogs exploit the fluid dynamics of the generated column. The results demonstrate that effects of acceleration govern lapping frequency, which suggests that dogs curl the tongue to create a larger liquid column. Comparing lapping in dogs and cats reveals that, despite similar morphology, these carnivores lap in different physical regimes: a high-acceleration regime for dogs and a low-acceleration regime for cats. In the third study how bats drink on the wing is investigated. Bats are unique in nature in that they are one of the only animals that ingest fluids during non-hovering flight. This behavior has the advantage that bats can drink and maintain flight while hunting for food. We find that bats simply extend the tongue and drag it on the water surface while flying. The bats ingest water that coats the inside of the mouth and tongue after removal from a water bath. Bats also change their wing-beat pattern to avoid hitting the water. We investigate the crown splash instability formed when a rounded rod impacts a fluid bath. The crown splash has been widely studied; however, it has not been seen in the configuration we present. When a rounded rod impacts water, it displaces fluid, and that fluid forms a lamella that climbs up the side of the rod. Depending on the speed of impact, rod size, and other fluid parameters an instability similar to a crown splash forms. In this study, we characterize the growth of the fluid lamella along with the wavelength of the instability. Finally, we investigate the dynamics of squeezed fluids inspired by clapping wet hands. When water splashes, numerous water droplets, rather than fluid threads, are dispersed. This squeezing motion of the hands makes the fluid in between eject and eventually break into drops. In this study, the trajectory of a rim formed by fluid squeezed between two plates is measured and captured by a theoretical model. Additionally, the spacial distribution of the rim perturbation is predicted using Rayleigh-Plateau instability theory.
Ph. D.

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27

Nugent, Charles Patrick. "Studies of fluid interfaces". Thesis, Queen's University Belfast, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317468.

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28

Marshall, G. S. "Muiticomponent fluid flow computation". Thesis, Teesside University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384659.

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29

Jiao, Chaoying. "Miscible displacements in porous media with variation of fluid density and viscosity /". [Karlsruhe] : Die Universität, 2001. http://www.ubka.uni-karlsruhe.de/vvv/2002/bio-geo/1/.

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Thesis (Doctoral)--Universität Karlsruhe, 2001.
Abstract in German. Hochschulschrift = Thèse/Mémoire. Includes bibliographical references (p. 109-133). Also available via the World Wide Web. http://www.ubka.uni-karlsruhe.de/indexer-vvv/2002/bio-geo/1

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30

Scotte, Anton, i Emil Zeidlitz. "Investigating the Numerical Applicability of Analogies between Quantum Mechanics and Fluid Mechanics". Thesis, KTH, Skolan för teknikvetenskap (SCI), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-276578.

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31

Oswell, J. E. "Fluid loading with mean flow". Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239158.

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32

Anselme, Marc Joseph. "The critical properties of thermally stable and unstable fluids and dilute fluid mixtures". Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/11778.

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33

Pêgo, João Pedro Gomes Moreira. "Advanced fluid mechanics studies of ship propulsion systems". [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=983754853.

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34

Chikatamarla, Shyam S. "Hierarchy of lattice Boltzmann models for fluid mechanics /". Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17893.

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35

Wake, Amanda Kathleen. "Modeling Fluid Mechanics in Individual Human Carotid Arteries". Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7562.

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In the interest of furthering the understanding of hemodynamics, this study has developed a method for modeling fluid mechanics behavior in individual human carotid arteries. A computational model was constructed from magnetic resonance (MR) data of a phantom carotid bifurcation model, and relevant flow conditions were simulated. Results were verified by comparison with previous in vitro experiments. The methodology was extended to create subject-specific carotid artery models from geometry data and fluid flow boundary conditions which were determined from MR and phase contrast MR (PCMR) scans of human subjects. The influence of subject-specific boundary conditions on the flow field was investigated by comparing a model based on measured velocity boundary conditions to a model based on the assumption of idealized velocity boundary conditions. It is shown that subject-specific velocity boundary conditions in combination with a subject-specific geometry and flow waveform influence fluid flow phenomena associated with plaque development. Comparing a model with idealized Womersley flow boundary conditions to a model with subject-specific velocity boundary conditions demonstrated the importance of employing inlet and flow division data obtained from individual subjects in order to predict accurate, clinically relevant, fluid flow phenomena such as low wall shear stress areas and negative axial velocity regions. This study also illustrates the influence of the bifurcation geometry, especially the flow divider position, with respect to the velocity distribution of the common carotid artery on the development of flow characteristics. Overall it is concluded that accurate geometry and velocity measurements are essential for modeling fluid mechanics in individual human carotid arteries for the purpose of understanding atherosclerosis in the carotid artery bifurcation.

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36

Holm, Richard. "Fluid mechanics of fibre suspensions related to papermaking". Doctoral thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-100.

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37

Dunham, David. "Unsteady fluid mechanics of annular swirling shear layers". Thesis, Loughborough University, 2011. https://dspace.lboro.ac.uk/2134/8483.

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The vast majority of gas turbine combustor systems employ swirl injectors to produce a central toroidal recirculation zone (CTRZ) which entrains and recirculates a portion of the hot combustion gases to provide continuous ignition to the incoming air-fuel mix. In addition to these primary functions, swirl injectors often generate multiple aerodynamic instability modes which are helical in nature with characteristic frequencies that can differ by many orders of magnitude. If any of these frequencies are consistent with prevalent acoustic modes within the combustor there is a potential for flow-acoustic coupling which may reinforce acoustic oscillations and drive combustion instabilities via the Rayleigh criterion. The aerodynamic performance of the swirl injector is thus of great practical importance to the design and development of combustion systems and there is a strong desire within industry for reliable computational methods that can predict this highly unsteady behaviour. This assessment can be made under isothermal conditions which avoids the complex interactions that occur in reacting flow. The goal of the present work was to compare and contrast the performance of Unsteady Reynolds- Averaged Navier-Stokes (URANS) and Large-Eddy Simulation (LES) CFD methodologies for a combustion system equipped with a derivative of an industrial Turbomeca swirl injector as this exhibits similar unsteady aerodynamic behaviour under reacting and isothermal conditions. The influence of the level of swirl, SN = 0.51−0.8, was first investigated experimentally using Particle Image Velocimetry (PIV) by varying the inlet swirl vane angle. Based on a qualitative assessment of instantaneous velocity data, and a range of coherent structure eduction techniques, it was found that ®1 = 30± (SN ¼ 0.8) would be the most challenging test case for LES and URANS as this contained near and far-field instability modes that differ in frequency by around two orders of magnitude and the highest levels of normal Reynolds-stress anisotropy. Based on extensive simulations performed with both in-house (LULES and Delta) and commercial (Fluent) CFD codes it was found that, despite the relative modest computational cost of URANS which is between one-third (RST) to an order of magnitude (k−²) less than that demanded by LES, only LES captures the all-important frequency content in accordance with experimental evidence and, thus, only LES can be recommended for use in swirl injector flows. The increased cost is believed to be an absolutely worthwhile expense because of the high fidelity of the predicted results in the important area of flow instabilities.

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38

Grant, O. "The bio-fluid mechanics of obstructed nasal airways". Thesis, Queen's University Belfast, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426728.

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39

Gardikis, J. "The fluid mechanics of Forties/Brae oil slicks". Thesis, University of Nottingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384691.

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40

Dekam, E. I. "The fluid mechanics of transition sections between ducts". Thesis, University of Southampton, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373968.

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41

Chenvidyakarn, Torwong. "The fluid mechanics of pre-cooled natural ventilation". Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614695.

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42

Myhrberg, Viktor. "Fluid Dynamics as a Foundation for Game Mechanics". Thesis, Uppsala universitet, Institutionen för speldesign, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-419539.

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This thesis investigates whether a game world based solely on fluid dynamics could be an interesting alternative to one based on rigid bodies by presenting a prototype to players where they can control the movement of a fluid. The players evaluate the prototype’s responsiveness, intuitiveness, visual appeal, immersion, and how well they think the fluid could represent ghosts, flocks, magic, and a platformer avatar by rating them vocally while playing. The fluid physics engine prototype is a simple grid-based one that utilizes the ideal gas law and pressure gradient force to calculate the flow between its cells. It is unstable and thus cannot handle too large time-steps. Therefore, simulating many cells (more than 10000 for two fluids) at the same is a slow process, and the prototype can only present a pixelated result. If a highresolution game is in general preferred by players, a computationally efficient solution could consist of utilizing shaders for cell blending. In the experiments, all categories except the platform avatar received positive evaluations despite the prototype’s early stage, which according to theories presented within Swink’s Game Feel (Swink, 2009) and the MDA framework (Hunicke et al., 2004) may indicate that a game based on a fluid physics engine like this one could be entertaining. The simulation could possibly be run as a separate system to add game mechanics to a game based on rigid bodies as well.

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43

Hunt, Gary Richard. "The fluid mechanics of the Aaberg exhaust hood". Thesis, University of Leeds, 1994. http://etheses.whiterose.ac.uk/4623/.

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In this thesis an investigation of the fluid mechanics of the Aaberg exhaust hood is presented. The Aaberg exhaust hood is unique in its design as the speed of the air flow towards the exhaust inlet is enhanced by the entrainment of fluid into the hood's jet flow. The complex air flow pattern of the hood is governed by the Navier-Stokes equations. However, in this thesis modelling techniques have been developed in order to reduce the complexity of determining the fundamental air flow pattern. The modelling procedure adopted considers the hood's overall air flow to be composed of three component flows, namely, (i) the flow in the jet region, (ii) the jet-induced flow and (Ui) the suction flow. In practice the fluid flow pattern generated by the hood is such that the Reynolds number is very large, and hence the suction and jet-induced flows are modelled as potential flows with the boundary conditions governing the jet-induced flow coming from the solution of the shear-layer equations. This solution procedure enables the parameters which govern the hood's air flow to be identified and their effect on the flow produced by the hood may then be determined. Both two-dimensional and three-dimensional axisymmetric exhaust designs have been examined and for the latter case a new numerical model for the axisymmetric radial flow of a fluid from the space between two identical concentric discs, for laminar and turbulent flows, has been developed. Agreement between the turbulent radial jet model developed and the results of numerous other established theoretical and experimental investigations is very good. The inviscid models for the overall air flow have been developed in terms of the stream functionand. except for in the simplest case considered where an analytical solution is possible. the equations of motion which govern the fluid flow in the region of interest have been solved numerically using finite-difference techniques. The models developed illustrate all of the flow phenomena observed experimentally and comparisons made between the predictions of both the two-dimensional and three-dimensional axisymmetric mathematical models and (i) the available experimental data and (ii) the commercially available CFD code FLUENT. which solves the full turbulent Navier-Stokes equations. show good agreement. thereby confirming the credibility of the cost-effective modelling approach adopted in this thesis.

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44

Liu, Ying. "Measurements of jet velocity in unstratified and stratified fluids". Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/19474.

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45

Mallone, Kevin Charles. "A more robust wall model for use with the two-equation turbulence model". Thesis, University of Hertfordshire, 1995. http://hdl.handle.net/2299/14149.

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The applicability of computational fluid dynamics (CFD) modelling schemes to turbulent wall-bounded flows is a matter of concern. In the near-wall region of bounded flows, the standard high Reynolds number k-e model is not valid and requires the use of empirical wall models to mimic the behaviour of this region. A theoretical study of the physics of prevalent wall modelling techniques showed that the velocity distribution took no account of the pressure gradient. To determine the effect of this shortcoming, a typical transient three-dimensional flow was analysed using current CFD methods and the results compared with experimental flow measurements. Consideration of these results showed that the 'traditional' wall model was unable to replicate observed flow features in the near-wall region: further analysis of the computational results confirmed that these poor flow predictions arose from the inability of the model to consider local pressure gradient effects. Consequently, a strong case was made for a more robust wall model for use in conjunction with the standard high Reynolds number k-e model. A number of boundary layer analyses were reviewed and Coles' law of the wake (1956) presented as a viable candidate for the development of a new wall modelling scheme. In theory, Coles' law (1956) provides a description of bounded flows under arbitrary pressure gradients up to the point of near-separation and may be extended to the study of reversed flows. A generic algorithm for Coles' law was prepared and used to study the fundamental test cases of U-bend and backward facing step flows. In a comparison between documented experimentation, 'conventional' CFD modelling and Coles' law models of these flows, the Coles' law model was shown to provide a viable alternative to 'traditional' schemes. Consequently, the Coles' law model of the near-wall region, being valid for pressure-driven flows, offers an extension to the range of flows for which the standard high Reynolds number k-e model may be used.

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46

Holder, Alexander Joseph. "Experimental studies of complex fluids in complex flows". Thesis, Swansea University, 2014. https://cronfa.swan.ac.uk/Record/cronfa42995.

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47

García, Aragón Juan Antonio. "Experimental and analytical investigations of granular-fluid mixtures down inclines". Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41021.

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Granular-fluid mixtures flowing down an incline in the grain-inertia regime were studied experimentally and analytically. The equations of motion are based on the kinetic theory for granular flow. The boundary conditions are formulated following two methods. The first is a simple mechanical approach based on the energy exchange at the wall. The other is based on the kinetic theory for granular flow. Solutions for dry granular flow down a chute are studied in order to compare both methods. The extension of the kinetic theory presented here, includes drag forces resulting from the interstitial fluid that cushions interparticle collisions and particle-wall collisions. Frictional stresses, produced when long term contacts are present, and fluid turbulent fluctuations are introduced in the model.
The results are compared with measurements from an experimental chute in which the inclination, the solids flow rate and fluid flow rate are all varied. The theory is found to give a good qualitative account of the observed behaviour. Finally an application of the model to the description of the mechanical behaviour of the Nevado del Ruiz 1985 debris flow is attempted.

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48

Peshkin, David Annesley. "Computational fluid dymanics using transputer systems". Thesis, Queen's University Belfast, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335585.

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49

Betancourt, Arturo. "Computational study of the heat transfer and fluid structure of a shell and tube heat exchanger". Thesis, Florida Atlantic University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10172609.

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A common technique to improve the performance of shell and tube heat exchangers (STHE) is by redirecting the flow in the shell side with a series of baffles. A key aspect in this technique is to understand the interaction of the fluid dynamics and heat transfer. Computational fluid dynamics simulations and experiments were performed to analysis the 3-dimensional flow and heat transfer on the shell side of an STHE with and without baffles. Although, it was found that there was a small difference in the average exit temperature between the two cases, the heat transfer coefficient was locally enhanced in the baffled case due to flow structures. The flow in the unbaffled case was highly streamed, while for the baffled case the flow was a highly complex flow with vortex structures formed by the tip of the baffles, the tubes, and the interaction of flow with the shell wall.

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50

Holm, Richard. "Fluid mechanics of fibre suspension related to paper making". Doctoral thesis, KTH, Mechanics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-100.

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This thesis deals with fluid dynamic mechanisms related to papermaking, specif- ically: the initial dewatering mechanisms during roll-forming and fibre motion in sedimentation and in shear flow.

Pressure and wire position measurements have been conducted in a model resembling the forming zone and the measured pressure distributions are shown to have more complex patterns than the simple model p / T/R (where T is the wire tension and R is the roll radius). It is shown that an increase in wire tension has a similar effect as a decrease in flow-rate on the shape of the pressure distribution. In addition, it is shown that the drainage has a stabilizing effect on the dewatering pressure.

The flow around the forming roll has also been modelled with the assump- tion that the wire is impermeable. A non-linear equation for the position of the wire is derived that clearly shows that the Weber number, We, is an im- portant parameter. The equation is linearized around the trivial solution and has a standing wave solution with a specific wavelength that scales with the We-number.

Motion of non-Brownian fibre settling in a Newtonian fluid at a small but finite Reynolds number has been studied experimentally. Two different regimes of sedimentation were identified. For dilute suspensions, fibres gener- ally fall without flipping and may travel at velocities larger than that of an isolated particle. In the semi-dilute regime we found the settling process to be dominated by large-scale fluctuations. The velocity fluctuations scale with the suspension volume concentrationφ according toφ1/3, which is similar to the findings for settling spheres.

The influence of shear on fibre orientation in the near wall region was studied in cellulose acetate fibre suspensions. At low concentration and low aspect ratio fibres were observed to orient perpendicular to the streamwise direction (named rollers) in the near wall region whereas the orientation further into the suspension was unchanged. As the concentration and aspect ratio increased the fraction of rollers decreased.

Finally, an evaluation of a commercial Ultra Velocity Profiler unit in fibre suspensions are presented. The idea was to determine the velocity and characterise the turbulence from ultra sound echoes from particles in the fluid. However, the spatial and/or temporal resolution of the measurements did not permit turbulence characterisation. These limitations might be possible to overcome and some procedures are proposed and evaluated.

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