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1
Koulakis, John. "The viscous catenary". Pomona College, 2006. http://ccdl.libraries.claremont.edu/u?/stc,3.
Testo completoAbstract (sommario):
Variational techniques are used to develop a theory for the time evolution of a thin strand of viscous fluid suspended from two points. The shape of the strand is approximated to be a parabola and energy conservation is used to derive a differential equation modeling the change in height over time. Data is collected with a high resolution camera and a strobe light to obtain the position and shape of the strand over multiple intervals of time. Three very different and unexpected types of behaviors are observed depending on the initial thickness and shape of the filament. The approximation fits well with one type of behavior but variations in the thickness of the strand, and consequently in the center of mass, need to be factored in to predict the others.
2
Corvera, Poiré Eugenia. "Anisotropic viscous fingering". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29002.
Testo completoAbstract (sommario):
We have qualitatively explained the experiments of McCloud and Maher (McCloud and Maher (95)) for the viscous fingering problem in which an anisotropy in the surface tension parameter was imposed by engraving a grid in one of the plates of the Hele-Shaw cell. We saw the need to approach the problem in an analytical form. Therefore we decided to extend solvability theory to incorporate the effect of anisotropy. We have introduced the anisotropy through a moving boundary condition by considering an effective anisotropic surface tension with an anisotropy entering as the simplest cosine term having the right symmetry for a square lattice. We carried out the singular perturbation appropriate for the surface tension parameter assuming the length scale introduced by the anisotropy is small in comparison with the length scale introduced by the surface tension. In this sense, the perturbation can be said to be microscopic. For the case in which the surface tension has a maximum at the finger tip, our theory provides two possible solutions: one corresponding to the solution of the isotropic case and a new solution which, below a threshold of the surface tension parameter, predicts a wider finger than the isotropic solution. Intuitively, we expect the "old" solution, namely the one that does not differ from the isotropic case, to be the selected solution for large values of the surface tension parameter and we expect the new solution to be selected for small values of the surface tension parameter. This was confirmed by dynamical simulations of the interface done by David Jasnow. His simulation predicts that for the case in which the surface tension has a maximum at the finger tip, anisotropy is irrelevant for large values of the surface tension parameter. Furthermore below a threshold in this surface tension parameter, the selected finger width is systematically wider than the corresponding isotropic case. We conclude that our solvability theory together with the dynamic
3
Savva, Nikos. "Viscous fluid sheets". Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/41725.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 2007.Includes bibliographical references (leaves 108-117).
We present a general theory for the dynamics of thin viscous sheets. Employing concepts from differential geometry and tensor calculus we derive the governing equations in terms of a coordinate system that moves with the film. Special attention is given to incorporating inertia and the curvature forces that arise from the thickness variations along the film. Exploiting the slenderness of the film, we assume that the transverse fluid velocity is small compared to the longitudinal one and perform a perturbation expansion to obtain the leading order equations when the center-surface that defines the coordinate system is parametrized by lines of curvature. We then focus on the dynamics of flat film rupture, in an attempt to gain some insights into the sheet breakup and its fragmentation into droplets. By combining analytical and numerical methods, we extend the prior work on the subject and compare our numerical simulations with experimental work reported in the literature.
by Nikos Savva.
Ph.D.
4
Beeson-Jones, Timothy. "Controlling viscous fingering". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275358.
Testo completoAbstract (sommario):
Viscous fingering occurs when one fluid displaces another fluid of a greater viscosity in a porous medium or a Hele-Shaw cell. Linear stability analysis is used to predict methods of suppressing instability. Then, experiments in which nonlinear growth dominates pattern formation are analysed to explore the nonlinear impact of strategies of suppressing finger growth. Often, chemical treatment fluid is injected into oil reservoirs in order to prevent sand production. This treatment fluid is usually followed by water injection to clean up the well. We explore the potential for viscous instability of the interface between the treatment fluid and the water, and also the treatment fluid and the oil, as a function of the volume of treatment fluid and the injection rate and viscosity ratios of the different fluids. For a given volume of treatment fluid and a given injection rate, we find the optimal viscosity of the treatment fluid to minimise the viscous instability. In the case of axisymmetric injection, the stabilisation associated with the azimuthal stretching of modes leads to a further constraint on the optimisation of the viscosity. In the case of oil production, polymers may be added to the displacing water in order to reduce adverse viscosity gradients. We also explore the case in which these polymers have a time-dependent viscosity, for example through the slow release from encapsulant. We calculate the injection flow rate profile that minimises the final amplitude of instability in both rectilinear and axisymmetric geometries. In a development of the model, we repeat the calculation for a shear-thinning rheology. Finally, experiments are analysed in which the nonlinear growth of viscous fingers develops to test the influence of different injection profiles on the development of instability. Diffusion Limited Aggregation (DLA) simulations are performed for comparison. In all cases, the evolving pattern has a saturation distribution, with an inner zone in which the fingers are static and an outer zone in which the fingers advance and grow. In the very centre of the viscous fingering patterns, there is a small fully-saturated region. In the experiments, the mass distribution in the inner zone varies with radius as a power law which relates to the fractal dimension for the analogue DLA simulations. In the outer region the saturation decreases linearly with radius. The radius of the inner frozen zone is approximately 2/3 of the outer radius in the cases of DLA and -- after a period of evolution -- the viscous fingering experiments. This allows the radial extents of the inner and outer zones to be predicted. The ratio of each radius to the extent of the fully-saturated region is independent of the injection profile and corresponds to values for DLA.
5
Siklos, Malin. "Aspects of viscous shocks". Doctoral thesis, KTH, Numerical Analysis and Computer Science, NADA, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-89.
Testo completoAbstract (sommario):
This thesis consists of an introduction and five papers concerning different numerical and mathematical aspects of viscous shocks.
Hyperbolic conservation laws are used to model wave motion and advect- ive transport in a variety of physical applications. Solutions of hyperbolic conservation laws may become discontinuous, even in cases where initial and boundary data are smooth. Shock waves is one important type of discontinu- ity. It is also interesting to study the corresponding slightly viscous system, i.e., the system obtained when a small viscous term is added to the hyper- bolic system of equations. By a viscous shock we denote a thin transition layer which appears in the solution of the slightly viscous system instead of a shock in the corresponding purely hyperbolic problem.
A slightly viscous system, a so called modified equation, is often used to model numerical solutions of hyperbolic conservation laws and their beha- vior in the vicinity of shocks. Computations presented elsewhere show that numerical solutions of hyperbolic conservation laws obtained by higher order accurate shock capturing methods in many cases are only first order accurate downstream of shocks. We use a modified equation to model numerical solu- tions obtained by a generic second order shock capturing scheme for a time dependent system in one space dimension. We present analysis that show how the first order error term is related to the viscous terms and show that it is possible to eliminate the first order downstream error by choosing a special viscosity term. This is verified in computations. We also extend the analysis to a stationary problem in two space dimensions.
Though the technique of modified equation is widely used, rather little is known about when (for what methods etc.) it is applicable. The use of a modified equation as a model for a numerical solution is only relevant if the numerical solution behaves as a continuous function. We have experimentally investigated a range of high resolution shock capturing methods. Our experiments indicate that for many of the methods there is a continuous shock profile. For some of the methods, however, this not the case. In general the behavior in the shock region is very complicated.
Systems of hyperbolic conservation laws with solutions containing shock waves, and corresponding slightly viscous equations, are examples where the available theoretical results on existence and uniqueness of solutions are very limited, though it is often straightforward to find approximate numerical solu- tions. We present a computer-assisted technique to prove existence of solu- tions of non-linear boundary value ODEs, which is based on using an approx- imate, numerical solution. The technique is applied to stationary solutions of the viscous Burgers' equation.We also study a corresponding method suggested by Yamamoto in SIAM J. Numer. Anal. 35(5)1998, and apply also this method to the viscous Burgers' equation.
6
Siklosi, Malin. "Aspects of viscous shocks". Doctoral thesis, Stockholm, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3905.
Testo completo
7
Crosby, Andrew. "Buoyancy-driven viscous flows". Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648304.
Testo completo
8
Chakrabarti, Brato. "Catenaries in Viscous Fluid". Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/53832.
Testo completoAbstract (sommario):
Slender structures in fluid flow exhibit a variety of rich behaviors. Here we study the equilibrium shapes of perfectly flexible strings that are moving with a uniform velocity and axial flow in viscous fluid. The string is acted upon by local, anisotropic, linear drag forces and a uniform body force. Generically, the configurations of the string are planar, and we provide analytical expressions for the equilibrium shapes of the string as a first order five parameter dynamical system for the tangential angle of the body ($theta$). Phase portraits in the angle-curvature ($theta,partial_s theta$) plane are generated, that can be shown to be $pi$ periodic after appropriate scaling and reflection operations. The rich parameter space allows for different kinds of phase portraits that give rise to a variety of curve geometries. Some of these solutions are unstable due to the presence of compressive stresses. Special cases of the problem include sedimenting filaments, dynamic catenaries, and towed strings. We also discuss equilibrium configurations of towed cables and other relevant problems with fixed boundary conditions. Special cases of the boundary value problem involve towing of neutrally buoyant cables and strings with pure axial flow between two fixed points.Master of Science
9
Panda, Satyananda. "The dynamics of viscous fibers". [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=979183138.
Testo completo
10
Stropky, Dave. "A viscous-inviscid interaction procedure". Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28521.
Testo completoAbstract (sommario):
A new viscous-inviscid semi-inverse (VISI) interaction method has been developed for predicting the flow field arising from a combination of inviscid potential flow and viscous flow. The technique involves matching the bounding velocities for each region by iteratively solving for the displacement thickness, δ*(x). The formula used to update δ*(x) after each iteration is generated by linearly perturbing the governing equations.
Application of the VISI procedure to predict the unseparated flow past a flat plate gives excellent results, producing numerical solutions essentially indistinguishable from the appropriate analytical solution in less than 0.5 seconds of CPU time on an Amdahl 5850 computer.
Application of the technique to external flow over a backward facing step (BFS) indicates that the region of strong interaction between the viscous and inviscid flows is much larger than reported for internal flow. Calculated reattachment lengths, LR, are clearly influenced by the thickness of the boundary layer upstream of the step, thicker boundary layers producing longer reattachment lengths. Good accuracy is achieved for a relatively coarse distribution of control points, and rapid convergence (< 2 seconds on the Amdahl 5850) usually occurs.
Finite-difference predictions using an elliptic code (TEACH-T), modified at the outer boundary to simulate external flow, have also been made for the BFS, largely as a basis of comparison for the VISI results. Comparison of results for the two models (VISI and TEACH) gives similar trends in LR as a function of Rh and x₈, (a measure of the displacement thickness at the step). The values of LR obtained with the VISI method, however, are 15-80% longer than those from TEACH. Direct comparison with experiments is difficult because the experimental data does not clearly identify the effects of x₈, in the resulting values of LR. Trends appear to be the same for all computed and observed cases however. Disagreement between the VISI and TEACH results is thought to be due to a combination of neglecting velocities in the recirculation region in the VISI model, and numerical error and inaccurate boundary conditions in the TEACH code.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
11
Campanile, Fabio. "Atomisation of very viscous liquids". Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366413.
Testo completo
12
Philip, J. "Viscous liquids in bubble columns". Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235274.
Testo completoAbstract (sommario):
This dissertation is concerned with studies of highly viscous Newtonian and non-Newtonian liquids in bubble columns with, and without, draft tubes. The importance of the parameters influencing bubble column reactors is discussed with reference to previous work. The shapes and rise velocities of single bubbles in these liquids were studied in an 8.8cm diameter column, and the gas holdup, resulting from continuous bubbling of gas into this column, was also measured. Agreement between holdup predicted by the equation of Nicklin et al (1962), and experimental data in die present work and that of other workers is good. The limiting result of Dumitrescu (1943) was found to apply for fully developed slug flow in viscous non-Newtonian liquids in large columns. Gas holdup, in a 15cm diameter bubble column with a draft tube, consisted of large bubbles (slugs), which rapidly rose through the liquid, and very small bubbles, which accumulated in the liquid. These small bubbles were generated near the gas distributor and also at the liquid surface; less than 1% of the total gas flowrate into the system was converted into small bubbles for a highly viscous Newtonian liquid. The gas holdup due to small bubbles in non-Newtonian liquids was much less than that in Newtonian liquids. Large bubble velocities deduced from the bubble column measurements were consistent with the single bubble measurements. Liquid velocities in the 15cm column were measured by a neutrally buoyant flow follower; the liquid circulation rate was found to decrease with an increase in liquid viscosity. A model to predict the liquid circulation rate is outlined. The effect of scale-up on the gas holdup and liquid circulation rate was also studied experimentally in a 60cm square bubble column with a 30cm square draft tube. The bubble size distribution in this column was similar to the 15cm column but liquid velocities were higher, and gas holdup was smaller in the 60cm column.
13
Kallinderis, Ioannis. "Adaptation methods for viscous flows". Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14525.
Testo completo
14
Pienaar, Veruscha. "Viscous flow through sudden contractions". Thesis, Cape Technikon, 2004. http://hdl.handle.net/20.500.11838/929.
Testo completoAbstract (sommario):
Thesis (DTech (Chemical Engineering))--Cape Technikon, Cape Town, 2004Despite efforts since the 1950s, laminar flow through pipe fittings is still a topic that needs investigation (Jacobs, 1993). Most experimental studies on this topic include fittings such as contractions, expansions, elbows, valves and orifices (Edwards et aI., 1985; Turian et al., 1998; Pal & Hwang, 1999). Although sudden contractions are not often found in industry, most researchers included these fittings as part of their experimental investigation. The volume of work done on flow through sudden contractions over the last 50 years (e.g. Bogue, 1959; Christian et aI., 1972; Vrentas & Duda, 1973; Boger, 1987; Bullen et aI., 1996; Sisavath et aI., 2002), establishes its place of importance in the fundamental understanding offluid flow and fluid mechanics. There are inconsistent reports on the status ofthe study ofNewtonian fluids flowing through sudden contractions, i.e., that "it is a solved problem" (Boger, 1987) and "that it is far from being resolved" (Sisavath et aI., 2002). One reason for this apparent contradiction is the fact that most experimental studies do not agree with one another or with analytical and numerical studies. A state-of-the-art literature review by Pienaar et al. (2001) confirmed this and that further investigation of this topic is required. To explore these contradictions, it was necessary for one study to do both an experimental and numerical investigation and compare the results with existing literature. It was also important to find some basis for agreement of experimental work and not just add another data set to the existing scattered database. A test facility was built for testing three contraction ratios, i.e., ~ = 0.22, 0.50 and 0.85. A range ofNewtonian and non-Newtonian fluids was tested over a wide range ofReynolds number (Re = 0.01 - 100 000).
15
Spencer, Diane Susan. "Viscous waves in ⁴He films". Thesis, Royal Holloway, University of London, 1986. http://repository.royalholloway.ac.uk/items/b8e3b448-7abb-447f-8016-7b4539cea48c/1/.
Testo completoAbstract (sommario):
A quartz crystal resonator has been used to excite shear waves at a frequency of 20.5 MHz in He films above and below the superfluid transition and just above the liquid-gas critical point. The wave has a viscous penetration depth 6-20 nm and the transverse acoustic impedance Z = R - iX of the film was found from changes in the quality factor and resonant frequency of the crystal. The thickness of a He I film was swept at constant temperature by creating a small temperature difference between the He film on the crystal and bulk liquid helium below it. Calculations of the impedance of a homogeneous film as a function of d/6 using transmission line theory show the film's thickness d could be swept from 1.5 to >60 nm . The impedance of six superfluid films of constant thickness in the range 14-23 nm has been measured for 0.4 T T . From the impedance in the ballistic limit, wI >> 1, the average probability of the quantum evaporation of a ⁴He atom by a roton incident upon the liquid-vapourinterface is estimated to be ~0.35 . A resonance, the temperature of which was dependent on film thickness, was observed in the superfluid film and has tentatively been identified with the resonance in the A/4 Kelvin mode of vortices pinned to the crystal surface. The transverse acoustic impedance Z of helium has also been measured 49 mK above the liquid-gas critical point for pressures up to 2000 torr. In the highly compressible critical region, the impedance shows the effects of the large density gradients that develop close to the crystal surface under van der Waals1 forces. At low pressures, the transition to non-hydrodynamic behaviour is observed, and it is estimated that a fraction 0.2 of He atoms incident upon the crystal are diffusely scattered from it.
16
Rojas, Nicolás. "Dynamics of thin viscous layers". Nice, 2011. http://www.theses.fr/2011NICE4074.
Testo completoAbstract (sommario):
L’objectif principal de cette thèse est d’étudier les différents problèmes en mécanique des fluides et de l’élasticité impliquant une mince et visqueuse couche de fluides. L’ensemble minimal d’équations contenant les effets d’inertie dans un régime fortement directement dissipatives ont été trouvés, appelée la théorie de lubrification d’inertie (ILT). Nous étudions les structures observées dans le voisinage de l’instabilité de Faraday, dans la limite d’une couche très fine de fluide visqueux. Notre modèle tient compte quantitativement le seuil d’instabilité. La simulation directe de notre système permet de prédire les tendances observées dans les expériences. Le problème du ressaut hydraulique à symétrie axiale est également étudié en utilisant la théorie de la lubrification d’inertie. Des solutions asymptotiques sont trouvées et des paramètres libres sont déterminés. Les solutions de la surface libre ont été obtenues pour une large gamme de débits en bon accord avec les expériences. Différentes lois d’échelle ont été obtenues dans une certaine limite. Enfin, nous avons utilisé une approche viscoélastique pour comprendre le mouvement des sporanges lorsque les spores sont éjectées de la fougère dans l’atmosphère dans un mécanisme de reproductionThe main objective of this thesis is to study different problems in fluid mechanics and elasticity involving thin and viscous fluid layers. The minimal set equations containing inertial effect in a strongly dissipative regime has been derived, called the inertial lubrification theory (ILT). We study the patterns observed in the vicinity of the Faraday instability, in the limit of a very thin layer ova viscous fluid. Our model captures quantitatively the threshold of instability. The direct simulation of our system permits to predict the patterns observed in experiments. The hydraulic jump problem with axial symmetry is also studied using the inertial lubrification theory. Known asymptotical solutions are found and free parameters are determined. Solutions of the free surface were obtained for a wide range of flows in good agreement with experiments. Also different scaling laws were obtained in a particular limit. Finally, we have used a viscoelastic approach to understand the movement of the sporangia when spores are ejected from the fern to the atmosphere as a reproduction mechanism
17
McLachlan, Robert I. Keller Herbert Bishop Keller Herbert Bishop. "Separated viscous flows via multigrid /". Diss., Pasadena, Calif. : California Institute of Technology, 1990. http://resolver.caltech.edu/CaltechETD:etd-03122007-112956.
Testo completo
18
Marcotte, Michèle. "Ohmic heating of viscous liquid foods". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ55357.pdf.
Testo completo
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Rees, S. "Stochastic computer simulations of viscous fingering". Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235262.
Testo completoAbstract (sommario):
This thesis aims to develop a computer simulation of the process that occurs when one displaces a viscous fluid such as oil by a less viscous one such as water in a porous medium. Chapter 1 outlines the problem and explains why a computer simulation rather than analytical treatment is necessary for the problem. Previous computer simulations of the problem are reviewed and their respective advantages and disadvantages are considered. Chapter 2 introduces the concept of 'simulated annealing', a stochastic computational technique for solving minimisation problems with many variables and this technique is used to make a crude model of the displacement problem. The results from this are considered and the reasons for the model's failure to adequately solve the problem are discussed. In chapter 3, simulated annealing is applied to the simpler problem of the travelling salesman where one has to find the shortest route around a collection of points. The aim of this chapter is to try and find an optimum simulated annealing schedule to minimise the computer time needed to achieve a satisfactory solution. This is successfully accomplished for this particular problem by fitting the relaxation time of the system as a function of temperature to an Arrhenhius type law. But this optimisation is problem specific and it is concluded that the complicated nature of the oil displacement problem effectively precludes treatment by annealing. In chapter 4 a stochastic micro model is developed in which a pressure gradient across the system forces water into oil bearing pores. The pores have varying sizes which represent sizes which represent the varying permeability in a porous medium. A modified Gauss Seidel method is used to solve for the pressure field and an analytic expression for the saturation update is developed. The final chapter, chapter 5, develops the above model further and in particular develops a scheme whereby conservation of fluid is guaranteed. The profiles of the fingering of the water into the oil are studied and it is found that their interface fractal dimension varies monotonically with viscosity ratio.
20
Cummings, Linda Jane. "Free boundary models in viscous flow". Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339364.
Testo completo
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Pancholi, Ketan Pinakin. "Microbubbling of viscous liquids and suspensions". Thesis, University College London (University of London), 2009. http://discovery.ucl.ac.uk/17281/.
Testo completoAbstract (sommario):
This research comprises of device designing and processing of biomaterial suspensions based on co-flowing medium and air. The preparation of stable microbubble suspensions is fundamental to a wide range of technological applications across the scientific, engineering, medical and industrial sectors; from the production of basic foodstuffs to the self-assembly of smart materials. A key requirement in such preparation is to control the size distribution (i.e. mean and standard deviation) of the resulting microbubbles, with ideally a monodispersion being achieved. Such quality control is important because when the microbubbles are used in, for example, in ultrasound imaging, the response of such a microbubble to ultrasound excitation is strongly influenced by the radius and the thickness of the microbubble and also the mechanical properties of any coating material. This response, in tum, determines the amplitude and frequency of the ultrasound signal scattered by the microbubbles and the threshold for microbubble destruction. In first part of the work, a device is designed and optimized to microbubble silicone oils of different viscosities. All the important physical parameters like liquid and air flow rate, capillary diameter, gap between two capillaries, viscosity and surface tension are investigated to understand the mechanisms of bubble formation and to idealise the processing technique. The condition of bubble formation; a ratio of air to liquid pressure is found to be related to viscosity of liquid which is important in materials processing. Bubble dynamics are also modelled to predict the air jet diameter which can control the diameter of bubble being produced. It was shown that air jet diameter has a strong relationship to viscosity of the liquid. Secondly, using a similar device and technique, lipid suspension and nano gold particulate colloids are microbubbled to show that process is suitable for producing near monodisperse microbubbles with more than 20 minutes life time. These microbubbles have immediate application as ultrasound contrast agent and drug delivery vehicle. Moreover, it is also found that nano-particulate reinforced bubbles can enhance the non-linearity of backscatter at low amplitude pressure. To further reduce the diameter of bubbles, a hybrid flow focussing and electrospraying device is developed to show that monodisperse size of bubbles less than 10 μm can be produced. This process has been syslematically studied to conclude that the product of applied voltage and flow ratio governs the diameter of bubbles generated.
22
Kitagawa, K. "Boundary element analysis of viscous flow". Thesis, University of South Wales, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383682.
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Kobine, James Jonathan. "Bifurcations and symmetries in viscous flow". Thesis, University of Oxford, 1992. http://ora.ox.ac.uk/objects/uuid:1a1a45bb-0d5a-4553-a93d-b0fa6814fc56.
Testo completoAbstract (sommario):
The results of an experimental study of phenomena which occur in the flow of a viscous fluid in closed domains with discrete symmetries are presented. The purpose is to investigate the role which ideas from low-dimensional dynamical systems have to play in describing qualitative changes that take place with variation of the governing parameters. Such a descriptive framework already exists for the case of the Taylor-Couette system, where the domain possesses a continuous azimuthal symmetry group. The present investigation is aimed at establishing the typicality of previously reported behaviour under progressive reductions of azimuthal symmetry. In the first investigations, the fixed outer circular cylinder of the standard system is replaced with one of square cross-section. Thus there is now discrete Ζ4 symmetry in the azimuthal direction. Knowledge of the two-dimensional flow field is used to establish the nature of the steady three-dimensional motion equivalent to Taylor vortex flow. It is shown that similar bifurcation sequences exist in both standard and square systems for the case of very small aspect ratio where a single Taylor cell is formed. This flow develops as the result of a bifurcation which breaks the Ζ2 symmetry that is imposed on the annulus by two solid stationary ends. The study is then extended to consider time-dependent effects in the square system. Two different oscillatory single-cell flows are identified, and it is shown that each is the result of a Hopf bifurcation. Selection of a particular dynamic mode is found to depend on the aspect ratio of the system. A low-dimensional bifurcation structure is uncovered which connects the two modes in parameter space, and involves a novel type of steady single-cell flow. Finally, observations are reported of a nontrivial type of dynamical behaviour which bears strong resemblance to motion found in a circularly symmetric Taylor-Couette system that is related to the Šilnikov mechanism for finite-dimensional chaos. A second variant on the Taylor-Couette system is considered where the outer cylinder is shaped like a stadium. The effect is to reduce further the overall symmetry of the domain to a Ζ2 × Ζ2 group. The two-dimensional flow field is investigated using both numerical and experimental techniques. Time-dependent phenomena are then investigated in the three-dimensional flow over a relatively wide range of aspect ratio. It is found that a sequence of a Hopf bifurcation followed by period-doubling bifurcations exists up to a certain aspect ratio, beyond which there is an apparently sudden and reversible transition between regular and irregular dynamical behaviour. Although this transition is not of a low-dimensional nature, the experimental results suggest that it exists as the result of a coalescence of the bifurcations which are found at lower values of aspect ratio.
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Mc, Laughlin Declan T. "Gas entrainment into viscous polymer solutions". Thesis, Queen's University Belfast, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252316.
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Kirsten, Julius. "Viscous-inviscid interaction on moving walls". Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/60591.
Testo completoAbstract (sommario):
This thesis consists of two parts. In part I, the viscous-inviscid interaction in su- personic flows over down- and upstream moving walls is analysed. The separation is assumed to be provoked by an impinging shock or expansion wave. For large val- ues of the Reynolds number and under the assumption that the speed of the wall is [Mathematical equation appears here. To view, please open pdf attachment], the interaction is described by the classical triple deck theory. For the case [Mathematical equation appears here. To view, please open pdf attachment], the Navier-Stokes equations are analysed in a vicinity of the separation point using the method of matched asymptotic expansions. In chapter 2, the linearised interaction problem for a downstream moving wall is stud- ied and the upstream influence of small perturbations is shown to be exponentially decaying. Moreover, it is found that small perturbations to the skin friction decay alge- braically downstream. The focus then shifts towards the fully non-linear problem, when the strength of the impinging shock wave is of [Symbol appears here. To view, please open pdf attachment], and it is shown numerically that a singularity, indicative of separation, develops at the outer edge of the viscous sublayer. In chapter 3, supersonic flow over an upstream moving wall is considered for which the development of a singularity is observable in the non-linear problem, when the imping- ing shock wave is replaced by an expansion wave. Part II consists of chapter 4, in which hypersonic flows are investigated. In this case the viscous-inviscid interaction extends over the entire body surface and is described by a two-layer model. On motionless and downstream moving walls, the solution to the interaction problem near the leading edge is not unique and there exists an alge- braic upstream influence of perturbations. The associated eigenvalue problem near the leading edge is solved numerically using an iterative procedure and it is shown that the upstream influence becomes smaller as the speed of the wall is increased.
26
Barker, Tobias. "Uniqueness results for viscous incompressible fluids". Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:db1b3bb9-a764-406d-a186-5482827d64e8.
Testo completoAbstract (sommario):
First, we provide new classes of initial data, that grant short time uniqueness of the associated weak Leray-Hopf solutions of the three dimensional Navier-Stokes equations. The main novelty here is the establishment of certain continuity properties near the initial time, for weak Leray-Hopf solutions with initial data in supercritical Besov spaces. The techniques used here build upon related ideas of Calderón. Secondly, we prove local regularity up to the at part of the boundary, for certain classes of solutions to the Navier-Stokes equations, provided that the velocity field belongs to L∞(-1; 0; L3, β(B(1) ⋂ ℝ3 +)) with 3 ≤ β < ∞. What enables us to build upon the work of Escauriaza, Seregin and Šverák [27] and Seregin [100] is the establishment of new scale-invariant estimates, new estimates for the pressure near the boundary and a convenient new ϵ-regularity criterion. Third, we show that if a weak Leray-Hopf solution in ℝ3 +×]0,∞[ has a finite blow-up time T, then necessarily limt↑T||v(·, t)||L3,β(ℝ3 +) = ∞ with 3 < β < ∞. The proof hinges on a rescaling procedure from Seregin's work [106], a new stability result for singular points on the boundary, suitable a priori estimates and a Liouville type theorem for parabolic operators developed by Escauriaza, Seregin and Šverák [27]. Finally, we investigate a notion of global-in-time solutions to the Navier- Stokes equations in ℝ3, with solenoidal initial data in the critical Besov space ?-1/44,∞(ℝ3), which has certain continuity properties with respect to weak* convergence of the initial data. Such properties are motivated by the strategy used by Seregin [106] to show that if a weak Leray-Hopf solution in ℝ3×]0,∞[ has a finite blow-up time T, then necessarily limt↑T ||v(·, t)||L3(ℝ3) = ∞. We prove new decomposition results for Besov spaces, which are key in the conception and existence theory of such solutions.
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Holloway, Craig Roy. "Stability of fibre-reinforced viscous flows". Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7427/.
Testo completoAbstract (sommario):
This thesis focusses on two models (inactive and active) for fibre-reinforced viscous flows, examples of which may be found in numerous industrial and biological applications. In chapters 2-4 we consider Ericksen's model for a transversely isotropic fluid, which treats suspensions of nonmotile particles as a continuum with an evolving preferred direction; this model describes fibrous materials as diverse as extracellular matrix, textile tufts and cellulose microfibers. Linear stability analyses of transversely isotropic viscous fluid between two rotating co-axial cylinders and two horizontal boundaries of different temperatures are undertaken in chapters 3 and 4 respectively. In both cases, the inclusion of transversely isotropic effects delays the onset of instability. In chapter 5 we describe a framework commonly used to model active suspensions, which has been applied to suspensions of self-propelling bacteria, algae and sperm, and artificial swimmers. Through linking this model for an active suspension with that for a transversely isotropic fluid, we identify previously neglected components of the stress tensor that significantly alter the rheology. In chapter 6 we examine the linear stability of isotropic and nearly-aligned suspensions of elongated particles, before giving a summary of our findings in chapter 7.
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Teichman, Jeremy Alan 1975. "Wrinkling and sagging of viscous sheets". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29257.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002.Vita.
Includes bibliographical references (p. 131-133).
This thesis explores the wrinkling and sagging behavior of thin viscous Newtonian sheets and filaments motivated by analogous scenarios in elasticity. These problems involve dynamic free boundaries and geometric nonlinearities but use simple physics. The first problem examined concerns an annular viscous sheet subjected to torsional shearing which consequently develops spiral wrinkles. Examination of the behavior of this system leads to a scaling of the Stokes equations for zero Reynolds number flow resulting in a reduced order mathematical model for the evolution of the sheet that includes the effects of gravity and surface tension. Linear stability analysis yields the most unstable modes for wrinkling of the sheet and their associated growth rates at onset which agree with experimental observations. In the limit of a narrow annular gap, the problem reduces to that of a sheared rectilinear sheet. Interestingly, this Couette problem shows instabilities even in the zero Reynolds number limit. The second problem examined concerns the sagging of a horizontal viscida (fluid filament) under the influence of gravity. Resistance of the viscida to bending controls the initial phase of deformation, while resistance to stretching begins to play a principal role in later stages. At very late times the process resembles droplet break-off from two thin filaments.
by Jeremy Alan Teichman.
Ph.D.
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Rożeń, Antoni. "Investigation of micromixing in viscous liquids". Praca doktorska, Warszawa : Politechnika Warszawska, 1995. https://bcpw.bg.pw.edu.pl/dlibra/docmetadata?showContent=true&id=1705.
Testo completo
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Park, Sang-Hyuk. "Viscous-inviscid interactions of dense gases". Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/27648.
Testo completo
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Kotikalapudi, Sivaramakrishna. "Spreading of initially spherical viscous droplets". Link to electronic version, 2000. http://www.wpi.edu/Pubs/ETD/Available/etd-0930100-201701/restricted/kotikalapudi.pdf.
Testo completoAbstract (sommario):
Thesis (M.S.)--Worcester Polytechnic Institute.Keywords: crown; splash; spreading; oscillatory; droplets; microgravity; viscosity; map; stability; solid surface; surface tension; gravity. Includes bibliographical references (p. 111-113).
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Kwok, Loong-Piu. "Viscous cross-waves: Stability and bifurcation". Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184441.
Testo completoAbstract (sommario):
In the first part of this thesis, the nonlinear Schrodinger equation for inviscid cross-waves near onset is found to be modified by viscous linear damping and detuning. The accompanying boundary condition at the wavemaker is also modified by damping from the wavemaker meniscus. The relative contributions of the free-surface, sidewalls, bottom, and wavemaker viscous boundary layers are computed. It is shown that viscous dissipation due to the wavemaker meniscus breaks the symmetry of the neutral curve. In the second part, existence and stability of steady solutions to the nonlinear Schrodinger equation are examined numerically. It is found that at forcing frequency above a critical value, f(c), only one solution exists. However, below f(c), multiple steady solutions, the number of which is determined, are possible. This multiplicity leads to hysteresis for f < f(c), in agreement with observation. A Hopf bifurcation of the steady solutions is found. This bifurcation is compared with the transition from unmodulated to periodically modulated cross-waves observed experimentally.
33
Smith, Diana Elizabeth. "Viscous Relaxation of Craters on Enceladus". Thesis, The University of Arizona, 2008. http://hdl.handle.net/10150/193360.
Testo completoAbstract (sommario):
Cassini spacecraft images of Enceladus' surface have revealed diverse terrains---some heavily cratered, others almost devoid of craters, and even some with ridges and fractures. We have documented crater morphologies in regions for which high-resolution data are available (140 to 360 W and 90 S to 60 N). The south polar region shows a dearth of craters, in sharp contrast to the heavily cratered northern latitudes. Tectonized regions such as Sarandib and Diyar Planitiae also have low crater densities. Viscously relaxed craters are found in the apparently young regions of the anti-Saturnian and trailing hemispheres, as well as in the older, upper northern latitudes. By modeling the viscoelastic relaxation of craters on Enceladus using TEKTON, a finite-element code, we predict large geographical variation in heat flow and a complicated thermal history on Enceladus. Our results are consistent with the planitiae being older examples of the South Polar Terrain, supporting a satellite-reorientation hypothesis.
34
Stokes, Yvonne Marie. "Very Viscous Flows Driven by Gravity with particular application to Slumping of Molten Glass". Title page, contents and abstract only, 1998. http://thesis.library.adelaide.edu.au/public/adt-SUA20020724.171358.
Testo completoAbstract (sommario):
Bibliography: leaves 247-257. Electronic publication; Full text available in PDF format; abstract in HTML format. This thesis examines the flow of very viscous Newtonian fluids driven by gravity, with emphasis on the lumping of molten glass into a mould, as in the manufacture of optical components, which are in turn used to manufacture ophthalmic lenses. Electronic reproduction.[Australia] :Australian Digital Theses Program,2001.
35
Kanschat, Guido. "Discontinuous Galerkin methods for viscous incompressible flow". Wiesbaden : Deutscher Universitäts-Verlag, 2008. http://dx.doi.org/10.1007/978-3-8350-5519-3.
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Rowan, Scott A. "Viscous drag reduction in a scramjet combustor /". St. Lucia, Qld, 2003. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe17438.pdf.
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Dressler, Marco Dressler Marco Dressler Marco. "On the flow of highly viscous emulsions". Zürich : [Institut für Agrar- und Ernährungsökonomie, Eidgenössische Technische Hochschule Zürich], 2006. http://e-collection.ethbib.ethz.ch/show?type=habil&nr=26.
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Pauné, i. Xuriguera Eduard. "Interface Dynamics in Two-dimensional Viscous Flows". Doctoral thesis, Universitat de Barcelona, 2002. http://hdl.handle.net/10803/1584.
Testo completoAbstract (sommario):
The subject of this thesis is viscous fingering in Hele-Shaw cells, or Hele-Shaw flows. We look for insights into the fundamental mechanismsunderlying the physics of interface dynamics, which we hope will exhibit some degree of universality. The aim is twofold: on the one hand we focus on the role of surface tension and viscosity contrast in the dynamics of fingering patterns. On the other hand we introduce a modification of the original problem and study the effects of a inhomogeneous gap between the
plates of a Hele-Shaw cell.
A dynamical systems approach to competition of Saffman-Taylor (ST) fingers in a Hele-Shaw channel is developed. This is based on global analysis of the phase space flow of the ODE sets associated to the exact solutions of the problem without surface tension. A general proof of the existence of finite-time singularities for broad classes of solutions is given. The existence of a continuum of multifinger fixed points and its dynamical implications are discussed. We conclude that exact zero-surface tension solutions taken in a global sense as families of trajectories in phase space are unphysical because the multifinger fixed points are nonhyperbolic. Hyperbolicity (saddle-point structure) of multifinger fixed points is argued to be essential to the physically correct qualitative
description of finger competition. The restoring of hyperbolicity by surface tension is proposed as the key point to formulate a generic Dynamical Solvability Scenario for interfacial pattern selection.
We study the singular effects of vanishingly small surface tension on the dynamics of finger competition in the Saffman-Taylor problem, using the asymptotic techniques developed by Tanveer and Siegel, and numerical computation, following the numerical scheme of Hou, Lowengrub, and
Shelley. We demonstrate the dramatic effects of small surface tension on the late time evolution of two-finger configurations with respect to exact
(non-singular) zero-surface tension solutions. The effect is present even when the zero surface tension solution has asymptotic behavior consistent with selection theory. Such singular effects therefore cannot be traced back to steady state selection theory, and imply a drastic global change in the structure of phase-space flow.
Finger competition with arbitrary viscosity contrast (or Atwood ratio) is
studied by means of numerical computation. Two different types of dynamics
are observed, depending on the value of the viscosity contrast an the
initial condition. One of them exhibits finger competition and ends up in
the ST finger. In opposition, the second dynamics does not exhibit finger
competition and the long time dynamics seems attracted to bubble shaped
solutions. An initial condition appropriate to study the ST finger basin
of attraction is identified, and used to characterize its dependence on
the viscosity contrast, obtaining that its size decreases for decreasing
viscosity contrast, being very small for zero viscosity contrast. The ST
finger is not the universal attractor for arbitrary viscosity contrast. An
alternative class of attractors is identified as the set of Taylor-Saffman
bubble solutions, and one important implication of this result is that the
interface is strongly attracted to finite time pinchoff.
A nonlocal interface equation is derived for two-phase fluid flow, with
arbitrary wettability and viscosity contrast c, in a model porous medium defined as a Hele-Shaw cell with random gap b. Fluctuations of both capillary and viscous pressure are explicitly related to the microscopic quenched disorder, yielding conserved, non-conserved and power-law correlated noise terms. Two length scales are identified that control the possible scaling regimes and which depend on capillary number Ca as l sub 1 = b sub zero (c Ca)(superindex -1/2) and l sub 2 = b sub zero/Ca. Exponents for forced fluid invasion are obtained from numerical simulation and compared with recent experiments,obtaining good partial agreement.
39
Nguyen, Toan. "Asymptotic stability of noncharacteristic viscous boundary layers". [Bloomington, Ind.] : Indiana University, 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3378375.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--Indiana University, Dept. of Mathematics, 2009.Title from PDF t.p. (viewed on Jul 12, 2010). Source: Dissertation Abstracts International, Volume: 70-10, Section: B, page: 6259. Adviser: Kevin R. Zumbrun.
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Raoofi, Mohammadreza. "Asymptotic behavior of perturbed viscous shock profiles". [Bloomington, Ind.] : Indiana University, 2005. http://wwwlib.umi.com/dissertations/fullcit/3178477.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--Indiana University, Dept. of Mathematics, 2005.Source: Dissertation Abstracts International, Volume: 66-06, Section: B, page: 3170. Adviser: Kevin Zumbrun. "Title from dissertation home page (viewed Dec. 4, 2006)."
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Hovrud, Jan Marius. "Interaction between bodies in a viscous flow". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15824.
Testo completoAbstract (sommario):
Using the open-source CFD-solver OpenFOAM with a numerical scheme which is first order in time and second order in space, calculations of unsteady 3D flow around two cylinders in tandem arrangement at low Reynolds number (Re = 200) have been performed. Calculations have been done both with and without the assumption of symmetry with respect to y = 0; the latter being a crude model of a free surface. For the case of no symmetry aspect ratio, number of elements in spanwise direction and boundary condition on the front and back faces is discussed. The investigation has been done with special emphasis on the effect of separation distance and the flow in the gap between the cylinders. For the cases where symmetry about y = 0 is assumed, the influence of the boundary condition on this plane has also been investigated. For the case of no symmetry it is found that the 3D effects inherent in a flow in infinite fluid at Re = 200 are inhibited for separation distances less than four diameters when an aspect ratio of six diameters is used. For S ≤ 0.5 and S ≥ 3 distinct low-frequency force pulsations are observed. Pulsations are suppressed for S = 1, 2. The differences and actual changeover between single and double vortex shedding flow schemes is discussed. For the case of symmetry the flow is always 2D and the final solution is time-independent. Different boundary conditions on y = 0 are investigated. The influence of varying S/D is generally smaller than for the case without symmetry. Detached and reattached flow is studied and differences between cases with and without mirror condition are discussed. Recirculations zones below, behind and between the cylinders are studied. The results are presented as integral quantities such as average and rms drag and lift coefficients, Strouhal number and pulsation periods, as well as more detailed quantities such as pressure, vorticity, velocity, velocity vectors and streamlines.
42
Levold, Pål. "Viscous Flow Around Finite Lenght Circular Cylinder". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18641.
Testo completoAbstract (sommario):
Viscous flow around circular cylinders is a classical research topic in fluid dynamics with a vast amount of practical applications in the field of offshore marine technology. In the flow around cylinders of finite length, complex wake behaviours and coherent structures occur even at relatively low Reynolds numbers. An understanding of the nature and dynamics behind such behaviour could form a basis for improved designs and innovative solutions for offshore and subsea constructions.In the present study, flow around long finite cylinders at Re = 100 is investigated numerically using the incompressible Navier-Stokes Equations solver MGLET. To study the isolated flow near the free end, a cylinder with aspect ratio L/D = 50 is chosen. The flow over the free end gives rise to a wake consisting of two vortex shedding cells with different shedding frequencies; one small near the free end and one larger in the central region of the span. It is found that each vortex shed in the end cell bends horizontally and connects with the upstream vortex shed from the opposite side of the cylinder. The horizontal vortex shedding is found to give rise to a pair of trailing vortices in the time averaged flow.When a vortex is shed with a large phase difference between the two cells, the vortex is split and connects with other surrounding vortices. This phenomena is commonly referred to as vortex dislocations and occurs with the beat frequency, i.e. the difference between the two vortex shedding frequencies. It is found that this frequency can be detected in time histories of $u$ in the wake at the spanwise centre.A second configuration, consisting of a wall mounted cylinder with aspect ratio L/D = 25 is simulated in order to study the effect of introducing a no-slip surface. The effect on the end cell is found to be minimal, while the central cell shedding frequency is reduced. Comparisons with published data on a cylinder with aspect ratio L/D = 25 and two free ends shows that both the reduction of aspect ratio and the introduction of the no-slip boundary condition contributes to the reduced shedding frequency.
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Nazer, Nor Shahidah Binti Mohd. "Viscous response in shear of clayey geomaterial". Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27390.
Testo completoAbstract (sommario):
Translational slides in clays are often characterized by long-lasting intermittent movements associated with the fluctuations of pore-water pressures. These are in turn associated with either the rise or fall of the groundwater table for the case where the failure surface develops in the saturated zone below the phreatic surface or the infiltration of rainwater for the case where the failure surface is located above the phreatic surface in the unsaturated zone. Physically-based models designed to support hazard analysis of landslide movements and early warning systems require the integration of time-dependent (viscous) constitutive models for the shear displacements because landslide movements are typically controlled by the viscous behaviour of the clay geo-material. However, little information is available on the creep response of clay geo-materials under unsaturated conditions concerning different water content and matric suction values. This thesis presents an investigation of the viscous response of a clay geo-material under saturated and unsaturated conditions. Creep and relaxation tests have been first carried out on saturated clay samples by means of direct shear box. For the creep tests, the shear force was increased to a target value and maintained constant while monitoring the shear displacements. For the relaxation tests, shear displacement was applied to a target value and maintained constant while monitoring the shear stress decay. To gain a conceptual understanding of the viscous response of the clay in shear, analogue models were developed based on combinations of springs and dashpots. The aim of this modelling simulation was to identify a single mechanical model to simulate both creep and relaxation response using single set of parameters. Tests on unsaturated samples at different water content were finally carried out to gain insight into viscous response of the clay under unsaturated conditions.
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Mahajan, Sandeep Prakash. "Viscous Effects on Penetrating Shafts in Clay". Diss., Tucson, Arizona : University of Arizona, 2006. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1689%5F1%5Fm.pdf&type=application/pdf.
Testo completo
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Liu, Hongwei. "Gas-kinetic methods for viscous fluid flows /". View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?MATH%202007%20LIU.
Testo completo
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Kanschat, Guido. "Discontinuous Galerkin methods for viscous incompressible fl". Wiesbaden Dt. Univ.-Verl, 2004. http://dx.doi.org/10.1007/978-3-8350-5519-3.
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Khomenko, Maria. "Viscous fluid instabilities under an elastic sheet". Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/23813.
Testo completoAbstract (sommario):
This thesis considers the flow of thin fluid film between an elastic sheet and a rigid plane. We derive a mathematical model for the flow from the Navier-Stokes equations using the lubrication approximation and develop numerical and similarity solutions to this problem. An experimental apparatus was developed to investigate this phenomenon, and the results of the mathematical model were compared with experimental data.
Chapter 3 examines the evolution of a fixed fluid volume under gravitational forces on a horizontal plane. The evolution of the fluid mass profile and the progression of the fluid front are determined from the numerical solutions, as well as experimentally. The favourable comparison between the numerical solutions and the experimental results establishes the validity of the model.
Chapters 4-5 considers the evolution of a thin fluid flow under an elastic on an inclined plane. We establish a traveling wave solution for this flow. A linear stability analysis yields the criterion for the existence of unstable modes and establishes the growth rate and wavelength of the most unstable mode. Instability is promoted by increasing the inclination of the plane. For low angles, the numerical and experimental growth rates were in good agreement, while the wavelengths were experimentally of the same order and numerically computed wavelengths had little variation.
The long term behaviour of the fluid front is studied analytically via a similarity solution in Chapter 6.
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Aydin, Murat. "Boundary element analyses of laminar viscous flows". Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391707.
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Stallard, Timothy J. "Simulation of unsteady viscous flow-structure interaction". Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.418130.
Testo completoAbstract (sommario):
The design of slender structures such as longspan bridges, masts, offshore risers and cables is strongly influenced by their response behaviour when subjected to unsteady loads due to wind, waves and current. Simulation of the behaviour of a viscous flow past a structural cross section is of great importance to engineers concerned with the design of such structures. Offshore engineers are concerned with estimating the magnitude of structural forces induced by the most severe storm-induced wave events. Numerous studies have been conducted in an effort to estimate the structural forces induced by both regular and irregular waves. However, estimation of the maximum extreme wave-induced structural forces, particularly for relatively small diameter horizontal components, has received less attention. Since the most widely used method for estimating the force experienced by a bluff body subjected to wave loading is the empirical drag-inertia equation developed by Morison, O’ Brien, Johnson, and Schaaf (1950), it is important to determine whether this equation is adequate to describe the forces imposed by extremely large ocean waves. A method is presented for the simulation of incompressible viscous flow past acylinder using a stream function vorticity-transport formulation discretised on a cutcell quadtree mesh. A cut-cell technique is employed to provide accurate boundary representation and to facilitate the simulation of flow past a moving boundary. The finite volume discretisation consists of second-order accurate central difference approximations within uncut flow cells and a polynomial reconstruction technique within the cut-cells that are intersected by the solid boundary. Several preliminary validation tests concerned with flow past a circular cylinder are presented to confirm the accuracy of the numerical model. Firstly, the cut-cell discretisation is applied to the solution of the Euler equations and is shown to be almost second order accurate. Comparisons of wake geometry and force coefficients for steady and oscillatory flows at low Reynolds number are then made with existing results, and show satisfactory agreement. Preliminary tests are presented to assess the accuracy of a cut-cell based method for simulating flow past a circular body that moves across a background mesh. A series of experiments is also presented concerned with the measurement of theforce experienced by a circular cylinder undergoing a pre-defined two-dimensionalmotion within a still fluid. The cylinder trajectory is representative of the motionof a fluid particle beneath an idealised large ocean wave as defined by the NewWave formulation (Tromans et al. 1991). It is observed that, whilst the magnitude of high frequency vortex induced force fluctuations varies with the ratio of wave amplitude to cylinder diameter (A=D) and the wave spectrum shape, the overall shape of both x- and y-direction force time histories is very similar for all wave groups for which the underlying spectrum has the same shape. For all of the two-dimensional cylinder motions considered, the spectrum of both measured forces closely approximates the spectrum of uq (where u is a component of the velocity vector and q the absolute velocity) and, as a result, the vector form of the well known equation developed by Morison et al. (1950) is shown to provide a satisfactory estimate of the cartesian force components. The high frequency component of the force that is not captured by the Morison et al. equation is clearly identified as a lift-type force in the radial direction. For design purposes, a reasonable estimate of the magnitude of the peak force is obtained by neglecting inertial forces and employing a drag coefficient CD = 1.0.
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Khobeiz, Mohamed Hussien. "Numerical simulation of viscous incompressible turbomachinery flow". Thesis, University of Sheffield, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338828.
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