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Two algorithms commonly used for solving low-speed flow fields are evaluated using an unsteady turbulent flow formulation. The first algorithm is the method of artificial compressibility which solves the incompressible Navier-Stokes equations. The second is a preconditioned system for solving the compressible Navier-Stokes equations. Both algorithms have been implemented into GASP Version 4, which is the flow solver used in this investigation. Unsteady numerical simulations of unsteady, 2-D flow over square cylinders are performed with comparisons made to experimental data. Cases studied include both a single-cylinder and a three-cylinder configuration. Two turbulence models are also used in the computations, namely the Spalart-Allmaras model and the Wilcox k-ω (1998) model. The following output data was used for comparison: aerodynamic forces, mean pressure coefficient, Strouhal number, mean velocity magnitude and turbulence intensity. The main results can be summarized as follows. First, the predictions are more sensitive to the turbulence model choice than to the choice of algorithm. The Spalart-Allmaras model overall produced better results with both algorithms than the Wilcox k-ω model. Second, the artificial compressibility algorithm produced slightly more consistent results compared with experiment. / Master of Science

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Esta tese se insere na temática da crise dos grandes discursos, reconhecendo que ao contrário do colapso ou do fim das metanarrativas, eles se abriram, possibilitando a reapropriação de uma outra ideia de homem. Uma ideia que traz como base a gramática trágica. Trágico, aqui, é o que vislumbra o real como idiota, simples, aprovador de todos os acontecimentos, suficiente para reconfigurar a imageria contemporânea e identificar, no âmbito de sua gramática, a presença do sujeito idiotès (vulgar e idiota), uma presença que foi negligenciada ao longo de toda modernidade. Para tratar dessa reapropriação do homem e do sujeito , este estudo se desenvolve a partir de três esferas de observação: a) o advento da racionalidade e a construção de um modelo de sujeito forte, que se tornará a base de uma tradição; b) a crise deste modelo e o seu encontro com o pensamento fraco (Vattimo); e c) o reordenamento da gramática moderna que, intensificando-­se idiota, aponta para um outro imaginário. Na primeira, exponho a preferência da racionalidade moderna por um homem e um sujeito fortes e sua consequente reprovação das narrativas que desprezam a noção de natureza ou afirmam o homem vulgar, fruto do acaso e da idiotia humana; na segunda, analiso a época contemporânea apontando para uma reconfiguração conceitual que, a partir da crise das noções de ser e de natureza (impostas por Nietzsche), aponta para o surgimento do pensamento fraco/débil; no terceiro, com foco na filosofia trágica rossetiana, fixo os desdobramentos de suas noções de acaso, de convenção, de aprovação, de um real idiotès, para a constituição do sujeito contemporâneo. Por fim, aponto para a liberação da imageria trágica e sua expressão idiota, que aproximam o homem de sua condição mais humana: essa idiotia. Ou seja, o objetivo é reapropriar-­se de uma gramática e de um homem que nunca apareceram como aspiração no âmbito dos discursos hegemônicos e que agora evidenciam-­se no campo da contemporaneidade. / This theses stands on the theme of the crisis of great discourses, acknowledging that instead of a collapse or an ending of metanarratives, they unfasten, allowing the reappropriation of another idea of man. An idea that brings as groundwork the tragic philosophy. Tragic, here, is seeing the real as idiot, simplistic, an accepter of everything, enough to reconfigurate the contemporary imagery and identificate, on its own grammar, the presence of an idiots subject (vulgar and idiot), a presence that was neglected all through the modernity. To approach such reappropriation of man and of subject , this research develops departing of three spheres of observation: a) the advent of rationality and the construction of a strong subject model, that will became the base of a tradition; b) a crisis of such model and its clash with the weak thought (Vattimo); and c) the reordering of the modern grammar that, becoming more idiot, points to another imaginary. On the first, I Expose the preference of modern rationality for a strong man and a subject and its Consecutive reprobation of narratives that despises the notion of nature or asserts the vulgar man, product of chance and of human idiocy; the second, I analyse the contemporaneity pointing to a conceptual reconfiguration that, departing from the crisis of notions of being and nature (imposed by Nietzsche), points to the emergence of weak thought; on the third, focusing on the rossetian tragic philosophy, assert the developments of its notions of chance, of convention, of approval, of a idiots real, for the constitution of the contemporary subject. Lastly, I point to the liberation of tragic imagery and its idiotic expression that approximates the man to its most human condition: this idiocy. In other words, the aim is reappropriate a grammar and a man that never appear as ambition on scope of hegemonic discourses and now come to light in the field of contemporaneity.

The effects of shape and relative submergence (the ratio of flow depth to obstacle height, d/H) were investigated on the wakes around four different low-aspect-ratio wall-mounted obstacles: semi-ellipsoids with the major axes of the base ellipses aligned in the streamwise and transverse directions, two cylinders with aspect ratios matching the ellipsoids. Wake structure of a fully submerged, spherical obstacle was also investigated in the same flow conditions to provide insight into the flow obstacle interaction with ramification to sediment transport. A low-aspect-ratio semi-ellipsoid was chosen as broad representative of a freshwater mussel projecting from a river bed, and a sphere was employed as representative of a boulder. Two cylinders were used due to their similarity to geometries investigated in other studies. Digital Particle Image Velocimetry and thermal anemometry were used to interrogate the flow. For ellipsoids and cylinders, streamwise features observed in the mean wake included counter-rotating distributions of vorticity inducing downwash (tip structures), upwash (base structures), and horseshoe vortices. In particular, the relatively subtle change in geometry produced by the rotation of the ellipsoid from the streamwise to the transverse orientation resulted in a striking modification of the mean streamwise vorticity distribution in the wake. Tip structures were dominant in the former case while base structures were dominant in the latter. A vortex skeleton model of the wake is proposed in which arch vortex structures, shed from the obstacle, are deformed by the competing mechanisms of Biot-Savart self-induction and the external shear flow. An inverse relationship was observed between the relative submergence and the strength of the base structures for the ellipsoids, with a dominant base structure observed for d/H = 1 in both cases. The wake of the sphere is more complex than ellipsoidal geometries. Streamwise features observed in the mean wake including tip, horseshoe structures, and weak upwash. The shedding characteristics and dynamics of the wake were examined. Weak symmetric shedding was observed in the wakes of streamwise and transverse ellipsoids at d/H = 3.9 while cross-spectral measurements confirmed downstream and upstream tilting of arch structures shed by the transverse and streamwise ellipsoids, respectively. Much weaker peaks in the power spectrum were observed for low- and high-aspect-ratio cylinders. While the dominant Strouhal number remained constant as the relative submergence was reduced to d/H = 2.5 for the ellipsoids, it increased abruptly at d/H = 1 and transitioned to an antisymmetric mode. For sphere geometry at d/H = 3.9, a weak dominant frequency was observed close to obstacle junction and the cross-correlation function for symmetric measurements in the wake indicates symmetric shedding. These results demonstrate a means by which to achieve significant modifications to flow structure and transport mechanisms in the flow.

More than a century of dredging for oysters in the Foveaux Strait has resulted in a decimated fishery. In 1999 the Parliamentary Commissioner for the Environment asked the question: Where did we go wrong? This thesis provides answers to this question by presenting information provided by the Bluff oyster fishermen. In order to gain as much exposure to the community of fishermen as possible, a cumulative period of approximately six months was spent living in the town of Bluff between 2002 and 2007. During this time relationships were built with key informants, and a total of more than 50 community members were interviewed. The thesis describes the practical knowledge of the oyster fishermen, and places it in the context of more that 40 years of modem scientific studies concerned with the fishery. The finding are that since 1996 when the Quota Management System was introduced in the fishery, the most knowledgeable and responsible people in the fishery have been systematically excluded from roles in management. The practical knowledge of fishermen has been discounted in an industry and government led management system, which is an elaborate justification for continued maximum exploitation of the fishery. The theoretical contribution of the thesis lies in its description of belonging as a factor as important as that of property-rights in a sustainable resource system. The practical knowledge and conservation-mindedness of the fishery elders are characteristics of belonging, but not necessarily of ownership. Fishery management should recognize belonging as cultural capital, and make use of it under the present system (i.e. the Quota Management System) by according fishermen rights of management and access to the oyster fishery.

Nonlinearity in the Navier-Stokes equations can originate from a variety of sources, such as contributions stemming from the advective term, constitutive closure models or external factors such as chemical reactions and capillarity. Needless to say, a combination of any of the above sources has the potential to exasperate the problem significantly. This dissertation explores cases that predominantly feature advective and/or capillary effects. In particular, we first consider the inertia-dominated problem of single-phase flow past a confined square cylinder, followed by a study focused on the low-Re dynamics of rigid particles straddling non-planar interfaces. The first part of the thesis investigates transient, three-dimensional, incompressible and isothermal flow of a Newtonian fluid past a symmetrically confined obstacle at zero incidence. Results from both Laser Doppler Velocimetry (LDV) experiments and direct simulations upto Re = 250 have been reported. Beyond the onset of instability (Recr ≈ 58), an inflexion point around Re ≈ 115 is detected for the Strouhal number with no evidence of hysteresis in any of the measurements. Furthermore, incommensurate frequencies observed in the range 127 ≤ Re ≤ 175 suggest a quasi-periodic transition to three-dimensionality. This is shown to be followed by an intermediate periodic window starting around Re ≈ 180. Fourier analysis and spanwise velocity correlations are then used to characterize the observed phenomena. Subsequent analysis of consolidated data suggest that only a parametric variation of transverse and spanwise blockage ratios can bring closure to the subject of bluff-body wake transitions. The second part of the thesis implements and validates a physically consistent continuum model for the Moving Contact Line (MCL) through direct simulations. After elaborately discussing the MCL conundrum, a fundamental framework for the simulations is outlined in a theoretical orientation which combines the Level set method with a Fictitious domain approach in a finite-element scheme. The thesis objectives are then realized through simulation of various case studies that show favorable comparisons with theoretical and/or published experimental data. In short, the current work successfully illustrates the potential of novel boundary conditions (such as the GNBC) to accurately describe MCL dynamics. / Chemical Engineering

In this thesis, two dimensional, incompressible, viscous flow past bluff bodies and a bridge section, in which strong vortex shedding and unsteady attribute of flow are generally found, is simulated by means of random vortex method. The algorithm and method are described in detail. The validation and applicability of the developed numerical implementation to general wind engineering problems is illustrated by solving a number of classical problems, such as flow past circular and square cylinders. An application of the numerical implementation in the area of computational wind engineering is performed by analyzing a bridge deck section. Moreover, all results are compared with experimental and numerical studies in literature.

Relatively few studies have been carried out on the turbulent wake structure of a finite circular cylinder and a stack partially immersed in a flat-plate turbulent boundary layer. There is a need to develop a better understanding of the wakes of these structures, since they have many important engineering applications. This thesis investigates the influence of the aspect ratio on the wake of a finite circular cylinder and the effects of the ratio of jet flow velocity to crossflow velocity (velocity ratio, R) on the wake of a stack in a cross-flow. <p>The wake characteristics of flows over a finite circular cylinder at four different aspect ratios (AR = 3, 5, 7 and 9) were investigated experimentally at a Reynolds number of ReD = 6104 using two-component thermal anemometry. Each cylinder was mounted normal to a ground plane and was either completely or partially immersed in a flat-plate turbulent boundary layer. The ratio of boundary layer thickness to the cylinder diameter was 3. <p>A similar turbulent wake structure (time-averaged velocity, turbulence intensity, and Reynolds shear stress distributions) was found for the cylinders with AR = 5, 7, and 9, while a distinctly different turbulent wake structure was found for the cylinder with AR = 3. This was consistent with the results of a previous study that focused on the time-averaged streamwise vortex structures in the wake. In addition, irrespective of the value of AR, high values were observed for the skewness and flatness factors around the free end of the cylinders, which may be attributed to the interaction of the tip vortex structures and downwash flow that dominates this region of the cylinder.<p>The wake characteristics of a stack of aspect ratio AR = 9 were investigated using both the seven-hole pressure probe and thermal anemometry. The seven-hole probe was used to measure the three components of the time-averaged velocity field, while the thermal anemometry was used to measure two components of the turbulent velocity field at various downstream locations from the stack. The stack was mounted normal to the ground plane and was partially immersed in a flat-plate turbulent boundary layer, for which the ratio of boundary layer thickness to the stack diameter was 4.5. In addition, measurements of the vortex shedding frequency were made with a single-component hot-wire probe. The cross-flow Reynolds number was ReD = 2.3 x 104, the jet Reynolds number ranged from Red = 7.6 x 103 to 4.7 x 104, and R was varied from 0 to 3. <p>In the stack study, three flow regimes were identified depending on the value of R: the downwash (R < 0.7), cross-wind-dominated (0.7 < R < 1.5), and jet-dominated (R ≥ 1.5) flow regimes. Each flow regime had a distinct structure for the time-averaged velocity and streamwise vorticity fields, and turbulence characteristics, as well as the variation of the Strouhal number and the power spectrum of the streamwise velocity fluctuations along the stack height. The turbulence structure is complex and changes in the streamwise and wall-normal directions within the near and intermediate stack and jet wakes. In the downwash and crosswind-dominated flow regimes, two pairs of counter-rotating streamwise vortex structures were identified within the stack wake. The tip-vortex pair and base-vortex pair were similar to those found in the wake of a finite circular cylinder, located close to the free end and the base of the stack (ground plane), respectively. In the jet-dominated flow regime, a third pair of streamwise vortex structures was observed, referred to as the jet-wake vortex pair, which occurred within the jet-wake region above the free end of the stack. The jet-wake vortex pair has the same orientation as the base vortex pair and is associated with the jet rise.

Relatively few studies have been carried out on the turbulent wake structure of a finite circular cylinder and a stack partially immersed in a flat-plate turbulent boundary layer. There is a need to develop a better understanding of the wakes of these structures, since they have many important engineering applications. This thesis investigates the influence of the aspect ratio on the wake of a finite circular cylinder and the effects of the ratio of jet flow velocity to crossflow velocity (velocity ratio, R) on the wake of a stack in a cross-flow. <p>The wake characteristics of flows over a finite circular cylinder at four different aspect ratios (AR = 3, 5, 7 and 9) were investigated experimentally at a Reynolds number of ReD = 6104 using two-component thermal anemometry. Each cylinder was mounted normal to a ground plane and was either completely or partially immersed in a flat-plate turbulent boundary layer. The ratio of boundary layer thickness to the cylinder diameter was 3. <p>A similar turbulent wake structure (time-averaged velocity, turbulence intensity, and Reynolds shear stress distributions) was found for the cylinders with AR = 5, 7, and 9, while a distinctly different turbulent wake structure was found for the cylinder with AR = 3. This was consistent with the results of a previous study that focused on the time-averaged streamwise vortex structures in the wake. In addition, irrespective of the value of AR, high values were observed for the skewness and flatness factors around the free end of the cylinders, which may be attributed to the interaction of the tip vortex structures and downwash flow that dominates this region of the cylinder.<p>The wake characteristics of a stack of aspect ratio AR = 9 were investigated using both the seven-hole pressure probe and thermal anemometry. The seven-hole probe was used to measure the three components of the time-averaged velocity field, while the thermal anemometry was used to measure two components of the turbulent velocity field at various downstream locations from the stack. The stack was mounted normal to the ground plane and was partially immersed in a flat-plate turbulent boundary layer, for which the ratio of boundary layer thickness to the stack diameter was 4.5. In addition, measurements of the vortex shedding frequency were made with a single-component hot-wire probe. The cross-flow Reynolds number was ReD = 2.3 x 104, the jet Reynolds number ranged from Red = 7.6 x 103 to 4.7 x 104, and R was varied from 0 to 3. <p>In the stack study, three flow regimes were identified depending on the value of R: the downwash (R < 0.7), cross-wind-dominated (0.7 < R < 1.5), and jet-dominated (R ≥ 1.5) flow regimes. Each flow regime had a distinct structure for the time-averaged velocity and streamwise vorticity fields, and turbulence characteristics, as well as the variation of the Strouhal number and the power spectrum of the streamwise velocity fluctuations along the stack height. The turbulence structure is complex and changes in the streamwise and wall-normal directions within the near and intermediate stack and jet wakes. In the downwash and crosswind-dominated flow regimes, two pairs of counter-rotating streamwise vortex structures were identified within the stack wake. The tip-vortex pair and base-vortex pair were similar to those found in the wake of a finite circular cylinder, located close to the free end and the base of the stack (ground plane), respectively. In the jet-dominated flow regime, a third pair of streamwise vortex structures was observed, referred to as the jet-wake vortex pair, which occurred within the jet-wake region above the free end of the stack. The jet-wake vortex pair has the same orientation as the base vortex pair and is associated with the jet rise.