Natural and commercially available particles of uniform shape and size were used to study the effect of particle shape on hindered settling in creeping flow (Re₀< 0.1), where fluid flow behaviour is independent of particle Reynolds number and the effect of shape is most prominent. Particles of different shapes used were spherical glass beads, cubic salt (NaCl) crystals and ABS plastic pellets, flaky sugar crystals and angular mineral (silicate) crystals. They were carefully sized by sieving and liquid elutriation to avoid other effects like size segregation. Constant settling data were processed in the form of uѵ rather than u to eliminate the effect of temperature variation on viscosity. The effect of the wall on hindered settling rate was found to be small in most cases. The method proposed by Beranek and Klumpar for correlating fluidization data on different shaped particles was found to be only moderately successful in correlating the present settling data for different shapes. Results were plotted as loguѵ versus log €, and the index n of the equation uѵ/(uѵ)ext = €ⁿ was calculated by least squares. It varied from an average value of 4.8 for the smooth spheres to 5.4 for the cubes to 5.8 for the flaky or angular particles. In contrast to the corresponding term proposed by Richardson and Zaki, the term (uѵ)ext was measurably lower than uѵ for free settling of the spherically isotropic particles. More significantly, the index n was graphically found to display a definite trend with the random loose fixed bed porosity, which is shape dependent and easily measured, and may therefore turn out to be a simple and useful parameter for taking account of shape variation. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Friction factors have been determined experimentally for flow of water and various aqueous solutions of polyethylene glycol in four different concentric annuli. The annuli studied covered a diameter ratio range of 0.0406 to 0.6331. The annular entrance was sharp-edged and no spacers were used within the system. The Reynolds number range investigated was approximately 200 to 26,000, based on equivalent diameter equal to four times the hydraulic radius. The fully developed friction factors for all four diameter ratios were correlated by the Nikuradse equation for a smooth pipe when the Reynolds number exceeded 3500 and by the Knudsen and Kata theory for laminar flow when the Reynolds number was less than 2200. Deviations from the theory of Hanks for laminar - turbulent transition in the well-developed flow region of concentric annuli could be tentatively accounted for by the extra turbulence arising from the sharp-edged entrance in the present investigation. For well-developed flow the critical Reynolds numbers for the various diameter ratios ranged between 2650 and 3700, and the mode of transition was sharp. However, for low, intermediate and high values of entrance length, respectively, three different modes of transition were found to exist in the annuli studied. Local friction factors were based on pressure gradient, uncorrected for changes in kinetic energy due to the developing velocity profile. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

A procedure is described for the redesign of undamped unforced linear structural systems to meet specified changes in natural frequency or mode shape. A baseline analysis is conducted using finite elements to obtain a subset of the natural frequencies and mode shapes. A two stage perturbation analysis is then used to obtain the structural changes required to meet the specified changes in natural frequency or mode shape. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

A comprehensive eigen-mode analysis of an intermediate coupled model linearized with respect to arrays of basic states is performed to study the regimes of leading ocean-atmosphere coupled modes of relevance to the El Niño Southern Oscillation phenomenon. Different kinds of leading modes are found to coexist and to become unstable under wide ranges of basic states and parameter conditions. In particular, two main kinds of modes have periods around 4 years and 2 years. They are thus referred as to quasi-quadrennial (QQ), quasi-biennial (QB) modes, respectively. The positive coupled feedback destabilizes and quantizes the near-continuous spectrum for the low-frequency modes of the upper ocean dynamics giving rise to these leading modes with distinct periodicities. The QQ mode can be understood to a large extent by the mechanisms elucidated in the simple conceptual recharge oscillator which relays on slow oceanic dynamic adjustment of equatorial heat content, whereas anomalous advection of sea surface temperature by equatorial zonal current anomalies plays an important role in the QB mode. One of the findings of this study is that the QQ and QB mode may coalesce under realistic conditions through a codimension-2 degeneracy in the parameter space. The coexistence or multiplicity of ENSO-related coupled modes under present climate conditions may provide a plausible explanation for the observed dominating QQ and QB variability of rich ENSO behaviors. / A Dissertation Submitted to the Geophysical Fluid Dynamics Institute in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy. / Summer Semester, 2006. / April 17, 2006. / Advective Feedback, Thermocline Feedback, Heat Budget Analysis, Stability Analysis, Unstable Coupled Modes, Coexistence / Includes bibliographical references. / Fei-Fei Jin, Professor Directing Dissertation; Guosheng Liu, Outside Committee Member; Xiaolei Zou, Committee Member; Ming Cai, Committee Member; Allan Clarke, Committee Member; James J. O'Brien, Committee Member.

No description available.

No description available.

The purpose of this research was to improve the smoothing operation in smoothed particle hydrodynamics, SPH, when the flow of matter is not smooth. Our main focuses are on the kernel selection, identifying the discontinuities in the sequences to be smoothed, and use of the Laplacian as opposed to artificial viscosity for improved physical accuracy. The results show that alternative kernels result in differences in how matter flows. These effects are explained by the kernels' gradient and Laplacian properties. Five alternative kernels were included in our analysis and our SPH-based simulation cases. Further, the sequences to be smoothed by the kernel function were found to contain numerous discontinuities. As it is well known from multiple areas of science, such discontinuities lead to degraded accuracy if the smoothing is performed without taking discontinuities into consideration. Several methods are introduced to detect discontinuities and perform smoothing by individually and independently smoothing the segments between discontinuities. We analyzed results from sloshing tank SPH simulations and found such segmentwise smoothing impacts the flow. Discontinuities were identified by first-generation wavelets. We found that in about 24 to 27 percent of the fluid particles have sequences containing discontinuities, independent of time step. A second-generation wavelet analysis showed coherent vorticity structure in the flow, and the fluid particles with discontinuous sequences combined with coherent vorticity were the focus of our quantification of effects on particle movement. The research work presented here serves as a tool for further improvement of the SPH method, and is substantiated by the results obtained herein.

The Southern Ocean is a high-nutrient, low-chlorophyll region where primary productivity is limited mainly by iron and light availability, yet it accounts for ~30-40% of global ocean CO2 absorption annually. Marine plankton play a major role in the Southern Ocean CO2 sink as they fix dissolved atmospheric CO2 into organic carbon biomass, much of which supports the ocean food web and a portion of which sinks into the ocean interior, thereby removing atmospheric CO2 on decadal to centennial timescales (i.e., the biological carbon pump). The importance of plankton diversity and dynamics in modulating carbon production and export remains poorly understood, particularly around the many (Sub)Antarctic islands where physical and biogeochemical variability is high. The major motivation for the work presented in this thesis is an improved understanding of the role of the plankton system in Southern Ocean fertility and carbon export, and relatedly, the response of the plankton to environmental forcing such as changes in nutrient dynamics driven by hydrography and island mass effects. To that end, I investigated plankton community diversity and ecological dynamics in the context of nutrient cycling, primary production, and carbon export potential in the open Southern Ocean and in the vicinity of its many island systems. Specifically, I used carbon and nitrogen stable isotope ratios as a tool to quantify carbon export potential and food web dynamics across all major hydrographic zones and basins of the Southern Ocean. Five main findings emerged. Firstly, I developed insights into the major drivers of spatial and temporal variability in the carbon and nitrogen isotope ratios (δ13C and δ15N) of the Southern Ocean's plankton system using circum-Antarctic carbon and nitrogen isoscapes. Along with the drivers commonly invoked by previous studies, I further determined a relationship between the δ13C and δ15N of suspended particulate matter (SPM) and phytoplankton community composition, with diatoms exerting a particularly strong influence on the δ13C and δ15N of the SPM, which is subsequently transferred to the zooplankton. Secondly, I observed that the (Sub)Antarctic islands tend to increase the δ13C and δ 15N of phytoplankton and zooplankton relative to the open Southern Ocean. This trend can be explained by the input of terrestrially-derived iron and other nutrients (e.g., ammonium and/or urea from birds and seals) into the surface layer, which stimulate diatom growth on nitrate and/or exogenous reduced nitrogen sources that are high in δ15N. Thirdly, I applied a new approach using the δ15N of seawater nitrate and SPM to quantify carbon export potential across the summertime Southern Ocean. I found that carbon export potential is highest near the islands and melting sea ice, driven by the input of limiting nutrients (i.e., iron) and by the dominance of diatoms. Fourthly, I found that the δ15N of SPM is a reliable baseline for trophic analysis of the zooplankton system over a large spatial extent of the Southern Ocean (i.e., circum-Antarctic). Since the collection and analysis of SPM samples for δ15N is relatively straightforward, this result should be welcomed by researchers who use such data to reconstruct trophic flows through plankton food webs, as well as the movements and dietary histories of zooplankton in the Southern Ocean. Finally, my new zooplankton δ13C and δ15N isoscapes reveal that during the summer, the primary zooplankton consumers in the Subantarctic waters of the Southern Ocean occupy a low trophic position akin to herbivores, implying that the Subantarctic food web may act to retain organic carbon within the euphotic zone instead of exporting it to depth. By contrast, the primary consumers in Antarctic waters occupy a higher trophic position that suggests they are omnivores and carnivores, which potentially indicates a shorter food chain and thus a stronger biological pump. The work detailed in this thesis suggests new methodological approaches for studying the Southern Ocean plankton system and offers an improved understanding of plankton dynamics and their relationship(s) with the biogeochemical processes that govern the different zones of the Southern Ocean.

Impinging gas jets have many engineering applications, including propulsion, cooling, drying, and coating control processes. In continuous hot-dip galvanizing, a molten zinc-based coating is applied to a steel substrate for corrosion protection. Planar impinging gas jets (industrially called air-knives) are employed to wipe the protective coating from the steel sheet to control the final coating weight. The maximum skin friction and pressure gradient developed by the impinging gas jet on the steel sheet heavily influences the final coating weight. In the thesis, the maximum skin friction developed on an rigid impingement plate positioned downstream of a planar impinging gas jet (scaled-up model air-knife) is measured using oil film interferometry (OFI). A maximum skin friction map based on the jet operating conditions is established, which can be used in conjunction with industrial coating weight models for film thickness prediction, and can be further employed in the assessment and verification of computational fluid dynamic (CFD) models. As impinging gas jets reach higher flow velocities, inherent instabilities in the jet can amplify due to feedback loops created between the jet exit and the impingement plate. The flow field characteristics under resonance conditions are known to exhibit large amplitude jet column oscillations, and strong coherent fluid structures propagating down the impinging shear layers. This work examined the global effect of planar impinging gas jet oscillations on the maximum mean skin friction developed in the stagnation region using external jet forcing. Reductions in maximum mean impingement plate skin friction were confirmed and found to be caused by increased levels of fluid entrainment under jet forcing conditions. The fluctuating velocity fields under external jet forcing was also examined. The velocity fluctuations due to both the coherent motion of the jet column, and the turbulence were obtained and analyzed using fluid dynamic tools such as particle image velocimetry (PIV) and proper orthogonal decomposition (POD). The fluctuating velocity of the planar impinging gas jet displayed increased levels of fluctuation intensity and unique flow field characteristics under external forcing, as well as, exhibited similar features to that of a high speed impinging planar gas jet under fluid resonance conditions. Overall, it is determined that enhanced planar impinging gas jet oscillations (or equivalent air-knife oscillations) is associated with adverse fluid effects, which degrade the wiping performance of the jet. / Thesis / Doctor of Philosophy (PhD)

No description available.