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.

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.

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)

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Thesis (Ph. D.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on Dec. 22, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Applied Mathematics, Department of Mathematical and Statistical Sciences, University of Alberta." Includes bibliographical references.

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No description available.

Thesis (Ph.D.)-- University of Tulsa, 1994. / Includes bibliographical references (leaves 159-163).

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

The formation process and characteristics of sprays from annular liquid jet breakup in moving gas streams have been investigated. In the first part of the thesis, a linear instability analysis is carried out for the instability and breakup of annular liquid jets. A dispersion relation has been derived and solved numerically by using Muller's method. Temporal instability analysis shows that two independent unstable modes, para-sinuous and para-varicose, exist for the annular jet instability. The para-sinuous mode outgrows the para-varicose one at relatively low gas-liquid density ratios and large Weber numbers as typically encountered in the twin-fluid atomization. The curvature of the annular jet promotes the jet instability and may not be neglected for the breakup processes of annular liquid jets. Not only the velocity difference across each interface but also the absolute velocity of each fluid is important for the jet instability. Co-flowing gas at high velocities is found to significantly improve atomization performance. A mesh-searching method has been developed to determine absolute mode of instability. The numerical results indicate that both absolute and convective instability exist for para-sinuous and para-varicose modes under certain flow conditions. Para-sinuous unstable waves outgrow para-varicose ones, and hence dominate the jet instability according to both absolute and convective instability analysis. The liquid viscosity has a simple stabilizing effect on the jet instability while the gas inertial force shows fairly complex influence on the absolute instability of the jet. The convective growth rates for various inner gas velocities indicate that not only the velocity difference between, but also the absolute velocity of the liquid and gas, determine the jet breakup process. In the second part of this thesis, experimental investigations have been conducted for the breakup process of annular water jets exposed to an inner air stream by photographic technique, and the characteristics of the resultant sprays by Phase Doppler Particle Analyzer. Two annular nozzles of the same structure but different dimensions are designed and constructed especially to provide smooth contraction for the liquid flow. The test apparatus is constructed to produce the annular liquid sheets or sprays of good quality. Flow visualization reveals that there exist three regimes. i.e., bubble formation, annular jet formation and atomization regime for the jet breakup process. Within the bubble formation regime, the jet breakup characteristics measured from the photographs taken under various liquid and gas velocities show that uniform bubbles are observed for various air-to-water velocity ratios. The jet breakup and wave lengths decrease with the air-to-water velocity ratio. The measurements are compared with the predictions by the linear instability analysis, and fair agreement is obtained. Spray characteristics measured by a Phase Doppler Particle Analyzer indicate that using atomizing air enhances the jet breakup process and improves the atomization performance by producing fine sizes of droplets and increasing the uniformity of drop sizes. The drop axial velocity has a jet-type distribution in the radial direction, and decreases monotonically along the spray axis. Increase in the water and air velocities results in higher drop axial velocity. The droplet size described by its Sauter mean diameter (SMD) reaches a minimum value at the central region of the spray and increases towards the spray edge. The SMD has a complex variation along the spray axis. / Graduate