Graduation date: 2000

Thesis (Ph. D.)--University of Washington, 2008. / Vita. Includes bibliographical references (leaves 100-107).

Thesis (M.S.)--University of Wisconsin, 1971. / Bound typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

In this work high-resolution numerical simulation (Large-Eddie Simulation, LES) has been used to study the characteristic factors causing and influencing the development of moist convective clouds. Through this work a 1D cloud-model was derived from first principles to represent the vertical profile of individual convective clouds. A microphysics framework was implemented to ensure identical behaviour in LES and cloud-model integration where the microphysical processes represented are numerically integrated using a novel adaptive step microphysics integration which uses the physical speed at which a process takes place to adjust the integration step size (in space and time). This work also introduces a simple representation of cloud-droplet formation which allows for super-saturation to exist in-cloud and through this provide more physical representation of the in-cloud state. Together with high-resolution simulation of isolated individual and interacting multiple clouds in environmental conditions leading to shallow convection, the 1D cloud-model was used to infer that the principal influence on moist convective clouds is the entrainment of air from a cloud’s immediate environment which is significantly different from the environmental mean state. This suggests that convection parameterisations must represent the influence of moist convective downdrafts to properly predict the vertical structure of convective clouds so as to correctly predict the cloud-top height and vertical transport. Finally it was found that cloud-base radius is not in itself adequate as a means of classification for defining cloud-types as clouds with the same cloud-base radius showed large variation (≈ 600m) in cloud-top height. Based on simulations of individual convective clouds it was found that 3D simulations are necessary to capture the full dynamic behaviour of convective clouds (2D axisymmetric simulations have too little entrainment) and that agreement with the 1D cloud-model could only be found when entrainment was diagnosed from simulation instead of being parameterised by the traditional Morton-Turner model and only for 2D axisymmetric simulations, suggesting that the 1D cloud-model will require further extension or the diagnosis of entrainment improved.

M.Ing (Electrical and Electronic Science) / High frequency magnetic components have significant advantages related to cost and physical size compared to their low frequency counterparts. The advent of high frequency power switch technology made the transformer frequency a variable and recent advances in this field have been ever pushing the switching frequency of higher power converters. Although high frequency inductors and transformers have been used and applied extensively to an increasingly broad range of applications over recent decades, analysis and design of these devices involves certain difficulties, related to extra losses due to eddy currents as well as smaller cooling surfaces, to the developer and designer. Numerical simulations of eddy currents in windings are slow, if not impossible in many cases, due to the large mesh impositions required in order to converge. Eddy currents and thermal constraints impose limitations on flux- and current densities, complicating the design. As yet, a convenient means of design, analysis and optimization of the physical magnetic topology does not exist. In this study, a method for analysing eddy currents in windings, usmg a combined analytical and numerical approach, is presented and implemented in a CAD tool. The one dimensional solutions for eddy currents in strip conductors are written in a more flexible form. A new approach to magnetic component design, called scant modelling, is presented and applied to two practical examples. The scant model comprises a minimum number of functional and form parameters in analysing and optimizing a design, but considers eddy current effects, thermal constraints and the effects of physical size and shape of core and windings at high frequencies.

Eddies are one of the key features of the Red Sea circulation. They are not only crucial for energy conversion among dynamics at different scales, but also for materials transport across the basin. This thesis focuses on studying the characteristics of Red Sea eddies, including their temporal and spatial properties, their energy budget, the mechanisms of their evolution, and their predictability. Remote sensing data, in-situ observations, the oceanic general circulation model, and data assimilation techniques were employed in this thesis. The eddies in the Red Sea were first identified using altimeter data by applying an improved winding-angle method, based on which the statistical properties of those eddies were derived. The results suggested that eddies occur more frequently in the central basin of the Red Sea and exhibit a significant seasonal variation. The mechanisms of the eddies’ evolution, particularly the eddy kinetic energy budget, were then investigated based on the outputs of a long-term eddy resolving numerical model configured for the Red Sea with realistic forcing. Examination of the energy budget revealed that the eddies acquire the vast majority of kinetic energy through conversion of eddy available potential energy via baroclinic instability, which is intensified during winter. The possible factors modulating the behavior of the several observed eddies in the Red Sea were then revealed by conducting a sensitivity analysis using the adjoint model. These eddies were found to exhibit different sensitivities to external forcings, suggesting different mechanisms for their evolution. This is the first known adjoint sensitivity study on specific eddy events in the Red Sea and was hitherto not previously appreciated. The last chapter examines the predictability of Red Sea eddies using an ensemble-based forecasting and assimilation system. The forecast sea surface height was used to evaluate the overall performance of the short-term eddy predictability. Different ensemble sampling schemes were implemented, and the investigation among different schemes is followed by a discussion of performance and challenges based on the results of a case study. The thesis not only enhances understanding of the Red Sea dynamics, but also deepens knowledge of the physical-biological and air-sea interactions within the basin. Further, it is a stepping stone to building a robust regional operational system with refined forecasting skills.

Satellite sea surface height (SSH) data over 1992-2012 are analyzed to study the spatial and temporal variability of sea level in the Red Sea. Empirical orthogonal functions (EOF) analysis suggests the remarkable seasonality of SSH in the Red Sea, and a significant correlation is found between SSH variation and seasonal wind cycle. A winding-angle based eddy identification algorithm is employed to derive the mesoscale eddy information from SSH data. Totally more than 5500 eddies are detected, belonging to 2583 eddy tracks. Statistics suggest that eddies generate over the entire Red Sea, with two regions in the central basin of high eddy frequency. 76% of the detected eddies have a radius ranging from 40km to 100km, of which both intensity and absolute vorticity decrease with eddy radius. The average eddy lifespan is about 5 weeks, and eddies with longer lifespan tend to have larger radius but less intensity. Different deformation rate exists between anticyclonic eddies (AEs) and cyclonic eddies (CEs), those eddies with higher intensity appear to be less deformed and more circular. Inspection of the 84 long-lived eddies suggests the AEs tend to move a little more northward than CEs. AE generation during summer is obviously lower than that during other seasons, while CE generation is higher during spring and summer. Other features of AEs and CEs are similar with both vorticity and intensity reaching the summer peaks in August and winter peaks in January. Inter-annual variability reveals that the eddies in the Red Sea are isolated from the global event. The eddy property tendencies are different from the south and north basin, both of which exhibit a two-year cycle. Showing a correlation coefficient of -0.91, Brunt–Väisälä frequency is negatively correlated with eddy kinetic energy (EKE), which results from AE activities in the high eddy frequency region. Climatological vertical velocity shear variation is identical with EKE except in the autumn, suggesting the vertical shear could convert the energy from baroclinic instability into eddy activity. Finally, numerical simulation results from the MIT general circulation model (MITgcm) are validated with previous studies and observations. The vertical structure of the simulated flux through Bab el Mandeb is successfully reproduced. Further validation with the 2010 cruise suggests that the thermocline occurs at ~200m, but the model vertical salinity gradient is lower than the observations. The model surface eddy variability is also examined, suggesting good agreement with satellite observations.

Atmospheric boundary layer flows around wind turbines distributed in a large wind farm can be examined by the use of large eddy simulation (LES), which is based on the assumption that large eddies in the flow are anisotropic and depend on the mean flow and the configuration geometry, while smaller eddies are isotropic and homogeneous, and can be modeled via subgrid scale models. In this thesis, a pseudo-spectral LES code with inflow conditions imposed through a precursor concurrent simulation is utilized to model the flow around a single wind turbine or a large wind farm operating in thermally-stratified conditions. The effect of the wind turbines on humidity is monitored through an additional scalar convection equation. It is found that on average, the effect of an individual wind turbine on the humidity is less than 1%, while the effect of the wind farm on humidity can reach 1-2% in the cumulative wakes.

No description available.

Eddy current inspection methods are used extensively in industry for the nondestructive testing of a wide variety of materials and product applications. The general theory of eddy current inspection is described. Equations defining the depth of penetration are derived from Maxwell's equations. Signal analysis methods are described using coil impedance diagrams. The impedance diagrams for a number of inspection applications are presented. A discussion of the techniques for theoretical calculation of the impedance of a coil is described. Typical coil configurations and instrumentation techniques are discussed.