Master of Science, The Ohio State University, 2007, Graduate School

Committee: Not Provided (Other) Subjects:

Doctor of Philosophy (PhD), Wright State University, 2024, Engineering PhD

It is generally accepted that there exist two types of laminar separation bubbles (LSBs): short and long. The process by which a short LSB transitions to a long LSB is known as bursting. In this research, large eddy simulations (LES) are used to study the evolution of an LSB that develops along the suction surface of the L3FHW-LS at low Reynolds numbers. The L3FHW-LS is a new high-lift, high-work low-pressure turbine (LPT) blade designed at the Air Force Research Laboratory. The LSB is shown to burst over a critical range of Reynolds numbers. Bursting is discussed at length and its effect on transition, vortex shedding, and profile loss development are analyzed in depth. The results of these analyses make one point very clear: the effects of bursting are non-trivial. That is, long LSBs are not just longer versions of short LSBs. They are phenomena unto themselves, distinct from short LSBs in terms of their vortex dynamics, profile loss footprint, time-averaged topology, etc. This work culminates in a demonstration of how, with the aid of unsupervised machine learning, these differences can be leveraged to reduce the energy requirements of steady vortex generator jets (VGJs). Relative to pulsed VGJs, steady VGJs require significantly more energy to be effective but are more realistic to implement in actual application. By tailoring VGJ actuation to LSB type (i.e., actuating differently in response to a long LSB than to a short LSB), it is shown that significant energy savings can be realized.

Committee: Mitch Wolff Ph.D. (Advisor); George Huang Ph.D. (Committee Member); John Clark Ph.D. (Committee Member); Christopher Marks Ph.D. (Committee Member) Subjects: Fluid Dynamics

Bachelor of Arts, Walsh University, 2024, Honors

Currently, in the world of investing, the accurate classification grade for Bitcoin has become a current debate. Due to Bitcoin being incapable of having a bottom line and no real demand, many argue that it should not be considered an investment-grade or speculative-grade asset. As a result, this study calls for the creation of a third investment grade, called the greater fool grade, to be created to appropriately classify Bitcoin. The goal of this study is to provide sufficient evidence that shows Bitcoin is unlike any investment and speculative asset, supporting the creation of the greater fool grade to accurately categorize the asset. This was done by analyzing the risk and return characteristics of Bitcoin through three different analyses. The first analysis conducted was a comparative analysis of Bitcoin's continuous bubble cycle. In this analysis, Bitcoin was compared to the five most notorious bubbles in history and displayed comparable traits to the studied historical asset bubbles. An applied analysis of statistical significance was also conducted. In this analysis, Bitcoin and a combined 18 different investment-grade and speculative-grade assets' financial measurements were analyzed and compared over multiple time periods, which showed that a majority of Bitcoin's financial measurements were vastly different and more volatile than those of the other studied assets. Lastly, a statistical hypothesis test with 110 regressions was conducted to see if Bitcoin's total risk was statistically distinct from the investment and speculative assets. These regressions compared the total risk of Bitcoin to the total risk of a combined 18 different investment-grade and speculative-grade assets. Upon completion of this model, it was found that there was no significance in correlation of Bitcoin's total risk when compared to the total risk of the other measured assets. The results of this study show overwhelming support surrounding the creation of the greater fool grade for (open full item for complete abstract)

Committee: Dr. Marc Fusaro (Advisor) Subjects: Economic History; Economic Theory; Economics; Finance

Doctor of Philosophy, The Ohio State University, 2018, Political Science

Why do states sometimes adopt wildly overconfident foreign policy choices – choices that have unreasonable expectations about potential benefits of success and unreasonable expectations about the absence of risks of failure? In this dissertation, I argue that extreme cases of these choices can occur as a consequence of mania: a wave of irrational, excessive optimism. One example of mania in foreign policy was the drive to enlarge NATO to incorporate Georgia and Ukraine in 2007 and 2008, prior to the Russian invasion of Georgia and later invasion of Ukraine. Derived ultimately from the work of John Maynard Keynes in economics, I argue that mania in international relations is both expected and inevitable under certain circumstances. Manias primarily occur as part of a three stage process: a sudden, unexpected shock that changes the nature of the international system (“displacement”), followed by new stories that explain both the causes of the shock and explain their consequences for the future (“New Era Thinking”). The new era opens up possibilities for foreign policy success that had not existed before, leading policy elites to “invest” in foreign policies. If those policies do not fail, skepticism about New Era Thinking diminishes and optimism about future success grows. This process produces a feedback loop where New Era Thinking and policy choices interact with each iteration – and with each iteration have higher expectations for gains and lower cognizance of risk. Similar to the psychological dynamics that drive stock market bubbles in economics, the result is a foreign policy process that dismisses both uncertainty and risk, creating the potential for failure. I will show how the end of the Cold War was a displacement that produced New Era Thinking, and that as NATO enlargement – which was predicated on New Era Thinking – progressed eastward it became manic. Mania has its basis in the human need to overcome uncertainty: the inability to know the future. (open full item for complete abstract)

Committee: Jennifer Mitzen PhD (Committee Chair); Christopher Gelpi PhD (Committee Member); Alex Wendt PhD (Committee Member) Subjects: International Relations; Political Science

Doctor of Philosophy, The Ohio State University, 1987, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, Case Western Reserve University, 2015, Chemical Engineering

Metal electrodeposition is often associated with simultaneous hydrogen co-evolution. The presence of bubbles complicates the design and control of electrodeposition processes. This is particularly relevant to the electrodeposition from aqueous electrolytes of numerous metals with standard potentials that are negative to hydrogen. As shown in this study, hydrogen co-evolution enhances the transport rates of the metal deposition reaction beyond those predicted by the classical, steady-state mass transport model. Available models addressing transport in the presence of gas co-evolution are based on free convection that is enhanced by the rising bubble cloud. However, there are no models that address mass transfer enhancement by bubbles under forced convection, such as analyzed here for the commonly used, facing-down rotating disk electrode (RDE). This study characterizes experimentally the phenomenon and introduces a model for quantifying it. Experimental data was collected in plating copper at high cathodic overpotentials (-0.4 to -1.0V vs SHE) from acidified copper sulfate on a RDE. The transport enhancement (~2-6 fold) was determined by measuring the copper deposition by gravimetry. Pulse experiments, where the current decay was measured following a short bubble generation confirmed the linkage between the current enhancement and the presence of bubbles. A model based on fresh electrolyte replenishing the volume vacated by the translating bubbles and thus subjecting regions of the electrode to enhanced transient currents has been derived. The model correlates the experimental data indicating higher transport enhancement with increasing cathodic polarization and dependence of the enhancement on the rotation rate and on the bulk copper concentration.

Committee: Uziel Landau (Committee Chair); Rohan Akolkar (Committee Member); Donald Feke (Committee Member); Daniel Scherson (Committee Member); Mohan Sankaran (Committee Member) Subjects: Applied Mathematics; Chemical Engineering; Chemistry; Engineering; Materials Science; Mechanical Engineering; Physics; Technology

PhD, University of Cincinnati, 2000, Engineering : Nuclear and Radiological Engineering

This work describes the magnetic resonance (MR) imaging techniques and image processing algorithms developed for radiation dosimetry with the superheated emulsion chamber. The chamber contains an emulsion of chloropentafluoroethane droplets in a tissue-equivalent glycerin-based gel. The droplets are highly superheated and expand into vapor bubbles upon exposure to irradiation. Brachytherapy sources can be inserted into the superheated emulsion chamber to create distributions of bubbles. The distribution of bubbles is then representative of the dose distribution to which the emulsion is exposed. Cumulating data from multiple independent exposures is required to calculate statistically significant bubble densities. MR imaging is well suited to determining the bubble distribution. Susceptibility gradients at the interfaces between bubbles and gel are exploited to enhance contrast so microscopic bubbles can be imaged using relatively large voxel sizes. A conventional three-dimensional gradient echo imaging method is developed and applied to multiple independent irradiations of the superheated emulsion chamber from an 125I source. An image post-processing technique is developed to semi-automatically segment the bubbles from the images and to assess dose distributions based on the measured bubble densities. Relative bubble densities compare favorably to relative radial dose distributions calculated as recommended by Task Group 43 (TG43) of the American Association of Physicists in Medicine as well as Monte Carlo radiation transport simulations. A three-dimensional, segmented, double sampled, echo-planar imaging (EPI) technique is subsequently developed and applied to an 125I source. Combining two-dimensional EPI with a conventional phase encode in the third dimension provides for rapid acquisition of susceptibility weighted images. Segmentation reduces artifacts produced by magnetic field inhomogeneities, while double sampling removes Nyquist ghosting. Post-processing is (open full item for complete abstract)

Committee: Henry Spitz (Advisor) Subjects:

BA, Oberlin College, 2000, Economics

This paper takes a different approach by developing a model based on the boom and bust cycle of Japan during the mid to late 1980's, using currently accepted theory. In section II, I review the general characteristics of asset bubbles to familiarize the reader and offer some historical examples. Section III offers a review of many of the theoretical papers on asset bubbles, as well as empirical papers, which involve similar phenomena in order to gain some insight in building the model. In section IV, I build a theoretical model. Section V begins preliminary testing to examine this theory and reviews the results. Finally, in section VI, I provide concluding remarks and discuss areas that I plan to explore in future research.

Committee: Luis Fernandez (Advisor) Subjects: Economic History; Economic Theory; Economics

Doctor of Philosophy, Case Western Reserve University, 2008, Chemical Engineering

Previous research endeavors resulted in a process to recover solid particles and oil droplets from aqueous suspensions. This process involves applying a one-dimensional resonant ultrasonic field to the suspension while it is flowing through or resting in a rectangular chamber. The same process has been utilized here for gas bubbles in an aqueous medium. Bubbles in this system move to the acoustic pressure antinodes, based on the density and compressibility of the bubble and the surrounding fluid as well as the driving frequency and the radius of the bubble.To obtain a fundamental understanding of the movement of a single bubble within the acoustic chamber, a balance of the relevant physical forces was completed: primary acoustic force, buoyancy force, and drag force. The resulting equations could be used to determine the position of a single bubble within the chamber and the velocity at which that bubble would be moving toward those positions. A microscopic mathematical model was developed to predict the relative trajectory of a bubble pair in an acoustic field. This model not only took into account the primary forces previously discussed, but also inter-bubble effects: secondary acoustic force, van der Waals force, hydrodynamic interactions, and Brownian diffusivity. The trajectory analysis was used to track the movement of the bubble pairs under a variety of operating conditions and the results were compared to experimental data. This data was then used to calculate volume cleared by the collision of different bubble pairs, thus describing the kinetics of the collision process. The results from the models were then compared to experimental data obtained by injecting small numbers of bubbles into an acoustic chamber. This comparison was done by taking video of bubbles colliding, mapping their path, and comparing this to the trajectory determined from the bubble pair model. The projected trajectory and the experimental trajectory were shown to be in good agreement. (open full item for complete abstract)

Committee: Donald Feke PhD (Advisor); J. Adin Mann PhD (Committee Member); Robert Edwards PhD (Committee Member); Dov Hazony PhD (Committee Member) Subjects: Chemical Engineering