Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 40-41). Also available on the World Wide Web.

Thesis (M.S.)--Naval Postgraduate School, 1964. / Includes bibliographical references (leaves 94-96).

Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 218-230).

Thesis (Ph.D.)--Brown University, 2005. / Vita. Thesis advisor: Humphrey Maris. Includes bibliographical references (leaves 141-145). Also available online.

Dissertation (Ph.D.) -- Worcester Polytechnic Institute. / Keywords: Multiphase flow; Two-fluid modeling; Direct numerical simulation; Two fluid modeling. Includes bibliographical references (leaves 116-119).

This study investigates the self noise from a ventilated supercavitating vehicle. A ventilated supercavity is a gaseous envelope surrounding an underwater vehicle that significantly reduces the drag felt by the vehicle. But the hydrodynamic noise generated by the creation of the supercavity could impact the successful deployment of the vehicle. A principal source of self noise for these types of vehicles is sound created by the ventilating gas jets impinging on the air-water interface. Analytical models of the radiated sound through the interface have been developed. Sometimes jets impinging on the interface entrain bubbles beneath the surface. This thesis outlines a theory to predict the influence of bubbles near the interface. Experimental measurements were made at the Naval Undersea Warfare Center (NUWC) in Newport, RI to test the accuracy of the model. These measurements include the unsteady force spectrum of a gas jet impinging on a rigid wall. The acoustic pressure spectrum of a gas jet striking the air-water interface was also recorded. The experimental results were compared to theoretical models for validation.

The dissertation consists of three chapters. In the first chapter, I develop a model to study the production of private safe assets by the banking sector. In response to a shortage of safe assets, the banking sector produces more private safe assets which alleviate the decline of aggregate investment and output. However, producing more private safe assets exposes the bank to more aggregate risk. Macroprudential policies can adjust the production of private safe assets with a tradeoff: encouraging the production of private safe assets alleviates the safe asset shortage problem and improves output, at the cost of a more volatile economy. In the second chapter, I document that during the 2008 financial crisis, U.S. shadow banks deleveraged sharply while commercial banks maintained their leverage. I find that banks that relied more on short-term funding tended to deleverage more during the crisis. I build a model to incorporate both shadow banks and commercial banks with different leverage determination mechanisms. The model can explain the leverage dynamics of the banking sector and the flight-to-quality phenomenon observed in data. The third chapter is coauthored with Jianjun Miao and Pengfei Wang. We revisit Galí’s (2014) analysis by extending his model to incorporate persistent bubble shocks. We find that under adaptive learning, a stable bubbly steady state and the associated sunspot solutions under optimal monetary policy are not E-stable. When deriving the unique forward-looking minimum stable variable (MSV) solution around an unstable bubbly steady state, we obtain results that are consistent with the conventional views: leaning against the wind policy reduces bubble volatility and is optimal. Such a steady state and the associated MSV solution are E-stable.

No description available.

No description available.

Droplets and bubbles are important for understanding natural phenomena such as falling raindrops, airborne disease transmission, and plant respiration systems, and also for engineering contexts such as semiconductor fabrication, nuclear power plants, and electronics cooling. However, still, more understanding is needed of these complex dynamics problems. This dissertation will talk about the droplet impact and bubble departure dynamics that are happening on various surfaces. In Chapters 2 and 3, we will explore how raindrops can transmit plant pathogens. When the raindrop impacts the infected wheat leaf, the micron-sized dry spore can liberate from the surface in two different ways: dry dispersal and wet dispersal. The dry spore can liberate from the surface by the inertia of the drop, after that, the air vortex generated by the drop impact can carry the dry spores above the laminar boundary layer, with the potential for long-distance transport. For the wet dispersal, spore-laden droplets can be generated after raindrop impact, but how these spore-laden droplets can make neighboring plant diseases is still a mystery. We have shown that the splashed droplets can stick to the adjacent healthy leaf depending on the inertia of the impacting droplet, anisotropic leaf orientation, and whether it is treated with fungicide or not. In Chapter 4, We design a micropillar aluminum substrate that preferentially grows frost on top of the pillars. When deposited droplets impact the frost-tipped pillars, the dynamic pressure causes the water to wick within the frost faster than it can impale the gaps between the pillars. Upon freezing, this safely suspends the resulting ice sheet in the air-trapping Cassie state, without any surface coatings required. For the last part (Chapter 5), we investigated the bubble coalescence dynamics that can depart the bubble with a micrometer size. We made the micro-structured surfaces tailored to nucleation sites to enable the coalescence-induced departure of micro-bubbles. A scaling model reveals two different modes of bubble departure following the coalescence-induced depinning: capillary-inertial jumping for micrometric bubbles and a buoyant-inertial departure for millimetric ones. Eventually, this small bubble departure can delay film boiling which can be the barrier to the boiling heat transfer. / Doctor of Philosophy / Dynamic interaction of droplets and bubbles with different surfaces is ubiquitous: an impacting rain droplet on a plant leaf is responsible for transmitting thousands of plant pathogens, or decreasing the departure size of bubbles on the surface of heat exchangers would increase their efficiency. It is now well-understood that the departure of condensed droplets on water repellent surfaces exhibits superior heat transfer compared to all other modes of condensation and also enables self-cleaning, delayed frosting, and anti-fogging surface technology.In Chapters 2 and 3, we are studying the dynamic interaction of raindrops and wheat leaves. By depositing water droplets on diseased leaves, we found out a raindrop can transmit wheat pathogens. This simple but important phenomenon would adversely affect the quality of our wheat which is the most widely grown crop in the world, contributing to a large amount of portion the global food supply. Chapter 4 sheds light on another example of the dynamic interaction of raindrops and an icy surface. We designed a pillared aluminum substrate that preferentially grows condensation frosting on top of the pillars. With this passive anti-frosting technology, we are able to trap water droplets and ice in the suspending water droplets in the air-trapping Cassie state without using a fragile nanotextured structure or a complex re-entrant structure. Upon freezing, this safely suspends the resulting ice sheet in the air-trapping Cassie state, without any surface coatings required. Under a cold and humid environment, Cassie water freezes into Cassie ice which is advantageous for its low surface adhesion. In Chapter 5, we show that rationally micro-structured surfaces tailor nucleation sites to enable the coalescence-induced departure of micro-bubbles. With this technique, we are able to remove surface bubbles at smaller sizes that would result in enhancing the critical heat flux of nucleate boiling. We have used a blend of experiments and scaling to understand the underlying physics of this phase-change problem.