UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Nonlinear Fluid-Structure Interactions in Flapping Wing Systems(2013) Fitzgerald, Timothy; Balachandran, Balakumar; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work relates to fluid-structure interactions in the context of flapping wing systems. System models of flapping flight are explored by using a coupling scheme to provide communication between a fluid model and a structural model describing a flexible wing. The constructed computational models serve as a tool for investigating complex fluid-structure interactions and characterizing them. Primary goals of this work are construction of models to understand nonlinear phenomena associated with the flexible flapping wing systems, and explore means and methods to enhance their performance characteristics. Several system analysis tools are employed to characterize the coupled fluid-structure system dynamics, including proper orthogonal decomposition, dimension calculations, time histories, and frequency spectra. Results obtained from two-dimensional simulations conducted for a combination of a two-link structural system and a fluid system are presented and discussed. Comparisons are made between the use of direct numerical simulation and the unsteady vortex lattice method as the fluid model in this coupled dynamical system. To enable three-dimensional studies, a novel solid model is formulated from continuum mechanics for geometrically exact finite elements. A new partitioned fluid-structure interaction algorithm based on the Generalized-α method is formulated and implemented in a large scale fluids solver inside the FLASH framework. Consistent boundary conditions are also formulated by using Lagrangian particles. Several examples demonstrating the effectiveness of the methods and implementation are shown, in particular, for flapping flight at low Reynolds numbers. Unique experiments have also been undertaken to determine the first few natural frequencies and mode shapes associated with hawkmoth wings. The computational framework developed in this dissertation and the research findings can be used as a basis to understand the role of flexibility in flapping wing systems, further explore the complex dynamics of flapping wing systems, and also develop design schemes that might make use of nonlinear phenomena for performance enhancement.Item Essays on Split Estate in Energy Development(2008) Fitzgerald, Timothy; McConnell, Kenneth; Agricultural and Resource Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Taking advantage of randomly-assigned federal mineral rights, the first essay establishes the discount that mineral developers place on oil and gas leases with divided ownership. This discount is interpreted as an expectation of reduced profits as a result of transaction costs incurred in obtaining surface access. Results of 53 bimonthy federal oil and gas lease auctions in Wyoming between February 1998 and October 2006 are examined. Bidders discount split estate by 11 to 14 percent on average, but by as much as 24 percent for more expensive leases. Impacts of multiple ownerships and additional leasing stipulations are also explored. The second essay examines how conflict between surface and subsurface owners affects production from coalbed methane wells in Wyoming. Using well-level production data from 1987-2006, wells on federal minerals with private surface are compared to those on federal minerals with federal surface. A kernel matching estimator is used to control for selection of well sites on the basis of observable information. Delays in entry on split estate are found, but are not associated with reduced production after entry. Some support is found for strategic incentives firms face regarding property rights. One way coalbed methane production differs from traditional oil and gas extraction is in the large quantities of produced water. Surface discharge has proven to be a low-cost alternative but raises the possibility of externalities. In the third essay a unique dataset linking coalbed methane wells in Wyoming to water disposal permit violations is used to explore differences in environmental performance across severed and unified minerals. A propensity score matching model is used to control for the endogeneity of tenure. The results suggest that split estate wells using surface discharge have a higher number of violations, but the severity of those violations is not significantly different from those on unified estates.