Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

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 give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    EXPERIMENTAL CHARACTERIZATION OF ATMOSPHERIC TURBULENCE SUPPORTED BY ADVANCED PHASE SCREEN SIMULATIONS
    (2020) PAULSON, DANIEL A; Davis, Christopher C; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Characterization of optical propagation through the low turbulent atmosphere has been a topic of scientific investigation for decades, and has important engineering applications in the fields of free space optical communications, remote sensing, and directed energy. Traditional theories, starting with early radio science, have flowed down from the assumption of three dimensional statistical symmetry of so-called fully developed, isotropic turbulence. More recent experimental results have demonstrated that anisotropy and irregular frequency domain characteristics are regularly observed near boundaries of the atmosphere, and similar findings have been reported in computational fluid dynamics literature. We have used a multi-aperture transmissometer in field testing to characterize atmospheric transparency, refractive index structure functions, and turbulence anisotropy near atmospheric boundaries. Additionally, we have fielded arrays of resistive temperature detector probes alongside optical propagation paths to provide direct measurements of temperature and refractive index statistics supporting optical turbulence observations. We are backing up these experimental observations with a modified algorithm for modeling optical propagation through atmospheric turbulence. Our new phase screen approach utilizes a randomized spectral sampling algorithm to emulate the turbulence energy spectrum and improve modeling of low frequency fluctuations and improve convergence with theory. We have used the new algorithm to investigate open theoretical topics, such as the behavior of beam statistics in the strong fluctuation regime as functions of anisotropy parameters, and energy spectrum power law behavior. These results have to be leveraged in order to develop new approaches for characterization of atmospheric optical turbulence.
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    The Effects of Liquid Alkane Fuel Structure on Catalyst-Enhanced Combustion
    (2018) Dube, Grant; Oran, Elaine S; Lee, Ivan C; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The U.S. Army is developing micro-combustors for use in soldier-portable power generation systems. Many of the challenges associated with micro-combustion can be potentially overcome using a catalyst, but the effects of the catalyst on ignition under the low temperature, atmospheric conditions seen in the field are not well understood. To better understand catalytic ignition phenomena under these conditions, a Catalytic Ignition and Emissions Tester (CIET) was developed and used to investigate the effects of liquid alkane fuel structure during catalyst enhanced ignition. Various mixtures of n-octane and iso-octane, as well as single component n-dodecane and n-hexadecane, were chosen as simple, surrogate test fuels to represent gasoline, jet fuel, and diesel, respectively. Fuel reactivity was shown to decrease with increased branching for all metrics tested while the effects of chain length were less definitive. The global apparent activation energies of all fuels tested were found to be in the range of 41-61 kJ/mol with 95% confidence, significantly lower than those previously reported for non-catalytic hydrocarbon combustion (>100 kJ/mol).