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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2007 - 200912010 - 20131

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    Mechanisms of Vortex-Induced Particle Transport from a Mobile Bed below a Hovering Rotor
    (2013) Reel, Jaime Lynn; Leishman, J. Gordon; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A study has been conducted to examine rotor-generated blade tip vortices that pass near to a ground plane covered with mobile sediment particles and to explore whether they induce a pressure field that may affect the problem of rotor-induced dust fields. It was hypothesized that fluctuating pressures lower than ambient at the ground could potentially affect the processes of sediment particle mobilization and uplift into the flow. To investigate the relationship between the vortex wake characteristics and the motion of the mobilized sediment particles, single-phase and dual-phase (particle) flow experiments were conducted using a small laboratory-scale rotor hovering overing a ground plane. Time-resolved particle image velocimetry was used to quantify the flow velocities in the rotor wake and near the ground plane, and particle tracking velocimetry was used to quantify the particle velocities. Measurements were also made of the unsteady pressure over the ground plane using pressure transducers that were sensitive enough to resolve the small induced pressures. Time-histories of the measured responses showed significant pressure fluctuations occurred before, during, and after the rotor wake impinged upon the ground. While it was not possible to separate out the effects of pressure forces from other forces acting on the particles, the present work has shown good evidence of vortex-induced pressure effects on the particles in that particle trajectories significantly deviated from the directions of the surrounding flow in the immediate presence of the vortices. The characteristics of the pressure responses produced at the ground by vortices passing nearby was also predicted using a model based on unsteady potential flow theory, and was used to help interpret the measurements. The vortex strength (circulation), height of the vortex above the ground, and the vortex convection velocity, were all shown to affect the pressures at the ground and were likely to affect particle motion.
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    Reliability-Based Design Of Piping: Internal Pressure, Gravity, Earthquake, and Thermal Expansion
    (2007-08-09) Avrithi, Kleio; Ayyub, Bilal M.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Although reliability theory has offered the means for reasonably accounting for the design uncertainties of structural components, limited effort has been made to estimate and control the probability of failure for mechanical components, such as piping. The ASME B&PV Code, Section III, used today for the design of safety piping in nuclear plants is based on the traditional Allowable Stress Design (ASD) method. This dissertation can be considered as a primary step towards the reliability-based design of nuclear safety piping. Design equations are developed according to the Load and Resistance Factor Design (LRFD) method. The loads addressed are the sustained weight, internal pressure, and dynamic loading (e.g., earthquake). The dissertation provides load combinations, and a database of statistical information on basic variables (strength of steel, geometry, and loads). Uncertainties associated with selected ultimate strength prediction models -burst or yielding due to internal pressure and the ultimate bending moment capacity- are quantified for piping. The procedure is based on evaluation of experimental results cited in literature. Partial load and resistance factors are computed for the load combinations and for selected values of the target reliability index, β. Moreover, design examples demonstrate the procedure of the computations. A probabilistic-based method especially for Class 2 and 3 piping is proposed by considering only cycling moment loading (e.g., thermal expansion). Conclusions of the study and provided suggestions can be used for future research.