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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Item Sampling Errors Arising from Entrainment and Insufficient Flushing of Oceanographic Sampling Bottles(2017) Paver, Christopher Raymond; Codispoti, Louis A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Collection of representative water samples is important for accurately determining biological and chemical constituents. Modern carousel packages can permit bottle “soak times” to approach zero while increasing the impacts of entrainment due to their large size. In addition, some modern sampling bottles have relatively small openings relative to their volumes, a factor that inhibits flushing. Examination of qualitative evidence from various expeditions suggested that insufficient “soak times” can produce unrepresentative water samples. In this study, historical data are presented, but the emphasis is on field experiment data that better quantifies the errors that can arise from insufficient bottle flushing. The experiments suggest that under some conditions, soak times of more than 2 minutes may be required to collect representative water samples. The experiments also suggest the occurrence of stratification within bottles. The impact of insufficient soak times on some chemical gradients is discussed and improved sampling protocols are suggested.Item 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.Item AN INTEGRAL MODEL FOR TURBULENT FLAME RADIAL LENGTHS UNDER A CEILING(2010) Ding, Haiwen; Quintiere, James G; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An analytical study using an integral model for turbulent flame radial lengths under a ceiling is presented. Dimensionless equations give results in terms of Q* -- dimensionless firepower, and D/H -- the ratio of fire diameter to ceiling height. The model used an empirical relationship for the mixing ratio of air entrained to stoichiometric air needed for the ceiling jet flame. This value varies from 9.6 for short radial flames to 1 for long flames that tend to become laminar. Predictions from the model are in good agreement with the experimental data from previous work found in the literature. They span a range that contains data where the fire plume flame just touches the ceiling to the case where long ceiling flames become laminar. An alternative empirical fit of the theoretical results finds that the radial flame length is independent of ceiling height once the flame hits the ceiling.