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 DYNAMIC EQUILIBRIUM BEACH PROFILES: FORCES OF OFFSHORE SEDIMENT TRANSPORT IN MARYLAND’S CHESAPEAKE BAY(2020) Bell, Lynda Jean; Sanford, Lawrence P.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)To examine the impact of shoreline erosion on the near shore environment, it is necessary to estimate the quantity and quality of yearly sediment mass that is likely to be added by erosion. Data were collected in 2008 at ten sites along the Maryland shoreline of the Chesapeake Bay and compared to both empirical and theoretical models of offshore profiles. The data collected at each site included a series of three-dimensional bathymetric profiles from offshore transects run at each site, as well as a series of sediment core data that were acquired along each transect. Relationships between grain size, beach type, sediment composition, and strength of eroding sediments were also explored. The results showed that sands dominated offshore surficial sediments at most locations, even though the source sediments were mixtures of sands and muds. The observed offshore profiles were consistent with expectation from ocean beach profile paradigms, with the exception that the steepness proportionality factor was not related to sediment grain size. An adjusted form of the classic Bruun relationship for predicting shoreline retreat was in approximate agreement with long-term observations.Item Near Threshold Sediment Transport by a Forced Jet Impinging on a Mobile Sediment Bed(2015) Corfman, Kyle; Kige, Kenneth; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Although sediment transport has been extensively studied in the past, flows such as rotorcraft brownout with large-scale coherent structures call many of the simplifying assumptions into question. The objective of this study is to develop a model for the prediction of sediment removal, referred to as erosion, based on independent measurements of the single-phase flow and the evolution of bedforms on the surface of a mobile sediment bed. A series of phase-resolved particle image velocimetry (PIV) flow measurements have been conducted to quantify the stress induced by an acoustically forced impinging jet, analagous to tip-vortices within the rotor wake. The threshold conditions for incipient particle motion are quantified through a series of PIV measurements of the single-phase flow at conditions found to produce quantifiable erosion of the surface. A force balance approach is used to develop a model, following the theory presented by Bagnold (1966), to predict the transport of sediment due to the stress above the theshold. A series of surface elevation measurements are analyzed to quantify the removal of sediment, for the evaluation of the predicted model. An additional series of PIV measurements are performed on a prototype bedform, modeled after the observed bedforms, to quantify the changes in the flow field caused by their developement. The proposed model is shown to provide a better prediction of the observed erosion than classical sediment transport models, especially for cases close to the threshold conditions. For higher speed cases however, the model dramatically over predicts the observed erosion. Several physcially-based explanations are provided for this kink in the trend.Item PARTICLE-TURBULENCE INTERACTION OF SUSPENDED LOAD BY A FORCED JET IMPINGING ON A MOBILE SEDIMENT BED(2014) Mulinti, Rahul; Kiger, Ken; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Phase-resolved two-phase flow experiments have been conducted to predict particle suspension and sedimentation within coupled particle-laden flows relevant to rotorcraft brownout conditions. Single phase and dual-phase PIV experiments have been conducted to study the interaction of a mobile sediment bed with characteristic flow structures similar to those within a rotor wake. Even though sediment transport has been extensively studied in the past, the rapidly evolving transient nature of brownout calls many of the simplifying assumptions that have been made to understand sediment transport mechanisms into question. Image intensity based phase-separation and a hybrid PIV/PTV techniques have been implemented to identify the gas and solid phases as well as to the resolve multi-valued velocity displacements within a given interrogation region. A calibration technique to identify the measurement volume using size-brightness as well as PIV correlation based criteria has been outlined. Simultaneous velocity measurements of the fluid and dispersed phase in two vertical co-planar planes are analyzed to examine the role of vortex interaction and its subsequent breakdown on sediment transport process. The mobilization conditions and wall-normal flux of particulates by the vortex-wall interaction are reported and are correlated to the local vortex conditions such as proximity to the wall and subsequent decay. The effect of the changing sediment bed profile on sediment transport rates is also studied. Modulation of mean and stochastic fluid flow properties due to the presence of particles and the effect of turbulent coupling between the particle and fluid momentum, as based on a modified drag law with dependence on particle Reynolds number as well as local volume fraction has been examined. A mesoscopic Eulerian formalism has been implemented to study the effect of particle inertia on the suspension process.Item Water Flow and Sediment Texture as Co-Varying Submersed Aquatic Vegetation (SAV) Habitat Requirements(2013) Swerida, Rebecca M.; Koch, Evamaria W; Sanford, Lawrence P; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study examined the importance of water flow and sediment texture as co-varying habitat parameters of submerged aquatic vegetation (SAV) in the Chesapeake Bay. An outdoor mesocosm experiment was conducted to test the response of SAV (Zostera marina and Ruppia maritima) to combinations of water flows and sediment grain sizes characterized by sediment deposition, bedload transport and erosion. Water flow, sediment and SAV characteristics were also determined at vegetated and adjacent unvegetated areas at 11 study sites and sediment motion conditions assessed. Greater SAV biomass was developed by Z. marina and R. maritima experiencing sediment motion than sediment deposition. Although habitat parameter thresholds in situ were site-specific, overall SAV presence was limited to moderate ranges of both water flow and sediment grain size. All SAV habitat observed was characterized by sediment bedload transport. Consideration of both water flow and sediment habitat requirements will improve SAV restoration success.Item EFFECTS OF BAR FORMATION ON CHANNEL STABILITY AND SEDIMENT LOADS IN AN URBAN WATERSHED(2009) Blanchet, Zachary; Prestegaard, Karen L; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study investigates channel adjustment due to urbanization in the Little Paint Branch creek of the Anacostia River watershed. In the past 15 years, large gravel bars have formed in the channels, more than doubling the active channel width of some reaches. Field data was collected to analyze downstream hydraulic geometry and the effects of gravel bars on shear stress, turbidity, and morphological change. The watershed was gauged at three locations to document the contributions of discharge and sediment to the downstream Anacostia Estuary. The results indicate that Little Paint Branch Creek generates proportionally more runoff per basin area than the watershed does as a whole, even though the impervious surface area is lower in the upstream tributaries, like Little Paint Branch Creek. Bar formation induces channel widening, which decreases flow depth and thus shear stress for bankfull and higher stages. This shoaling limits bed transport and will eventually limit bank erosion.