Theses and Dissertations from UMD
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Item Dual water quality responses after more than 30 years of agricultural management practices in the rural headwaters of the Choptank River basin in the Chesapeake Bay watershed(2023) Silaphone, Keota; Fisher, Thomas R; Natural Resource Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Eutrophication is the water quality response to over-enrichment by nitrogen (N) and phosphorus (P) in fresh, estuarine, and coastal waters globally. Agricultural best management practices (BMPs) are the primary tool for controlling eutrophication in rural areas, particularly in the Chesapeake Bay watershed, where BMPs are vital to achieving TMDL goals. However, despite the application of BMPs, local water quality in the headwaters of the Choptank River, a major tributary of the Chesapeake Bay on the Delmarva Peninsula, has not improved. Thus, further investigation of agricultural BMP impacts on water quality in the Greensboro watershed is needed. My overarching research question is, “Why have N and P concentrations increased at the USGS Greensboro gauge if agricultural Best Management Practices (BMPs) have been implemented?” I applied statistical approaches to three linked, testable hypotheses to systematically evaluate agricultural BMPs and their impacts on nutrient (N and P) export from the Greensboro watershed. My first hypothesis was that agricultural BMPs have increased significantly in the Greensboro watershed. To test this hypothesis, I obtained publicly available modeling data via the Chesapeake Assessment Scenario Tool (CAST) and estimated the subsequent edge-of-stream N and P export. My findings indicated that the number of BMPs in the agricultural sector increased significantly between 1985 and 2021, supporting the hypothesis. Overall, modeled agricultural N and P export significantly decreased between 2010 and 2021 (p < 0.001). However, the modeled edge-of-stream agricultural nutrient export resulted in no significant change in N export and an increase of 3% in agricultural P export resulting from BMP implementation levels in 2021 compared to 2010. This study demonstrated the use of CAST to acquire reported BMP implementation levels and increased nutrient inputs into the Greensboro watershed between 1985 and 2021. The watershed nutrient inputs mirror the upward trends in N and P export captured by the USGS long-term monitoring station at Greensboro. With this improved access to BMP implementation and nutrient data, decision-makers can consider adaptive management measures to decrease nutrient export downstream. My second hypothesis was that agricultural BMPs have an adequate basis for estimating their capacity to reduce N export. To test this hypothesis, I conducted a meta-analysis on 689 cover crop N efficiencies reported in 18 empirical and modeling studies. The cover crop N efficiency was calculated as the ratio of an N interception by cover crop biomass or a reduction in soil or groundwater N divided by an N input, e.g., previous spring fertilizer or a previous soil or groundwater N concentration or flux. These variable approaches resulted in wide ranges in mean cover crop N efficiency (10-80%) due to empirical and modeling experimental approaches, varying methods, and parameters used to calculate efficiency. The modeling approach generally resulted in N efficiency values significantly higher than the empirical approach, as did the parallel control-treatment experiments compared to the sequential before-and-after implementation method. Because of these variables, there appears to be no standard methodology to report the effects of cover crops or standardized metadata describing the variables used in the N efficiency calculations. I suggest a standard methodology and metadata that should accompany future reports of cover crop N efficiencies to improve the modeled effects of BMPs on nutrient export. My third hypothesis was that three methods of estimating N and P concentrations and yields are in agreement and show a relationship to BMP implementation in the Greensboro watershed. To test this hypothesis, I compiled annual nutrient (N and P) datasets based on (1) USGS field measurements of concentrations and discharge, (2) USGS flow-normalized weighted regression based on time, discharge, and season (WRTDS) of concentrations and yields, and (3) CAST-modeled nutrient yields. Statistical analyses revealed time, discharge, agricultural BMPs, and animal waste management practice trends of the three methods. Results indicated that the USGS field measurements and WRTDS flow-normalization methods consistently showed an increase in N and P concentrations and yields. In contrast, all CAST-modeled regressions showed significantly decreasing nutrient concentrations and yields (p ≤ 0.05), which did not support the hypothesis that all three methods are in agreement. Despite CAST-modeled results decreasing with increasing BMPs, which supports the hypothesis that N and P concentrations and yields show a relationship with BMP implementation, USGS methods resulted in increasing nutrient concentrations and trends. These results indicated significant underestimates of modeled N and P export by CAST. I recommend using adjusted BMP efficiencies during cultural and structural BMP lifespans to improve model outputs. I also suggest two approaches to reflect the role of annual poultry manure applications: (1) model nutrient transport via artificial drainage ditches that interfere with natural nutrient flow pathways and exacerbate N and P transport, and (2) model the accumulation of soil-P and saturated soil-P, resulting in increases in dissolved P and particulate P in downstream surface waters. Agronomic recommendations include developing efficient manure recycling approaches within the local agricultural systems via nutrient management practices and concurrent research and development to support alternative uses of animal waste, including composting, bioenergy generation, granulating/pelletizing, and establishing a marketplace to support the sale of these products and to offset the costs of transporting manure from areas of manure surplus to manure deficit areas. This dissertation revealed that modeling studies overestimate cover crop N efficiencies in the United States Coastal Plain province and that CAST modeling is not in agreement with the USGS field measurements. CAST-modeled nutrient concentrations and yields decrease over time, indicating improvements in water quality. In contrast, USGS methods consistently show that nutrient concentrations and yields increase, indicating that BMPs are insufficient, inadequate, overwhelmed by nutrient inputs, or efficiencies are overestimated. Indeed, nutrient-reducing BMPs have increased between 1985 and 2021. With over 35 years of BMP implementation, measurable water quality response is expected. However, BMPs that relocate and apply higher amounts of manure annually have also increased with nutrient-reducing BMPs. Rising manure application rates combined with higher fertilizer application rates due to economic pressures on farmers to increase crop yields appeared to have overwhelmed implemented BMPs. Continued manure applications onto croplands in the Greensboro watershed suggest nutrient export will continue to rise; thus, reaching water quality goals is unlikely.Item MECHANISMS OF SORPTION OF PHARMACEUTICAL AND PERSONAL CARE PRODUCTS TO MICROPLASTICS(2021) Sanchez, Alterra; Gonsior, Michael; Yonkos, Lance; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microplastics (MPs) are found in almost every ecosystem and in many commercially important seafood species. MPs have been found to be physically harmful to marine organisms, but also may act as vectors for organic pollutants and together have been shown to cause toxic effects in a variety of species. Wastewater effluent is a significant source of MPs to aquatic systems, as well as pharmaceutical and personal care product compounds (PPCPs). The first research contribution was to create a reference material for secondary fragment type microplastics of the polymer’s high-density polyethylene (HDPE) and polypropylene (PP) that is standardized by surface area (SA) for use in sorption and toxicity studies. Standardization for both polymers was successful, with a SA coefficient of variation of ~3%. PP MPs had greater SA due to it being a less crystalline polymer than HDPE. This reference material may act as a more realistic material than purchased powders or beads, as well as provide a more readily comparable material for fragment type MPs. The second research contribution used the reference material to create an extraction methodology for measuring semi-polar PPCPs associated with MPs. Acetone was chosen as the best solvent for extraction and extraction efficiency for both polymers was ~88% (first extraction). This methodology was then used to measure the equilibrium of the antimicrobial triclocarban with PP and PE of different MP particle sizes. Smaller particles with greater SA sorbed more triclocarban, rather than larger particles. PP had greater sorption of triclocarban than PE. This was due to PP MPs having greater SA due to being a less crystalline polymer. The third contribution created a framework for prioritizing study compounds based on environmental relevance for MP sorption using polyethylene as a model polymer, water solubility, and a correlation with the octanol water-distribution ratio, DOW, rather than the octanol-water partition coefficient, KOW. A possible threshold for polyethylene sorption was found for compounds with water solubility ~20-60mg/L and DOW ~3.7. This dissertation advances the understanding of MP reference materials, extraction methodology, sorption mechanisms, and modeling of sorption data of PPCPs.Item Characterization and Modeling of Brushless DC Motors and Electronic Speed Controllers with a Dynamometer(2019) Brown, Robert; Chopra, Inderjit; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The global drone market is expected to grow from $4.9 billion to $14.3 billion within the next decade, indicating a heavy demand for high performance electric aircraft. Modern drones are propelled with brushless DC (BLDC) motors and electronic speed controllers (ESCs). However, a current lack of information concerning the performance and efficiency of BLDC motors and ESCs prevents their use in rigorous aircraft design. Low cost hobby ESCs and BLDCs are typically used in research aircraft, but few technical details are released by their manufacturers. To better understand these devices, a custom dynamometer was constructed to study the performance of ESCs and BLDC motors. By properly recording the DC, AC, and mechanical power, information on peak efficiency and performance for the ESCs and BLDC motors are determined experimentally. Motors between 920 KV to 2500 KV were tested with 18 A, 30 A, and 40 A ESCs. A combination of these tests were carried out at 7.2 V, 11.1 V, and 14.8 V DC to explore trade offs in the design process. While typically neglected in formal analysis, this work seeks to better understand the power loss mechanisms in ESCs, as it was found that ESCs could have efficiencies as low as 65%, reducing the overall efficiency of the system considerably. This custom dynamometer features a load varying device, power analyzers, and a unique two DAQ setup to properly capture the high frequency electrical signals of BLDC motors. From the sets of experimentally recorded motor and ESC tests, a novel analytical model is developed to predict the performance of ESCs and BLDC motors. At the heart of this modeling effort is describing the 3 phase AC circuit as a single equivalent circuit, which encapsulating the motor’s performance. This work is critical in the design process, as properly sizing ESCs, motors, and rotors for an electric aircraft can improve aircraft endurance and range. Performance metrics are extracted from experimental results and are fit into the analytical model. Predictions for the system’s mechanical power, AC power, and DC power agree well with experimental results, demonstrating applicability of the robust model.Item Phonon Modeling in Nano- and Micro- scale Crystalline Systems(2018) VanGessel, Francis; Chung, Peter; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Submicrometer phonon systems are becoming increasingly relevant in modern day technology. Phonon mechanisms are notably relevant in a number of solid-state devices including lasers, LEDs, transistors, and thermoelectrics. Proliferation of these devices has been driven by advancements in silicon-on-insulator technology. These advancements have allowed for the manufacture of devices with complex nanostructures and dimensions deep in the sub-microscale regime. However, accompanying improvements in the manufacture and design of novel crystalline systems is the requirement for accurate computational approaches for phonon modeling in nanostructured, anisotropic, and complex materials. The phonon Boltzmann transport equation is uniquely well suited to modeling energy transfer at the nano- and micro- meter length scales and is therefore an excellent candidate for this simulation task. However, current Boltzmann modeling approaches utilize a range of assumptions and simplifications that restrict their validity to isotropic, nominally one or two dimensional, or compositionally simple systems. In this dissertation we present an original finite volume-based methodology for the solution of the three dimensional full Brillouin zone phonon Boltzmann transport equation. This methodology allows for separate real and reciprocal space discretization. By taking a sampling of vibrational modes throughout the first Brillouin zone our methodology captures three unique sources of phonon anisotropy. We investigate the effect of phonon anisotropy in a fin field effect transistor, calculating the effect that incorporating various sources of anisotropy has on the resultant temperature fields. In a second study, we consider phonon flow through silicon nanowires with a modified boundary geometry. The three-dimensional flow fields are calculated and thermal transport below the Casimir limit is observed. Reduction in thermal conductivity is a result of maximizing the phonon backscatter that occurs in our phononic system. The backscatter serves to create regions of highly misaligned phonon flux. In addition, our silicon nanowire geometry has properties analogous with a high-pass phonon filter. In the final study we apply our Boltzmann transport methodology to the simulation of phonon transport in the energetic material, RDX. We study phonon transport in the vicinity of a material hotspot, the location at which chemistry initiates in the material. By applying Boltzmann modeling, applied for the first time to this material, we gain valuable insights into the interplay between thermal transport and phonon modes linked with initiation.Item Multi-sensor Cloud and Aerosol Retrieval Simulator and Its Applications(2016) Wind, Galina; Salawitch, Ross J; Platnick, Steven; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Executing a cloud or aerosol physical properties retrieval algorithm from controlled synthetic data is an important step in retrieval algorithm development. Synthetic data can help answer questions about the sensitivity and performance of the algorithm or aid in determining how an existing retrieval algorithm may perform with a planned sensor. Synthetic data can also help in solving issues that may have surfaced in the retrieval results. Synthetic data become very important when other validation methods, such as field campaigns,are of limited scope. These tend to be of relatively short duration and often are costly. Ground stations have limited spatial coverage whilesynthetic data can cover large spatial and temporal scales and a wide variety of conditions at a low cost. In this work I develop an advanced cloud and aerosol retrieval simulator for the MODIS instrument, also known as Multi-sensor Cloud and Aerosol Retrieval Simulator (MCARS). In a close collaboration with the modeling community I have seamlessly combined the GEOS-5 global climate model with the DISORT radiative transfer code, widely used by the remote sensing community, with the observations from the MODIS instrument to create the simulator. With the MCARS simulator it was then possible to solve the long standing issue with the MODIS aerosol optical depth retrievals that had a low bias for smoke aerosols. MODIS aerosol retrieval did not account for effects of humidity on smoke aerosols. The MCARS simulator also revealed an issue that has not been recognized previously, namely,the value of fine mode fraction could create a linear dependence between retrieved aerosol optical depth and land surface reflectance. MCARS provided the ability to examine aerosol retrievals against “ground truth” for hundreds of thousands of simultaneous samples for an area covered by only three AERONET ground stations. Findings from MCARS are already being used to improve the performance of operational MODIS aerosol properties retrieval algorithms. The modeling community will use the MCARS data to create new parameterizations for aerosol properties as a function of properties of the atmospheric column and gain the ability to correct any assimilated retrieval data that may display similar dependencies in comparisons with ground measurements.Item Data-Driven Wildfire Propagation Modeling with FARSITE-EnKF(2016) Theodori, Maria Faye; Trouve, Arnaud; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The goal of this study is to provide a framework for future researchers to understand and use the FARSITE wildfire-forecasting model with data assimilation. Current wildfire models lack the ability to provide accurate prediction of fire front position faster than real-time. When FARSITE is coupled with a recursive ensemble filter, the data assimilation forecast method improves. The scope includes an explanation of the standalone FARSITE application, technical details on FARSITE integration with a parallel program coupler called OpenPALM, and a model demonstration of the FARSITE-Ensemble Kalman Filter software using the FireFlux I experiment by Craig Clements. The results show that the fire front forecast is improved with the proposed data-driven methodology than with the standalone FARSITE model.Item MODELING AND EXPERIMENTAL ANALYSIS OF PHASED ARRAY SYNTHETIC JET CROSS-FLOW INTERACTIONS(2014) HASNAIN, ZOHAIB; Flatau, Alison B; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Synthetic Jet Actuators (SJAs) are fluidic devices capable of adding momentum to static or non-static bodies of fluid without adding mass. They are therefore categorized as zero-net-mass-flux (ZNMF) momentum source. In its simplest compact form a SJA consists of an oscillatory surface connected to a cavity with a single exit orifice through which the fluid enters and exits. SJA technology has been utilized in applications ranging from boundary layer control over aerodynamic surfaces to fluidic mixing in dispersion applications. The ZNMF nature of the technology means it is not subject to constraints experienced by traditional momentum sources that require the addition of mass in order to impart momentum. The momentum that can be added by a single SJA is limited by the energy transfer capabilities of the oscillating surface. In modern SJAs this surface usually is a piezoceramic/metal composite subjected to a high voltage AC signal. For applications such as flow control over aerodynamic surfaces, modern SJAs are used in an array configuration and are capable of altering the flow momentum by values ranging from 0.01-10%. While it is possible to build larger actuators to increase this value the benefits associated with the compact size would be lost. It is therefore desirable to tune other parameters associated with SJA arrays to increase this value. The specific motivation for this study comes from the desire to control the momentum addition capacity of a specific SJA array, without having to alter any geometric parameters. In a broader sense this study focuses on understanding the physics of SJA interaction in array configuration through experiments which are then used to guide in the design of modeling technique that predicts SJA array behavior in cross-flows. The first half of the project focused on understanding SJA behavior through modeling. Numerical techniques were initially used to model SJA and SJA arrays in cross-flows. Reduced numerical models were then developed from the full momentum equations. Analytical methods to solve these reduced order models were then implemented in order to cut down on solution time. A wave equation based solution to the stream and vorticity formulation of the momentum equations was implemented to predict SJA behavior. For the experimental component of the project, a finite span high aspect ratio orifice SJA was designed and characterized through Constant Temperature Anemometry (CTA). Two of these SJA were then placed in close proximity to one another. The relative phase of operation between the two jets was altered and the resulting flow field was measured through Particle Image Velocimetry (PIV). This process was repeated for different sets of array spacing, and SJA to cross-flow velocity ratio. For specific choices of these parameters a 40% increase in momentum addition was observed. The experimental results were used to validate the modeling techniques. In general reasonable agreement between the modeling and experiment was observed in specific domains of the flow field.Item Detailed Measurements of Fire-Induced Mixing Phenomena(2014) Layton, Thomas George; Marshall, Andre W; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study successfully validated the use of salt-water analog modeling as an effective diagnostic tool for predicting fire-induced flows. A technique was developed for taking measurements using combined Planar Laser-Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV), and results were analyzed with respect to smoke filling as well as transient ceiling layer dynamics, and turbulent mixing intensity. Data was shown to be in good agreement with theory, further validating the salt-water analogy as a tool for diagnostics, prediction, and scaling of fire phenomena.Item VALUING FOREST ECOSYSTEM SERVICES IN MARYLAND AND SUGGESTING FAIR PAYMENT USING THE PRINCIPLES OF SYSTEMS ECOLOGY(2012) Campbell, Elliott Thomas; Tilley, David R; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Forests provide a multitude of vital benefits to the ecosystems, economies and people of Maryland. Forests regulate atmospheric gas exchange, ameliorate micro-climates, stabilize coastlines and riverbanks, provide wildlife habitat, generate and maintain soils, improve water quality, dampen storm flows, abate air pollution, and provide food, fiber, fuel and shelter. While markets exist to set the price for an economic good like timber, many of the ecosystem services listed above are poorly valued, if at all. This research provides a connection between biophysical and economic methods for evaluating the environment. The hydrology, soil, carbon, air pollution, pollination and biodiversity of a forest are measured from a biophysical standpoint with emergy and converted to dollars using new emergy-to-dollar ratios; termed eco-prices. The functioning of the forest is compared to the most likely alternative land-use (suburbia) and biophysical value is assigned based on this difference. The novel method for assigning value to ecosystem services and the ability to link biophysical evaluation and economic valuation has the potential to be influential in how ecosystem services are incorporated into the economy and used to guide decision making in the future. This research seeks to value ecosystem services provided by forests in Maryland and proposes that an Ecological Investment Corporation (EIC) could be an additional tool for society to direct payments from consumers to land stewards to encourage the production of ecosystem services. To ensure that Maryland forests continue to produce ecosystem services at the current rate, land stewards should receive compensation between $178 and $744 million. On a per capita basis, a resident of Maryland enjoys $850 worth of ecosystem services from the forest as public value. On an area basis, the typical acre of forest in Maryland generates over $2000 of ecosystem services as public value. Based on our compensation estimates for ecosystem services, a land steward should receive a fair payment price of $71 to $298 per year per a typical acre of forest. This research is a step forward for emergy science, providing novel methods for quantifying ecosystem services, calculating ecological debt, and converting renewable emergy flows to dollars.Item Development of a Model for Flaming Combustion of Double-Wall Corrugated Cardboard(2012) McKinnon, Mark; Stoliarov, Stanislav I; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Corrugated cardboard is used extensively in a storage capacity in warehouses and frequently acts as the primary fuel for accidental fires that begin in storage facilities. A one-dimensional numerical pyrolysis model for double-wall corrugated cardboard was developed using the Thermakin modeling environment to describe the burning rate of corrugated cardboard. The model parameters corresponding to the thermal properties of the corrugated cardboard layers were determined through analysis of data collected in cone calorimeter tests conducted with incident heat fluxes in the range 20-80 kW/m2. An apparent pyrolysis reaction mechanism and thermodynamic properties for the material were obtained using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The fully-parameterized bench-scale model predicted burning rate profiles that were in agreement with the experimental data for the entire range of incident heat fluxes, with more consistent predictions at higher heat fluxes.
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