Digital Commons Network^™

Design And Evaluation Of An Elevated Temperature Cutting Force Dynamometer For Hybrid Manufacturing, Justin West

Doctoral Dissertations

Cutting force coefficients, workpiece dynamics, and uncut chip area all change as a function of temperature during machining processes at elevated temperatures. In a traditional milling process, these parameters are nearly constant. The bulk workpiece temperature remains well below the working limit of the material, generally near room temperature. However, workpiece temperatures in hybrid manufacturing, where additive deposition precedes machining, are spatially and temporally variable. A milling force model that does not incorporate temperature effects will generally overestimate the cutting force and workpiece dynamic stiffness and underestimate the chip area. Milling parameters that are stable at room temperature may be …

Characterizing Silicate Materials Via Raman Spectroscopy And Machine Learning: Implications For Novel Approaches To Studying Melt Dynamics, Blake O. Ladouceur

Doctoral Dissertations

Silicate melt characteristics impose dramatic influence over igneous processes that operate, or have operated on, differentiated bodies: such as the Earth and Mars. Current understanding of these melt properties, such as composition, primarily comes from investigations on their volcanic byproducts. Therefore, it is imperative to innovate on modalities capable of constraining melt information in environments where a reliance on laboratory methods is severed. Recent investigations have turned to Raman Spectroscopy and amorphous volcanics as a suitable pairing for exploring these ideas. Silicate glasses are a proxy for igneous melts; and Raman spectroscopy is a robust analytical technique capable of operating …

Multiphysics Modeling To Understand Microwave-Food Interactions In A Multi-Port Solid-State Microwave System., Kartik Verma

Masters Theses

Multiphysics modeling plays a crucial role in understanding the complexities of microwave-food interactions, especially in multi-port solid-state microwave systems where microwave parameters can be precisely and dynamically controlled. However, previous models using simplistic or manually measured oven geometries face challenges in accurately simulating the microwave heating process. This study first developed a robust 3-D scanning approach to capture precise geometric details of the oven cavity, incorporating them into multiphysics modeling for solid-state microwave heating. Furthermore, a quantitative validation approach was also developed to characterize modeling accuracy against experimental results. The results showed that multiphysics modeling with 3-D scanned geometry demonstrated …

Nuclear Thermal Rocket Engine Instrumentation Addressing Environmental Limitations On Temperature Measurements, Dan C Floyd

Doctoral Dissertations

The development of nuclear thermal rockets has received renewed interest in recent years due to the benefits that can attained from this method of propulsion. Currently, instrumentation work is focused on the evaluation of current and near-term technology for implementation within a nuclear thermal rocket engine. One aspect of this evaluation is focused on the various instrumentation requirements of the system regarding necessary measurement parameters and environmental conditions for survivability. Historical nuclear rocket programs that have been conducted in the United States provide the basis for this information and indicates a critical need for high temperature measurement technology that can …

Scale-Bridging Computational Modeling Of Irradiation Effects In Alpha-Zirconium And Its Alloys, Jose Francisco March-Rico

Doctoral Dissertations

One of the issues concerning the long-term lifespan of Zr cladding tubes is an axial expansion and radial contraction that occurs in response to neutron irradiation. This volume-conservative response in the absence of an applied stress has been termed irradiation growth, a consequence of both the inherent anisotropy of alpha-Zr hexagonal close-packed crystal structure, and crystalline texture in tube fabrication. Irradiation growth strains generally saturate at low doses, but suddenly accelerate after an incubation dose. This growth breakaway has been correlated with the nucleation of faulted vacancy loops on basal planes (c-loops); at lower doses, the irradiated Zr microstructure is …

Modelling, Sensing, And Control Of Weld Beads In Gravity Aligned And Non-Gravity Aligned Orientations For Wire Arc Additive Manufacturing, Joshua J. Penney

Doctoral Dissertations

Wire Arc Additive Manufacturing (WAAM) has recently developed into a viable manufacturing process for large, complex metal parts. The WAAM process uses a Gas Metal Arc Welding (GMAW) torch mounted to an automated motion platform to execute a predetermined path plan based on a desired CAD geometry. As the desired geometry becomes more complex, it is advantageous to utilize out-of-position welding techniques used by human welders to stabilize the weld pool during the deposition of large overhangs. To ensure part accuracy and quality, adding layers of real-time control to manage various aspects of the WAAM process is critical. First, a …

Data Center Power System Emulation And Gan-Based High-Efficiency Rectifier With Reactive Power Regulation, Jingjing Sun

Doctoral Dissertations

Data centers are indispensable for today's computing and networking society, which has a considerable power consumption and significant impact on power system. Meanwhile, the average energy usage efficiency of data centers is still not high, leading to significant power loss and system cost.

In this dissertation, effective methods are proposed to investigate the data center load characteristics, improve data center power usage efficiency, and reduce the system cost.

First, a dynamic power model of a typical data center ac power system is proposed, which is complete and able to predict the data center's dynamic performance. Also, a converter-based data center …

Mathematical Modeling Suggests Cooperation Of Plant-Infecting Viruses, Joshua Miller, Vitaly V. Ganusov, Tessa Burch-Smith

Chancellor’s Honors Program Projects

No abstract provided.

Sustainable Underground Reactive Barrier To Attenuate Contaminants From Agricultural Drainage, Yuchuan Fan

Doctoral Dissertations

Denitrifying bioreactor (DNBR) has become a popular edge-of-field practice applied to reduce nitrate over the Mississippi river and to prevent a downstream hypoxic zone occurring at the Gulf of Mexico. Despite widespread field and laboratory studies, fewer investigations have been directed toward a systematic means of evaluating the nitrate removal performance achieved by various filling materials, abiotic factors, and other critical parameters. Our ultimate goal is to improve the nitrate removal by choosing the optimum fill materials and operate under optimal conditions, meanwhile, modeling the DNBR by critical variables. This study begins by establishing a global database. Forty filling materials …

Distribution, Ecological Niche, Movement, And Home Range Of The Sickle Darter (Percina Williamsi) In The Upper Tennessee River Basin., Kyler Hecke

Doctoral Dissertations

The Sickle Darter (Percina williamsi) is a rare and imperiled species that is endemic to the upper Tennessee River basin. Over the last ~50 years it has declined across much of its range, and as a result it has been petitioned for federal listing under the Endangered species Act. This species has been relatively understudied, and important questions remain to be addressed: 1.) What is the current distribution of the Sickle darter and how has it varied spatiotemporally? 2.) What is the ecological niche of the Sickle Darter? and 3.) What is the movement capability of the Sickle …

Influence Of Physical Variability Of Highly Weathered Sedimentary Rock On Nitrate In Area 3 Of The Enigma Field Research Site At Y-12, Erin Kelly

Masters Theses

Uranium processing and waste storage in unlined waste ponds leached contaminants into the groundwater at Y-12, Oak Ridge, Tennessee, from the 1950s to 1980s. Groundwater wells near the S-3 ponds have had the highest nitrate concentrations of groundwater anywhere in the world (>10,000 mg/L). For reference, the maximum contaminant level for nitrate in drinking water set by the U.S. Environmental Protection Agency is 10 mg/L. Since 2012, the ENIGMA (Ecosystems and Networks Integrated with Genes and Molecular Assemblies) group has been characterizing, monitoring, and conducting field experiments to understand the interactions between contaminants, microbes, and the subsurface. The goals …

Digital Cutting Force Modeling For Milling Operations, Timothy T. No

Doctoral Dissertations

Process improvement in milling through improved understanding of machining dynamics is an on-going research endeavor. The objective of this project is to advance digital modeling of the milling process by incorporating tool-specific geometry in the machining analysis. Structured light scanning will be used to perform tool geometry measurements and produce a 3D model. The 3D model data will include the spatial location of the cutting edges, as well as the rake and relief profiles from the tool cross section. The rake and relief profiles will be imported, together with the work material flow stress model, into a finite element analysis …

Costs Of Protected Areas In The United States, Diane Le Bouille

Doctoral Dissertations

Protected areas, or land owned in fee by agencies and non-profits to further conservation goals, have traditionally been the go-to choice for conservation interests. The UN Environment World Conservation Monitoring Centre estimates that, currently, close to 15% of all terrestrial and inland water areas are protected. This figure falls short of the Aichi Biodiversity Target of 17% in 2020, that was added to the Convention on Biological Diversity by its 196 signatories in 2010. But as the Convention prepares to set new post-2020 targets, this percentage is expected to keep increasing. Although acquiring a parcel of land is only one …

Modeling And Optimization Algorithm For Sic-Based Three-Phase Motor Drive System, Ren Ren

Doctoral Dissertations

More electric aircraft (MEA) and electrified aircraft propulsion (EAP) becomes the important topics in the area of transportation electrifications, expecting remarkable environmental and economic benefits. However, they bring the urgent challenges for the power electronics design since the new power architecture in the electrified aircraft requires many benchmark designs and comparisons. Also, a large number of power electronics converter designs with different specifications and system-level configurations need to be conducted in MEA and EAP, which demands huge design efforts and costs. Moreover, the long debugging and testing process increases the time to market because of gaps between the paper design …

A Study Of Drainmod-Urban For Enhanced Bioretention Cell Modeling, Whitney A. Lisenbee

Doctoral Dissertations

Bioretention has become a leading infiltration-based stormwater control measure for mitigating urban hydrology by reducing urban stormwater runoff volumes and peak flows. Despite widespread field and laboratory studies, less investigation has been directed toward effectively modeling these systems. This is critical, as modeling of bioretention systems provides an avenue for evaluating their effectiveness prior to devoting time and resources into installation. Many hydrologic models capable of simulating bioretention consist of lumped parameters and simplifications that do not fully account for fundamental hydrologic processes such as soil-water interactions. One model, DRAINMOD, has overcome many limitations of other models by incorporating the …

Data-Driven Modeling Of The Heroin And Fentanyl Epidemic And The Harvesting Of Trees In West Africa, Tricia Marie Phillips

Doctoral Dissertations

The opioid epidemic has had a strong presence in the United States in recent years. Drug overdose deaths involving opioids have skyrocketed and the lacing of heroin with fentanyl has played a significant role in this. In order to investigate the dynamics behind the opioid epidemic and predict its trajectory, we formulate a system of ordinary differential equations that incorporate the movement of individuals among classes of opioid use. We estimate parameter values by fitting to Tennessee data since the time the epidemic was established in the state. The trajectory of the epidemic suggests the number of addicts and overdose …

Rationalization Of Crystallographic Texture Evolution In High Gamma Prime Ni-Based Superalloys During Laser Powder Feed Directed Energy Disposition, Kevin Michael Smith

Masters Theses

Single-crystal nickel superalloy components are widely used in high temperature aerospace applications due to their excellent high temperature strength and creep resistance. Mechanical properties of single-crystal nickel superalloys are affected by chemical composition and the method of manufacture. Production of these components is costly and repair offers opportunity to sustain system performance while reducing costs. Additive Manufacturing by Laser Powder Feed Directed Energy Deposition (DED) is a promising method for repair due to selective application of material and the ability to tailor heat input. However, laser processing of these materials presents several challenges due to the high potential for cracking …

Study Of The Dynamic Behavior Of Molten-Salt Reactors, Vikram Singh

Masters Theses

Molten-Salt Reactors (MSR) are a Gen-IV reactor concept being investigated by companies and institutions alike. These reactors are considerably different from the current fleet of Light-Water Reactors and outside the experience base of most Nuclear Engineers. The fluid nature of the fuel leads to delayed temperature and reactivity feedback effects unique to each reactor design that need to be characterized to determine operability and safety limits. Moreover, the design space under consideration encompasses various fuel-cycles, neutron spectra, and materials. This requires a modeling methodology that can be applied to the breadth of designs under development and is the subject of …

Interfacing To Biological Systems Using Microfluidics, Peter Golden Shankles

Doctoral Dissertations

Biological systems operate on scales ranging from nanoscale chemical reactions to the global flow of nutrients and energy. Building knowledge of each level requires techniques and technologies that can address the biological system at the chosen level of interest. On the cellular and community levels, microfluidics are able to replicate the spatial scales of the natural system from the cellular, to community through the local microenvironment while providing engineering solutions to control flow through the system and interfaces with the system through microscopy and chemical sampling. Herein, biological interfaces were created using microfluidics to control cellular interactions and chemical reactions. …

Remote Characterization Of Physical Surface Characteristics Of Mars Using Diurnal Variations In Apparent Thermal Inertia, Cameron Blake Mccarty

Masters Theses

Analysis of the Martian surface today can provide insight into the processes that may have affected it over its history. Information about the physical surface characterization of a region can help determine the degree of sorting it has experienced and/or its geologic maturity. Sub-resolved “checkerboard” mixtures of materials with different horizontal thermal inertia mixtures can lead to differences in the apparent thermal inertia values inferred from night and day radiance observations. Standard methods for deriving thermal inertia from orbit via the THermal EMission Imaging System (THEMIS) can give values for the same location that vary by as much as 20% …

Analytics Improving Professional Sports Today, Logan C. Mcdavid

Chancellor’s Honors Program Projects

No abstract provided.

Development Of Novel Thin Membrane Electrode Assemblies (Meas) For High-Efficiency Energy Storage, Zhenye Kang

Doctoral Dissertations

Hydrogen is a ‘zero-emission’ energy carrier, which could be an important part of environment-friendly solutions to the global energy crisis via energy storage without producing greenhouse gases. The proton exchange membrane electrolyzer cell (PEMEC) is one of the most practical and energy efficient methods for producing high purity hydrogen from renewable sources, such as wind, hydro and solar energy. Since the wide commercialization of PEMECs is still hindered by their performance, cost and durability, superior performance PEMECs with low-cost and high-efficiency are strongly desired. The membrane electrode assembly (MEA), which consists of liquid/gas diffusion layers (LGDLs), catalyst layers (CLs) and …

Dynamic Simulation And Analysis Of Gait Modification For Treating Knee Osteoarthritis, Taylor Elyse Schlotman

Doctoral Dissertations

Roughly 47.5 million people in the US have a disability, with 8.6 million reporting arthritis as their main cause of disability, making arthritis the leading cause of physical disability. With decreased mortality rates and a large, aging baby boomer generation, there will be more adults living with chronic musculoskeletal conditions causing disabilities that limit walking. Since walking ability is directly related to an individual’s independence at home and in the community, losing this ability is a major setback for patients with arthritis. Knee osteoarthritis (OA) is the most prevalent form of arthritis affecting approximately 27 million adults and accounts for …

Fundamental Studies Of Electrochemical Reactions And Microfluidics In Proton Exchange Membrane Electrolyzer Cells, Jingke Mo

Doctoral Dissertations

In electrochemical energy devices, including fuel cells, electrolyzers and batteries, the electrochemical reactions occur only on triple phase boundaries (TPBs). The boundaries provide the conductors for electros and protons, the catalysts for electrochemical reactions and the effective pathways for transport of reactants and products. The interfaces have a critical impact on the overall performance and cost of the devices in which they are incorporated, and therefore could be a key feature to optimize in order to turn a prototype into a commercially viable product. For electrolysis of water, proton exchange membrane electrolyzer cells (PEMECs) have several advantages compared to other …

On The Quantification Of Complexity And Diversity From Phenotypes To Ecosystems, Zachary Harrison Marion

Doctoral Dissertations

A cornerstone of ecology and evolution is comparing and explaining the complexity of natural systems, be they genomes, phenotypes, communities, or entire ecosystems. These comparisons and explanations then beget questions about how complexity should be quantified in theory and estimated in practice. Here I embrace diversity partitioning using Hill or effective numbers to move the empirical side of the field regarding the quantification of biological complexity.

First, at the level of phenotypes, I show that traditional multivariate analyses ignore individual complexity and provide relatively abstract representations of variation among individuals. I then suggest using well-known diversity indices from community ecology …

Mass And Charge Transport In Hydrated Polymeric Membranes, Marshall T. Mcdonnell

Doctoral Dissertations

Mass and charge transport through hydrated polymer membranes has significant importance for many areas of engineering and industry. Multi-scale modeling and simulation techniques were used to study transport in relation to two specific membrane applications: (1) food packaging and (2) additives for polymer electrolytes.

Chitosan/chitin films were studied due to their use as a sustainable, biodegradable food packaging film. The effects of hydration on the solvation, diffusivity, solubility, and permeability of oxygen molecules in these films were studied via molecular dynamics and confined random walk simulations. With increasing hydration, the membrane was observed to have a more homogeneous water distribution …

Bankfull Geomorphic Relationships And Hec-Ras Assessment In Small Catchments Of The Cumberland Plateau Ecoregion, Ryan Lee Hodges

Masters Theses

There is a great need for state governments to have effective watershed restoration and mitigation efforts to return degraded ecosystems to a stable, healthy condition. Given the growing investment in stream restoration efforts, there is an urgent need for tools to assess and improve the effectiveness of restoration efforts at local, state, and nationwide scales. In 2000 there was less than ten stream restoration permits provided by the state of Tennessee and has increased each year with almost forty permits issued in 2013. To better achieve successful stream restoration, appropriate channel designs must be used that reflect the hydraulic conditions …

Spatial Variation In Fine Sediment And Microbial Transport Along Stream Cross Sections: Implications To Modeling And Monitoring, Thomas Michael Walton

Masters Theses

Spatial variations in suspended concentrations of fine sediment and indicator bacteria in streams is noted as a source of uncertainty in various applications of water quality datasets. Without proper analysis of the persistence and reasoning for this variance in natural systems, a finer resolution of model calibration is necessary to account for spatial variation in stream cross sections. This level of calibration has become of utmost importance due to technological advancements presenting the ability for water quality modeling frameworks to generate a much finer resolution of outputs. While the importance of model calibration has been noted for remediating levels of …

A Site-Specific And Dynamic Modeling System For Zoning And Optimizing Variable Rate Irrigation In Cotton, Amir Haghverdi

Doctoral Dissertations

Cotton irrigation has been rapidly expanding in west Tennessee during the past decade. Variable rate irrigation is expected to enhance water use efficiency and crop yield in this region due to the significant field-scale soil spatial heterogeneity. A detailed understanding of the soil available water content within the effective root zone is needed to optimally schedule irrigation. In addition, site-specific crop-yield mathematical relationships should be established to identify optimum irrigation management. This study aimed to design and evaluate a site-specific modeling system for zoning and optimizing variable rate irrigation in cotton. The specific objectives of this study were to investigate …

Modeling Water Quality For Switchgrass Crop Production: Implications For Bioenergy Sustainability In East Tennessee, Zachariah Tzvi Seiden

Masters Theses

With passing of the US Energy Independence and Security Act (EISA) of 2007, there has been considerable research conducted on the sustainability of bioenergy crop production in the United States; switchgrass has shown particular potential for bioenergy production in East Tennessee. Many studies evaluating the environmental impact switchgrass has on runoff and water quality use the Soil and Water Assessment Tool (SWAT) for watershed modeling. Because SWAT is a lumped watershed model, it evaluates the result of hydrological processes for each hydrologic response unit (HRU), without accounting for the physical interactions between these HRUs. The Water Erosion Prediction Project (WEPP) …