Engineering Commons^™

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 …

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 …

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 …

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 …

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 …

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 …

Saturable Reactor For Power Flow Control In Electric Transmission Systems: Modeling And System Impact Study, Marcus Aaron Young Ii

Doctoral Dissertations

A Saturable Reactor for Power Flow Control (SRPFC) is a novel application of a concept well known to electronics and power electronics engineers that provides continuous modulation of line reactance by controlling the magnetization in a ferromagnetic core. The novelty of the SRPFC is the target application, which is power flow control in meshed electric power networks. Modulation of the line impedance occurs by altering the current in a DC winding to control the magnetization of the ferromagnetic core, thereby varying the reactance of the AC winding. The deployment of power system equipment, like SRPFC, requires careful planning and study …

Bedload Transport Sampling, Characterization And Modeling On A Southern Appalachian Ridge And Valley Stream, Patrick Lasater Mcmahon

Doctoral Dissertations

Estimates of bedload transport rates developed from existing transport models are notoriously inaccurate(Wilcock 2001). The gravel bed models addressed in this study include the Meyer-Peter and Muller; Parker, Klingeman, and McLean; and Wilcock two-fraction models. The question of whether or not these models predict bedload transport rates in a Southern Appalachian Ridge and Valley stream is complicated by the fact that these models have only been previously assessed in terms of their agreement with bedload transport rates measured in the Western regions of the U.S. Further, due to the strongly non-linear form of bedload transport models discrete errors and cumulative …

Fully Coupled Fluid And Electrodynamic Modeling Of Plasmas: A Two-Fluid Isomorphism And A Strong Conservative Flux-Coupled Finite Volume Framework, Richard Joel Thompson

Doctoral Dissertations

Ideal and resistive magnetohydrodynamics (MHD) have long served as the incumbent framework for modeling plasmas of engineering interest. However, new applications, such as hypersonic flight and propulsion, plasma propulsion, plasma instability in engineering devices, charge separation effects and electromagnetic wave interaction effects may demand a higher-fidelity physical model. For these cases, the two-fluid plasma model or its limiting case of a single bulk fluid, which results in a single-fluid coupled system of the Navier-Stokes and Maxwell equations, is necessary and permits a deeper physical study than the MHD framework. At present, major challenges are imposed on solving these physical models …

Multiscale Modeling Of Toxoplasma Gondii, Adam Michael Sullivan

Doctoral Dissertations

Toxoplasma gondii is a potentially deadly parasite that uses a very unique way of manipulating the cell and immune systems. To investigate the mechanics of how the parasite spreads within hosts, several interwoven topics related to the study of within-host dynamics of Toxoplasma gondii are presented here. Understanding the complicated methods of how the parasite grows, dies, invades, replicates, and evades the host immune response is the critical aim of this independent research. Understanding the processes of acute and chronic infection are studied independently, followed by modeling the two processes in the same model. Finally, the dynamic models are simulated …

Modeling And Development Of A Mems Device For Pyroelectric Energy Scavenging, Salwa Mostafa

Doctoral Dissertations

As the world faces an energy crisis with depleting fossil fuel reserves, alternate energy sources are being researched ever more seriously. In addition to renewable energy sources, energy recycling and energy scavenging technologies are also gaining importance. Technologies are being developed to scavenge energy from ambient sources such as vibration, radio frequency and low grade waste heat, etc. Waste heat is the most common form of wasted energy and is the greatest potential source of energy scavenging.

Pyroelectricity is the property of some materials to change the surface charge distribution with the change in temperature. These materials produce current as …