Engineering Commons^™

Constrained Multi-Group Project Allocation Using Mahalanobis Distance, Abdulaziz Saud Alkabaa

Doctoral Dissertations

Optimal allocation is one of the most active research areas in operation research using binary integer variables. The allocation of multi constrained projects among several options available along a given planning horizon is an especially significant problem in the general area of item classification. The main goal of this dissertation is to develop an analytical approach for selecting projects that would be most attractive from an economic point of view to be developed or allocated among several options, such as in-house engineers and private contractors (in transportation projects). A relevant limiting resource in addition to the availability of funds is …

Characteristics Of Thick Concrete Neutron Reflection, Richard Gordon Taylor

Doctoral Dissertations

Water is considered as a neutron reflector in nuclear criticality safety evaluations because it is readily available and easily forms a close-fitting shape around fissile material. Concrete is commonly encountered industrial environments and can be a more effective reflector than water. Nuclear criticality safety literature reporting experimental and analytical studies involving concrete as a reflector from the 1950’s to the present was reviewed. Nuclear criticality safety community perspective on concrete reflection has evolved from acknowledgement that concrete is a reflector through recognition that concrete can be a more effective reflector than water to current interest in identifying which constituents are …

Multiscale Modeling Of Electrolytes For Energy Storage And Conversion, Fatemeh Sepehr

Doctoral Dissertations

Fuel cells, redox flow batteries, and secondary ion batteries are under active investigation to fulfill the requirements of efficient and sustainable energy storage and conversion technologies. The discovery of high-performance stable electrolytes that are relatively cheap and versatile is crucial to the commercialization of these electrochemical devices and necessitates a comprehensive understanding of the materials (i.e., from the atomistic to continuum levels). This dissertation is on multiscale modeling and simulations of several electrolytes under consideration in vanadium redox flow batteries (VRFBs), alkaline fuel cells (AFCs), or secondary magnesium batteries.

The hydrated structure and associated solvation Gibbs energies were determined for …

Microstructure Control And Correlation To Creep Properties In Grade 91 Steel Weldment After Thermo-Mechanical Treatments And An Fe-30cr-3al Alloy Strengthened By Fe2nb Laves Phase, Benjamin Allen Shassere

Doctoral Dissertations

Type IV cracking in weldments of steel pipes after creep deformation is a concern in modern fossil-fueled power plants. Two possible methods for minimizing or eliminating Type IV cracking will be discussed. The first method alters the initial microstructure of typical Grade 91 steel base metal before welding, while the second provides baseline microstructure characteristics and creep performance of a new alloy that is strengthened by the intermetallic Fe2Nb Laves phase. The initial microstructure of the Grade 91 steel can be controlled by Thermo-Mechanical Treatments, which aids in precipitation of fine (5-10 nm) MX particles in austenite before transformation to …

Deterministic Neutron Transport And Multiphysics Experimental Safety Analyses At The High Flux Isotope Reactor, Christopher James Hurt

Doctoral Dissertations

The computational ability to accurately predict the conditions in an experiment under irradiation is a valuable tool in the operation of a research reactor whose scientific mission includes isotope production, materials irradiation, and neutron activation analysis. Understanding of different governing physics is required to ascertain satisfactory conditions within the experiment: the neutron transport behavior throughout the reactor and the coupled behavior of heat transfer, structural mechanics and fluid flow. Computational methods and tools were developed for robust numerical analysis of experiment behavior at the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor (HFIR), including fully-coupled thermo-mechanics in three plutonium-238 …

Development, Synthesis, And Analysis Of Surrogate Post-Detonation Nuclear Melt Glass, Andrew Vincent Giminaro

Doctoral Dissertations

With the threats facing the world today, there is an ever-increasing need for training the the fields of radiochemistry and nuclear forensics. Training and research in these fields requires reference materials that accurately represent materials that could potentially be encountered. Unfortunately, many of the historical samples of debris from nuclear weapons tests remains classified. Because of this, there is a need for realistic surrogates. This research focuses on the development of surrogates for the bulk and particulate nuclear melt glass that is expected to be found in an urban setting after a nuclear event.

A mathematical model for the creation …

Ecology Of Organohalide-Respiring Dehalococcoides Mccartyi: Corrinoid Cofactor-Related Community Interactions And Controls Over Strain Selection, Burcu Şimşir

Doctoral Dissertations

Organohalides such as tetrachloroethene (PCE) and trichloroethene (TCE) are among the most prevalent toxic groundwater contaminants. Remediation of organohalide-contaminated sites has high priority, and efficient and cost-effective remedies are needed to prevent environment and human exposure through contaminated water. Bacterial organohalide-respiration plays a major role in organohalide detoxification. Dehalococcoides mccartyi (Dhc) are key mediators in bioremediation, since only Dhc strains have been documented in complete detoxification of chlorinated ethenes to benign ethene. Dhc depends on other microorganisms in the environment for essential growth requirements (e.g., hydrogen and vitamins). For successful implementation of the reductive dechlorination to remediate contaminated …

Bioremediation Of Chlorinated Ethenes: Ph Effects, Novel Dechlorinators And Decision-Making Tools, Yi Yang

Doctoral Dissertations

Chlorinated solvents have been widely used in different areas of modern society. Usage of these chlorinated solvents was not necessarily accompanied with proper handling and disposal of these hazardous compounds, which caused a variety of environmental problems and continues to affect human health. Remediation of chlorinated ethenes contaminated sites has high priority for state regulators and site owners. Among the available treatment technologies, bioremediation shows great promise as a cost-effective corrective strategy for a variety of environmental pollutants. Prerequisites are that the microbiology involved in contaminant degradation and geochemical factors, such as pH, are understood, so that bioremediation technologies can …

Studies Of Uncertainties In Smart Grid: Wind Power Generation And Wide-Area Communication, Can Huang

Doctoral Dissertations

This research work investigates the uncertainties in Smart Grid, with special focus on the uncertain wind power generation in wind energy conversion systems (WECSs) and the uncertain wide-area communication in wide-area measurement systems (WAMSs).

For the uncertain wind power generation in WECSs, a new wind speed modeling method and an improved WECS control method are proposed, respectively. The modeling method considers the spatial and temporal distributions of wind speed disturbances and deploys a box uncertain set in wind speed models, which is more realistic for practicing engineers. The control method takes maximum power point tracking, wind speed forecasting, and wind …

Innovative Electrode Nanocomposites For Energy Storage And Conversion Systems, Yiran Wang

Doctoral Dissertations

Nanocomposites emerged as suitable alternatives for electrode materials, are defined as “two or more materials with different properties remain separate and distinct on a macroscopic level within one unity and with any dimension in any phase less than 100 nm”. Recently, polymer/carbon based nanocomposites have attracted significant research interests for energy applications due to their multi-functionalities, improved structure stability and ease of production. This dissertation work focusing on the development of innovative electrode nanocomposites for proton exchange membrane fuel cell, supercapacitor and electrochromic applications.

Chapter 1 is an introduction. Chapter 2 & 3 focus on the synthesis of Pd-based nanocatalysts …

Beta-Delayed Neutron Data And Models For Scale, Kemper Dyar Talley

Doctoral Dissertations

Recent advancements in experimental and theoretical nuclear physics have yielded new data and models that more accurately describe the decay of fission products compared to historical data currently used for many applications. This work examines the effect of the adopting the Effective Density Model theory for beta-delayed neutron emission probability on calculations of delayed-neutron production and fission product nuclide concentrations after fission bursts as well as the total delayed neutron fraction in comparison with the Keepin 6-group model. We use ORIGEN within the SCALE code package for these calculations. We show quantitative changes to the isotopic concentrations for fallout nuclides …

Structure And Properties Of Cnt Yarns And Cnt/Cnf Reinforced Pan-Based Carbon Fibers, Nitilaksha Phalaxayya Hiremath

Doctoral Dissertations

There is continuing effort to enhance the strength and modulus of carbon fibers by various combinations of materials and processing. Carbon fibers are produced from various precursors, and the strength of the CFs are directly related to the type of precursor used to make them. Carbon Nanotubes (CNTs) have received a great deal of attention due to their unique structure and properties. Major focus of this research is on the evaluation of processing, structure and properties of CNT based yarns and composite fibers.

High strength and low cost carbon fibers (CFs) are needed for today’s applicatio ns. A low cost …

Integrating The Cost Of Quality Into Multi-Products Multi-Components Supply Chain Network Design, Waleed Abdussalam Gueir

Doctoral Dissertations

More than ever before the success of a company heavily depends on its supply chain and how efficient the network. A supply chain needs to be configured in such a manner as to minimize cost while still maintaining a good quality level to satisfy the end user and to be efficient, designing for the network and the whole chain is important. Including the cost of quality into the process of designing the network can be rewording and revealing. In this research the concept of cost of quality as a performance measure was integrated into the supply chain network designing process …

Large Scale Brownian Dynamics Simulation Of Dilute And Semidilute Polymeric Solutions, Amir Saadat

Doctoral Dissertations

Excluded Volume (EV) and Hydrodynamic Interactions (HI) play a central role in static and dynamic properties of macromolecules in solution under equilibrium and nonequilibrium settings. The computational cost of incorporating HI in mesoscale Brownian dynamics (BD) simulations, particularly in the semidilute regime has motivated significant research aimed at development of high-fidelity and efficient techniques.

In this study, I have developed several algorithms for the mesoscale bead-spring representation of a macromolecular solution in dilute and semidilute regimes. The Krylov subspace method enables fast calculation of single chain dynamics with simulation time scaling of O(N_b²) [order N …

Helium Diffusion And Accumulation In Gd2ti2o7 And Gd2zr2o7, Caitlin Anne Taylor

Doctoral Dissertations

The effects of helium accumulation on bubble formation and mechanical properties, as well as the fundamentals of helium diffusion in pyrochlores, are experimentally investigated in Gd₂Ti₂O₇ [gadolinium titanate] and Gd₂Zr₂O₇ [gadolinium zirconate]. We find that helium accumulation results in bubble formation at concentrations of 6 at.% in pre-damaged Gd₂Ti₂O₇ and 4.6 at.% in pre-damaged Gd₂Zr₂O₇. Lattice parameter, residual stress, and hardness changes due to helium accumulation were investigated in Gd₂Zr₂O₇, which remains crystalline …

Study Of Graphitization In Carbon Steel Weldments For Remaining Life Assessment, Maneel Bharadwaj

Doctoral Dissertations

Carbon steels and low-alloy steels are often used in various stages of the refining process in petrochemical industries and power plants where they are susceptible to graphitization after prolonged exposure at temperatures of 800°F (427°C) or above. Graphitization is a result of solid-state phase transformation of metastable iron carbide to form iron and graphite structure. The formation of graphite results in the loss of tensile strength, ductility, and creep strength, which may result in untimely catastrophic failure of the component. The current study focused on developing a further understanding of graphitization on ex-service welded carbon steel components, which were removed …

Design, Control And Protection Of Modular Multilevel Converter (Mmc)-Based Multi-Terminal Hvdc System, Yalong Li

Doctoral Dissertations

Even though today’s transmission grids are predominantly based on the high voltage alternating current (HVAC) scheme, interests on high voltage direct current (HVDC) are growing rapidly during the past decade, due to the increased penetration of remote renewable energy. Voltage source converter (VSC) type is preferred over the traditional line-commutated converter (LCC) for this application, due to the advantages like smaller station footprint and no need for strong interfacing ac grid. As the state-of-the-art VSC topology, modular multilevel converter (MMC) is mostly considered. Most renewable energy sources, such as wind and solar, is usually sparsely located. Multi-terminal HVDC (MTDC) provides …

Generation And Microwave Scattering Diagnostics Of Small Volume Plasmas, Jordan Chase Sawyer

Doctoral Dissertations

This dissertation focuses on the development of novel generation and microwave scattering diagnostic techniques for small volume plasmas. The small volume plasmas presented in this work fall under the two generalized categories: 1) laser-induced plasmas and 2) non-equilibrium microdischarges.

Chapter I presents the application of microwave scattering theory to laser-induced breakdown in air. The MIE solution to Maxwell’s equations is employed to reveal three distinct phases of the evolution of the laser-induced breakdown in air. Chapter II presents a novel method of quantifying thresholds for laser-induced breakdown. These thresholds are established via total electron number measurement from dielectric calibration of …

Temperature Dependent Mechanical Behavior Of Solid Acids, Ryan Scott Ginder

Doctoral Dissertations

Existing literature data on the creep behavior of superprotonic solid acids, which is important for their use in fuel cell applications, is scant and unreliable. Steady state creep behavior for the model material system cesium hydrogen sulfate (CHS) is probed using nanoindentation and corroborated using uniaxial compression testing. To facilitate nanoindentation creep result interpretation, a radial flow model of power law indentation creep is developed. This model is compared with the related model from Bower, et. al. for several pre-existing literature datasets showing that the nonlinear, steady state creep law underpinning both appears valid for power law indentation creep.

Algorithms And Methods For Optimizing The Spent Nuclear Fuel Allocation Strategy, Gordon Matthew Petersen

Doctoral Dissertations

Commercial nuclear power plants produce long-lasting nuclear waste, primarily in the form of spent nuclear fuel (SNF) assemblies. Spent fuel pools (SFP) and canisters or casks that sit at an independent spent fuel storage installation (ISFSI) at the reactor site store the fuel assemblies that are removed from operating reactors. The federal government has developed a plan to move the SNF from reactor sites to a Consolidated Interim Storage Facility (CISF) or a geological repository. In order to develop a predictable pick-up schedule and give utilities notice of an impending pickup from a reactor site, the federal government developed a …

A Quantitative Measure Of Mono-Componentness For Time-Frequency Analysis, Austin P. Albright

Doctoral Dissertations

Joint time-frequency (TF) analysis is an ideal method for analyzing non-stationary signals, but is challenging to use leading to it often being neglected. The exceptions being the short-time Fourier transform (STFT) and spectrogram. Even then, the inability to have simultaneously high time and frequency resolution is a frustrating issue with the STFT and spectrogram. However, there is a family of joint TF analysis techniques that do have simultaneously high time and frequency resolution – the quadratic TF distribution (QTFD) family. Unfortunately, QTFDs are often more troublesome than beneficial. The issue is interference/cross-terms that causes these methods to become so difficult …

Strategies For Controlling Bulk Heterojunction Morphology, Zach Daniel Seibers

Doctoral Dissertations

Organic photovoltaic devices have been extensively studied as a means to produce sustainable energy. However, the performance of organic-photovoltaic (OPV) devices is dependent upon a number of factors including the morphology of the active layer, device architecture, and processing conditions. Recent research has indicated that fullerenes in the bulk heterojunction are entropically driven to the silicon and air interfaces upon crystallization of P3HT, which occurs during thermal annealing. The first chapter of this research focuses on investigating the structure and function of end-tethered poly(3-hexylthiophene) chains to a transparent electrode as an anode buffer layer. Neutron reactivity reveals that these P3HT …

A Study On Wide-Area Measurement-Based Approaches For Power System Voltage Stability, Haoyu Yuan

Doctoral Dissertations

With the development of wide-area monitoring system (WAMS) enabled by the synchrophasor technology, measurement-based approaches for power system voltage stability and control have been widely discussed in recent years. Based on high-frequency synchronized measurement signals collected from phasor measurement units (PMUs), these approaches have great potentials to significantly improve the situational awareness and to effectively guide the controls of interconnected modern power systems.

If compared with conventional model-based voltage stability assessment (VSA) and control methods, the measurement-based methods are relatively new. Although their simplicity and independence of system models make them suitable for online deployment, the applications of these measurement-based …

Impedance-Resolved Performance And Durability In Redox Flow Batteries, Alan Michael Pezeshki

Doctoral Dissertations

The realization of redox flow batteries (RFBs) as a grid-scale energy solution depends on improving the performance and lifetime of the technology to decrease the high capital costs. The electrodes are a key component in the RFB; performance enhancement is often achieved through chemical or thermal treatments of commercially available porous carbon materials.

This dissertation uses impedance spectroscopy-based methods to gain insight into performance and durability in RFBs, enabling intelligent cell design. Initial work focused on understanding the impact of improved electrode and membrane properties on system performance. An accelerated stress test was then developed that can be used to …

Design And Analysis Of A Fully-Integrated Resonant Gate Driver, Yu Long

Doctoral Dissertations

Several decades ago the resonant gate driving technique was proposed. Given the recent rapid growth in GaN HEMT power device applications for high-frequency power applications, research has been conducted in the power electronics field using resonant gate driving for GaN power devices. Previous research for resonant gate drivers for GaN HEMT devices mostly focused on implementing the gate driving function itself, and mostly for normally-on HEMT devices.

The normally-off (enhancement mode) GaN power device was introduced to the commercial market in 2009. A new resonate gate driver is proposed in this work to implement resonant gate driving for commercial high-speed …

Development Of Instrumentation And Control Systems For An Integral Large Scale Pressurized Water Reactor, Matthew Rowland Morrow Lish

Doctoral Dissertations

Small and large scale integral light water reactors are being developed to supply electrical power and to meet the needs of process heat, primarily for water desalination. This dissertation research focuses on the instrumentation and control of a large integral inherently safe light water reactor (designated as I²S-LWR) which is being designed as part of a grant by the U.S. Department of Energy Integrated Research Project (IRP). This 969 MWe integral pressurized water reactor (PWR) incorporates as many passive safety features as possible while maintaining competitive costs with current light water reactors. In support of this work, the …

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 …

Design And Control Of Close Proximity Indirect Exposure For Nonthermal Atmospheric Pressure Plasma-Based Oxidation Of Carbon Fiber Precursor, Truman Andrew Bonds

Doctoral Dissertations

A new plasma-based method for the stabilization of polyacrylonitrile carbon fiber precursor utilizing reactive chemical species derived from a custom atmospheric pressure plasma generation system was developed and demonstrated. As opposed to the conventional stabilization method of convective heating in air, plasma-based stabilization efficiently introduces oxidative reactive species that both diffuse through and react faster with the precursor filaments, resulting in a faster and more efficient process. This method was successfully demonstrated with a variety of precursor chemistries, grades and sizes. The development effort was entirely experimental, with successive processing devices designed and constructed to examine various aspects of the …

Investigation Of Localized Performance And Gas Evolution In All-Vanadium Redox Flow Batteries Via In-Situ Distributed Diagnostic Techniques, Jason Thomas Clement

Doctoral Dissertations

All-vanadium redox flow batteries (VRFBs) are an emerging grid-scale energy storage technology; however, enhancements in terms of performance, efficiency, durability, and cost are required before it can become commercially viable. These improvements are achievable through the development of advanced materials, superior architecture, and ultimately a deeper fundamental understanding of the influence of various phenomena and operational parameters on cell performance. There currently are a lack of in-situ experimental diagnostic techniques which can help in achieving this fundamental understanding.

Two separate distributed diagnostic techniques were developed in this work: in-plane current distribution, and neutron radiography. Localized current distribution measurements can identify …

Potential Emissions And Exposures Of Toxic Organics From Storage Tanks For Chemical Additions In Hydraulic Fracturing: A Modeling Approach, Huan Chen

Doctoral Dissertations

Hydraulic fracturing has promoted the exploitation of natural gas in the United States (U.S.). However, the storing and emptying of chemical additives in hydraulic fracturing wells may pose adverse effects through inhalation exposures. Based on the information about hydraulic fracturing fluids, this study investigated: 1) water volumes used to mix chemical additives for making up the hydraulic fracturing fluids; 2) chemical species, concentrations and their degradability in the hydraulic fracturing fluids; 3) emissions of organics from chemical storage tanks; and 4) the occupational inhalation exposures by toxic and organic vapors.

Results shows for 80,047 wells fractured between 2008 and 2014 …