Engineering Commons^™

Stability Analysis And Control Of Nonlinear Power System Oscillations, Xin Xu

Doctoral Dissertations

This work investigates the nonlinear oscillatory behaviors of multi-machine power systems. New model-based and measurement-based approaches are proposed for stability analysis and control of nonlinear oscillations.

For stability analysis, a recently proposed model-based nonlinear oscillation analysis method, nonlinear modal decoupling (NMD), is investigated on its ability in capturing the stability information of a multi-machine power system. From the differential-equation model of the power system, the NMD inversely constructs a set of 1-degree-of-freedom nonlinear oscillators, referred to as decoupled oscillators or subsystems, with each one corresponding to an oscillation mode of the original system. It is shown that retaining high order …

Thermoplastic Additive Manufacturing For Composites And Molds, Pritesh S. Yeole

Doctoral Dissertations

Recent inventions in the ability of additive manufacturing (AM) to use carbon fiber (CF) reinforced pellets as a feedstock material to manufacture components has complemented its purpose from prototypes to structural load-bearing parts. In the first part of this research, we investigated the processability, microstructure, and mechanical performance of twin-screw compounded short CF reinforced polyphenylene sulfide (PPS) pellets as a feedstock material for extrusion deposition fabrication-additive manufacturing (EDF-AM) using big area AM (BAAM). The performance of the BAAM components was compared to that of traditional processing methods, namely injection molding (IM) and extrusion-compression molding (ECM). It was found that the …

Analysis And Enhancement Of Human Cognitive Control Using Noninvasive Brain-Computer Interfaces, Soheil Borhani

Doctoral Dissertations

Cognitive control including attention and working memory are crucial to human daily life. Whether a civilian who walks across a street or a military service member who is responsible for navigating a mission, cognitive control is involved, entirely. This ability is subject to impairment. People with attention disorder are easily disposed to distraction and lacks the ability to maintain the focus to a task. Multiple treatment strategies have been suggested which most of them has been pharmaceutical. Evidently, the medical treatment has side effects for long-term use. Moreover, it has a risk of drug misuse. Another line of treatment is …

Development Of A Robust Wideband Gnss Rf Frontend With Resilient Interference Blocking, Farshid Tamjid

Doctoral Dissertations

Recently, there has been an increasing demand for GNSS systems’ use for numerous applications such as public security, disaster relief, weather forecast, transportation, hydrologic monitoring, aviation, navigation positions and so on. Such systems must have a wideband performance (1.16 GHz to 1.61 GHz), high quality reception (which requires antenna with low AR, high RHCP gain, high F/B ratio, and high RL), portable size, and low cost. Our efforts here are geared towards the receiving side of such communication. The antennas are the first stage of the long receiver chain. Development of such wideband high quality antennas is challenging as most …

A Method For Developing And Testing Nuclear Reactor Systems With Space Applications And Improving Performance Of Heat Pipe Reactor Systems, David Duff Dixon

Doctoral Dissertations

The concept of using nuclear reactor technology in propulsion systems is nearly as old as nuclear reactors themselves. Numerous publications, many at very primitive conceptual levels, suggested nuclear propulsion in the 1940s. Since then, numerous attempts have been made to build and fly a nuclear rocket, yet there have been no such systems advanced to the point of a system test in more than half a century.

This dissertation presents an approach to reactor system development, a testing approach developed by the author that resulted in the operation of the world’s first heat pipe reactor system, and the world’s first …

Development Of (Α,N) Signatures As A Viable Safeguards Measurement For Electrochemical Reprocessing, Stephen N. Gilliam

Doctoral Dissertations

As interest grows in electrochemistry for material separations and reprocessing of nuclear fuel research and development into the safegaurdability of such a system is needed. Plutonium quantification via (α,n) neutrons within the electrorefiner vessel is examined as a potential alternative means to the traditional spontaneous fission tracking. An MCNP model of an Epi-Thermal Neutron Multiplicity counter was used in the calculation of curium from a sample of curium, plutonium, and eutectic salt. This and the multiplicity variable alpha, the ratio between (α,n) neutron and spontaneous fission, were then used to define the plutonium mass as it related to its (α,n) …

Engineering Platforms For Advancing Plant Synthetic Biology, Tayler Marie Schimel Mcneillie

Doctoral Dissertations

This work describes research aimed at adapting advanced engineering systems for plant biotechnology. The droplet interface bilayer (DIB) is a robust and versatile platform for replicating model cell membranes, providing a bottom-up approach for synthetic cell- and tissue-like structures. In this work, a microfluidic device featuring five inlets, one for the continuous oil phase and four discrete aqueous channels for droplet generation was designed. Droplet production rates were controlled by adjusting the applied pressure of each inlet; and thus, altering the droplet sequence for capturing linear DIB networks in a downstream hydrodynamic trapping array. This microfluidic system provides a high-throughput …

Local Structure And Dynamic Studies Of Mixed Ch4-Co2 Gas Hydrates Via Computational Simulation And Neutron Scattering, Bernadette Rita Cladek

Doctoral Dissertations

Permeated throughout the ocean floor and arctic permafrost, natural gas hydrates contain an estimated 3000 trillion cubic meters, over three times that of traditional shale deposits, of CH₄ that is accessible for extraction. Gas hydrates are a crystal structure in which water molecules form a cage network, the host, through hydrogen bonds while trapping a guest molecule such as CH₄ in the cavities. These compounds form naturally where the appropriate low temperature and high pressure conditions occur. A promising and tested method of methane recovery is through exchange with CO₂, which energetically takes place of the …

Vibration Behavior In Modulated Tool Path (Mtp) Turning, Ryan William Copenhaver

Doctoral Dissertations

This project studies the process dynamics and surface finish effects of modulated tool path (MTP) turning. In MTP turning, a small amplitude (typically less than 0.5 mm), low frequency oscillation (typically less than 10 Hz) is superimposed on the feed motion by the machine controller to intentionally segment the traditionally long, continuous chips. The basic science to be examined is the vibration behavior of this special case of interrupted cutting, which is not turning because the chip formation is intentionally discontinuous and is not milling because the time-dependent chip geometry is defined by the oscillatory feed motion, not the trochoidal …

Approaches To Studying Bacterial Biofilms In The Bioeconomy With Nanofabrication Techniques And Engineered Platforms., Michelle Caroline Halsted

Doctoral Dissertations

Studies that estimate more than 90% of bacteria subsist in a biofilm state to survive environmental stressors. These biofilms persist on man-made and natural surfaces, and examples of the rich biofilm diversity extends from the roots of bioenergy crops to electroactive biofilms in bioelectrochemical reactors. Efforts to optimize microbial systems in the bioeconomy will benefit from an improved fundamental understanding of bacterial biofilms. An understanding of these microbial systems shows promise to increase crop yields with precision agriculture (e.g. biosynthetic fertilizer, microbial pesticides, and soil remediation) and increase commodity production yields in bioreactors. Yet conventional laboratory methods investigate these micron-scale …

Dynamic Neuromechanical Sets For Locomotion, Aravind Sundararajan

Doctoral Dissertations

Most biological systems employ multiple redundant actuators, which is a complicated problem of controls and analysis. Unless assumptions about how the brain and body work together, and assumptions about how the body prioritizes tasks are applied, it is not possible to find the actuator controls. The purpose of this research is to develop computational tools for the analysis of arbitrary musculoskeletal models that employ redundant actuators. Instead of relying primarily on optimization frameworks and numerical methods or task prioritization schemes used typically in biomechanics to find a singular solution for actuator controls, tools for feasible sets analysis are instead developed …

Investigating The Compactability Of Hot Mix Asphalt Utilizing The Concept Of The Locking Point, Pawel Andrzej Polaczyk

Doctoral Dissertations

Compaction is an important process for the asphalt mixture service life. An adequately compacted mixture is crucial for long-lasting pavement. Compaction is a procedure utilized to compress and decrease the volume of the material, which provides essential ingredients that influence the pavement's performance. During asphalt mix compaction, the aggregate coated with asphalt binder are compressed together, following an increase of interparticle friction and surface contact and finally interlocking to provide the resistance to deformation. At the same time, the permeability is decreased, and the durability is increased. Compactability is utilized to evaluate how much compaction energy is required to compact …

Characterization Of A Digital Holography Diagnostic For In Situ Erosion Measurement Of Plasma-Facing Components In Fusion Devices, Cary Dean Smith

Doctoral Dissertations

Fusion energy devices, particularly tokamaks, face the challenge of interior surface damage occurring over time from the heat flux of the high-energy plasma they generate. The ability to monitor the rate of surface modification is therefore imperative, but to date no proven technique exists for real-time erosion measurement of planar regions of interest on plasma-facing components in fusion devices. In order to fill this diagnostic gap, a digital holography system has been established at ORNL [Oak Ridge National Laboratory] for the purpose of measuring the erosion effects of plasma-material interaction in situ.

The diagnostic has been designed with the …

Synchronized Measurement Data Conditioning And Real-Time Applications, Xianda Deng

Doctoral Dissertations

Phasor measurement units (PMU), measuring voltage and current phasor with synchronized timestamps, is the fundamental component in wide-area monitoring systems (WAMS) and reveals complex dynamic behaviors of large power systems. The synchronized measurements collected from power grid may degrade due to many factors and impacts of the distorted synchronized measurement data are significant to WAMS. This dissertation focus on developing and improving applications with distorted synchronized measurements from power grid. The contributions of this dissertation are summarized below. In Chapter 2, synchronized frequency measurements of 13 power grids over the world, including both mainland and island systems, are retrieved from …

Multiscale Simulations Of Polymeric Electrolytes For Electrochemical Devices, Xubo Luo

Doctoral Dissertations

Polymeric electrolytes are polymers containing the ionic moieties used for ion conduction in electrochemical devices. The strategic design of these materials requires the in-depth understanding of the relation between the molecular structure and the properties. This dissertation reports on computational simulations for two types of materials: hydrated anion exchange membranes (AEMs) for fuel cells and the polymerized ionic liquids (PolyILs). Various chemical structures were covered for systematic investigations.

For AEMs, the ion conducting channels or domains are essential for the efficient ion transport, and thus the morphology of the hydrated membrane is worthy of study. Dissipative particle dynamics simulations were …

Phylogenetics And Association Analyses Illustrate Substantial Cryptic Diversity Of A Newly Isolated Collection Of Cenococcum Geophilum, Jessica Velez

Doctoral Dissertations

The ectomycorrhizal fungus Cenococcum geophilum is distributed worldwide across multiple climates and soil types and is known to positively associate with a multitude of plant genera, possibly contributing to plant ability to tolerate inorganic contaminants in a soil environment. New C. geophilum isolates are easily cultured from soils in a laboratory setting, making this an ideal candidate for a model species with which to study multiple plant-fungal effects across a collection of novel isolates. However, C. geophilum is also genetically complex and, at 178Mbp, features one of the largest fungal genomes, necessitating the use of the novel restriction-associated DNA sequencing …

Automated Intelligent Cueing Device To Improve Ambient Gait Behaviors For Patients With Parkinson's Disease, Nader Naghavi

Doctoral Dissertations

Freezing of gait (FoG) is a common motor dysfunction in individuals with Parkinson’s disease (PD). FoG impairs walking and is associated with increased fall risk. Although pharmacological treatments have shown promise during ON-medication periods, FoG remains difficult to treat during medication OFF state and in advanced stages of the disease. External cueing therapy in the forms of visual, auditory, and vibrotactile, has been effective in treating gait deviations. Intelligent (or on-demand) cueing devices are novel systems that analyze gait patterns in real-time and activate cues only at moments when specific gait alterations are detected. In this study we developed methods …

Effect Of Ambient Oxidation On Chemical Composition And Structural Properties Of Iron Nanoparticles For Hyperthermia And Medical Imaging, Adam Wesley Evans

Doctoral Dissertations

With magnetization saturation roughly twice that of iron oxide nanoparticles, metallic iron nanoparticles (also termed zero-valent iron nanoparticles) have desirable properties for use as a magnetic resonance imagining (MRI) contrast agent as well as a medium for hyperthermia treatment of cancer. Metallic iron nanoparticles, however, are difficult to synthesize and maintain due to their high degree of reactivity and proclivity for oxidation. The main goal of this study was to investigate how ambient oxidation affects the chemical composition and structural properties of metallic iron nanoparticles initially synthesized through a facile reduction reaction of iron (III) chloride with sodium borohydride. A …

Rapid Design, Construction, And Validation Of Synthetic Metabolic Pathways In A Modular Escherichia Coli (Chassis) Cell, Jong-Won Lee

Doctoral Dissertations

Current strain development has been hindered by the vast biochemical space in nature. The concept of modular cell design has been invented to enable rapid and predictable construction of multiple optimal production strains for efficient production of a large variety of biochemicals with minimal experimental effort. While modular cell design principles have been successfully validated in some cases, its development is still limited by the small library of the production modules demonstrated.

The goals of this thesis are i) to establish a framework for rapid design, construction, and validation of production modules to explore a large space of molecules (e.g., …

Robust And Sustainable Energy Pathways To Reach Mexico’S Climate Goals, Rodrigo Mercado Fernandez

Doctoral Dissertations

As countries set climate change goals for adaptation and mitigation efforts, there are many questions regarding to how to reach these targets. These efforts will necessitate the transition of our electricity infrastructure from relying on conventional electricity generation technologies including natural gas, coal and oil, to clean energy generation with renewables. Through the three essays presented in this dissertation, we explore various pathways of development for the electricity system to reach long term climate change goals. We are interested in identifying: Is there a unique optimal development option or are there various? How do different mixes of electricity generation technologies …

Market-Conscious Strategies To Improve The Performance And Stability Of Planar, P-I-N Hybrid Organic-Inorganic Metal Halide Perovskite Solar Cells, Brandon Dunham

Doctoral Dissertations

Planar, p-i-n (inverted) hybrid organic-inorganic perovskite solar cells that use low-temperature, solution-processable charge-transport layers have garnered much attention due to their direct compatibility with flexible substrates and cost-effective roll-to-roll manufacturing. Nevertheless, this architecture has failed to repeatedly achieve the superior power conversion efficiencies frequently attained by its n-i-p counterpart. Additionally, the perovskite active layer has poor stability in the presence of prolonged light exposure, high temperatures, and moisture. In this study, we propose commercially viable strategies to improve the performance and stability of inverted methylammonium lead iodide perovskite solar cells. First, we show that a simple two-step method comprising evaporation-induced …

Design And Implementation Of A Multi-Modal Sensor With On-Chip Security, Ava Hedayatipour

Doctoral Dissertations

With the advancement of technology, wearable devices for fitness tracking, patient monitoring, diagnosis, and disease prevention are finding ways to be woven into modern world reality. CMOS sensors are known to be compact, with low power consumption, making them an inseparable part of wireless medical applications and Internet of Things (IoT). Digital/semi-digital output, by the translation of transmitting data into the frequency domain, takes advantages of both the analog and digital world. However, one of the most critical measures of communication, security, is ignored and not considered for fabrication of an integrated chip. With the advancement of Moore's law and …

Design And Development Of Strong And Ductile Single Bcc Refractory High-Entropy Alloys For High-Temperature Applications, Chanho Lee

Doctoral Dissertations

The objectives of this proposed study are to (1) design and develop single BCC phase refractory high-entropy alloys (HEAs) for the high-temperature applications, (2) investigate the deformation mechanisms of refractory HEAs, (3) improve an integrated approach, coupling focused experiments and theoretical modeling, to design, discover, and develop HEAs, and (4) understand the alloy design-microstructure-property-performance links underlying the mechanical behavior of refractory HEA systems for gas-turbine applications

A traditional alloy system generally includes one or two principal elements that form the matrix with other additional elements, e.g., iron or aluminum alloys, to strengthen some specific properties, such as strength and corrosion …

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 …

Manufacturing Of Carbon-Based Hybrid Nanocomposites With Engineered Functionalities Via Laser Ablation Synthesis In Solution (Lasis) Techniques, Erick Leonardo Ribeiro

Doctoral Dissertations

Carbon-based composite materials have long been fabricated and extensively used in our daily lives. In the past decades, with rapid development of nanotechnology, these class of material have gained even more attention owing to their outstanding properties which directly results in their prospects to revolutionize technological development in many fields, ranging from medicine to electronics. Nevertheless, for certain applications, including electrochemical energy storage/conversion devices, the chemically inert nature of these materials creates obstacles and thus requires their coupling with other active species. This thesis explores the use of Laser Ablation Synthesis in Solution (LASiS) in tailoring promising strategies and pathways …

Leveraging Conventional Internet Routing Protocol Behavior To Defeat Ddos And Adverse Networking Conditions, Jared M. Smith

Doctoral Dissertations

The Internet is a cornerstone of modern society. Yet increasingly devastating attacks against the Internet threaten to undermine the Internet's success at connecting the unconnected. Of all the adversarial campaigns waged against the Internet and the organizations that rely on it, distributed denial of service, or DDoS, tops the list of the most volatile attacks. In recent years, DDoS attacks have been responsible for large swaths of the Internet blacking out, while other attacks have completely overwhelmed key Internet services and websites. Core to the Internet's functionality is the way in which traffic on the Internet gets from one destination …

A Datacentric Algorithm For Gamma-Ray Radiation Anomaly Detection In Unknown Background Environments, James M. Ghawaly Jr

Doctoral Dissertations

The detection of anomalous radioactive sources in environments characterized by a high level of variation in the background radiation is a challenging problem in nuclear security. A variety of natural and artificial sources contribute to background radiation dynamics including variations in the absolute and relative concentrations of naturally occurring radioisotopes in different materials, the wet-deposition of $^{222}$Rn daughters during precipitation, and background suppression due to physical objects in the detector scene called ``clutter." This dissertation presents a new datacentric algorithm for radiation anomaly detection in dynamic background environments. The algorithm is based on a custom deep neural autoencoder architecture called …

Exploring The Potentials Of Using Crowdsourced Waze Data In Traffic Management: Characteristics And Reliability, Zhihua Zhang

Doctoral Dissertations

Real-time traffic information is essential to a variety of practical applications. To obtain traffic data, various traffic monitoring devices, such as loop detectors, infrastructure-mounted sensors, and cameras, have been installed on road networks. However, transportation agencies have sought alternative data sources to monitor traffic, due to the high installation and maintenance cost of conventional data collecting methods. Recently, crowdsourced traffic data has become available and is widely considered to have great potential in intelligent transportation systems. Waze is a crowdsourcing traffic application that enables users to share real-time traffic information. Waze data, including passively collected speed data and actively reported …

Exploration Of Thin Films For Neuromorphic, Electrofluidic, And Magneto-Plasmonic Applications, Walker L. Boldman

Doctoral Dissertations

Due to the limit in computing power arising from the Von Neumann bottleneck, computational devices are being developed that mimic neuro-biological processing in the brain by correlating the device characteristics with the synaptic weight of neurons. We demonstrate a platform that combines ionic liquid gating of amorphous indium gallium zinc oxide (aIGZO) thin film transistors and electrowetting for programmable placement/connectivity of the of the ionic liquid. In this platform, both short term potentiation (STP) and long-term potentiation (LTP) are realized via electrostatic and electrochemical doping of the aIGZO, respectively, and pulsed bias measurements are demonstrated for low power considerations. Using …

Cracking And Earing Phenomenon In Deep-Drawn Stainless Steel Alloys: Role Of Transformation Kinetics, Microstructure, And Texture, Peijun Hou

Doctoral Dissertations

The enhancement of formability of advanced high-strength TRIP-assisted steel alloys is a challenging assignment for industrial application due to the cracking phenomenon. The critical factor governing the cracking behavior is residual-stress concentration resulting from the inhomogeneous plastic deformation and microstructural evolution during the forming processes. Martensitic phase transformation kinetics, constituent phases, and crystallographic texture in TRIP-assisted steel alloys are correlated to the microstructure evolution, resulting in phase-specific stress concentration. In the current study, we are aiming at understanding the fundamental mechanisms responsible for the cracking phenomenon and thus improving the formability of TRIP-assisted steel alloys. Four stainless steel (SS) alloys …