Engineering Commons^™

A Study Of Nonlinear Combustion Instability, Eric J. Jacob

Doctoral Dissertations

Combustion instability (CI) has been persistent in all forms of propulsion since their inception. CI is characterized by pressure oscillations within the propulsion system. If even a small fraction of the dense energy within the system is converted to acoustic oscillations the system vibrations can be devastating. The coupling of combustion and fluid dynamic phenomena in a nonlinear system poses CI as a significant engineering challenge.

Drawing from previous analysis, second order acoustic energy models are taken to third order. Second order analysis predicts exponential growth. The addition of the third order terms capture the nonlinear acoustic phenomena (such as …

Congestion And Price Prediction In Locational Marginal Pricing Markets Considering Load Variation And Uncertainty, Rui Bo

Doctoral Dissertations

This work investigates the prediction of electricity price and power transmission network congestions under load variation and uncertainty in deregulated power systems. The study is carried out in three stages.

In the first stage, the mathematical programming models, which produce the generation dispatch solution, the Locational Marginal Price (LMP), and the system statuses such as transmission congestions, are reviewed. These models are often referred to as Optimal Power Flow (OPF) models, and can be categorized into two major groups: Alternating Current OPF (ACOPF) and Direct Current OPF (DCOPF). Due to the convergence issue with the ACOPF model and the concern …

Automated Correction And Optimized Contrast Enhancement Of Multi-Line Ccd Images, Zhiyu Chen

Doctoral Dissertations

This dissertation addresses automated correction and optimized contrast enhancement of multi-line CCD images for inspection and surveillance applications, focusing on three topics: multi-line CCD imaging systems setup, automated correction of multi-line CCD images, and automatic optimized image contrast enhancement.

generation, low cost, etc. However, due to the physical separation of line CCD sensors for the red (R), green (G), blue (B) color channel, the color images acquired by multi-line CCD cameras intrinsically exhibit a color misalignment defect, which is expressed as that the edges of objects in the scene are separated by a certain number of pixels in the R, …

Effects Of Overload And Underload On Internal Strains/Stresses And Crack Closure During Fatigue-Crack Propagation, Soo Yeol Lee

Doctoral Dissertations

The overload and/or underload occurring during constant-amplitude fatiguecrack growth result in the retardation and/or acceleration in the crack-growth rate, making it difficult to predict the crack-propagation behavior and fatigue lifetime. Although there have been numerous investigations to account for these transient crackgrowth behavior, the phenomena are still not completely understood.

Neutron and X-ray diffraction, and electric-potential measurements were employed to investigate these transient crack-growth micromechanisms; gain a thorough understanding of the crack-tip deformation and fracture behaviors under applied loads; and establish a quantitative relationship between the crack-tip-driving force and crack-growth behavior. Five different fatigue-crack-growth experiments (i.e., fatigued, tensile overloaded, compressive …

An Automated Diagnostic Tool For Predicting Anatomical Response To Radiation Therapy, Carley Elizabeth Harris

Doctoral Dissertations

A "Clinical Decision Support System" (CDSS) is a concept which has advanced rapidly in health care over the last few decades, and it is defined as "an interactive computer program that is designed to assist physicians and other health professionals with decision-making tasks." Radiation therapy oncologists are required to make decisions that do not involve making a disease diagnosis. Therefore this work focuses on developing a modified CDSS which can be used to aid oncology staff in identifying cancer patients who will require adaptive radiation therapy (ART).

An image-guided radiation therapy (IGRT) tool was developed that consists of both diagnostic …

Development And Analysis Of Interior Permanent Magnet Synchronous Motor With Field Excitation Structure, Seong Taek Lee

Doctoral Dissertations

Throughout the years Hybrid Electric Vehicles (HEV) require an electric motor which has high power density, high efficiency, and wide constant power operating region as well as low manufacturing cost. For these purposes, a new Interior Permanent Magnet Synchronous Motor (IPMSM) with brushless field excitation (BFE) is designed and analyzed. This unique BFE structure is devised to control the amount of the air-gap flux for the purpose of achieving higher torque by increasing the air-gap flux at low speed and wider operating speed range by weakening the flux at high speed.

On the process of developing the new IPMSM, the …

Experimental And Theoretical Investigation Of Adsorption Of Water Vapor On Carbon Nanotubes, Pyoungchung Kim

Doctoral Dissertations

The adsorption of water in nanoporous materials becomes an important issue in the environmental fate and applications when one considers the practical use of these materials as adsorbents for hazardous organic compounds in the diverse environments.

In this study, the complexity of water-SWNTs interaction was investigated by morphological and chemical characterization techniques, by gravimetric adsorption measurement and by interpretation of experimental adsorption isotherms by fitting to several existing semi-empirical water adsorption models. Commercially available SWNTs samples were measured for chemical and physical characterization such as O% by x-ray photoelectron spectroscopy, I_D/I_G by Raman spectroscopy and surface and …

Fundamental Mechanical-Behavior Studies Of Annealed And Nano-Particle-Strengthened Nickel-Based Alloys Using In-Situ Neutron-Diffraction Experiments, E-Wen Huang

Doctoral Dissertations

This dissertation addresses two issues concerning the fundamental mechanical behavior of the nickel-based superalloys: (1) the deformation mechanisms and (2) the nano-precipitate-strengthening effect. The precipitates are known to fortify the mechanical behavior of the metallic alloys. These precipitates can interact with the matrix upon the applied load. While the precipitation strengthening has been facilitated for many purposes, this research puts forward the mechanistic understanding.

The dissertation considers the thesis that Deformation Mechanisms and Nanoprecipitate Strengthening and their effects on the microstructure are central to the mechanical behavior of nickel-based superalloys.

The experimental methods employed in this research are in-situ neutrondiffraction …

Influence Of Turning On Military Vehicle Induced Rut Formation, Kun Liu

Doctoral Dissertations

Rut formation can severely influence soil conditions and vegetation, and reduce vehicle mobility. Vehicle operations can affect rut formation. Ruts formed in straight vehicle paths are different than when the vehicle turns. This research is mainly to investigate the effects of vehicle turning maneuvers on soil rut formation, including field tests, lab tests, and model development.

Field tests were conducted at Yuma Training Center, Fort Riley and Fort Lewis on wheeled and tracked military vehicles. In field tests, rut depth, rut width and rut index were used as the main indicators to quantify a rut. A Vehicle Tracking System was …

Design And Application Of Hybrid Multilevel Inverter For Voltage Boost, Haiwen Liu

Doctoral Dissertations

Today many efforts are made to research and use new energy sources because the potential for an energy crisis is increasing. Multilevel converters have gained much attention in the area of energy distribution and control due to its advantages in high power applications with low harmonics. They not only achieve high power ratings, but also enable the use of renewable energy sources. The general function of the multilevel converter is to synthesize a desired high voltage from several levels of dc voltages that can be batteries, fuel cells, etc.

This dissertation presents a new hybrid multilevel inverter for voltage boost. …

Direct Cooled Ceramic Substrate For Thermal Control Of Automotive Power Electronics, Kirk Townsend Lowe

Doctoral Dissertations

As electric vehicle technology develops, manufacturers would like to move toward hotter coolants for power electronic components to reduce system level costs. Thus, unique designs of inverter designs were sought to enable operation with 105°C coolant. The proposed solution in this research incorporated flow channels into the ceramic layer of the direct-bonded copper substrate typically found in power electronic packages. The focus of this research details the design and analysis of the direct cooled ceramic substrate from the perspective of its thermal performance and innovative packaging concept.

The research was directed to pursue alumina as the substrate ceramic because of …

A Study Of Polymer Electrolyte Membranes And Associated Interfacial Systems Via Molecular Dynamics Simulations, Junwu Liu

Doctoral Dissertations

The development of novel polymer electrolyte membrane (PEM) materials which operate at high temperature (i.e. > 100˚C) and low humidity conditions and efficiently transport protons has been a major focus for PEM fuel cell technology. The motivation behind a high temperature PEM fuel cell is based on the fact that, at high temperature, the catalysts used in the fuel cell are more active and less susceptible to poisoning due to impurities in the feed stream. The challenge lies in the fact that as the temperature is increased, the membrane loses water and its ability to transport protons. The successful design and …

Structural Health Monitoring And Damage Evaluation Of Full-Scale Bridges Using Triaxial Geophones: Controlled In-Situ Experiments And Finite Element Modeling, William S. Ragland Ii

Doctoral Dissertations

The purpose of this study was to evaluate the effectiveness of various vibration-based damage detection methods using triaxial vibration records obtained using inexpensive geophones during in-situ, full-scale, damaged bridge tests.

Geophones are passive directional sensors and much cheaper than accelerometers which are typically used for structural vibration measurements. However, magnitude and phase errors associated with a geophone’s output must be corrected for if they are implemented in bridge monitoring systems. This research discusses correction procedures for magnitude and phase errors associated with geophones. A simply supported beam was analyzed to verify that the correction procedures and modal parameter identification procedures …

Localized Deformation In Metallic Glasses At The Ambient Temperature, Shuangxi Song

Doctoral Dissertations

Metallic glasses have many unusual properties, such as extremely high strength and large elastic limit. However, they are also brittle, failing in a catastrophic manner, as a result of the formation of highly localized shear bands at room temperature. Such flow localization has been attributed to the influence of strain softening or local heating, or a combination of both, which leads to the local drop in viscosity and, finally, the runaway of the shear band.

In this thesis, a novel method was developed for in situ observation of the localized shear processes. The inhomogeneous deformation of metallic glasses at room …

Development Of Dbt Bridge System With Continuous Joints For Accelerated Construction, Lungui Li

Doctoral Dissertations

Speed of construction has become a critical issue to minimize disruption of traffic and commerce. One of the promising systems for accelerated bridge construction is the use of the decked bulb-tee (DBT) girders for the bridge superstructure. An integral deck that is precast and prestressed with the girder provides benefits of rapid construction along with improved structural performance. However, the limited research and concerns about the use of longitudinal joints as well as intermediate diaphragms limit widespread of the DBT bridge system.

This dissertation presents a study of the continuous for both moment and shear transfer longitudinal joint detail and …

Mechanical Behavior And The Role Of Deformation Twinning In Wrought Magnesium Alloys Investigated Using Neutron And Synchrotron X-Ray Diffraction, Liang Wu

Doctoral Dissertations

The mechanical behaviors and the associated deformation mechanisms with a focus on extension twinning under monotonic and cyclic loadings are investigated using neutron and synchrotron diffractions in the wrought magnesium alloys, ZK60A and AZ31B. It has been demonstrated that the extension twinning plays significant roles in the mechanical behaviors.

The significant tension-compression asymmetries and high anisotropies are observed. The tension-compression asymmetries are related to the twinning activation in one direction but not in the opposite direction. The high anisotropies are correlated with the initial texture distinction relative to the loading directions. The similar yielding stresses are noted irrespective of the …

Automated System To Debug Under-Performing Network Flows In Wide Area Networks, Harika Tandra

Masters Theses

Locating the cause of performance losses in large high performance Wide Area Networks (WAN) is an extremely challenging problem. This is because WANs comprise several distributed sub-networks (Autonomous Networks), with their own independent network monitoring systems. Each individual monitoring system has limited or no access to network devices outside its own network. Moreover, conventional network monitoring systems are designed only to provide information about the health of individual network devices, and do not provide sufficient information to monitor endto- end performance – thus, adding severe overhead on debugging end-toend performance issues.

In this thesis, an automated tool is designed that …

Characterizing Episodic Stream Acidification Using A Concentration-Duration-Frequency Methodology In Watersheds Of The Great Smoky Mountains National Park, John Leland Mauney Iii

Masters Theses

Episodic stream acidification occurs as storm events temporarily reduce acid neutralizing capacity and pH. Stream acidification is suspected to have damaging effects on the health of aquatic ecosystems and biota and is dependent on various watershed characteristics such as drainage area, elevation, slope, and surficial geology. Here, a stochastic modeling approach is applied to continuous pH data for multiple stream monitoring sites within the Great Smoky Mountains National Park in order to characterize episodic acidification responses during stormflows for different streams. The approach summarizes voluminous pH data recorded by water quality sondes at 15-minute intervals into concentration-duration-frequency relationships. Unique to …

Integral Formulation Of The Compressible Flowfield In Solid Rocket Motors, Michel Henry Akiki

Masters Theses

In this thesis, a semi-analytical formulation is provided for the rotational, steady, inviscid, compressible motion in a solid rocket motor that is modeled as a slender porous chamber. The analysis overcomes some of the deficiencies encountered in previous work on the subject. The method that we employ consists of reducing the problem’s mass, momentum, energy, ideal gas, and isentropic relations into a single integral equation that can be solved numerically. Furthermore, Saint-Robert’s power law is used to link the pressure to the sidewall mass injection rate. At the outset, results are presented for the axisymmetric and planar porous chambers and …

Design And Implementation Of A High Temperature Fully-Integrated Bcd-On-Soi Under Voltage Lock Out Circuit, Nora Dianne Bull

Masters Theses

As concern about the environment has grown in recent years, alternatives in the automotive industry have become an important topic for researchers. One alternative being considered is electric vehicles, which utilize electric motors. DC/AC inverters and DC/DC power converters control these electric motors. A logic circuit is needed to power these converters; however, the logic generators inherently operate at a voltage too low to power the motors. A device known as the gate driver is the interface between the logic generators (or microcontroller) and the power devices (power converter). The gate driver provides the power needed to drive the power …

Vibration Analysis Of Heavy-Duty Diesel Vehicles, Christopher Jack Campbell

Masters Theses

Truck drivers are more susceptible than other workers to lower back pain and spinal disorders caused by whole body vibrations, which are among the most common long term health effects for drivers. The dynamic behavior of trucks can be modeled and simulated to improve the design of the trucks, which can reduce the exposure of drivers to whole body vibrations.

The main purposes of this study are to analyze vibrations for different manufacturers and road types, and to create a computer-based model using Adams to predict vibration anywhere on the model using acceleration data collected previously from on-road tests of …

A Business Process Modeling Approach For Evaluating A Government Contract Closeout Process, Clayton Jerrett Capizzi

Masters Theses

This thesis examines the practice of Business Process Modeling (BPM) in the field of contracts management. Government defense contractors are heavily burdened by contracts which have ended, but have not been finalized and closed. In order to keep good relations with organizations regulating government contracts, contractors have been forced to devise a strategy to address contract closeouts. Through utilization of BPM practices, an organization is able to not only model the flow of their contract closeout process, but simulate the performance of their process under varying conditions so that goals and deadlines may be met. Data was collected about a …

Export Of Carbon, Nutrients And Microbiological Indicators In Beaver Creek Watershed, Tennessee, Si Chen

Masters Theses

Storms are the most important events impacting stream water quality at the watershed-scale. With the goal to develop effective water resource management strategies for the impaired Beaver Creek Watershed in East Tennessee, the impacts of storm events on water quality were assessed by monitoring the intra-storm dynamics of the export of carbon, nutrients, and microbiological indicators (E. coli), which are parameters critical to water quality and ecological functions of the target watershed. The dynamics of carbon export from the Beaver Creek Watershed as represented by dissolved organic carbon revealed distinct carbon transport mechanisms as a function of storm …

A Condition Assessment Process For Aerospace Ground Test Systems, Larry Michael Davis

Masters Theses

This research developed a process to identify condition deficiencies and sustainment requirements to assist in the development of strategic management plans for aerospace ground test systems that may be unique in design, operation, and/or maintenance.

Subject matter experts can use the process to evaluate the condition of a test asset by inputting data into the developed software system. The process was designed around the concept of evaluating the condition of a system against ten parameters that encompass all of the aspects of a system that would be considered in determining its overall condition. A scale of zero (failed) to ten …

Identification And Quantification Of Cotton Yield Monitor Errors, Jason Clay Head

Masters Theses

Cotton yield monitors are an important part of a precision agriculture program and are becoming widely used by cotton producers for making management decisions. Members of the cotton industry have shown interest in using cotton yield monitors for collecting data from production scale variety yield trials (experiments that test yield performance for numerous varieties). Weighing boll buggies are the current industry standard for measuring yield in variety trials. This process is time consuming and requires extra equipment and labor. The ability to use a yield monitor for measuring yield would streamline variety trial harvesting. Recommendations for the Ag Leader cotton …

Accelerating The Stochastic Simulation Algorithm Using Emerging Architectures, David Dewayne Jenkins

Masters Theses

In order for scientists to learn more about molecular biology, it is imperative that they have the ability to construct and evaluate models. Model statistics consistent with the chemical master equation can be obtained using Gillespie's stochastic simulation algorithm (SSA). Due to the stochastic nature of the Monte Carlo simulations, large numbers of simulations must be run in order to get accurate statistics for the species populations and reactions. However, the algorithm tends to be computationally heavy and leads to long simulation runtimes for large systems. In this research, the performance of Gillespie's stochastic simulation algorithm is analyzed and optimized …

Stream Channel Stability And Channel Evolution In A Rapidly Urbanizing, Ridge-And-Valley Watershed, Beaver Creek, Knox County, Tennessee, Francis Bartholomew Keaney

Masters Theses

In Tennessee, sedimentation is among the leading causes of stream impairment. Excessive loads of alluvium are detrimental to the ecological health and human use of these resources. Sediments in streams have many sources, but there is evidence that stream bank erosion is a major contributing factor. Development and urbanization in a stream’s watershed will have impacts on the concentration of stream sediment because the increase in the area covered by impervious surfaces, which reduces initial abstraction and retention times. This, in turn will increase the peak storm water discharge and sediment carrying capacity. If the stream channel cannot accommodate these …

Development And Testing Of A Self-Contained, Portable Instrumentation System For A Fighter Pilot Helmet, Michael Anthony Kamp

Masters Theses

A self-contained, portable, inertial and positional measurement system was developed and tested for an HGU-55 model fighter pilot helmet. The system, designated the Portable Helmet Instrumentation System (PHIS), demonstrated the recording of accelerations and rotational rates experienced by the human head in a flight environment. A compact, self-contained, “knee-board” sized computer recorded these accelerations and rotational rates during flight. The present research presents the results of a limited evaluation of this helmet-mounted instrumentation system flown in an Extra 300 fully aerobatic aircraft. The accuracy of the helmet-mounted, inertial head tracker system was compared to the aircraft-mounted referenced system. The ability …

A Study To Evaluate The Suitability Of A Centrifuge As A Dynamic Flight Simulator For F/A-18 Strike Fighter Mission Training, Richard Michael Masica

Masters Theses

The purpose of this study was to evaluate the suitability of using an existing 25-ft radius centrifuge as a dynamic flight simulator for “full mission” F/A-18 strike fighter mission training with respect to the representativeness of pilot-perceived motion and acceleration cues.

The methodology employed in this study consisted of analyzing F/A-18 mission tasks, collecting pilot opinion surveys of important sensory cues needed in simulator training, and conducting an analysis of human pilot perceptual problems caused by centrifuge motion constraints.

This study identified a number of issues indicating that a centrifuge-based flight simulator shows limited potential for use in “full mission” …

Vision-Based Reinforcement Learning Using A Consolidated Actor-Critic Model, Christopher Allen Niedzwiedz

Masters Theses

Vision-based machine learning agents are tasked with making decisions based on high-dimensional, noisy input, placing a heavy load on available resources. Moreover, observations typically provide only partial information with respect to the environment state, necessitating robust state inference by the agent. Reinforcement learning provides a framework for decision making with the goal of maximizing long-term reward. This thesis introduces a novel approach to vision-based reinforce- ment learning through the use of a consolidated actor-critic model (CACM). The approach takes advantage of artificial neural networks as non-linear function approximators and the reduced com- putational requirements of the CACM scheme to yield …