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 …

Radiation Detectors And Sources Enhanced With Micro/Nanotechnology, Chad Michael Whitney

Doctoral Dissertations

The ongoing threat of nuclear terrorism presents major challenges to maintaining national security. Currently, only a small percentage of the cargo containers that enter America are searched for fissionable bomb making materials. This work reports on a multi-channel radiation detection platform enabled with nanoparticles that is capable of detecting and discriminating all types of radiation emitted from fissionable bomb making materials. Typical Geiger counters are limited to detecting only beta and gamma radiation. The micro-Geiger counter reported here detects all species of radiation including beta particles, gamma/X-rays, alpha particles, and neutrons. The multi-species detecting micro-Geiger counter contains a hermetically sealed …

Improvement Of Eeg Based Brain Computer Interface By Application Of Tripolar Electrodes And Independent Component Analysis, Hongbao Cao

Doctoral Dissertations

For persons with severe disabilities, a brain computer interface (BCI) may be a viable means of communication, with scalp-recorded electroencephalogram (EEG) being the most common signal employed in the operation of a BCI. Various electrode configurations can be used for EEG recording, one of which was a set of concentric rings that was referred to as a Laplacian electrode. It has been shown that Lapalacian EEG could improve classification in EEG recognition, but the complete advantages of this configuration have not been established.

This project included two parts. First, a modeling study was performed using Independent Component Analysis (ICA) to …

Coupled Flow Discrete Element Method Application In Granular Porous Media Using Open Source Codes, Feng Chen

Doctoral Dissertations

The flow of fluid through an assembly of particles is of interest to a range of fields such as civil engineering, powder technology, and liquid chromatography. The Discrete Element Method (DEM) is a numerical approximation used to model the interaction of particles and fluid. This study starts with the verification of the open source 3D DEM code (YADE) by investigating simple, one and two-particle contact problems, and DEM results are shown to compare very well with the classical 1D vibration solutions.

2D and 3D simulations of particles flowing through a hopper were then investigated. The stability of the sinkhole repair …

Scheduling For Service Stability And Supply Chain Coordination, Yuerong Chen

Doctoral Dissertations

This dissertation studies scheduling for service stability and for supply chain coordination as well. The scheduling problems for service stability are studied from the single perspective of a firm itself, while the scheduling problems for supply chain coordination are investigated from the perspective of a supply chain. Both the studies have broad applications in real life.

In the first study, several job scheduling problems are addressed, with the measure of performance being job completion time variance (CTV). CTV minimization is used to represent service stability, since it means that jobs are completed in a relative concentrated period of time. CTV …

Automated Surveillance Systems With Multi-Camera And Robotic Platforms, Chung Hao Chen

Doctoral Dissertations

This dissertation addresses automated surveillance systems focusing on four topics: (1) spatial mappings of omnidirectional and PTZ cameras, and PTZ and PTZ cameras; (2) target hopping application for dual camera systems; (3) camera handoff and placement; (4) the mobile tracking platform. The four topics represent four contributions in this dissertation.

Dual camera systems have been widely used in surveillance because of the ability to explore the wide field of view (FOV) of the omnidirectional camera and the wide zoom range of the PTZ camera. Most existing algorithms require a priori knowledge of the projection models of omnidirectional and PTZ cameras …

Accelerating Quantum Monte Carlo Simulations With Emerging Architectures, Akila Gothandaraman

Doctoral Dissertations

Scientific computing applications demand ever-increasing performance while traditional microprocessor architectures face limits. Recent technological advances have led to a number of emerging computing platforms that provide one or more of the following over their predecessors: increased energy efficiency, programmability/flexibility, different granularities of parallelism, and higher numerical precision support. This dissertation explores emerging platforms such as reconfigurable computing using fieldprogrammable gate arrays (FPGAs), and graphics processing units (GPUs) for quantum Monte Carlo (QMC), a simulation method widely used in physics and physical chemistry. This dissertation makes the following significant contributions to computational science. First, we develop an open-source userfriendly hardware-accelerated simulation …

Structure And Properties Of Nanoclay Reinforced Polymer Films, Fibers And Nonwovens, Raghavendra Ratnakar Hegde

Doctoral Dissertations

In this research, influence of different levels of Closite Na⁺ additives on the microstructure, morphology and mechanical properties of polymer products was studied. Importance was given to understand the additive level, extent of dispersion in matrix, change in microstructure and respective property observed in the end product. Polypropylene spunbond and meltblown web samples with various levels of Closite Na⁺ additives were produced and characterized. Injection molded polypropylene nanocomposite with 1 to 15 wt% nanoclay additives were also prepared and characterized for microstructure and mechanical properties.

Crystallization kinetics studies showed significant increase in crystallization rates on nylon 6 even …

An Investigation Of The Transferability Of Trip Generation Models And The Utilization Of Aspatial Context Variable, Jerry Don Everett

Doctoral Dissertations

The cost of collecting data for travel demand modeling is high and increasing each year. Data collection costs could easily exceed the annual budget of a metropolitan planning organization (MPO) in small or medium-sized area. Many of these agencies borrow or transfer data and/or models from other areas since they cannot afford the cost of collecting local data. This study included two primary research objectives. The first was to test the appropriateness of transferring commonly used trip generation models from one urban area to another under specific circumstances. The second was to improve the transferability of models by including a …

Flame Retardant Mattress Pads, Manjeshwar Ganeshaq Kamath

Doctoral Dissertations

Focus of this research is on developing cotton-based nonwoven mattress pads with flame retardant (FR) properties by blending cotton with other commercially available fibers, binders, and followed by chemical treatments; offering a cost-effective recipe to meet the upcoming flammability standards. Furthermore this research explores the opportunities taking advantage of possible synergistic effects to achieve maximum performance.

Recent changes in the flammability regulations require improvements in the flame resistance of cotton-containing consumer goods such as upholstered furniture, mattresses, and pillows. Cotton, synthetic fibers, fabrics, and foam are the basic constituents of these goods that are often the first to be engulfed …

Towards Universality In Automatic Freeway Incident Detection: A Calibration-Free Algorithm, Manoel Mendonca De Castro-Neto

Doctoral Dissertations

Freeway automatic incident detection (AID) algorithms have been extensively investigated over the last forty years. A myriad of algorithms, covering a broad range of types in terms of complexity, data requirements, and efficiency have been published in the literature. However, a 2007 nationwide survey concluded that the implementation of AID algorithms in traffic management centers is still very limited. There are a few reasons for this discrepancy between the state-of-the-art and the state-of the-practice. First, current AID algorithms yield unacceptably high rates of false alarm when implemented in real-world. Second, the complexities involved in algorithm calibration require levels of efforts …

Morphological Characterization Of Irradiated Ultra High Molecular Weight Polyethylene (Uhmwpe), Christopher Phillip Stephens

Doctoral Dissertations

Effects of radiation (gamma and proton) on Ultra High Molecular Weight Polyethylene (UHMWPE) is studied for prosthetic joints and for radiation shielding for manned space missions. The first section of the dissertation will cover gamma radiation effects on UHMWPE by means of solubility, hardness, three-phase model, crystallite thickness, and molecular mobility studies. The second part will cover proton radiation effects on UHMWPE by means of solubility, three-phase crystallite model, and crystallite thickness study. The combined studies of the gamma irradiated samples shows that chain scission occurs on the surface and crosslinking in the center. The combined studies of the proton …

Unique Characteristics Of Liquid Metal Extended Meniscus Evaporation, Joseph Brown Tipton, Jr.

Doctoral Dissertations

The research in this dissertation addresses the steady evaporation of a capillary pore with a liquid metal working fluid. First, the interline region of an extended meniscus thin film is considered for the unique physical case of a liquid metal. A new thin film evaporation model is presented that captures the unsimplified dispersion force along with an electronic disjoining pressure component that is unique to liquid metals. The resulting nonlinear 4th-order ODE is solved using an implicit orthogonal collocation technique along with the Levenberg-Marquardt method. Results show that the electronic component of the disjoining pressure should be considered when modeling …

Forecasting Dose And Dose Rate From Solar Particle Events Using Locally Weighted Regression Techniques, Theodore Franklin Nichols

Doctoral Dissertations

Continued human exploration of the solar system requires the mitigating of radiation effects from the Sun. Doses from Solar Particle Events (SPE) pose a serious threat to the health of astronauts. A method for forecasting the rate and total severity of such events would give time for the astronauts to take actions to mitigate the effects from an SPE. The danger posed from an SPE depends on dose received and the temporal profile of the event. The temporal profile describes how quickly the dose will arrive (dose rate). Previously deployed methods used neural networks to predict the total dose from …

A Current-Mode Multi-Channel Integrating Analog-To-Digital Converter, Neena Balakrishnan Nambiar

Doctoral Dissertations

Multi-channel analog to digital converters (ADCs) are required where signals from multiple sensors can be digitized. A lower power per channel for such systems is important in order that when the number of channels is increased the power does not increase drastically. Many applications require signals from current output sensors, such as photosensors and photodiodes to be digitized. Applications for these sensors include spectroscopy and imaging. The ability to digitize current signals without converting currents to voltages saves power, area, and the design time required to implement I-to-V converters.

This work describes a novel and unique current-mode multi-channel integrating ADC …