Engineering Commons^™

Coordinated Control Of Power Electronic Converters In An Autonomous Microgrid, Gholamreza Dehnavi

Theses and Dissertations

Advances in power electronics and generation technologies have increased the viability of distributed generation systems. A microgrid is a special category of distributed generation systems that is distinguished by its size and the ability to operate independently as an islanded system. As long as a microgrid is connected to a large grid, quality of the voltage is supported by the main grid and each power source connected to the microgrid generates independently. In contrast, in the islanded operation of microgrids and in electrical islands such as shipboard distribution systems, dynamics are strongly dependent on the connected sources and on the …

Passive Equalizer Topology Analysis For Signal Integrity Applications, Kuo-Lun Yen

Theses and Dissertations

In high-speed, high density PCB bus systems, high frequency signal losses and crosstalk can have great impacts on signal integrity and digital timing, which can distort transmitted signals, worsen eye diagrams, and attenuate signal amplitudes. Also, these impacts make digital signals and their energy smearing over multiple bit positions as known as jitters, and cause the phenomenon of inter-symbol interference (ISI) in digital signal transmissions.

The main objective of this thesis is to analyze and develop efficient topology circuits for compensating bus system high frequency losses by using equalization techniques. The thesis has focused on study of various practical and …

Three-Dimensional Evolution Of Mechanical Percolation In Nanocomposites With Random Microstructures, Bethany Suzanne Fralick

Theses and Dissertations

One mechanism that is expected to play a large role in the enhanced, and sometimes novel, mechanical properties of nanocomposites is the probabilistic formation of percolated or connected microstructures. The majority of the models used to describe mechanical percolation have the functional form of a power law and depend on prior knowledge of a percolation threshold or critical volume fraction. While these models have been fairly accurate predictors of electrical conductivity in composites, they do not take any microstructural mechanisms, other than connectivity, into consideration. Classic mean-field micromechanics models, however, do not capture the variability in effective properties due to …

Microstructural-Based Modeling Of Electrical Percolation In Polymer Nanocomposites, Neelima Yellepeddi

Theses and Dissertations

Polymer nanocomposites (PNCs) represent a radical alternative to conventional filled polymers or polymer blends. In contrast to conventional composites, where the included phase is on the order of micrometers, PNCs are defined as those that have discrete constituents on the order of a few hundred nanometers. The value of PNCs is not solely based on tailoring mechanical properties, as in traditional composite design and manufacture, but rather on the potential for the design and optimization of multi-functional properties. There is major interest in these polymeric materials embedded with a conductive nanoscale filler. This is due to the possibility of designing …

Boiling And Evaporation On Micro/Nanoengineered Surfaces, Xianming Dai

Theses and Dissertations

Two-phase transport is widely used in energy conversion and storage, energy efficiency and thermal management. Surface roughness and interfacial wettability are two major impact factors for two-phase transport. Micro/nanostructures play important roles in varying the surface roughness and improving interfacial wettability. In this doctoral study, five types of micro/nanoengineered surfaces were developed to systematically study the impacts of interfacial wettability and flow structures on nucleate boiling and capillary evaporation. These surfaces include: 1) superhydrophilic atomic layer deposition (ALD) coatings; 2) partially hydrophobic and partially hydrophilic composite interfaces; 3) micromembrane-enhanced hybrid wicks; 4) superhydrophilic micromembrane-enhnaced hybrid wicks, and 5) functionalized carbon …

Toward Sophisticated Controls Of Two-Phase Transport At Micro/Nano-Scale, Fanghao Yang

Theses and Dissertations

Through the use of latent heat evaporating, flow boiling in microchannels offers new opportunities to enable high efficient heat and mass transport for a wide range of emerging applications such as high power electric/electronic/optical cooling, compact heat exchangers and reactors. However, flow boiling in microchannels is hampered by several severe constraints such as bubble confinement (e.g., slug flow), viscosity and surface tension force-dominated flows, which result in unpredictable flow pattern transitions and tend to induce severe flow boiling instabilities (i.e. low-frequency and large magnitude flows) and suppress evaporation and convection.

In this dissertation, three novel micro/nanoscale thermo-fluidic control methodologies were …

Multi-Label Segmentation Propagation For Materials Science Images Incorporating Topology And Interactivity, Jarrell Waggoner

Theses and Dissertations

Segmentation propagation is the problem of transferring the segmentation of an image to a neighboring image in a sequence. This problem is of particular importance to materials science, where the accurate segmentation of a series of 2D serial-sectioned images of multiple, contiguous 3D structures has important applications. Such structures may have prior-known shape, appearance, and/or topology among the underlying structures which can be considered to improve segmentation accuracy. For example, some materials images may have structures with a specific shape or appearance in each serial section slice, which only changes minimally from slice to slice; and some materials may exhibit …

Assessing Corrosion Damage In Post -Tensioned Concrete Structures Using Acoustic Emission & A Preliminary Investigation Of Biopolymer Doped Cement Mortar For Use In Structural Restoration, Aditya Appalla

Theses and Dissertations

A sizeable portion of the civil infrastructure is made from concrete. An estimate shows that about 7 billion cubic meters of concrete is made annually worldwide. With the deterioration of the infrastructure due to aging or external factors, significant monetary and technological investment is needed for condition evaluation, maintenance and repair. Two areas that account for a considerable portion of this investment are condition evaluation for maintenance of corroded concrete structures and mortar patching for repair and rehabilitation.

The primary method of evaluation of a structure is by visual inspection. But this method is limited as some crucial areas in …

Effect Of Nanoparticle Size, Support, And Potassium Dopant On Ruthenium Activity For Levulinic Acid (La) Hydrogenation To Γ-Valerolactone (Gvl), Shuo Cao

Theses and Dissertations

The purpose of this thesis is to study the effect of nano-particle size, support and potassium dopant on ruthenium activity on the levulinic acid (LA) hydrogenation to ã-valeroactone (GVL).In hydrogenation reaction, H2 as the gas phase reactant reacts with the metal atoms at the surface of particle size, thus a high level of metal dispersion is critical to maximize the amount of atoms on the surface. This reaction has been widely investigated by varied metal supported catalysts and proved that Ru is the most active metal for it. However, most of researchers only focused on the reaction pathway, rather than …

New Approach For Modeling Hybrid Pressure Swing Adsorption-Distillation Processes, Fan Wu

Theses and Dissertations

A new methodology for modeling hybrid pressure swing adsorption (PSA)-distillation processes has been developed. Two hybrid systems were simulated as examples. One is for ethanol dehydration, and the other is for propane/propylene separation. Firstly, a distillation process simulator such as Chemsep was used to simulate the distillation process of the hybrid system, in which the PSA unit was treated as a "black box" with an assumed process performance. In this way, a hybrid PSA-distillation process can be analyzed simply by performing mass balances around these units and running Chemsep to determine the possibility of energy saving compared to a reference …

Effect Of Matrix Modulus On Cancer Stem Cells And Tumorsphere Formation In Three-Dimensional-Engineered Matrix, Samaneh Kamali Sarvestani

Theses and Dissertations

Maintenance of cancer stem cells (CSCs) is regulated by their microenvironment. As cancer cells are affected by many factors in their microenvironment, a major challenge is to isolate the effect of a specific factor on cancer stem cells (CSCs) while keeping other factors unchanged. We have developed a synthetic inert 3D polyethylene glycol diacrylate (PEGDA) gel culture system as a unique tool to study the effect of microenvironmental factors on CSCs response. Synthetic hydrogels provide the flexibility to design three-dimensional (3D) matrices to isolate and study individual factors in the tumor microenvironment.

The objective of this work was to investigate …

Polyspectral Signal Analysis Techniques For Condition Based Maintenance Of Helicopter Drive-Train System, Mohammed Ahmed Hassan Mohammed

Theses and Dissertations

For an efficient maintenance of a diverse fleet of air- and rotorcraft, effective condition based maintenance (CBM) must be established based on rotating components monitored vibration signals.

In this dissertation, we present theory and applications of polyspectral signal processing techniques for condition monitoring of critical components in the AH-64D helicopter tail rotor drive train system. Currently available vibration-monitoring tools are mostly built around auto- and cross-power spectral analysis which have limited performance in detecting frequency correlations higher than second order. Studying higher order correlations and their Fourier transforms, higher order spectra, provides more information about the vibration signals which helps …

Impedance Estimation Using Randomized Pulse Width Modulation And Power Converters, William M. Mccoy

Theses and Dissertations

With the adoption of technologies such as alternative energy production, DC power grids, and electric vehicles, the use of high power switching converters has seen a dramatic increase. These power converters serve many rolls such as grid-tied inverters in solar farms, high power charging for electric vehicles, motor drives for industrial applications, and DC links in transmission systems. With the increased prevalence of such devices, it is only natural to attempt to optimize their operation. As with any level of converter, it is desirable to have accurate control over the generated voltages and currents. Often, these controllers implement some form …

Crystal Growth, Characterization And Fabrication Of Cdznte-Based Nuclear Detectors, Ramesh Madhu Krishna

Theses and Dissertations

In today's world, nuclear radiation is seeing more and more use by humanity as time goes on. Nuclear power plants are being built to supply humanity's energy needs, nuclear medical imaging is becoming more popular for diagnosing cancer and other diseases, and control of weapons-grade nuclear materials is becoming more and more important for national security. All of these needs require high-performance nuclear radiation detectors which can accurately measure the type and amount of radiation being used. However, most current radiation detection materials available commercially require extensive cooling, or simply do not function adequately for high-energy gamma-ray emitting nuclear materials …

High Resistivity Amorphous Selenium Alloy Semiconductors For Radiation Detection Applications, Abhinav Mehta

Theses and Dissertations

High resolution noninvasive tools of diagnosis has always derived and enabled scientific and medical research to probe and better understand subtleties of matter, intangible to the human eye. Radiation detection systems are highly dependent on advancements in materials and devices with front-end electronics. There are various discrete applications of these radiation detectors and each application imposes certain requirements so there is no single optimum radiation detector.

Flat panel x-ray imagers have gained high demand in the past decade because of exponential improvement in readout electronics. We have synthesized and investigated stabilized amorphous selenium (a-Se) alloys suitable for high resolution flat …

Iii-V Nitride Micro- And Nano-Scale Cantilevers For Multimodal Sensing Applications, Ehtesham Bin Quddus

Theses and Dissertations

Recent research trends in chemical and biological sensing have been geared toward developing molecular sensor devices that are fast, label free, miniaturized and portable. The performance of these devices can be dramatically improved by utilizing multimodal detection techniques, new materials and micro-/nanofabrication technologies. This is especially true for micro-/nanoscale cantilever sensors, which undergo changes in mechanical or electrical properties upon the specific binding of molecules. To develop the sensor devices with the above attributes, we utilized III-V nitride materials: InN nanowires for realizing nanoscale cantilevers and AlGaN/GaN heterostuctures with or without embedded HFETs, for developing microcantilevers. There are mainly two …

Wireless Pressure Sensor System For Medical Applications, Xuehe Wang

Theses and Dissertations

Telemedicine in the modern era is a rapidly developing industry. In a telemedicine system, sensor is the key elements and play important role in any telemedicine applications, especially implantable sensors. Unlike traditional in vitro sensors, there are some special requirements for them like battery-less, compact, and bio-friendly. Therefore, many researchers in institutes as well as in industry are continually developing implantable sensor and sensor system to fulfill the requirements of medical applications.Nine in one thousand people in the United States are born with congenital heart defects and sixty percent die before one year old. As a result, it will be …

Stabilizing Controller Design For A Dc Power Distribution System Using A Passivity-Based Stability Criterion, Antonino Riccobono

Theses and Dissertations

In modern times there has been an increased penetration of power electronic converters into Power Distribution Systems. In particular, there has been a strong interest in DC Power Distribution Systems as opposed to conventional AC Power distribution systems. These DC Power Distribution Systems are enabled by power electronics converters. The strong interest is motivated by improvements in power electronic converter technology, like advances in power semiconductor devices, magnetics, control, and converter topologies which have made possible to build high-performance converters at low cost. In many systems, such as cars, ships and airplanes, there has also been a trend towards the …

High Quality Silicon Carbide Epitaxial Growth By Novel Fluorosilane Gas Chemistry For Next Generation High Power Electronics, Tawhid Rana

Theses and Dissertations

High quality, thick (~100µm), low doped and low defect density SiC epitaxial films are essential for high voltage (blocking voltage >10kV), light, compact and reliable next generation power devices. One of the significant challenges in obtaining high quality thick SiC epitaxial films is to restrict/eliminate the Si gas-phase nucleation or aerosol formation during growth. The generated aerosol particles adversely influence growth by reducing the growth rate due to precursor losses, and also affect crystal quality, since the Si droplets are carried to the crystal growth surface. Moreover, liquid aerosol particles adhere to the various reactor parts (parasitic deposition), and contribute …

Experimental And Simulation Predicted Crack Paths For Al-2024-T351 Under Mixed-Mode I/Ii Fatigue Loading Using An Arcan Fixture, Eileen Miller

Theses and Dissertations

Mixed mode I/II fatigue experiments and simulations are performed for an Arcan fixture and a 6.35mm thick Al-2024-T351 specimen. Experiments were performed for Arcan loading angles that gave rise to a range of Mode I/II crack tip conditions from 0 ¡Ü ¦¤KII/¦¤KI ¡Ü ¡Þ. Measurements include the crack paths, loading cycles and maximum and minimum loads for each loading angle. Simulations were performed using three-dimensional finite element analysis (3D-FEA) with 10-noded tetrahedral elements via CRACK3D. While modeling the entire fixture-specimen geometry, a modified version of VCCT with automatic crack tip re-meshing and a maximum normal stress criterion were used to …

Studying On Capacity Fade Mechanisms Of Li-Ion Batteries Through Modeling, Yiling Dai

Theses and Dissertations

Li-ion batteries are promising candidates as power sources for hybrid electric/electric vehicles, as well as storage devices for renewable energies (wind, solar). Longer life batteries are more desirable for large-scale application, which would help lower the capital cost ($/KW) and improve the system stability. However, the aging problem of Li-ion batteries obstructs their fast penetration into these markets. The cell life can be improved based on an in-depth understanding of the fade mechanisms. The purpose of this dissertation is to explore, through a mathematical modeling approach, failure mechanisms of Li-ion batteries.

To study the capacity fade of a LiMn2O4 (LMO) …

Development Of High-Throughput Catalyst Screening For Ammonia Based Selective Catalytic Reduction Of Nitric Oxide With Parallel Analysis Using Fourier Transform Infrared Imaging, Shahriar Salim

Theses and Dissertations

Lean-burn engines, which operate under excess air to fuel ratio offer significant fuel efficiency as well as contribute to the reductions of greenhouse gas emissions. However, lean burn engines produce three main pollutants carbon monoxide (CO), nitrogen oxides (NOx) and unburned or partially burned hydrocarbons (HC), which have detrimental effect on both environment and human life. The conventional three way catalyst (TWC) which was designed to reduce NOx under stoichiometric conditions is not effective under lean-burn engine exhaust condition. Recent studies have shown that copper (Cu) exchanged chabazite (CHA) type zeolites are very promising catalysts for urea or ammonia (NH3) …

Structural Health Monitoring Of Concrete Systems, Matthew Kelly Jones

Theses and Dissertations

Concrete material is widely used around the world for the construction of many infrastructure including highway bridges, residential and commercial building, dams, electric power generation plants, and nuclear power plants. It is therefore practical to continue development of both improved structural systems as well as innovative condition assessment techniques for new and existing concrete structures. This thesis includes two studies which focus on structural health monitoring of concrete systems. The first project deals with performance assessment of an in-situ precast approach slab system and the second is an investigation of acoustic emission (AE) as a condition assessment technique for alkali-silica …

Efficient Generation Of Power In Medium Voltage Direct Current Systems: Variable Speed Operation And Rectifier Considerations, Dan Li

Theses and Dissertations

By investigating variable speed operation of an engine and different types of ac-dc rectifier topologies, this dissertation provides procedures to develop and implement efficient Medium Voltage Direct Current (MVDC) power systems. The research reported here offered solutions to the following issues:

1) Efficiency improvement of a gas turbine by running it in variable speed operation mode.

2) The advantages and disadvantages of different ac-dc rectifier topologies considering both the efficiency and rectifier performance (dc bus voltage regulation, weight/size/volume of passive components, number of semi-conductor devices, displacement power factor, complexity of control strategy, etc.)

3) Implementation of variable speed MVDC power …

Optimal Design And Control Of Dc-Dc Resonant Converters For Wireless Power Transfer Applications, Isaac Nam

Theses and Dissertations

Wireless power transfer (WPT) technology provides galvanic isolation for improved safety and also provides reliability by eliminating the need for dedicated connectors/adapters that can get damaged due to frequent usage. For these reasons, it has become popular in medical implant charging and electric vehicle (EV) charging. Beyond these niche applications, due to aesthetic features and convenience provided by the cord-free environment, it is rapidly becoming an attractive charging solution for various portable electronics as well as household appliances. However, currently available WPT technology demonstrates several shortcomings and various challenges due to allowed receiver position variation with respect to transmitter position. …

Squeeze Flow Of Highly Concentrated Suspensions, Mohsen Nikkhoo

Theses and Dissertations

In this thesis we investigated through experiment and model, the anomalous normal stress distribution during constant-force squeeze flow of highly concentrated suspensions. Using pressure-sensitive films the normal stress distribution is measured in suspensions of glass spheres in a Newtonian liquid undergoing constant-force squeeze flow. At volume fractions of solids up to 0.55, the normal stress distribution is independent of volume fraction and almost identical to the parabolic pressure distribution expected for Newtonian fluids. However, at higher volume fractions, the normal stresses become an order of magnitude larger near the center and very low beyond that region. At these high volume …

Numerical Study Of Stable Tearing Crack Growth Events Using The Cohesive Zone Model Approach, Xin Chen

Theses and Dissertations

Numerical analysis of stable tearing crack growth events plays an important role in assessing the structural integrity and residual strength of critical engineering structures. The cohesive zone model (CZM) has been widely applied to simulate fracture processes in a variety of material systems. However, its application to the study of elastic-plastic stable tearing crack growth events in ductile materials, especially under mixed-mode loading conditions, has been limited. The current study is aimed at investigating the applicability of the CZM based approach in simulating mixed-mode stable tearing crack growth events in aluminum alloys. In the simulations, which are carried out using …

Structural Origin Of Mechanical Prowess In Conch Shells, Haoze Li

Theses and Dissertations

Conch shells are natural nanocomposites with an exquisite multiscale hierarchical architecture which exhibit coupled ultrahigh mechanical strength and toughness. What materials design strategy renders conch shells such mechanical prowess? In this study, micro/nanoscale structural and mechanical characterization of conch shells (Busycon carica) has been carried out. We demonstrate, for the first time, direct evidence that the previously claimed single-crystal third-order lamellae - the basic building blocks in conch shells are essentially assembled with aragonite nanoparticles of the size ranging from 20 to 45 nm. The third-order lamellae exhibit not only elasticity but also plasticity with the strain up to 0.7% …

Synthesis And Characterization Of One Dimensional Boron-Based Nanomaterials, Rui Li

Theses and Dissertations

One dimensional (1D) metal borate and boride nanomaterials have attracted tremendous attention due to their good chemical inertness, high-temperature stability, excellent mechanical properties, and low thermal expansion coefficient.

Beta-BaB2O4 (BBO) is a well-known nonlinear optical material with a high second-order nonlinear susceptibility, wide transparency range, and high damage threshold. Using a low temperature, organic-free hydrothermal technique, single-crystalline barium polyborate Ba3B6O9(OH)6 (BBOH) nanorods were synthesized. It was found that BBO nanospindles can be achieved by annealing the BBOH nanorods at a relatively low temperature of 810 oC. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques were …

Parsing The Effects Of Physical Microenvironmental Cues On Stem Cell Adhesion And Lineage Specification, Greg M. Harris

Theses and Dissertations

Tissue engineering is a broad field geared toward improving or replacing biological material and comprises an immense collection of biological nuances to consider before strategies for clinical applications can be fully realized. Physical and biochemical signals are responsible for making up a cell's microenvironment to guide morphology and function through cell-extracellular matrix signaling, cell-cell signaling, and soluble signaling. In particular, a deeper understanding of these cell-extra cellular matrix factors guiding stem cell adhesion, spreading, and differentiation is crucial to harnessing the potential to develop tissue for regenerative purposes. Mounting evidence suggests that physical cues are a key to understanding the …