Engineering Commons^™

Optimized Techniques For Real-Time Microwave And Millimeter Wave Sar Imaging, Joseph T. Case

Doctoral Dissertations

"Microwave and millimeter wave synthetic aperture radar (SAR)-based imaging techniques, used for nondestructive evaluation (NDE), have shown tremendous usefulness for the inspection of a wide variety of complex composite materials and structures. Studies were performed for the optimization of uniform and nonuniform sampling (i.e., measurement positions) since existing formulations of SAR resolution and sampling criteria do not account for all of the physical characteristics of a measurement (e.g., 2D limited-size aperture, electric field decreasing with distance from the measuring antenna, etc.) and nonuniform sampling criteria supports sampling below the Nyquist rate. The results of these studies demonstrate optimum sampling given …

Risk Analysis: Comparative Study Of Various Techniques, Hanan Mohammad Altabbakh

Doctoral Dissertations

"Researchers in the safety field are facing more challenges everyday with the expanding modern socio-technical systems. Safety analysis such as hazard analysis, accident causation analysis, and risk assessment are being revisited to overcome the shortcoming of the conventional safety analysis. With increasingly complex human system interaction in today's modern systems, new safety challenges are being faced that needed to be assessed and addressed. Managers and engineers face the challenge to choose from the vast amount of techniques available and utilize the correct one. Indeed, new or improved risk assessment tools that can address these complexities are needed. One of the …

Scaleup And Hydrodynamics Study Of Gas-Solid Spouted Beds, Shreekanta Basavaraj Aradhya

Doctoral Dissertations

"A thorough understanding of the complex flow structure of gas-solid spouted bed is crucial for design, scale-up and performance. Advanced gas-solid optical probes were developed and used to evaluate different hydrodynamic parameters of spouted beds. These optical probes measure solids concentration, velocity and their time series fluctuations. Since solids concentration needs to be converted to solids holdup through calibration, for meaningful interpretation of results, a novel calibration method was proposed (which is inexpensive and reliable compared to the current reported methods) and validated in the present study. The reported dimensionless groups approach of spouted bed scale-up was assessed and was …

Approximate Dynamic Programming Based Solutions For Fixed-Final-Time Optimal Control And Optimal Switching, Ali Heydari

Doctoral Dissertations

"Optimal solutions with neural networks (NN) based on an approximate dynamic programming (ADP) framework for new classes of engineering and non-engineering problems and associated difficulties and challenges are investigated in this dissertation. In the enclosed eight papers, the ADP framework is utilized for solving fixed-final-time problems (also called terminal control problems) and problems with switching nature. An ADP based algorithm is proposed in Paper 1 for solving fixed-final-time problems with soft terminal constraint, in which, a single neural network with a single set of weights is utilized. Paper 2 investigates fixed-final-time problems with hard terminal constraints. The optimality analysis of …

Reactive Self-Heating Model Of Aluminum Spherical Nanoparticles, Karen S. Martirosyan, Maxim Zyskin

Physics and Astronomy Faculty Publications and Presentations

Aluminum-oxygen reaction is important in highly energetic and high pressure generating systems. Recent experiments with nanostructured thermites suggest that oxidation of aluminum nanoparticles occurs in a few microseconds. Such rapid reaction cannot be explained by a conventional diffusion-based mechanism. We present a rapid oxidation model of a spherical aluminum nanoparticle, using Cabrera-Mott moving boundary mechanism, and taking self-heating into account. In our model, electric potential solves the nonlinear Poisson equation. In contrast with the Coulomb potential, a “double-layer” type solution for the potential and self-heating leads to enhanced oxidation rates. At maximal reaction temperature of 2000 C, our model predicts …

Source Reconstructions For Ic Radiated Emissions Based On Magnitude-Only Near-Field Scanning, Ji Zhang

Doctoral Dissertations

"In this dissertation, a source reconstruction method is proposed to model the emission behavior of an IC by using magnitude-only information during near-field scanning. The phase-retrieval is accomplished during the back-forth iterations between two scanning planes of different heights. The magnitudes of fields on two planes of different heights are recorded and used to constrain the amplitude of the calculated fields during iterations. Three essential transformations among dipoles and fields are continued at each iteration step, until the convergence condition is achieved. The proposed algorithm has been verified by using a set of dipole-array as the original emitting sources, and …

Paste Development And Co-Sintering Test Of Zirconium Carbide And Tungsten In Freeze-Form Extrusion Fabrication, Ang Li

Masters Theses

"Ultra-high temperature ceramics are being investigated for future use in aerospace applications due to their superior thermo-mechanical properties, as well as oxidation resistance, at temperatures above 2000°C. However, their brittle properties make them susceptible to thermal shock failure. Components fabricated as functionally graded materials (FGMs) can combine the superior properties of ceramics with the toughness of an underlying refractory metal by fabricating graded composites. This paper discusses the grading of two materials through the use of a Freeze-form Extrusion Fabrication (FEF) system to build FGMs parts consisting of zirconium carbide (ZrC) and tungsten (W). Aqueous-based colloidal suspensions of ZrC and …

Manual Modification And Plasma Exposure Of Boron Nitride Ceramic To Study Hall Effect Thruster Plasma Channel Material Erosion, Alexander J. Satonik

Masters Theses

"Worn Hall effect thrusters (HET) show a variety of unique microstructures and elemental compositions in the boron nitride thruster channel walls. Worn thruster channels are typically created by running test thrusters in vacuum chambers for hundreds of hours. Studies were undertaken to manually modify samples of boron nitride without the use of a hall effect thruster. Samples were manually abraded with an abrasive blaster and sandpaper, in addition to a vacuum heater. Some of these samples were further exposed to a xenon plasma in a magnetron sputter device. Sandpaper and abrasive blaster tests were used to modify surface roughness values …

Parameter Optimization For Controlling Aluminum Loss When Laser Depositing Ti-6al-4v, Richard Charles Barclay

Masters Theses

"The ability to predict the mechanical properties of engineering materials is crucial to the manufacturing of advanced products. In the aerospace industry, Ti-6Al-4V is commonly used to build structures. Any deviation from the alloy's standard properties can prove detrimental. Thus, the compositional integrity of the material must be controlled. The ability to directly build and repair large, complicated structures directly from CAD files is highly sought after. Laser Metal Deposition (LMD) technology has the potential to deliver that ability. Before this process can gain widespread acceptance, however, a set of process parameters must be established that yield finished parts of …

Transmission Shaft Design For Hydrokinetic Turbine With Reliability Consideration, Goutham Pusapati

Masters Theses

"Hydrokinetic energy, a relatively new kind of renewable energy, can be generated from flowing water in rivers or oceans. Hydrokinetic turbines (HKTs) are a major system for hydrokinetic energy, and the reliability of the HKTs is critical for both their lifecycle cost and safety. The objective of this work is to apply advanced methodologies of reliability analysis and reliability-based design to the transmission shaft design for a horizontal-axis, non-submerged HKT. The deterministic shaft design is performed first by considering failure modes of strength and deflection using distortion energy, maximum shear and deflection theories. Then the reliability analysis of the shaft …

A Modification Of Freeze-Core Technology For Collecting Granular Fluvial Sediment Samples, David Charles Smith

Masters Theses

"The presence of coarse grained sediment can potentially reduce the effectiveness of conventional sampling methods in recovering fluvial sediments. A modification to freeze-core technology was used to collect fine grained sediments for the purpose of characterizing the extent of heavy metal contamination in fluvial deposits that contain significant amounts of coarse-grained material such as cobbles and boulders. This material greatly reduces the effectiveness of conventional sampling methods. This method uses 2.5-cm and 2.9-cm diameter by 30-cm long finned samplers that were mechanically- and hand-driven into the ground. The sediment is frozen to the outside of the sampler by injecting liquid …

Parallel-Connected Solar Arrays, Majed Meshal Alabbass

Masters Theses

"The purpose of this thesis is to investigate the advantages of having various series-parallel configurations of solar arrays and make a comparison between them. The objective is to determine the best PV system configuration and thus improve the overall efficiency of a solar array. The primary focus of this thesis is to study the parallel connection of PV panels for achieving maximum efficiency while extracting maximum energy from the solar radiation. A comparison between a series connected and a parallel connected solar PV array justifies the need for installing a parallel configured solar PV array to achieve optimum performance. The …

Fabry-Perot Interferometer Based Co₂ Sensor Using Ionic-Liquid, Mujahid Abdul

Masters Theses

"Anthropogenic greenhouse gas emission has become an eminent problem today especially CO₂ gas emission is of major importance. Statistics show that CO₂ concentration is consistently increasing in atmosphere every year. Having cognizance of this problem, better CO₂ absorbents, ionic liquids, has been suggested through this thesis. To prove Ionic liquid's efficiency, a unique sensor was developed by a sophisticated fabrication using Femto-second (fs) laser. Sensor is built to work as an extrinsic Fabry-Perot Interferometer (EFPI) to sense CO₂. EFPI sensor consists of a glass tube fused between two single mode fibers, and a miniature hole is fabricated in the tube …

A Computational Study Of Driven Micro-Cavities In Supersonic Flat Plate Flow, Thomas Ryan Rehmeier

Masters Theses

"Driven micro-cavities embedded in the wall beneath turbulent supersonic boundary layers are analyzed using two-dimensional computational fluid dynamics. This concept is a passive flow control technique in which very small cavities formed by arrays of thin vertical walls are oriented transverse to the flow direction and underlie the boundary layer. The purpose is to reduce or eliminate skin friction drag. Various micro-cavity configurations were analyzed at locations (0.1 m and 1 m) downstream of the leading edges of flat plates, for free-stream Mach numbers of 1.2, 2.0, and 3.0. Results focus on net drag reduction achieved, cavity flow-field effects, perforation …

Water Management Capabilities Of Bio-Inspired Flow Field Configurations For Polymer Electrolyte Membrane Fuel Cells, Nicholas Warren Freer

Masters Theses

"Fuel cells have received an increasing amount of attention over the past decade for their power production capabilities. Polymer electrolyte membrane (PEM) fuel cells in particular are researched because of their high power density, large range of operating conditions, green products, and ease of scalability. PEM fuel cells do have a number of issues that reduce their overall performance. These issues include variations in reactant distribution, materials issues for the bipolar plate, and flooding caused by poor water management. Variations in the reactant distribution causes lower overall power output due to regions of low reactant density. This means that optimizing …

Liquid Phase Sintering Of 20bi(Zn₀.₅Ti₀.₅)O₃-80batio₃ Dielectrics With Bismuth-Zinc-Borate And Bismuth Borosilicate Glasses, David I. Shahin

Masters Theses

"Dielectrics in the Bi(Zn₀.₅Ti₀.₅O₃-BaTiO₃ system (specifically 20BZT-80BT, in mol%) are promising candidates for high energy density capacitor applications due to broad temperature-dependent dielectric constant maxima and a relatively field-independent permittivity. Bulk samples require sintering temperatures of greater than 1180ºC to reach useful densities. Due to incompatibility of Bi with low-pO₂ processing, BZT-BT-based multilayer capacitors must utilize noble metal electrodes that resist oxidation during sintering. Sintering temperatures must be reduced to allow use of less expensive electrode materials (Cu, etc.). This work studies the reduced temperature sintering behavior and dielectric properties of BZT-BT sintered with 30 Bi₂O₃-30ZnO-40B₂O₃ and 50Bi₂O₃-25B₂O₃-25SiO₂ (mol%) liquid …

Communication Protocols For Integrated Fiber Optic Sensor Interrogator, Tameem Ahmed Khan

Masters Theses

"Fiber optic sensors have gained rapid recognition in sensing environmental factors such as strain, stress, acoustics, pressure, temperature among emerging other sensing applications. Major advantages of fiber based systems are small size, light weight, multiplex-ability of sensors on a single fiber, and immunity to Radio Frequency (RF) interference. However, single most major disadvantage of such technology is that traditionally the interrogation systems are typically bulky and heavy lab only equipment. Embed-ability of sensors into different structures and environments requires that the whole systems (sensors + interrogator) be small, modular and portable. This thesis presents such a custom Fiber optic Sensor …

Harmonic Compensation In A Grid Using Doubly Fed Induction Generators, Omkar Amol Ghatpande

Masters Theses

"Ideally, electric utilities are expected to deliver a sinusoidal voltage with a constant rated frequency, while customers are expected to draw a sinusoidal current with unity power factor. The recent widespread use of harmonic producing equipment in industrial applications, especially non-linear loads, has increased the distortion of electric currents and voltages in transmission and distribution systems. This thesis proposes a method of using multiple reference frame theory for measuring and mitigating harmonic currents of nonlinear loads using a doubly fed induction generator. The most significant low-order harmonics to be compensated are calculated using a multiple reference frame harmonic observer. This …

Direct Shear Transfer Of Lightweight Aggregate Concretes With Non-Monolithic Interface Conditions, Dane Michael Shaw

Masters Theses

"This thesis describes the results of a study initiated to examine the influence of concrete unit weight on the direct shear transfer across an interface of concretes cast at different times. This type of interface is common with structural precast concrete connections, such as corbels, for which shear friction design provisions are commonly used. Increasing use of lightweight aggregate concretes prompted this investigation to determine the appropriateness of current shear friction design provisions with respect to all-lightweight and sand-lightweight concrete. The experimental investigation included thirty-six push-off test specimens, each of which was constructed with a cold-joint at the interface shear …

Design And Analysis Of An Open-Ended Waveguide Probe For Material Characterization, Matthew Alan Kempin

Masters Theses

"Nondestructive evaluation of stratified (layered) composite structures at microwave and millimeter wave frequencies is of great interest in many applications where simultaneous determination of the complex dielectric properties and thicknesses of multiple layers is desired. Open-ended rectangular waveguide probes are effective tools for this purpose. The technique requires a full-wave electromagnetic model that accurately calculates the complex reflection coefficient as a function of frequency and material properties. Subsequently, this information is used in conjunction with the measured complex reflection coefficient to evaluate the sought for material properties. This thesis presents simulated and measured data to investigate the influence that measurement …

Examining The Efficiency Of Multimodal Transportation Systems: A Systems Dynamics Approach, Lizzette Pérez-Lespier

Masters Theses

"With international trade becoming a big part of the world's economic activity, the demand for good freight transportation systems has grown substantially. The appropriate use of transportation is an integral part of the supply chain's effectiveness. Therefore, the continuous economic globalization, the growing demand for speed-to-market product delivery, and the need to manage global supply chains more effectively, has led to the sustained increase in demand towards multimodal transportation systems (MTS). MTS play an essential role in corporations competing in global markets in the 21st century. In transportation, the effectiveness and efficiency of the whole system depends upon the interconnectivity …

Tensile Failure During Structural Development Of Single-Layer Buckle Folds, Xiaolong Liu

Masters Theses

"Folds and fold trains of sedimentary strata are among the most common structural traps systems for hydrocarbon reservoirs. The existence of tensile fractures associated to buckle folding is associated to the distribution of extensional strain in the outer arc of the fold hinges. This study investigates the conditions under which tensile stresses develop due to buckling in a realistic in situ stress scenario. By applying a 2D finite element modeling approach, the influence of realistic mechanical stratigraphy (including strain rate, overburden depth, competence contrasts, viscosity, and permeability) on the development of single-layer buckle folds with Newtonian viscous rheology is studied. …

New Sensorless, Efficient Optimized And Stabilized V/F Control For Pmsm Machines, Seyed Hesam Jafari

Masters Theses

"With the rapid advances in power electronics and motor drive technologies in recent decades, permanent magnet synchronous machines (PMSM) have found extensive applications in a variety of industrial systems due to its many desirable features such as high power density, high efficiency, and high torque to current ratio, low noise, and robustness. In low dynamic applications like pumps, fans and compressors where the motor speed is nearly constant, usage of a simple control algorithm that can be implemented with least number of the costly external hardware can be highly desirable for industry. In recent published works, for low power PMSMs, …

Processing And Properties Of Zrb₂-Zrsi₂ Matrix Composites Reinforced With Continuous Sic Fiber, Benjamin John Bowin Lai

Masters Theses

"The research presented in this thesis focuses on the processing, microstructure, and mechanical properties of ZrB₂-based composites. The main goal was to develop a process that incorporates high strength continuous SiC fiber in a ZrB₂-based matrix. In order to achieve this, the densification, microstructure, and mechanical properties of ZrB₂-ZrSi₂ monolithic ceramics were characterized along with various SiC fiber reinforced ceramic matrix composites (CMCs) utilizing the same matrix.

There were two main areas of study in this thesis. The initial study demonstrated that additions of ZrSi₂ into a ZrB₂ ceramic increases densification at significantly reduced processing temperatures ≤1600ºC). This study revealed …

Rethinking Networking For The Internet Of Things, Robert Iannucci

Robert A Iannucci

No abstract provided.

Leveraging Machine-Learned Detectors Of Systematic Inquiry Behavior To Estimate And Predict Transfer Of Inquiry Skill, Ryan Baker, Michael Sao Pedro, Janice Gobert, Orlando Montalvo, Adam Nakama

Ryan S.J.d. Baker

We present work toward automatically assessing and estimating science inquiry skills as middle school students engage in inquiry within a physical science microworld. Towards accomplishing this goal, we generated machine‐learned models that can detect when students test their articulated hypotheses, design controlled experiments, and engage in planning behaviors using two inquiry support tools. Models were trained using labels generated through a new method of manually hand‐coding log files, “text replay tagging”. This approach led to detectors that can automatically and accurately identify these inquiry skills under student‐level cross‐validation. The resulting detectors can be applied at run‐time to drive scaffolding intervention. …

Decision Diagrams And Dynamic Programming, John Hooker

John Hooker

No abstract provided.

Sensor Data As A Service - A Federated Platform For Mobile Data-Centric Service Development And Sharing, Jia Zhang, Robert Iannucci, Mark Hennessy, Kaushik Gopal, Sean Xiao, Sumeet Kumar, David Pfeffer, Basmah Aljedia, Yuan Ren, Martin Griss, Steven Rosenberg, Jordan Cao, Anthony Rowe

Robert A Iannucci

No abstract provided.

Evaluation Of Beach Nourishment Evolution Models Using Data From Two South Carolina Beaches: Folly Beach And Hunting Island, Sc, Usa, Harry Weathers, George Voulgaris

George Voulgaris

Beach nourishment is a common method used for mitigating coastal erosion. However, it is also a costly undertaking and requires an appropriate cost-to-benefit analysis. Although the costs can be estimated relatively easily, the benefits are directly related to the life expectancy of the proposed project. With this in mind, three existing beach replenishment time-evolution models (the Linear Erosion, the Verhagen, and the One-Line models) were compared for their ability to represent data from two beach nourishment projects that have taken place in South Carolina, USA, at Folly Beach and Hunting Island. Another newly introduced model that combines the One-Line model …

Voltage Tuning Of Ferromagnetic Resonance With Bistable Magnetization Switching In Energy-Efficient Magnetoelectric Composites, Ming Liu, Ziyao Zhou, Tianxiang Nan

Tianxiang Nan

No abstract provided.