Engineering Commons^™

Acoustic And Ultrasonic Beam Focusing Through Aberrative And Attenuative Layers, Hossain Ahmed

Theses and Dissertations

Ultrasonic nondestructive evaluation (NDE) is a well-established technique to assess material properties and material state in noninvasive way. However, conventional NDE technologies are limited by the thick top coatings over the structure and, therefore, require time consuming removal and replacement of the coatings to perform the inspection. In biological application, although ultrasonic NDE is a safer method in compared to other radioactive non-invasive techniques, aberration of acoustic beams is more common as it encounters multiple tissue layers of complex geometry with nonhomogeneous properties. These limit the use of ultrasonic NDE in engineering and biological applications. To alleviate this problem, recently …

Local Eigenvalue Modification Procedure For Real-Time Model Updating Of Structures Experiencing High-Rate Dynamic Events, Claire Rae Drnek

Theses and Dissertations

Estimating the state of structures that experience high-rate dynamics requires real-time model updating capabilities. In this work, high-rate dynamic events are characterized by 1) large uncertainties in the external loads, 2) high levels of non-stationarities and heavy disturbances, and 3) unmodeled dynamics generated from changes in system configurations. To achieve real-time model updating, an algorithm must circumvent any pre-calculations and be able to update the structure’s state on the timescale of 2 ms or less. This can be accomplished in one of two ways: either by creating a simplified model of a complex structure or by simplifying the calculations needed …

Artificial Intelligence Approaches For Structural Health Monitoring Of Aerospace Structures, Kimberly A. Cardillo

Theses and Dissertations

Structural health monitoring (SHM) and non-destructive evaluation (NDE) have been a significant research topic to help with damage detection in aerospace structures. SHM and NDE techniques are based on extracting damage sensitive features to determine the criticality of damage and lifetime of a structure. Acoustic emission (AE) signal detection is an important technique in SHM and NDE especially for fatigue crack growth. AE signals for thin aerospace structures consist of ultrasonic guided Lamb waves that propagate through the structure. This thesis focuses on AE signal repeatability, load at which AE signals occur, feature extraction, artificial intelligence and electro-mechanical impedance of …

Autonomous Drone-Based Sensor Package Deployment To The Underside Of Structures, Sabrina Rose Carroll

Theses and Dissertations

The objective of this project is to design, develop and experimentally test an Unmanned Aircraft System (UAS, commonly known as a drone) for the deployment of sensor packages to the underside of structures. This work begins with an in-depth review of existing automation techniques for various drone applications focusing on applications requiring interaction with the environment. Further reviewed is the impact of structures above the UAS during flight on the behavior of the aircraft.

Considering these topics, the development of a custom drone is presented to address the difficulties of delivering a package to the underside of a structure. Starting …

Lamb Wave Nondestructive Evaluation And Imaging On Plate-Like Structures, Zhaoyun Ma

Theses and Dissertations

Structure components are designed with a certain service life and damage may occur, or they may come with manufacture defects. Such damage and defects may lead to structural failure if not detected in time. To ensure the structural safety and prevent catastrophic failure, effective inspection is critical for in-time maintenance. Nondestructive evaluation (NDE) and structural health monitoring (SHM) have been widely applied for damage inspection and evaluation in various industries due to their noninvasive nature. Lamb wave based NDE/SHM has become the most popular ultrasonic methods that has been proved effective in different engineering applications that can be used to …

Development Of A Cfd Model For The Drying Of Aluminum-Clad Spent Nuclear Fuel, Nathaniel Cooper

Theses and Dissertations

The United States Department of Energy (DOE) currently manages approxi- mately 2500 metric tons of heavy metal (MTHM) of spent nuclear fuel (SNF), pri- marily from naval sources and domestic research reactors, and has agreements in place to accept 10,000 MTHM of aluminum-clad SNF from foreign reactors by 2029. However, due to the closure and the Yucca Mountain site and difficulties in the vitrification process, the majority of this fuel is expected to be placed in intermediate dry storage.

Before being placed in interim storage, all assemblies must be subjected to a drying process, either by forced gas recirculation (FGR) …

Steady-State And Transient Study Of Flow Boiling In Microchannels With Microgrooves/Micronozzles, Congcong Ren

Theses and Dissertations

Microchannel flow boiling is one of the most desired cooling solutions for high power electronics. Owing to the high latent heat of vaporization, high heat fluxes can be achieved through phase-change heat transfer. However, the enhancements of (critical heat flux) CHF and heat transfer coefficient (HTC) are usually inhibited by the transitional flow patterns, which highly influence the liquid rewetting. In the past two decades, many techniques have been explored to enhance the liquid rewetting in microscale.

In this dissertation, four parallel micro-grooves fabricated on the bottom of five microchannels (W=200 μm, H=250 μm, L=10 mm) were designed to promote …

Ultrasonic Nondestructive Evaluation Using Non-Contact Air-Coupled Lamb Waves, Wenfeng Xiao

Theses and Dissertations

Ultrasonic Lamb waves have been proved as an effective nondestructive evaluation (NDE) method due to their ability to propagate a long distance with less energy loss as well as their sensitivity to various defects on the surface or inside the structure. However, there are still challenges towards using them as a rapid inspection method for complex structural geometries, various damage types, and harsh environments, such as efficiency in Lamb wave actuation and sensing, understanding of the complicated multi-modal Lamb wave propagation, and robust detection algorithms for damage quantification and evaluation. To address these challenges, this dissertation focuses on developing a …

Exploration And Evaluation Of Novel Cathode Materials For Intermediate-To-Low Temperature Solid Oxide Fuel Cells, Chunyang Yang

Theses and Dissertations

Solid oxide fuel cells (SOFCs) have attracted considerable attentions due to its high conversion efficiency, fuel flexibility, and clean nature. However, the high cost and poor long-term stability induced by the high operating temperature (> 800 °C) of the conventional SOFCs hinder the further application. Therefore, lowering operating temperature to intermediate temperature range (IT, 650-800 °C) or even low temperature range (LT, 400-650 °C) is of practical importance for realizing SOFCs’ full commercial potential. Nevertheless, due to the large activation energy associated with oxygen reduction reaction (ORR), cathode polarization resistance becomes the dominate loss limiting SOFCs performance as operating temperature …

Enhancing Single And Two-Phase Heat Transfer Of Microgap Heat Sinks Using Nano-Structure Coatings, Yueyang Zhao

Theses and Dissertations

Due to the shrinking size and increasing power of electronics, the heat flux generated by electronic devices has greatly increased and imposed challenges to thermal management technologies. Numerous cooling technologies have been developed to cool high-power electronics. Among them, flow boiling in microchannels or a microgap has been one of the most efficient ways to remove high heat flux, which requires less coolant compared with single-phase cooling techniques. However, the flow boiling instability is the one of the most challenging issues, which lead to the premature critical heat flux (CHF) conditions and deteriorate heat transfer rate. The capillary force generated …

Guided-Wave Shm And Nde Of Composite Structures: Modeling And Experiments, Hanfei Mei

Theses and Dissertations

The extensive use of composites in aerospace structures has posed new challenges for implementing effective structural health monitoring (SHM) and nondestructive evaluation (NDE) techniques due to the general anisotropic behavior and complex damage scenarios in composites. This dissertation addresses the SHM and NDE of composites using ultrasonic guided waves, with an emphasis on theoretical modeling and experimental validation of guided-wave propagation and interaction with damage in composites. A semi-analytical finite element (SAFE) approach is presented to calculate guided-wave dispersion curves in composites. The theoretical framework is formulated using the finite element method (FEM) to describe the material variation along the …

Fundamental Understanding Of Plasma Discharge Formation In Liquid And Multiphase Configurations Through Multiphysics Modeling, Ali Charchi Aghdam

Theses and Dissertations

During the last two decades, non-thermal plasma discharges in and in contact with liquids have received significant attention due to their wide range of applications including chemical analysis, medical, water treatment, fuel processing, etc. Despite the tremendous interest and advances attained in the experimental studies, modeling efforts providing a comprehensive understanding of the underlying physicochemical processes are limited. There is still no unified theory on plasma formation in dense medium and various theories have been proposed such as the presence of bubbles and tunneling which are topics of debate. In the first part of this study, a mathematical model is …

Kinetic And Multidimensional Transport Coupled Numerical Investigation Of Nox Formation During Syngas And Natural Gas Combustion, Sheikh Farhan Ahmed

Theses and Dissertations

The primary objective of this thesis work is focused on the chemical kinetic modeling of the formation of Oxides of Nitrogen (collectively termed as NOx), regarded as a major pollutant emitted by combustion devices, and the application of that model to simulate transport coupled multidimensional distribution of NOx in a reacting flow. The underlying motivation of this kinetic modeling is the noted discrepancies among the existing models, which become critical in selecting the correct model in advanced gas turbine and engine research. The first part of this work is the performance evaluation and comparison of the existing models. Based on …

The Manufacturing And Characterization Of Pseudo-Woven Carbon Fiber Composite Architectures For Enhanced Damage Tolerance, Cyrus Vakili Rad

Theses and Dissertations

Traditional unidirectional carbon fiber reinforced polymer matrix composites exhibit brittle failure, limited toughness, and poor damage tolerance often resulting in the overdesign of composite systems. This work focuses on the automated fiber placement (AFP) manufacturing and characterization of a new family of pseudo-woven (PW) laminate architectures aimed to enhance impact resistance and damage tolerance. The PW laminate architecture uses a specialized in situ AFP process implementing tow skips to produce its laminate architecture. This results in a heterogeneous architecture possessing spatially variable in-plane material properties unlike traditional laminated composites. This heterogeneity is associated with topological variations in the fiber orientations …

Design Of Bio-Inspired Multifrequency Acoustic Sensors And Metamaterial Energy Harvesting Smart Structures, Mohammadsadegh Saadatzi

Theses and Dissertations

Due to the limited availability and high depletion rates of nonrenewable sources of energy as well as environmental concerns, the scientific community has started to explore many alternative clean sources of energies. It is identified that civil, mechanical and Aerospace structures are always subjected to acoustic noises and vibration which could potentially be used as renewable source of energy. Roads and Industrial noise barriers are used inside industrial facilities alongside the walls, around construction pillars, nearby machinery and other equipment to separate quite work zones, protect walls, deliver extra safety and precautions while diminish sound and vibrational pressure. We hypothesized …

Damage Evaluation Of Rolling Element Bearings For Shipboard Machinery, Brenna Lyn Feirer

Theses and Dissertations

Rolling element bearings perform an essential role in most all rotating machinery. To prevent degradation to machine performance, unforeseen costs and unexpected system failure, bearing fault diagnosis and prognosis are used. Acoustic Emission (AE) introduces high sensitivity, early and rapid detection of cracking, and real time monitoring that can alarm once cracking is noticed.

The purpose of this research is to nondestructively monitor the crack growth in rolling element bearings in a marine environment and to determine the acoustic emission parameters which embody crack initiation and propagation. The intellectual merit lies in:

1. the signal alarm developed from an AE …

Effects Of Material Characteristics And Equipment Configuration On Profilometry Scanning Results For Error Mitigation In Automated Fiber Placement, Jacob Ondeck

Theses and Dissertations

The Automated Fiber Placement manufacturing process is a method for constructing layered composite parts. This is done by placing tapes of material on a tool using a compaction roller and heat to tackify the material [1]. This manufacturing process is not new, but latest equipment generations can still introduce randomly occurring defects, presenting often as tow twists, gaps, unintentional overlaps and even missing tows during the layup process. These defects deviate the manufactured structure from the as-designed structure, and have been proven to introduce stress concentration sources, which can ultimately undermine the performance of a structure [2]. To detect and …

Influence Of Dynamic Multiaxial Transverse Loading On Ultrahigh Molecular Weight Polyethylene Single Fiber Failure, Frank David Thomas

Theses and Dissertations

High performance fibers such as ultrahigh molecular weight polyethylene (UHMWPE) are often used for ballistic impact applications in the form of textile fabrics and composite laminates. In order to predict the ballistic performance of such materials, single-fiber experiments are performed to quantify the material behavior at smaller length scales, which can be applied to larger length scales as a result. Failure of UHMWPE is well understood as a function of simple tension at low and high strain rates, as well as under various multiaxial loading states. However, experimental characterization of single UHMWPE fibers under transverse loading at high strain rates …

Efficient Design Optimization Methodology For Manufacturable Variable Stiffness Laminated Composite Structures, Mazen Albazzan

Theses and Dissertations

Because of their superior mechanical and environmental properties compared to traditional metals, fiber-reinforced composite materials have earned a widespread acceptance for different structural applications. The tailoring potential of composites to achieve high specific stiffness and strength has promoted them as promising candidates for constructing lightweight structures. From that aspect, designers have tackled the problem of designing composite laminates, which is inherently challenging due to the presence of non-linear, non-convex, and multi-dimensional optimization problems with discrete and continuous design variables. However, despite their increased usage, the possible improvements that can be achieved by composite laminates have not been fully exploited. With …

Acoustic Emission And Guided Wave Modeling And Experiments For Structural Health Monitoring And Non-Destructive Evaluation, Roshan Prakash Joseph

Theses and Dissertations

This dissertation is organized into major parts. In Part I of the dissertation, plate guided waves due to an acoustic emission (AE) event are analytically studied in the context of seismic moment tensor sources. The guided wave propagation elastodynamic equation corresponding to a point source applied to the plate in an arbitrary direction is modified in order to describe the case when the source is a seismic moment tensor of various tensor components. This part of the dissertation also discusses the analytical modeling of AE test sources such as pencil lead break, hammer hit excitation, etc.

In Part II of …

Strain Components In Friction Stir Extrusion, Megan Ryan

Theses and Dissertations

Friction stir extrusion is a solid state process that uses a rotating die to perform extrusions. This process can be used to directly recycle waste from machining processes and has been shown to produce wires with desirable mechanical properties. In order to better understand the friction stir extrusion process, the effect of the process parameters on the strain distribution in the wires needs to be understood. The process parameters evaluated in this work are die advance rate, die rotational seed, and die geometry. A total of 16 wires were extruded using different combinations of these process parameters. Marker wires were …

Tow-Path Characterization For Automated Fiber Placement, Roudy Wehbe

Theses and Dissertations

Automated Fiber Placement (AFP) is a manufacturing process used to fabricate large composite structures for aerospace applications. During the process, the machine head deposits multiple bands of composite material named tows over a prescribed path. Temperature, speed, and compaction pressure can be varied to obtain a good layup quality. For conventional laminated plate structures manufactured using the AFP process, fibers are laid at constant angles (0°, 90°, ±45°) in straight paths. However, to manufacture complex shell structures or variable stiffness plates, curved paths are necessary in the design leading to a length mismatch between the parallel edges of the towpath. …

Design And Testing Of A Supercritical Carbon Dioxide Plasma Reactor, Gregory Belk

Theses and Dissertations

The objective of this project was to design, build, and test a plasma reactor capable of operating in the supercritical conditions. The reactor allows for the initiation of a plasma discharge in different fluids driven by a direct current (DC) power supply operating either in steady state mode or pulsing mode. The reactor was specifically designed for igniting plasmas within supercritical carbon dioxide, which has a pressure of 72.9 atm and 31.1 degrees Celsius.

A series of runs were conducted for varying pressures and inter-electrode separation, which allowed testing the operation regimes of the reactors. Finally, plasma experiments were conducted …