Mechanical Engineering Commons^™

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 …

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 …

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 …

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 …

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 …

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 …

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) …

Bioprinted In Vitro Model Of Human Glioblastoma, Rachel Lauren Schwartz

Theses and Dissertations

Glioblastoma multiform (GBM) is one of the most aggressive forms of primary brain tumors. GBM is fast progressing and resistant to treatment, resulting in a low survival rate. Conventional 2-dimensional tissue culture models cannot fully replicate the complexities of cancer lesions that contain multiple cell types and structures (e.g. vessels composed of endothelial cells, cancer cells, normal cells, etc.) as well as an intricate scaffold of proteins comprising the extracellular matrix (ECM). In addition, animal models cannot translate into the clinical disease in patients. Thus, this study has developed a bioprintable organ-on-a-chip (OOAC) model that mimics the important ECM factors …

Analysis Of Inlet Distortion Patterns On Distortion Transfer And Generation Through A Highly Loaded Fan Stage, Andrew Dallin Orme

Theses and Dissertations

Characterization of distortion transfer and generation through fans with distorted inlet conditions enables progress towards designs with improved distortion tolerance. The abruptness of transition from undistorted to distorted total pressure regions at the inlet impacts the induced swirl profile and therefore the distortion transfer and generation. These impacts are characterized using URANS simulations of PBS Rotor 4 geometry under a variety of inlet distortion profiles. A 90° and a 135° sector, both of 15% total pressure distortion, are considered. Variants of each sector size, with decreasing levels of distortion transition abruptness, are each applied to the fan. Fourier-based distortion descriptors …

On Creases And Curved Links: Design Approaches For Predicting And Customizing Behaviors In Origami-Based And Developable Mechanisms, Jared J. Butler

Theses and Dissertations

This work develops models and tools to help designers address the challenges associated with designing origami-based and developable mechanisms. These models utilize strain energy, kinematics, compliant mechanisms, and graphical techniques to make the design of origami-based and developable mechanisms approachable and intuitive. Origami-based design tools are expanded through two methods. First presented is a generalized approach for identifying single-output mechanical advantage for a multiple-input compliant mechanism, such as many origami-based mechanisms. The model is used to predict the force-deflection behavior of an origami-based mechanism (Oriceps) and is verified with experimental data from magnetic actuation of the mechanism. Second is a …

Investigating The Use Of 3d Printing Pens For Additive Manufacturing Component Repair, Kyle Andrew Koren

Theses and Dissertations

The work presented in this thesis provides fundamental research for investigating the application of 3D printing pens for the repair of components manufactured by 3D printers. Test specimens of three different print orientations were 3D printed with acrylonitrile-butadiene-styrene (ABS) and underwent a tensile load test, through rupture, to determine the maximum tensile load experienced. These ruptured specimens were then manually repaired with a 3D printing pen and put through another tensile test to determine the percentage of maximum tensile load retained. The two print orientations that had the axis of tensile load applied parallel to their print layers experienced rupture …

Lead Free Piezoelectric And Triboelectric Energy Film For Energy Harvesting And Sensory Applications, Abu Musa Abdullah

Theses and Dissertations

In recent times, Triboelectricity and Piezoelectricity has been widely used for utilizing mechanical energy from ambient environment. Scientists are focusing towards developing advanced material composites for utilizing piezoelectricity and triboelectricity for energy harvesting and sensory applications. This work includes two projects regarding the application of lead free piezoelectric and triboelectric energy for energy harvesting and sensory applications. Human motion has been attributed as a source of mechanical energy to drive electronic devices and sensors through Triboelectric Nanogenerator (TENG). Based on the principles of single electrode TENG, we have developed a Triboelectricity based Stepping and Tapping Energy Case (TESTEC) which magnifies …

Development Of Plant Extract-Based Composite Fibers And Aerogels, Raul C. Barbosa

Theses and Dissertations

The aim of this study is to use the solid templating process of pullulan nanofibers in order to produce biocompatible, biodegradable, and antibacterial aerogels. The developed aerogels were produced using cross-linked pullulan nanofibers, which provide a water-stable structure allowing them to be used as wound dressing material. The morphology, thermal properties, water solubility, and thermal and physical properties of the nanofibers and aerogels were characterized. Furthermore, the antibacterial effect against gram-negative bacteria, Escherichia coli, and the biocompatibility using mouse embryonic fibroblasts (NIH 3T3) were investigated.

Alternative Material Selection For Oyster Restoration With An Emphasis On Living Docks, Bridgette Soucy

Theses and Dissertations

Oyster restoration efforts, including Living Shoreline and Living Dock projects, utilize aquaculture-grade plastic oyster mats to mitigate the decline of benthic communities. Aquaculture-grade plastic are known for strength, durability, and resilience to degradation in seawater. Over time, plastics break into microscopic segments commonly referred to as microplastics. Microplastics represent a major concern as marine organisms mistake the small particles for food. Plastics bioaccumulate in marine species, which impacts the marine food web and humans. In order to reduce further negative anthropogenic impacts, natural fibers and nature-inspired concrete mixtures were utilized across a series of experiments in order to determine an …

Experimental Study Of Graphene Energy Absorbing Layer In Femtosecond Infrared Laser Assisted Bioprinting, Chaoran Dou

Theses and Dissertations

The bioprinting, as a new branch of additive manufacturing, already shown its potential in organ transplantation, medicine develop and personalized medicine. There are three types of bioprinting: droplet based bioprinting, extrusion based bioprinting and laser assisted bioprinting (LAB). Compared with other types of bioprinting, the LAB is the only bioprinting method that does not have a nozzle, which gives it the ability to print high viscosity bioink. The LAB also enjoys higher resolution and cell viability than other methods.

The bubble/jet formation process is the most important process for the LAB, which deposits the bioink to the substrate. To utilize …

An Experimental Thrust Measurement Study On The Nozzle Asymmetry Of Turbulent Pulsed Jets, Cesar Alberto Leos Jr.

Theses and Dissertations

The resurgence of pulsejet engines has renewed the interest of the flow characteristics responsible for the high levels of thrust augmentation that are necessary for Vertical/Short Take-Off and Landing (V/STOL) aircraft. It is well known that pulsation of the engine plays an important role on the thrust performance, but many of the characteristics that are primarily responsible for these enhancements are not well understood. This study is carried out to elucidate the effect of nozzle exit Mach number and the nozzle exit geometry on the characteristics of a high Reynolds number (~105), turbulent free pulsed jet.

Direct thrust measurements are …

A Feature-Based Approach To Function Modeling And Reasoning For Thermal-Fluid Systems Engineering, Lakshmi Narasimhon Athinarayana Venkatanarasimhan

Theses and Dissertations

This research is focused on extending the language of function modeling by developing CAD-like features that are built using primitive functions. These features are reusable units of functions that represent the working principle of a system of higher level of abstraction than the ones of the primitive functions published in prior literature. This approach can be used to also establish an alternate concept/working principle that satisfies the same features, and thus enabling the integration of function models into previously established concept generation programs. It is expected that designers perceive concepts at different levels of abstractions. As a result, the feature-based …

Implementation Of Cholesteric Liquid Crystals In Fibrous Based Membranes, Ydana Yanell Virgen Gracia

Theses and Dissertations

The project consists of an investigation of optical sensors. On this project, the main focus was to implement materials that had properties such as thermochromism, piezochromism, and be able to detect volatile organic compounds with a color change response. The materials selected for this project were Cholesteric Liquid Crystals (CLCs) in different combinations and ratios. There were also four different methods using Forcespinning © technology to apply the CLCs into a polymer matrix; these were, In-Solution, Dip Coating, Coaxial Spinning, and Emulsion. The best results were given by Dip Coating, but the method with the best viable solution was Coaxial …

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 …

Polyimide/Silicon Dioxide Nanocomposites As Dielectrics For Helium-Cooled High-Temperature Superconducting Cables, Harrison Michael Hones

Theses and Dissertations

In this thesis, polyimide (PI) and silicon dioxide (SiO2) were combined in the form of a nanocomposite for use as a dielectric on helium-cooled high-temperature superconducting (HTS) cables. Further, a cryogenic chamber was designed with the intent of cooling samples to 40 K for dielectric and thermal contraction testing. Composites were created through an in situ process which resulted in nanoparticle formation within the host matrix. Samples were tested for dielectric strength at room temperature (300 K) as well as cryogenic temperature (92 K) using liquid nitrogen as the coolant. Composite samples tested at 300 K averaged a dielectric strength …

Improving The Piezoelectric Properties Of Flexible Polymer-Nanoparticle Energy Harvesters, Muhammet Emin Cavusoglu

Theses and Dissertations

In this research, one of the widely used polymers, poly(vinylidene fluoride)(PVDF), was used to develop thin-film polymer energy harvesters. Dimethylformamide (DMF) and methyl ethyl ketone (MEK) were used to dissolve the PVDF powder. Four different (0%, 3%, 5%, and 7%) ZnO nanoparticle (NP) concentrations were used to enhance the electrical output of the thin-film energy harvesters. A sonication bath and additional MEK were used in dispersing the ZnO NPs to obtained uniform PVDF/ZnO NP solution. The electrode poling technique was used for dipole alignment to improve the electrical performance of the devices. The fabricated samples were tested using the tensile …

Design Of An Environmentally Responsive Grooming Tool To Aid In Underwater Navigation, Bruce Huntress Walker Iii

Theses and Dissertations

Underwater hull grooming is a proactive approach to ship hull husbandry. It has been defined as the frequent and gentle wiping of a ship hull coating to maintain it free of fouling. One of the challenges to implementing a grooming schedule is the control and navigation of the devices over the surface of the hull. This thesis presents prior research that has developed self-attaching rotating brushes as an effective method to groom fouling control coatings and the results from several years of implementation in the marine environment. The hypothesis of this thesis is that the condition of the ship hull …

Design, Analysis, And Demonstration Of A Multipurpose Fluid Tank Dynamics Characterization Platform, Cameron Ian Hume

Theses and Dissertations

The development of a highly versatile multiphase fluid tank characterization platform is essential to the analysis and improvement of propellant storage tanks. The performance of these tanks is highly critical to the safety and performance of their carriers, especially in the space industry where the propellant makes up the overwhelming majority of the mass of the vehicle. This thesis outlines the design and development of a linear stage used to test and validate the characteristic of multiphase fluids inside moving specific tanks. This document will walk through the steps taken to bring a new linear stage to life, from the …

Development Of Vegetable Oil Based Nano-Lubricants, Vicente Cortes

Theses and Dissertations

Nowadays, the depletion of crude oil reserves in the world and the global concern in protecting the environment from contamination have renewed interest in developing environment friendly lubricants derived from alternative sources such as vegetable oils. Mineral oil is the most common lubricant, however, it also has poor biodegradable properties. Vegetable oils exhibit good viscosity index, flash point, pour point, tribological properties, and are biodegradable. Furthermore, the use of nanoparticles as additives has shown to improve anti wear and anti-friction properties of the base lubricant. The present research project will evaluate experimentally the rheological and tribological behavior of coconut oil, …

Processing And Microstructural Characterization Of Silicon Carbide, Silicon Nitride, And Tungsten Carbide Fibers, Christian Garcia

Theses and Dissertations

This research focuses on developing polymer-derived ceramic fibers. The spun micro/nanofibers were sintered into silicon carbide/silicon nitride and tungsten carbide respectively. The relationship between processing, fiber microstructure, morphology, and purity is investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and thermogravimetric analysis. Dynamic Mechanical Analysis was used to test the reinforcement capabilities of tungsten carbide fibers. EDS identified a near-perfect 1:1 Si-C ratio in silicon carbide fibers sintered between 1200 °C -1400 °C, Silicon carbide was confirmed by FTIR between 1000 °C – 1400 °C. Silicon Nitride peaks were noted in FTIR between 1200 °C – …

Residual Service Life Prognostic Models For Tapered Roller Bearings, Jennifer Danni Lima

Theses and Dissertations

There are a few different bearing health monitoring technologies currently used in the railroad industry, both reactive and preventative detection systems. Reactive models have proven to be ineffective in monitoring bearing health, which has resulted in either unnecessary train stoppages and delays or in-service failures and bearing burn-off leading to catastrophic train derailments. Wayside preventative detection systems, while more effective than reactive technologies, are scarce and neglect railcars’ that do not travel over a specific route. This knowledge prompted the University Transportation Center for Railway Safety at UTRGV to develop an onboard bearing health monitoring system that can accurately assess …