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Articles 1 - 30 of 37
Full-Text Articles in Mechanical Engineering
Additive Manufacturing Of Nanomaterial Based Hierarchical Structures, John Michael Gardner
Additive Manufacturing Of Nanomaterial Based Hierarchical Structures, John Michael Gardner
Dissertations, Theses, and Masters Projects
Aerospace systems demand high performance materials that minimize weight while functioning under extreme environmental conditions. One way to meet these requirements is by incorporating hierarchical structures into part design. These structures are known to impart unique mechanical properties not characteristic of the bulk material such as high strength and toughness. It is difficult, however, to manufacture these structures due to the inherent trade-off between part size and feature resolution in traditional manufacturing processes. Additive manufacturing offers a potential solution to these issues by allowing material placement directly at desired locations. This loosens geometric constraints and allows for multiple contiguous materials …
An Evaluation Of A Reduced Bar Spacing Turtle Excluder Device In The U.S Gulf Of Mexico Offshore Shrimp Trawl Fishery, Michel Anthony Nalovic
An Evaluation Of A Reduced Bar Spacing Turtle Excluder Device In The U.S Gulf Of Mexico Offshore Shrimp Trawl Fishery, Michel Anthony Nalovic
Dissertations, Theses, and Masters Projects
Shrimp are the most economically valuable internationally-traded seafood commodity, and wild-caught, trawled shrimp make up almost half of the ~6.6 million metric tons of annual global production. Shrimp trawling is responsible for one-third of the world’s total fisheries bycatch, leading many to consider shrimp trawling to be the single most destructive fishing practice in the world. Though the bycatch of large marine animals can be significantly reduced by use of turtle excluder devices (TEDs) on shrimp trawls, current TED designs are ineffective at reducing the capture of smaller organisms which represent a large portion of the total bycatch. To further …
Use Of Pattern Classification Algorithms To Interpret Passive And Active Data Streams From A Walking-Speed Robotic Sensor Platform, Eric Allen Dieckman
Use Of Pattern Classification Algorithms To Interpret Passive And Active Data Streams From A Walking-Speed Robotic Sensor Platform, Eric Allen Dieckman
Dissertations, Theses, and Masters Projects
In order to perform useful tasks for us, robots must have the ability to notice, recognize, and respond to objects and events in their environment. This requires the acquisition and synthesis of information from a variety of sensors. Here we investigate the performance of a number of sensor modalities in an unstructured outdoor environment, including the Microsoft Kinect, thermal infrared camera, and coffee can radar. Special attention is given to acoustic echolocation measurements of approaching vehicles, where an acoustic parametric array propagates an audible signal to the oncoming target and the Kinect microphone array records the reflected backscattered signal. Although …
Investigation Of Ultrasonic Wave Scattering Effects Using Computational Methods, Cara Ann Campbell Leckey
Investigation Of Ultrasonic Wave Scattering Effects Using Computational Methods, Cara Ann Campbell Leckey
Dissertations, Theses, and Masters Projects
Advances in computational power and expanded access to computing clusters has made mathematical modeling of complex wave effects possible. We have used multi-core and cluster computing to implement analytical and numerical models of ultrasonic wave scattering in fluid and solid media (acoustic and elastic waves). We begin by implementing complicated analytical equations that describe the force upon spheres immersed in inviscid and viscous fluids due to an incident plane wave. Two real-world applications of acoustic force upon spheres are investigated using the mathematical formulations: emboli removal from cardiopulmonary bypass circuits using traveling waves and the micromanipulation of algal cells with …
Applications Of Pattern Classification To Time-Domain Signals, Crystal Ann Bertoncini
Applications Of Pattern Classification To Time-Domain Signals, Crystal Ann Bertoncini
Dissertations, Theses, and Masters Projects
Many different kinds of physics are used in sensors that produce time-domain signals, such as ultrasonics, acoustics, seismology, and electromagnetics. The waveforms generated by these sensors are used to measure events or detect flaws in applications ranging from industrial to medical and defense-related domains. Interpreting the signals is challenging because of the complicated physics of the interaction of the fields with the materials and structures under study. often the method of interpreting the signal varies by the application, but automatic detection of events in signals is always useful in order to attain results quickly with less human error. One method …
Twine-Top Modifications Of Sea-Scallop Dredges: Reducing Yellowtail-Flounder Bycatch, Kelli A. Milleville
Twine-Top Modifications Of Sea-Scallop Dredges: Reducing Yellowtail-Flounder Bycatch, Kelli A. Milleville
Dissertations, Theses, and Masters Projects
No abstract provided.
Ultrasonic Guided Wave Interpretation For Structural Health Inspections, Jill Paisley Bingham
Ultrasonic Guided Wave Interpretation For Structural Health Inspections, Jill Paisley Bingham
Dissertations, Theses, and Masters Projects
Structural Health Management (SHM) combines the use of onboard sensors with artificial intelligence algorithms to automatically identify and monitor structural health issues. A fully integrated approach to SHM systems demands an understanding of the sensor output relative to the structure, along with sophisticated prognostic systems that automatically draw conclusions about structural integrity issues. Ultrasonic guided wave methods allow us to examine the interaction of multimode signals within key structural components. Since they propagate relatively long distances within plate- and shell-like structures, guided waves allow inspection of greater areas with fewer sensors, making this technique attractive for a variety of applications.;This …
Parallel Three-Dimensional Acoustic And Elastic Wave Simulation Methods With Applications In Nondestructive Evaluation, Kevin Edward Rudd
Parallel Three-Dimensional Acoustic And Elastic Wave Simulation Methods With Applications In Nondestructive Evaluation, Kevin Edward Rudd
Dissertations, Theses, and Masters Projects
In this dissertation, we present two parallelized 3D simulation techniques for three-dimensional acoustic and elastic wave propagation based on the finite integration technique. We demonstrate their usefulness in solving real-world problems with examples in the three very different areas of nondestructive evaluation, medical imaging, and security screening. More precisely, these include concealed weapons detection, periodontal ultrasography, and guided wave inspection of complex piping systems. We have employed these simulation methods to study complex wave phenomena and to develop and test a variety of signal processing and hardware configurations. Simulation results are compared to experimental measurements to confirm the accuracy of …
Sonar Sensor Interpretation For Ectogeneous Robots, Wen Gao
Sonar Sensor Interpretation For Ectogeneous Robots, Wen Gao
Dissertations, Theses, and Masters Projects
We have developed four generations of sonar scanning systems to automatically interpret surrounding environment. The first two are stationary 3D air-coupled ultrasound scanning systems and the last two are packaged as sensor heads for mobile robots. Template matching analysis is applied to distinguish simple indoor objects. It is conducted by comparing the tested echo with the reference echoes. Important features are then extracted and drawn in the phase plane. The computer then analyzes them and gives the best choices of the tested echoes automatically. For cylindrical objects outside, an algorithm has been presented to distinguish trees from smooth circular poles …
Ultrasonic Guided Wave Tomography Of Pipes: A Development Of New Techniques For The Nondestructive Evaluation Of Cylindrical Geometries And Guided Wave Multi-Mode Analysis, Kevin Raymond Leonard
Ultrasonic Guided Wave Tomography Of Pipes: A Development Of New Techniques For The Nondestructive Evaluation Of Cylindrical Geometries And Guided Wave Multi-Mode Analysis, Kevin Raymond Leonard
Dissertations, Theses, and Masters Projects
This dissertation concentrates on the development of two new tomographic techniques that enable wide-area inspection of pipe-like structures. By envisioning a pipe as a plate wrapped around upon itself, the previous Lamb Wave Tomography (LWT) techniques are adapted to cylindrical structures. Helical Ultrasound Tomography (HUT) uses Lamb-like guided wave modes transmitted and received by two circumferential arrays in a single crosshole geometry. Meridional Ultrasound Tomography (MUT) creates the same crosshole geometry with a linear array of transducers along the axis of the cylinder. However, even though these new scanning geometries are similar to plates, additional complexities arise because they are …
Evaluating Restored Oyster Reefs In Chesapeake Bay: How Habitat Structure Influences Ecological Function, Janet A. Nestlerode
Evaluating Restored Oyster Reefs In Chesapeake Bay: How Habitat Structure Influences Ecological Function, Janet A. Nestlerode
Dissertations, Theses, and Masters Projects
A shortage of shell resources for restoring reefs of the Eastern oyster, Crassostrea virginica, has led to widespread use of substitute materials. The effectiveness of such alternative substrates as habitat for reef-associated fauna other than oysters is largely unresolved. I investigated the habitat value of oyster shell, surf clam (Spisula solidissima) shell, and pelletized coal ash reefs for benthic and nektonic communities. Oyster recruitment, survival, and growth were monitored on reefs of oyster and surf clam shell near the mouth of Chesapeake Bay and York River, USA. Oyster shell supported greater oyster growth and survival and offered the highest degree …
Laboratory Oxide Coatings: Physical Form And Surface Chemistry, Kea U. Duckenfield
Laboratory Oxide Coatings: Physical Form And Surface Chemistry, Kea U. Duckenfield
Dissertations, Theses, and Masters Projects
The impact of dissolved trace metals on aquatic ecosystems and human health is controlled by sorption, i.e., binding to the surfaces of environmental particles. Since many environmental particles are coated with highly reactive substances, and since discrepancies in trace metal sorption behavior persist between oxides developed in the laboratory and environmental oxide phases, it was hypothesized that the physical form of oxide coatings may influence the chemical properties of the coated particle. Therefore, relationships between the physical forms of several different Fe(III) oxide coatings and the Cu(II) sorption behavior of the coated solids were investigated in comparison with the component …
A Semi-Empirical Cellular Automata Model For Wildfire Monitoring From A Geosynchronous Space Platform, Brian D. Killough
A Semi-Empirical Cellular Automata Model For Wildfire Monitoring From A Geosynchronous Space Platform, Brian D. Killough
Dissertations, Theses, and Masters Projects
The environmental and human impacts of wildfires have grown considerably in recent years due to an increase in their frequency and coverage. Effective wildfire management and suppression requires real-time data to locate fire fronts, model their propagation and assess the impact of biomass burning. Existing empirical wildfire models are based on fuel properties and meteorological data with inadequate spatial or temporal sampling. A geosynchronous space platform with the proposed set of high resolution infrared detectors provides a unique capability to monitor fires at improved spatial and temporal resolutions. The proposed system is feasible with state-of-the-art hardware and software for high …
Theoretical And Experimental Study Of Generation Mechanisms For Laser Ultrasound In Woven Graphite /Epoxy Composites With Translaminar Stitching, Adam D. Friedman
Theoretical And Experimental Study Of Generation Mechanisms For Laser Ultrasound In Woven Graphite /Epoxy Composites With Translaminar Stitching, Adam D. Friedman
Dissertations, Theses, and Masters Projects
The aerospace industry is beginning to use advanced composite materials for primary load bearing structures and their failure mechanisms must be better understood to predict their behavior in service. The Combined Loads Tests (COLTS) facility is being constructed at the NASA Langley Research Center to characterize these failure mechanisms. Laser based ultrasonic NDE can monitor the samples during dynamic loading without interfering with the structural tests. However, the constraints of implementing laser ultrasound in a structures laboratory reduces the efficiency of the technique. The system has to be "eye-safe" because many people will be present during the structural tests. Consequently, …
Lamb Wave Diffraction Tomography, Eugene V. Malyarenko
Lamb Wave Diffraction Tomography, Eugene V. Malyarenko
Dissertations, Theses, and Masters Projects
As the worldwide aviation fleet continues to age, methods for accurately predicting the presence of structural flaws, such as hidden corrosion and disbonds, that compromise air worthiness become increasingly necessary. Ultrasonic guided waves, Lamb waves, allow large sections of aircraft structures to be rapidly inspected. However, extracting quantitative information from Lamb wave data has always involved highly trained personnel with a detailed knowledge of mechanical waveguide physics. In addition, human inspection process tends to be highly subjective, slow and prone to errors. The only practical alternative to traditional inspection routine is a software expert system capable of interpreting data with …
Nitrate Reduction At The Groundwater - Salt Marsh Interface, Craig -1967 Tobias
Nitrate Reduction At The Groundwater - Salt Marsh Interface, Craig -1967 Tobias
Dissertations, Theses, and Masters Projects
The influence of groundwater discharge on the hydrology and biogeochemical cycling of nitrogen in a fringing intertidal wetland was studied by characterizing groundwater discharge, determining N-cycling rates in cores, and examining nitrate reduction in situ using 15N enrichment and natural gradient tracer techniques. Groundwater discharge was estimated by three independent methods: Darcy's Law, a water/salt mass balance, and a subsurface tracer test. Seasonal patterns of discharge predicted by Darcy's Law and the mass balance were similar. Discharge maxima and minima occurred in April and September, respectively. The water/salt mass balance provided the more reasonable estimate of groundwater flux at high …
Ecosystem Analysis Of Water Column Processes In The York River Estuary, Virginia: Historical Records, Field Studies And Modeling Analysis, Yongsik Sin
Dissertations, Theses, and Masters Projects
Analyses of EPA long-term datasets (1985--1994) combined with field studies and ecosystem model development were used to investigate phytoplankton and nutrient dynamics in the York River estuary. Analysis of the EPA dataset showed that algal blooms occurred during winter-spring followed by smaller summer blooms. Peak phytoplankton biomass during the winter-spring blooms occurred in the mid reach of the mesohaline zone whereas during the summer bloom it occurred in the tidal fresh-mesolialine transition zone. River discharge appears to be the major factor controlling the location and timing of the winter-spring blooms and the relative degree of potential nitrogen (N) and phosphorus …
Tomography Applied To Lamb Wave Contact Scanning Nondestructive Evaluation, James Christopher P. Mckeon
Tomography Applied To Lamb Wave Contact Scanning Nondestructive Evaluation, James Christopher P. Mckeon
Dissertations, Theses, and Masters Projects
The aging world-wide aviation fleet requires methods for accurately predicting the presence of structural flaws that compromise airworthiness in aircraft structures. Nondestructive Evaluation (NDE) provides the means to assess these structures quickly, quantitatively, and noninvasively. Ultrasonic guided waves, Lamb waves, are useful for evaluating the plate and shell structures common in aerospace applications. The amplitude and time-of-flight of Lamb waves depend on the material properties and thickness of a medium, and so they can be used to detect any areas of differing thickness or material properties which indicate flaws. By scanning sending and receiving transducers over an aircraft, large sections …
On-Line System Identification For Control System Applications In Particle Accelerators, Mahesh Chowdhary
On-Line System Identification For Control System Applications In Particle Accelerators, Mahesh Chowdhary
Dissertations, Theses, and Masters Projects
Particle accelerators require a number of feedback systems in order to stabilize a variety of parameters. The Continuous Electron Beam Accelerator at Thomas Jefferson National Accelerator Facility presents a unique set of control and identification problems. This accelerator produces a continuous electron beam with energies between 0.5 and 4.0 GeV to be delivered to the experimental halls. In order to meet stringent beam quality requirements specified by the experimental halls, the position and the energy of the electron beam needs to stabilized at various locations in the accelerator.;A number of noise measurement tests were conducted at various locations in the …
Propagation Of Rayleigh Waves In Thin Films, Agus A. Ananda
Propagation Of Rayleigh Waves In Thin Films, Agus A. Ananda
Dissertations, Theses, and Masters Projects
With the advent of thin film technology and more recently its applications in microelectronics and control of surface properties, the interest in mechanical properties of thin films has grown tremendously. Mechanical defects such as creep, fracture and adhesion loss, play a very important role in physical instabilities of thin film materials. An acoustic microscope has been built to study mechanical properties of thin-films. The microscope operates at a nominal frequency of 50 MHz. Rayleigh surface waves velocities on the surface of film-substrate systems were measured from V(z) curves generated by the acoustic microscope. V(z) curves are produced from interference between …
Gaseous Flux And Distribution Of Polycyclic Aromatic Hydrocarbons Across The Air-Water Interface Of Southern Chesapeake Bay, Kurt E. Gustafson
Gaseous Flux And Distribution Of Polycyclic Aromatic Hydrocarbons Across The Air-Water Interface Of Southern Chesapeake Bay, Kurt E. Gustafson
Dissertations, Theses, and Masters Projects
Gaseous fluxes of polycyclic aromatic hydrocarbons (PAHs) across the air-water interface of Southern Chesapeake Bay were calculated for the period January 1994 through May 1995 using a modified two-film model. Additionally, the distributions of PAHs between the vapor and aerosol phase in the atmosphere, and between the freely dissolved and suspended particulate phase in the water column were investigated. Net instantaneous gaseous fluxes of PAHs were determined to vary in direction and magnitude both spatially and temporally across the air-water interface of Southern Chesapeake Bay at four sites ranging from remote to urban and highly industrialized. The magnitude of gas …
Propagation Of Guided Acoustic Waves In Composite Media, Michael David Seale
Propagation Of Guided Acoustic Waves In Composite Media, Michael David Seale
Dissertations, Theses, and Masters Projects
Composite materials are being more widely used today by aerospace, automotive, and a number of other commercial industries because of their advantages over conventional metals. Composites are finding applications ranging from bicycle frames to the proposed High-Speed Civil Transport (HSCT). Determining the response to a variety of damage mechanisms is necessary for a complete understanding of the total use environment of composite structures. The objective of the research presented here is to provide a method of quantifying the amount of damage in composite materials for a number of different damage scenarios. Components which have non-visible damage, but have degraded performance, …
Impact Of Artificial Reef Associates On Macrobenthic Community Structure In Florida Bay, Heinz Michael Proft
Impact Of Artificial Reef Associates On Macrobenthic Community Structure In Florida Bay, Heinz Michael Proft
Dissertations, Theses, and Masters Projects
No abstract provided.
Crassostrea Virginica On Constructed Intertidal Oyster Reefs: The Effects Of Tidal Height And Substrate Level On Settlement, Growth, And Mortality, Ian K. Bartol
Dissertations, Theses, and Masters Projects
No abstract provided.
Fabrication Of Thermoplastic Polymer Composite Ribbon, Donald Allan Sandusky
Fabrication Of Thermoplastic Polymer Composite Ribbon, Donald Allan Sandusky
Dissertations, Theses, and Masters Projects
The goal of this research was to develop a controllable process to convert a thermoplastic powder-coated carbon-fiber towpreg into uniform and consolidated ribbon. The approach comprised four primary activities. (1) The patent and processing literature was studied to evaluate the state of the art. (2) A functional ribbon fabrication technique was developed by scaling-up, in a novel configuration, hardware components found in the literature. (3) The ex parte ribbonizing process was characterized by calibrating equipment, determining steady state and studying cause and effect between process parameters and ribbon quality. (4) Process design and control methods were derived from heat transfer …
Directional Wave Spectra Using An Acoustic Doppler Current Profiler, William T. Stockhausen
Directional Wave Spectra Using An Acoustic Doppler Current Profiler, William T. Stockhausen
Dissertations, Theses, and Masters Projects
No abstract provided.
Interspecific And Intraspecific Variability In Placoid Scale Morphology In Relation To Body Form Variability In Squaliformes, Christopher R. Tabit
Interspecific And Intraspecific Variability In Placoid Scale Morphology In Relation To Body Form Variability In Squaliformes, Christopher R. Tabit
Dissertations, Theses, and Masters Projects
An ontogenetic series of nine species; Centrophorus granulosus, Centroscymnus coelolepis, Dalatias licha, Deania calcea, Echinorhinus cookei, Isistius brasiliensis, Oxynotus centrina and Squalus acanthias were studied to determine swimming capabilities, boundary-layer flow conditions and placoid scale functional morphologies. Body morphometric variables included the girth and the distance from snout to the orbitals, origin of the median and paired fins, and the caudal peduncle, body and fin surface area, fin aspect ratios and caudal fin angles. Placoid scales were sampled from sixteen regions across the body. Morphometric variables included the number of scales per area of integument, scale crown width, length and …
Dynamics Of Fish Assemblages Associated With An Offshore Artificial Reef In The Southern Mid-Atlantic Bight, Aaron J. Adams
Dynamics Of Fish Assemblages Associated With An Offshore Artificial Reef In The Southern Mid-Atlantic Bight, Aaron J. Adams
Dissertations, Theses, and Masters Projects
No abstract provided.
Characterization Of Anti-Tumor Immunity In Oyster Toadfish (Opsanus Tau), And The Effects Of 7,12 -Dimethylbenz(A)Anthracene On This Immune Response, Kenneth R. Seeley
Characterization Of Anti-Tumor Immunity In Oyster Toadfish (Opsanus Tau), And The Effects Of 7,12 -Dimethylbenz(A)Anthracene On This Immune Response, Kenneth R. Seeley
Dissertations, Theses, and Masters Projects
Cell-mediated lysis of cultured tumor target cells by nonspecific cytotoxic cells (NCC) was examined in the oyster toadfish (Opsanus tau), an estuarine teleost. NCC activity was evaluated in cells taken from the head kidney, peripheral blood, spleen and peritoneal cavity. NCC activity was a property of plastic nonadherent cells which lacked phagocytic activity, indicating that in terms of their functional capacity, the cells which mediate nonspecific cytoxic immune responses in oyster toadfish do not appear to be monocytes or macrophages. However, light and electron microscopic examination of these cells revealed that morphologically, they resemble monocytes and macrophages. A new technique …
Beach Forms Induced By Coastal Structures Forming Embayments In Fetch-Limited Environments, Jian Hua Li
Beach Forms Induced By Coastal Structures Forming Embayments In Fetch-Limited Environments, Jian Hua Li
Dissertations, Theses, and Masters Projects
No abstract provided.