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2007

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Articles 1951 - 1980 of 3831

Full-Text Articles in Engineering

Investigation Into Nanocomposites For Applications In Lightning Strike Protection, Matthew S. Bond, James A. Rodriguez, Hieut T. Nguyen Mar 2007

Investigation Into Nanocomposites For Applications In Lightning Strike Protection, Matthew S. Bond, James A. Rodriguez, Hieut T. Nguyen

Theses and Dissertations

The United States Air Force is continually researching ways to reduce costs associated with aircraft maintenance and improve operational safety. This study focuses on creating a systems engineering process to develop an Integrated Structural Health Monitoring System (ISHMS). The overarching process was then applied to design a conceptual ISHMS for a real-world scenario involving the F-15. Sensor selection, integration and testing were explored in detail using frequency response methods to detect structural damage. Testing was accomplished using a simplified structural specimen with Monitoring & Evaluation Technology Integration System (METIS) disk nodes attached at various locations. Two different METIS disk operation …

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Autonomous Unmarked Aerial Rendezvous For Automated Aerial Refueling (Aar), Brian S. Burns Mar 2007

Autonomous Unmarked Aerial Rendezvous For Automated Aerial Refueling (Aar), Brian S. Burns

Theses and Dissertations

As unmanned aerial vehicles (UAVs) increase in capability, the ability to refuel them in the air is becoming more critical. Aerial refueling will extend the range, shorten the response times, and extend loiter time of UAVs. Executing aerial refueling autonomously will reduce the command and control, logistics, and training efforts associated with fielding UAV systems. Currently, the Air Force Research Lab is researching the various technologies required to conduct automated aerial refueling (AAR). One of the required technologies is the ability to autonomously rendezvous with the tanker. The goal of this research is to determine the control required to fly …

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Optimal Wind Corrected Flight Path Planning For Autonomous Micro Air Vehicles, Michael D. Zollars Mar 2007

Optimal Wind Corrected Flight Path Planning For Autonomous Micro Air Vehicles, Michael D. Zollars

Theses and Dissertations

This research effort focuses on determining the optimal flight path required to put a micro air vehicle's (MAVs) fixed sensor on a target in the presence of a constant wind. Autonomous flight is quickly becoming the future of air power and over the past several years, the size and weight of autonomous vehicles has decreased dramatically. As these vehicles were implemented into the field, it was quickly discovered that their flight paths are severely altered by wind. However, since the size of the vehicle does not allow for a gimbaled camera, only a slight perturbation to the attitude of the …

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Modeling In Situ Bioremediation Of Perchlorate-Contaminated Groundwater, Roland E. Secody Mar 2007

Modeling In Situ Bioremediation Of Perchlorate-Contaminated Groundwater, Roland E. Secody

Theses and Dissertations

Perchlorate-contaminated groundwater is a significant problem for the Department of Defense and the United States Air Force. An innovative technology was recently developed which uses dual-screened treatment wells to mix an electron donor into perchlorate-contaminated groundwater in order to effect in situ bioremediation of the perchlorate by indigenous perchlorate reducing bacteria without the need to extract the contaminated water from the subsurface. In this study, a model that simulates operation of the technology is calibrated and validated using 761 days of observational data obtained from a field-scale technology evaluation project. A genetic algorithm was used with the first 113 days …

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Biofiltration As A Viable Alternative For Air Pollution Control At Department Of Defense Surface Coating Facilities, David M. Hudock Mar 2007

Biofiltration As A Viable Alternative For Air Pollution Control At Department Of Defense Surface Coating Facilities, David M. Hudock

Theses and Dissertations

Surface coating operations at aircraft depot facilities are common throughout the Department of Defense (DoD). During paint application processes at Navy and Marine Corps Fleet Readiness Centers (FRCs), spray paints emit volatile organic compounds (VOCs) known to have harmful effects on human health and the environment. FRC East at Marine Corps Air Station Cherry Point, does not control the emissions of VOCs from any of its paint booths. The purpose of this research is to determine if FRC East and its surrounding area can benefit both economically and environmentally from a biofiltration system for air pollution control (APC) rather than …

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Precise Calculation Of Complex Radioactive Decay Chains, Logan J. Harr Mar 2007

Precise Calculation Of Complex Radioactive Decay Chains, Logan J. Harr

Theses and Dissertations

This thesis documents a new approach to investigate the gamma radiation activity of the fission products of three different fuels (U-235, U-238, and U-239) exposed to three different incident neutron energy spectra (thermal, fast spectrum, and high energies). An application of the exponential moments function is used with a transmutation matrix in the calculation of complex radioactive decay chains to achieve greater precision than can be attained through current methods. The result of this research is a code which can calculate the decay products from complex radioactive decay chains with a high degree of precision while quantifying the uncertainty in …

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Filtered Rayleigh Scattering Measurements In A Bouyant Flowfield, Christopher C. Mcgaha Mar 2007

Filtered Rayleigh Scattering Measurements In A Bouyant Flowfield, Christopher C. Mcgaha

Theses and Dissertations

Filtered Rayleigh Scattering (FRS) is a non-intrusive technique for studying flowfields. Molecular scattering provides the signal to the camera, and the difference in molecular cross section can be used to discriminate between unmixed gaseous components. The focus of this research is to document the behavior of a horizontal buoyant jet using FRS. A helium jet of precisely controlled mass flow rate is injected into a standard room temperature environment, and FRS provides the means to measure its core trajectory and mixing rate. Trajectory analysis, conducted with consideration of the Reynolds number and Grashof number, can be used to compare these …

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Optical Parametric Oscillation In Orientation-Patterned Gallium Arsenide, Scott A. Shell Mar 2007

Optical Parametric Oscillation In Orientation-Patterned Gallium Arsenide, Scott A. Shell

Theses and Dissertations

Tunable laser sources in the mid-infrared (MIR) spectral range are required for several Air Force applications. Existing lasers with output in the near-infrared can be converted to more desirable MIR by using nonlinear effects. Orientation patterned gallium arsenide (OPGaAs) is a promising nonlinear conversion material because it has broad transparency and can be engineered for specific pump laser and output wavelengths using quasi-phase matching techniques. This research examines optical parametric oscillation (OPO) of several OPGaAs samples using a 2.052 micrometers wavelength Tm, Ho:YLF pump laser. Of the seven samples available the five that were capable of getting OPO output with …

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Comparative Analysis Of A High Bypass Turbofan Using A Pulsed Detonation Combustor, Ionio Q. Andrus Mar 2007

Comparative Analysis Of A High Bypass Turbofan Using A Pulsed Detonation Combustor, Ionio Q. Andrus

Theses and Dissertations

It has been proposed that the implementation of a pulsed detonation combustor in a high-bypass turbofan engine would result in an engine that is both more efficient and more reliable. The validity of the performance claims are evaluated based on a comparison between the baseline and hybrid turbofans. The hybrid pulsed detonation engine was modeled in the Numerical Propulsion Simulation System (NPSS) and shares a common architecture with the baseline turbofan model, except that the combustor of the baseline engine is replaced with a pulsed detonation combustor. Detonation effects are calculated using a closed form solution of the Chapman-Jouguet Mach …

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Tension-Compression Fatigue Behavior Of A Carbon Fiber/Epoxy (Im7/Epon 862) Composite Fabricated Using Vacuum Assisted Resin Transfer Molding Process, David W. Katwyk Mar 2007

Tension-Compression Fatigue Behavior Of A Carbon Fiber/Epoxy (Im7/Epon 862) Composite Fabricated Using Vacuum Assisted Resin Transfer Molding Process, David W. Katwyk

Theses and Dissertations

New composite materials and processing methods are continually being developed for use in high performance aerospace systems. One of these new processing methods is the vacuum assisted resin transfer molding (VARTM) process, which shows promise in producing large structural components that have good properties at a lower cost than traditional manufacturing methods. Future widespread use of components manufactured using the VARTM process depends on understanding how these components perform under service conditions, specifically under impact and fatigue conditions. The tension-compression fatigue behavior of a four-harness satin weave carbon fiber/epoxy (IM7/EPON 862) composite manufactured using the VARTM process is investigated in …

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Structure And Nitrogen Chemistry In Coal, Biomass, And Cofiring Low-Nox Flames, Bradley David Damstedt Mar 2007

Structure And Nitrogen Chemistry In Coal, Biomass, And Cofiring Low-Nox Flames, Bradley David Damstedt

Theses and Dissertations

Addressing global climate change will require increasing sustainable energy usage. Cofiring biomass fuels with coal for electrical power generation is an efficient, cost effective method of CO2 mitigation. This work is an experimental investigation of the flame structure and nitrogen chemistry differences occurring between coal, biomass and cofiring flames. A pilot-scale facility was fired with a dual-feed low-NOx burner capable of independently conveying 2 separate fuels unblended to the burner. Spatially detailed gas species measurements were made for 8 flames, including a coal, straw, finely ground straw, wood, and 4 straw/coal cofiring flames. Particle samples were also obtained from 5 …

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Spacecraft Proximity Operations Used To Estimate The Dynamical & Physical Properties Of A Resident Space Object, Abraham F. Brunner Mar 2007

Spacecraft Proximity Operations Used To Estimate The Dynamical & Physical Properties Of A Resident Space Object, Abraham F. Brunner

Theses and Dissertations

When conducting a space proximity operation, developing high-fidelity estimates of the dynamical and physical properties of a Resident Space Object (RSO) based on post-rendezvous observational data acquired, is imperative for the understanding of the RSO itself and the operating environment. This research investigates the estimation of relative motion dynamics, rotational dynamics, and the feasibility of estimating the moments of inertia of a RSO. Using the Hill-Clohessy-Wiltshire equations, rigid-body dynamics, and estimation theory, a nonlinear least squares estimation algorithm is implemented in the processing of range data from tracked observation points on the RSO body. Through simulation, it was determined that …

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Parameter Importance Of An Analytical Model For Transport In The Vadose Zone, Tanner Hans Bushnell Mar 2007

Parameter Importance Of An Analytical Model For Transport In The Vadose Zone, Tanner Hans Bushnell

Theses and Dissertations

The American Society of Testing and Materials (ASTM) has established a three tier risk-based corrective action (RBCA) program for cleaning up petroleum release sites, which is supported by the Environmental Protection Agency. RBCA programs make the cleanup of spill sites more efficient by requiring additional site information only when a more accurate risk assessment is needed. For spill sites that do not pass the first tier general assessment, a Tier 2 evaluation involving site specific information and screening level models to assess the potential risk must be conducted. Screening level models generally require site specific input parameters. To increase efficiency …

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A High-Resolution Microscopic Electrical Impedance Imaging Modality: Scanning Impedance Imaging, Hongze Liu Mar 2007

A High-Resolution Microscopic Electrical Impedance Imaging Modality: Scanning Impedance Imaging, Hongze Liu

Theses and Dissertations

Electrical impedance imaging is an imaging technique which has the capability of revealing the spatial distribution of the electrical impedance inside biological tissues. Classical electrical impedance imaging including Electrical Impedance Tomography (EIT) typically has low resolution. Advances in electrical impedance imaging typically involve methods that either increase image resolution or image contrast. This study investigates the possibility of the resolution improvement for electrical impedance imaging using motion, and presents a novel high-resolution and calibrated impedance imaging method called Scanning electrical Impedance Imaging (SII). SII uses an electrical probe held at a known voltage and scanned over a thin sample immersed …

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Determination Of Young’S Modulus Of Individual Electrospun Nanofibers, Philip A. Yuya, Yongkui Wen, Joseph A. Turner, Yuris A. Dzenis, Zheng Li Mar 2007

Determination Of Young’S Modulus Of Individual Electrospun Nanofibers, Philip A. Yuya, Yongkui Wen, Joseph A. Turner, Yuris A. Dzenis, Zheng Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

The authors report a technique for measuring Young’s modulus of a single electrospun nanofiber using the vibrations of two microcantilevers coupled with the nanofiber. The modulus is calculated from the resonant frequency shift resulting from the nanofiber. Polyacrylonitrile nanofibers (200 nm diameter) were collected during electrospinning and wrapped on two similar microcantilevers causing a shift in first resonance from 10.0 to 19.4 kHz. Finite element analysis was used to analyze the frequency shift using images from a scanning electron microscope giving a modulus of the as-spun polyacrylonitrile nanofiber of 26.8 GPa.

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An Evaluation Of High Velocity Wear, Gregory J. Cameron Mar 2007

An Evaluation Of High Velocity Wear, Gregory J. Cameron

Theses and Dissertations

The Holloman High Speed Test Track (HHSTT) is a rocket-powered sled track facility used for testing a variety of hypervelocity aerospace applications. The current speed record is 6,453 miles per hour. While this seems fast there are customers at the track that have requirements demanding even faster speeds. Significant research has been conducted in the area of rail gouging as it relates to the test track, and efforts are under way to reduce and even eliminate this phenomenon. Any steps taken in this effort may eliminate catastrophic sled failures caused by gouging, however wear is another damaging issue that needs …

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Damage Detection Using Lamb Waves For Structural Health Monitoring, Jeffrey S. Crider Ii Mar 2007

Damage Detection Using Lamb Waves For Structural Health Monitoring, Jeffrey S. Crider Ii

Theses and Dissertations

Nondestructive structural health monitoring (SHM) is an evolving technology being developed for monitoring air and space systems. The information gathered on a system's structural integrity through SHM detection methods may result in reduced costly maintenance inspections, enhanced safety, and system failure predictions. This study evaluates Lamb wave approaches used to detect simulated cracks in laboratory experiments on thin plates to detect more realistic damage in a test article representing the complex geometry of an existing aircraft bulkhead. We take a "hot-spot" monitoring approach, where we monitor an area of the structure known to fail. In our experiment, we evaluated the …

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Quick-Turn Finite Element Analysis For Plug-And Play Satellite Structures, Jeffrey E. Naff Mar 2007

Quick-Turn Finite Element Analysis For Plug-And Play Satellite Structures, Jeffrey E. Naff

Theses and Dissertations

Plug-and-play (PnP) satellite construction is a key component of the US Air Force Operational Responsive Space (ORS) effort. The goal of ORS is to provide mission specific satellite support by configuring and launching a satellite to a selected orbit within days of the request. One major challenge during the time limited process is to accurately predict the response of the satellite to harmonic loads that occur during launch and satellite operation. Given the time limitations, constructing finite element (FE) models by traditional methods is not currently a viable option for the ORS timeline. By implementing an approach for rapid FE …

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Culvert Hydraulics: Comparison Of Current Computer Models, Elizabeth Anne Thiele Mar 2007

Culvert Hydraulics: Comparison Of Current Computer Models, Elizabeth Anne Thiele

Theses and Dissertations

The hydraulic analysis of culverts is complicated when using hand calculations. Fortunately, several computer programs are available to assist in analyzing culvert hydraulics, some of which include HY-8, Fish X-ing, Broken-back Culvert Analysis Program (BCAP), Hydraflow Express, Culvert Master, Culvert, and Hydrologic Engineering Center River Analysis System (HEC-RAS). While all of these programs can simulate the behavior of flow through a culvert, slightly different methodologies are utilized among the programs to complete a full hydraulic analysis, resulting in different predictions for headwater depth, flow control, and outlet velocities. The purpose of this paper is to compare (1) the available hydraulic …

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Adhesion-Delamination Mechanics Of A Prestressed Rectangular Film Adhered Onto A Rigid Substrate, Ming Fung Wong, Gang Duan, Kai-Tak Wan Mar 2007

Adhesion-Delamination Mechanics Of A Prestressed Rectangular Film Adhered Onto A Rigid Substrate, Ming Fung Wong, Gang Duan, Kai-Tak Wan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A prestressed rectangular film clamped at both ends delaminates from a rigid punch. based on a thermodynamic energy balance, the delamination mechanics is derived to relate the simultaneous external tensile force applied to the punch, punch displacement, and contact area. Effects of the coupled tensile residual membrane stress and adhesion energy at the punch-film interface are investigated. a "pinch off" (stable shrinking of the contact area to a line) is predicted, contrasting the nonzero "pull-off" radius in a clamped circular film. the model is useful in understanding the behavior of various adhesion-delamination phenomena, especially in one dimensional capacitive microelectromechanical systems …

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Use Of Tabu Search In A Solver To Map Complex Networks Onto Emulab Testbeds, Jason E. Macdonald Mar 2007

Use Of Tabu Search In A Solver To Map Complex Networks Onto Emulab Testbeds, Jason E. Macdonald

Theses and Dissertations

The University of Utah's solver for the testbed mapping problem uses a simulated annealing metaheuristic algorithm to map a researcher's experimental network topology onto available testbed resources. This research uses tabu search to find near-optimal physical topology solutions to user experiments consisting of scale-free complex networks. While simulated annealing arrives at solutions almost exclusively by chance, tabu search incorporates the use of memory and other techniques to guide the search towards good solutions. Both search algorithms are compared to determine whether tabu search can produce equal or higher quality solutions than simulated annealing in a shorter amount of time. It …

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Effects Of Temperature And Environment On Creep Behavior Of An Oxide-Oxide Ceramic Matrix Composite, Jason C. Braun Mar 2007

Effects Of Temperature And Environment On Creep Behavior Of An Oxide-Oxide Ceramic Matrix Composite, Jason C. Braun

Theses and Dissertations

This research investigated the creep behavior of an N720/Al203 composite. The composite consists of a porous alumina matrix reinforced with laminated, woven mullite/alumina fibers (NextelTM 720). This ceramic matrix composite (CMC) has no fiber coating and relies on the porous matrix for flaw tolerance. The tensile stress-strain behavior was investigated and the tensile properties measured in the 800-1100 °C temperature range. Tensile creep behavior was examined at 1000 and 1100 °C in laboratory air and in steam environment. In air creep stress was 150 MPa. In steam creep stresses ranged from 100 to 160 MPa. Primary …

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Experimental Investigation Of Turbojet Thrust Augmentation Using An Ejector, David A. Hoffman Mar 2007

Experimental Investigation Of Turbojet Thrust Augmentation Using An Ejector, David A. Hoffman

Theses and Dissertations

The use of computer simulation in the development of autonomously controlled unmanned combat aerial vehicles (UCAV) for wide area search and engagement applications is addressed. Computer simulation is an essential tool to analyze control algorithms designed to optimally employ multiple UCAVs in wide area search and engagement. To be representative of real world mission conditions a simulation must be able to accurately duplicate the performance of the automatic target recognition (ATR) methods that will be used to discriminate between targets and non-targets in actual combat. The objective of this research is to demonstrate a method to validate a simulation's ATR …

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Satellite Formation Control Using Atmospheric Drag, Blake B. Hajovsky Mar 2007

Satellite Formation Control Using Atmospheric Drag, Blake B. Hajovsky

Theses and Dissertations

This study investigates the use of a linear quadratic terminal controller to reconfigure satellite formations using atmospheric drag actuated control while minimizing the loss of energy of the formation. The linearized Clohessy-Wiltshire equations of motion are used to describe the motion of the two-satellite formation about an empty reference position maintained at the formation center. Reconfigurations to final in-plane and elliptical formations are simulated at orbital radii of 6800 km and 7000 km, and the altitude loss and a ?v budget were recorded as performance measures for each reconfiguration. The final states of the spacecraft upon reconfiguration were propagated forward …

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Method And Apparatus For Nondestructive Sample Inspection, R. Zoughi, Sergey Kharkovsky, Mohammad Tayeb Ahmad Ghasr Mar 2007

Method And Apparatus For Nondestructive Sample Inspection, R. Zoughi, Sergey Kharkovsky, Mohammad Tayeb Ahmad Ghasr

Electrical and Computer Engineering Faculty Research & Creative Works

An apparatus for inspecting a sample for defects includes a signal generator for generating a signal and a device for splitting the signal into two separate signals which have substantially equal phase and magnitude. A sensor radiates the two signals on the sample and receives the two signals reflected from the sample. A device is provided for determining a difference between the two signals reflected from the sample without unwanted influence of variations of distance between the sensor and sample, and reflections from nearby sample edges and boundaries. A defect is determined to exist when a difference is found between …

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Biolaunch: Ssdl Astrobiology Initiative High-Altitude Balloons And Nanosatellites, Stanford University, Space And Systems Development Laboratory Mar 2007

Biolaunch: Ssdl Astrobiology Initiative High-Altitude Balloons And Nanosatellites, Stanford University, Space And Systems Development Laboratory

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by the Stanford University, Space and Systems Development Laboratory  titled "BioLaunch: SSDL Astrobiology Initiative High-Altitude Balloons and NanoSatellites" from March 13, 2007.

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Biolaunch: Ssdl/Astrobiology Initiative High-Altitude Balloons And Picosatellites, Stanford University, Space And Systems Development Laboratory Mar 2007

Biolaunch: Ssdl/Astrobiology Initiative High-Altitude Balloons And Picosatellites, Stanford University, Space And Systems Development Laboratory

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by the Stanford University, Space and Systems Development Laboratory titled "BioLaunch: SSDL/Astrobiology Initiative High-Altitude Balloons and PicoSatellites" from March 13, 2007.

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Development Of A Screening Model For Design And Costing Of An Innovative Tailored Granular Activated Carbon Technology To Treat Perchlorate-Contaminated Water, William C. Powell Mar 2007

Development Of A Screening Model For Design And Costing Of An Innovative Tailored Granular Activated Carbon Technology To Treat Perchlorate-Contaminated Water, William C. Powell

Theses and Dissertations

Perchlorate contamination of drinking water is a problem that has recently gained national attention. The purpose of this research was to develop a tool to predict the cost and performance of tailored granular activated carbon (T-GAC), an innovative technology to treat perchlorate-contaminated water. The ability to predict cost and performance is essential to promote transfer and commercialization of innovative technologies. This study investigated how data obtained from small-scale laboratory tests could be applied to predict cost and performance of a full-scale T-GAC system to treat perchlorate-contaminated water. A technology model was developed using GAC design principles and using a multi-component …

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Point Spread Function Characterization Of A Radially Displaced Scatterer Using Circular Synthetic Aperture Radar, Uttam K. Majumder Mar 2007

Point Spread Function Characterization Of A Radially Displaced Scatterer Using Circular Synthetic Aperture Radar, Uttam K. Majumder

Theses and Dissertations

This research effort investigated characterizing the point spread function (PSF) behavior of radially displaced point scatterers using circular synthetic aperture radar (CSAR). Thus far, research has been conducted to understand PSF of a scatterer located at the imaging scene center. An analytic closed-form solution has been derived assuming the scatterer is located at the origin of the CSAR imaging geometry. However, it is difficult to derive an analytic PSF solution for a scatterer that is radially displaced from the imaging scene center. Using the back projection image formation algorithm, PSF responses are generated at various point target locations. Consistent with …

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Cobalt Doping Of Semiconducting Boron Carbide Using Cobaltocene, Lonnie Carlson Mar 2007

Cobalt Doping Of Semiconducting Boron Carbide Using Cobaltocene, Lonnie Carlson

Theses and Dissertations

The decomposition of cobaltocene and metacarborane (closo-1,7-dicarba-decaborane) under low energy electron irradiation at about 200 K results in a material with the Fermi level closer to the valence band than the material resulting from the decomposition of metacarborane alone. This indicates that cobaltocene provides a relatively p-type dopant as seen in ultraviolet photoemission spectroscopy/inverse photoemission spectroscopy. Upon warming to room temperature, however, the Fermi level shifts towards the conduction band, suggesting an n-type dopant. This temperature dependent surface photovoltage effect is not compelling evidence for the majority carrier type but does suggest an increase in the carrier concentration …

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