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Articles 3361 - 3390 of 5700
Full-Text Articles in Engineering
Microelectromechanical Systems (Mems) Interrupter For Safe And Arm Devices, Steven S. Mink
Microelectromechanical Systems (Mems) Interrupter For Safe And Arm Devices, Steven S. Mink
Theses and Dissertations
This thesis addresses the development of a new micro-scale interrupter mechanism for a safe and arm device used in modern weapon systems. The interrupter mechanism often consists of a physical barrier that prevents an initial source of energy, in an explosive train, from being transferred to subsequent charges. In general, when the physical barrier is removed, the weapon is considered armed, and the charge is allowed to propagate. Several issues facing current safe and arm devices systems are the shrinking industrial base for manufacturing these devices and the desire for modern safe and arm devices to be compatible with next …
Non-Cooperative Detection Of Frequency-Hopped Gmsk Signals, Clint R. Sikes
Non-Cooperative Detection Of Frequency-Hopped Gmsk Signals, Clint R. Sikes
Theses and Dissertations
Many current and emerging communication signals use Gaussian Minimum Shift Keyed (GMSK), Frequency-Hopped (FH) waveforms to reduce adjacent-channel interference while maintaining Low Probability of Intercept (LPI) characteristics. These waveforms appear in both military (Tactical Targeting Networking Technology, or TTNT) and civilian (Bluetooth) applications. This research develops wideband and channelized radiometer intercept receiver models to detect a GMSK-FH signal under a variety of conditions in a tactical communications environment. The signal of interest (SOI) and receivers have both fixed and variable parameters. Jamming is also introduced into the system to serve as an environmental parameter. These parameters are adjusted to examine …
Estimation And Mitigation Of Unmodeled Errors For A Pseudolite Based Reference System, Jeremiah A. Shockley
Estimation And Mitigation Of Unmodeled Errors For A Pseudolite Based Reference System, Jeremiah A. Shockley
Theses and Dissertations
Current flight reference systems rely heavily on the Global Positioning System (GPS), causing susceptibility to GPS jamming. Additionally, an increasing number of tests involve jamming the GPS signal. A need exists to develop a system capable of GPS-level accuracy during these outages. One promising solution is a ground-based pseudolite system capable of delivering sub-centimeter level accuracy, yet operating at non-GPS frequencies. This thesis attempts to determine the unknown errors in the Locata system, one such pseudolite-based system, to achieve the accuracy required. The development of a measurement simulation tool along with a Kalman filter algorithm provides confirmation of filter performance …
Supplementing An Ad-Hoc Wireless Network Routing Protocol With Radio Frequency Identification (Rfid) Tags, Leroy S. Willemsen
Supplementing An Ad-Hoc Wireless Network Routing Protocol With Radio Frequency Identification (Rfid) Tags, Leroy S. Willemsen
Theses and Dissertations
Wireless sensor networks (WSNs) have a broad and varied range of applications, yet all of these are limited by the resources available to the sensor nodes that make up the WSN. The most significant resource is energy. A WSN may be deployed to an inhospitable or unreachable area, leaving it with a non-replenishable power source. This research examines a way of reducing energy consumption by augmenting the nodes with radio frequency identification (RFID) tags that contain routing information. It was expected that RFID tags would reduce the network throughput, the ad hoc on-demand distance vector (AODV) routing traffic sent, and …
Bio-Inspired, Odor-Based Navigation, Maynard John Porter Iii
Bio-Inspired, Odor-Based Navigation, Maynard John Porter Iii
Theses and Dissertations
The ability of moths to locate a member of the opposite sex, by tracking a wind-borne plume of odor molecules, is an amazing reality. Numerous scenarios exist where having this capability embedded into ground-based or aerial vehicles would be invaluable. The main crux of this thesis investigation is the development of a navigation algorithm which gives a UAV the ability to track a chemical plume to its source. Inspiration from the male moth's, in particular Manduca sexta, ability to successfully track a female's pheromone plume was used in the design of both 2-D and 3-D navigation algorithms. The algorithms were …
Graphitized Carbon Foam With Phase Change Material, Angelinda D. Fedden
Graphitized Carbon Foam With Phase Change Material, Angelinda D. Fedden
Theses and Dissertations
This thesis examines the transient heating and cooling responses of graphitized carbon foam infiltrated with phase change material (PCM). The carbon foam provides rapid heat transfer throughout the PCM volume, while the PCM stores the heat for later removal. The foam/PCM system was heated with a copper heating block, and then cooled with a liquid-cooled heat removal block. Infiltrating the foam with PCM significantly increased the length of time before the system reached maximum temperature. The temperature response of the foam/PCM system was consistent over multiple cycles of heating and cooling. A high density foam had a faster heating and …
Lqg/Ltr Tilt And Tip Control For The Starfire Optical Range 3.5-Meter Telescope's Adaptive Optics System, Neil D. Paris
Lqg/Ltr Tilt And Tip Control For The Starfire Optical Range 3.5-Meter Telescope's Adaptive Optics System, Neil D. Paris
Theses and Dissertations
The Air Force Research Laboratory has sponsored research on the tracking control loop portion of the adaptive optics system in the Starfire Optical Range 3.5-meter telescope at Kirtland Air Force Base. The control loop includes two steering mirrors (Coarse Steering Mirror and Fine Steering Mirror) used to remove wavefront tilt and tip phase distortion from light entering the telescope. The objective of this research is to design a single Linear Quadratic Gaussian controller to control both steering mirrors in order to eliminate wavefront tilt and tip distortions induced by the earth's atmosphere, and to evaluate the stability robustness and performance …
Detailed Design Of The Rigidizable Inflatable Get-Away-Special Experiment, Jeremy S. Goodwin
Detailed Design Of The Rigidizable Inflatable Get-Away-Special Experiment, Jeremy S. Goodwin
Theses and Dissertations
The Rigidizable Inflatable Get-Away-Special Experiment is a Space Shuttle experiment that will study the effects of the zero-gravity space environment on the deployment and modal analysis of three inflatable and rigidizable tubes using a sub-Tg rigidization technique. In 2004, RIGEX was transitioned from the Space Shuttle's Get-Away-Special (GAS) canister to its Canister for All Payload Ejections (CAPE), requiring several modifications to the design. The results of these modifications, along with further refinements made to previous efforts, combine to form the detailed design of the experiment. In addition to the design modifications, analyses were conducted to determine the containment capabilities of …
Inertia Measurement And Dynamic Stability Analysis Of A Radio-Controlled Joined-Wing Aircraft, William A. Mcclelland
Inertia Measurement And Dynamic Stability Analysis Of A Radio-Controlled Joined-Wing Aircraft, William A. Mcclelland
Theses and Dissertations
Dynamic stability and stall during steady level turns were examined for VA-1, a joined-wing flight demonstrator aircraft. Configurations with a lower vertical tail and fairings over the main landing gear were compared with a recommendation on the combination had the best drag and dynamic stability characteristics. The dynamic stability analysis was broken into four key parts: a twist test experimentally measured mass moments of inertia, a panel method was used to find non-dimensional stability derivatives, lateral and longitudinal state space models estimated dynamic stability characteristics and handling quality levels were evaluated using a Cooper-Harper based rating system. VA-1 was found …
The Effects Of Using Solar Radiation Pressure To Alleviate Fuel Requirements For Orbit Changing And Maintenance Of The Dscs Ii F-13 Satellite, Jody A. Paris
Theses and Dissertations
Orbit disposal and maintenance of aging satellites has become a significant concern over the past few years, as the increasing number of orbiting objects threatens to limit the launching of future satellites. Many of the satellites currently in orbit, however, were not built with disposal considerations. The DSCS II series was launched into orbit beginning in the 1970s, and many satellites are now without the fuel required to conventionally transition to a sanctioned disposal orbit. In GEO orbit the largest non-gravitational perturbation is solar radiation pressure. By adjusting the attitude of a satellite with a controller to maximize the perturbing …
Cost Comparison Of Expendable, Hybrid And Reusable Launch Vehicles, Greg J. Gstattenbauer
Cost Comparison Of Expendable, Hybrid And Reusable Launch Vehicles, Greg J. Gstattenbauer
Theses and Dissertations
This study compares the developmental, production, and maintenance costs (DPM) of twostage- to-orbit (TSTO) expendable (ELV), hybrid (HLV), and reusable (RLV) launch systems. This comparison was accomplished using top level mass and cost estimating relations (MERs, CERs). Mass estimating relationships were correlated to existing launch system data and ongoing launch system studies. Cost estimating relations were derived from Dr. Dietrich Koelle's 'Handbook of Cost Engineering for Space Transportation Systems'. Hybrid launch vehicles appear to be preferable if current or modest increases in launch rates are projected while reusable launch vehicles appear preferable for large projected increases in launch rates.
Characterizing And Controlling The Effects Of Differential Drag On Satellite Formations, James T. Wedekind
Characterizing And Controlling The Effects Of Differential Drag On Satellite Formations, James T. Wedekind
Theses and Dissertations
The ability to fly satellites in close formations represents a capability that could revolutionize the way satellite missions are designed in the future. This study examines three of the primary formation flying designs and characterizes the effects that an anomalous satellite with a slightly different cross-sectional area would have on the stability of the formation. Following the characterization of these effects, a controller is implemented to mitigate the cross-sectional area differences between the satellites. The results show that, with the addition of a straightforward controller, small cross-sectional area differences can be mitigated and corrected such that the satellites will remain …
Performance Capability Of A Damaged Lighter-Than-Air Vehicle Operating In The Near Space Regime, Charles W. Vogt Jr.
Performance Capability Of A Damaged Lighter-Than-Air Vehicle Operating In The Near Space Regime, Charles W. Vogt Jr.
Theses and Dissertations
This study investigates the ability of a high-altitude airship to maintain lift following the compromise of its lifting gas envelope. Accepted engineering principles are applied to develop a model that provides comparative analyses for airship depressurization alternatives following hull compromise. Specifically, maintaining lifting gas envelope overpressure to provide controllability in wind currents while sacrificing some buoyancy is compared with allowing envelope depressurization to occur with the goal of maintaining greater buoyancy as long as possible. The model provides insights to alternatives for recovering a damaged vehicle and its payload. In particular, the analysis demonstrates that maintaining the ability to navigate …
Application Of Spline Variational Analysis Method In The Modeling Of Composite Repairs, Brian M. Fredrickson
Application Of Spline Variational Analysis Method In The Modeling Of Composite Repairs, Brian M. Fredrickson
Theses and Dissertations
The purpose of this thesis is to apply a non-commercialized spline-based (BSpline Analysis Method or BSAM) computer program to model and predict strain fields in two composite repairs, a scarf joint and a stepped-lap joint, subjected to static tensile loading. Test specimens with scarf and stepped-lap joints are fabricated using quasiisotropic sixteen ply panels made from IM6/3501-6 prepreg with a [+452/02/-452/902]s lay-up. The panels were bonded together with FM-300M (0.05psf), a 176°C cure film adhesive, under positive pressure. A total of five coupons of each joint type are made. Two of …
Cycle Performance Of A Pulse Detonation Engine With Supercritical Fuel Injection, Timothy M. Helfrich
Cycle Performance Of A Pulse Detonation Engine With Supercritical Fuel Injection, Timothy M. Helfrich
Theses and Dissertations
Pulse detonation engines (PDE) rely on rapid ignition and formation of detonation waves. Because hydrocarbon fuels are composed typically of long carbon chains that must be reduced in the combustion process, it would be beneficial to create such reduction prior to injection of fuel into the engine. This study focused on PDE operation enhancements using dual detonation tube, concentric-counter-flow heat exchangers to elevate the fuel temperature up to supercritical temperatures. Variation of several operating parameters included fuel type (JP-8, JP-7, JP-10, RP-1, JP-900, and S-8), ignition delay, frequency, internal spiral length, and purge fraction. To quantify the performance, four key …
Characterization Of Compressive Creep Behavior Of Oxide/Oxide Composite With Monazite Coating At Elevated Temperature, Patrick R. Jackson
Characterization Of Compressive Creep Behavior Of Oxide/Oxide Composite With Monazite Coating At Elevated Temperature, Patrick R. Jackson
Theses and Dissertations
The compressive creep behavior of a N610/monazite/alumina composite was investigated in this work. The composite consists of a porous alumina matrix reinforced with NextelTM610 fibers coated with monazite in a symmetric cross-ply (0°/90°/0°/90°)s orientation. Compressive stress-strain behavior was investigated as well. The addition of monazite coating resulted in ~ 35% loss in compressive strength at 900°C and in ~45% loss in compressive strength at 1100°C. Compressive creep behavior was examined at 900 and 1100°C for creep stresses ranging from 50 to 95 MPa. Primary and secondary creep regimes were observed at both temperatures. Minimum creep rate was reached in all …
A Comparison Of Main Rotor Smoothing Adjustments Using Linear And Neural Network Algorithms, Nathan A. Miller
A Comparison Of Main Rotor Smoothing Adjustments Using Linear And Neural Network Algorithms, Nathan A. Miller
Theses and Dissertations
Helicopter main rotor smoothing is a maintenance procedure that is routinely performed to minimize airframe vibrations induced by non-uniform mass and/or aerodynamic distributions in the main rotor system. This important task is both time consuming and expensive, so improvements to the process have long been sought. Traditionally, vibrations have been minimized by calculating adjustments based on an assumed linear relationship between adjustments and vibration response. In recent years, artificial neural networks have been trained to recognize non-linear mappings between adjustments and vibration response. This research was conducted in order observe the character of the adjustment mapping of the Vibration Management …
Carrier Lifetime Dynamics Of Epitaxial Layer Hvpe Gallium Arsenide Using Time-Resolved Experiments, Wayne E. Eikenberry
Carrier Lifetime Dynamics Of Epitaxial Layer Hvpe Gallium Arsenide Using Time-Resolved Experiments, Wayne E. Eikenberry
Theses and Dissertations
GaAs is a potential semiconductor material for producing both mid-infrared and terahertz radiation using the new technique of quasi-phase matching in an orientationally patterned GaAs (OP-GaAs) crystal. OP-GaAs is grown using a fast growth process called hydride vapor phase epitaxy (HVPE). Unfortunately, HVPE produces a high number of defects. These defects cause Shockley-Read-Hall recombination rates to dominate over Auger and radiative recombination rates. The carrier lifetime from four OP-GaAs samples are reported here using two different experimental techniques. The first experiment used a streak camera to measure the carrier lifetime via time-resolved photoluminescence. The temporal resolution of the streak camera …
Characterization Of Pulse Detonation Engine Performance With Varying Free Stream Stagnation Pressure Levels, Wesley R. Knick
Characterization Of Pulse Detonation Engine Performance With Varying Free Stream Stagnation Pressure Levels, Wesley R. Knick
Theses and Dissertations
A pulse detonation engine operates on the principle that a fuel-air mixture injected into a tube will ignite and undergo a transition from a deflagration to a detonation and exit the tube at supersonic velocities. Studies in the field of combustion have shown that both ignition time and deflagration to detonation transition time can vary as a function of pressure. It can be hypothesized that if ignition and deflagration to detonation transition times can be reduced by increasing the free stream stagnation pressure level of the tube, it would then be possible to shorten the detonation tube length and increase …
Doppler-Only Multistatic Radar, Dustin G. Mixon
Doppler-Only Multistatic Radar, Dustin G. Mixon
Theses and Dissertations
In order to estimate the position and velocity of a target, most multistatic radar systems require multiple independent target measurements, such as angle-of-arrival, time-of-arrival, and Doppler information. Though inexpensive and reliable, Doppler-only systems have not been widely implemented due to the inherent nonlinear problem of determining a target’s position and velocity from their measurements. We solve this problem. In particular, we first establish the lack of observability in the Doppler-only bistatic system, thereby demonstrating the need for multiple transmitters and/or receivers. Next, for a multistatic system with a sufficient number of transmitter-receiver pairs, we invoke classical optimization techniques, such as …
A Climatological Study Of Equatorial Gps Data And The Effects On Ionospheric Scintillation, Katharine A. Wicker
A Climatological Study Of Equatorial Gps Data And The Effects On Ionospheric Scintillation, Katharine A. Wicker
Theses and Dissertations
Ionospheric scintillation is detrimental to radio signals, especially those from the global positioning system. Such scintillation is caused when a signal permeates the ionosphere through plasma bubbles. The signal’s phase and amplitude can be altered, and a receiver on the ground can lose lock on the GPS signal. Measured using a zero to one index known as S4, scintillation severity is based upon season, solar cycle, time of day, location and frequency. The most severe scintillation occurs at the equatorial anomaly, or fifteen degrees north and south of the equator. Seven years of data from fifteen different locations around the …
Roadblocks To Software Modernization, Dyan E. Mcclamma
Roadblocks To Software Modernization, Dyan E. Mcclamma
Theses and Dissertations
Failed or troubled modernization efforts, such as the multi-million dollar 1997-2000 ROCC/SOCC failure, are a serious acquisition problem for the Air Force. Using both historical data and a survey of current Air Force software acquisition program key staff, this research examined the Air Forces ability to modernize legacy software systems. The search of historical program data, to identify trends or similarities between known failed software modernization efforts, failed to uncover sufficient data for analysis. This lack of project data indicates a knowledge management issue (i.e. lessons learned are not recorded and stored so that they can be accessed by other …
Optimizing Mean Mission Duration For Multiple-Payload Satellites, John A. Flory
Optimizing Mean Mission Duration For Multiple-Payload Satellites, John A. Flory
Theses and Dissertations
This thesis addresses the problem of optimally selecting and specifying satellite payloads for inclusion on a satellite bus to be launched into a constellation. The objective is to select and specify payloads so that the total lifetime utility of the constellation is maximized. The satellite bus is limited by finite power, weight, volume, and cost constraints. This problem is modeled as a classical knapsack problem in one and multiple dimensions, and dynamic programming and binary integer programming formulations are provided to solve the problem. Due to the computational complexity of the problem, the solution techniques include exact methods as well …
Polar Phase Screens: A Comparison With Other Methods Of Random Phase Screen Generation, Rebecca J. Eckert
Polar Phase Screens: A Comparison With Other Methods Of Random Phase Screen Generation, Rebecca J. Eckert
Theses and Dissertations
This research provides the first organized comparison of random phase screen generation methods, including logarithmic polar Fourier series, using structure functions. Random phase screens are essential elements of simulating light propagation through turbulent media. In order to be effective, they must accurately reflect theory and be practical to implement. This research explains and evaluates three methods of generating random phase screens: using a Fourier series upon a polar frequency grid with logarithmic spacing; using the fast Fourier transform, with its Cartesian frequency grid; and using Zernike polynomials. It provides a comparison of the Polar Fourier Series technique with the two …
Power-Scavenging Mems Robots, Daniel J. Denninghoff
Power-Scavenging Mems Robots, Daniel J. Denninghoff
Theses and Dissertations
This thesis includes the design, modeling, and testing of novel, power-scavenging, biologically inspired MEMS microrobots. Over one hundred 500-μm and 990-μm microrobots with two, four, and eight wings were designed, fabricated, characterized. These microrobots constitute the smallest documented attempt at powered flight. Each microrobot wing is comprised of downward-deflecting, laser-powered thermal actuators made of gold and polysilicon; the microrobots were fabricated in PolyMUMPs® (Polysilicon Multi-User MEMS Processes). Characterization results of the microrobots illustrate how wing-tip deflection can be maximized by optimizing the gold-topolysilicon ratio as well as the dimensions of the actuator-wings. From these results, an optimum actuator-wing configuration was …
Evaluating The Correlation Characteristics Of Arbitrary Am And Fm Radio Signals For The Purpose Of Navigation, Bryan S. Kim
Evaluating The Correlation Characteristics Of Arbitrary Am And Fm Radio Signals For The Purpose Of Navigation, Bryan S. Kim
Theses and Dissertations
The Global Positioning System (GPS) provides position estimates on the Earth at anytime, anywhere and in any weather. However, to provide robust positioning, GPS requires an unobstructed path to satellite signals. As such, GPS performance generally degrades or becomes non-existent in environments such as large urban areas. This research investigates and analyzes the correlation characteristics of arbitrary AM and FM radio signals for the purpose of navigation. Simulations are conducted with different combinations of correlation methods (`fixed' or `varying'), modulation types (AM or FM), and signal types (song or voice). Out of the eight different variations considered, only two provided …
Investigation Of The Effects Of Target Feature Variations On Ballistic Missile Rcs, Sang H. Lee
Investigation Of The Effects Of Target Feature Variations On Ballistic Missile Rcs, Sang H. Lee
Theses and Dissertations
Uncertainties about certain features of target geometries can result in a loss of confidence in target signature assessment. This thesis describes the development of a general "rule-of-thumb" to determine how the radar signature of a target varies as a function of the target's specific features. The targets of interest in this study are fictitious ballistic missiles. Four target features of these missiles are investigated: fin size, nose cone shape, panel riveting along the sides of the missile, and heat shielding on the nose cone. By varying these target features in different missile configurations, and comparing them to each other, a …
Characterization And Design Of High-Level Vhdl I/Q Frequency Downconverter Via Special Sampling Scheme, Jesse P. Somann
Characterization And Design Of High-Level Vhdl I/Q Frequency Downconverter Via Special Sampling Scheme, Jesse P. Somann
Theses and Dissertations
This study explores the characterization and implementation of a Special Sampling Scheme (SSS) for In-Phase and Quad-Phase (I/Q) down conversion utilizing top-level, portable design strategies. The SSS is an under-developed signal sampling methodology that can be used with military and industry receiver systems, specifically, United States Air Force (USAF) video receiver systems. The SSS processes a digital input signal-stream sampled at a specified sampling frequency, and down converts it into In-Phase (I) and Quad-Phase (Q) output signal-streams. Using the theory and application of the SSS, there are three main objectives that will be accomplished: characterization of the effects of input, …
Multi-Dimensional Wave Front Sensing Algorithms For Embedded Tracking And Adaptive Optics Applications, Christopher C. Wood
Multi-Dimensional Wave Front Sensing Algorithms For Embedded Tracking And Adaptive Optics Applications, Christopher C. Wood
Theses and Dissertations
Current tracking and adaptive optics techniques cannot compensate for fast-moving extended objects, which is important for ground-based telescopes providing space situational awareness. To fill this need, a vector-projection maximum-likelihood wave-front sensing algorithm development and testing follows for this application. A derivation and simplification of the Cramer-Rao Lower Bound for wavefront sensing using a laser guide star bounds the performance of these systems and guides implementation of a vastly optimized maximum-likelihood search algorithm. A complete analysis of the bias, mean square error, and variance of the algorithm demonstrates exceptional performance of the new sensor. A proof of concept implementation shows feasibility …
Evaluation Of Factors Contributing To Damping Of Coated And Uncoated Titanium Plates, Dustin W. Lee
Evaluation Of Factors Contributing To Damping Of Coated And Uncoated Titanium Plates, Dustin W. Lee
Theses and Dissertations
High Cycle Fatigue (HCF) is the leading cause of component failure in gas turbine engines today, which poses great risk to aircraft, engines, and their crews. Mitigation of HCF effects has become a priority topic, and the damping benefits of hard coatings are being reevaluated for this purpose. Research was conducted to further understanding of damping measurements on these coatings. This study continues work to characterize the damping effects of a magnesium aluminate spinel (mag spinel) coating applied to a titanium plate via vibration testing. Two different plate sizes were evaluated in a clamped-free-free-free condition and a free-free-free-free condition, respectively. …