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Articles 3781 - 3810 of 5699
Full-Text Articles in Engineering
Stepped Waveguide Electromagnetic Material Characterization Technique, Sean P. Dorey
Stepped Waveguide Electromagnetic Material Characterization Technique, Sean P. Dorey
Theses and Dissertations
Electromagnetic material characterization is the process of determining the complex permittivity and permeability of a material. A new waveguide material measurement technique is developed to reduce test sample size requirements for low-frequency applications. Specifically, a waveguide sample holder having a reduced aperture is utilized to decrease the time and cost spent producing large precision test samples. This type of sample holder causes a disruption in the waveguide-wall surface currents that results in the excitation of higher-order modes. This thesis will demonstrate how these higher-order modes can be accommodated using a modal-analysis technique, thus resulting in the ability to measure smaller …
An Analysis Of Coast Guard Hh-65 Engine Reliability: A Comparison Of Malfunctions To Component Removals, Donna L. Cottrell
An Analysis Of Coast Guard Hh-65 Engine Reliability: A Comparison Of Malfunctions To Component Removals, Donna L. Cottrell
Theses and Dissertations
The Coast Guard HH-65 helicopter experienced 31 in-flight loss of power incidents during FY 2003 and 21 during the first two months of FY 2003. Concurrent with this apparent decrease in reliability, the Coast Guard seeks ways to expand the HH- 65’s Airborne Use of Force capabilities as a result of the September 11th, 2001 terrorists’ attacks. This study is an exploratory, empirical analysis of engine and airframe component replacements as related to engine mishaps and reliability in the HH-65. We use contingency table analysis, ordinary least squares regression, and logistic regression to examine the mishap history and component replacement …
Optimal Constellation Design For Orbital Munitions Delivery System, Jason Anderson
Optimal Constellation Design For Orbital Munitions Delivery System, Jason Anderson
Theses and Dissertations
Rather than delivering conventional munitions through the airspace of uncooperative nations, a constellation of space-stored weapons could potentially target any point on the Earth and arrive within the time it takes to de-orbit and re-enter through the atmosphere. The research involves applying the dynamics of atmospheric re-entry to a Common Aero Vehicle (CAV) and defining a footprint of attainable touchdown points. The footprint is moved forward to create a swath representing all the possible touchdown points in a 90 minute window. A nominal constellation of CAVs is established using a streets of coverage technique, and both analytic studies and numeric …
Outside Loop Control In Asymmetrical Trimmed Flight Conditions, Gary D. Miller
Outside Loop Control In Asymmetrical Trimmed Flight Conditions, Gary D. Miller
Theses and Dissertations
Traditionally flight control systems have used linearized equations of motion solved around a single trim point. This thesis proposes a nested-loop controller directly solved from the equations of motion. The control equations were developed as a solution to asymmetrically trimmed flight conditions. A two-loop design was proposed for the controller. The outer loop modeled the aircraft as a point mass and all forces were balanced to find the aircraft states. The equations input the control variables and output the aircraft states. The inner-loop utilizes the six-degree of freedom model of the aircraft to solve the moment equations. With the input …
Surveying Cost Growth, Michael A. Greiner, Vince Sipple, Edward D. White
Surveying Cost Growth, Michael A. Greiner, Vince Sipple, Edward D. White
Faculty Publications
Cost growth that weapon systems incur throughout their acquisition life cycle concerns those who work in the acquisition environment. One way to reduce the amount of unexpected cost growth is to develop better cost estimates. In attaining better cost estimates though, it is often helpful to understand and account for potential cost drivers. Several cost studies, some of which specifically focus on the aircraft industry, have been performed documenting and investigating these growth factors. Overviews of these various cost growth studies are presented as other tools for the cost estimators and program managers.
A Communications Modeling System For Swarm-Based Sensors, Brian A. Kadrovach
A Communications Modeling System For Swarm-Based Sensors, Brian A. Kadrovach
Theses and Dissertations
Today's information age has exploded the amount of data available to decision makers at all levels of the control hierarchy. The miniaturization and proliferation of sensor technology has enabled extensive detection and monitoring and advances in computational capabilities have provided for embedded data analysis and the generation of information from raw data. Additionally, with the miniaturization of mechanical systems it is possible to provide platforms for sensor suites that are capable of mobility and limited autonomy. Swarming or bio-emergent behavior problems, provides a robust scalable mechanism for organizing large numbers of mobile sensor platforms. However, the mobility dynamics of swarm …
Electron Paramagnetic Resonance Spectroscopy And Hall Effect Studies Of The Effects Of Low Energy Electron Energy On Gallium Nitride (Gan), Kevin D. Greene
Electron Paramagnetic Resonance Spectroscopy And Hall Effect Studies Of The Effects Of Low Energy Electron Energy On Gallium Nitride (Gan), Kevin D. Greene
Theses and Dissertations
The nature of native donors in GaN, types and interactions of radiation-induced defects, and damage creation coefficients for 1.0 MeV electron irradiation have been ascertained by the concerted application of electron paramagnetic resonance spectroscopy and Hall effect measurements to virgin and electron-irradiated GaN epilayers. Samples produced via molecular beam epitaxy and hydride vapor phase epitaxy, both silicon doped and nominally undoped, were subjected to Van de Graff generator produced monoenergtic electron beams with total fluences of 1016- 1018 electrons/cm2. Nitrogen vacancies are rejected as a possible cause of n-type conductivity in nominally undoped GaN due …
Cooperative Control Simulation Validation Using Applied Probability Theory, Christopher S. Schulz
Cooperative Control Simulation Validation Using Applied Probability Theory, Christopher S. Schulz
Theses and Dissertations
Several research simulations have been created to support development and refinement of teamed autonomous agents using decentralized cooperative control algorithms. Simulation is the necessary tool to evaluate the performance of decentralized cooperative control algorithms, however these simulations lack a method to validate their output. This research presents a method to validate the performance of a decentralized cooperative control simulation environment for an autonomous Wide Area Search Munition (WASM). Rigorous analytical methods for six wide area search and engagement scenarios involving Uniform, Normal, and Poisson distributions of N real targets and M false target objects are formulated to generate expected numbers …
Controlled-Stress Large-Area Pulsed Laser Deposition Of Yttria Stabilized Zirconia, Paul C. Rounsavall
Controlled-Stress Large-Area Pulsed Laser Deposition Of Yttria Stabilized Zirconia, Paul C. Rounsavall
Theses and Dissertations
The US Air Force has need of parabolic-shaped membrane mirrors for surveillance satellites. The current polymer membrane technology has been unable to overcome shape deformation problems caused by intrinsic stresses from the membrane casting and mounting processes. One proposed solution was to coat the membrane mirrors with a stressed coating to compensate for shape deformations. Thus, the research presented in this dissertation produced controlled-stress large-area pulsed laser deposition (PLD) grown thin films on polymer substrates and investigated optical time-of-flight (TOF) sensor systems and Raman spectroscopy for control for the PLD process with respect to thin film stress. Initially, the PLD-grown …
Classification Of Radar Targets Using Invariant Features, Gregory J. Meyer
Classification Of Radar Targets Using Invariant Features, Gregory J. Meyer
Theses and Dissertations
Automatic target recognition ATR using radar commonly relies on modeling a target as a collection of point scattering centers, Features extracted from these scattering centers for input to a target classifier may be constructed that are invariant to translation and rotation, i.e., they are independent of the position and aspect angle of the target in the radar scene. Here an iterative approach for building effective scattering center models is developed, and the shape space of these models is investigated. Experimental results are obtained for three-dimensional scattering centers compressed to nineteen-dimensional feature sets, each consisting of the singular values of the …
Electrical Activation Studies Of Silicon Implanted Alx Gal-X N And Coimplanted Gan, Elizabeth A. Chitwood
Electrical Activation Studies Of Silicon Implanted Alx Gal-X N And Coimplanted Gan, Elizabeth A. Chitwood
Theses and Dissertations
A comprehensive study of the electrical activation of silicon implanted AlxGa1-xN was performed as a function ion dose, anneal temperature, and aluminum mole fraction, Also, GaN coimplanted with silicon and nitrogen was investigated. Room temperature Hall effect measurements were used to determine carrier concentration and mobility. All the samples had a 500 Å encapsulant of AlN, and were implanted at room temperature with 200 keV silicon ions at doses ranging from 1x1013 to 1x1015 /sq cm. The GaN was also implanted with nitrogen under the same conditions in doses of 9x1012 to 9x10 …
Luminescence Studies Of Ion-Implanted Gallium Nitride And Aluminum Gallium Nitride, Erin N. Claunch
Luminescence Studies Of Ion-Implanted Gallium Nitride And Aluminum Gallium Nitride, Erin N. Claunch
Theses and Dissertations
Recently, research on the wide bandgap semiconductors such as GaN and Al(x)Ga(1-x)N became very popular for their applications on various devices. Therefore comprehensive and systematic luminescence studies of Si implanted AlxGa1-xN, Mg doped GaN, and Si+N implanted GaN grown on sapphire substrates by molecular beam epitaxial method have been made as a function of ion dose and anneal temperature.
An Analysis Of Microbial Contamination In Military Aviation Fuel Systems, Harold W. Graef
An Analysis Of Microbial Contamination In Military Aviation Fuel Systems, Harold W. Graef
Theses and Dissertations
Military aviation fuel systems can be an ideal environment for microorganisms. Microbial growth in hydrocarbon fuel systems arises because of the impracticality of keeping fuel tanks sterile and the inevitable presence of water from condensation. Microbial contaminants in aviation fuel systems are a concern because of their potential to degrade the fuel, accelerate tank corrosion, and threaten flight safety. This research addresses the concern of using more environmentally friendly Fuel System Icing Inhibitors (FSII), which are also biocidal. Are significant levels of microorganisms growing in military aviation fuel systems, and if so, are there any common variables? Forty aviation fuel …
Characterization Of Chlorinated Solvent Degradation In A Constructed Wetland, Nathan D. Clemmer
Characterization Of Chlorinated Solvent Degradation In A Constructed Wetland, Nathan D. Clemmer
Theses and Dissertations
Widespread chlorinated ethene contamination of aquifers coupled with high costs of current treatment technologies demand innovative remediation solutions. Wetlands, maintaining anaerobic and aerobic zones promoting the complete degradation of chlorinated ethenes such as Tetrachloroethylene (PCE), could be the answer. This thesis characterized the chlorinated solvent contamination levels in three strata of an upward flow constructed wetland. Analysis of samples was accomplished by purge-and-trap gas chromatography. Water quality parameters, Dissolved Oxygen (DO), Oxidation Reduction Potential (ORP), pH, Conductivity, and Temperature, were also measured in monitoring wells with a water monitoring sonde. After removing data outliers caused by short-circuiting flow, PCE concentrations …
Inquisitive Pattern Recognition, Amy L. Magnus
Inquisitive Pattern Recognition, Amy L. Magnus
Theses and Dissertations
The Department of Defense and the Department of the Air Force have funded automatic target recognition for several decades with varied success. The foundation of automatic target recognition is based upon pattern recognition. In this work, we present new pattern recognition concepts specifically in the area of classification and propose new techniques that will allow one to determine when a classifier is being arrogant. Clearly arrogance in classification is an undesirable attribute. A human is being arrogant when their expressed conviction in a decision overstates their actual experience in making similar decisions. Likewise given an input feature vector, we say …
Development Of An Experimental Test Section For Forcing Unsteady Flow In A Linear Compressor Cascade Using Circular Rods, Patrick C. Wade
Development Of An Experimental Test Section For Forcing Unsteady Flow In A Linear Compressor Cascade Using Circular Rods, Patrick C. Wade
Theses and Dissertations
Upstream propagating waves impinging on a cascade of compressor blades were examined in an effort to better understand the influence of downstream components on high cycle fatigue in turbine engines. An array of cylinders was used to simulate the unsteady field generated by a rotor downstream of a set of stators. The unsteady flow upstream of a single cylinder and an array of cylinders, with and without an upstream cascade, was examined experimentally and computationally. Computational results indicate that the cylinders would only shed coherently when placed downstream of a set of blades. Coherent shedding is created when each of …
Cold-Flow Testing Of A Subscale Model Exhaust System For A Space-Base Laser, Ian S. Bautista
Cold-Flow Testing Of A Subscale Model Exhaust System For A Space-Base Laser, Ian S. Bautista
Theses and Dissertations
The purpose of this research was to continue a study of gas-dynamic phenomena that occurred in stacked cylindrical rings of nozzles and an exhaust manifold as reported by Captain Scott Bergren in 2002. The rings and exhaust manifold were part of a 1/5-scale model of one quadrant of the conceptual Space Based Laser Integrated Flight Experiment (SBL IFX) gas dynamic laser. This model was mated to a blow- down/vacuum wind tunnel and consisted of a nozzle array, centerbody, supersonic diffuser, and a transition structure to mate the vacuum and test section. During Capt Bergren's research, supersonic flow was found to …
Experimental Demonstration Of An Algorithm To Detect The Presence Of A Parasitic Satellite, Vincent J. Dabrowski
Experimental Demonstration Of An Algorithm To Detect The Presence Of A Parasitic Satellite, Vincent J. Dabrowski
Theses and Dissertations
Published reports of microsatellite weapons testing have led to a concern that some of these "parasitic" satellites could be deployed against US satellites to rendezvous dock and then disrupt, degrade disable or destroy the system. An effective detection method is essential. Various sensing solutions were investigated including visual, impact, and dynamic techniques. Dynamic detection, the most effective solution, was further explored. A detection algorithm was constructed and validated on the Air Force Institute of Technology's ground-based satellite simulator, SIMSAT. Results indicate that microsat microsatellites rigidly connected to a satellite can be detected with a series of small identical maneuvers utilizing …
Experimental Results For A High Swirl, Ultra Compact Combustor For Gas Turbine Engines, Ryan J. Quaale
Experimental Results For A High Swirl, Ultra Compact Combustor For Gas Turbine Engines, Ryan J. Quaale
Theses and Dissertations
Laser Doppler Velocimeter (LDV) experiments have been conducted within the cavity of an atmospheric pressure, small scale, Ultra Compact Combustor (UCC). The UCC uses highly swirled flow in a cavity around the outside periphery of the combustor to generate high centripetal acceleration in the fluid. This enhances mixing and leads to a very short axial flame length. Additionally, due to the circumferential velocity, much of the residence time required by the flame is provided by the circumference of the engine rather than axial length as in conventional combustors.
Nonlinear, Transonic Flutter Prediction For F-16 Stores Configuration Clearance, Raymond G. Toth
Nonlinear, Transonic Flutter Prediction For F-16 Stores Configuration Clearance, Raymond G. Toth
Theses and Dissertations
Wing flutter, or more accurately limit cycle oscillation (LCO), has been an issue for the F-16 since its operational deployment. Different store configurations and the permutations of those configurations after weapons are released will cause LCO to either disappear or appear. Unfortunately, the current method used by engineers for predicting LCO onset is based on linear, subsonic aerodynamic theory with no corrections for transonic effects. Predictions using this method are often good in frequency, but can be far off in predicting onset speed, forcing flutter engineers to rely more on experience and interpolation from similar configurations to design flight test …
Application Of Maneuver-Based Control In Variable Autonomy Unmanned Combat Aerial Vehicles, Alexander M. G. Walan
Application Of Maneuver-Based Control In Variable Autonomy Unmanned Combat Aerial Vehicles, Alexander M. G. Walan
Theses and Dissertations
The rise in the capability and lethality of unmanned combat aerial vehicles (UCAVs) historically has been paralleled by an increase in the complexity of the command and control of these systems. This trend has continued with the command and control of the current fleet of unmanned aerial vehicles such as the Predator and Global Hawk. The control of these vehicles falls on the extremes on the manual vs autonomous spectrum. As the missions tasked to these vehicles increase in complexity and lethality, operators will increasingly require the ability to tailor the amount of control exercised over the vehicle. Maneuver Based …
Experimental And Computational Failure Analysis Of Graphite/Bismaleimide Laminated Composite And Carbon Foam In Sandwich Construction, Troy C. Welker
Experimental And Computational Failure Analysis Of Graphite/Bismaleimide Laminated Composite And Carbon Foam In Sandwich Construction, Troy C. Welker
Theses and Dissertations
Sandwich beams consisting of a carbon foam core and graphite/bismaleimide face sheets were constructed and tested. Nine specimens were fabricated using three distinct cross-ply symmetric face sheet layups with a constant core thickness. Four-point bend testing controlled by a constant rate of midspan vertical displacement was used to load the specimens to failure. Displacements and strains from the experiment were compared to analytical sandwich beam theory and displacements and failure loads were compared to a layerwise finite element solution. A phenomenological failure criterion was developed that compares favorably with experimental failure data. The finite element solution gives failure within an …
Hybrid Control Strategies For Rapid, Large Angle Satellite Slew Maneuvers, David B. French
Hybrid Control Strategies For Rapid, Large Angle Satellite Slew Maneuvers, David B. French
Theses and Dissertations
This research investigated hybrid control strategies for rapid satellite pointing. First, a detailed computer simulation model of AFIT's SIMSAT satellite simulator was constructed. Control strategies were developed to enable the system to perform large-angle, 3-axis slewing maneuvers using a combination of both thrusters and reaction wheels. To handle the non-linear model, a State Dependent Riccati Equation controller was programmed and successfully controlled the computer-modeled satellite for any given slewing maneuver. A simpler PD controller was then programmed and demonstrated on the computer simulation of SIMSAT, using a combination of thruster and reaction wheel control inputs for large-angle single axis maneuvers …
Development, Fabrication And Ground Test Of An Inflatable Structure Space-Flight Experiment, Thomas L. Philley Jr.
Development, Fabrication And Ground Test Of An Inflatable Structure Space-Flight Experiment, Thomas L. Philley Jr.
Theses and Dissertations
Inflatable, rigidizable structures provide a solution to reduce the costs associated with design, fabrication and launch of a space system while simultaneously increasing the deployment reliability and mission success of the system%. This research focused on the follow on design, fabrication, and ground test of the Rigidizable Inflatable Get-Away-Special Experiment (RIGEX). RIGEX is a self-contained experiment that will test the deployment and structural characteristics of three inflatable rigidizable tubes. Once inflated and rigidized, each tube will be excited using piezoelectric transducers in order to collect vibration data for structural characterization. The goal of this research was to collect ground testing …
Auto Carrier Transporter Loading And Unloading Improvement, Brian M. Miller
Auto Carrier Transporter Loading And Unloading Improvement, Brian M. Miller
Theses and Dissertations
Thousands of vehicles (cars, trucks and vans) are transported every day from one location to another. These vehicles are moved around the country on Auto Carrier Transports (ACTs). Delivering these vehicles involves large quantities of time, money and energy. Any reduction in time and energy will result in a significant savings of money. The intent of this research is to develop an algorithm to solve the Auto Carrier Transport Pickup and Delivery Problem. In doing so, the focus is to limit the total times vehicles are placed on and taken off the carrier, otherwise known as the number of loads, …
A Simulation-Based Analysis Of The Impact Of In-Sourcing A Major Process Element On The Coast Guard Hh-601 Depot Maintenance Process, Steven E. Vigus
A Simulation-Based Analysis Of The Impact Of In-Sourcing A Major Process Element On The Coast Guard Hh-601 Depot Maintenance Process, Steven E. Vigus
Theses and Dissertations
Leaders at the United States Coast Guard's Aircraft Repair and Service Center (ARSC) in Elizabeth City, North Carolina recently formalized their planning and analysis functions by adding a dedicated branch to their command structure. The Planning and Analysis Branch intends to apply computer modeling and simulation to study the impact of process changes to the various Programmed Depot Maintenance (PDM) lines. This research considers the applicability of this type of modeling and simulation, using ARENA to study the current HH-6OJ PDM process. The contribution of this research is a methodology specific to ARSC needs, an analysis of methodology based on …
Estimating Engineering And Manufacturing Development Cost Risk Using Logistic And Multiple Regression, John V. Bielecki
Estimating Engineering And Manufacturing Development Cost Risk Using Logistic And Multiple Regression, John V. Bielecki
Theses and Dissertations
Cost Growth in Department of Defense (DoD) major weapon systems has been an on-going problem for more than 30 years. Previous research has demonstrated the use of a two-step logistic and multiple regression methodology to predicting cost growth produces desirable results versus traditional single-step regression. This research effort validates, and further explores the use of a two-step procedure for assessing DoD major weapon system cost growth using historical data, We compile programmatic data from the Selected Acquisition Reports (SARs) between 1990 and 2001 for programs covering all defense departments. Our analysis concentrates on cost growth in the research and development …
Performance Analysis Of Protocol Independent Multicasting-Dense Mode In Low Earth Orbit Satellite Networks, Mark D. Saeger
Performance Analysis Of Protocol Independent Multicasting-Dense Mode In Low Earth Orbit Satellite Networks, Mark D. Saeger
Theses and Dissertations
This research explored the implementation of Protocol Independent Multicasting - Dense Mode (PIM-DM) in a LEO satellite constellation. PIM-DM is a terrestrial protocol for distributing traffic efficiently between subscriber nodes by combining data streams into a tree-based structure, spreading from the root of the tree to the branches. Using this structure, a minimum number of connections are required to transfer data, decreasing the load on intermediate satellite routers. The PIM-DM protocol was developed for terrestrial systems and this research implemented an adaptation of this protocol in a satellite system. This research examined the PIM-DM performance characteristics which were compared to …
Internet Protocol (Ip) Over Link-16, Clinton W. Stinson
Internet Protocol (Ip) Over Link-16, Clinton W. Stinson
Theses and Dissertations
The purpose of Link- 16 is to exchange real-time tactical data among units of the United States and allied forces. Primary Link- 16 functions include exchange of friendly unit position and status data, fl%the dissemination of tactical surveillance track data, and the control/management of air, surface, and subsurface engagements. Because Link- 16 will play an integral role in fl% network-centric Joint Battlespace Infosphere (JBI), the performance of Internet Protocol version six (IPv6) and IP Security (IPSec) over Link-16 needs to be determined. Using OPNET modeling software to simulate a Link- 16 network, the investigation of this research revealed that the …
Using Future Value Analysis To Select An Optimal Portfolio Of Force Protection Initiatives, Robert P. Eskridge
Using Future Value Analysis To Select An Optimal Portfolio Of Force Protection Initiatives, Robert P. Eskridge
Theses and Dissertations
With the recent increase in terrorist activity, force protection has become a key issue for the Department of Defense, Leading the research for new ideas and concepts in force protection for the US Air Force is the Air Force Force Protection Battlelab (FPB). The FPB is charged with searching out force protection ideas and selecting those most worthy for future consideration. In 2002, a Value-Focused Thinking (VFT) hierarchy was created to help the FPB select those ideas that provided the most value to the Air Force and its force protection goals. This research effort uses the Future Value Analysis (FVA) …