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Articles 4711 - 4740 of 5699
Full-Text Articles in Engineering
Compressible Turbulence Measurement In The Mixing Layer Of An Adiabatic Normal Slot Injection Into Supersonic Flow, Christopher D. Whitcomb
Compressible Turbulence Measurement In The Mixing Layer Of An Adiabatic Normal Slot Injection Into Supersonic Flow, Christopher D. Whitcomb
Theses and Dissertations
In this study mean flow and compressible turbulence measurements were taken at a station x = 72W downstream of the injection, where W is the injector throat width, of an adiabatic 2-D Mach 1.6 normal slot injection into a Mach 2.9 flow. Data were collected using a conventional Pitot probe, a cone-static probe, and multiple overheat cross-wire anemometry. In addition, schlieren and shadowgraph flow visualization was used to investigate the flow structure at both the injection point and at the downstream data collection point. From these measurements, mass flux component turbulence intensities of 8% to 10% were seen. The total …
Fatigue Response Of Cracked Aluminum Panel With Partially Bonded Composite Patch, Jason J. Denney
Fatigue Response Of Cracked Aluminum Panel With Partially Bonded Composite Patch, Jason J. Denney
Theses and Dissertations
More and more aircraft, both commercial and military, are being called upon to fly well beyond their economic and structural service lives. Budget cuts and dwindling new aircraft development has forced the United States Air Force (USAF) to look toward more reliable structural repairs. One of these repair techniques, which was the subject of this study, is the repair of metallic aircraft structures using high strength composite materials. This study investigated the fatigue response of a precracked, 508x1 52x1 mm, 2024-T3 aluminum panel repaired with a partially bonded, unidirectional, three-ply boron/epoxy composite reinforcement with ply lengths of 68, 56 and …
Sub-Optimal Control Of Rigid Spacecraft Reorientation Using Three Momentum Wheels, Gregory W. Schultz
Sub-Optimal Control Of Rigid Spacecraft Reorientation Using Three Momentum Wheels, Gregory W. Schultz
Theses and Dissertations
This thesis addresses sub-optimal employment of 3 momentum wheels for large angle reorientation of rigid spacecraft with minimal induced spacecraft motion during maneuvers. In addition to development of general theory for 3 wheel vehicles, simulation results for a vehicle using momentum wheels for secondary attitude control (GPS Block IIR) are compared to results for a vehicle using them for primary attitude control (the Hubble Space Telescope), to demonstrate practical applications and limitations. While the control laws were developed assuming no external perturbing torques on the vehicle, reorientation scenarios were run both in a torque free environment as well as an …
Electrical Characterization Of 4h-And 6h-Silicon Carbide Schottky Diodes, Jeffrey C. Wiemeri
Electrical Characterization Of 4h-And 6h-Silicon Carbide Schottky Diodes, Jeffrey C. Wiemeri
Theses and Dissertations
The electrical properties of silicon carbide (SiC) make it an excellent candidate for use in high temperature/high power devices due to its wide bandgap, high breakdown field, high electron mobility, etc. In this work two Schottky diodes of platinum (Pt) on n-type carbon faced 4H-SiC and three Schottky diodes of nickel (Ni) on n-type silicon faced 6H-SiC were electrically characterized. The diodes exhibited good performance up to 698 K for both the forward and reverse (up to -100v) bias voltages. The barrier heights measured by I-V-T tests were found to be 0.32 and 0.61 eV for the Pt/4H-SiC samples, but …
Validation Of Operational Multiscale Environment Model With Grid Adaptivity (Omega), Gordon R. Taylor
Validation Of Operational Multiscale Environment Model With Grid Adaptivity (Omega), Gordon R. Taylor
Theses and Dissertations
The Defense Nuclear Agency (DNA) is improving the military's capability to forecast dosage and hazard levels due to release of chemical, biological, and nuclear agents. During Operation DESERT STORM the military realized the need for models to predict risk levels for military personnel assigned proximate to missile attacks. One project associated with this is the continuing development of the Operational Multiscale Environmental Model with Grid Adaptivity (OMEGA). DNA has sponsored AFIT to validate OMEGA with focus on incorporating weather data obtained from Air Force Combat Climatology Center for the period of the Chernobyl Nuclear Accident. The physics of the model …
The Effect Of Meteorological Data Averaging Times On Plume Concentrations From Explosive Ordnance Disposal Open Burning Operations, Ida L. Widmann
The Effect Of Meteorological Data Averaging Times On Plume Concentrations From Explosive Ordnance Disposal Open Burning Operations, Ida L. Widmann
Theses and Dissertations
Explosive Ordnance Disposal (EOD) Open Burning (OB) operations are performed to treat and dispose of unserviceable munitions in the Department of Defense (DOD) inventory. Air pollution modeling of OB operations is an Environmental Protection Agency requirement for permit issuance at OB sites. Specific OB regulation is still in its infancy; therefore, establishment of OB modeling techniques is still in the early stages. This thesis effort sought to develop a computer model, based upon the Gaussian Puff Equation. The model varies from standard plume modeling practices by not making the assumption that the wind direction, wind speed and turbulence are uniform …
A Decision Tool To Optimally Select Pollution Prevention Projects Within A Constrained Budget, Charlotte Hudson
A Decision Tool To Optimally Select Pollution Prevention Projects Within A Constrained Budget, Charlotte Hudson
Theses and Dissertations
Pollution prevention managers need to select the best environmental projects for an installation within a constrained budget but have no standard way of selecting the optimal mix of projects. This thesis proposes a decision tool to aid decision makers in choosing this optimal mix. The model was built using decision analysis theory which provides a framework to aid the decision maker. Criteria sed in the model for selection was determined using a questionnaire sent to base-level pollution prevention managers. The model ses DPL, a software package designed to build, analyze, and conduct sensitivity analysis of decision problems to perform the …
Decision Support Model For Municipal Solid Waste Management At Department Of Defense Installations, John F. Muratore
Decision Support Model For Municipal Solid Waste Management At Department Of Defense Installations, John F. Muratore
Theses and Dissertations
This research focuses on the development of a decision support model to identify the preferred strategy for managing municipal solid waste using the principles of decision analysis theory. The model provides an effective decision making tool to evaluate and compare different municipal solid waste management strategies. The users of this model, the Environmental Manager or decision maker at a given installation, can enter installation-specific waste stream characteristics, treatment and disposal costs, and material buy-back prices to determine the expected value for various alternative strategies. The strategy having the greatest expected value is considered the preferred alternative. In calculating the expected …
Validation Testing A Contaminant Transport And Natural Attenuation Simulation Model Using Field Data, Steven J. Flier
Validation Testing A Contaminant Transport And Natural Attenuation Simulation Model Using Field Data, Steven J. Flier
Theses and Dissertations
This research extends the work begun by Enyeart (1994) which evaluated the process of intrinsic bioremediation, and which developed a model for predicting the velocity of an aerobic degradation front, as it traverses the length of a JP-4 contaminant plume. It is assumed this aerobic front will traverse the contaminant plume as dissolved oxygen is carried by the ground water through the sorption-retarded contaminant. The ultimate purpose of Enyeart's model is to use it to develop field guidance for assessing the feasibility of intrinsic bioremediation to restore petroleum-contaminated soils. After simulating intrinsic bioremediation many times with a spreadsheet model, results …
A Comparison Of Remediation Priorities Developed By The Defense Priority Model, The Relative Risk Evaluation Method, And A Quantitative Risk Assessment Approach, David M. Hunter
Theses and Dissertations
The Superfund, established by the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980, seriously underestimated both the number of severely contaminated sites and the associated cleanup cost. The magnitude of projected cleanup costs, coupled with shrinking federal budgets, necessitated the development and use of risk-based prioritization models among some federal agencies. Among these tools, the DOD prioritization models are meant to give priority to sites posing the greatest threat to human health. Their failure to properly rank sites could incorrectly shift the focus from those that pose substantial risk to sites of lesser risk. The DOD site ranking …
Evaluation Of The Sensitivity Of Radar Cross Section Predictions To Uncertainties In Material Characteristics, Greg A. Barnhart
Evaluation Of The Sensitivity Of Radar Cross Section Predictions To Uncertainties In Material Characteristics, Greg A. Barnhart
Theses and Dissertations
The purpose of this study was to evaluate the effects of material characteristics uncertainties on Radar Cross Section (RCS) predictions. Many methods have been developed to predict the RCS of metal objects, but for material coated objects, these methods depend on the accuracy of measured material characteristics. Material characteristics of three dielectrics were measured by two separate X-band waveguide set-ups. RCS measurements were then made to evaluate the accuracy of RCS predictions using these measured material characteristics. A six inch square slab of each material was measured with and without a metal plate backing. A six inch square flat metal …
A Differential Gps Aided Ins For Aircraft Landings, Ryan L. Britton
A Differential Gps Aided Ins For Aircraft Landings, Ryan L. Britton
Theses and Dissertations
The Department of Defense (DOD) and the commercial airline industry are in the process of replacing the instrument landing system (ILS) for aircraft precision approach landings. The use of differential Global Positioning System (DGPS) is thought to be a viable replacement for ILS precision approaches. This thesis explores the integration of an INS, DGPS, Barometric Altimeter, Pseudolite, and Radar Altimeter for a tanker type and a single engine aircraft precision approach. These devices are integrated using an extended Kalman filter (EKF). For the tanker type aircraft federal Aviation Administration (FAA) requirements for a Category I and a Category II precision …
Velocity Determination For An Inverted Pseudolite Navigation Reference System, Jeffrey M. Hebert
Velocity Determination For An Inverted Pseudolite Navigation Reference System, Jeffrey M. Hebert
Theses and Dissertations
As navigation systems continue to improve in performance and features, the Air Force must develop better Navigation Reference Systems (NRS) to keep pace with technology. Specifically, with the advent of enhanced, integrated Global Positioning System (GPS) and Inertial Navigation System (INS) navigators, emphasis is placed on the measuring performance in the presence of GPS jamming. To meet these needs, a new NRS, dubbed the Sub-Meter Accuracy Reference System (SARS), is being developed by the 746th Test Squadron, Holloman AFB, New Mexico. SARS uses a unique, inverted GPS pseudolite positioning system to determine a reference trajectory. This research investigates two post …
A Quantitative Feedback Theory Fcs Design For The Subsonic Envelope Of The Vista F-16 Including Configuration Variation And Aerodynamic Control Effector Failures, Vicent J. Cacciatore
A Quantitative Feedback Theory Fcs Design For The Subsonic Envelope Of The Vista F-16 Including Configuration Variation And Aerodynamic Control Effector Failures, Vicent J. Cacciatore
Theses and Dissertations
Fault tolerant flight control systems for combat aircraft are an alternative to excessively redundant aircraft designs or reconfigurable control laws. However, due to the range of flight conditions within a combat aircraft's operational flight envelope, the variety of its configurations, and the unavailability of an aerodynamic data base for damaged aircraft, designing fault tolerant systems is a complicated endeavor. Quantitative Feedback Theory is a robust control design technique especially well-suited to manage the structured parametric uncertainty inherent in this problem, and consequently is applied as the primary design tool for this research. Furthermore, realistic failure models are developed for the …
Wing Flexure Compensation For Aircraft Attitude And Position Determination In An Inverted Carrier-Phase Positioning System, Bradley W. Mahlum
Wing Flexure Compensation For Aircraft Attitude And Position Determination In An Inverted Carrier-Phase Positioning System, Bradley W. Mahlum
Theses and Dissertations
In response to the ever increasing accuracies in inertial navigation systems, the U. S. Air Force must develop higher accuracy reference systems. These reference systems must also be small enough to be utilized in the testing of navigation systems onboard fighter aircraft. One such proposed system utilizes carrier-phase Global Positioning System (CPGPS) transmitters mounted on MM-9 pods with receivers on the ground. This research examines one possible method of utilizing this system to determine the attitude and position of the aircraft, given position estimates for the transmitter's locations. The transmitter positioning algorithm showed that the geometry will be problematic for …
Optimal Formation Flight Control, Shawn B. Mccamish
Optimal Formation Flight Control, Shawn B. Mccamish
Theses and Dissertations
Automatic formation flight involves controlling multiple wing aircraft equipped with standard Mach-hold, altitude-hold, and heading-hold autopilots in order to maintain a desired position relative to a lead aircraft throughout formation maneuvers. Changes in the lead aircraft's states, including formation heading, velocity, altitude, and geometry changes, are treated as disturbance and are rejected by the formation flight control system. The work in this thesis is a continuation of five previous theses, dealing with the design of formation flight control systems. The goal of the optimal formation flight control design is to achieve robust formation maintenance in the face of formation maneuvers …
Computer Aided Detection Of Microcalcifications Utilizing Texture Analysis, Ronald C. Dauk
Computer Aided Detection Of Microcalcifications Utilizing Texture Analysis, Ronald C. Dauk
Theses and Dissertations
A comparative study of texture measures for the classification of breast tissue is presented. The texture features investigated include Angular Second Moments, Power Spectrum Analysis and a novel feature, Laws Energy Ratios. The texture study was accomplished as part of the development of a Model Based Vision (MBV) system for the automatic detection of microcalcifications. An overview of the Microcalcification Detection System is presented, which applies image differencing techniques, feature selection methods, and neural networks for locating microcalcification clusters in mammograms. The Power Spectrum Analysis feature set had the best overall performance with an 83% Probability of Detection and an …
Exmis: An Expert System For The Autonomous Onboard Command System (Aocs), Kevin D. Benedict
Exmis: An Expert System For The Autonomous Onboard Command System (Aocs), Kevin D. Benedict
Theses and Dissertations
The primary objective of this study is the creation of a prototype expert system called EXMIS (EXpert MIssile System) that performs the flight termination logic sequence of the Autonomous Onboard Command System (AOCS). The AOCS is a proposed system that would take the "man-in-the-loop" out of the self-destruct decision making process and place the entire decision on the launch vehicle. Through the use of a six degree of freedom trajectory program called BOOST, simulated flight data for four different flight scenarios is obtained. The launch vehicle selected for the simulations is the Peacekeeper ICBM. EXMIS is developed using an expert …
Analysis Of Gravity-Gradient Satellite Attitude Inversion, Jules-Francois D. Desamours
Analysis Of Gravity-Gradient Satellite Attitude Inversion, Jules-Francois D. Desamours
Theses and Dissertations
The purpose of this research is to understand and describe the process by which the 1986 Polar BEAR gravity- gradient research satellite of John Hopkins University/Applied Physics Laboratory achieved an orbital attitude correction (re-inversion) from an inverted orientation through the utilization of its momentum wheel. Understanding this process provides an analytical foundation from which a universal attitude inversion process for other gravity-gradient satellites with similar anomalous motions may be sought and developed. The equations of motion for a gravity-gradient satellite with a momentum wheel are derived and implemented in FORTRAN for simulation of the dynamics of the spacecraft. Several re-inversion …
Three Dimensional Localization Of Lesions From Digitized Mammograms, Amy L. Magnus
Three Dimensional Localization Of Lesions From Digitized Mammograms, Amy L. Magnus
Theses and Dissertations
This thesis describes new algorithms to localize regions-of-interests (ROIs) three dimensionally from a pair of digitized mammograms. This work is intended to add a layer of sophistication to computer aided diagnosis by putting to use the fixed and measurable parameters of mammographic imaging. The fixed parameters are the source to film orientation and the podium-image distance. Measurable parameters are the rotation angle of the x-ray tube from the horizontal and the compression depth (the distance from compression paddle to contact podium distance) at the time of imaging. As an additional benefit, three dimensional localization algorithms alleviate the confusion radiologists may …
Development And Testing Of A New Optimum Design Code For Hypersonic Wind Tunnel Nozzles, Including Boundary Layer, Turbulence, And Real Gas Effects, Ralph C. Tolle
Theses and Dissertations
A robust and efficient optimization code is developed and validated. The code is used to redesign an existing Mach 12 wind tunnel nozzle and utilizes response surface methodology (RSM) techniques. Explicit, globally second-order, flux-difference-splitting algorithms are used to solve the Navier-Stokes (NS) and Parabolized Navier-Stokes (PNS) flow solvers incorporated into the optimizer code. Either the Baldwin-Lomax or the Yang-Shih k-s turbulence model may be employed in the optimization code. First, 2-D/axisymmetric NS and PNS flow solvers are developed/modified and account for perfect gas/nonequilibrium chemically reacting flows. All solvers are validated against Computational Fluid Dynamics (CFD) and experimental data. The optimization …
Analysis Of Soil Vapor Extraction Expenses To Estimate Bioventing Expenses, Steven M. Loken
Analysis Of Soil Vapor Extraction Expenses To Estimate Bioventing Expenses, Steven M. Loken
Theses and Dissertations
An in-depth analysis of the expenses incurred with five soil venting petroleum remediation projects was accomplished. The data was obtained from receipts provided by a major United States petroleum refiner and distributor. Cost categories were designed that incorporated all costs and provided a method to analyze the data. The five cost categories used were: permits, equipment, management, utilities, and analysis. Further analysis showed trends and described the behavior of the costs related to remediation events. The relative percentile for each cost category was found to be consistent among the projects. Many costs were also found to be very linear throughout …
Use Of Respirometry To Determine The Effect Of Nutrient Enhancement On Jp-8 Biodegradability, Christian T. Totten
Use Of Respirometry To Determine The Effect Of Nutrient Enhancement On Jp-8 Biodegradability, Christian T. Totten
Theses and Dissertations
The purpose of this study was to use respirometry to measure the impact of nutrient combinations or treatments on JP - 8 biodegradation under simulated fuel spill soil conditions. The study was designed observe one soil type at a constant fuel exposure level of 1% and a constant moisture of 60% of field capacity. Three experiments conducted were of two and three factor designs with potassium nitrate and sodium phosphate addition levels serving as two factors and fuel serving as a third factor in Experiments 1 and 2. Cumulative oxygen values obtained by the respirometer were assumed to be a …
Optimal Inputs For System Identification, James M. Brown Ii
Optimal Inputs For System Identification, James M. Brown Ii
Theses and Dissertations
The derivation of the power spectral density of the optimal input for system identification is addressed in this research. Optimality is defined in information theoretic terms, with entropy quantifying the parameter information content of the input and output measurement sequences pertaining to a discrete time plant. The maximization of entropy is performed in the context of three different scenarios. First, the case in which the average output power of the plant is constrained is considered. Second, input average power is constrained. Finally, the optimization is carried out unconstrained, but with penalties applied to both the input and output powers. Although …
Non-Imaging Infrared Spectral Target Detection, Matthew R. Whiteley
Non-Imaging Infrared Spectral Target Detection, Matthew R. Whiteley
Theses and Dissertations
Automatic detection of time-critical mobile targets using spectral-only infrared radiance data is explored. A quantification of the probability of detection, false alarm rate, and total error rate associated with this detection process is provided. A set of classification features is developed for the spectral data, and these features are utilized in a Bayesian classifier singly and in combination to provide target detection. The results of this processing are presented and sensitivity of the class separability to target set, target configuration, diurnal variations, mean contrast, and ambient temperature estimation errors is explored. This work introduces the concept of atmospheric normalization of …
An Investigation Into Aircraft Availability, Michael S. Kapitzke
An Investigation Into Aircraft Availability, Michael S. Kapitzke
Theses and Dissertations
The Air Force currently uses an expected value model in the Aircraft Availability Model (AAM) to calculate aircraft availability. However, even with the application of Lean Logistics, the failure-demand rate and the depot repair time are not fixed and the mean value is still used in the model. This research looks at the effect of the magnitude of the variance of the distributions of failure-demand rate and depot repair time. Also, this research evaluates the effect of variable mean failure-demand rates on the variability of aircraft availability. A simulation model was developed which applied the variable failure-demand rates and depot …
Assisting Defense Conversion Technology Transfer Efforts. A Case Study Of Ohio's Miami Valley, Marissa C. Salvador
Assisting Defense Conversion Technology Transfer Efforts. A Case Study Of Ohio's Miami Valley, Marissa C. Salvador
Theses and Dissertations
Major changes in the geopolitical environment and the social and economic needs of the United States have resulted in resources being shifted away from national defense. Although the expected decrease in defense spending should not be harmful in macroeconomic terms, it can be devastating locally. To mitigate the effects of the drawdown, individual states and local communities must search for ways to bolster their local economies. One avenue that can be pursued to enhance future economic growth is the transferring of technologies to the commercial sector. Intermediary organizations have emerged to facilitate the process of technology transfer by serving as …
The Process Of Technology Transfer: A Case Study Of The National Aero-Space Plane Program, Brett T. Smith
The Process Of Technology Transfer: A Case Study Of The National Aero-Space Plane Program, Brett T. Smith
Theses and Dissertations
Due to reduced funding levels and increased pressure towards cooperation with industry, government research and development (R&D) organizations are becoming increasingly involved in the transfer of technology to the commercial sector. However, the process of technology transfer is complex, and transfer activities are being applied inconsistently across the Department of Defense. This research explores the approaches, processes and mechanisms to accomplish technology transfer. A comprehensive literature review documents many of the transfer concepts that have been proposed or are currently in use. A detailed case study then examines the technology transfer efforts of an advanced government research organization: the National …
Just In Time Manufacturing: A Migration From Materials Requirements Planning, Scott A. Koehler
Just In Time Manufacturing: A Migration From Materials Requirements Planning, Scott A. Koehler
Theses and Dissertations
Manufacturing planning and control systems play an important role in an organization's effectiveness. Over the past twenty to thirty years, U.S. manufacturing companies have faced increasing competition for market share from Japanese and other Pacific rim countries. This thesis will investigate the evolutionary path followed by manufacturing companies that have implemented various manufacturing planning and control systems. Specifically, Materials Requirements Planning (MRP) and Just In Time (JIT) production will be analyzed. MRP is a means of convening demand for the final product into a requirements schedule for the various components comprising that product. The JIT philosophy calls for continuously improving …
A Study Of The Factors Associated With Successful Technology Transfer And Their Applicability To Air Force Technology Transfers, James B. Rose
A Study Of The Factors Associated With Successful Technology Transfer And Their Applicability To Air Force Technology Transfers, James B. Rose
Theses and Dissertations
Although the United States is a world leader in scientific research, it lags behind some economic powers in the application of technologies. As quality and manufacturing excellence were critical to US competitiveness in the l98Os, so is commercializing technologies in the 199Os. With billion dollar budgets and exceptional scientific talent, the potential for fruitful technology transfer is abundant. By definition, federal-to-commercial technology transfer is the ability to leverage national investments in technology beyond their traditional customer base. The technology can be physical devices, processes, knowledge, or proprietary information. Unfortunately, and despite exhaustive legislative efforts, US industry has fallen behind its …