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Articles 8161 - 8190 of 11510
Full-Text Articles in Engineering
Uncorrelated Track Avoidance, Darrell L. Grob
Uncorrelated Track Avoidance, Darrell L. Grob
Theses and Dissertations
The purpose of this thesis is to examine what data requirements are necessary to avoid continual series of uncorrelated tracks when gathering observations. The constants of the motion for simple two-body motion for a satellite orbiting the Earth, known as the classical orbital elements or COEs, do not remain constant due to zonal and sectoral harmonic variations in the Earth’s gravitational field. There are other elements of the motion that should be considered and this paper discusses the constancy of three elements: the Hamiltonian (H) of the Earth-Centered Rotating System, Ẑ-component of inertial angular momentum (Hk), …
Initial Determination Of Low Earth Orbits Using Commercial Telescopes, Matthew M. Schmunk
Initial Determination Of Low Earth Orbits Using Commercial Telescopes, Matthew M. Schmunk
Theses and Dissertations
Within the last decade, many new technologies have significantly changed the face of private astronomy. Developments such as inexpensive but high-quality sensors, rapid personal computing, and easy networking inspire a reexamination of an old problem: how practical is it to develop initial orbit estimates for Low Earth Orbiting (LEO) satellites using optical tracking? This paper documents the design and implementation of a commercial telescope system used to answer precisely that question. This analysis deter- mined there are some challenging barriers to successful single-site orbit determination, but it is possible given the right conditions. Considering the low cost and small sup- …
Determining The Capability Requirements For A Space Based Optical Sensor To Determine The Trajectory Of An Incoming Antisatellite Weapon, Mesut Gulmus
Theses and Dissertations
The goal of this research is to build up a logic to catch and track incoming ASAT weapons by using space-based onboard optical sensors. The satellite orbit and ASAT trajectory of the Chinese test were generated to relate the research to the real world application. These position and velocity values are used to generate simulated observation data for a hypothetical sensor on the targeted satellite. These observation values are assumed to be true, and some representative amounts of error was added to these data. Only two body dynamics are considered; drag effect and other perturbations are neglected. The modern orbit …
A Multi-Objective Linear Program Model To Test Hub-And-Spoke Networks As A Potential Air Force Deployment Alternative, Andrew J. Cullen
A Multi-Objective Linear Program Model To Test Hub-And-Spoke Networks As A Potential Air Force Deployment Alternative, Andrew J. Cullen
Theses and Dissertations
The purpose of this research is to develop a multiple-objective mixed-integer linear programming model that determines the feasibility of a new deployment paradigm, which offers greater flexibility to home station and deployed location civil engineers (CE) by applying hub-and-spoke networking. The research covers the histories of CE and Air and Space Expeditionary Force (AEF), current CE deployment needs, multiple-objective decision analysis, hub-and-spoke networking, and organizational behavior benefits of the new paradigm. The methodology section provides details on each objective, explains the model, defines weights, and explains the objective function’s calculation. Next, an analysis of the model’s resulting scenarios helps determine …
Effects Of Environment On Creep Behavior Of Nextel 720/Alumina-Mullite Ceramic Composite At 1200°C, Christopher L. Genelin
Effects Of Environment On Creep Behavior Of Nextel 720/Alumina-Mullite Ceramic Composite At 1200°C, Christopher L. Genelin
Theses and Dissertations
The creep behavior of an oxide-oxide ceramic matrix composite (CMC) was investigated at 1200°C in laboratory air, in steam and in argon. The composite consisted of a porous alumina-mullite matrix reinforced with laminated, woven mullite/alumina (Nextel/720) fibers. The composite had no fiber coating and relied on its porous alumina/mullite matrix for flaw tolerance. Tensile stress-strain behavior was investigated and the tensile properties were measured at 1200°C in laboratory air. Tensile creep behavior of the CMC was examined for creep stress levels of 73, 91, 114 and 136 MPa. Creep run-out, set to 100 h, was achieved for stress levels ≤ …
Understanding The Emergence Of Disruptive Innovation In The Air Force Science And Technology Organizations, David E. Shahady
Understanding The Emergence Of Disruptive Innovation In The Air Force Science And Technology Organizations, David E. Shahady
Theses and Dissertations
Although innovation is widely discussed in both military and industry venues, many organizations continue to struggle with what it means to be creative as well as maintain a competitive advantage. The United States Air Force has specifically struggled with the balance between improving existing technologies and employing revolutionary technologies. The purpose of this thesis was to study the motivation, focus, barriers, and culture needed to foster disruptive innovation in Air Force Science and Technology (S&T) and to investigate how industry innovation strategies could improve breakthrough Air Force technology emergence. The Air Force Research Laboratory (AFRL), the primary organization responsible for …
Piv-Based Examination Of Deep Stall On An Oscillating Air Foil, Daniel E. Fredberg
Piv-Based Examination Of Deep Stall On An Oscillating Air Foil, Daniel E. Fredberg
Theses and Dissertations
A number of studies suggest that the deep stall flow fields produced by a pure-pitch and a pure-plunge oscillating airfoil are equivalent, when effective angles of attack are matched. This assumption is examined using particle image velocimetry (PIV). Sinusoidal oscillations of a pure-plunge and pure-pitch airfoil with matched reduced frequency k = 3.93 and with kinematically equivalent amplitudes of effective angle of attack are comparatively examined using results of PIV in a free surface water tunnel at AFRL/RB, Wright Patterson AFB. Experiments were conducted at Re = 10,000 and Re = 40,000, based on free stream velocity and airfoil chord, …
Contamination Study Of Micro Pulsed Plasma Thrusters, Ceylan Kesenek
Contamination Study Of Micro Pulsed Plasma Thrusters, Ceylan Kesenek
Theses and Dissertations
Satellite designing trend is progressing towards building smaller satellites. Small satellites require micro propulsion devices for accurate control by the propulsion system. Micro-Pulsed Plasma Thrusters (μPPTs) are highly reliable and simple micro propulsion systems that will offer attitude control, station keeping, constellation flying, and drag compensation for such satellites. As an unfortunate side effect, the plume induces contamination on spacecraft surfaces and may lead to significant problems with sensors and power generation. Solid particulates in the exhaust plume may deposit on spacecraft instrument and the solar array surfaces limiting or reducing the mission capability as well as the lifetime of …
Shi(El)Ds: A Novel Hardware-Based Security Backplane To Enhance Security With Minimal Impact To System Operation, Matthew G. Judge
Shi(El)Ds: A Novel Hardware-Based Security Backplane To Enhance Security With Minimal Impact To System Operation, Matthew G. Judge
Theses and Dissertations
Computer security continues to increase in importance both in the commercial world and within the Air Force. Dedicated hardware for security purposes presents and enhances a number of security capabilities. Hardware enhances both the security of the security system and the quality and trustworthiness of the information being gathered by the security monitors. Hardware reduces avenues of attack on the security system and ensures the trustworthiness of information only through proper design and placement. Without careful system design, security hardware leaves itself vulnerable to many attacks that it is capable of defending against. Our SHI(EL)DS architecture combines these insights into …
Composable Distributed Access Control And Integrity Policies For Query-Based Wireless Sensor Networks, David W. Marsh
Composable Distributed Access Control And Integrity Policies For Query-Based Wireless Sensor Networks, David W. Marsh
Theses and Dissertations
An expected requirement of wireless sensor networks (WSN) is the support of a vast number of users while permitting limited access privileges. While WSN nodes have severe resource constraints, WSNs will need to restrict access to data, enforcing security policies to protect data within WSNs. To date, WSN security has largely been based on encryption and authentication schemes. WSN Authorization Specification Language (WASL) is specified and implemented using tools coded in JavaTM. WASL is a mechanism{independent policy language that can specify arbitrary, composable security policies. The construction, hybridization, and composition of well{known security models is demonstrated and shown to preserve …
Wind/Rain Backscatter Modeling And Wind/Rain Retrieval For Scatterometer And Synthetic Aperture Radar, Congling Nie
Wind/Rain Backscatter Modeling And Wind/Rain Retrieval For Scatterometer And Synthetic Aperture Radar, Congling Nie
Theses and Dissertations
Using co-located space-borne satellite (TRMM PR, ESCAT on ERS 1/2) measurements, and numerical predicted wind fields (ECMWF), the sensitivity of C-band backscatter measurement to rain is evaluated. It is demonstrated that C-band radar backscatter can be significantly altered by rain surface perturbation, an effect that has been previously neglected. A low-order wind/rain backscatter model is developed that has inputs of surface rain rate, incidence angle, wind speed, wind direction, and azimuth angle. The wind/rain backscatter model is accurate enough for describing the total backscatter in raining areas with relatively low variance. Rain has a more significant impact on measurements at …
Extending Cfd Modeling To Near-Continuum Flows Using Enhanced Thermophysical Modeling, Abram E. Claycomb
Extending Cfd Modeling To Near-Continuum Flows Using Enhanced Thermophysical Modeling, Abram E. Claycomb
Theses and Dissertations
The constitutive relations found in traditional Navier-Stokes-based computational fluid dynamics solvers are known to be limited in altitude. The presence of nonequilibrium phenomena beyond what these methods are able to predict becomes more prevalent at higher altitudes, or increasing Knudsen number. The bulk viscosity, normally assumed to be zero in most computational fluid dynamics applications, is examined as a means of increasing the range of applicability of computational fluid dynamics. The bulk viscosity model used was from recent calculations available in the literature, from a new anisotropic potential energy surface, and is restricted to temperatures below 2000 K. The normal …
Damage Detection Analysis Using Lamb Waves In Restricted Geometry For Aerospace Applications, Roman T. Underwood
Damage Detection Analysis Using Lamb Waves In Restricted Geometry For Aerospace Applications, Roman T. Underwood
Theses and Dissertations
Today many USAF aircraft are approaching the end of their projected service life. However, those aircraft, such as the F-15 Eagle, are still being operated to accomplish the mission of the USAF. As the F-15 ages the required maintenance increases, as does the risk of structural failure. A goal of structural health monitoring (SHM) programs is to increase aircraft safety by monitoring areas known to have structural failures. Currently, time intensive manual inspections are used to monitor failure “hotspots” decreasing the readiness of the F-15 fleet. The lead ziconate titanate (PZT) is a commonly used piezoelectric transducer that has shown …
Advanced Cathodes For Next Generation Electric Propulsion Technology, Dustin J. Warner
Advanced Cathodes For Next Generation Electric Propulsion Technology, Dustin J. Warner
Theses and Dissertations
The research presented here investigated the feasibility of 6.4 mm Lanthanum Hexaboride (LaB6) and Cerium Hexaboride (CeB6) hollow cathodes for low power electric propulsion applications (100-300W). Two orifice geometries, one anode configuration, several anode and keeper currents, and a range of xenon flow rates were tested for the LaB6 cathode. The CeB6 cathode underwent the same tests, with the exception of the second orifice geometry due to time constraints. An oscilloscope measured waveform behavior and a single Langmuir probe for plasma properties. Infrared imaging studied the thermal characteristics of both cathodes and electron microscopy …
Dialable Cryptography For Wireless Networks, Marnita T. Eaddie
Dialable Cryptography For Wireless Networks, Marnita T. Eaddie
Theses and Dissertations
The objective of this research is to develop an adaptive cryptographic protocol, which allows users to select an optimal cryptographic strength and algorithm based upon the hardware and bandwidth available and allows users to reason about the level of security versus the system throughput. In this constantly technically-improving society, the ability to communicate via wireless technology provides an avenue for delivering information at anytime nearly anywhere. Sensitive or classified information can be transferred wirelessly across unsecured channels by using cryptographic algorithms. The research presented will focus on dynamically selecting optimal cryptographic algorithms and cryptographic strengths based upon the hardware and …
Constellation Design Of Geosynchronous Navigation Satellites Which Maximizes Availability And Accuracy Over A Specified Region Of The Earth, Halil Ibrahim Ozdemir
Constellation Design Of Geosynchronous Navigation Satellites Which Maximizes Availability And Accuracy Over A Specified Region Of The Earth, Halil Ibrahim Ozdemir
Theses and Dissertations
Currently, there are four Global Navigation Satellite Systems (GNSS) either being developed or in existence-GPS, GLONASS, Compass, and Galileo. Additionally, there are several Regional Navigation Satellite Systems (RNSS) planned or in existence, as well as numerous augmentation systems (which require a GNSS for operation). It can be anticipated that there will be interest in developing additional independent regional navigation satellite systems to cover areas of interest to particular countries or regions, who want to have their own system. In this paper, a genetic algorithm is used in an effort to determine near-optimal RNSS constellations. First, a cost function is setup, …
Increasing Combat Aircraft Survivability Through Coherent Self-Protection Jammers, Soner Ozer
Increasing Combat Aircraft Survivability Through Coherent Self-Protection Jammers, Soner Ozer
Theses and Dissertations
When the battlefields were within the visual range, the objective of deception tactics in warfare was to deceive the human senses. In the battlefield of electromagnetic spectrum, the objective of deception is to deceive the sensors of the enemy weapon systems. The survivability of the aircraft operating in hostile environment is of prime importance to the mission planner. If the aircraft can deny its location information to the tracking radar of the radar guided threat missile system, this, in return, may increase its survivability. The deception, a tactic which stems from the wisdom of ancient battles, incarnated in the form …
Microfluidic Power Generation, Aaron J. Sprecher
Microfluidic Power Generation, Aaron J. Sprecher
Theses and Dissertations
This thesis includes the detailed mathematical calculations used to determine the feasibility of harnessing electrical energy from the blood flow through human capillaries. The designs are inspired by human physiology and well established electromagnetic energy harvesting techniques and the fabrication methods have been proposed for the various components of the device. The fabrication and the design of these components have also been extensively analyzed using calculations based on the governing principles of microfluidics, kinetics, and electromagnetics. The analysis has confirmed that this design can produce sufficient energy to power a MEMS device using non-standard materials and fabrication methods. The designs …
Anti-Tamper Method For Field Programmable Gate Arrays Through Dynamic Reconfiguration And Decoy Circuits, Samuel J. Stone
Anti-Tamper Method For Field Programmable Gate Arrays Through Dynamic Reconfiguration And Decoy Circuits, Samuel J. Stone
Theses and Dissertations
As Field Programmable Gate Arrays (FPGAs) become more widely used, security concerns have been raised regarding FPGA use for cryptographic, sensitive, or proprietary data. Storing or implementing proprietary code and designs on FPGAs could result in the compromise of sensitive information if the FPGA device was physically relinquished or remotely accessible to adversaries seeking to obtain the information. Although multiple defensive measures have been implemented (and overcome), the possibility exists to create a secure design through the implementation of polymorphic Dynamically Reconfigurable FPGA (DRFPGA) circuits. Using polymorphic DRFPGAs removes the static attributes from their design; thus, substantially increasing the difficulty …
Optimization Of The Metamorphic Development Process Via The Genetic Algorithm, Keith Daniel Joseph Goren
Optimization Of The Metamorphic Development Process Via The Genetic Algorithm, Keith Daniel Joseph Goren
Theses and Dissertations
This main investigation of this thesis was the integration of the metamorphic development process with a genetic algorithm in order to optimize the metamorphic development process. Since the origin of the metamorphic development process, there has been a need for the user to input parameters in order to coax structural development to obtain an optimum structure. By utilizing the genetic algorithm to manipulate this input information, this new marriage of the metamorphic development process and the genetic algorithm can save time and computation for the user of the program. It was found that the genetic algorithm with the metamorphic development …
Construction And Testing Of Broadband High Impedance Ground Planes (Higps) For Surface Mount Antennas, Bora Cakiroglu
Construction And Testing Of Broadband High Impedance Ground Planes (Higps) For Surface Mount Antennas, Bora Cakiroglu
Theses and Dissertations
The purpose of this research was to design and build appropriate broadband high impedance ground planes for surface mount antennas. Broadband, low-profile antennas, such as spirals, log-periodics, and bow-ties, suffer substantially in gain and bandwidth performance when they are brought close to a conducting surface. Thus, when standard broadband antenna designs are conformally placed on vehicle bodies, they can no longer achieve the high data rates required by modern communication. A simple remedy for this has been to place an absorber lined cavity behind the antenna to preserve some bandwidth, at the expense of reduced gain. However, recently introduced high …
Improvement Of Ecm Techniques Through Implementation Of A Genetic Algorithm, James D. Townsend
Improvement Of Ecm Techniques Through Implementation Of A Genetic Algorithm, James D. Townsend
Theses and Dissertations
This research effective effort develops the necessary interfaces between the radar signal processing components and an optimization routine, such as genetic algorithms, to develop Electronic Countermeasure (ECM) waveforms under a Hardware-in-the-Loop (HILS) architecture. The various ECM waveforms are stored in an ECM library, where an operator selects the desired function to use against a particular system. This optimization works with modular components, compared to previous research that embedded a genetic algorithm into the Range Gate Pull-off (RGPO) waveform optimization loop, which can be interchanged based upon the operator's desired hardware/ software testing setup. The ECM library's first entries contain the …
Sensitivity Analysis Of Algan/Gan Hemts To Process Variation, Adam J. Liddle
Sensitivity Analysis Of Algan/Gan Hemts To Process Variation, Adam J. Liddle
Theses and Dissertations
A sensitivity analysis of AlGaN/GaN HEMT performance on material and process variations was performed. Aluminum mole fraction, barrier thickness, and gate length were varied ± 5% over nominal values to determine how sensitive simulated device performance was to changes in these 3 parameters. Simulated data was generated with the Synopsys TCAD software suite using a physics-based HEMT model. To validate model performance, simulated data was correlated with experimental data, which consisted of wafer epilayer characterization data as well as DC and small-signal RF device performance data from 1-26 GHz. Trends were observed in the experimental data due to variations in …
Electrically Steerable Diffraction Gratings For Hyperspectral Imaging: A Microelectromechanical System Design And Fabrication, Saban Atinc Delican
Electrically Steerable Diffraction Gratings For Hyperspectral Imaging: A Microelectromechanical System Design And Fabrication, Saban Atinc Delican
Theses and Dissertations
The current research is focused on the design and fabrication of an electrically programmable diffraction grating using standard micro electro mechanical systems (MEMS) technology. The goal is to design a beam steering element required to build very small hyperspectral imaging (HSI) sensors. The diffraction grating will be used to perform beam-dispersion - a critical step in the imaging process. The proposed transmissive diffraction grating based approach will minimize the overall size and the number of components in the physical design of the hyperspectral imagers, thereby enabling us to exploit the traditional advantages of MEMS such as increased reliability, smaller size, …
Molecular Characterization Of Wetland Soil Bacterial Communities In Constructed Mesocosms, Elisabeth M. Leon
Molecular Characterization Of Wetland Soil Bacterial Communities In Constructed Mesocosms, Elisabeth M. Leon
Theses and Dissertations
16S rRNA gene analysis was performed on soil samples from a subsurface flow mesocosm experiment, mimicking a constructed wetland. Three typical wetland species of plant were used in nine of the columns and three columns were unplanted controls. Analyses showed that plant presence, plant species, and depth did not have a significant effect on microbial community composition. However, richness analyses illustrated that plant presence had a positive effect on richness, plant species analyses indicated that there was evidence that plant species affected richness in a significant manner, and lastly richness was negatively affected in the bottom depth for the control …
Intelligence Surveillance And Reconnaissance Asset Assignment For Optimal Mission Effectiveness, Ryan D. Kappedal
Intelligence Surveillance And Reconnaissance Asset Assignment For Optimal Mission Effectiveness, Ryan D. Kappedal
Theses and Dissertations
This research develops mathematical programming techniques to solve an intelligence, surveillance, and reconnaissance sensor assignment problem for USSTRATCOM. The problem as specified is hypothesized to be difficult (i.e. np-hard). With the smallest test cases, the true optimal solution is found using simple optimization techniques, but, due to intractability, the optimal solutions for larger test cases are not found using these same techniques. Instead, heuristic techniques are applied to several test cases in order to determine the best, robust methodologies to find true or near optimal solutions. Specifically, simulated annealing (SA) is tested for convergence properties across several different parameter settings. …
An Analysis Of Methodologies & Best Practices For Rapidly Acquiring Technologies To Meet Urgent Warfighter Needs, Charles D. Solomon
An Analysis Of Methodologies & Best Practices For Rapidly Acquiring Technologies To Meet Urgent Warfighter Needs, Charles D. Solomon
Theses and Dissertations
The rapidly changing global security environment that today's military operates within requires an ever-increasing ability to quickly adapt to non-traditional threats. This has forced the United States to re-examine the traditional means of equipping its forces to ensure more agile acquisition practices are available to the Science and Technology (S&T) and acquisition communities. While there have been significant efforts to look towards industry for potential solutions to this problem, the heavily bureaucratic and restrictive government environment has made applying commercial lessons learned difficult. To effectively implement rapid fielding approaches within the government context, research into organizations facing the same or …
Laser Diagnostic System Validation And Ultra-Compact Combustor Characterization, Terry B. Hankins
Laser Diagnostic System Validation And Ultra-Compact Combustor Characterization, Terry B. Hankins
Theses and Dissertations
The AFIT combustion optimization and analysis laser (COAL) lab is now completely operational and is state-of-the-art in combustion diagnostics. The objective of this research is to perform a validation of a laser diagnostic system and to begin the characterization of a small-scale model of an ultra-compact combustor (UCC). Validation of the laser system was accomplished by using planar laser induced fluorescence (PLIF) on a laminar premixed hydrogen-air flame produced by a Hencken burner. OH species concentrations are measured. Flame temperatures are determined with a two line fluorescence technique using different transitions in the (1,0) band of the OH (A-X) electronic …
Real-Time Navigation And Flight Path Generation For Tracking Stop-And-Go Targets With Miniature Air Vehicles, Nate A. Terning
Real-Time Navigation And Flight Path Generation For Tracking Stop-And-Go Targets With Miniature Air Vehicles, Nate A. Terning
Theses and Dissertations
This research effort focuses on using a heuristic approach to determine the optimal flight path required to put an Unmanned Aircraft System’s (UAS) sensor on a moving target in the presence of a constant wind field. This thesis builds on past work using dynamic optimization techniques to calculate minimum time to target. The computationally intensive dynamic optimization routines in their current form take a prohibitive amount of time to calculate and ultimately result in erroneous flight path predictions due to inherent execution time latencies. Therefore an iterative, suboptimal heuristic approach was explored to mitigate excessive calculation times and ultimately yield …
Investigation Into Fretting Fatigue Under Cyclic Contact Load And In Conjuction With Fatigue Of Titanium Alloy, Abdulla A. Al-Noaimi
Investigation Into Fretting Fatigue Under Cyclic Contact Load And In Conjuction With Fatigue Of Titanium Alloy, Abdulla A. Al-Noaimi
Theses and Dissertations
Fretting fatigue is the surface damage that occurs at the interface between two components that are undergoing a small amplitude oscillatory movements. It results in a reduction of the material life comparing to the plain fatigue. Most of the previous works were accomplished under a constant applied contact load and a little effort has been done under a variable contact load, while none of these studies have taken the phase difference between the axial and the contact load. The primary goal of this study is to investigate the effect of phase difference between axial and contact loads on fretting fatigue …