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Articles 2731 - 2760 of 5700
Full-Text Articles in Engineering
Thermo-Mechanical Characterization Of Silicon Carbide-Silicon Carbide Composites At Elevated Temperatures Using A Unique Combustion Facility, Ted T. Kim
Theses and Dissertations
This research investigated four different types of CMCs in a simulated gas turbine engine hot section condition that involved the simultaneous application of a combustion environment and mechanical fatigue loading using a unique burner rig facility developed for this study at AFIT. Three of the materials were woven Melt-Infiltrated (MI) BN/SiC reinforced by Hi-Nicalon Type S (Hi-Nic-S), Sylramic (Syl) and Sylramic with insitu BN coating (Syl-iBN) fibers, respectively. They were made by the slurry cast method. The other CMC was MI Hi-Nic-S/BN/SiC made using the prepreg MI processing. Prepreg MI CMC and Sylramic-iBN fiber reinforced CMC showed better resistance to …
Least-Squares, Continuous Sensitivity Analysis For Nonlinear Fluid-Structure Interaction, Douglas P. Wickert
Least-Squares, Continuous Sensitivity Analysis For Nonlinear Fluid-Structure Interaction, Douglas P. Wickert
Theses and Dissertations
A least-squares, continuous sensitivity analysis method is developed for transient aeroelastic gust response problems to support computationally efficient analysis and optimization of aeroelastic design problems. A key distinction between the local and total derivative forms of the sensitivity system is introduced. The continuous sensitivity equations and sensitivity boundary conditions are derived in local derivative form which is shown to be superior for several applications. The analysis and sensitivity problems are both posed in a first-order form which is amenable to a solution using the least-squares finite element method. Several example and validation problems are presented and solved, including elasticity, fluid, …
Alternative Methods To Standby Gain Scheduling Following Air Data System Failure, Matthew W. Coldsnow
Alternative Methods To Standby Gain Scheduling Following Air Data System Failure, Matthew W. Coldsnow
Theses and Dissertations
The United States Air Force has advanced fighter aircraft that lose the ability to operate in a large portion of their operating flight envelope when an air data system failure is experienced. These aircraft are reverted to a fixed set of standby-gains that limit their maneuverability, degrade handling qualities, and increase susceptibility to departure. The purpose of this research was to determine if three alternative methods of standby-gain-scheduling could provide robust control with minimal performance degradation despite the lack of air data. To accomplish this, three methods of standby-gain-scheduling were developed, integrated, and tested in the Infinity Cube simulator at …
Electronic Image Stabilization For Mobile Robotic Vision Systems, Michael John Smith
Electronic Image Stabilization For Mobile Robotic Vision Systems, Michael John Smith
Theses and Dissertations
When a camera is affixed on a dynamic mobile robot, image stabilization is the first step towards more complex analysis on the video feed. This thesis presents a novel electronic image stabilization (EIS) algorithm for small inexpensive highly dynamic mobile robotic platforms with onboard camera systems. The algorithm combines optical flow motion parameter estimation with angular rate data provided by a strapdown inertial measurement unit (IMU). A discrete Kalman filter in feedforward configuration is used for optimal fusion of the two data sources. Performance evaluations are conducted by a simulated video truth model (capturing the effects of image translation, rotation, …
Signal Classification In Fading Channels Using Cyclic Spectral Analysis, Zhiqiang Wu, Eric C. Like, Vasu D. Chakravarthy, Paul Ratazzi
Signal Classification In Fading Channels Using Cyclic Spectral Analysis, Zhiqiang Wu, Eric C. Like, Vasu D. Chakravarthy, Paul Ratazzi
Student Publications
Cognitive Radio (CR), a hierarchical Dynamic Spectrum Access (DSA) model, has been considered as a strong candidate for future communication systems improving spectrum efficiency utilizing unused spectrum of opportunity. However, to ensure the effectiveness of dynamic spectrum access, accurate signal classification in fading channels at low signal to noise ratio is essential. In this paper, a hierarchical cyclostationary-based classifier is proposed to reliably identify the signal type of a wide range of unknown signals. The proposed system assumes no a priori knowledge of critical signal statistics such as carrier frequency, carrier phase, or symbol rate. The system is designed with …
The Navigation Potential Of Ground Feature Tracking, Guner Mutlu
The Navigation Potential Of Ground Feature Tracking, Guner Mutlu
Theses and Dissertations
This research effort examines the reduction of error in inertial navigation aided by vision. This is part of an effort focused on navigation in a GPS denied environment. The navigation concept examined here consists of two main steps. First, extract the position of a tracked ground object using vision and geo-locate it in 3 dimensional navigation frame. In this first step multiple positions of the UAV are assumed known; think of a synthetic aperture. The only information about the tracked ground objects/features is the unit vector that points to the objects from the center of the camera. Two such vectors …
Synthesis, Interdiction, And Protection Of Layered Networks, Kevin T. Kennedy
Synthesis, Interdiction, And Protection Of Layered Networks, Kevin T. Kennedy
Theses and Dissertations
This research developed the foundation, theory, and framework for a set of analysis techniques to assist decision makers in analyzing questions regarding the synthesis, interdiction, and protection of infrastructure networks. This includes extension of traditional network interdiction to directly model nodal interdiction; new techniques to identify potential targets in social networks based on extensions of shortest path network interdiction; extension of traditional network interdiction to include layered network formulations; and develops models/techniques to design robust layered networks while considering trade-offs with cost. These approaches identify the maximum protection/disruption possible across layered networks with limited resources, find the most robust layered …
Changes In Structural Health Monitoring System Capability Due To Aircraft Environmental Factors, Jeffrey D. Kuhn
Changes In Structural Health Monitoring System Capability Due To Aircraft Environmental Factors, Jeffrey D. Kuhn
Theses and Dissertations
Structural Health Monitoring (SHM) promises to decrease the maintenance cost and increase the availability of aging aircraft fleets by fundamentally changing the way structural inspections are performed. But this promise can only be realized through the consistent and predictable performance of a SHM system throughout the entire remaining life of an aircraft. In a sensor-based SHM system, sensor signal changes are analyzed and interpreted to identify structural flaws. But aircraft environmental factors such as temperature fluctuations, cyclic strain and exposure to various aircraft fluids also have the potential to change SHM sensor signals, raising questions about long term SHM system …
Analysis And Modeling Of Motor Vehicle Crashes Involving Air Force Military Personnel, Antonios Markopoulos
Analysis And Modeling Of Motor Vehicle Crashes Involving Air Force Military Personnel, Antonios Markopoulos
Theses and Dissertations
The primary purpose of this thesis was to improve the data analysis of Motor Vehicle Crashes (MVCs). This thesis employed the Air Force Safety Center (AFSC) data, collected over 20 years, of MVCs in which US Air Force (USAF) military personnel are involved when off duty and off base. Categorical Data Analysis and Analysis of Variance (ANOVA) were applied to identify risk factors related to MVCs and influence the severity of injuries and those factors associated with the alcohol consumption before driving, and affect the number of lost workdays resulting from MVCs. Categorical Data Analysis showed that male USAF members …
Formation Flight Of Earth Satellites On Kam Tori, Christopher T. Craft
Formation Flight Of Earth Satellites On Kam Tori, Christopher T. Craft
Theses and Dissertations
Kolmogorov, Arnold and Moser (KAM) theory provides that orbits of satellites whose dynamics are representable by an integrable Hamiltonian plus a small, real perturbation lie on tori in phase space and remain on the KAM tori for all time, unless acted upon by a non-conservative force. A refined technique for constructing KAM tori for Earth-orbiting satellites is developed and implemented using numerically integrated orbital data for hypothetical satellites and involving methods of Fourier analysis and spectral decomposition. Definition of satellite formations on the KAM tori is performed and analyses conducted to investigate both constellations with large separations and clusters with …
Kc-135 Simulator Systems Engineering Case Study, Air Force Center For Systems Engineering, Macaulay-Brown, Inc., Don Chrislaghi, Richard Dyer, Free Jay
Kc-135 Simulator Systems Engineering Case Study, Air Force Center For Systems Engineering, Macaulay-Brown, Inc., Don Chrislaghi, Richard Dyer, Free Jay
AFIT Documents
No abstract provided.
Global Hawk Systems Engineering Case Study, Air Force Center For Systems Engineering, Bill Kinzig
Global Hawk Systems Engineering Case Study, Air Force Center For Systems Engineering, Bill Kinzig
AFIT Documents
No abstract provided.
Abstracting Gis Layers From Hyperspectral Imagery, Torsten E. Howard, Michael J. Mendenhall, Gilbert L. Peterson
Abstracting Gis Layers From Hyperspectral Imagery, Torsten E. Howard, Michael J. Mendenhall, Gilbert L. Peterson
Faculty Publications
The spectral-spatial relationship of materials in a hyperspectral image cube is exploited to partially automate the creation of Geographic Information System (GIS) layers. The topological neighborhood preservation property of the Self Organizing Map (SOM) is clustered into six (partially overlapping) neighborhoods that are mapped into the image domain to locate in-scene structures of similar material type. GIS layers are abstracted through spatial logical and morphological operations on the six image domain material maps and a novel road finding algorithm connects road segments under significant tree-occlusion resulting in a contiguous road network. It is assumed that specific knowledge of the scene …
Effects Of Prior Aging At 288°C In Argon Environment On Creep Response Of Carbon Fiber Reinforced Pmr-15 Composite With ±45°Fiber Orientation At 288°C, Tyler F. Gruters
Effects Of Prior Aging At 288°C In Argon Environment On Creep Response Of Carbon Fiber Reinforced Pmr-15 Composite With ±45°Fiber Orientation At 288°C, Tyler F. Gruters
Theses and Dissertations
The creep and recovery response of carbon fiber reinforced PMR-15 composite with a + or - 45 fiber orientation was examined in an argon environment at 288 deg C. Mechanical testing was executed for unaged specimens as well as specimens aged up to 1000 hours. Tensile tests were performed to determine Young's modulus of elasticity and ultimate tensile strength. The creep tests were carried out at stress levels of 30 and 60 MPa. Creep periods of 25 hours were followed by recovery periods of 50 hours at zero stress. Weight loss measurements as a function of aging time were taken …
Cavity Coupled Aeroramp Injector Combustion Study, Dell T. Olmstead
Cavity Coupled Aeroramp Injector Combustion Study, Dell T. Olmstead
Theses and Dissertations
The difficulties with fueling of supersonic combustion ramjet engines with hydrocarbon based fuels presents many challenges that are currently being tackled by the Air Force Research Lab Propulsion Directorate Aerospace Propulsion Division. As the scramjet engine designs are scaled up, the need for a better solution to supersonic mixing has led to the development of many different styles of fuel injection. An aerodynamic ramp injector has been shown to have a quantitative improvement over a physical ramp while still achieving desirable mixing characteristics. The objectives for this research was quantifying the performance and operability implications of replacing four 15 degree …
Aeroelastic Optimization Of Sounding Rocket Fins, Joseph R. Simmons Iii
Aeroelastic Optimization Of Sounding Rocket Fins, Joseph R. Simmons Iii
Theses and Dissertations
This research effort develops a multidisciplinary design tool to optimize sounding rocket fin geometries that minimize the mass of the fins while maintaining aerodynamic performance. This research grew out of a design problem experienced by the US Air Force Academy's Falcon LAUNCH program. The Falcon LAUNCH program is a senior design capstone project during which Air Force Academy cadets design, build and fly a sounding rocket over the course of an academic year. In the Spring of 2007, the Falcon LAUNCH V vehicle experienced a catastrophic failure when three of its four fins sheared off due to flutter. When the …
Performance And Operability Of A Dual Cavity Flame Holder In A Supersonic Combustor, Mackenzie J. Collatz
Performance And Operability Of A Dual Cavity Flame Holder In A Supersonic Combustor, Mackenzie J. Collatz
Theses and Dissertations
The current generation of hydrocarbon fueled scramjet combustors typically requires a flame holding device to facilitate flame ignition and stable combustion. The amount of time available for fuel injection, fuel-air mixing, and combustion is very short, on the order of 1 millisecond. This short dwell time, along with the relatively long ignition delay times of hydrocarbon fuels, makes the flow path and flame holder design extremely important. This study investigates the performance and operability of using a symmetric dual cavity flame holder flow path to stabilize and enhance supersonic combustion. Testing of this flow path configuration, as well as a …
An Efficient And Effective Implementation Of The Trust System For Power Grid Compartmentalization, Juan M. Carlos Gonzalez
An Efficient And Effective Implementation Of The Trust System For Power Grid Compartmentalization, Juan M. Carlos Gonzalez
Theses and Dissertations
As utility companies develop and incorporate new technologies, such as moving to utility Internet technology based architecture and standard; it is crucial that we do so with history in mind. We know that traditional utility protection and control systems were not designed with security in their top priorities. This presents a danger in an environment where near real-time responses are required to ensure safe operations. As a consequence, system security becomes a burden to the system rather than necessary protection. Unfortunately, technology implementation is not the only concern. The number of utility privately-owned companies has multiplied as the market has …
System Identification Of An On Orbit Spacecraft's Antenna Dynamics, Christopher M. Sylvester
System Identification Of An On Orbit Spacecraft's Antenna Dynamics, Christopher M. Sylvester
Theses and Dissertations
As a result of previous efforts [Pachter, Barba, 2007] a tight control loop was designed to meet performance specifications while minimizing the feedback control system’s gains of a spacecraft mounted flexible antenna. Emphasis is now shifted to on orbit system identification of the antenna dynamics in order to increase nominal plant knowledge, estimate plant uncertainty bounds, as well as determine the disturbance band. Non-parametric system identification is undertaken. Knowledge of the plant dynamics along with the corresponding uncertainty bounds will provide for the design of a control system which meets the specifications (tracking and disturbance rejection) while at the same …
Nondestructive Electromagnetic Material Characterization Using A Dual Waveguide Probe: A Full Wave Solution, Milo W. Hyde Iv, James W. Stewart, Michael J. Havrilla, William P. Baker, Edward Rothwell, Dennis P. Nyquist
Nondestructive Electromagnetic Material Characterization Using A Dual Waveguide Probe: A Full Wave Solution, Milo W. Hyde Iv, James W. Stewart, Michael J. Havrilla, William P. Baker, Edward Rothwell, Dennis P. Nyquist
Faculty Publications
A nondestructive technique for determining the complex permittivity and permeability of a perfect electric conductor backed magnetic shielding material using a dual waveguide probe is presented. The dual waveguide probe allows for the simultaneous collection of reflection and transmission coefficients which distinguishes it from single probe methods common in the literature. Theoretical development of these coefficients, which is accomplished through a coupled magnetic field integral equations formulation using Love's equivalence principle and solved via the method of moments (MOM), is discussed. Evaluation of the resulting MOM impedance matrix elements is performed using complex plane integration leading to enhanced computational efficiency …
Structural Optimization Of Joined-Wing Beam Model With Bend-Twist Coupling Using Equivalent Static Loads, Nicholas S. Green
Structural Optimization Of Joined-Wing Beam Model With Bend-Twist Coupling Using Equivalent Static Loads, Nicholas S. Green
Theses and Dissertations
This study is based on the merger of two separate theories to further the efficiency with which joined-wing structural models are designed. The first theory is Geometrically Exact Beam Theory (GEBT). GEBT is a small strain beam theory which is capable of accurately capturing the geometric bend-twist coupling in beam elements that are experiencing large global deformations. This is crucial to the joined-wing problem as it is geometrically nonlinear. The second theory concerns Equivalent Static Loads (ESL). These ESL consist of a load vector that produces the same nodal displacements and rotations as those computed from a pure nonlinear analysis. …
Time Domain Equalizer Design Using Bit Error Rate Minimization For Uwb Systems, Syed Imtiaz Husain, Jinhong Yuan, Jian Zhang, Richard K. Martin
Time Domain Equalizer Design Using Bit Error Rate Minimization For Uwb Systems, Syed Imtiaz Husain, Jinhong Yuan, Jian Zhang, Richard K. Martin
Faculty Publications
Ultra-wideband (UWB) communication systems occupy huge bandwidths with very low power spectral densities. This feature makes the UWB channels highly rich in resolvable multipaths. To exploit the temporal diversity, the receiver is commonly implemented through a Rake. The aim to capture enough signal energy to maintain an acceptable output signal-to-noise ratio (SNR) dictates a very complicated Rake structure with a large number of fingers. Channel shortening or time domain equalizer (TEQ) can simplify the Rake receiver design by reducing the number of significant taps in the effective channel. In this paper, we first derive the bit error rate (BER) of …
Influence Of Structural Flexibility On Flapping Wing Propulsion, Aaron M. Mcclung
Influence Of Structural Flexibility On Flapping Wing Propulsion, Aaron M. Mcclung
Theses and Dissertations
The inelastic deformation behavior of PMR-15 neat resin, a high-temperature thermoset polymer, was investigated at 288 degrees C. The experimental program was designed to explore the influence of strain rate on tensile loading, unloading, and strain recovery behaviors. In addition, the effect of the prior strain rate on the relaxation response of the material, as well as on the creep behavior following strain controlled loading were examined. The experimental data were modeled with the Viscoplasticity Based on Overstress (VBO) theory. A systematic procedure for determining model parameters was developed and the model was employed to predict the response of the …
Characterizing Component Hiding Using Ancestral Entropy, Jason A. Williams
Characterizing Component Hiding Using Ancestral Entropy, Jason A. Williams
Theses and Dissertations
In this research, the problem of software protection and the attributes that define that protection is considered. Specifically, how to protect programs defined as structural combinational logic gates. Obfuscation is one technique for protecting such circuits and involves replacing an original circuit with a functionally equivalent variant that has some definable hiding property. The difficulty of reverse engineering versus identifying and recovering the original components or sub-circuits within an original circuit is compared. With a polymorphic circuit engine that produces semantically equivalent variations of standard benchmark circuits the level of component hiding across variants with different physical configurations is determined …
Removing Redundant Logic Pathways In Polymorphic Circuits, Hanseok Kim
Removing Redundant Logic Pathways In Polymorphic Circuits, Hanseok Kim
Theses and Dissertations
Evaluating the quality of software and circuit obfuscators is a research goal of great interest. However, there exists little research about evaluation of obfuscation effectiveness through analyzing and investigating redundancies found in the obfuscated variants. In this research, we consider programs represented as structural combinational circuits and then analyze obfuscated variants of those circuits through a tool that produces functionally equivalent variants based on subcircuit selection and replacement. We then consider how Boolean logic and reduction affects the size and levelization of circuit variants, giving us a concrete metric by which to consider obfuscation effectiveness. To accomplish these goals, we …
Determining The Orbit Locations Of Turkish Airborne Early Warning And Control Aircraft Over The Turkish Air Space, Nebi Sarikaya
Determining The Orbit Locations Of Turkish Airborne Early Warning And Control Aircraft Over The Turkish Air Space, Nebi Sarikaya
Theses and Dissertations
The technology improvement affects the military needs of individual countries. The new doctrine of defense for many countries emphasizes detecting threats as far away as you can from your homeland. Today, the military uses both ground RADAR and Airborne Early Warning and Control (AEW&C) Aircraft. AEW&C aircraft has become vital to detect low altitude threats that a ground RADAR cannot detect because of obstacles on the earth. Turkey has ordered four AEW&C aircraft for her air defense system because of the lack of complete coverage by ground RADAR. This research provides optimal orbit locations that can be updated according to …
Frequency Diversity For Improving Synthetic Aperture Radar Imaging, Jawad L. Farooq
Frequency Diversity For Improving Synthetic Aperture Radar Imaging, Jawad L. Farooq
Theses and Dissertations
In this work, a novel theoretical framework is presented for using recent advances in frequency diversity arrays (FDAs). Unlike a conventional array, the FDA simultaneously transmits a unique frequency from each element in the array. As a result, special time and space properties of the radiation pattern are exploited to improve cross-range resolution. The idealized FDA radiation pattern is compared with and validated against a full-wave electromagnetic solver, and it is shown that the conventional array is a special case of the FDA. A new signal model, based on the FDA, is used to simulate SAR imagery of ideal point …
Methodology For Value-Driven Enterprise Architecture Development Goals: Application To Dodaf Framework, Justin W. Osgood
Methodology For Value-Driven Enterprise Architecture Development Goals: Application To Dodaf Framework, Justin W. Osgood
Theses and Dissertations
The Department of Defense Architectural Framework (DoDAF) describes 29 distinct views but offers limited guidance on view selection to meet system needs. This research extends the Value-Driven Enterprise Architecture Score (VDEA-Score) from a descriptive, evaluation protocol toward a prescriptive one by evaluating each DoDAF view and its contribution to the overall objective of the completed architecture. This extension of VDEA is referred to as VDEA-Development Goals (VDEA-DG). The program manager or other decision-makers may use this insight to justify the allocation of resources to the development of specific architecture views considered to provide maximum value. This research provides insight into …
Application Of Time-Frequency Representation To Non-Stationary Radar Cross Section, John D. Mcshane
Application Of Time-Frequency Representation To Non-Stationary Radar Cross Section, John D. Mcshane
Theses and Dissertations
Radar Cross Section (RCS) imaging of a non-wide sense stationary signal poses significant problems in identifying scattering centers in the post processed radar- generated image. A non-wide sense stationary RCS is typically encountered when moving parts on the target impress a phase shift into the backscatter signal that is uncorrelated to the previous return pulse. When the Fourier transform of the phase shifted complex signal is taken, range and cross range information on scattering centers are misplaced. Time Frequency Representations (TFR) must be used to help locate these scattering centers so they can be properly treated to reduce the target’s …
Fuel Composition And Performance Analysis Of Endothermically Heated Fuels For Pulse Detonation Engines, Christopher A. Stevens
Fuel Composition And Performance Analysis Of Endothermically Heated Fuels For Pulse Detonation Engines, Christopher A. Stevens
Theses and Dissertations
Waste heat from a pulse detonation engine (PDE) was extracted via concentric, counter flow heat exchangers to produce supercritical pyrolytic conditions for JP-7 and JP-8 fuels. A sampling system and method was utilized to collect samples of reacted fuel to be extracted during steady state operation. Samples were collected over a range of heat exchanger exit temperatures from 820 K (1016° F) to 940 K (1232 degrees F) and for two sets of heat exchangers, one set coated with zeolite catalyst and one set left uncoated. Variation in fuel mass flow rate required the calculation of heat addition as an …