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2011

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Articles 181 - 210 of 368

Full-Text Articles in Aerospace Engineering

Follower-Force Experiments With Geometric Non-Linear Coupling For Analytical Validation, Tae H. Kim Mar 2011

Follower-Force Experiments With Geometric Non-Linear Coupling For Analytical Validation, Tae H. Kim

Theses and Dissertations

This study was a follow-up of a previous study where static deflection data of a joined-wing test article was collected from a series of experiments using a laser scanner and a laser tracker while the test articles were subjected to follower-forces. One of the goals of this study was to collect accurate experimental data which could be used to validate analytical methods, such as geometrically exact beam theory, which are used to predict the nonlinear response of joined-wings. The load application system used on the previous study was not able to provide a follower-force on the test articles, and therefore …

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Using A Gatling-Gun Configured Micro Pulsed Plasma Thruster As A Means To Control Micro Satellites With Extreme Precision, Lee I. Watson Mar 2011

Using A Gatling-Gun Configured Micro Pulsed Plasma Thruster As A Means To Control Micro Satellites With Extreme Precision, Lee I. Watson

Theses and Dissertations

Micro-Pulsed Plasma Thrusters (µPPT) are becoming increasingly attractive for their low power consumption and moderately high specific impulse in the range of 800-1200s. The Gatling Gun micro-Pulsed Plasma Thruster (GG-µPPT) is a new device offering reduced mass and higher thrust than single µPPTs and solid application in precise pointing and orbit maintenance applications. The performance of µPPTs depends on frequency and applied voltage/power levels. Variation of these input parameters and effects on operation and performance of this thruster system were the focus of this research. Contamination aspects were also considered and discussed, since the buildup of carbon results in decreased …

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Stochastic Orbit Prediction Using Kam Tori, Max W. Yates Mar 2011

Stochastic Orbit Prediction Using Kam Tori, Max W. Yates

Theses and Dissertations

Kolmogorov-Arnold-Moser (KAM) Theory states that a lightly perturbed, conservative, dynamical system will exhibit lasting quasi-periodic motion on an invariant torus. Its application to purely deterministic orbits has revealed exquisite accuracy limited only by machine precision. The theory is extended with new mathematical techniques for determining and predicting stochastic orbits for Earth satellite systems. The linearized equations of motion are developed and a least squares estimating environment is pioneered to fit observation data from the International Space Station to a phase space trajectory that exhibits drifting toroidal motion over a dense continuum of adjacent tori. The dynamics near the reference torus …

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Kernelized Locality-Sensitive Hashing For Fast Image Landmark Association, Mark A. Weems Mar 2011

Kernelized Locality-Sensitive Hashing For Fast Image Landmark Association, Mark A. Weems

Theses and Dissertations

As the concept of war has evolved, navigation in urban environments where GPS may be degraded is increasingly becoming more important. Two existing solutions are vision-aided navigation and vision-based Simultaneous Localization and Mapping (SLAM). The problem, however, is that vision-based navigation techniques can require excessive amounts of memory and increased computational complexity resulting in a decrease in speed. This research focuses on techniques to improve such issues by speeding up and optimizing the data association process in vision-based SLAM. Specifically, this work studies the current methods that algorithms use to associate a current robot pose to that of one previously …

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Airborne Pseudolites In A Global Positioning System Degraded, Halit Oktay Mar 2011

Airborne Pseudolites In A Global Positioning System Degraded, Halit Oktay

Theses and Dissertations

The high accuracy of the Global Positioning System allows for precision navigation in support of current and future military operations. However, generating a three-dimensional position using GPS requires a clear line-of-sight between the user and at least four GPS satellites, and so the GPS service can be denied in scenarios such as a street surrounded by tall buildings. Therefore, there is a need for augmentation in these environments. Pseudolites, which transmit GPS-like ranging signals, can be deployed in order to improve the geometry and provide additional ranging signals. Users can then receive and process both GPS and pseudolite signals simultaneously …

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Creep Performance Of Oxide Ceramic Fiber Materials At Elevated Temperature In Air And In Steam, Clinton J. Armani Mar 2011

Creep Performance Of Oxide Ceramic Fiber Materials At Elevated Temperature In Air And In Steam, Clinton J. Armani

Theses and Dissertations

The effects of steam on the creep performance for several ceramic materials were investigated at temperatures in the 1100-1300 deg. C range. Experimental programs were designed to explore both tensile and compressive creep behaviors as well as the response in monotonic tension. Subcritical crack growth was determined to be the dominant failure mechanism in ceramic fibers at elevated temperatures in steam. The creep life prediction analysis of ceramic fiber tows was performed using linear elastic fracture mechanics and a power-law crack velocity model. Additionally, the effects of steam at 1300 deg. C on creep performance of high-purity polycrystalline yttrium aluminum …

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An Experimental Characterization Of Damping Properties Of Thermal Barrier Coatings At Elevated Temperatures, Oliver T. Easterday Mar 2011

An Experimental Characterization Of Damping Properties Of Thermal Barrier Coatings At Elevated Temperatures, Oliver T. Easterday

Theses and Dissertations

This research program developed the apparatus and associated techniques to mechanically characterize the complex modulus of hard coatings across a temperature range from about 70 deg F to 900 deg F. Major effort in designing, analyzing, and experimentally validating the chamber were performed to establish that it isothermally heated a beam specimen, accomplished modal detuning, and achieved a near free-free boundary condition, and that the chamber was characterized for its forcing excitation. Novel aspects of the chamber include non-contact for the excitation, nearly non-contacted boundary conditions, and measurement of the field variables within the specimen using a hybrid experimental-numerical approach. …

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Architecture Based Workload Analysis Of Uas Multi-Aircraft Control: Implications Of Implementation On Mq-1b Predator, Jason D. Mcgrogan, Michael F. Schneider Mar 2011

Architecture Based Workload Analysis Of Uas Multi-Aircraft Control: Implications Of Implementation On Mq-1b Predator, Jason D. Mcgrogan, Michael F. Schneider

Theses and Dissertations

An increased demand for use of Unmanned Aircraft Systems (UASs) without commensurate increases in pilot manpower has prompted proposals for simultaneous control of multiple aircraft by a single pilot or Multi-Aircraft Control (MAC). To understand the potential effects of MAC, an IMPRINT Pro, Multi-Resource Theory, pilot workload model was developed from pedigreed system architecture. Feedback from active UAS pilots was used to validate the model and establish a workload saturation threshold value of 60, above which pilots may experience performance degradation over extended periods of time. The model predicts that pilots experience low workload when operating one or two UASs …

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Airborne Wind Energy: Implementation And Design For The U.S. Air Force, Troy L. Cahoon Mar 2011

Airborne Wind Energy: Implementation And Design For The U.S. Air Force, Troy L. Cahoon

Theses and Dissertations

Excitement among researchers about Airborne Wind Energy (AWE) technology matches DoD aims to advance and employ renewable energy. AWE seeks to cost-effectively tap the vast supply of wind energy available at altitudes high above the reach of conventional, ground-based wind turbines (e.g. 500-12,000m). This paper explores viability and implementation of AWE technology for fulfilling USAF energy needs. Characteristics, potential, and developmental status of the AWE resource are presented. A design tool for a rotor-based AWE system is developed, facilitating the analysis of blade performance to simplify design and provide the best efficiencies for a range of conditions. USAF bases are …

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Ch-47d Rotating System Fault Sensing For Condition Based Maintenance, Stephen M. Dickerson Mar 2011

Ch-47d Rotating System Fault Sensing For Condition Based Maintenance, Stephen M. Dickerson

Theses and Dissertations

The Department of Defense (DoD) has mandated the use of maintenance practices based on component condition rather than component time in service or age. This new practice is known as Condition Based Maintenance, and it relies on accurate detection and identification of material deficiencies in system components. Rotor system components in rotary-wing aircraft can be difficult to monitor due to the rotational environment experienced by the sensors and the difficulty of signal transmission. Current methods are able to detect the existence of a fault in the rotor system but cannot link the vibrations experienced in the airframe to a specific …

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Cubesat Packaged Electrospray Thruster Evaluation For Enhanced Operationally Responsive Space Capabilities, Scott T. Ober Mar 2011

Cubesat Packaged Electrospray Thruster Evaluation For Enhanced Operationally Responsive Space Capabilities, Scott T. Ober

Theses and Dissertations

A new specialized electrospray thruster with a potential to be used with a 3-U CubeSat was operated. The key difference in this thruster from traditional colloid thrusters is the porous stainless steel surface used for the emission sites. With this porous surface the actual location and number of the Taylor cones formations vary with changing fuel flow. The understanding of these formations is discussed with low, moderate, and high flow rates. The limitations of the experiment and observed system response are discussed. Due to these limitations, the colloid thruster was only able to operate in the low mass flow rate …

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Experimental Measurements Of Store Separation Using Dry Ice Models In A Subsonic Flow, Michael C. Paul Mar 2011

Experimental Measurements Of Store Separation Using Dry Ice Models In A Subsonic Flow, Michael C. Paul

Theses and Dissertations

Testing free-drop store separation from a cavity in wind tunnels proves a difficult task because the models are typically destroyed during the test. Furthermore, there is potential for damage to wind tunnel components. Prior work has shown that small dry ice models released within the test section do not cause damage to the AFIT pressure-vacuum wind tunnel components or vacuum chamber. Rather, the dry ice models break apart and sublimate harmlessly into gaseous carbon dioxide. Therefore, this study was undertaken to determine whether dry ice models might prove useful in free-drop store separation testing. A generic aircraft cavity was constructed …

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Effect Of Atmospheric Pressure And Temperature On A Small Spark Ignition Internal Combustion Engine's Performance, Peter J. Schmick Mar 2011

Effect Of Atmospheric Pressure And Temperature On A Small Spark Ignition Internal Combustion Engine's Performance, Peter J. Schmick

Theses and Dissertations

The ever increasing use of man portable unmanned aerial vehicles, UAV, by the US military in a wide array of environmental conditions calls for the investigation of engine performance under these conditions. Previous research has focused on individual changes in pressure or temperature conditions of the air stream entering the engine. The need was seen for a facility capable of providing an environment representative of various simulated altitude conditions. A mobile test facility was developed to test small internal combustion engines with peak powers less than 10 hp. A representative engine was tested over a range of speeds from 2000 …

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Vision-Aided Autonomous Precision Weapon Terminal Guidance Using A Tightly-Coupled Ins And Predictive Rendering Techniques, Jonathan W. Beich Mar 2011

Vision-Aided Autonomous Precision Weapon Terminal Guidance Using A Tightly-Coupled Ins And Predictive Rendering Techniques, Jonathan W. Beich

Theses and Dissertations

This thesis documents the development of the Vision-Aided Navigation using Statistical Predictive Rendering (VANSPR) algorithm which seeks to enhance the endgame navigation solution possible by inertial measurements alone. The eventual goal is a precision weapon that does not rely on GPS, functions autonomously, thrives in complex 3-D environments, and is impervious to jamming. The predictive rendering is performed by viewpoint manipulation of computer-generated of target objects. A navigation solution is determined by an Unscented Kalman Filter (UKF) which corrects positional errors by comparing camera images with a collection of statistically significant virtual images. Results indicate that the test algorithm is …

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Multiple Integrated Navigation Sensors For Improving Occupancy Grid Fastslam, Christopher P. Weyers Mar 2011

Multiple Integrated Navigation Sensors For Improving Occupancy Grid Fastslam, Christopher P. Weyers

Theses and Dissertations

An autonomous vehicle must accurately observe its location within the environment to interact with objects and accomplish its mission. When its environment is unknown, the vehicle must construct a map detailing its surroundings while using it to maintain an accurate location. Such a vehicle is faced with the circularly defined Simultaneous Localization and Mapping (SLAM) problem. However difficult, SLAM is a critical component of autonomous vehicle exploration with applications to search and rescue. To current knowledge, this research presents the first SLAM solution to integrate stereo cameras, inertial measurements, and vehicle odometry into a Multiple Integrated Navigation Sensor (MINS) path. …

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Time Resolved Filtered Rayleigh Scattering Measurement Of A Centrifugally Loaded Buoyant Jet, Firas Benhassen Mar 2011

Time Resolved Filtered Rayleigh Scattering Measurement Of A Centrifugally Loaded Buoyant Jet, Firas Benhassen

Theses and Dissertations

The combustion process within the Ultra-Compact Combustor (UCC) occurs in the circumferential direction. The presence of variable flow density within the circumferential cavity introduces significant buoyancy issues. On the other hand, G-loading caused by the presence of centrifugal forces, ensures the circulation of the flow in the circumferential cavity and enhances the completion of the combustion process before allowing the exit of the hot gases to the main flow. The coupling between buoyancy and high G-loading is what predominately influences the behavior of the flow within the UCC. In order to better understand the combustion process within the UCC, three …

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Kam Torus Frequency Generation From Two-Line Element Sets, Gregory R. Frey Mar 2011

Kam Torus Frequency Generation From Two-Line Element Sets, Gregory R. Frey

Theses and Dissertations

The Kolmogorov Arnold and Moser (KAM) theorem states that a lightly perturbed Hamiltonian system will have solutions which lie on a torus. Earlier work by the second author has shown that most Earth satellite orbits perturbed by the geopotential lie on KAM tori. The problem then arises as to how to convert the current satellite tracking orbits to KAM tori. A KAM torus is characterized by three frequencies and three phase angles. The frequencies are essentially the rates of change of the mean anomaly, the longitude of the ascending node, and the argument of perigee. In this paper we explore …

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Implementation Of A Rule-Based Open-Loop Control Strategy For A Hybrid-Electric Propulsions System On A Small Rpa, Collin Greiser Mar 2011

Implementation Of A Rule-Based Open-Loop Control Strategy For A Hybrid-Electric Propulsions System On A Small Rpa, Collin Greiser

Theses and Dissertations

Currently fielded electric-powered small remotely-piloted aircraft (RPA) lack endurance desired by warfighters, and internal combustion engine (ICE) RPAs generate undesirable acoustic and thermal signatures. Hybrid-electric (HE) propulsion systems would combine both electric power for endurance and ICE power for cruise and climb modes. Use of HE systems would eliminate undesirable signatures in addition to providing considerable fuel savings over time. Five components were used in this HE system: the ICE, electric motor (EM), electromagnetic clutch, battery pack, and a propeller. Control of such a system in a small RPA has never been attempted before. A rulebased controller was developed to …

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X-Hale: The Development Of A Research Platform For The Validation Of Nonlinear Aeroelastic Codes, Alexander A. Kaszynski Mar 2011

X-Hale: The Development Of A Research Platform For The Validation Of Nonlinear Aeroelastic Codes, Alexander A. Kaszynski

Theses and Dissertations

In conjunction with the Air Force Institute of Technology (AFIT) and the Air Force Research Laboratory (AFRL), the University of Michigan has designed and is currently building a remotely piloted aircraft (RPA) experimental high altitude long endurance (X-HALE) aircraft to collect non-linear aeroelastic data to validate HALE aircraft design codes developed by academia, industry, and the federal government. While X-HALE is representative of HALE aircraft, the manufacturing and evaluation techniques are applicable to larger full size HALE aircraft such as the concepts being developed under Defense Advanced Research Projects Agency's (DARPA's) Vulture program. This paper documents the development of the …

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Optimization Of Hybrid-Electric Propulsion Systems For Small Remotely-Piloted Aircraft, Todd A. Rotramel Mar 2011

Optimization Of Hybrid-Electric Propulsion Systems For Small Remotely-Piloted Aircraft, Todd A. Rotramel

Theses and Dissertations

Small electric-powered remotely-piloted aircraft (RPA) used by today's warfighters for intelligence, surveillance, and reconnaissance (ISR) missions lack desired endurance and loiter times, while the acoustics and thermal signatures of those configured with internal combustion engines (ICE) may make them unpractical for ISR. Outfitting RPA with parallel hybrid-electric propulsion systems (H-EPS) would meet the military's needs by combining the advantages of both systems while reducing fuel consumption and environmental impacts. An analysis tool was created, using constrained static optimization, to size the H-EPS components. Based on the RPA's required power and velocity for the endurance phase, an electric motor (EM) can …

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Biological Investigation Of The Stimulated Flapping Motions Of The Moth, Manduca Sexta, Travis B. Tubbs Mar 2011

Biological Investigation Of The Stimulated Flapping Motions Of The Moth, Manduca Sexta, Travis B. Tubbs

Theses and Dissertations

No abstract provided.

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Long Term Quadrotor Stabilization, Nicolas S. Hamilton Mar 2011

Long Term Quadrotor Stabilization, Nicolas S. Hamilton

Theses and Dissertations

The work of this thesis focuses on the IMU and getting the best performance possible out of the IMU to achieve better long term stability and a better navigation solution. This is done in two ways. First, the IMU accelerometer output is examined to determine if it is possible to use accelerometers to determine attitude. If the quadrotor is stationary or moving at constant velocity, the roll and pitch angles can be determined. Additionally, the accelerometers can be used to determine angular accelerations and angular rates which are integrated to determine heading. The second approach models the quadrotor and uses …

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Effects Of Cyclic Prefix Jamming Versus Noise Jamming In Ofdm Signals, Amber L. Scott Mar 2011

Effects Of Cyclic Prefix Jamming Versus Noise Jamming In Ofdm Signals, Amber L. Scott

Theses and Dissertations

Signal jamming of an orthogonal frequency-division multiplexing (OFDM) signal is simulated in MATLAB. Two different means of jamming are used to see, which is a more efficient way to disrupt a signal using the same signal power. The first way is a basic additive white Gaussian noise (AWGN) jammer that equally jams the entire signal. The second way is an AWGN jammer that targets only the cyclic prefix (CP) of the signal. These two methods of jamming are simulated using different channel models and unknowns to get varying results. The three channel models used in the simulations are the no …

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Non-Gps Navigation Using Vision-Aiding And Active Radio Range Measurements, Erich H. Lichtfuss Mar 2011

Non-Gps Navigation Using Vision-Aiding And Active Radio Range Measurements, Erich H. Lichtfuss

Theses and Dissertations

The military depends on the Global Positioning System (GPS) for a wide array of advanced weaponry guidance and precision navigation systems. Lack of GPS access makes precision navigation very difficult. Inclusion of inertial sensors in existing navigation systems provides short-term precision navigation, but drifts significantly over long-term navigation. This thesis is motivated by the need for inertial sensor drift-constraint in degraded and denied GPS environments. The navigation system developed consists of inertial sensors, a simulated barometer, three Raytheon DH500 radios, and a stereo-camera image-aiding system. The Raytheon DH500 is a combat communication radio which also provides range measurements between radios. …

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Tension-Compression Fatigue Of Hi-Nicalon/Sic Ceramic Matrix Composite At 1200°C In Air And Steam, Tyler P. Jones Mar 2011

Tension-Compression Fatigue Of Hi-Nicalon/Sic Ceramic Matrix Composite At 1200°C In Air And Steam, Tyler P. Jones

Theses and Dissertations

The primary tenet of the aircraft survivability discipline is threat definition. In order to deliver relevant capabilities and protection to the warfighter it is imperative; therefore, to provide timely, accurate, and actionable threat data to the survivability community. In an attempt to identify the evolution of aircraft threats in today's combat environment, an analysis of fixed-wing aircraft battle damage was conducted. This analysis reports battle damage incidents from OPERATIONS ENDURING FREEDOM (OEF) and IRAQI FREEDOM(OIF). Additionally, reported damage incidents were then validated by crosschecking aircraft maintenance records from this period to eliminate non-hostile fire data points. This revolutionary approach uncovered …

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An Investigation Of Cavity Resonance And Its Relationship To Store Force And Moment Loading, Christopher J. Coley Mar 2011

An Investigation Of Cavity Resonance And Its Relationship To Store Force And Moment Loading, Christopher J. Coley

Theses and Dissertations

A store which is released from an internal bay is subjected to a highly unsteady flowfield which influences the release characteristics for the store. Pressure transducer information is often used to estimate store loading, although no direct correlation between the observed frequencies from the pressure transducers and the store loading has been developed. The relationship between the acoustic modes present in the cavity and the force and moment loading on a store released from a bay are investigated through a CFD study using the OVERFLOW 2.1 solver. The acoustic modes of the cavity are calculated from the pressure fluctuation histories …

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Performance Characterization Of A Novel Plasma Thruster To Provide A Revolutionary Operationally Responsive Space Capability With Micro- And Nano-Satellites, John-David C. De La Harpe Mar 2011

Performance Characterization Of A Novel Plasma Thruster To Provide A Revolutionary Operationally Responsive Space Capability With Micro- And Nano-Satellites, John-David C. De La Harpe

Theses and Dissertations

Few options currently exist to provide propulsion for extremely small satellites due to design constraints on power, volume, and weight. However, future operation will require a capability to conduct orbital maneuvers, momentum dumping, and precision pointing for these low cost satellites. The research presented here represents the first effort to operate and quantify the performance of a new micro plasma thruster design which provides a novel solution to these disparate competing constraints. The thruster in this study represents a deviation from traditional circular Hall thruster design practices, because it eschews a central magnetic circuit, which results in nearly parallel electric …

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Manufacturing And Evaluation Of A Biologically Inspired Engineered Mav Wing Compared To The Manduca Sexta Wing Under Simulated Flapping Conditions, Nathanial E. Deleon Mar 2011

Manufacturing And Evaluation Of A Biologically Inspired Engineered Mav Wing Compared To The Manduca Sexta Wing Under Simulated Flapping Conditions, Nathanial E. Deleon

Theses and Dissertations

In recent years, researchers have expressed a vested interest in the concepts surrounding flapping wing micro air vehicles (FWMAVs) that are capable of both range and complex maneuvering. Most research in this arena has found itself concentrated on topics such as flapping dynamics and the associated fluid-structure interactions inherent in the motion, however there still remains myriad questions concerning the structural qualities intrinsic to the wings themselves. Using nature as the template for design, FWMAV wings were constructed using carbon fiber and Kapton and tested under simplified flapping conditions by analyzing frozen' digital images of the deformed wing by methods …

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Vibration Interaction In A Multiple Flywheel System, Jordan A. Firth Mar 2011

Vibration Interaction In A Multiple Flywheel System, Jordan A. Firth

Theses and Dissertations

This study uses a linear model of an Integrated Power and Attitude Control System (IPACS) to investigate the vibration interaction between multiple flywheels. An easily extendable Matlab® script is created for the analysis of flywheel vibrations. This script is used to build a vibration model consisting of two active magnetic bearing flywheels mounted on a support structure. The flywheels are rotated at varying speeds, with an imbalance-induced centripetal force in one or both wheels causing vibrations in both wheels. Flywheel and system responses are examined for low frequency vibrations which would cause undesirable excitation to a satellite using IPACS, with …

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Effects Of Air Drag And Lunar Third-Body Perturbations On Motion Near A Reference Kam Torus, Luke J. Hagen Mar 2011

Effects Of Air Drag And Lunar Third-Body Perturbations On Motion Near A Reference Kam Torus, Luke J. Hagen

Theses and Dissertations

The KAM Theory was developed in the 1960s but only in the last decade has it been applied to Earth orbiting satellites. Physical state variables of position and velocity are transformed into KAM Torus variables. The KAM Torus is a geometrical structure similar to that of a multi-dimensional donut. The Earth satellite's motion can be described as traversing the surface of this donut. There are two primary advantages of this transformation: (1) The new generalized coordinates which are analogous with mean anomaly, right ascension of the ascending node, and argument of perigee, increment linearly with time, and (2) Perturbations due …

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