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Articles 8851 - 8880 of 11122

Full-Text Articles in Engineering

Thermal Characterization Of A Hall Effect Thruster, Alex M. Bohnert Mar 2008

Thermal Characterization Of A Hall Effect Thruster, Alex M. Bohnert

Theses and Dissertations

The thermal characteristics of a Hall thruster directly influence thruster and spacecraft design. High temperatures affect the magnetic coil capabilities and cause higher insulator erosion rates, influencing both thruster performance and lifetime. The Hall thruster transfers heat through both radiation and conduction, and the spacecraft must handle this additional thermal energy. An infrared camera provides a non-intrusive method to analyze the thermal characteristics of an operational Hall thruster. This thesis contains the thermal analysis of a Busek Co. Inc. 200 W Hall thruster, using a FLIR ThermaCAM SC640 infrared camera. The Space Propulsion Analysis and System Simulator Laboratory at the …

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Crew Exploration Vehicle (Cev) Skip Entry Trajectory, Emre Kaya Mar 2008

Crew Exploration Vehicle (Cev) Skip Entry Trajectory, Emre Kaya

Theses and Dissertations

This research effort develops a program using MATLAB® to solve the equations of motion for the atmospheric reentry of the Crew Exploration Vehicle (CEV) which is assumed to be in the phase of a lunar return trajectory that could be initiated any time during the mission. The essential reason for this research is to find a solution for the problem of an unplanned lunar return in addition to the normal procedures. Unlike Apollo type missions, the CEV would still be able to land on any preplanned available landing sites without any additional delay. In Apollo type missions, the return phase …

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Determination Of Static And Dynamic Stability Derivatives Using Beggar, Michael E. Bartowitz Mar 2008

Determination Of Static And Dynamic Stability Derivatives Using Beggar, Michael E. Bartowitz

Theses and Dissertations

The static and dynamic pitch and roll stability derivatives of a finned, axisymmetric missile known as the Basic Finner were examined using a Computational Fluid Dynamics (CFD) approach. Stability derivatives are used to characterize vehicle motion, and knowledge of them is critical to the design of stable uncontrolled vehicles and control systems for controlled vehicles. Using CFD to characterize the motion of new munition designs has the potential to improve overall performance and reduce research and testing costs. The present analysis simulated forced oscillation and free oscillation of the Basic Finner model using the Air Force SEEK EAGLE Office's Beggar …

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A Comparison Of Moiré Interferometry And Digital Image Correlation, Ryan J. Davidson Mar 2008

A Comparison Of Moiré Interferometry And Digital Image Correlation, Ryan J. Davidson

Theses and Dissertations

This research effort studied the effect of subset size and step size on the spatial resolution and accuracy of Digital Image Correlation (DIC). In addition, DIC was compared with moiré interferometry in an attempt to give future researchers guidance on which method would be appropriate for their research. Strains fields were calculated from displacement fields measured by each method. The strain fields were then compared. The main findings of the research were that: increased subset sizes caused a smoothing of data; increased step sizes reduced the resolution of the data; DIC is an accurate displacement measurement technique; the spatial resolution …

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Characterization And Control Of Carbon Dioxide Seed Particle Image Velocimetry, Bartt G. Greene Mar 2008

Characterization And Control Of Carbon Dioxide Seed Particle Image Velocimetry, Bartt G. Greene

Theses and Dissertations

Particle Image Velocimetry (PIV) data was acquired in two separate supersonic wind tunnels with carbon dioxide (CO2) particles utilized as the seed material. Previous work in clean seeding showed CO2 could be used as seed material to produce velocity maps. This research provides the first quantitative assessment of particle response, particle size control via purge gas, and scalability using CO2 particles. A variety of feed tube and shroud configurations, in combination with varying volumetric flow rates of purge air were measured using a laser diffraction device. The CO2 particles were injected into the stilling chamber …

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Demonstrative Maneuvers For Aircraft Agility Predictions, David M. Hall Mar 2008

Demonstrative Maneuvers For Aircraft Agility Predictions, David M. Hall

Theses and Dissertations

This study was motivated by a need to develop a reliable method of predicting the agility characteristics of various aircraft. To fully investigate the agility of an aircraft, maneuvers which push the limits of an aircraft’s maneuvering capabilities must be simulated. In these cases, classic trajectory optimization techniques either require too many assumptions for a realistic solution or require a good guess of the final solution before the problem is even attempted. This study investigated both the utility of pseudospectral optimization methods for robust trajectory optimization as well as the potential for demonstrating differences in aircraft agility characteristics of several …

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Uncorrelated Track Avoidance, Darrell L. Grob Mar 2008

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), …

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Initial Determination Of Low Earth Orbits Using Commercial Telescopes, Matthew M. Schmunk Mar 2008

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- …

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Determining The Capability Requirements For A Space Based Optical Sensor To Determine The Trajectory Of An Incoming Antisatellite Weapon, Mesut Gulmus Mar 2008

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 …

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Effects Of Environment On Creep Behavior Of Nextel 720/Alumina-Mullite Ceramic Composite At 1200°C, Christopher L. Genelin Mar 2008

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 ≤ …

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Direct Initiation Through Detonation Branching In A Pulsed Detonation Engine, Alexander R. Hausman Mar 2008

Direct Initiation Through Detonation Branching In A Pulsed Detonation Engine, Alexander R. Hausman

Theses and Dissertations

Pulsed Detonation Engines are currently limited in operating frequency to the order of 40 Hz due to lengthy ignition and deflagration to detonation transition (DDT) times. An experimental study is conducted to determine the requirements necessary to eliminate these constraints through the concept of direct initiation. A branched detonation crossover setup is constructed and the operational requirements are determined. This research demonstrates the ability to directly initiate a detonation in a vacant tube from a detonation obtained through detonation branching. Using a hydrogen-air mixture, a tail-to-head detonation branching is achieved in which a detonation is seen to propagate from a …

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Piv-Based Examination Of Deep Stall On An Oscillating Air Foil, Daniel E. Fredberg Mar 2008

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, …

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Contamination Study Of Micro Pulsed Plasma Thrusters, Ceylan Kesenek Mar 2008

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 …

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Extending Cfd Modeling To Near-Continuum Flows Using Enhanced Thermophysical Modeling, Abram E. Claycomb Mar 2008

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 …

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Damage Detection Analysis Using Lamb Waves In Restricted Geometry For Aerospace Applications, Roman T. Underwood Mar 2008

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 …

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Mission Results For Sapphire, A Student-Built Satellite, Michael Swartwout, Christopher Kitts, Robert J. Twiggs, Thomas Kenny, Billy Ray Smith, Rick Lu, Kevin Stattenfield, Freddy Pranajaya Mar 2008

Mission Results For Sapphire, A Student-Built Satellite, Michael Swartwout, Christopher Kitts, Robert J. Twiggs, Thomas Kenny, Billy Ray Smith, Rick Lu, Kevin Stattenfield, Freddy Pranajaya

Robert "Bob" Twiggs STEM Education Collection

A article published in the Journal of the International Academy of Astronautics titled "Mission results for Sapphire, a student-built satellite" published on March 7, 2008.

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Advanced Cathodes For Next Generation Electric Propulsion Technology, Dustin J. Warner Mar 2008

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 …

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Analysis And Optimization Of A Crashworthy Helicopter Seat, Nauman A. L Mhaskar Mar 2008

Analysis And Optimization Of A Crashworthy Helicopter Seat, Nauman A. L Mhaskar

Mechanical and Aerospace Engineering Theses - Archive

The objective of a crashworthy seat is to improve the survivability of occupants (cockpit and cabin) in helicopter crashes. All modern helicopter seats are equipped with an energy absorber to reduce lumbar spine load during crash landing. The main objective of this research is to carry out the structural analysis and optimization of a helicopter crashworthy troop seat assembly using finite element methods. The transient dynamic nonlinear finite element analysis helps in identifying whether the seat structure will survive in a crash landing situation, and optimization helps in reducing the weight of the crashworthy seat. The seat is analyzed using …

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Monotonic Convergence Of Iterative Learning Control For Uncertain Systems Using A Time-Varying Filter, Douglas A. Bristow, Andrew G. Alleyne Mar 2008

Monotonic Convergence Of Iterative Learning Control For Uncertain Systems Using A Time-Varying Filter, Douglas A. Bristow, Andrew G. Alleyne

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Iterative learning control (ILC) is a learning technique used to improve the performance of systems that execute the same task multiple times. Learning transient behavior has emerged as an important topic in the design and analysis of ILC systems. In practice, the learning control is often low-pass filtered with a ldquoQ-filterrdquo to prevent transient growth, at the cost of performance. In this note, we consider linear time-invariant, discrete-time, single-input single-output systems, and convert frequency-domain uncertainty models to a time-domain representation for analysis. We then develop robust monotonic convergence conditions, which depend directly on the choice of the Q-filter and are …

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Laser Diagnostic System Validation And Ultra-Compact Combustor Characterization, Terry B. Hankins Mar 2008

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 …

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Output Feedback Controller For Operation Of Spark Ignition Engines At Lean Conditions Using Neural Networks, Jonathan B. Vance, Brian C. Kaul, Jagannathan Sarangapani, J. A. Drallmeier Mar 2008

Output Feedback Controller For Operation Of Spark Ignition Engines At Lean Conditions Using Neural Networks, Jonathan B. Vance, Brian C. Kaul, Jagannathan Sarangapani, J. A. Drallmeier

Electrical and Computer Engineering Faculty Research & Creative Works

Spark ignition (SI) engines operating at very lean conditions demonstrate significant nonlinear behavior by exhibiting cycle-to-cycle bifurcation of heat release. Past literature suggests that operating an engine under such lean conditions can significantly reduce NO emissions by as much as 30% and improve fuel efficiency by as much as 5%-10%. At lean conditions, the heat release per engine cycle is not close to constant, as it is when these engines operate under stoichiometric conditions where the equivalence ratio is 1.0. A neural network controller employing output feedback has shown ability in simulation to reduce the nonlinear cyclic dispersion observed under …

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Velocity Estimate Following Air Data System Failure, Scott A. Mclaren Mar 2008

Velocity Estimate Following Air Data System Failure, Scott A. Mclaren

Theses and Dissertations

Modern high performance aircraft can provide amazing performance due in part to their advanced flight control systems that require gain scheduling to provide optimum performance over a huge flight envelope. In modern fighter aircraft, this gain scheduling is a function of airspeed, and almost all of the research involving aircraft gain scheduling assumes aircraft airspeed to be a known quantity. The purpose of this research was to investigate a method of determining an aircraft’s airspeed in the event of total air data system failure. The process began by combining known aircraft information following an air data system failure to determine …

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Handling Qualities Evaluation Of A Supersonic Tailless Air Vehicle, Steven W. Speares Mar 2008

Handling Qualities Evaluation Of A Supersonic Tailless Air Vehicle, Steven W. Speares

Theses and Dissertations

This thesis presents the results of a handling qualities evaluation of a supersonic tailless air vehicle. The 2006 Quadrennial Defense Review mandated the need for the next generation of long-range strike aircraft by 2018. Due to speed and stealth requirements, this resulted in a tailless aircraft with an instantaneous center of rotation located well forward of that of a conventional aircraft. This thesis examines how this center of rotation affected pilot handling qualities ratings. This effect should have been the most pronounced during approach and landing, and was where the testing focused. The goal of this research was to develop …

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Design Of An Oxygen Turbopump For A Dual Expander Cycle Rocket Engine, William S. Strain Mar 2008

Design Of An Oxygen Turbopump For A Dual Expander Cycle Rocket Engine, William S. Strain

Theses and Dissertations

The design of a pump intended for use with a dual expander cycle (LOX/H2) engine is presented. This arrangement offers a number of advantages over hydrogen expander cycles; among these are the elimination of gearboxes and inter-propellant purges and seals, an extended throttling range, and higher engine operating pressures and performance. The target engine has been designed to meet the needs of Phase III of the Integrated High Payoff Rocket Propulsion Technology (IHPRPT) program; thus, this pump must meet the program’s reliability, maintainability, and service life goals. In addition, this pump will be driven by warm gaseous oxygen. …

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Real-Time Navigation And Flight Path Generation For Tracking Stop-And-Go Targets With Miniature Air Vehicles, Nate A. Terning Mar 2008

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 …

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Space Based Satellite Tracking And Characterization Utilizing Non-Imaging Passive Sensors, Bradley R. Townsend Mar 2008

Space Based Satellite Tracking And Characterization Utilizing Non-Imaging Passive Sensors, Bradley R. Townsend

Theses and Dissertations

A technique is developed to determine the orbit of a sunlight illuminated satellite passing through the field-of-view of a sensor platform in a Highly Elliptical Orbit (HEO) and Geosynchronous orbit (GEO). The technique develops two different methods of initial orbit determination. The first relies on the Gauss initial orbit determination method to develop an estimate of the state from angular data. The second method relies on positional data of the target relative to the Earth’s background to determine an estimate of the state. These estimates are then refined in a non-linear least squares routine. This estimate of the state is …

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Development And Flight Of A Robust Optical-Inertial Navigation System Using Low-Cost Sensors, Michael B. Nielsen Mar 2008

Development And Flight Of A Robust Optical-Inertial Navigation System Using Low-Cost Sensors, Michael B. Nielsen

Theses and Dissertations

This research develops and tests a precision navigation algorithm fusing optical and inertial measurements of unknown objects at unknown locations. It provides an alternative to the Global Positioning System (GPS) as a precision navigation source, enabling passive and low-cost navigation in situations where GPS is denied/unavailable. This paper describes two new contributions. First, a rigorous study of the fundamental nature of optical/inertial navigation is accomplished by examining the observability grammian of the underlying measurement equations. This analysis yields a set of design principles guiding the development of optical/inertial navigation algorithms. The second contribution of this research is the development and …

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Space - A Place To Learn & Play: Astrobiology, Robert J. Twiggs Feb 2008

Space - A Place To Learn & Play: Astrobiology, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "Space - A Place to Learn & Play: Astrobiology" from February 19, 2008.

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Cricket Satellite Project: Hall Elementary School, Robert J. Twiggs Feb 2008

Cricket Satellite Project: Hall Elementary School, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "Cricket Satellite Project: Hall Elementary School" from February 18, 2008.

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Aerodynamic Performance Enhancement Of A Naca 66-206 Airfoil Using Supersonic Channel Airfoil Design, David Giles, David D. Marshall Jan 2008

Aerodynamic Performance Enhancement Of A Naca 66-206 Airfoil Using Supersonic Channel Airfoil Design, David Giles, David D. Marshall

Aerospace Engineering

Supersonic channel airfoil design techniques have been shown to significantly reduce drag in high-speed flows over diamond shaped airfoils by Ruffin and colleagues. The effect of applying these techniques to a NACA 66-206 airfoil is presented. The design domain entails channel heights of 8-16.6% thickness-to-chord and speeds from Mach 1.5-3.0. Numerical simulations show an increase in the lift-to-drag ratio for airfoils at Mach 2.5 at a 35,000-ft altitude with a 12% channel height geometry showing a benefit of 17.2% at 6-deg angle of attack and a sharp channel leading edge. Wave drag is significantly reduced while viscous forces are slightly …

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