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Articles 9541 - 9570 of 11199

Full-Text Articles in Aerospace Engineering

Timing Of Increasing Electron Counts From Geosynchronous Orbit To Low Earth Orbit, Kirk M. Olson Mar 2005

Timing Of Increasing Electron Counts From Geosynchronous Orbit To Low Earth Orbit, Kirk M. Olson

Theses and Dissertations

Under certain conditions, high energy electron fluxes can increase over short periods of time in the outer radiation belt and diffuse to low altitudes. Sudden increases of high energy electron densities at low altitudes can drastically damage unsuspecting low-earth-orbit satellites. The progression of electron flux increases from a geosynchronous orbit to low-earth orbit during an electron event is somewhat unknown. If the beginning of electron flux increases at low-earth-orbits could be anticipated, warnings could be issued to space system operators allowing time to take proper measures to protect and minimize satellite damage extending satellite lifetimes and space mission operations. The …

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A Systematic Method For Characterizing The Elastic Properties And Adhesion Of A Thin Polymer Membrane, Bing Feng Ju, Yang Ju, Masumi Saka, Kuo Kang Liu, Kai Tak Wan Mar 2005

A Systematic Method For Characterizing The Elastic Properties And Adhesion Of A Thin Polymer Membrane, Bing Feng Ju, Yang Ju, Masumi Saka, Kuo Kang Liu, Kai Tak Wan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The elastic properties and adhesion of a thin silicone rubber membrane have been characterized. an effective instrumentation embodying a video-enhanced microscope, which meets force and displacement resolution of 0.1μN and 10 nm, was developed. It provides the capability of simultaneously measuring both the applied force and the resultant displacement of the thin polymer membrane. a linear theoretical elastic solution was applied to quantitatively interpret the measured central deflection of the membrane under a circular concentrical load. Young's modulus of the membrane can be easily determined once the applied force and the central deflection, together with the essential dimensions, are known. …

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Numerical Analysis And Optimization Of The Ultra Compact Combustors, Roger T. Greenwood Mar 2005

Numerical Analysis And Optimization Of The Ultra Compact Combustors, Roger T. Greenwood

Theses and Dissertations

In an effort to increase thrust per weight ratio and decrease pollutant emissions of aero-turbine jet engines, a circumferentially burning Ultra Compact Combustor (UCC) with a Cavity-in-a-Cavity design has been developed. A numerical analysis of this design has been conducted and compared with experimental results. The CFD model has been validated through a wide range of conditions and four alternative physical configurations of the UCC have been modeled. Emissions, combustor efficiencies, temperature and velocity profiles, and pressure drop values were used as comparison parameters. Numerical results indicate that increasing the outflow area will increase the pressure drop over the combustor …

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Pulse Detonation Engine Thrust Tube Heat Exchanger For Flash Vaporization And Supercritical Heating Of Jp-8, Christen L. Miser Mar 2005

Pulse Detonation Engine Thrust Tube Heat Exchanger For Flash Vaporization And Supercritical Heating Of Jp-8, Christen L. Miser

Theses and Dissertations

Research has shown that performance of liquid hydrocarbon fueled pulse detonation engines is limited by the time required to evaporate liquid fuel droplets within the mixture. Vaporization of liquid fuels prior to injection has been shown to decrease ignition times and also increases fuel efficiency; however, the size and efficiency of the vaporization system used are not feasible for use in future pulse detonation aircraft concepts. The purpose of this research is to harness the waste heat of pulse detonation engine thrust tubes to generate a steady-state, self-sustained flash vaporization and supercritical heating system using JP-8 as the working fluid …

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A Redesigned Tail Rotor For Improvement Of Ch-53e High-Altitude Performance, James A. Pritchard Mar 2005

A Redesigned Tail Rotor For Improvement Of Ch-53e High-Altitude Performance, James A. Pritchard

Theses and Dissertations

The Global War on Terror with specific emphasis on the recent military operation in Afghanistan has shown the invaluable contribution that heavy lift helicopters bring to the combatant commander. However, the flight range, altitudes and lift capability required to operate effectively in such an austere environment are pushing the limits of these helicopters. In an attempt to increase the operational capability of the CH-53E, this study will investigate methods for maximizing tail rotor effectiveness at high gross weights and high altitudes. This thesis records an analytical study designed to investigate the intricacies of tail rotor design and, by the computational …

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Boundary Layer Flow Control Using Plasma Induced Velocity, Brian E. Balcer Mar 2005

Boundary Layer Flow Control Using Plasma Induced Velocity, Brian E. Balcer

Theses and Dissertations

An examination of the effects of plasma induced velocity on boundary layer flow was conducted. A pair of thin copper film electrodes spanned the test section, oriented at thirty degrees from normal to the free stream flow. An adverse pressure gradient was imposed over the electrode configuration using a pressure coefficient profile similar to that associated with suction side of a Pac-B low pressure turbine blade. In addition, suction was applied to keep flow attached on the upper wall, inducing separation over the electrode. The electrode is supplied by an AC source at three different power levels with the free …

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Characterization Of Upstream Mixing Cavities And A Downstream Combustion Cavity In Supersonic Flow, Adam P. Quick Mar 2005

Characterization Of Upstream Mixing Cavities And A Downstream Combustion Cavity In Supersonic Flow, Adam P. Quick

Theses and Dissertations

A key area of study in air-breathing hydrocarbon-fueled scramjet combustors is the characterization of cavity-based fuel injection and flame holding. One issue concerns oscillatory disturbances caused by trapped vortices in the main flame holder cavity as a fuel-air mixing enhancement technique. Previous research demonstrates that oscillatory disturbances can be carried downstream via the shear layer and alter the oscillatory characteristics of a downstream cavity. This study investigates the mixing effectiveness of three upstream direct-fueled mixing cavities as well as the effect on the oscillatory behavior of the downstream combustion cavity by the upstream mixing cavity. The three upstream mixing cavities …

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Weight Analysis Of Two-Stage-To-Orbit Reusable Launch Vehicles For Military Applications, Richard A. Caldwell Mar 2005

Weight Analysis Of Two-Stage-To-Orbit Reusable Launch Vehicles For Military Applications, Richard A. Caldwell

Theses and Dissertations

In response to Department of Defense (DoD) requirements for responsive and low-cost space access, this design study provides an objective empty weight analysis of potential reusable launch vehicle (RLV) configurations. Each two-stage-to-orbit (TSTO) RLV has a fixed payload requirement of 20,000 lbf to low Earth orbit. The propulsion systems considered in this study include pure rocket, pure turbine, rocket-based-combined-cycle (RBCC), and turbine-based-combined-cycle (TBCC). The hydrocarbon dual-mode scramjet (DMSJ) engines used in the RBCC and TBCC propulsion systems represent possible applications of the current research being performed in the U.S. Air Force HyTech program. Two sensitivity analyses were then performed on …

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Experimental Study Of The Subsonic Aerodynamics Of A Blended Wing Body Air Vehicle With A Focus On Rapid Technology Assessment, David A. Gebbie Mar 2005

Experimental Study Of The Subsonic Aerodynamics Of A Blended Wing Body Air Vehicle With A Focus On Rapid Technology Assessment, David A. Gebbie

Theses and Dissertations

The subsonic aerodynamic performance of a blended wing body aircraft constructed using selective laser sintering was assessed in the AFIT low-speed wind tunnel. The scaled-down model of a strike tanker aircraft consisted of a shaped fuselage and sweptback wings. The Reynolds number, based on mean wing chord, during testing was on the order of 105 while the Mach number ranged from 0.10 to 0.20. The model evaluation and analysis process included force and moment measurements acquired from a wind tunnel balance, pressure data measured with 8 taps located on the model’s upper surface, a comparison to computational fluid dynamics (CFD) …

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A Study In Drag Reduction Of Close Formation Flight Accounting For Flight Control Trim Positions And Dissimilar Formations, Michael T. Morgan Mar 2005

A Study In Drag Reduction Of Close Formation Flight Accounting For Flight Control Trim Positions And Dissimilar Formations, Michael T. Morgan

Theses and Dissertations

This thesis further defines the position of greatest fuel savings benefit for the trail aircraft flying in a two-ship formation. The HASC95 vortex lattice code was used for the examination. Investigations of a similar formation of F-16 aircraft and a dissimilar formation of a lead KC-135 aircraft and a trail F-16 aircraft were conducted. The analyses determined the effects of varying airspeed on the optimal position. In addition, flight control surface deflections were taken into account during the analyses. Both investigations trimmed the aircraft in the yaw and roll axes to determine the optimal savings. The similar analysis was conducted …

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Mixing Effects Of Pylon-Aided Fuel Injection Located Upstream Of A Flameholding Cavity In Supersonic Flow, Daniel R. Montes Mar 2005

Mixing Effects Of Pylon-Aided Fuel Injection Located Upstream Of A Flameholding Cavity In Supersonic Flow, Daniel R. Montes

Theses and Dissertations

The Air Force Research Lab (AFRL), Propulsion Directorate, Wright-Patterson Air Force Base, Ohio is conducting ongoing research into propulsive efficiency in supersonic ramjet (scramjet) technology. One current focus of this research is the usefulness of flameholding cavities implemented in the supersonic hydrocarbon-fueled combustion chamber. Because good mixing and proper cavity-core interaction lead to more efficient combustion, methods of optimizing fuel/air mixing both within and upstream the cavity are investigated. In a cooperative effort with the Air Force Institute of Technology (AFIT), AFRL provided a supersonic wind tunnel outfitted with an existing cavity design. A circular injection port was placed upstream …

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Structures Of Angled Aerated-Liquid Jets In March 1.94 Supersonic Cross Flow, Dion R. Dixon Mar 2005

Structures Of Angled Aerated-Liquid Jets In March 1.94 Supersonic Cross Flow, Dion R. Dixon

Theses and Dissertations

The structures of aerated-liquid jets injected into a supersonic crossflow have been studied experimentally. Aerated-liquid injectors with diameters of 0.020", 0.040" and 0.060" were flush mounted on the bottom plate of a supersonic wind tunnel to provide normal and angled injection. Free stream Mach number and temperature were held constant at 1.94 and 500°F, respectively. Water at room temperature was used as the liquid injectant and nitrogen gas used as the aerating gas. Wide ranges of test conditions for injection angle (θ), injector orifice diameter (d0), jet-to-air momentum flux ratios (q0), and gas-to-liquid ratios (GLR), were …

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Full Capability Formation Flight Control, Ryan K. Osteroos Mar 2005

Full Capability Formation Flight Control, Ryan K. Osteroos

Theses and Dissertations

The subject of automatic formation flight control is of current interest to the development of Unmanned Aerial Vehicles (UAV). Previous control approaches have been refined in this work to allow more robust maneuvering and to include a fourth control parameter. The equations of motion for each aircraft as a point mass, expressed in a wind-axis coordinate system, are coupled into differential equations that model the two aircraft system dynamics. Control laws are developed that include proportional and integral action. Gains are determined based on formation performance. Lead maneuvers are simulated and the controller is gauged on its ability to maintain …

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Parachute Extraction Of A Generic Store From A C-130; A Cfd Proof Of Concept, Stephen C. Platt Mar 2005

Parachute Extraction Of A Generic Store From A C-130; A Cfd Proof Of Concept, Stephen C. Platt

Theses and Dissertations

This thesis encompasses a feasibility analysis of a parachute extracted generic precision guided munition from the cargo bay of a C-130 aircraft in flight. This analysis utilizes the USAF Beggar code and incorporates full physics effects as well as aerodynamic loading assuming an inviscid aircraft and viscous store for a time-accurate solution. Both an immediate and time varying application of the parachute force are utilized as well as two different ordnance body styles at zero and 5 degrees AOA with the store placed on centerline and offset in the cargo bay. The time accurate parachute model is based on empirical …

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Entropy Generation As A Means Of Examining Continuum Breakdown, Christopher R. Schrock Mar 2005

Entropy Generation As A Means Of Examining Continuum Breakdown, Christopher R. Schrock

Theses and Dissertations

To quantify the validity and breakdown of the continuum equations of fluid flow, the concept of entropy generation is examined. This parameter is formulated utilizing statistical mechanics and kinetic theory to avoid the use of equilibrium assumptions. This analysis leads to expressions in terms of energy distribution functions. These results are applied to monatomic and diatomic molecules. A numerical procedure for computing these values using the Direct Simulation Monte Carlo Method (DSMC) is presented. Normal shock waves in argon and nitrogen were simulated at Mach numbers ranging from 1.2 to 10. Results are compared to Navier-Stokes predictions. The Navier-Stokes equations …

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Evaluation Techniques For Determining Damping Mechanisms On Titanium Plates, Kyle S. Allen Mar 2005

Evaluation Techniques For Determining Damping Mechanisms On Titanium Plates, Kyle S. Allen

Theses and Dissertations

High cycle fatigue (HCF) is the single largest cause of component failure for all modern military gas turbine engines. Hard coatings, such as magnesium aluminate spinel, have been found to provide significant damping properties. Past studies have had difficulties isolating the contributions of these hard coating damping layers from other damping mechanisms. This study explored techniques for assessing the contribution of different damping mechanisms on titanium plates during vibration testing. The study investigated 2nd bend and 2-stripe modes. Two different specimen sizes were tested in both a clamped-free-free-free and free-free-free-free condition. Specimens were tested at varying pressures. Increases in pressure …

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Maneuver Estimation Model For Relative Orbit Determination, Tara R. Storch Mar 2005

Maneuver Estimation Model For Relative Orbit Determination, Tara R. Storch

Theses and Dissertations

While the use of relative orbit determination has reduced the difficulties inherent in tracking geosynchronous satellites that are in close proximity, the problem is often compounded by stationkeeping operations or unexpected maneuvers. If a maneuver occurs, observations will no longer fit predicted data, increasing the risk of misidentification and cross-tagging. The goal of this research was to develop a model that will estimate the magnitude, direction, and time of a suspected maneuver performed by a collocated satellite in geosynchronous orbit. Relative motion was modelled using Hill's equations, and least squares estimation was employed to create both a linear non-maneuver model …

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Performance Study Of Staging Variable On Two-Stage-To-Orbit Reusable Launch Vehicles, James K. Nilsen Mar 2005

Performance Study Of Staging Variable On Two-Stage-To-Orbit Reusable Launch Vehicles, James K. Nilsen

Theses and Dissertations

The purpose of this research is to investigate the effects of staging variables on Two-Stage-To-Orbit reusable launch vehicles, specifically, the question of what measurable factors play important roles in staging performance. Three different configurations (Rocket-Rocket, Turbojet-Rocket and Turbine Based Combined Cycle-Rocket) were considered. The software, Program to Optimize Simulated Trajectories (POST), was used to analyze these configurations. Vehicle coasting time, staging dynamic pressure and staging Mach number were all varied to determine their influence on the final payload.

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Technical Feasibility Of Loitering Lighter-Than-Air-Near-Space Maneuvering Vehicles, Eric R. Moomey Mar 2005

Technical Feasibility Of Loitering Lighter-Than-Air-Near-Space Maneuvering Vehicles, Eric R. Moomey

Theses and Dissertations

The near-space region of earth's atmosphere above 20 kilometers altitude is greatly underutilized. Lighter-than-air maneuvering vehicles, or airships, using the principle of buoyancy can take advantage of this region to become potential platforms for precision navigation, environmental monitoring, communication relays, missile warning, surveillance, and weapon delivery. These vehicles purportedly provide persistent coverage over large areas of the earth's surface at substantially lower costs than orbiting satellites. This study investigated the technical requirements to loiter an operational payload within this high altitude region using a lighter-than-air maneuvering platform. A parametric analysis was conducted to identify the critical technologies needed to achieve …

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Modeling And Simulation Of Commercial Satellite Imagery Processes, David A. Shultz Mar 2005

Modeling And Simulation Of Commercial Satellite Imagery Processes, David A. Shultz

Theses and Dissertations

The purpose of this research was to develop a general, statistical model of order-to-delivery times for commercial satellite imagery. The research looked at the current four satellite providers with 3-meter or better imagers in the context of a generalized model of commercial imaging satellite operations. Existing methods use orbit analysis tools to determine the imaging time of a specified target based on defined satellite position and times, but can only develop shortest and longest times to an imaging opportunity. To address the general question of the time it takes to deliver an image for non-specific targets, this research develops a …

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Investigation Of Aerobraking To Return The Space Maneuver Vehicle To Low Earth Orbit From Geotransfer Orbit, Benjamin M. Berlin Mar 2005

Investigation Of Aerobraking To Return The Space Maneuver Vehicle To Low Earth Orbit From Geotransfer Orbit, Benjamin M. Berlin

Theses and Dissertations

This study investigated the use of ballistic and Double-Dip'' aerobraking reentry to return the Space Maneuver Vehicle (SMV) from geotransfer orbit in no more than two atmosphere passes. Lift and drag accelerations were applied to the two-body problem when either of their magnitudes exceeded 1/1000 g. Lift and drag coefficients, along with the SMV model, were taken from Investigation of Atmospheric Reentry for the Space Maneuver Vehicle by Captain McNabb, AFIT/GA/ENY/04-M03. Target perigees were formulated using the two-body problem. The orbit from each target perigee was numerically integrated around a planar earth model using a fourth order Runge-Kutta method. Ballistic …

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Stochastic Capability Models For Degrading Satellite Constellations, Cole W. Gulyas Mar 2005

Stochastic Capability Models For Degrading Satellite Constellations, Cole W. Gulyas

Theses and Dissertations

This thesis proposes and analyzes a new measure of functional capability for satellite constellations that incorporates the instantaneous availability and mission effectiveness of individual satellites. The capability measure yields a continuous score between zero and one accounting for the degree to which the constellation meets operational requirements. The measure is computed from an average of satellite capabilities, composed of the product of the satellite's instantaneous availability and value score. Instantaneous availability is acquired by modeling the satellite degradation status as either a time-homogenous, continuous-time Markov chain (CTMC) if it possesses functions with exponential lifetime distributions, or as a time-homogenous, semi-Markov …

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Katysat: Kids Aren’T Too Young For Satellites, Robert J. Twiggs, Ben Yuan Feb 2005

Katysat: Kids Aren’T Too Young For Satellites, Robert J. Twiggs, Ben Yuan

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs and Bob Yuan titled "Katysat: Kids Aren’t Too Young for Satellites" from February 8, 2005.

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Modelling And Validation Of A Propellant Mixer For Controller Design, Hanz Richter, Enrique Barbieri, Fernando Figueroa Nasa Stennis Space Center Feb 2005

Modelling And Validation Of A Propellant Mixer For Controller Design, Hanz Richter, Enrique Barbieri, Fernando Figueroa Nasa Stennis Space Center

Mechanical Engineering Faculty Publications

A mixing chamber used in rocket engine testing at the NASA Stennis Space Center is modelled by a system of two nonlinear ordinary differential equations. The mixer is used to condition the thermodynamic properties of cryogenic liquid propellant by controlled injection of the same substance in the gaseous phase. The three inputs of the mixer are the positions of the valves regulating the liquid and gas flows at the inlets, and the position of the exit valve regulating the flow of conditioned propellant. Mixer operation during a test requires the regulation of its internal pressure, exit mass flow, and exit …

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Experimental Verification Of The Aerodynamics Of Stream Thrust Probes, Robert S. Hiers Iii, James R. Sirbaugh, Capt Barrett T. Mccann, Russell M. Cummings, Cadet Laura S. Luft, Cadet Dimitrios P. Grillos Jan 2005

Experimental Verification Of The Aerodynamics Of Stream Thrust Probes, Robert S. Hiers Iii, James R. Sirbaugh, Capt Barrett T. Mccann, Russell M. Cummings, Cadet Laura S. Luft, Cadet Dimitrios P. Grillos

Aerospace Engineering

Determining the local stream thrust (a vector quantity) from a measured pitot pressure (a scalar quantity) requires either knowledge of the flow direction or a probe shape that compensates for flow direction. This compensation ideally would make the measured pressure directly proportional to the component of momentum along the probe axis. The flow angle sensitivity required to resolve this component of momentum was previously determined theoretically. A proposed probe nose shape was analyzed using computational fluid dynamics (CFD) and was found to produce a flow angle sensitivity close to the required sensitivity. In the current work, the proposed nose shape …

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Computational Aerodynamics Goes To School: A Course In Cfd For Undergraduate Students, Russell M. Cummings, Scott A. Morton Jan 2005

Computational Aerodynamics Goes To School: A Course In Cfd For Undergraduate Students, Russell M. Cummings, Scott A. Morton

Aerospace Engineering

As aerodynamics education has evolved over the past decades, a slow transition from important analytic methods to increasingly powerful computational methods has taken place. While a basic understanding of theoretical aerodynamics should always be included in coursework, the realities of modern design practices make the usefulness of the traditional approach less and less practical. A new undergraduate course in computational aerodynamics has been developed that attempts to give students experience with the modern computational tools of aerodynamics, primarily from an applications perspective. While introducing students to the important computational topics of accuracy and stability, the course stresses the practical tools …

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Des Turbulence Modeling On The C-130 Comparison Between Computational And Experimental Results, Malcom P. Claus, Scott A. Morton, Russell M. Cummings, Yannick Bury Jan 2005

Des Turbulence Modeling On The C-130 Comparison Between Computational And Experimental Results, Malcom P. Claus, Scott A. Morton, Russell M. Cummings, Yannick Bury

Aerospace Engineering

This paper represents the results from the initial phase of a research program to determine the flow characteristics of the C-130 Hercules transport aircraft. The initial phase of the program consists of evaluation and comparison of the flow-field obtained from flow visualization methods. Specifically CFD (Computational Fluid Dynamics) results are compared with experimental Hot Wire results produced by wind tunnel tests on the C-130 in clean configuration. This paper outlines the results to date and provides a description of further work. The CFD element of this research features the use of Detached Eddy Simulation (DES) in order to extend its …

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Deformation Of Unstructured Viscous Grids, Denis B. Kholodar, Scott A. Morton, Russell M. Cummings Jan 2005

Deformation Of Unstructured Viscous Grids, Denis B. Kholodar, Scott A. Morton, Russell M. Cummings

Aerospace Engineering

A mesh deformation algorithm for unstructured grids is presented. It is designed for high Reynolds number flow problems. Such grids are employed in aerodynamic and aeroelastic studies of wings or complete aircraft configurations in flows where the viscous effects are important. Given a surface deformation, the method efficiently recalculates new locations of high aspect ratio cells that make up the viscous layers of the grid and then deforms the inviscid part of the grid using an established method based on a torsional spring analogy technique. Results are presented for monitoring the deterioration of the quality of the grid during subsequent …

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Robust Control Techniques For State Tracking In The Presence Of Variable Time Delays, Jarrett Goodell, Marc Compere, Miguel Simon, Wilford Smith, Ronnie Wright, Mark Brudnak Jan 2005

Robust Control Techniques For State Tracking In The Presence Of Variable Time Delays, Jarrett Goodell, Marc Compere, Miguel Simon, Wilford Smith, Ronnie Wright, Mark Brudnak

Publications

In this paper, a distributed driver-in-the-Ioop and hardware-in-the-Ioop simulator is described with a driver on a motion simulator at the U.S. Army TARDEC Ground Vehicle Simulation Laboratory (GVSL). Realistic power system response is achieved by linking the driver in the GVSL with a full-sized hybrid electric power system located 2,450 miles away at the TARDEC Power and Energy Systems Integration Laboratory (P&E SIL), which is developed and maintained by Science Applications International Corporation (SAIC). The goal is to close the loop between the GVSL and P&E SIL over the Internet to provide a realistic driving experience in addition to realistic …

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Engineering Tools For Variable Stiffness Vibration Suppression And Isolation, Michael F. Winthrop Jan 2005

Engineering Tools For Variable Stiffness Vibration Suppression And Isolation, Michael F. Winthrop

Theses and Dissertations

With the advent of smart materials, the concept of semi-active control or dynamic control of stiffness and/or damping for vibration control of structures has become practical and has seen limited use. Semi-active control has advantages over active and passive control methods, since it provides almost as much capability as active control while requiring much less power. Its main disadvantage is its inherent nonlinearity, greatly complicating engineering design. The purpose of this research is to extend semi-active control vibration isolation tools and methods considering space launch and on-orbit systems.

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