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Articles 10051 - 10080 of 11196

Full-Text Articles in Aerospace Engineering

Computational Fluid Dynamics Testing For Drag Reduction Of An Aircraft Laser Turret, Gregory J. Schwabacher Mar 2000

Computational Fluid Dynamics Testing For Drag Reduction Of An Aircraft Laser Turret, Gregory J. Schwabacher

Theses and Dissertations

A computational study was conducted on the use of aft-mounted fairings for passive drag reduction on a sphere at Re=866,000. The sphere dimensions and operating Reynolds number were selected to approximate the flow around a proposed aircraft laser turret for which experimental data was available. To establish the validity of the computational model, flow predictions were compared to sphere data available in the open literature. The model, exercised in both the laminar and turbulent modes, showed good agreement with the published data. Two proposed laser turret fairings were then evaluated computationally: a large fairing (beginning at 49.5 degrees past the …

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Mission Route Planning With Multiple Aircraft & Targets Using Parallel A* Algorithm, Ergin Sezer Mar 2000

Mission Route Planning With Multiple Aircraft & Targets Using Parallel A* Algorithm, Ergin Sezer

Theses and Dissertations

The general Mission Route Planning (MRP) Problem is the process of selecting an aircraft flight path in order to fly from a starting point through defended terrain to target(s), and return to a safe destination. MRP is a three-dimensional, multi-criteria path search. Planning of aircraft routes involves an elaborate search through numerous possibilities, which can severely task the resources of the system being used to compute the routes. Operational systems can take up to a day to arrive at a solution due to the combinatorial nature of the problem, which is not acceptable, because time is critical in aviation. Also, …

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Improving Uav Handling Qualities Using Time Delay Compensation, Andrew J. Thurling Mar 2000

Improving Uav Handling Qualities Using Time Delay Compensation, Andrew J. Thurling

Theses and Dissertations

This research investigated control loop time delay and its effect on UAV handling qualities. Compensation techniques to improve handling qualities in the presence of varying amounts of time delay were developed and analyzed. One technique was selected and successfully flight-tested on a UAV. Flight-testing occurred at a constant flight condition with varying levels of additional time delay introduced into the control loop. Research pilots performed a pitch tracking task and gave Cooper-Harper ratings and comments. Tracking errors were used as a quantitative measure of Pilot/Display/UAV system performance. Predictive pitch compensation was found to significantly reduce pilot workload and improve Cooper-Harper …

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Integrating Automated Multi-Disciplinary Optimization In Preliminary Design Of Non-Traditional Aircraft, Mehmet Fidanci, Jeffrey R. Miller, Douglas J. Strauss Mar 2000

Integrating Automated Multi-Disciplinary Optimization In Preliminary Design Of Non-Traditional Aircraft, Mehmet Fidanci, Jeffrey R. Miller, Douglas J. Strauss

Theses and Dissertations

Current methods of aircraft conceptual design lack the ability to quickly generate detailed analysis, particularly of nontraditional designs such as blended wing body craft. This study developed a method to resolve this problem by creating a flexible, parametrically driven conceptual model in an object-oriented, adaptive modeling environment from which analysis and optimization may rapidly be performed. These object-oriented techniques are incorporated into a traditional conceptual design process. All objects inherit dependency-tracking and demand-driven calculations. Design Analysis was performed within the modeling language and utilized interfaces to other software packages. A detailed mesh, suitable for input into finite element analysis programs, …

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A Comparative Analysis Of Cockpit Display Development Tools, Matthew J. Gebhardt Mar 2000

A Comparative Analysis Of Cockpit Display Development Tools, Matthew J. Gebhardt

Theses and Dissertations

Currently, no standard methodology exists that enables cockpit display engineers to evaluate software tools used in the development of graphical cockpit displays. Furthermore, little research has been accomplished in comparing current software development tools with traditional hand-coded methods, This research effort discusses a framework for analyzing cockpit display software development tools and follows through with a detailed analysis comparing today's hand-coding standard, OpenGL, with two of today's cockpit display software development suites, Virtual Application Prototyping System (VAPS) and Display Editor. The comparison exploits the analysis framework establishing the advantages and disadvantages of the three software development suites. The analysis framework …

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Optical Metrology Of Adaptive Membrane Mirrors, John W. Wagner Mar 2000

Optical Metrology Of Adaptive Membrane Mirrors, John W. Wagner

Theses and Dissertations

Current space-based imaging platforms are significantly constrained in both size and weight by the launch vehicle. Increased payload size and weight results in increased cost and a decrease in launch responsiveness. The USAF Scientific Advisory Board (SAB) identified "Large lightweight structures for optics and antennas" as a revolutionary primary technology to be developed for the Air Force of the 21st Century. A membrane primary mirror in a space-based imaging system has the ability to overcome current payload constraints and meet evolutionary needs of the future. The challenge of membrane optics in space is the process of implementing adaptive optics technology …

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Active And Adaptive Control For Payload Launch Vibration Isolation, Julian R. Jarosh Mar 2000

Active And Adaptive Control For Payload Launch Vibration Isolation, Julian R. Jarosh

Theses and Dissertations

The Department of Defense has identified launch vibration isolation as a major research interest. Reducing the loads a satellite experiences during launch will greatly enhance its reliability and lifetime, and reduce payload structural mass. DoD space programs stand to benefit significantly from advances in vibration isolation technology. This study explores potential hybrid vibration isolation using active and adaptive control with a passive vibration isolator. The active control methods are Proportional-Integral-Derivative (PID) control and a skyhook damper. Lyapunov analysis is used to develop the structural adaptive control scheme. Simulink and Matlab simulations investigate these control methodologies on a lumped mass dynamic …

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Modeling Piezoceramic Twist Actuation In Single-Cell Anisotropic Torque Box Of Low-Observable Uav Wing, Peter Cseke Jr. Mar 2000

Modeling Piezoceramic Twist Actuation In Single-Cell Anisotropic Torque Box Of Low-Observable Uav Wing, Peter Cseke Jr.

Theses and Dissertations

The reduction of an aircraft's radar cross section can increase its survivability in hostile airspace by making it more difficult to locate and track by enemy radar. Replacing articulated flight control surfaces with adaptive controls will reduce surface discontinuities, and enhance low observability. Actuation of the aerodynamic surfaces is achieved by an electric field applied to PZT actuators embedded in the top and bottom skins, creating differential strain and shear in the host substrate. This creates torsion about the elastic axis, and a change in the wing lift coefficient. The torsion of the designed baseline UAV's wing torquebox was modeled …

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Damage Identification In A Real Structure Using Resonant And Anti-Resonant Frequencies, Douglas E. Gaeta Mar 2000

Damage Identification In A Real Structure Using Resonant And Anti-Resonant Frequencies, Douglas E. Gaeta

Theses and Dissertations

There exists a need to remotely monitor the structural integrity of large space structures without costly manned missions. This work focused on further damage detection characterization of the Air Force Institute of Technology's Flexible Truss Experiment (FTE). The FTE is intended to be representative of a large space structure. Several damage detection algorithms were developed and tested for the FTE using 112 different damage conditions and the one undamaged condition. The algorithms were trained using two frequency response functions (FRFs) from each damage case and then tested using the same two FRFs, but from newly acquired data. A data reduction …

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Attitude Control And Multimedia Representation Of Air Force Institute Of Technology’S (Afit’S) Simulation Satellite (Simsat), Joseph M. Fulton Mar 2000

Attitude Control And Multimedia Representation Of Air Force Institute Of Technology’S (Afit’S) Simulation Satellite (Simsat), Joseph M. Fulton

Theses and Dissertations

This document describes the systematic construction of the AFIT-sponsored program to develop a laboratory-based satellite simulator. The simulation satellite (SIMSAT) system will provide a useful tool for resident staff while teaching attitude control concepts. A brief overview of attitude control theory is provided as well as a discussion of the benefits of multimedia use in education. A detailed discussion of the satellite's components allows the reader to become familiar with each piece of SIMSAT. Software control models are provided as well as a multimedia lesson plan on satellite attitude control. Also included in this document are potential experimental uses in …

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Three Dimensional Formation Flight Control, James K. Hall Mar 2000

Three Dimensional Formation Flight Control, James K. Hall

Theses and Dissertations

Automating the control of an aircraft flying in formation necessitates the extension of the theory of formation flight control to allow for three dimensional maneuvers. The formation was modeled as a two-aircraft, leader and wingspan, formation. Both aircraft has its own three dimensional, rotating and translating, Cartesian axes system, with special attention being given to the motion of the leader in relation to the wingspan. The controller operated using the equations of motion expressed in the rotating reference frame of the wing aircraft. The control system has seven states, three inputs and three disturbance signals to model the dynamics of …

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Measurements Of The Effects Of Tunnel Wall Proximity On The Velocity Field Upstream Of A Rod With Vortex Shedding In Low-Speed Flow, David R. Hopper Mar 2000

Measurements Of The Effects Of Tunnel Wall Proximity On The Velocity Field Upstream Of A Rod With Vortex Shedding In Low-Speed Flow, David R. Hopper

Theses and Dissertations

High cycle fatigue is an important consideration in blade design for turbomachinery. Blades in an engine undergo countless loading cycles in a lifetime, the result of pressure waves that propagate upstream and downstream from disturbances in the flow. Better understanding of these effects would allow blade designers to reduce the effects of high cycle fatigue, such as costly recurring maintenance or catastrophic engine failure. An experimental study was undertaken to determine the unsteady flow field upstream of a single cylinder in a subsonic flow. Von Karman vortex shedding from the cylinder produced a forcing function much like periodic blade passage …

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Space Range Scheduling And The Lean Aerospace Initiative (Lai), Alan M. Matuszak Mar 2000

Space Range Scheduling And The Lean Aerospace Initiative (Lai), Alan M. Matuszak

Theses and Dissertations

This study describes how lean principles and thinking can be applied to space range operations. The "lean" concepts of the right thing, right place, and the right time are applicable and relevant to this study. The basis for the lean concepts and principles considered is the Lean Aerospace Initiative (LAI). The LAI originated from the International Motor Vehicle Program (IMVP) that was conducted by a team from the Massachusetts Institute of Technology (MIT). The LAI is a collaborative research program involving government, industry, labor, and academia (primarily MIT). The partnership began in 1993 through support of the U.S. Air Force …

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Investigation Into The Adaptation Of A Steam Injector For Use On A Liquid Rocket Engine, Charles B. Mcfarland Mar 2000

Investigation Into The Adaptation Of A Steam Injector For Use On A Liquid Rocket Engine, Charles B. Mcfarland

Theses and Dissertations

This thesis investigated the properties of a steam injector to see if the concept might be suitable for use on a liquid rocket engine. A steam injector is a device developed in the 1850's to inject feedwater into the boiler on a steam locomotive without any moving parts. The injectors uses a small portion of the steam generated in the boiler to increase the pressure of the feedwater to a level high than the pressure in the boiler. Previous experiments claim that condensation of steam to water was necessary for an injector to work. This experiment tested injection without condensation …

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Dynamic Route Replanning And Retasking Of Unmanned Aerial Reconnaissance Vehicles, David E. Pritchard Mar 2000

Dynamic Route Replanning And Retasking Of Unmanned Aerial Reconnaissance Vehicles, David E. Pritchard

Theses and Dissertations

Many common operational situations in High Altitude Endurance (HAE) UAV reconnaissance necessitate more direct human involvement in the aircraft control process than is currently acknowledged or allowed. The In-Flight Replanning System (IFRS) is developed as a notional solution, with the Global Hawk HAE UAV as the reconnaissance system model. Problematic scenarios for current in-flight mission replanning systems are presented and revisited with the IFRS, demonstrating improved replanning results.

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Monotonic And Fatigue Loading Behavior Of An Oxide/Oxide Ceramic Matrix Composite, Steven G. Steel Mar 2000

Monotonic And Fatigue Loading Behavior Of An Oxide/Oxide Ceramic Matrix Composite, Steven G. Steel

Theses and Dissertations

This thesis evaluates an oxide/oxide ceramic matrix composite, N720/A, for high temperature aerospace applications. The composite consists of a porous alumina matrix reinforced by ten plies of Nextel 720 fibers in a balanced 8 harness satin weave. Monotonic tensile and fatigue tests were performed at room temperature and 1200 °C. The effect of moisture on 1200 °C fatigue life was also examined. Modulus, maximum and minimum strain, and stress-strain hysteresis were monitored to characterized fatigue damage. Retained strength of all specimens that survived 100000 fatigue cycles was tested. Microscopy and fractography were used to examine damage and fracture surfaces. N720/A …

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Simulations Of Flowing Supercritical N-Decane, Jeffery T. Thornburg Mar 2000

Simulations Of Flowing Supercritical N-Decane, Jeffery T. Thornburg

Theses and Dissertations

The Air Force is interested in the research of supercritical jet and rocket fuels, as well as the effects of thermally induced fuel degradation. As future flight vehicles travel at ever increasing Mach numbers, greater heat loads will be imposed upon the fuel. The primary purpose of this study is to develop a computational model for predicting fuel decomposition and bulk fuel temperatures in a stimulated heated flow reactor. The System for Thermal Diagnostic Studies (STDS), located in the Air Force Research Laboratory's Fuels Branch, is used to analyze fuels under supercritical temperatures and pressures. Computational simulations of the STDS …

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Sharp: Sharp Hypersonic Aerothermal Research Probe, Sean Dougherty Feb 2000

Sharp: Sharp Hypersonic Aerothermal Research Probe, Sean Dougherty

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Sean Dougherty titled "SHARP: Sharp Hypersonic Aerothermal Research Probe" from February 25, 2000.

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Sapphire: Stanford's First Amateur Satellite, Robert J. Twiggs, Michael Swartwout Feb 2000

Sapphire: Stanford's First Amateur Satellite, Robert J. Twiggs, Michael Swartwout

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs and Michael Swartwout titled "SAPPHIRE: Stanford's First Amateur Satellite" from February 16, 2000.

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High-Temperature Characteristics Of 1.3 Μm Ingaasn:Sb/Gaas Multiple-Quantum-Well Lasers Grown By Molecular-Beam Epitaxy, Xiaodong Yang, J. B. Heroux, M. J. Jurkovic, W. I. Wang Feb 2000

High-Temperature Characteristics Of 1.3 Μm Ingaasn:Sb/Gaas Multiple-Quantum-Well Lasers Grown By Molecular-Beam Epitaxy, Xiaodong Yang, J. B. Heroux, M. J. Jurkovic, W. I. Wang

Mechanical and Aerospace Engineering Faculty Research & Creative Works

1.3 μm InGaAsN:Sb/GaAs multiple-quantum-well laser diodes have been grown by solid-source molecular-beam epitaxy using Sb as a surfactant. A low threshold of 1.1 kA/cm² was achieved for broad-area laser diodes under pulsed operation at room temperature. High-temperature device characterization revealed characteristic temperatures (T₀) of 92 and 54 K for operating temperatures below and above 75°C, respectively, as well as a lasing-wavelength temperature dependence of 0.36 nm/°C.

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Kennedy Middle School - Arliss - 1999, Robert J. Twiggs Feb 2000

Kennedy Middle School - Arliss - 1999, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint presentation created by Professor Bob Twiggs titled "Kennedy Middle School - ARLISS - 1999" from February 11, 2000.

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Orion/Emerald Formation Flying Experiments, Brian Engberg, Jonathon How Jan 2000

Orion/Emerald Formation Flying Experiments, Brian Engberg, Jonathon How

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Brian Engberg and Jonathon How titled "Orion/Emerald Formation Flying Experiments" from January 7, 2000.

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Safety, Integration, And Test, Robert J. Twiggs Jan 2000

Safety, Integration, And Test, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "Safety, Integration, and Test" from January 6, 2000.

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Emerald System, Robert J. Twiggs Jan 2000

Emerald System, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs on the "Emerald System" from January 6, 2000.

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Emerald Nanosatellite, Freddy Pranajaya, Scott Crumine, Julie Townsend, Esther Dutton Jan 2000

Emerald Nanosatellite, Freddy Pranajaya, Scott Crumine, Julie Townsend, Esther Dutton

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Freddy Pranajaya, Scott Crumine, Julie Townsend, and Esther Dutton on the "Emerald Nanosatellite" project from January 6, 2000.

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Project Based Learning, Robert J. Twiggs Jan 2000

Project Based Learning, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "Project Based Learning" from 2000.

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Midcourse Guidance Law With Neural Networks, Dongchen Han, S. N. Balakrishnan Jan 2000

Midcourse Guidance Law With Neural Networks, Dongchen Han, S. N. Balakrishnan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A neural network-based synthesis of an optimal midcourse guidance law is presented in this study. We use a set of two-neural networks; the first network called 'a critic' outputs the Lagrange's multipliers arising in an optimal control formulation and second network called 'an action network' outputs the optimal guidance/control. In this so-called 'adaptive critic' approach, the inputs to the networks are the current values of the states. This approach needs no external training. System equations, optimality conditions and the costate equations are used in conjunction with the network outputs to provide the targets for the neural networks. When the critic …

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A Heuristic Method For Identifying Modules For Product Architectures, Robert B. Stone, Kristin L. Wood, Richard H. Crawford Jan 2000

A Heuristic Method For Identifying Modules For Product Architectures, Robert B. Stone, Kristin L. Wood, Richard H. Crawford

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Developing product architectures is a key phase in design and development processes. It encompasses the transformation of product function to alternative product layouts. In this paper, we describe a new approach for identifying modules for product architectures. We begin by reviewing the terminology and motivation for modular products. The new concepts of a functional basis and time ordered function chains are used to formally derive functional models of products. Then, three heuristic methods for identifying modules from functional models are presented. Using the formal functional decomposition and heuristic methods, modular design can be executed earlier in the product development process, …

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Development Of A Functional Basis For Design, Robert B. Stone, Kristin L. Wood Jan 2000

Development Of A Functional Basis For Design, Robert B. Stone, Kristin L. Wood

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Functional models represent a form independent blueprint of a product. As with any blueprint or schematic, a consistent language or coding system is required to ensure others can read it. This paper introduces such a design language, called a functional basis, where product function is characterized in a verb-object (function-flow) format. The set of functions and flows is intended to comprehensively describe the mechanical design space. Clear definitions are provided for each function and flow. The functional basis is compared to previous functional representations and is shown to subsume these attempts as well as offer a more consistent classification scheme. …

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Using Quantitative Functional Models To Develop Product Architectures, Robert B. Stone, Kristin L. Wood, Richard H. Crawford Jan 2000

Using Quantitative Functional Models To Develop Product Architectures, Robert B. Stone, Kristin L. Wood, Richard H. Crawford

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Developing product architectures is a key phase in design and development processes. It encompasses the transformation from functional model to alternative product layouts. In this paper, we introduce a methodology for representing a functional model of a product in a quantitative manner. In addition to describing product functionality, the quantitative functional model also incorporates customer need ratings. Product design knowledge can be archived and transmitted in databases using this novel representation. Numerical manipulations of such a database assist in developing product architectures. In particular, product families and customer need ratings for modules are easily computed. Prior to the methodology, a …

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