Aerospace Engineering Commons^™

Stability Of Three-Dimensional Compressible Boundary-Layers, Samarasingham Jeyasingham

Mechanical & Aerospace Engineering Theses & Dissertations

The failure repair process of a continuously operating device is studied in this research. Different cases that incorporate modeling of equipment deterioration, inspection, and maintenance for optimal maintenance policy are proposed. Markov processes are used to determine state probabilities, and the optimal value of the mean time to preventive maintenance is determined by maximizing the availability of the equipment with respect to the meantime preventive maintenance. The approach uses models that assume that equipment can fail due to both deterioration and random failures. Preventive maintenance can be performed from each working state to avoid deterioration failure. Economic effects are integrated …

Fatigue Response Of Repaired Thick Aluminum Panels With Bondline Flaws, David S. Conley

Theses and Dissertations

his research investigated the fatigue response of precracked 558 x 177.8 x 6.35 mm (22.0 x 7.0 x 0.25 in) 2024-T351 aluminum panels repaired with single-sided partially bonded, unidirectional, eighteen ply boron/epoxy reinforcements. Disbonds were introduced into the bondline of each repair during the adhesion process using teflon inserts. Five different disbond configurations, with varying disbond locations and sizes, were tested. Each repaired panel was subjected to constant amplitude cyclic fatigue loading with a maximum stress of 120MPa. Results from the different configurations were compared against one another and against repaired panels with no debonds to assess the effect of …

Effects Of Pressure Gradients On Turbulent Boundary Layer Flow Over A Flat Plate With Riblets, Franklin L. Dement Jr.

Theses and Dissertations

The Air Force Institute of Technology Boundary Layer Research Facility test section was modified to create controlled non-zero streamwise pressure gradients. The capability of the modified facility to reproduce theoretical laminar boundary layer velocity profiles and to create a self-preserving flow with an adverse streamwise pressure gradient was verified with three-dimensional laser Doppler anemometry. The effects of streamwise adverse and favorable pressure gradients on turbulent boundary layer flow characteristics (velocity profiles, turbulence and skin friction) and vortex formation over a flat plate with riblets at low speed (U = 5 mIs) were studied. Normal and spanwise velocity profiles for both …

Robust Eigenstructure Assignment Using Positive Definite Output Feedback Control, Adam G. Harris

Theses and Dissertations

This research investigates a method of eigenstructure assignment for the classes of controllers known as positive definite output feedback control. The research began with a closed loop system with output feedback control that utilizes a collocated actuator-sensor pair. It is shown that this system is robust because it is globally stable for positive definite feedback. Analytical analysis is then completed to determine gains that minimize a cost function that is the error between the desired and achievable (assuming positive definite output feedback) eigenstructure. Examples are given at the end of the thesis to validate the computer code and theory results.

Progressive Failure Analysis Of Composite Panels, Stephen M. Spottswood

Theses and Dissertations

The objective of this research was to determine the physical response, including material failure, of a curved composite panel designed to resist transverse loading. The cause of the material failure, in the form of delamination, fiber and/or matrix failure, was determined through various criterion based on non-linear movement using a finite element analysis technique. Data generated both with and without the addition of progressive failure criteria, was compared with previously published experimental data, noting where the theory diverges from the experimental results. The inclusion of various failure criterion, to include maximum stress, Lee, and Hashin, provided a more realistic representation …

Design And Analysis Of On-Orbit Servicing Architectures For The Global Positioning System Constellation, Gregg A. Leisman, Adam D. Wallen

Theses and Dissertations

Satellites are the only major Air Force systems with no maintenance, routine repair, or upgrade capability. The result is expensive satellites and a heavy reliance on access to space. At the same time, satellite design is maturing and reducing the cost to produce satellites with longer design lives. This works against the ability to keep the technology on satellites current without frequent replacement of those satellites. The Global Positioning System Joint Program Office realizes that it must change its mode of operations to quickly meet new requirements while minimizing cost. The possibility of using robotic servicing architectures to solve these …

East Coast Abort Modeling With Rtls Elimination For The Space Shuttle-Liquid Fly Back Booster Launch System, Thomas L. Miller Jr.

Theses and Dissertations

This study investigates the ability of the proposed Liquid Fly Back Booster, a replacement for the Space Shuttle's Solid Rocket Boosters (SRBs), to eliminate the need for the Return to Launch Site (RTLS) abort mode. A Fortran model of a nominal launch trajectory was perturbed to simulate a single Space Shuttle Main Engine-out (SSME-out) abort scenario at different times in the launch with the goal being to abort to the southern most landing site possible. The model accounts for vehicle lift, drag, dynamic pressure, throttling times and includes atmospheric effects to enhance fidelity. Results show the RTLS abort mode can …

Tip Vortex And Crenulation Effects In A Compressor Cascade With Moving Endwall, Barry W. St Germain

Theses and Dissertations

The effects of changing Reynolds number and flow coefficients on the velocity and pressure flow fields within a linear cascade with moving endwall were investigated in this experimental thesis. All flow field measurements were taken at a constant compressor blade tip gap clearance of 1.0 % chord and endwall speed of 318.6 ft/s (97.1 m/s), with flow coefficients of 0.40, 0.52, 0.62 and 0.72. All data acquisition occurred in a plane 23 % chord downstream of the trailing edge plane of the linear cascade. Hotwire probes determined the complete passage, three-dimensional fowled behind both crenulated and regular blade geometries. Vector …

A Statistical Analysis Of Space Structure Mode Localization, Amy M. Cox

Theses and Dissertations

Cyclic structures, such as antenna arrays, multi-bay trusses, and compressor blades, are significantly impacted by slight changes to system periodicity. Manufacturing errors of 5% or less can result in drastic changes to a structure's modal behavior. This change in modal behavior is significant, since it may result in the focusing of modal energy to individual substructures of the system. Poor modal identification can result in poorly designed control systems, resulting in shape control and pointing issues for space antennae. Additionally, modal energy localization may damage individual system components due to unanticipated levels of cyclic loading, leading to high cycle fatigue.

Toward Development Of An Integrated Aerospace Power Doctrine, Toby G. Doran

Theses and Dissertations

This thesis discusses the state of the Air Force, decision making factors in the making of military doctrine, the definition of doctrine, Air Force doctrines today, new ways to develop doctrine, including models and hypothesis-research-analysis loops, space doctrine, control of space, space superiority and a call for aerospace power doctrine.

Simsat: A Satellite System Simulator And Experimental Test Bed For Air Force Research, James E. Colebank, R. Dan Jones, Randall D. Pollak, Donald M. Mannebach, George R. Nagy

Theses and Dissertations

SIMSAT (the SIMulation SATellite) is an AFIT-sponsored program to develop a laboratory-based physical satellite simulator. SIMSAT supports experimentation in areas of attitude control, precision pointing, and vibration suppression. SIMSAT development began with the purchase of a three-axis gas bearing which simulates a torque-free space environment. SIMSAT subsystems provide power, attitude control, telemetry, and structural support to experimental payloads. Project challenges included integration of attitude control software/hardware, high-output power storage devices, remote communications, high-frequency data collection, structural design, and computer display outputs.

Space Launch Operations And The Lean Aerospace Initiative, Troy L. Endicott

Theses and Dissertations

This study analyzes current expendable launch procedures and identifies truly lean, value-added steps in launch operation enterprises as they relate to the Lean Aerospace Initiative (LAI). LAI and the concepts of lean thinning are discussed and followed by a review of current and future launch system requirements and their opportunities for lean practices. The study also discusses in detail current Delta II expendable launch processing operations and presents results in a case study that show how lean principles have helped the Delta II launch team drastically reduce on-pad time, restructure its testing philosophy, and streamline its operations flow. Many of …

Electro-Hydrodynamic Pumped Hydraulic Actuation With Application To Active Vibration Control, Ahmad Reza Kashani, Sung Kang, Kevin P. Hallinan

Mechanical and Aerospace Engineering Faculty Publications

A new type of actuation device has been conceptualized that meets the needs of both large displacement, force and bandwidth within a package more compact than currently available magnetostrictive and stack-type piezoelectric actuators of similar rating. This concept relies on micro-scale electrohydrodynamic (EHD) pumping of a dielectric liquid within small channels. Configured as an actuator, the EHD pump(s) would be used to move fluid between two reservoirs—each having a compliant membrane that interfaces to the world to provide the means to achieve vibration cancellation or micro actuation.

Ordinarily limited to generating flow in macroscale applications, the EHD pump, when operating …

Space Maneuver Vehicle Orbital Mission Planner: Development Of Application And Analysis Of On-Demand Maneuvering Ability, Shon P. Williams

Theses and Dissertations

The USAF has developed the Space Maneuver Vehicle (SMV) to fulfill the requirement for flexibility, rapid response, and on-demand maneuverability of space assets. This reusable satellite merges the efficiency and readiness of aircraft-like operations with the capability of global coverage from space. Designed to provide over 10,500 fps of velocity change (or delta-v) while in orbit, the SMV out-maneuvers existing satellites by up to 100 times. This thesis helps transition the SMV to the operational area by demonstrating their responsiveness to varied mission taskings. The SMV Orbital Mission Planner allows the operator to place any number of SMVs in orbit …

Whole Spacecraft Vibration Isolation, Gregory G. Karahalis

Theses and Dissertations

The Department of Defense identified launch vibration isolation as a major research interest. Reducing the loads a satellite experiences during launch will greatly enhance the reliability, lifetime, and payload to structure ratio. DoD satellite programs stand to benefit significantly from advances in vibration isolation technology.

Heat Transfer To The Inclined Trailing Wall Of An Open Cavity, Orval A. Powell

Theses and Dissertations

Experimental and computational heat transfer investigations were performed on a cavity with an inclined trailing wall (20-degrees to the horizontal), simulating one under investigation for use in a scramjet engine. Heat transfer data are reported in the form of Stanton number obtained using a curve fit to the recorded transient surface temperature history under cold flow conditions. Ascending from the reattachment point, the Stanton number increased by nearly 50% due to flow compression. This effect of flow compression was also evident at the junction of the cavity floor and inclined trailing wall, where the Stanton number also increased by 50%. …

A Comparative Analysis Of The Iridium® And Globalstar® Satellite Transmission Paths, Kenneth E. Crowe

Theses and Dissertations

Globalstar and Iridium will provide valuable global communications assets for business, humanitarian aid and military operations. However, the level of coverage and the quality of the transmission path of these systems are strongly dependent on the latitude of the user and, due to their orbital characteristics, both systems provide reduced levels of coverage at low latitudes. Additionally, the L- and S-Band frequencies utilized by these systems are prone to ionospheric interference at low latitudes. The results of extensive simulation analysis indicate that the Globalstar constellation architecture provides a considerably better transmission path than Iridium's in several important areas, including path …

A Nonlinear Pre-Filter To Prevent Departure And/Or Pilot-Induced Oscillations (Pio) Due To Actuator Rate Limiting, Michael J. Chapa

Theses and Dissertations

Closed loop instability caused by excess phase lag induced by actuator rate limiting has been suspected in many aircraft departures from controlled flight and pilot-induced oscillations (PIO). As part of the joint Air Force Institute of Technology Test Pilot School (AFITITPS) program, a nonlinear rate limiter pre-filter (RLPF) was developed to minimize the phase lag induced by rate limiting. RLFF performance was evaluated inside the feedback path, but primary emphasis was on the pilot command path. Closed loop computer and motion-based flight simulation were conducted to prepare for the flight test. The HAVE FILTER flight test project was flown using …

Anti-Ballistic Missile Laser Predictive Avoidance Of Satellites: Theory And Software For Real-Time Processing And Deconfliction Of Satellite Ephemerides With A Moving Platform Laser, David J. Vloedman

Theses and Dissertations

The Anti-Ballistic missile Laser (ABL) Project is committed to defense against attack from enemy-launched Theater Ballistic Missiles using an airborne laser platform to disable an enemy missile in the boost phase of launch. Wielding a laser of this power and scope requires that no collateral damage be caused by laser energy which may escape from the theater of engagement. The most likely track of such a laser would pose a significant threat to space-based assets. The Predictive Avoidance algorithm is designed to predict the path of a given laser firing sequence, and perform real-time forecasting of, and deconfliction with, the …

Joint Space Systems Operations Program, Robert J. Twiggs, Billy Smith

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs and Lt. Colonel Billy Smith on the "Joint Space Systems Operations Program" from February 8, 1999.

Opal Picosatellite Launcher, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "OPAL Picosatellite Launcher" from February 3, 1999.

Opal Launch Opportunity, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "OPAL Launch Opportunity" from February 3, 1999.

Emerald: A Low-Cost Spacecraft Mission For Validating Formation Flying Technologies, Robert J. Twiggs, Chris Kitts, Jon How

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs, Chris Kitts, and Jon How titled "EMERALD: A Low-Cost Spacecraft Mission for Validating Formation Flying Technologies" from January 19, 1999.

Fundamentals Of Linear State Space Systems, John Bay

Electrical and Computer Engineering Faculty Scholarship

This book addresses two primary deficiencies in the linear systems textbook market: a lack of development of state space methods from the basic principles and a lack of pedagogical focus. The book uses the geometric intuition provided by vector space analysis to develop in a very sequential manner all the essential topics in linear state system theory that a senior or beginning graduate student should know. It does this in an ordered, readable manner, with examples drawn from several areas of engineering. Because it derives state space methods from linear algebra and vector spaces and ties all the topics together …

Location Effects Of Passive Damping Material In Cross-Ply Laminates On Natural Frequency And Mode Shape, E. I. Elghandour, F. A. Kolkailah

Aerospace Engineering

This study presents an experimental investigation of the free vibration of cantilevered composite laminated plates with embedded passive damping material at different stages. A total of five composite laminated plates are considered. The lay-up sequences for the five composite laminated plates with and without two embedded layers of passive damping material are [90°/0°/90°/0°]_s, [90°/0°/90°/0°/d]_s, [90°/0°/90°/d/0°]_s, [90°/0°/d/90°/0°]_s, and [90°/d/0°/90°/0°]_s. The passive damping material employed is a 3M material, SJ-2015 ISD 112, with peak damping properties in the ambient temperature range of 32°F to 140°F. The composite material used is a carbon …

Emerald: A Low Cost Spacecraft Mission For Validating Formation Flying Technologies, Robert J. Twiggs, Jonathan How, Freddy Pranajaya, Bryan Palmintier

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs, Robert Twiggs, Jonathon How, Freddy Pranajaya, and Bryan Palmintier titled "EMERALD: A Low Cost Spacecraft Mission for Validating Formation Flying Technologies" from 1999.

Control Of The Air: The Enduring Requirement, Richard P. Hallion

United States Air Force: Publications

Throughout the military history of the twentieth century, the role of aerospace forces has become more predominant. Today, wars typically start, are prosecuted, and reach their decisive culminating point--whether surrender of a foe, agreement to a ceasefire, or the ceasing of combat operations--thanks to air action. Given these circumstances, to lose control of the air is to lose a war, particularly in an era (as we now are in since the end of the Cold War) when deployable overseas forces are small, and, thus, particularly vulnerable to the tremendous leverage an opponent gains by sudden and swift air attack. If …

The Hygrothermal Response And Physical Aging Of Polymer Matrix Textile Composites, Natalie L. Dixon

Masters Theses

"Woven graphite/epoxy composite laminate is one type of composite currently being investigated for use in aircraft engine components. However, polymers tend to become brittle with age, especially when exposed to elevated temperature. It is necessary to understand the physical changes in a material during the aging process in order to predict the long-term behavior.

In addition to aging, materials used in aircraft will be exposed to a wide variety of temperatures and relative humidity levels. Variations in temperature and moisture content affect both the physical and the mechanical properties of composites.

Experimental methods are described for hygrothermal testing of a …

Hypersonic Drag And Heat Transfer Reduction Using A Forward Facing Jet, Benjamin Meyer, Harlan F. Nelson, David W. Riggins

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A two-dimensional numerical study of the effects of a forward-facing jet located at the stagnation point of a blunt body on wave drag, heat transfer, and skin friction drag is presented for Mach 6.5 flow at 30 km altitude. The full Navier-Stokes equations are used with variable viscosity and thermal conductivity. It is shown that upstream injection can significantly modify the flow field. If the jet conditions are chosen properly, large reductions in drag and heat transfer can be obtained resulting in possible increases in the volumetric efficiency and static stability of aircraft and reductions in heating protection requirements for …

A New Reflection Free Boundary In Uniform Flow Using Mapped Infinite Wave Envelope Elements, Walter Eversman, Indranil Danda Roy

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Variable order mapped infinite wave envelope elements are developed for finite element modeling of acoustic radiation in a uniformly moving medium. These elements can be used outside of the near field as a non-reflecting boundary condition for computations on an infinite domain in which a radiating body is immersed in a moving medium. Mapped infinite wave envelope elements provide a boundary condition equivalent to stiffness, mass, and damping matrices appended to the inner mesh. A demonstration of the characteristics of the mapped infinite wave envelope elements is given in the context of acoustic radiation from a turbofan inlet for which …