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Air Force Institute of Technology

2004

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Articles 61 - 90 of 141

Full-Text Articles in Engineering

Flow Around An Object Projected From A Cavity Into A Supersonic Freestream, Scott T. Bjorge Mar 2004

Flow Around An Object Projected From A Cavity Into A Supersonic Freestream, Scott T. Bjorge

Theses and Dissertations

The pressure and flow field of a supersonic flow over a cavity, with and without a store, was the focus of this experiment. One cavity geometry (length to depth ratio 3.6) was studied; the freestream Mach number and the placement of the store relative to the cavity floor were varied. The pressure spectra on the cavity floor were markedly different between Mach numbers of 1.8 and 2.9. The Mach 1.8 case exhibited clear spectral peaks consistent with predictions by Rossiter, whereas the Mach 2.9 flow did not. With the store placed within the free shear layer, the pressure fluctuations on …

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Characterization Of Ultra Wideband Multiple Access Performance Using Time Hopped-Biorthogonal Pulse Position Modulation, Donald J. Clabaugh Mar 2004

Characterization Of Ultra Wideband Multiple Access Performance Using Time Hopped-Biorthogonal Pulse Position Modulation, Donald J. Clabaugh

Theses and Dissertations

The FCC's release of its UWB First Report and Order in April 2002 spawned renewed interest in impulse signaling research. This work combines Time Hopped (TH) multiple access coding with 4-ary UWB Biorthogonal Pulse Position Modulation (TH-BPPM). Multiple access performance is evaluated in a multipath environment for both synchronous and asynchronous networks. Fast time hopping is implemented by replicating and hopping each TH-BPPM symbol NH times. Bit error expressions are derived for biorthogonal TH-BPPM signaling and results compared with previous orthogonal TH-PPM work. Without fast time hopping (NH = 1), the biorthogonal TH-BPPM technique provided gains equivalent to Gray-coded QPSK; …

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Optical Characterization And Modeling Of Compositionally Matched Indium Arsenide-Antimonide Bulk And Multiple Quantum Well Semiconductors, Scott C. Phillips Mar 2004

Optical Characterization And Modeling Of Compositionally Matched Indium Arsenide-Antimonide Bulk And Multiple Quantum Well Semiconductors, Scott C. Phillips

Theses and Dissertations

Indium arsenide-antimonide (InAsSb) semiconductors have been determined to emit in the 3-5 micrometer range, the window of interest for countermeasures against infrared electro-optical threats. This experiment set out to cross the bulk to quantum well characterization barrier by optically characterizing two sets of compositionally matched type I quantum well and bulk well material samples. Absorption measurements determined the band gap energy of the bulk samples and the first allowed subband transition for the quantum wells. By collecting absorption spectra at different temperatures, the trend of the energy transitions was described by fitting a Varshni equation to them. The expected result …

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Systems-Level Feasibility Analysis Of A Microsatellite Rendezvous With Non-Cooperative Targets, Allen R. Toso Mar 2004

Systems-Level Feasibility Analysis Of A Microsatellite Rendezvous With Non-Cooperative Targets, Allen R. Toso

Theses and Dissertations

The feasibility of using a microsatellite to accomplish an orbital rendezvous with a noncooperative target was evaluated. This study focused on identifying and further exploring the technical challenges involved in achieving a noncooperative rendezvous. A system engineering analysis and review of past research quickly led to a concentration on the guidance, navigation, and control elements of the microsatellite operation. The integration of control and orbit determination algorithms was investigated. A simple yet robust solution could not be found to meet reasonable rendezvous criteria, using essentially off-the-shelf technology and algorithms. System feasibility has been assessed to have a low probability in …

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Image Super-Resolution Using Adaptive 2-D Gaussian Basis Function Interpolation, Terence D. Hunt Mar 2004

Image Super-Resolution Using Adaptive 2-D Gaussian Basis Function Interpolation, Terence D. Hunt

Theses and Dissertations

Digital image interpolation using Gaussian radial basis functions has been implemented by several investigators, and promising results have been obtained; however, determining the basis function variance has been problematic. Here, adaptive Gaussian basis functions fit the mean vector and covariance matrix of a non-radial Gaussian function to each pixel and its neighbors, which enables edges and other image characteristics to be more effectively represented. The interpolation is constrained to reproduce the original image mean gray level, and the mean basis function variance is determined using the expected image smoothness for the increased resolution. Test outputs from the resulting Adaptive Gaussian …

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Decision Analysis With Value Focused Thinking As A Methodology To Assess Air Force Officer Retention Alternatives, Sang-Ho Moon Mar 2004

Decision Analysis With Value Focused Thinking As A Methodology To Assess Air Force Officer Retention Alternatives, Sang-Ho Moon

Theses and Dissertations

Many countries realize the importance of the retention of qualified military personnel, and have tried to solve this problem using various methods. Nevertheless, the effects of those methods have not been determined or proven yet. The military retention problem is closely related to each individual's separation decision from the military. The characteristics of this decision are multi-objective and highly subjective. Accordingly, the effectiveness of various methods is heavily dependant on the value set of each individual. Decision Analysis (DA) using Value Focused Thinking (VFT) can be an excellent process to deal with this decision. Also, the data can reflect the …

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Structural Design And Analysis Of A Rigidizable Space Shuttle Experiment, Raymond G. Holstein Iii Mar 2004

Structural Design And Analysis Of A Rigidizable Space Shuttle Experiment, Raymond G. Holstein Iii

Theses and Dissertations

AFIT is in the process of designing a Space Shuttle experiment designated as the Rigidized Inflatable Get-Away-Special Experiment (RIGEX) to study the effects of microgravity on the deployment of rigidizable composite structures. Once in space, the experiment will inflate and rigidize three composite structures and perform a vibration analysis on each by exciting the tubes using piezoelectric patches and collecting data via an accelerometer. This paper presents the structural and vibration analysis of the RIGEX assembly and inflatable composite tubes using ABAQUS Finite Element Analysis (FEA) software. Comparison of the analysis has been carried out with Eigenvalue/Eigenvector experimentation by means …

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Special Nuclear Material Imaging Using A High Purity Germanium Double Sided Strip Detector, Clifford V. Sulham Mar 2004

Special Nuclear Material Imaging Using A High Purity Germanium Double Sided Strip Detector, Clifford V. Sulham

Theses and Dissertations

The purpose of this research is to investigate the feasibility of using a High Purity Germanium Double Sided Strip Detector (HPGeDSSD) to image Special Nuclear Material (SNM) for use in the field of nuclear nonproliferation. SNM shape can be determined by using a gamma ray imaging system that is capable of imaging either Pu-239 or U-235. The detector used for this research is a liquid-nitrogen cooled germanium detector with five charge collection strips on both faces. The strips on the two faces are orthogonal to each other, creating a five by five array of data collection pixels. When the detector …

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Agent Based Simulation Seas Evaluation Of Dodaf Architecture, Gregory V. Destefano Mar 2004

Agent Based Simulation Seas Evaluation Of Dodaf Architecture, Gregory V. Destefano

Theses and Dissertations

With Department of Defense (DoD) weapon systems being deeply rooted in the command, control, communications, computers, intelligence, surveillance, and reconnaissance (C4ISR) structure, it is necessary for combat models to capture C4ISR effects in order to properly assess military worth. Unlike many DoD legacy combat models, the agent based model System Effectiveness and Analysis Simulation (SEAS) is identified as having C4ISR analysis capabilities. In lieu of requirements for all new DoD C4ISR weapon systems to be placed within a DoD Architectural Framework (DoDAF), investigation of means to export data from the Framework to the combat model SEAS began. Through operational, system, …

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Improving The Estimation Of Military Worth Of The Advanced Tactical Laser Through Simulation Aggregation, Michael T. Cook Mar 2004

Improving The Estimation Of Military Worth Of The Advanced Tactical Laser Through Simulation Aggregation, Michael T. Cook

Theses and Dissertations

Fielding High Energy Laser (HEL) weapon systems presents technological challenges as well as employment and financial challenges. The risk associated with the challenges mandates the development process include computer simulation models capable of predicting weapon system performance from the engineering level to assessing the military worth of employing HEL systems in combat scenarios. This research effort focuses on developing laser performance data at a higher fidelity engagement model and integrating the performance data into a mission level model. The propagation of the laser from the transmitting aperture to the target is modeled at the engagement level through the employment of …

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An Analysis Of The Effects Of Low Energy Electron Radiation Of AlXGa1-XN/Gan Modulation-Doped Field-Effect Transistors, James M. Sattler Mar 2004

An Analysis Of The Effects Of Low Energy Electron Radiation Of AlXGa1-XN/Gan Modulation-Doped Field-Effect Transistors, James M. Sattler

Theses and Dissertations

The effects of radiation on AlxGa1-xN/GaN MODFETs is an area of increasing interest to the USAF as these devices become developed and integrated in satellite-based systems Irradiation is also a valuable tool for analyzing the quantum-level characteristics and properties that are responsible for device operation AlxGa1-xN/GaN MODFETs were fabricated and irradiated at liquid nitrogen temperatures by 0,45-1,2MeV electrons up to doses of 6*1016 e/cm2. Following irradiation, low temperature I-V measurements were recorded providing dose-dependent measurements Temperature-dependent I-V measurements were also made during room temperature annealing following irradiation I-V measurements …

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Controlling The Primary Mirror In A Space-Based Telescope Utilizing An Eigenstructure Assignment Technique, Kim Kyongsoo Mar 2004

Controlling The Primary Mirror In A Space-Based Telescope Utilizing An Eigenstructure Assignment Technique, Kim Kyongsoo

Theses and Dissertations

The feasibility of using a sparse array of mirrors in a satellite system is being evaluated. This study focused on the control laws necessary for achieving the minimization of the effect of vibration which happens at the primary mirror of the satellite, by using the eigenstructure assignment technique. White Gaussian noise was assumed as the external input. AFRL has developed a 79 state model with 9 control inputs and 9 outputs, 3 sparse array mirrors, and a base. To extend the theory, a simplified model with 2 mirrors and a base which has 12 states, 4 control inputs and 8 …

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Design Of A Space Borne Autonomous Infrared Tracking System, Matthew B. Kimsal Mar 2004

Design Of A Space Borne Autonomous Infrared Tracking System, Matthew B. Kimsal

Theses and Dissertations

Complete characterization of the space environment in support of the United States goal of space Situational Awareness is not currently achievable. When confronted with recent increases in the deployment and miniaturization of microsatellites by numerous nations, the questions of foreign space capabilities are magnified. This study sought to determine the feasibility of and experimentally demonstrate a microsatellite capability to autonomously loiter about and track a target satellite. Various methods of passive remote sensing were investigated to determine the best means of detecting and tracking a target in space. Microbolometer-based infrared sensors were identified as the best alternative. A representative system …

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Enhancing The Instantaneous Dynamic Range Of Electronic Warfare Receivers Using Statistical Signal Processing, Bryan E. Smith Mar 2004

Enhancing The Instantaneous Dynamic Range Of Electronic Warfare Receivers Using Statistical Signal Processing, Bryan E. Smith

Theses and Dissertations

Accurately processing multiple, time-coincident signals presents a challenge to Electronic Warfare (EW) receivers, especially if the signals are close in frequency and/or mismatched in amplitude. The metric that quantifies an EW receiver's ability to measure time-coincident signals is the Instantaneous Dynamic Range (IDR), defined for a given frequency estimation accuracy, a given frequency separation and a given SNR as the maximum signal amplitude ratio that can be accommodated. Using a two sinusoid time-series model, this thesis analyzes IDR for ideal intercept and parametric digital EW receivers. In general, the number of signals contained in the EW receiver measurement interval is …

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Using Value-Focused Thinking To Evaluate The Effectiveness Of Air Force Utility Privatization, Carlos Braziel Mar 2004

Using Value-Focused Thinking To Evaluate The Effectiveness Of Air Force Utility Privatization, Carlos Braziel

Theses and Dissertations

The majority of the Air Force s stateside utility systems are old, obsolete, and unreliable. The cost to upgrade and repair these systems is currently estimated at over $4 billion. In response, the Air Force began efforts to convey ownership of these utility systems to the private sector through privatization efforts. However, privatization critics believe that newly privatized entities of government will cost the public more money and provide a lower level of service. Therefore, independent audits are a necessity to ensure government initiatives, meet their intended goals. However, the Air Force currently lacks an effective auditing tool to ensure …

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An Analysis Of Coast Guard Hh-65 Engine Reliability: A Comparison Of Malfunctions To Component Removals, Donna L. Cottrell Mar 2004

An Analysis Of Coast Guard Hh-65 Engine Reliability: A Comparison Of Malfunctions To Component Removals, Donna L. Cottrell

Theses and Dissertations

The Coast Guard HH-65 helicopter experienced 31 in-flight loss of power incidents during FY 2003 and 21 during the first two months of FY 2003. Concurrent with this apparent decrease in reliability, the Coast Guard seeks ways to expand the HH- 65’s Airborne Use of Force capabilities as a result of the September 11th, 2001 terrorists’ attacks. This study is an exploratory, empirical analysis of engine and airframe component replacements as related to engine mishaps and reliability in the HH-65. We use contingency table analysis, ordinary least squares regression, and logistic regression to examine the mishap history and component replacement …

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The Evaluation Of The Damping Characteristics Of A Hard Coating On Titanium, Christopher M. Blackwell Mar 2004

The Evaluation Of The Damping Characteristics Of A Hard Coating On Titanium, Christopher M. Blackwell

Theses and Dissertations

Engine failures due to fatigue have cost the Air Force an estimated $400 million dollars per year over the past two decades (Garrison, 2001). Damping treatments capable of reducing the internal stresses of fan and turbine blades to levels where fatigue is less likely to occur have the potential for reducing cost while enhancing reliability. This research evaluates the damping characteristics of magnesium aluminate spinel, MgO+Al2O3, (mag spinel) on titanium plates. The material and aspect ratio were chosen to approximate the low aspect ratio blades found in military gas turbine fans. The plates were tested with …

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Swarm Based Implementation Of A Virtual Distributed Database System In A Sensor Network, Wen C. Lee Mar 2004

Swarm Based Implementation Of A Virtual Distributed Database System In A Sensor Network, Wen C. Lee

Theses and Dissertations

The deployment of unmanned aerial vehicles (UAVs) in recent military operations has had success in carrying out surveillance and combat missions in sensitive areas. An area of intense research on UAVs has been on controlling a group of small-sized UAVs to carry out reconnaissance missions normally undertaken by large UAVs such as Predator or Global Hawk. A control strategy for coordinating the UAV movements of such a group of UAVs adopts the bio-inspired swarm model to produce autonomous group behavior. This research proposes establishing a distributed database system on a group of swarming UAVs, providing for data storage during a …

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An Investigation Relating Longitudinal Pilot-Induced Oscillation Tendency Rating To Describing Function Predictions For Rate-Limited Actuators, Joel B. Witte Mar 2004

An Investigation Relating Longitudinal Pilot-Induced Oscillation Tendency Rating To Describing Function Predictions For Rate-Limited Actuators, Joel B. Witte

Theses and Dissertations

The purpose of this study was to investigate pilot-induced oscillations (PIO) and determine a method by which PIO tendency rating could be predicted. In particular, longitudinal PIO in the presence of rate-limited actuators were singled out for examination. Sinusoidal input/triangular output describing function techniques using Nichols charts were used. A new criterion dubbed Gap Criterion was calculated for PIO sensitivity. This criterion consists of the product of pilot gain necessary to cause PIO and the normalized maximum amplitude of the commanded actuator. These results were paired with simulator and flight test PIO tendency rating data. The PIO rating scale used …

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Effect Of Dimple Pattern On The Suppression Of Boundary Layer Separation On A Low Pressure Turbine Blade, John P. Casey Mar 2004

Effect Of Dimple Pattern On The Suppression Of Boundary Layer Separation On A Low Pressure Turbine Blade, John P. Casey

Theses and Dissertations

Three dimple patterns were investigated to ascertain their relative effectiveness on controlling boundary layer separation from a low-pressure turbine blade. The three cases included a single row of dimples at 65% of the axial chord with 2.22 cm spacing, a single row of dimples at 65% of the axial chord with 4.44 cm spacing, and a two-row staggered pattern with rows at 65% and 76% of the axial chord with 4.44 cm spacing. The multiple row case was such that the center of the upstream dimple set at the midpoint between two downstream dimples. The dimple spacing was measured center-on-center. …

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Microprocessor-Based Systems Control For The Rigidized Inflatable Get-Away-Special Experiment, David C. Moody Mar 2004

Microprocessor-Based Systems Control For The Rigidized Inflatable Get-Away-Special Experiment, David C. Moody

Theses and Dissertations

As the demand for space based communications and faster data throughput increase, satellites are becoming larger. Larger satellite antennas help to provide the needed gain to increase communications in space. Compounding the performance and size trade-offs are the payload weight and size limit imposed by the launch vehicles. Inflatable structures offer a cost saving opportunity since the structure is significantly lighter and has a reduced storage volume. This allows for smaller launch vehicles and for increased performance capabilities. Inflatable structures offer possibilities for increased satellite lifetimes, increased communications capacity, and reduce launch costs. This thesis develops and implements the computer …

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Vibrometric Detection Of Beam Damage Due To Inclusions, Aaron J. Reifsnyder Mar 2004

Vibrometric Detection Of Beam Damage Due To Inclusions, Aaron J. Reifsnyder

Theses and Dissertations

The Air Force Institute of Technology, in conjunction with the Structural Health Monitoring branch of the Air Force Research Laboratory, is researching methods of determining effects of notch location and size on beam structures using modal frequency analysis. This thesis explores the ability to detect included notches of varying magnitudes and locations within the frequency domain of an isotropic cantilever beam. A series of experiments employing centerline-notched 2024 T3 and 2024 0 aluminum beams was used to determine whether natural frequency measurement in beam structures is a valid mechanism for damage detection. Each specimen was excited by a strain actuator …

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Magnetogasdynamic Flow Control Of A Mach Reflection, Brian E. Earp Mar 2004

Magnetogasdynamic Flow Control Of A Mach Reflection, Brian E. Earp

Theses and Dissertations

Two-dimensional regular and Mach reflections have been studied in the Mach 4.96 dual-solution domain for a 25° and 26° double-fin inlet. The steady-state computational Mach and regular reflections were subjected to magnetogasdynamic forces to determine whether these forces could be used as a possible flow control mechanism. The numerical code employed for this research solved the inviscid Euler equations with added source terms for the ponderomotive force and accompanying energy interactions. The 25° regular reflection was determined to be extremely sensitive to a decelerating Lorentz force. Transient application of the force led to the transition of the regular reflection to …

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Geolocation Of An Audio Source In A Multipath Environment Using Time-Of-Arrival, Jeffrey A. Boggs Mar 2004

Geolocation Of An Audio Source In A Multipath Environment Using Time-Of-Arrival, Jeffrey A. Boggs

Theses and Dissertations

The Air Force and the Department of Defense (DoD) are continually searching for ways to protect U.S. forces, both stateside and abroad. One continuing threat, especially in the current world environment, is gunfire from an unseen sniper. Designated areas, such as a forward deployed base or motorcade route, need to be continuously monitored for sniper fire. Once detected, these gunmen need to be located in real time. One possible method for accomplishing this task is to geolocate the audio signals generated using time-of-arrival (TOA) algorithms. These algorithms rely on direct-path measurements for accuracy. Multipath environments therefore pose a problem when …

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Modeling And Analysis Of Post-Conflict Reconstruction, Damon B. Richardson Mar 2004

Modeling And Analysis Of Post-Conflict Reconstruction, Damon B. Richardson

Theses and Dissertations

The forces at play in reconstruction operations are a complex system of time phased interlocking cause and effect relationships that are not thoroughly understood. A model capable of capturing the general dynamics involved in post-conflict reconstruction would provide insight to decision makers regarding potential policy alternatives. This research effort demonstrates the viability of using systems dynamics modeling techniques to simulate the establishment of public order and safety in a post-conflict reconstruction operation (Phase IV operations). A high level generic framework is developed that can be used as a general template for modeling post-conflict reconstruction. It is then demonstrated with a …

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Phase-Type Approximations For Wear Processes In A Semi-Markov Environment, Christopher J. Solo Mar 2004

Phase-Type Approximations For Wear Processes In A Semi-Markov Environment, Christopher J. Solo

Theses and Dissertations

The reliability of a single-unit system experiencing degradation (wear) due to the influence of a general, observable environment process is considered. In particular, the failure time distribution is evaluated using only observations of the unit's current operating environment which is characterized as a finite semi-Markov process (SMP). In order to impose the Markov property, generally distributed environment state sojourn times are approximated as phase-type (PH) random variables using observations of state holding times and transition rates. The use of PH distributions facilitates the use of existing analytical results for reliability evaluation of units subject to an environment process that evolves …

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Demonstrating Optothermal Actuators For An Autonomous Mems Microrobot, Francis R. Szabo Mar 2004

Demonstrating Optothermal Actuators For An Autonomous Mems Microrobot, Francis R. Szabo

Theses and Dissertations

There are numerous applications for microrobots which are beneficial to the Air Force. However, the microrobotics field is still in its infancy, and will require extensive basic research before these applications can be fielded. The biggest hurdle to be solved, in order to create autonomous microrobots, is generating power for their actuator engines. Most present actuators require orders of magnitude more power than is presently available from micropower sources. To enable smaller microrobots, this research proposed a simplified power concept that eliminates the need for on-board power supplies and control circuitry by using actuators powered wirelessly from the environment. This …

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Making The Business Case For Sustainable Design In The Department Of Defense, David M. Warnke Mar 2004

Making The Business Case For Sustainable Design In The Department Of Defense, David M. Warnke

Theses and Dissertations

Buildings are one of the largest consumers of natural resources, a major source of ecological pollution, and occasionally toxic to human health. Sustainable design is the common term associated with buildings which, during their construction, use, and eventual disposal, seek to minimize their negative impact on the environment and human health. The U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED) rating system helps to assess a building's sustainability level. In the Federal Government's push to set the example for the rest of the nation, nearly every Federal Agency has chosen to adopt the LEED assessment tool. Each …

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Axisymmetric Optical Membrane Modeling Based On Experimental Results, Brian J. Lutz Mar 2004

Axisymmetric Optical Membrane Modeling Based On Experimental Results, Brian J. Lutz

Theses and Dissertations

The United States Air Force, Department of Defense and commercial industry have recognized the great value of near-earth space development, specifically in satellites for use in communications, ground and space surveillance and more active roles. However, resolution, or the primary optic’s diameter, has been a limitation, especially for ground surveillance. Deployable optics has been investigated to allow larger optics in space and membrane optics has received increasing attention recently. The membrane’s flexible nature requires some passive and possibly active control to reduce optical distortion caused by manufacturing, deployment, or other effects during use. Piezoelectric surface controllers are one option to …

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Experimental And Computational Analysis Of Modes In A Partially Constrained Plate, Robert M. Vandawaker Mar 2004

Experimental And Computational Analysis Of Modes In A Partially Constrained Plate, Robert M. Vandawaker

Theses and Dissertations

The field of structural health monitoring (SHM) attempts to reduce labor and cost by allowing technicians to monitor selected properties of an aircraft's structure to detect impending failure. This research examines methods to detect damage to a thermal protection system (TPS) tile using representative 2024-T3 aluminum plates. Plates are subjected to modal analysis in single and joined conditions in an attempt to provide the capability of sensing damage to a tile on the surface of a vehicle while the sensors remain on the superstructure of the airframe. Jointly, the development of a means to model the system using finite element …

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