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Air Force Institute of Technology

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Articles 3991 - 4020 of 5699

Full-Text Articles in Engineering

An Interactive Decision Support System For Scheduling Fighter Pilot Training, Cuong T. Nguyen Mar 2002

An Interactive Decision Support System For Scheduling Fighter Pilot Training, Cuong T. Nguyen

Theses and Dissertations

The U.S. Air Force is developing Modular Aircraft Support System (MASS) program to replace the current Aerospace Ground Equipment (AGE). AGE supplies electricity, nitrogen, hydraulics and other support equipment to maintenance activities at the flight line. Current AGE makes up one-third of the deployment footprint. AGE is also mostly aircraft specific, and has reliability problems. The MASS alternative focuses on modularity based on a plug-and-play approach. The technological improvements and possible reduction in the footprint make MASS a good alternative. The AF has to determine now, whether MASS can supply similar functionality and decrease the deployment footprint to theater, while …

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Modeling And Analysis Of Multicommodity Network Flows Via Goal Programming, Matthew A. Scott Mar 2002

Modeling And Analysis Of Multicommodity Network Flows Via Goal Programming, Matthew A. Scott

Theses and Dissertations

In this research we focused on the mobility system modeled by the AMC mobility planner's calculator (AMPCALC). We developed AMPCALC as a user-friendly tool and allow the user to easily carry out strategic airlift, air refueling and aeromedical evacuation calculations that are covered in Air Force Pamphlet 10-1403. In this study, Excel software and its macro language, Visual Basic for Application, are our two main tools. In the methodology of the thesis we examined fundamental aspects of the mobility system in AMPCALC. We discussed formulation logic of the mobility cycle. We presented ramp use optimization and tanker optimization processes. We …

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Quicklook Air Mobility Modeling, Mustafa K. Pektas Mar 2002

Quicklook Air Mobility Modeling, Mustafa K. Pektas

Theses and Dissertations

This research is a framework for understanding issues in modeling the military aspect of space, with particular regard to capturing its value. Space power is a difficult and far-reaching topic, with implications that go beyond the military aspects. The United States military increasingly relies on space-based systems and information for success in daily operations. Telecommunications, navigation and timing, intelligence, surveillance, reconnaissance, and weather prediction are instances of services that have become dependent on satellite systems. If this reliance on space is not fully understood, U.S. national security will be at risk as the result of space information degradation or denial. …

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Commercial Regional Space/Airborne Imaging, Ugur Akyazi, Ali Durmus, Birce Boga Bakirli, Arif Arin Mar 2002

Commercial Regional Space/Airborne Imaging, Ugur Akyazi, Ali Durmus, Birce Boga Bakirli, Arif Arin

Theses and Dissertations

In this work goal programming is used to solve a minimum cost multicommodity network flow problem with multiple goals. A single telecommunication network with multiple commodities (e.g., voice, video, data, etc.) flowing over it is analyzed. This network consists of: linear objective function, linear cost arcs, fixed capacities, specific origin-destination pairs for each commodity. A multicommodity network flow problem with goals can be successfully modeled using linear goal programming techniques. When properly modeled, network flow techniques may be employed to exploit the pure network structure of a multicommodity network flow problem with goals. Lagrangian relaxation captures the essence of the …

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Laser Intensity Scaling Through Stimulated Scattering In Optical Fibers, Timothy H. Russell Dec 2001

Laser Intensity Scaling Through Stimulated Scattering In Optical Fibers, Timothy H. Russell

Theses and Dissertations

The influence of stimulated scattering on laser intensity in fiber optic waveguides is examined. Stimulated Brillouin scattering (SBS) in long, multimode optical waveguides is found to generate a Stokes beam that propagates in the fiber LP01 mode. Additionally, the same process is found to combine multiple laser beams into a single spatially coherent source. Limitations in beam cleanup and combining are also investigated to identify ways to overcome them. The last portion of the dissertation theoretically examines suppression of stimulated Raman scattering in fibers to eliminate the restriction this imposes on the power of a fiber laser or amplifier. The …

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Air Vehicle Path Planning, Jeffrey M. Hebert Dec 2001

Air Vehicle Path Planning, Jeffrey M. Hebert

Theses and Dissertations

This dissertation explores optimal path planning for air vehicles. An air vehicle exposed to illumination by a tracking radar is considered and the problem of determining an optimal planar trajectory connecting two prespecified points is addressed. An analytic solution yielding the trajectory minimizing the received radar energy reflected from the target is derived using the Calculus of Variations. Additionally, the related problem of an air vehicle tracked by a passive sensor is also solved. Using the insights gained from the single air vehicle radar exposure minimization problem, a hierarchical cooperative control law is formulated to determine the optimal trajectories that …

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Nonlinear Suppression Of Range Ambiguity In Pulse Doppler Radar, Jon M. Anderson Dec 2001

Nonlinear Suppression Of Range Ambiguity In Pulse Doppler Radar, Jon M. Anderson

Theses and Dissertations

Coherent pulse train processing is most commonly used in airborne pulse Doppler radar, achieving adequate transmitter/receiver isolation and excellent resolution properties while inherently inducing ambiguities in Doppler and range. First introduced by Palermo in 1962 using two conjugate LFM pulses, the primary nonlinear suppression objective involves reducing range ambiguity, given the waveform is nominally unambiguous in Doppler, by using interpulse and intrapulse coding (pulse compression) to discriminate received ambiguous pulse responses. By introducing a nonlinear operation on compressed (undesired) pulse responses within individual channels, ambiguous energy levels are reduced in channel outputs. This research expands the NLS concept using discrete …

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Reduced Order Modeling For High Speed Flows With Moving Shocks, David J. Lucia Dec 2001

Reduced Order Modeling For High Speed Flows With Moving Shocks, David J. Lucia

Theses and Dissertations

The use of Proper Orthogonal Decomposition (POD) for reduced order modeling (ROM) of fluid problems is extended to high-speed compressible fluid flows. The challenge in using POD for high-speed flows is presented by the presence of moving discontinuities in the flow field. To overcome these difficulties, a domain decomposition approach is developed that isolates the region containing the moving shock wave for special treatment. The domain decomposition implementation produces internal boundaries between the various domain sections. The domains are linked using optimization-based solvers which employ constraints to ensure smoothness in overlapping portions of the internal boundary. This approach is applied …

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Modeling And Analysis Of Social Networks, Robert S. Renfro Ii Dec 2001

Modeling And Analysis Of Social Networks, Robert S. Renfro Ii

Theses and Dissertations

This dissertation develops new methods for the modeling and analysis of social networks. Social networks describe the complex relationships of individuals and groups in multiple overlapping contexts. Influence in a social network impacts behavior and decision making in every setting in which individuals participate. This study defines a methodology for modeling and analyzing this complex behavior using a Flow-Model representation. Multiple objectives in an influencing effort targeted at a social network are modeled using Goal Programming. Value Focused Thinking is applied to model influence and predict decisions based on the reaction of the psychological state of individuals to environmental stimuli. …

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Electrical Activation Studies Of Ion Implanted Gallium Nitride, James A. Fellows Nov 2001

Electrical Activation Studies Of Ion Implanted Gallium Nitride, James A. Fellows

Theses and Dissertations

A comprehensive and systematic electrical activation study of Si-implanted GaN was performed as a function of ion implantation dose, anneal temperature, and implantation temperature. Additionally, Mg-implanted GaN was also investigated. Temperature-dependent Hall effect measurements and photoluminescence (PL) spectra were used to characterize the samples. GaN wafers capped with AlN were implanted with Si ions at doses ranging from 1x1013 to 5x1015 cm-2 and annealed from 1050 to 1350 °C. The optimum anneal temperature for samples implanted with the higher Si doses is around 1350 °C, exhibiting nearly 100% electrical activation efficiency. Exceptional mobilities and carrier concentrations were …

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Modeling Axisymmetric Optical Precision Piezoelectric Membranes, James W. Rogers Jr. Oct 2001

Modeling Axisymmetric Optical Precision Piezoelectric Membranes, James W. Rogers Jr.

Theses and Dissertations

The US Department of Defense (DOD), as well as the National Aeronautics and Astronautics Administration (NASA) and the Jet Propulsion Laboratory (JPL) are interested in developing and deploying precise, compliant, light-weight, space-based structures. More specifically, the Air Force’s core competencies ‘Aerospace Superiority’ and ‘Information Superiority’ demand ever-increasing depth and breadth of capability. Whether used for energy transmission or optical reconnaissance, current launch restraints limit rigid space-based optical reflector size. To support this requirement, the Air Force Research Laboratory (AFRL) is developing a large space-based optical membrane telescope. Inflatable reflectors can conceptually break this barrier, but controlling such a compliant structure …

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Techniques For Reduced Order Modeling Of Aeroelastic Structures With Deforming Grids, John S. R. Anttonen Oct 2001

Techniques For Reduced Order Modeling Of Aeroelastic Structures With Deforming Grids, John S. R. Anttonen

Theses and Dissertations

Reduced order modeling (ROM) seeks to make the modeling of aeroelastic behavior practical by reducing computation time for design codes. Deforming grids are often used in aeroelastic problems to account for the deformation of the structure. Proper Orthogonal Decomposition (POD/ROM) is a ROM technique that operates in an index-space for computations, not accounting for changes in grid dynamics, and must be modified to reflect grid deformation properly. To investigate and account for the effects of grid deformation on POD/ROM, a new algorithm is developed that incorporates modifications to the usual formulation. Evaluation of the new algorithm is accomplished through application …

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Length Selectable, Hardware Efficient Pseudorandom Code Generator, John F. Brendle Jr., James P. Stephens Sr., Michael A. Temple, Robert S. Parks Sep 2001

Length Selectable, Hardware Efficient Pseudorandom Code Generator, John F. Brendle Jr., James P. Stephens Sr., Michael A. Temple, Robert S. Parks

AFIT Patents

A method and device for generating a pseudorandom electrical signal for enabling spread spectrum communication scrambling by directing data entry into pseudorandom number generator integrated circuit chip controlling registers using a length selectable feedback logic data sequence and either computer programmable selector means or manual selector means to communicate the logic data sequence characters to buffers. The logic data sequence characters are clocked to a pseudorandom number generating register of an integrated circuit chip and the pseudorandom electrical signal is generated by selectively tapping a signal code therefrom. The method and device features a pseudorandom electrical signal length varying capability …

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A Decomposition Approach For The Multi-Modal, Resource-Constrained, Multi-Project Scheduling Problem With Generalized Precedence And Expediting Resources, Michael L. Fredley Sep 2001

A Decomposition Approach For The Multi-Modal, Resource-Constrained, Multi-Project Scheduling Problem With Generalized Precedence And Expediting Resources, Michael L. Fredley

Theses and Dissertations

The field of project scheduling has received a great deal of study for many years with a steady evolution of problem complexity and solution methodologies. As solution methodologies and technologies improve, increasingly complex, real-world problems are addressed, presenting researchers a continuing challenge to find ever more effective means for approaching project scheduling. This dissertation introduces a project scheduling problem which is applicable across a broad spectrum of real-world situations. The problem is based on the well-known Resource-Constrained Project Scheduling Problem, extended to include multiple modes, generalized precedence, and expediting resources. The problem is further extended to include multiple projects which …

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Theater-Level Stochastic Air-To-Air Engagement Modeling Via Event Occurrence Networks Using Piecewise Polynomial Approximation, David R. Denhard Sep 2001

Theater-Level Stochastic Air-To-Air Engagement Modeling Via Event Occurrence Networks Using Piecewise Polynomial Approximation, David R. Denhard

Theses and Dissertations

This dissertation investigates a stochastic network formulation termed an event occurrence network (EON). EONs are graphical representations of the superposition of several terminating counting processes. An EON arc represents the occurrence of an event from a group of (sequential) events before the occurrence of events from other event groupings. Events between groups occur independently, but events within a group occur sequentially. A set of arcs leaving a node is a set of competing events, which are probabilistically resolved by order relations. An important EON metric is the probability of being at a particular node or set of nodes at time …

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Microcavity Surface Emitting Laser, Stewart Feld, John P. Loehr, James A. Lott Jul 2001

Microcavity Surface Emitting Laser, Stewart Feld, John P. Loehr, James A. Lott

AFIT Patents

A three-dimensional waveguiding structure for a microcavity surface-emitting laser is described in which native aluminum oxide layers provide control of intracavity waveguiding and the laser optical mode structure of the emitted beam. Microcavity lasers described herein account for the blueshift of the emission wavelength as the laser lateral dimensions are reduced to or below the emission wavelength.

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Apparatus And Method For Two Stage Hybrid Space-Time Adaptive Processing In Radar And Communication Systems, Todd B. Hale, Michael C. Wicks, Raviraj S. Adve Jun 2001

Apparatus And Method For Two Stage Hybrid Space-Time Adaptive Processing In Radar And Communication Systems, Todd B. Hale, Michael C. Wicks, Raviraj S. Adve

AFIT Patents

A Two-Stage Hybrid algorithm offers significant improvement in the false alarm rate and detection performance of Space-Time Adaptive Processing in non-homogeneous environments for both radar and digital communications. The first stage analyzes data from a range cell of interest by direct data domain processing, suppressing discrete interferers within the range cell of interest. The second stage implements a purely statistical STAP algorithm, preferably an enhanced version of the Joint-Domain Localized ("JDL") statistical algorithm. For radar this second stage estimates the interference within the range cell of interest from the surrounding range cells. For a communications system, the second stage estimates …

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Single-Sided Noninvasive Inspection Of Multielement Sample Using Fan-Beam Multiplexed Compton Scatter Tomography, Matthew A. Lange Jun 2001

Single-Sided Noninvasive Inspection Of Multielement Sample Using Fan-Beam Multiplexed Compton Scatter Tomography, Matthew A. Lange

Theses and Dissertations

As aircraft age, corrosion forms upon unobservable surfaces, particularly at the junction of the sheet aluminum and the steel rivets used to attach the sheets to the airframe, degrading the aircraft s airworthiness. Previous research developed a noninvasive technique for the evaluation of the material composition of aluminum surfaces, utilizing the information encoded in the energy spectra of Compton-scattered gamma emissions. The spectra are gathered by a six-element, high purity germanium detector array. A, first principles, deterministic computer code is used to reconstruct a two-dimensional map of the electron density of aluminum samples. Previous efforts, to image pure aluminum samples, …

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Time-Resolved Photoluminescence Of Inas/Gainsb Quantum Well Lasers, Michael R. Mckay Jun 2001

Time-Resolved Photoluminescence Of Inas/Gainsb Quantum Well Lasers, Michael R. Mckay

Theses and Dissertations

In the world of semiconductor photonic device fabrication, one important objective may be to extract as much light as possible from the device. In these devices, photons are created when electrons recombine with holes by transitioning from a high-energy state to a lower one. Unfortunately, electron-hole recombination does not always result in the formation of a photon. There are three basic types of recombination: the first results in the formation of a photon and is called radiative recombination; and the second and third, known as Shockley-Read-Hall and Auger recombination, result in the heating of the device and do not produce …

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Adaptive And Reconfigurable Flight Control, Yih Shiun Huang Mar 2001

Adaptive And Reconfigurable Flight Control, Yih Shiun Huang

Theses and Dissertations

An indirect adaptive and reconfigurable flight control system is developed. The three-module controller consists of: (1) a system identification module, (2) a parameter estimate smoother, and (3) a proportional and integral compensator for tracking control. Specifically: (1) The identification of a linear discrete-time control system's open-loop gain is addressed. The classical Kalman filter theory for linear control systems is extended and the control system's state and loop gain are jointly estimated on-line. Explicit formulae for the loop gain's estimate and estimation error covariance are derived. The estimate is unbiased and the predicted covariance is reliable. (2) An adaptive smoother is …

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Influence Of Feedback And Comment Labels On Information Sharing In A Computer Mediated Collaborative Environment, Gary D. Denney Mar 2001

Influence Of Feedback And Comment Labels On Information Sharing In A Computer Mediated Collaborative Environment, Gary D. Denney

Theses and Dissertations

A group support system (GSS) uses a combination of networked personal computers, software, and human facilitation to improve the group decision-making process. Group support Systems are being used in the Air Force today in a variety of capacities and in particular by the Warner-Robins Air Logistics Center (WR-ALC) to assess acquisition risks. Prior GSS research has found that certain structural and social dimensions of GSS designs might influence whether optimal process improvements take place. However, the dimensions that positively influence group performance have continued to be a matter of debate. This thesis looked at several structural and social contingencies to …

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Turbine Blade Surface Roughness Effects On Shear Drag And Heat Transfer, Jess W. Drab Mar 2001

Turbine Blade Surface Roughness Effects On Shear Drag And Heat Transfer, Jess W. Drab

Theses and Dissertations

This work used scaled samples of actual turbine blade surfaces to characterize correlations between turbine surface roughness, friction coefficient, and convective heat transfer rate-parameters which affect an engine's efficiency and the blade's lifespan. For erosion/deposits, friction coefficients up to 250 times higher and convective heat transfer coefficients of up to 150 times higher were found when compared to a flat plate baseline. Other roughness types (pitting and fuel deposits) yielded less dramatic results. These results did not follow existing friction coefficient-to-heat transfer coefficient correlations, such as the Reynolds analogy. While these analytical and empirical correlations hold for flat plates, they …

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Multiple Model Adaptive Estimation For Time Series Analysis, Ibrahim Dulger Mar 2001

Multiple Model Adaptive Estimation For Time Series Analysis, Ibrahim Dulger

Theses and Dissertations

Multiple Model Adaptive Estimation (MMAE) is a Bayesian technique that applies a bank of Kalman filters to predict future observations. Each Kalman filter is based on a different set of parameters and hence produces different residuals. The likelihood of each Kalman filter's prediction is determined by a magnitude of the residuals. Since some researchers have obtained good forecasts using a single Kalman filter, we tested MMAE's ability to make time series predictions. Our Kalman filters have a dynamics model based on a Box-Jenkins Auto-Regressive Moving Average (ARMA) model and a measure model with additive noise. The time-series prediction is based …

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The Effect Of External Safeguards On Human-Information System Trust In An Information Warfare Environment, Gregory S. Fields Mar 2001

The Effect Of External Safeguards On Human-Information System Trust In An Information Warfare Environment, Gregory S. Fields

Theses and Dissertations

This research looks at how human trust in an information system is influenced by external safeguards in an Information Warfare (1W) domain. Information systems are relied upon in command and control environments to provide fast and reliable information to the decision-makers. The degree of reliance placed in these systems by the decision-makers suggests a significant level of trust. Understanding this trust relationship and what effects it is the focus of this study. A model is proposed that predicts behavior associated with human trust in information systems. It is hypothesized that a decision-maker's belief in the effectiveness of external safeguards will …

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Quality Initiatives In The Air Force Development Of Reusable Launch Vehicles, Charles S. Galbreath Mar 2001

Quality Initiatives In The Air Force Development Of Reusable Launch Vehicles, Charles S. Galbreath

Theses and Dissertations

This thesis identifies useful tools and techniques available to aid the Air Force development of a reusable launch vehicle (RLV). These tools are identified by comparing traits found within the Lean Aerospace Initiative, Six Sigma and systems engineering. While identified specifically for the RLV effort, these tools and techniques will be of use to many development programs. Historical perspectives of both RLV development efforts within the Air Force and origins of modern quality teachings are provided to establish a common foundation of knowledge, upon which, further analysis can be conducted. This thesis, also, summarizes the current RLV effort within the …

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Evaluation Of Strategy-Structure Fit Of Space And Missile Systems Center Detachment 11, Tommy M. Gates Mar 2001

Evaluation Of Strategy-Structure Fit Of Space And Missile Systems Center Detachment 11, Tommy M. Gates

Theses and Dissertations

Activated June 1,1998, Space and Missile Systems Center Detachment 11, located in Colorado Springs, integrates system support management for the Satellite Launch Control System (SLCS), MlLSTAR, the Defense Meteorological Support Program (DMSP), the Space Based Infrared System (SBlRSl, and the Global Positioning System (GPS). The Detachment performs operational software maintenance, satellite systems engineering, space testing and evaluation, and technology master planning. Contemporary management theory asserts that the appropriate match of strategy and structure determines an organization's level of performance. The Detachment is currently organized programmatically. The current programmatic organizational structure represents the physical manifestation of the Integrated Weapon System Management …

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Prediction Of Pilot Induced Oscillations (Pio) Due To Activator Rate Limiting Using The Open-Loop Onset Point (Olop) Criterion, Gregory P. Gilbreath Mar 2001

Prediction Of Pilot Induced Oscillations (Pio) Due To Activator Rate Limiting Using The Open-Loop Onset Point (Olop) Criterion, Gregory P. Gilbreath

Theses and Dissertations

Rate limiting has been a causal or contributing factor for Pilot Induced Oscillations (PIO). As part of the joint Air Force Institute of Technology/Test Pilot School (AFIT/TPS) program, an examination of the Open-Loop Onset Point (OLOP) criterion, developed by DLR German Aerospace, was conducted to see if it could predict PIO due to rate limiting and to evaluate its potential as a design tool. The criterion was applied to three previous flight test programs involving rate limiting. Findings from this analysis led to the HAVE OLOP flight test which was flown on the NF-16D Variable Stability In-flight Simulator Test Aircraft …

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An Objective Evaluation Of Four Sar Image Segmentation Algorithms, Jason B. Gregga Mar 2001

An Objective Evaluation Of Four Sar Image Segmentation Algorithms, Jason B. Gregga

Theses and Dissertations

Because of the large number of SAR images the Air Force generates and the dwindling number of available human analysts, automated methods must be developed. A key step towards automated SAR image analysis is image segmentation. There are many segmentation algorithms, but they have not been tested on a common set of images, and there are no standard test methods. This thesis evaluates four SAR image segmentation algorithms by running them on a common set of data and objectively comparing them to each other and to human segmentors. This objective comparison uses a multi-metric a approach with a set of …

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Cooperative Behavior Schemes For Improving The Effectiveness Of Autonomous Wide Area Search Munitions, Daniel P. Gillen Mar 2001

Cooperative Behavior Schemes For Improving The Effectiveness Of Autonomous Wide Area Search Munitions, Daniel P. Gillen

Theses and Dissertations

The problem being addressed is how to best find and engage an unknown number of targets in unknown locations using multiple autonomous wide area search munitions. In this research cooperative behavior is being investigated to improve the overall mission effectiveness. A simulation was used to emulate the behavior of autonomous wide area search munitions and measure their overall expected performance. This code was modified to incorporate the capability for cooperative engagement based on a parameterized decision rule. Using Design of Experiments and Response Surface Methodologies, the simulation was run to achieve optimal decision rule parameters for given scenarios and to …

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Control And Characterization Of Line-Addressable Micromirror Arrays, Harris J. Hall Mar 2001

Control And Characterization Of Line-Addressable Micromirror Arrays, Harris J. Hall

Theses and Dissertations

This research involved the design and implementation of a complete line-addressable control system for a 32x32 electrostatic piston-actuated micromirror array device. Line addressing reduces the number of control lines from N2 to 2N making it possible to design larger arrays and arrays with smaller element sizes. The system utilizes the electromechanical bi-stability of individual elements to bold arbitrary bi-stable phase patterns. The control system applies pulse width modulated (PWM) signals to the rows and columns of the micromirror array. Three modes of operation were conceived and built into the system. The first was the traditional signal scheme which requires …

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