Digital Commons Network^™

Modeling And Simulation Of Optical Characteristics Of Microelectromechanical Mirror Arrays, Peter C. Roberts

Theses and Dissertations

MEMS (Micro-Electro-Mechanical Systems) micromirror devices can be used to control the phase of a propagating light wavefront, and in particular to correct aberrations that may be present in the wavefront, due to either atmospheric turbulence or any other type of fixed or time and space varying aberrations. In order to shorten the design cycle of MEMS micromirror devices, computer software is developed to create, from MEMS micromirror device design data, a numerical model of the MEMS device. The model is then used to compute the far field diffraction pattern of a wavefront reflected from the device, and to predict the …

An Object-Oriented Discrete-Event Simulation System For Hierarchical Parallel Simulations, Kenneth W. Stauffer

Theses and Dissertations

The purpose of this research is to design and implement an object-oriented discrete-event simulation system which supports hierarchically constructed players in a parallel or distributed environment. This system design considers modularity and portability so additional modules may be implemented to experiment with new algorithms for both partitioning and synchronization. A simulation system which meets these requirements was partially implemented on an eight-node Intel Hypercube in C. A desired goal was to maintain the functionality of the existing BattleSim application. Test cases used measure the performance and correct operation of the new simulation architecture using a BattleSim subclass. Test results prove …

An Investigation Of Instantaneous Plume Rise From Rocket Exhaust, Paul F. Sand

Theses and Dissertations

Rocket launches at Vandenburg Air Force Base and Cape Canaveral Air Station produce exhaust clouds containing several toxic by-products, including HC1 and A12O3. These clouds rise to atmospheric stabilization heights, and then start dispersing and diffusing through the air. Upon reaching the ground, concentration levels of the toxins may present a human health risk. To predict these risks and concentration levels, range officials use a computer program titled the Rocket Effluent Exhaust Diffusion Model (REEDM). The version currently in use has been shown to underpredict the stabilization height of the exhaust cloud. This thesis examines the theory and algorithms used …

Interference Suppression For Spread Spectrum Signals Using Adaptive Beamforming And Adaptive Temporal Filter, Wonjin Park

Theses and Dissertations

Interference and jamming signals are a serious concern in an operational military communication environment. This thesis examines the utility and performance of combining adaptive temporal filtering with adaptive spatial filtering (i.e. adaptive beamforming) to improve the signal-to-jammer ratio (SJR) in the presence of narrowband and wideband interference. Adaptive temporal filters are used for narrowband interference suppression while adaptive beamforming is used to suppress wideband interference signals. A procedure is presented for the design and implementation of a linear constraints minimum variance generalized sidelobe canceler (LCMV-GSC) beamformer. The adaptive beamformer processes the desired signal with unity gain while simultaneously and adaptively …

Evaluation Of Design Tools For Rapid Prototyping Of Parallel Signal Processing Algorithms, James C. Savage

Theses and Dissertations

Digital signal processing (DSP) has become a popular method for handling not only signal processing, but communications, and control system applications. A DSP application of interest to the Air Force is high speed avionics processing. The real time computing requirements of avionics processing exceed the capabilities of current single chip DSP processors, and parallelization of multiple DSP processors is a solution to handle such requirements. Designing and implementing a parallel DSP algorithm has been a lengthy process often requiring different design tools and extensive programming experience. Through the use of integrated software development tools, rapid prototyping becomes possible by simulating …

Influence Of Tip Clearance On The Flowfield In A Compressor Cascade With A Moving Endwall, Richard J. Mcmullan

Theses and Dissertations

The effects of changing the blade tip clearances on the velocity and pressure flowfields within a compressor cascade were investigated in this experimental thesis. All moving endwall measurements were taken at a constant flow coefficient of 0.5 and tip clearances of 0.5, 1.0 and 2.0 percent chord. Hot-wire/film probes were used to determine the three-dimensional velocity vector components in various transverse planes - one upstream of the leading edges of the blades, three within the blade cascade and one downstream of the trailing edges of the blades. The transverse velocity vector plots showed a scraping of the tip leakage vortex …

Investigation Of Sorption Mass Transfer Models Using Synthetic Soils, Karla K. Mika

Theses and Dissertations

Grain-scale sorption mass transfer is an important process that must be considered when predicting clean-up time and choosing remediation techniques for subsurface hazardous waste contamination. Rate-limited sorption is responsible for the rebound effect, where remediated groundwater is recontaminated by desorption. Sorbed contaminants are not available for microbial degradation, and the desorption rate may govern the effectiveness of natural attenuation by biodegradation. Grain-scale sorption nonequilibrium is generally attributed to diffusive transport, either in SOM or in mineral micropores. Typically used sorption mass transfer models either fail to reproduce long-term slow desorption (first-order models), or are based on diffusion in assumed (often …

A Decision Support Model For Municipal Solid Waste Recycling At United States Air Force Installations, Gergory A. Williams

Theses and Dissertations

The United States Air Force requires each installation to operate a municipal solid waste recycling program. Two inherently conflicting objectives, waste material diversion and financial result, have been established for the program. Reducing landfill disposal is the primary objective, but the incentive for profit is strong because each installation can retain profits from the program. Installations can be divided into two distinct areas, commercial and residential, based on the waste stream composition and funding. Structuring of the recycling program is often done in an ad-hoc manner. A decision support model was developed to evaluate four methods for each area. The …

High-Pressure Oxidation Rates For Large Coal And Char Particles, James A. Mathias

Theses and Dissertations

The main objective of this study was to investigate the factors that influence the oxidation rate of large (five to eight millimeters in diameter) coal and char particles. To accomplish this, experiments were performed in which the gas temperature, gas velocity, particle size, partial pressure of oxygen, and total pressure were varied. The experiments were performed with the cantilever balance attachment and the high pressure controlled profile reactor.

Approximately 90 combustion experiments were performed with Pittsburgh, Utah Blind Canyon, and Wyodak-Anderson coal. These experiments were performed at atmospheric pressure with air and varied gas temperature, gas velocity, and particle size. …

Habitat Suitability Mapping Through Integration Of Multicriteria Evaluation Techniques With A Geographic Information System (Gis), Anthony A. Ference

Theses and Dissertations

The presence of an endangered species, the Pacific Pocket Mouse (PPM), in critical Marine Corps training areas aboard Camp Pendleton may adversely affect training activities that are crucial to meeting the Marine Corps' mission. Camp Pendleton must focus limited budgetary assets for live trapping surveys of the PPM in the areas of best habitat suitability and the purpose of this study was to develop a PPM habitat suitability map of Camp Pendleton. Suitability maps were developed by integrating expert opinion with the Camp Pendleton Geographic Information System (GIS) database.

Economic Valuation Of Air Force Environmental Resources: A Contingent Valuation Case Study, Timothy P. Haynie

Theses and Dissertations

The Air Force spends $1 billion each year to preserve, maintain, and restore environmental resources under its control (Budget of the United States Government, 1994). Assessing the benefit of this spending is a central issue in federal environmental management. As federal environmental management moves from a "clean it up at any cost" mentality to one which carefully considers the costs and benefits of spending, a fundamental question arises: What value of environmental resources does our environmental spending provide? As in any rational economic exchange benefits must exceed costs; the value of an environmental resource which benefits from public spending must …

Development Of A Basis For A Hazardous Materials And Waste Management System For Air Force Contingency Deployments, Christopher J. West

Theses and Dissertations

Increased awareness of the potential for adverse mission impact on deployments, recent experience on such deployments, and Air Force and Major Command interest establish the need for an integrated hazardous materials and waste management system for contingency environments. This research was focused toward establishing a basis for developing such a system. An intensive literature review was accomplished to justify the necessity of the research, characterize the contingency environment, review legal and regulatory requirements, review proper hazardous substance handling and processing procedures, and review existing and new material resources which may be employed in such a system. Further literature review led …

Multidisciplinary And Multiobjective Optimization In Conceptual Design For Mixed-Stream Turbofan Engines, Luc J. J. P. Nadon

Theses and Dissertations

Despite major advances in design tools such as engine cycle analysis software and computer aided design, conceptual gas turbine engine design is essentially a trial-and-error process based on the experience of engineers. Modern optimization concepts, such as multidisciplinary optimization (MDO), and multiobjective optimization (MOO), linked with sequential quadratic programming (SQP) methods and genetic algorithms (GA), were applied to the conceptual engine design process to automate the conceptual design phase. Robust integrated computer codes were created to find the optimal values of eight engine parameters in order to minimize fuel usage, aircraft cost and engine annulus area over a given mission. …

Experimental Investigation Of Transverse Supersonic Gaseous Injection Enhancement Into Supersonic Flow, Mark P. Wilson

Theses and Dissertations

In pursuit of more efficient and effective fuel-air mixing for a SCRAMJET combustor, this study was conducted to investigate relative near field enhancements of penetration and mixing of a discrete low-angled (25°) injected air jet into a supersonic (M=2.9) cross flow. The enhancements were achieved by injecting the transverse air jet parallel to the compression face of eight different ramp geometries. The jet-ramp interactions created collinear shock structures, baroclinic torque vorticity enhancement, ramp spillage enhanced vorticity, magnus effect penetration enhancement, and increased total pressure loss. Shadowgraph photography was used to identify the shock structures and interactions in the flow field. …

Performance Analysis Of A Liquid Metal Heat Pipe Space Shuttle Experiment, Timothy J. Dickinson

Theses and Dissertations

Future spacecraft technologies require advanced high-temperature thermal control systems. Liquid metal heat pipes are considered ideally suited for such applications. However, their behavior during microgravity operation is not yet understood. This study investigated liquid metal heat pipe performance in such an environment. Three stainless steel/potassium heat pipes were flown on space shuttle mission STS-77 in May 1996. The objectives of the experiment were characterization of the frozen startup and restart transients, comparison of flight and ground test data to establish a performance baseline for analytical model validation, and assessment of three different heat pipe designs. Heat pipe performance was characterized …

Application Of A Finite-Volume Time-Domain Maxwell Equation Solver To Three-Dimensional Objects, Frederick G. Harmon

Theses and Dissertations

Concurrent engineering approaches for the disciplines of computational fluid dynamics (CFD) and electromagnetics (CEM) are necessary for designing future high-performance, low-observable aircraft. A characteristic-based finite-volume time-domain (FVTD) computational algorithm, developed for CFD and now applied to CEM, is implemented to analyze the radar cross section (RCS) of two three-dimensional objects, the ogive and cone-sphere. The FVTD formulation implements a Monotone Upstream-Centered Scheme for Conservation Laws (MUSCL) algorithm for the flux evaluation and a Runge-Kutta multi-stage scheme for the time integration. Developmental FVTD work for the thesis focused on algorithm development to analyze scattering and obtain RCS data for closed-surface perfect …

Performance Analysis Of A Hartman Wavefront Sensor Used For Sensing Atmospheric Turbulence Statistics, Toby D. Reeves

Theses and Dissertations

Atmospheric turbulence parameters, such as Fried's coherence diameter, the outer scale of turbulence, and the turbulence power law, are related to the wavefront slope structure function (SSF). The SSF is defined as the second moment of the wavefront slope difference as a function of both time and position. Knowledge of the SSF allows turbulence parameters to be estimated. Hartmann wavefront sensor (H-WFS) slope measurements composed of both signal and noise, allow the SSF to be estimated by computing a mean square difference of H-WFS slope measurements. The quality of the SSF estimate is quantified by the signal-to-noise ratio (SNR) of …

Demonstrating Optical Aberration Correction With A Mems Micro-Mirror Device, Shaun R. Hick

Theses and Dissertations

This research conducted the first demonstrated use of a micro-electro-mechanical structure (MEMS) mirror array to correct a static optical aberration. A well-developed technique in adaptive optics imaging systems uses a deformable mirror to reflect the incident wave front to the imaging stage of the system. By matching the surface of the deformable mirror to the shape of the wave front phase distortion, the reflected wave front will be less aberrated before it is imaged. Typical adaptive optics systems use piezo-electric actuated deformable mirrors. This research used an electrostatically actuated, segmented mirror array, constructed by standard MEMS fabrication techniques, to investigate …

Evaluation Of Segmentation For Bone Structures In 3d Rendering Of Ultrasound Residual Limb Images, Min C. Baker

Theses and Dissertations

Prosthetists today widely practice manual socket fitting, which produces subjective, inconsistent results. To address this problem, the Computerized Anthropometry Research and Design (CARD) Laboratory is developing a computer-aided socket design system that acquires ultrasound datasets of an amputee's residual limb, creates a 3D model, and helps identify load- bearing and pressure-relief areas. This research project focuses on providing 3D visualization of a residual limb to support the CARD Laboratory's efforts. Creating the 3D model of the skin and two bone contours requires two major steps: segmentation to identify the objects of interest and a surface tracking algorithm to generate the …

Study Of Desorption Of Contaminant From Synthetic Soil, Kung-Fu Hwang

Theses and Dissertations

A better understanding of sorption and desorption processes could improve estimates of time and cost required for remedial activities, exposure times and health risk, and bioavailability. Conventional rate-limited sorption models do not accurately define the diffusion domain at the grain scale. Heyse (1994) proposed the multiple sites in series (MSS) model, which allows more general description of the geometry of the sorption domain than the classical spherical or discrete distributions. A version of this model was tested by deVenoge (1996). The model was able to accurately simulate sorption rate data, but could not estimate unique geometry parameters. This research is …

A Comparative Analysis Of Two Alternatives To Chemical Aircraft Paint Stripping, George P. Joyce Ii

Theses and Dissertations

The Air Force must periodically strip and paint its aircraft to prevent the damaging effects of corrosion. The paint removal process typically involves the use of toxic chemicals such as methylene chloride which are soon to be banned as a result of impending environmental regulations and increased costs associated with handling and disposing of such material. The Air Force must choose an alternative to methylene chloride chemical stripping which complies with environmental regulations and reduces costs. This thesis compares the life cycle costs and environmental impacts of two alternatives to chemical aircraft stripping. Plastic Media Blasting (PMB) and Modified Medium …

Modeling Plant Uptake Of Metal In Constructed Wetlands Supported By Experimentally Derived Uptake Rates, Michael B. Peake

Theses and Dissertations

Many communities and Air Force installations are using constructed wetlands to filter trace metals from their stormwater runoff. Constructed wetlands are attractive to industry for runoff mitigation because they are relatively cheap to build and operate and require little or no energy for operation. The purpose of this research project is to develop quantitative concepts for understanding the dynamics of metal uptake in constructed wetland plants by constructing a system dynamics model supported by experimental observation and offer environmental managers a tool to simulate, under a broad range of conditions, long term wetland exposure to stormwater runoff contaminated with trace …

Analysis Of Multimode Low-Probability-Of-Intercept (Lpi) Communications With Atmospheric Effects, Ala Ghordlo

Theses and Dissertations

This research expanded Low Probability of Intercept (LPI) communications analysis in two areas. First, multimode communication was included to account for ground to ground and air to ground links in addition to the standard air to air links traditionally used in LPI analysis. The propagation equations for the three modes of interest were derived and included in LPI analytic models in the form of a mode quality factor to account for multimode LPI scenarios. This new quality factor was used in studying several communication and interception link combinations. Variations due to differences between the communication and interception modes were presented …

Clustered Microcalcification Detection Using Optimized Difference Of Gaussians, Edward M. Ochoa

Theses and Dissertations

The objective of this thesis is to design an automated microcalcification detection system to be used as an aid in radiologic mammogram interpretation. This research proposes the following methodology for clustered microcalcification detection. First, preprocess the digitized film mammogram to reduce digitization noise. Second, spatially filter the image with a difference of Gaussians (DoG) kernel. To detect potential microcalcifications, segment the filtered image using global and local thresholding. Next, cluster and index these detections into regions of interest (ROIs). Identify ROIs on the digitized image (or hardcopy printout) for final radiologic diagnosis.

Requirements, Design, And Development Of A Rapidly Reconfigurable, Photo-Realistic, Virtual Cockpit Prototype, Terry A. Adams

Theses and Dissertations

The United States Air Force uses aircraft flight simulators for pilot training and mission rehearsal. They use a variety of simulators for this task ranging with prices ranging from $400,000 to $30,000,000. These simulators have specialized hardware that restricts reuse of their components and increases maintenance costs. Air Education and Training Command wants to reduce simulators cost and improve availability to the operational commands by supporting research in virtual reality flight simulators. This thesis looks at the development of a reconfigurable virtual cockpit in a distributed virtual environment that can be used for different aircraft as well as training scenarios. …

Optimization Of A Gps-Based Navigation Reference System, Jason B. Mckay

Theses and Dissertations

The development of increasingly accurate new aircraft navigation systems has caused the Air Force to develop a new Navigation Reference System to test them, called the Submeter Accuracy Reference System (SARS). The SARS is an inverted GPS system which consists of an array of GPS receivers on the ground and an airborne pseudolite mounted on the test aircraft. The SARS will provide a proof position estimate that is used to check the navigation system under test. Unfortunately, ground based inverted GPS systems tend to suffer from high geometric sensitivity to measurement errors. This research tackles the problem of optimizing the …

Mmae Detection Of Interference/Jamming And Spoofing In A Dpgs-Aided Inertial System, Nathan A. White

Theses and Dissertations

Previous research at AFIT has resulted in the development of a DGPS-aided INS-based precision landing system (PLS) capable of meeting the FAA precision requirements for instrument landings. The susceptibility of DGPS transmissions to interference/jamming and spoofing must be addressed before DGPS may be used in such a safety-of-flight critical role. This thesis applies multiple model adaptive estimation (MMAE) techniques to the problem of detecting and identifying interference/jamming and spoofing failures in the DGPS signal. Such an MMAE is composed of a bank of parallel filters, each hypothesizing a different failure status, along with an evaluation of the current probability of …

Model Predictive Control Of Aerospace Systems, Derek W. Ebdon

Theses and Dissertations

The primary objective of this thesis is to explore the fault tolerance capabilities of a state space formulation of MPC. Subsequent to a simulated control surface failure on the F-18 High Alpha Research Vehicle (HARV), the MPC controller will attempt to maintain stability and nominal performance while tracking a setpoint. Secondary objectives include studying the effect of data sample rate and MPC horizon lengths on system performance. These objectives will be accomplished using Matlab to develop the MPC controller and Simulink to demonstrate its effectiveness through simulation.

Independent Verification And Validation Of The Hazardous Material Cost Trade-Off Analysis Tool Developed By The Human Systems Center At Brooks Air Force Base, Thomas S. Choi

Theses and Dissertations

The Air Force realizes that the life cycle cost (LCC) associated with hazardous materials is a significant cost in the acquisition of major weapon systems. In trying to mitigate the growth of environmental LCC for future weapon systems, the Air Force has developed a tool called the Hazardous Material Cost Trade-off Analysis Tool (HAZMAT CTAT). The HAZMAT CTAT estimates the LCC for weapon system hazardous materials, so that intelligent decisions can be made in the early stages of the acquisition process. The problem with implementing this program into the acquisition process is that an independent computer model evaluation has never …

Residual Strength And Fatigue Characterization Of Scs-6/Ti-6-4, Sang-Myung Lee

Theses and Dissertations

Metal matrix composite have potential in a variety of aerospace applications, but they should be better understood before they can be employed. Despite the many studies that have contributed to characterizing the fatigue response of titanium alloy MMCs, few have researched the residual strength. The purpose of this study was to investigate the residual strength and the frequency effects on the residual strength of an unidirectional laminate of SCS-6/Ti-6-4, a titanium alloy matrix based composite under tension-tension, load-controlled conditions at elevated temperatures and different frequencies. Specimens were fatigued at frequencies of 1 and 0.01Hz, and at maximum stress of 900MPa …