Engineering Commons^™

An Invariance Transformation Algorithm For Defect Characterization Of Ultrasonic Signals For The Nondestructive Evaluation Of Concrete, Michael Dominic Ciocco

Theses and Dissertations

Nondestructive evaluation (NDE) techniques offer cost-effective strategies for monitoring the integrity of a variety of civil infrastructure, such as natural gas and sewer pipelines, without the need to take the system off-line. However, interpretation of NDE signals in terms of the location, size, and shape of underlying flaws in the material being inspected is fraught with difficulty. Typically, variations in the testing signal due to operational parameters have created a significant challenge for defect characterization. This thesis proposes, develops, and validates a defect characterization algorithm that compensates for operational variables and maps the test signal to a visual defect profile. …

Automated Segmentation Of Radiodense Tissue In Digitized Mammograms Using A Constrained Neyman-Pearson Classifier, Jeremy Thomas Neyhart

Theses and Dissertations

Breast cancer is the second leading cause of cancer related mortality among American women. Mammography screening has emerged as a reliable non-invasive technique for early detection of breast cancer. The radiographic appearance of the female breast consists of radiolucent (dark) regions and radiodense (light) regions due to connective and epithelial tissue. It has been established that the percentage of radiodense tissue in a patient's breast can be used as a marker for predicting breast cancer risk. This thesis presents the design, development and validation of a novel automated algorithm for estimating the percentage of radiodense tissue in a digitized mammogram. …

Use Of Dimples To Suppress Boundary Layer Separation On A Low Pressure Turbine Blade, Kurt P. Rouser

Theses and Dissertations

Flow separation on a low pressure turbine blade is explored at Reynolds numbers of 25k, 45k and 100k. Experimental data is collected in a low-speed, draw-down wind tunnel using a cascade of eight Pak-B blades. Flow is examined from measurements of blade surface pressures, boundary layer parameters, exit velocities, and total pressure losses across the blade. Two recessed dimple shapes are assessed for suppressing flow separation and associated losses. One dimple is spherical, and the second is asymmetric, formed from a full dimple spanwise half-filled. A single row of each dimple shape is tested at 50%, 55% and 65% axial …

A Framework For Prognostics Reasoning, Thomas C. Clutz

Theses and Dissertations

The use of system data to make predictions about the future system state commonly known as prognostics is a rapidly developing field. Prognostics seeks to build on current diagnostic equipment capabilities for its predictive capability. Many military systems including the Joint Strike Fighter (JSF) are planning to include on-board prognostics systems to enhance system supportability and affordability. Current research efforts supporting these developments tend to focus on developing a prognostic tool for one specific system component. This dissertation research presents a comprehensive literature review of these developing research efforts. It also develops presents a mathematical model for the optimum allocation …

Development And Design Of Constant-Force Mechanisms, Brent Lewis Weight

Theses and Dissertations

This thesis adds to the knowledge base of constant-force mechanisms (CFMs). It begins by reviewing past work done in the area of CFMs and then develops new nondimensionalized parameters that are used to simplify the calculations required to design a CFM. Comparison techniques are then developed that utilize these non-dimensionalized parameters to compare mechanisms based on stiffnesses, percent constant-force, actual lengths, normal displacements, and feasible design orientations. These comparison techniques are then combined with optimization to define new mechanisms with improved performance and range of capabilities. This thesis also outlines a design process, methods to identify mechanisms that are suitable …

Electromagnetic Scattering From A Gap In A Magneto-Dielectric Coating On An Infinite Ground Plane, George R. Simpson

Theses and Dissertations

The electromagnetic scattering from a gap in a magneto-dielectric coating on an infinite ground plane is analyzed. In this context, the gap forms a break only in the magneto-dielectric slab coating while the ground plane is continuous and unbroken. Volume equivalence is used to convert the gap region to one containing unknown volumetric equivalent electric and magnetic currents. The equivalent problem then is one of these currents radiating in the presence of an unbroken grounded magneto-dielectric slab. A Green's function for this geometry is developed consisting of two terms: a direct coupling term and correction term to account for the …

An Evaluation Of Facility Maintenance And Repair Strategies Of Select Companies, Christopher L. Sharp

Theses and Dissertations

Although initial construction costs are high, the cost of operation and maintenance over a facilities life-cycle is significantly higher. A common challenge for facility maintenance professionals is balancing the cost of facility Maintenance and Repair (M&R) with the benefits derived from those facilities. This thesis documents how a selection of companies implemented that balance by determining their facilities requirements based on their chosen facility condition level and how they then allocated funds. The research effort consisted of interviews with facility maintenance professionals at each company selected. The data was then used to perform a multiple case study analysis and comparison …

Automatic Target Recognition Classification System Evaluation Methodology, Christopher Brian Bassham

Theses and Dissertations

This dissertation research makes contributions towards the evaluation of developing Automatic Target Recognition (ATR) technologies through the application of decision analysis (DA) techniques. ATR technology development decisions should rely not only on the measures of performance (MOPs) associated with a given ATR classification system (CS), but also on the expected measures of effectiveness (MOEs). The purpose of this research is to improve the decision-makers in the ATR Technology development. A decision analysis framework that allows decision-makers in the ATR community to synthesize the performance measures, costs, and characteristics of each ATR system with the preferences and values of both the …

Adaptive Harmonic Balance Method For Unsteady, Nonlinear, One-Dimensional Periodic Flows, Raymond C. Maple

Theses and Dissertations

A new adaptive split-domain harmonic balance computational fluid dynamics (CFD) method is developed to solve highly nonlinear time-periodic flows such as those found in turbomachinery. The basic harmonic balance CFD method transforms an unsteady time-periodic problem into a steady-state problem by assuming a solution in the form of a Fourier series in time. The new method employs a unique multi-domain split-operator solution technique to remove a large-series stability restriction present in previous harmonic balance CFD approaches. In addition, the new method adapts the frequency content to the flow, starting with a small number of Fourier frequencies and augmenting the frequency …

Congruent Weak Conformance, Ronald W. Brower

Theses and Dissertations

This research addresses the problem of verifying implementations against specifications through an innovative logic approach. Congruent weak conformance, a formal relationship between agents and specifications, has been developed and proven to be a congruent partial order. This property arises from a set of relations called weak conformations. The largest, called weak conformance, is analogous to Milner's observational equivalence. Weak conformance is not an equivalence, however, but rather an ordering relation among processes. Weak conformance allows behaviors in the implementation that are unreachable in the specification. Furthermore, it exploits output concurrencies and allows interleaving of extraneous output actions in the implementation. …

Mean Performance Optimization Of An Orbiting Distributed Aperture By Warped Aperture Image Plane Comparisons, Timothy W. Parker

Theses and Dissertations

This work models the aggregate performance of satellite receiver formations functioning as orbiting interferometers as compared to filled apertures of similar geometries. These models facilitate selecting initial conditions for formations such that their control-free dynamics yield interferometry performance with minimal errors as compared to the filled apertures. The solution method draws on the dynamic models of an orbiting planar satellite formation to define the size and shape of a reference aperture and to define the degrees of freedom for the formation members. The paths of formation elements yield geometries for which the aggregate performance of the array of discrete receivers …

Analysis For Cooperative Behavior Effectiveness Of Autonomous Wide Area Search Munitions, Sang M. Park

Theses and Dissertations

The purpose of this study is to investigate how a simulation model can accurately represent the performance of the autonomous wide area search munitions, and to find the effectiveness of the cooperative behavior on the autonomous munitions. Though it does not provide a practical solution for the development of the autonomous wide area search munitions, this research will show some meaningful allocations of the munitions tasks that are applicable to the development of the autonomous munitions. For the first phase, this thesis presents how accurately a simplified simulation model can represent a proposed weapon system by comparing the simulation results …

A Combined Adaptive Tabu Search And Set Partitioning Approach For The Crew Scheduling Problem With An Air Tanker Crew Application, Todd E. Combs

Theses and Dissertations

This research develops the first metaheuristic approach to the complete air crew scheduling problem. It develops the first dynamic, integrated, set-partitioning based vocabulary scheme for metaheuristic search. Since no benchmark flight schedules exist for the tanker crew scheduling problem, this research defines and develops a Java™ based flight schedule generator. The robustness of the tabu search algorithms is judged by testing them using designed experiments. An integer program is developed to calculate lower bounds for the tanker crew scheduling problem objectives and to measure the overall quality of solutions produced by the developed algorithms.

Multicast Routing Algorithms And Failure Analyses For Low Earth Orbit Satellite Communication Networks, Jae Soong Lee

Theses and Dissertations

In the rapidly changing environment of mobile communications, the importance of the mobile satellite (e,g,, low earth orbit satellites (LEOsats)) networks will increase due to their global visibility and connection. Multicasting is an effective communication method in terms of frequency spectrum usage for a LEO network. It is devised to provide lower network traffic (i,e,, one-to-many transmissions). This research examines the system performance of two dissimilar terrestrially-based multicasting protocols: the Distance Vector Multicast Routing Protocol (DVMRP) and the On Demand Multicast Routing Protocol (ODMRP). These two protocols are simulated in large group membership density and in the presence of satellite …

Modification Of All-Hexadedral Finite Element Meshes By Dual Sheet Insertion And Extraction, Michael J. Borden

Theses and Dissertations

The development of algorithms that effectively modify all-hexahedral finite element mesh is currently an active area of research. Mesh modification can be used to improve mesh quality reduce the time required to mesh a model, and improve the finite element analysis results. However, general modification of all-hexahedral meshes has proven difficult because of the global effects of local modifications. This thesis explains the global constraints on modifying all-hexahedral meshes and then presents three mesh modification techniques that make it possible to do local modifications while accounting for the global effects. These techniques are sheet insertion, sheet extraction, and mesh cutting. …

Robustness Of Multiple Objective Decision Analysis Preference Functions, William K. Klimack

Theses and Dissertations

This research investigated value and utility functions in multiobjective decision analysis to examine the relationship between them in a military decision making context. The impact of these differences was examined to improve implementation efficiency. The robustness of the decision model was examined with respect to the preference functions to reduce the time burden imposed on the decision maker. Data for decision making in a military context supports the distinction between value and utility functions. Relationships between value and utility functions and risk attitudes were found to be complex. Elicitation error was significantly smaller than the difference between value and utility …

Airborne Radar Interference Suppression Using Adaptive Three-Dimensional Techniques, Todd B. Hale

Theses and Dissertations

This research advances adaptive interference suppression techniques for airborne radar, addressing the problem of target detection within severe interference environments characterized by high ground clutter levels, levels, noise jammer infiltration, and strong discrete interferers. Two-dimensional (2D) Space-Time Adaptive Processing (STAP) concepts are extended into three-dimensions (3D) by casting each major 2D STAP research area into a 3D framework. The work first develops an appropriate 3D data model with provisions for range ambiguous clutter returns. Adaptive 3D development begins with two factored approaches, 3D Factored Time-Space (3D-FTS) and Elevation-Joint Domain Localized (Elev-JDL). The 3D adaptive development continues with optimal techniques, i.e., …

Elasticity In Microstructure Sensitive Design Through The Use Of Hill Bounds, Benjamin L. Henrie

Theses and Dissertations

In engineering, materials are often assumed to be homogeneous and isotropic; in actuality, material properties do change with sample direction and location. This variation is due to the anisotropy of the individual grains and their spatial distribution in the material. Currently there is a lack of communication between the design engineer, material scientist, and processor for solving multi-objective/constrained designs. If communication existed between these groups then materials could be designed for applications, instead of the reverse. Microstructure sensitive design introduces a common language, a spectral representation, where both design properties and microstructures are expressed.

Using Hill bounds, effective elastic properties …

Characterization Of Structural Changes In Thermally Enhanced Kevlar-29® Fiber, James W. Downing Jr.

Theses and Dissertations

The purpose of this exploratory investigation was to elucidate the structural mechanism accounting for the enhanced compressive properties of heat-treated Kevlar-29® fibers. A novel theory was set forth that hydrogen bond disruption and concurrent misorientation of crystallites may account for the observed augmentation of compressive properties. To examine the said theory, virgin Kevlar-29® fibers were characterized by Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC) in an effort to determine if crosslinking and/or hydrogen bond disruption was responsible for the improved behavior in compression. Additionally, Kevlar-29® fibers that had been exposed to treatment temperatures of 400, 440, and 470 °C …

A Novel Membrane Process For Autotrophic Denitrification, Agnieszka Pierkiel

Theses and Dissertations

This research focused on the novel use of hollow fiber membranes for gas delivery in biological dentrification using hydrogen-oxidizing bacteria. Autotrophic denitrification is a biological process that reduces nitrate to nitrogen gas using an inorganic carbon source. Hydrogen gas is an electron donor and nitrate is the electron acceptor in the reaction. The specific research objectives were to:

• develop a mixed acclimated culture of hydrogen-oxidizing bacteria;
• evaluate biodegradation kinetics of the acclimated culture;
• evaluate hydrogen transfer characteristics of hollow fiber membrane modules;

and

• demonstrate technical feasibility of a continuous bioreactor-membrane system for denitrification.

The following kinetic coefficients were obtained: µ …

Characterization Of Residual Stress In Microelectromechanical Systems (Mems) Devices Using Raman Spectroscopy, Lavern A. Starman

Theses and Dissertations

Due to the small scale of MEMS devices, the inherent residual stresses during the deposition processes can affect the functionality and reliability of the fabricated devices. Residual stress often causes device failure due to curling, buckling, or fracture. Currently, few techniques are available to measure the residual stress in MEMS devices. In this dissertation, Raman spectroscopy is used to measure and monitor the residual and induced stresses in MUMPs polysilicon MEMS devices. Raman spectroscopy was selected since it is nondestructive, fast, and provides potential in situ stress monitoring. Raman spectroscopy scans on unreleased and released MEMS fixed-fixed beams, cantilevers, and …

Surfacing Splicing: A Method Of Quadrilateral Mesh Generation And Modification For Surfaces By Dual Creation And Manipulation, Benjamin Todd Grover

Theses and Dissertations

The effective generation high quality quadrilateral surface meshes is an area of important research and development for the finite element community. Quadrilateral elements generally lead to more efficient and accurate finite results. In addition, some all hexahedral volume meshing algorithms are based on an initial quadrilateral mesh surface mesh that has specific connectivity requirements. This thesis presents a new and unique procedure named "Surfaced Splicing". Surface Splicing allows for the generation of all quadrilateral surface meshes as well as the ability to edit these meshes via the dual. The dual contains the same data as the mesh but, unlike the …

Effects Of Shot-Peening On High Cycle Fretting Fatigue Behavior Of Ti-6al-4v, Halil I. Yuksel

Theses and Dissertations

Effects of Shot-peening on High Cycle Fretting Fatigue behavior of Ti-6Al-4V were investigated. Experiments were performed with 6.35 mm thick specimens which provided S/N curves. After the tests, it was observed that the specimens failed near the trailing edge of contact. Scanning Electron Microscopy showed that cracks initiated on the contact surface for 6.35 mm, and at the depth of specimen ranging from 200 to 300 microns for 3.81 mm thick specimens. Initial crack orientation was around 37 and 42 degrees respectively for 6.35 and 3.81 mm thicknesses. Finite Element Analysis (FEA) was conducted, and using FEA results, Smith-Watson-Topper, Findley, …

Fabrication Techniques For Iii-V Micro-Opto-Electro-Mechanical Systems, Jeremy A. Raley

Theses and Dissertations

This thesis studies selective etching techniques for the development of Al_xGa_1-xAs micro-opto-electro-mechanical systems (MOEMS). New MEMS technology based on materials such as Al_xGa_1-xAs enables the development of micro-systems with embedded active micro-optical devices. Tunable micro-lasers and optical switching based on MOEMS technology will improve future wavelength division multiplexing (WDM) systems. WDM vastly increases the speed of military communications and sensor data processing. From my designs, structures are prepared by molecular beam epitaxy. I design a mask set for studies of crystal plane selectivity. I perform a series of experiments on the selective …

Design Study Of Triggered Isomer Heat Exchanger-Combustion Hybrid Jet Engine For High Altitude Flight, Christopher E. Hamilton

Theses and Dissertations

This study investigated the possibility of utilizing a Triggered Isomer Heat Exchanger (TIHE) within a conventional jet engine in order to increase the endurance of a High Altitude Long Endurance (HALE) Intelligence, Surveillance, and Reconnaissance (ISR) aircraft. Optimizations of the conventional and TIHE engines along with selection of a switchover flight condition, where the aircraft switches from combustion to TIHE operations, were made utilizing engine design and mission analysis software. Radiation shield weights were determined utilizing point source gamma ray shielding methods. The jet engine best suited for the hybrid use, where both combustion and TIHE components located in a …

Issues In Modeling Military Space, Peter F. Olsen

Theses and Dissertations

Fighter Pilots students undertake an intense 120-day training program. New classes of students enter the training program at regular interval. Students endured rigorous academic, simulator, and aircraft training throughout the program. Squadron schedulers ensure the multiple classes and students are scheduled for the activities. Simulator and aircraft training are scheduled individual for each student. Academic training are taught to the class. Aircraft utilization must also be considered. Aircraft Sortie training are also constrained by daylight hours. Additionally, students are limited to a maximum of three training events in a given day. Squadron schedulers must balance these requirements to ensure students …

Evaluation And Analysis Of Array Antennas For Passive Coherent Location (Pcl) Systems, Baris Calikoglu

Theses and Dissertations

Passive Coherent Location (PCL) systems use a special form of a radar receiver that exploits the ambient radiation in the environment to detect and track targets. Typical transmissions of opportunity that might be exploited include television and FM radiobroadcasts. PCL implies the use of a non-radar electromagnetic sources of illumination, such as commercial radio or television broadcasts also referred as transmitters of opportunity. The use of such illumination sources means that the receiver needs to process waveforms that are not designed for radar purposes. As a consequence, the receivers for PCL systems must be much more customized than traditional receivers, …

Analysis Of Ultra Wide Band (Uwb) Technology For An Indoor Geolocation And Physiological Monitoring System, Cengiz Alabacak

Theses and Dissertations

The goal of this research is to analyze the utility of UWB for indoor geolocation and to evaluate a prototype system, which will send information detailing a person’s position and physiological status to a command center. In a real world environment, geolocation and physiological status information needs to be sent to a command and control center that may be located several miles away from the operational environment. This research analyzes and characterizes the UWB signal in the various operational environments associated with indoor geolocation. Additionally, "typical usage scenarios" for the interaction between UWB and other devices are also tested and …

A Multiobjective Approach Applied To The Protein Structure Prediction Problem, Richard O. Day

Theses and Dissertations

Interest in discovering a methodology for solving the Protein Structure Prediction problem extends into many fields of study including biochemistry, medicine, biology, and numerous engineering and science disciplines. Experimental approaches, such as, x-ray crystallographic studies or solution Nuclear Magnetic Resonance Spectroscopy, to mathematical modeling, such as minimum energy models are used to solve this problem. Recently, Evolutionary Algorithm studies at the Air Force Institute of Technology include the following: Simple Genetic Algorithm (GA), messy GA, fast messy GA, and Linkage Learning GA, as approaches for potential protein energy minimization. Prepackaged software like GENOCOP, GENESIS, and mGA are in use to …

Compare And Complexity - When Is Compare Not Enough?, Chris E. Greiman

Theses and Dissertations

The purpose of this case study research is to determine the utility of COMPARE, the DoD approved software for conducting A-76 competitions, in the more complex world of public-private competition. COMPARE serves as the baseline for establishing cost factors, while two Air Force Depots are used as a basis of comparison. Research questions answered are: 1. What are the baseline cost comparison factors established in COMPARE? 2. What are the common cost factors found in the Air Force Depot public-private competitions? 3. What are the similarities and differences between the cost factors established in COMPARE and those used in the …