Engineering Commons^™

Cold Flow Testing Of A Modified Subscale Model Exhaust System For A Space Based Laser, David B. Jarrett

Theses and Dissertations

The aim of this research was a continued study of gas-dynamic phenomena that occurred in a set of stacked nozzles as reported by Captains Ian Bautista in 2003 and Scott Bergren in 2002. The arrangement of the stacked nozzles was a modified version of a 1/5th scale-model of one quadrant of the conceptual Space Based Laser Integrated Flight Experiment (SBL IFX) gas dynamic laser. Rather than cylindrical rings of nozzles, the stacked nozzles were flat and able to be rotated about a vector normal to the nozzle exits. This set of stacked flat nozzles was installed on a blow-down/vacuum wind …

Fretting Fatigue Behavior Of Shot-Peened Titanium Alloy Tl-6al-4v Under Seawater Conditions, William Y. Allen

Theses and Dissertations

The fretting fatigue behavior of the shot-peened titanium alloy, Ti-6Al-4V, was investigated under a corrosive environment of synthetic seawater. Fretting fatigue tests were performed over a wide stress range to determine the effect of seawater at high and low cycle fatigue regimes. The results from this study showed: (1) seawater significantly reduces the fretting fatigue life of shot-peened Ti-6Al-4V at both high and low cycle fatigue relative to its counterpart in ambient laboratory conditions, (2) shot peening increases the fretting fatigue life of Ti-6Al-4V when tested under dry and seawater conditions relative to its counterpart of unpeened Ti-6Al-4V, (3) surface …

Modeling And Control Of Surface Micromachined Thermal Actuators, Robert K. Messenger

Theses and Dissertations

A model that accurately describes the transient and steady-state response of thermal microactuators is desirable to provide guidance for design and operation. However, modeling the full response of thermal actuators is challenging due to the temperature-dependent material properties and nonlinear deformations that must be included to obtain accurate results. To meet these challenges a three-dimensional multi-physics nonlinear finite-element model was developed using commercial code. The Thermomechanical Inplane Microactuator (TIM) was chosen as a candidate application to validate the model. TIMs were fabricated using the SUMMiT V™ process and their response was measured using a high-speed camera. The TIMs were modeled …

A Study Of A Skirtless Hovercraft Design, Edward A. Kelleher

Theses and Dissertations

Initial study into three possible skirtless hovercraft designs. The designs utilize Coanda nozzles and a Coanda wing surface to generate lift and create a pressure cushion below the craft. The pressure cushion is to be maintained by an air curtain created by flow spill from the Coanda wing surface. Three proposed skirtless hovercraft designs were analyzed via computational fluid dynamics to ascertain their lift generation capabilities. The three designs were adaptations from William Walter's hybricraft primer and his patent for a fan driven lift generation device. Each design featured Coanda nozzles, or nozzles that utilize the Coanda effect, to redirect …

Design And Analysis Of Charge-Transfer Amplifiers For Low-Power Analog-To-Digital Converter Applications, William Joel Marble

Theses and Dissertations

The demand for low-power A/D conversion techniques has motivated the exploration of charge-transfer amplifiers (CTAs) to construct efficient, precise voltage comparators. Despite notable advantages over classical, continuous-time architectures, little is understood about the dynamic behavior of CTAs or their utility in precision A/D converters. Accordingly, this dissertation presents several advancements related to the design and analysis of charge-transfer amplifiers for low-power data conversion.

First, an analysis methodology is proposed which leads to a deterministic model of the voltage transfer function. The model is generalized to any timing scheme and can be extended to account for nonlinear threshold modulation. The model …

Numerical Modeling Of Friction Stir Welding: A Comparison Of Alegra And Forge3, Alma H. Oliphant

Theses and Dissertations

The objective of this research was to evaluate the capabilities of ALEGRA, a Sandia National Labs hydrocode, and Forge3, a Transvalor S.A. product, to accurately model the Friction Stir Welding Process. ALEGRA and Forge3 are discussed in light of the inherent challenges of modeling Friction Stir Welding, and a rotational boundary condition is added to ALEGRA. Results are presented from Friction Stir Welding modeling outputs from both ALEGRA and Forge3. ALEGRA is shown to be incapable of modeling the Friction Stir Welding process, in large part due to its focus on shock propagation, which causes extremely small time steps. Forge3 …

Hardware Synthesis Of Synchronous Data Flow Models, Matthew R. Koecher

Theses and Dissertations

Synchronous Dataflow (SDF) graphs are a convenient way to represent many signal processing and dataflow operations. Nodes within SDF graphs represent computation while arcs represent dependencies between nodes. Using a graph representation, SDF graphs formally specify a dataflow algorithm without any assumptions on the final implementation. This allows an SDF model to be synthesized into a variety of implementation techniques including both software and hardware.

This thesis presents a technique for generating an abstract hardware representation from SDF models. The techniques presented here operate on SDF models defined structurally within the Ptolemy modeling environment. The behavior of the nodes within …

Source Level Debugging Of Circuits Synthesized From High Level Language Descriptions, Karl S. Hemmert

Theses and Dissertations

The rapid increase in the density of modern FPGAs has allowed ever increasingly complex designs to be mapped to FPGAs. However, this increase in logic resources is accompanied by an increase in the complexity of describing and verifying the operation of an application. This has prompted the search for new approaches to the design, debug and verification of circuits. The desire to find more effecient approaches to designing these large FPGA circuits has led to the creation of synthesizing compilers that can create hardware from high-level descriptions based on general purpose programming languages. Being able to describe the application at …

A Value Focused Thinking Model For The Development And Selection Of Electrical Energy Source Alternatives At Military Installations, Gregory T. Schanding

Theses and Dissertations

Electrical power on military installations is vital for mission accomplishment. Most installations obtain electrical power from a local commercial utility. Although commercial power service has a very low interruption rate, the threat of a sustained power outage resulting from a terrorist act or a natural disaster is of concern. The military should posture itself to prevent such power outages and prepare to mitigate the adverse effects associated with the loss of power. This thesis presents a Value Focused Thinking approach to the development of a decision analysis model to assist a decision maker at a military installation in the generation …

The Predictive Validity Of The Afit Graduate Management Program Admission Requirements: A Reassessment And Extension, Sarah E. Woods

Theses and Dissertations

This research is based on the Air Force and AFIT balancing mission requirements of personnel needed for duty and training airmen in advanced studies. Currently, over 50% of AFIT students do not meet AFIT entrance requirements. The purpose of this research was to examine criteria to determine its predictability of graduate success, as measured by graduate GPA, as well as determine whether performance is different for students who require criteria to be waived. Current AFIT eligibility criteria include undergraduate GPA, GRE test scores, or GMAT test scores. Other variables examined in this study include: GRE-Analytical test scores; rank/grade; prior enlistment; …

Coplanar Air Launch With Gravity-Turn Launch Trajectories, David W. Callaway

Theses and Dissertations

The purpose of this study was to determine the feasibility of launching a vehicle based on the Boeing AirLaunch System in a coplanar, direct to rendezvous trajectory with gravity-turn. The focus of the research was to model the launch trajectory and determine the ability to reach different coplanar orbits. The launch trajectory was modeled using two-dimensional equations of motion and a boundary value problem was posed and solved for the gravity-turn trajectory. Trajectories were then created in an attempt to reach different altitudes through coasting and transfer orbits. Finally a specific orbital altitude was chosen and the trajectories were analyzed …

Analytical Results For A Single-Unit System Subject To Markovian Wear And Shocks, Daniel E. Finkelstein

Theses and Dissertations

This thesis develops and analyzers a mathematical model for the reliability measures of a single-unit system subject to continuous wear due to its operating environment and randomly occurring shocks that inflict a random amount of damage to the unit. Assuming a Markovian operating environment and shock arrival mechanism, Laplace-Stieltjes transform expressions are obtained for the failure time distribution and all of its moments. Moreover, an analytical expression is derived for the long-run availability of the single-unit system when it is subject to an inspect-and-replace maintenance policy. The analytical results are illustrated, and their results compared with those of Monte Carlo-simulated …

Analysis And Forecasting Of U.S. Navy Operating And Support (O&S) Costs For Rotary Aircraft, Christopher J. Wilkes

Theses and Dissertations

This research explores forecasting techniques to estimate the Cost per Flying Hour (CPFH) for Navy rotary aircraft. Three separate forecasting techniques were evaluated to better predict the CPFH for better estimating and budgeting by the U.S. Navy. The process begins by empirically analyzing Operating & Support cost categories for each helicopter. Trends were examined in CPFH. For forecasting purposes, actual CPFH figures were compiled from 1997 to 2003 for the CH-46D, the CH-53D, the MH-53E, the SH-60F, the UH-1N, and the UH-3H helicopters. The forecasting techniques explored were the 3-year moving average, the single exponential smoothing method, and Holt's linear …

Coordinated Uav Target Assignment Using Distributed Calculation Of Target-Task Tours, David H. Walker

Theses and Dissertations

This thesis addresses the improvement of cooperative task allocation to vehicles in multiple-vehicle, multiple-target scenarios through the use of more effective preplanned tours. Effective allocation of vehicles to targets requires knowledge of both the team objectives and the contributions that individual vehicles can make toward accomplishing team goals. This is primarily an issue of individual vehicle path planning --- determining the path the vehicles will follow to accomplish individual and team goals. Conventional methods plan optimal point-to-point path segments that often result in lengthy and suboptimal tours because the trajectory neither considers future tasks nor the overall path. However, cooperation …

Low Temperature Hall Measurements Of Neutron Irradiated Silicon Carbide, Angelo M. Bonavita

Theses and Dissertations

The purpose of this research was to search for evidence of low temperature annealing from neutron irradiated 4H-silicon carbide. No features suggesting annealing were found below a temperature of 340K. Temperature dependant Hall effect measurements were taken over a range of 100K to 340K recording resistivity, carrier densities, and mobility. Resistivity was noted to increase with irradiations, and carrier densities appeared to decrease, while mobility appeared minimally affected by neutron irradiation. This suggests the creation of active acceptor defects decreasing carrier concentrations. N-type samples measured were 5mm x 5mm square with Nickel contacts, and irradiated to 10¹⁰ and 10 …

The Contextable: Building And Testing An Intelligent, Context-Aware Kitchen Table, Daniel Matthew Hoopes

Theses and Dissertations

The purpose of this thesis was to design and evaluate The ContexTable, a context-aware system built into a kitchen table. After establishing the current status of the field of context-aware systems and the hurdles and problems being faced, a functioning prototype system was designed and built. The prototype makes it possible to explore established, untested theory and novel solutions to problems faced in the field.

A Comprehensive Model For Technology Push Product Development, Gregory Loren Bishop

Theses and Dissertations

Successful product development has been a fundamental part of many of today's companies and their continued prosperity depends on continuing to develop new products in the future. There are many models of product development. The two most common classes of development are market pull (MP) and technology push (TP). TP product development differs from MP in that the development begins with a specified technology rather than a specified customer. Because TP development is generally considered more difficult and challenging, most of the product development research has focused on MP development and many researchers and practitioners favor MP development over TP …

Transmission Strategies For Wireless Multi-User, Multiple-Input, Multiple-Output Communication Channels, Quentin H. Spencer

Theses and Dissertations

Multiple-Input, Multiple-Output (MIMO) processing techniques for wireless communication are of interest for next-generation systems because of their potential to dramatically improve capacity in some propagation environments. When used in applications such as wireless LAN and cellular telephony, the MIMO processing methods must be adapted for the situation where a base station is communicating with many users simultaneously. This dissertation focuses on the downlink of such a channel, where the base station and all of the users have antenna arrays. If the transmitter has advance knowledge of the users' channel transfer functions, it can use that information to minimize the interuser …

High-Torque Capacity Compliant Centrifugal Clutches, Ryan G. Weight

Theses and Dissertations

This thesis developed high-torque-capacity floating opposing arm clutches that are manufactured with standard economical manufacturing processes, while maintaining critical performance characteristics. Contact engagement speed and torque capacity models were created for the Hoffco-Comet, floating-opposing-arm (FOA), and floating 1 (F1) clutches. Sensitivity analyses were performed to identify key design parameters. A robust compliant FOA clutch was designed by minimizing the tolerance for both contact engagement speed and torque capacity. The robust design insures that the clutch will operate within the prescribed application constraints. Additional modeling showed that using a layered clutch would significantly tighten the contact engagement speed and torque performance …

Floodplain Risk Analysis Using Flood Probability And Annual Exceedance Probability Maps, Christopher M. Smemoe

Theses and Dissertations

This research presents two approaches to determining the effects of natural variability and model uncertainty on the extents of computed floodplain boundaries. The first approach represents the floodplain boundary as a spatial map of flood probabilities -- with values between 0 and 100%. Instead of representing the floodplain boundary at a certain recurrence interval as a single line, this approach creates a spatial map that shows the probability of flooding at each point in the floodplain. This flood probability map is a useful tool for visualizing the uncertainty of a floodplain boundary. However, engineers are still required to determine a …

Analysis And Design Of Low-Jitter Oscillators, Justin Jennings Fitzpatrick

Theses and Dissertations

This thesis presents an examination of the jitter performance of different oscillator types in the presence of flicker noise, white noise and power supply noise. Key results are achieved using time domain simulations to determine cycle jitter of several different oscillator architectures, semiconductor processes and component features. In the end, a design procedure is developed for creating a low-jitter oscillator in a TSMC .25mm CMOS semiconductor process.

Purchasing And Supply Chain Management Costing: An Air Transport Perspective Derived Through Commercial Air Cargo Firms, Kurt Ettrich

Theses and Dissertations

The Air Force has struggled to completely understand the costs associated with its operations. The issue of understanding cost is complex, involving many perspectives, methods and techniques. When examined from a broad standpoint, total supply chain costs can include a firm's costs plus upstream and downstream costs. This perspective takes vendors, suppliers and end customers into consideration. From this broad standpoint, the Air Force does not know its total supply chain cost. Since the Air Force's supply chain is too broad to be a focus of this study, a smaller segment was chosen for a closer look. Specifically, air cargo …

Full-Scale Lateral-Load Tests Of A 3x5 Pile Group In Soft Clays And Silts, Jeffrey L. Snyder

Theses and Dissertations

A series of static lateral load tests were conducted on a group of fifteen piles arranged in a 3x5 pattern. The piles were placed at a center-to-center spacing of 3.92 pile diameters. A single isolated pile was also tested for comparison to the group response. The subsurface profile consisted of cohesive layers of soft to medium consistency underlain by interbedded layers of sands and fine-grained soils. The piles were instrumented to measure pile-head deflection, rotation, and load, as well as strain versus pile depth.

A Linear Subspace Approach To Burst Communication Signal Processing, Daniel E. Gisselquist

Theses and Dissertations

This dissertation focuses on the topic of burst signal communications in a high interference environment. It derives new signal processing algorithms from a mathematical linear subspace approach instead of the common stationary or cyclostationary approach. The research developed new algorithms that have well-known optimality criteria associated with them. The investigation demonstrated a unique class of multisensor filters having a lower mean square error than all other known filters, a maximum likelihood time difference of arrival estimator that outperformed previously optimal estimators, and a signal presence detector having a selectivity unparalleled in burst interference environments. It was further shown that these …

Experimental Investigation Into The Aerodynamic Performance Of Both Rigid And Flexible Wing Structured Micro-Air-Vehicles, Anthony M. Deluca

Theses and Dissertations

The Air Force Research Lab, Munitions Directorate, Eglin Air Force Base, Florida has designed a man-portable carbon-fiber Micro-Air-Vehicle (MA V) used for on-the-spot surveillance by Special Operations Forces (SOF) for enemy reconnaissance as well as post-strike Battle Damage Assessment (BDA).The main goals of this experiment are: 1) characterize the flow quality of the new AFIT 3' x 3' wind tunnel and 2) determine the aerodynamic performance characteristics of the 24" span, 6" chord flexible and rigid wing MA V s. The turbulent intensity of the wind tunnel was approximately 2%. Both MA Vs had an average lift slope within 3.5% …

Evaluating The Navigation Potential Of The National Television System Committee Broadcast Signal, Ryan J. Eggert

Theses and Dissertations

The accuracy and worldwide availability of the Global Positioning System (GPS) make it the dominant system for navigation and precise positioning. Unfortunately, many situations arise in which GPS may not be adequate, e.g., urban navigation. This research evaluates the navigation potential of the National Television System Committee (NTSC) broadcast signal using a time-difference-of-arrival (TDOA) algorithm. TDOA measurements are made using NTSC broadcast signals collected from low and high multipath environments. These measurements are then used to evaluate the severity and dynamic effects of NTSC broadcast multipath signals. Three data reduction algorithms were developed--one that modifies the classical cross-correlation TDOA approach, …

Simulating A Chromotomographic Sensor For Hyperspectral Imaging In The Infrared, Anthony J. Dearinger

Theses and Dissertations

Hyperspectral imaging systems passively sense radiant electromagnetic energy from a remote scene to form a three dimension profile of the remote scene. The data contained in this profile describes real images of the remote scene for a certain number of spectral wavelength bands across a finite spectral range of electromagnetic radiation. Typical grating type hyperspectral imaging systems collect spectral electromagnetic radiation in the visible and near infrared spectral range, by incrementally scanning across the spatial extent of the remote scene. The legacy of low optical throughput because of the optical scanning techniques employed in these systems means adapting these systems …

Monotonic, Creep-Rupture, And Fatigue Behavior Of Carbon Fiber Reinforced Silicon Carbide (C/Sic) At An Elevated Temperature, John M. Engesser

Theses and Dissertations

The main objective of this research effort was to examine the impact that cyclic loading frequency has on the life of a C/SiC composite at an elevated temperature of 550°C. Cyclic loading of C/SiC was investigated at frequencies of 375 Hz, 10 Hz, 1 Hz, and 0.1 Hz. Creep-Rupture tests and tests that were combinations of creep-rupture and fatigue were also accomplished. A monotonic tensile test was performed at 550°C and compared to a room temperature monotonic test. This study showed that an elevated temperature of 550°C has very little effect on the Ultimate Tensile Strength (UTS) of C/SiC. The …

An Experimental Design For Measuring In Situ Radiation Damage To A Piezoelectric Transducer, Michael R. Severson

Theses and Dissertations

An experiment was conducted investigating the use of an acoustic pulse waveguide to collect response measurements from three piezoelectric acoustic emission (AE) transducers while the transducers were exposed to an active nuclear reactor neutron flux ranging from 1 x 10¹¹ to 2.4 x 10¹² neutrons per sq cms. Material, mechanical, and radiation studies were performed to determine a practical design for the construction of the experiment. Discreet frequency pulses generated by an Arbitrary Waveform Generator were transmitted by an aluminum waveguide to the core of the Ohio State University Research Reactor (OSURR). Three AF transducers coupled to the …

An Analysis Of The Potential For Using Over-The-Horizon Radar Systems For Space Surveillance, Matthew J. Colbert

Theses and Dissertations

The Australian Defence Force is investigating the development of a space surveillance system. While several dedicated facilities for space surveillance are in operation around the world, Australia s Over-The-Horizon Radar (OTHR) network has some potential for this role. The OTHR operates in the HF band and is constrained by the propagation effects of the ionosphere. A spherically stratified ionospheric model and a model for a nominal OTHR antenna are developed that allow calculation of path propagation, power distribution, and clutter returns. A software-based radar receiver processing system is modeled to determine detection probabilities and the minimum detectable radar cross-section of …