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Articles 3091 - 3120 of 5700
Full-Text Articles in Engineering
Final Development, Testing, And Flight Preparation Of The Rigidizable Get-Away-Special Experiment (Rigex), Zachary R. Miller
Final Development, Testing, And Flight Preparation Of The Rigidizable Get-Away-Special Experiment (Rigex), Zachary R. Miller
Theses and Dissertations
The purpose of this research is to support the final development of the Rigidizable Inflatable Get-Away-Special Experiment (RIGEX). The RIGEX program is an experimental initial step in developing large-scale rigidizable inflatable structures, which can be utilized in space applications. The primary intent of RIGEX is to verify and validate ground testing of inflation and rigidization methods for inflatable space structures against a zero-gravity space environment. This is performed by designing a Canister for All Payload Ejections (CAPE) experiment to collect data on space rigidized structures for validation of ground testing methods. The results presented in this thesis provide documentation needed …
A Comparison Of Film Cooling Techniques In A High Speed, True Scale, Fully Cooled Turbine Vane Ring, Michael J. Umholtz
A Comparison Of Film Cooling Techniques In A High Speed, True Scale, Fully Cooled Turbine Vane Ring, Michael J. Umholtz
Theses and Dissertations
An effort was undertaken to understand the impact of different film cooling configurations in a true scale turbine vane for three proprietary airfoil designs. The measurements for this study were taken at the United States Air Force Turbine Research Facility (TRF). The TRF enabled heat transfer data to be obtained on full scale turbine hardware under realistic engine conditions. The surface heat flux of the turbine blades was analyzed using the impulse response method. The overall effectiveness was compared between airfoil types at 60% span over varying streamwise locations on both suction and pressure surfaces. Using an approximated massflow, a …
Effects Of Prior Aging At 191°C On Creep Response Of Im7/Bmi 5250-4, Robert A. Salvia
Effects Of Prior Aging At 191°C On Creep Response Of Im7/Bmi 5250-4, Robert A. Salvia
Theses and Dissertations
The creep behavior of IM7/BMI 5250-4 with fiber orientations of [± 45] and [0/90] that were aged in air at 191 °C for up to 1000 hours was evaluated. The total weight loss during the aging process was also evaluated. Weight loss due to aging was 0.64% for the [0/90] fiber orientation and 0.72% for the [± 45] fiber orientation. Tensile tests to failure were conducted to establish tensile properties. The [0/90] specimens have a much higher stiffness and Ultimate Tensile Strength (UTS) values than the [± 45] specimens. The tensile tests of the aged specimens revealed that the Ultimate …
Critical Life Prediction Research On Boron-Enhanced Ti-6al-4v, Kevin A. Schwendiman
Critical Life Prediction Research On Boron-Enhanced Ti-6al-4v, Kevin A. Schwendiman
Theses and Dissertations
Research on boron-enhanced Ti-6-4 has demonstrated the following improvements to the Ti-6-4 alloy: up to 40% increase in ultimate tensile strength, up to 30% increase in modulus/stiffness, while maintaining greater than 10% ductility at RT conditions. The increased properties are attributed to small additions of boron (-or= wt%), which refine the microstructure and result in a small volume fraction (~6 vol%) of fine TiB whiskers. Previous research indicates potential for substantial improvements in fatigue, fatigue crack growth, and fracture toughness. However, uncertainty regarding these second-tier mechanical properties is currently limiting implementation of this class of titanium alloys. This study of …
Cfd Investigation Of Effect Of Depth To Diameter Ratio On Dimple Flow // Computational Fluid Dynamics Investigation Of Effect Of Depth To Diameter Ratio On Dimple Flow Dynamics, Robert B. Etter
Theses and Dissertations
This study aimed to further the understanding of laminar flow through a dimple with the goal of mitigating flow separation. Dimples of various depth to diameter ratios (0.05, 0.15) were examined for three different dimple diameters and chordwise locations, corresponding to diameter based (ReD) and chordwise location based (Rex) Reynolds number combinations of ReD 20500\Rex 5000, ReD 20500 Rex 77000, and ReD 9000 Rex 21000. For the last combination, a dimple of depth to diameter ratio of 0.25 was also examined. The dimples were placed in a flat plate located in a diverging channel causing an adverse pressure gradient encouraging …
Efficiency And Pressure Loss Characteristics Of An Ultra-Compact Combustor With Bulk Swirl, James T. Radtke
Efficiency And Pressure Loss Characteristics Of An Ultra-Compact Combustor With Bulk Swirl, James T. Radtke
Theses and Dissertations
Research was conducted on a novel combustor design using a highly centrifugal loaded circumferential cavity to enhance flame speeds and lower mixing time to lower overall combustion time achieving improved efficiency and stability. This Ultra-Compact Combustor (UCC) is fed air with a bulk swirl, resembling gas leaving a compressor without the final set of compressor guide vanes to straighten the flow, at higher than normal Mach numbers for a combustor. The larger Mach numbers in the combustor do not cause a total pressure loss in excess of what Rayleigh theory would dictate for the given heat addition taking place within …
Parallel Fast Multipole Method For Molecular Dynamics, Reid G. Ormseth
Parallel Fast Multipole Method For Molecular Dynamics, Reid G. Ormseth
Theses and Dissertations
We report on a parallel version of the Fast Multipole Method (FMM) implemented in the classical molecular dynamics code, NAMD (Not Another Molecular Dynamics program). This novel implementation of FMM aims to minimize interprocessor communication through the modification of the FMM grid to match the hybrid force and spatial decomposition scheme already present in NAMD. This new implementation has the benefit of replacing all-to-all communications broadcasts with direct communications between nearest neighbors. This results in a significant reduction in the amount of communication compared to earlier attempts to integrate FMM into common molecular dynamics programs. The early performance of FMM …
Catalytic Partial Oxidation Reforming Of Jp8 And S8, Thomas G. Howell
Catalytic Partial Oxidation Reforming Of Jp8 And S8, Thomas G. Howell
Theses and Dissertations
Catalytic partial oxidation (CPOX) reforming experiments were performed using a 10 kW Aspen Products Group, Inc. fuel processing prototype utilizing military logistic fuels JP8 and S8. S8 is a sulfur-free Fisher-Tropsch fuel, while JP8 is a multi-fuel blend, which could impact reforming efficiency, product distribution and byproduct production. Sulfur contained within the JP8 will adversely affect the product distribution; therefore, desulfurization beds, capable of removing up to 1000 ppm sulfur, were incorporated into the system. The catalyst used in the prototype is noble metal dispersed on cordierite monolith. The goal of this experiment was to evaluate the efficiency and product …
Effects Of Prior Aging On The Creep Response Of Carbon Fiber Reinforced Pmr-15 Neat Resin At 288°C In An Air Environment, Christopher A. Back
Effects Of Prior Aging On The Creep Response Of Carbon Fiber Reinforced Pmr-15 Neat Resin At 288°C In An Air Environment, Christopher A. Back
Theses and Dissertations
The mechanical response of carbon fiber reinforced PMR-15 neat resin with a ± 45 fiber orientation was investigated at 288 °C. Mechanical testing was performed on unaged specimens and specimens that were aged up to 1000 hours in an air environment. Tensile tests were performed to determine Young's modulus of elasticity and Ultimate Tensile Strength. Creep tests were performed at creep stress levels of 30 and 60 MPa. Creep periods of at least 25 h in duration were followed by recovery at zero stress. Duration of the recovery period was at least twice the time of the creep period. Oxidation …
Process Improvements For The Ah-64 Tail Rotor Vibration Analysis, Mark C. Newkirk
Process Improvements For The Ah-64 Tail Rotor Vibration Analysis, Mark C. Newkirk
Theses and Dissertations
The Apache was the first helicopter of its kind to fly with the tail rotor blade offset by 55 degrees as opposed to the traditional 90 degrees. Current balancing methods approximate the rotor system as a traditional 4 bladed, same plane system with different weight sensitivity coefficients for each set of blades. The Apache tail rotor computer model was built using the Rotorcraft Comprehensive Analysis System (RCAS) program. The objective was not to develop solutions for the sensitivity coefficients, but to identify predictive trends that result from the tail rotor blade location. Currently, sensitivity coefficients applied to the adjustment algorithms …
High Temperature Degradation Of 5250-4 Polymer Resin, Patrick E. Link
High Temperature Degradation Of 5250-4 Polymer Resin, Patrick E. Link
Theses and Dissertations
5250-4 bismaleimide resin is used in high performance polymer matrix composites with high temperature aeronautical applications. This thesis investigated the thermal and oxidative degradation of 5250-4 neat resin powder in argon, air, and oxygen environments. The powder was aged at 163 deg. C, 177 deg. C, and 190 deg. C in all environments for at least 250 hours. Isothermal thermo-gravimetric analysis demonstrated that weight loss was negligible for aging in the argon environment, indicating weight loss is the result of an oxidative process at these temperatures. The 5250-4 powder exhibited an initial period of weight gain before eventually losing weight …
Compressive Creep Behavior Of Nextel™ 720/Alumina Ceramic Matrix Composite At 1200°C In Air And In Steam Environment, Neil R. Szymczak
Compressive Creep Behavior Of Nextel™ 720/Alumina Ceramic Matrix Composite At 1200°C In Air And In Steam Environment, Neil R. Szymczak
Theses and Dissertations
The aerospace community continues to push the envelope in engineering aircraft that fly higher, faster, and safer while operating with a greater degree of efficiency. To meet these operational requirements innovative aerospace components must be designed to operate in aggressive environments. This research will investigate the ultimate compressive strength and the compressive creep behavior of NextelTM 720/Alumina ceramic matrix composite at 1200 °C in air and 100% steam environments. The effects of creep loading history on the tensile and compressive material behavior will also be examined. The primary strengths of the N720/A composite are its oxide/oxide composition which inherently …
Air Mobility Command's En Route Support Infrastructure: A Construct Of Aircraft Type And Geographic Location Utilized To Assess En Route Aircraft Logistics Support, Robert D. Polomsky
Air Mobility Command's En Route Support Infrastructure: A Construct Of Aircraft Type And Geographic Location Utilized To Assess En Route Aircraft Logistics Support, Robert D. Polomsky
Theses and Dissertations
The ability of the United States Armed Forces to maintain a global presence and rapidly project military power anywhere in the world are key factors in preserving our freedom. To accomplish the demanding task of global reach support, Air Mobility Command employs an en route support infrastructure. These en route locations provide varying levels of command, control, and communications (C3), logistics support, and aerial port functions. The goal of the en route is to minimize delays for AMC mission aircraft. However, these en route locations comprise a small percentage of the locations that AMC aircraft visit. Given the critical demand …
Voice And Video Capacity Of A Secure Wireless System, Jason R. Seyba
Voice And Video Capacity Of A Secure Wireless System, Jason R. Seyba
Theses and Dissertations
Improving the security and availability of secure wireless multimedia systems is the purpose of this thesis. Specifically, this thesis answered research questions about the capacity of wireless multimedia systems and how three variables relate to this capacity. The effects of securing the voice signal, real-time traffic originating foreign to a wireless local area network and use of an audio-only signal compared with a combined signal were all studied. The research questions were answered through a comprehensive literature review in addition to an experiment which had thirty-six subjects using a secure wireless multimedia system which was developed as part of this …
Steganalysis Feature Improvement Using Expectation Maximization, Benjamin M. Rodriguez, Gilbert L. Peterson, Sos S. Agaian
Steganalysis Feature Improvement Using Expectation Maximization, Benjamin M. Rodriguez, Gilbert L. Peterson, Sos S. Agaian
Faculty Publications
No abstract provided.
Cfd Investigation Of Flow Past Idealized Engine Nacelle Clutter /// Computational Fluid Dynamics Investigation Of Flow Past Idealized Engine Nacelle Clutter, Matthew S. Caspers
Cfd Investigation Of Flow Past Idealized Engine Nacelle Clutter /// Computational Fluid Dynamics Investigation Of Flow Past Idealized Engine Nacelle Clutter, Matthew S. Caspers
Theses and Dissertations
This research modeled low-speed flow past idealized engine nacelle clutter in support of aircraft re suppression research. The idealized clutter was comprised of three vertical rows of staggered circular cylinders approximating typical nacelle obstructions such as fuel lines and wire bundles. Single-phase, Detached-Eddy Simulations (DES) were conducted using the commercial CFD solver, Fluent™, to resolve the flow-field dynamics inside the clutter element and determine mechanisms accounting for the failure of suppressant spray droplets from traversing the array under low-speed, free-stream conditions (ReD = 1, 575). The numerical models provided no evidence that span-wise vorticity or non-uniform shedding was responsible for …
Comparison Of Thermodynamic Equilibrium And Non-Equilibrium Representation Of Materials, Michael J. Vanderhyde
Comparison Of Thermodynamic Equilibrium And Non-Equilibrium Representation Of Materials, Michael J. Vanderhyde
Theses and Dissertations
Hydrocodes are valuable tools in the modeling of shock wave propagation through solids due to high speed impact phenomena. CTH is a hydrocode built with the ability to use multiple EOSs, including the semi-emperical Mie-Gruneisen EOS and tabular Sesame EOS. Modeling high speed impacts necessitates modeling the non-equilibrium thermodynamic states caused by these impacts. A discussion of the non-equilibrium thermodynamics that may be applied to the region directly behind a shock wave is presented, including details of recent attempts to model non-equilibrium impact phenomena in solids. Also, in order to better determine the applicability of the Mie-Gruneisen EOS anbd the …
Fuel Estimation Using Dynamic Response, Michael S. Hines
Fuel Estimation Using Dynamic Response, Michael S. Hines
Theses and Dissertations
New regulations governing satellites in geostationary orbit require satellites to transfer into a parking orbit as part of the decommissioning process. These regulations increase the demand for accurate fuel estimation techniques for satellites. This study estimates the change in fuel mass from the dynamic response of the Air Force Institute of Technology's simulated satellite (SimSAT) to known control inputs. With an iterative process, the moment of inertia of SimSAT about the yaw axis was estimated by matching a model of SimSAT to the measured angular rates. A change in fuel mass was then estimated from the known relation between the …
Satellite Attitude Control Using Atmopheric Drag, David B. Guettler
Satellite Attitude Control Using Atmopheric Drag, David B. Guettler
Theses and Dissertations
Attitude control is a requirement for most satellites. Many schemes have been devised over the years including control moment gyros, reaction wheels, spin stabilization and gravity gradient stabilization. For low Earth orbits, the Earth's atmosphere can have an affect on a satellite's orbit and attitude. This research effort examines the feasibility of using the atmosphere to actively control a spacecraft's attitude using drag panels. Using the atmosphere to control spacecraft attitude has been researched in the past however very little research has been done using an active feedback control system to maintain spacecraft attitude. A linear computer model was created …
Feasibility Study Of Variance Reduction In The Logistics Composite Model, George P. Cole Iii
Feasibility Study Of Variance Reduction In The Logistics Composite Model, George P. Cole Iii
Theses and Dissertations
The Logistics Composite Model (LCOM) is a stochastic, discrete-event simulation that relies on probabilities and random number generators to model scenarios in a maintenance unit and estimate optimal manpower levels through an iterative process. Models such as LCOM involving pseudo-random numbers inevitably have a variance associated with the output of the model for each run, and the output is actually a range of estimates. The reduction of the variance in the results of the model can be costly in the form of time for multiple replications. The alternative is a range of estimates that is too wide to realistically apply …
Forecasting Demand For Civilian Pilots: A Cost Savings Approach To Managing Air Force Pilot Resources, Justin W. Collup
Forecasting Demand For Civilian Pilots: A Cost Savings Approach To Managing Air Force Pilot Resources, Justin W. Collup
Theses and Dissertations
The purpose of this research was to create a model that could potentially predict demand for military trained pilots in the airline industry. Specifically, this thesis sought to answer the research question addressing whether or not military trained pilots are currently more in demand or less in demand. The research questions were answered through a comprehensive literature review, collection of data relevant to airline industry growth, and regression analysis. The Aviation Continuation Pay Bonus, offered to all eligible Air Force aviators, has risen from $12,000/year to its current value of $25,000/year. With shrinking budgets, and ever increasing costs of war, …
A Layered Social And Operational Network Analysis, Jennifer L. Geffre
A Layered Social And Operational Network Analysis, Jennifer L. Geffre
Theses and Dissertations
To provide maximal disruption to a clandestine/terrorist network's ability to conduct missions, we must develop a means to determine the individuals' importance to the network and operations. In a network centric world, this importance is represented as an additive value of their criticality across the convergence of multiple layers of network connections. The connections layers of the network are comprised of social layers (Acquaintance, Friendship, Nuclear Family, Relatives, Student-Teacher, and Religious Mentors, Reverent Power and others), as well as layers representing interactions involving Resources, Knowledge/Skills and Temporal Local. The social criticality of an individual is measured by centrality. Event Trees …
Rapid Runway Repair (Rrr): An Optimization For Minimum Operating Strip (Mos) Selection, David J. Duncan
Rapid Runway Repair (Rrr): An Optimization For Minimum Operating Strip (Mos) Selection, David J. Duncan
Theses and Dissertations
Minimum Operating Strip (MOS) selection determines the exact placement of the MOS on the damaged runway, and therefore, the amount of munitions that need to be neutralized and the amount of damage that will need to be repaired. MOS selection, in essence, is the key determinant of the time required to attain an operational takeoff and recovery surface. Since the MOS selection stage determines the events and scope of work for all of the Rapid Runway Repair (RRR) stages that follow, it could be argued that this is the most important stage in the entire RRR process. The primary purpose …
A Multireference Density Functional Approach To The Calculation Of The Excited States Of Uranium Ions, Eric V. Beck
A Multireference Density Functional Approach To The Calculation Of The Excited States Of Uranium Ions, Eric V. Beck
Theses and Dissertations
An accurate and efficient hybrid Density Functional Theory (DFT)/Multireference Configuration Interaction (MRCI) model for computing electronic excitation energies in heavy element atoms and molecules was developed. This model incorporated relativistic effects essential for accurate qualitative and quantitative spectroscopic predictions on heavy elements, while simultaneously removing spin-multiplicity limitations inherent in the original model on which it is based. This model was used to successfully compute ground and low-lying electronic states for atoms in the first two rows of the period table, which were used for calibration. Once calibrated, calculations on carbon monoxide, bromine fluoride, the bromine atom, uranium +4 and +5 …
A Multivariate Magnitude Robust Control Chart For Mean Shift Detection And Change Point Estimation, Ryan M. Harrell
A Multivariate Magnitude Robust Control Chart For Mean Shift Detection And Change Point Estimation, Ryan M. Harrell
Theses and Dissertations
Statistical control charts are often used to detect a change in an otherwise stable process. This process may contain several variables affecting process stability. The goal of any control chart is to detect an out-of-control state quickly and provide insight on when the process actually changed. This reduces the off-line time the quality engineer spends assigning causality. In this research, a multivariate magnitude robust chart (MMRC) was developed using a change point model and a likelihood-ratio approach. Here the process is considered in-control until one or more normally distributed process variables permanently and suddenly shifts to out-of-control, stable value. Using …
Decision Analysis With Value Focused Thinking As A Methodology To Select Building For Deconstruction, Erika E. Maiorano
Decision Analysis With Value Focused Thinking As A Methodology To Select Building For Deconstruction, Erika E. Maiorano
Theses and Dissertations
The purpose of this research was to examine the reuse and recycling of building materials on Wright-Patterson Air Force Base. There are a variety of conflicting factors concerning the removal of a building and the model quantitatively evaluates alternatives with respect to the decision maker’s values. The research questions were addressed with both a comprehensive literature review as well as the implementation of the value focused thinking methodology. The model found that the temporary living facilities are the alternatives that achieve the highest value. The result of this research effort was a value model that aids decision makers in identifying …
Development Of An Experimental Platform For Testing Autonomous Uav Guidance And Control Algorithms, Justin R. Rufa
Development Of An Experimental Platform For Testing Autonomous Uav Guidance And Control Algorithms, Justin R. Rufa
Theses and Dissertations
With the United States' push towards using unmanned aerial vehicles (UAVs) for more military missions, wide area search theory is being researched to determine the viability of multiple vehicle autonomous searches over the battle area. Previous work includes theoretical development of detection and attack probabilities while taking into account known enemy presence within the search environment. Simulations have been able to transform these theories into code to predict the UAV performance against known numbers of true and false targets. The next step to transitioning these autonomous search algorithms to an operational environment is the experimental testing of these theories through …
Internet Protocol Geolocation: Development Of A Delay-Based Hybrid Methodology For Locating The Geographic Location Of A Network Node, John M. Roehl
Internet Protocol Geolocation: Development Of A Delay-Based Hybrid Methodology For Locating The Geographic Location Of A Network Node, John M. Roehl
Theses and Dissertations
Internet Protocol Geolocation (IP Geolocation), the process of determining the approximate geographic location of an IP addressable node, has proven useful in a wide variety of commercial applications. Commercial applications of IP Geolocation include market research, redirection for performance enhancement, restricting content, and combating fraud. The potential for military applications include securing remote access via geographic authentication, intelligence collection, and cyber attack attribution. IP Geolocation methods can be divided into three basic categories based upon what information is used to determine the geographic location of the given IP address: 1) Information contained in databases, 2) information that is leaked during …
Wide Area Search And Engagement Simulation Validation, Michael J. Marlin
Wide Area Search And Engagement Simulation Validation, Michael J. Marlin
Theses and Dissertations
As unmanned aerial vehicles (UAVs) increase in capability, the ability to refuel them in the air is becoming more critical. Aerial refueling will extend the range, shorten the response times, and extend loiter time of UAVs. Executing aerial refueling autonomously will reduce the command and control, logistics, and training efforts associated with fielding UAV systems. Currently, the Air Force Research Lab is researching the various technologies required to conduct automated aerial refueling (AAR). One of the required technologies is the ability to autonomously rendezvous with the tanker. The goal of this research is to determine the control required to fly …
Active Control Of A Thin Deformable In-Plane Actuated Mirror, Thomas P. Gabriele Jr.
Active Control Of A Thin Deformable In-Plane Actuated Mirror, Thomas P. Gabriele Jr.
Theses and Dissertations
The constitutive relations traditionally used for finding shear stress and heat flux in a fluid become invalid in non-equilibrium flow. Their derivation from kinetic theory only demonstrates they are valid only for small deviations from equilibrium. Because it is fundamentally linked to non-equilibrium, entropy generation is used to investigate the limits of the continuum constitutive relations. However, the continuum equations are inherently limited to near equilibrium conditions due to the constitutive relations; thus kinetic theory must be used as a basis for comparison. Direct Simulation Monte Carlo (DSMC), a particle method alternative to continuum methods, is based on kinetic theory …