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Articles 4201 - 4230 of 5699
Full-Text Articles in Engineering
Reparable Inventory Reduction: Impacts On Air Force Fighter Aicraft Mission Capability, Gregory E. Hutson
Reparable Inventory Reduction: Impacts On Air Force Fighter Aicraft Mission Capability, Gregory E. Hutson
Theses and Dissertations
During the 1990's the Air Force experienced severe declines in serviceable inventory levels and a rise in their TNMCS rates. Air Force predictions of TNMCS hours during this time period did not account for the upward trend in TNMCS rates. The Air Force uses a regression equation, consisting of possessed hours, flying hours, and sorties, to predict TNMCS hours. This research, through simple linear regression, found a significant relationship between serviceable inventory levels and TNMCS rates for 8 of the 10 aircraft studied. Using this relationship, serviceable inventory levels were then added to the Air Force equations and new multiple …
Comparison Of The Effects Of Eight-Hour And Twelve-Hour Shifts On Air Force Aircraft Maintenance Production Levels, David P. Collette
Comparison Of The Effects Of Eight-Hour And Twelve-Hour Shifts On Air Force Aircraft Maintenance Production Levels, David P. Collette
Theses and Dissertations
his is a follow-on study that examined the effects of converting a large aircraft maintenance squadron from 8-hour shifts to 12-hour shifts. The squadron studied converted its 24-hour maintenance work force from three 8-hour work shifts to two 12-hour work shifts. Data was collected from four different time periods. Three time periods were used for a primary analysis and all four time periods were used for trend analysis. To determine if the 12-hour work shift was effective, workforce productivity was measured during the different work shift periods. Results showed an increase in two productivity measurements, no-change in two productivity measurements, …
The Effect Of Action Workouts On Aircraft Mission Capability Measurements, Michael P. Allison
The Effect Of Action Workouts On Aircraft Mission Capability Measurements, Michael P. Allison
Theses and Dissertations
Previous studies concerning quality improvement and the Action Workout Process attempted to define and describe the difficult concept of quality. A logical next step is to study to what extent implementation of a quality improvement program, such as ACC's Action Workout Process, positively or negatively affects performance factors within an Air Force organization. This study focused on exploring the fundamental question of whether there was, as a result of the Action Workout, a noticeable, statistically verifiable, positive or negative change in the mission capability of aircraft assigned to the units carrying out this quality improvement initiative. Research questions were developed …
Operational Risk Management And Military Aviation Safety, Park D. Ashley
Operational Risk Management And Military Aviation Safety, Park D. Ashley
Theses and Dissertations
The Air Force Class A aviation mishap rate has hovered around 1.5 mishaps per 100,000 flight hours since 1985. Recent attention on Air Force accidents has caused the leadership to seek to reduce its mishap rate. The Army's Class A aviation mishap rate declined after it implemented risk management (RM) principles in 1987. This reduction caught the attention of Air Force leadership who have since stated that the application of operational risk management (ORM) is how the Air Force will reduce, even eliminate, mishaps. With current budget constraints, ORM is considered to be the most cost-effective way the Air Force …
An Exploratory Analysis Of The Responsiveness Capability Of The Air Expeditionary Wing (Aew) Concept, Robert L. Charlesworth
An Exploratory Analysis Of The Responsiveness Capability Of The Air Expeditionary Wing (Aew) Concept, Robert L. Charlesworth
Theses and Dissertations
Seven AEF deployments have been accomplished in the Southwest Asia area of responsibility; none have met the Air Force's stringent 72 hour criterion. This exploratory study quantifies the responsiveness capability of the AEW concept. Based on a Monte Carlo simulation methodology this study concludes that the on call AEW at Mountain Home AFB does not have the capability to meet the 72 hour criterion. Additionally, this study examined the effect of three departures from the baseline model on responsiveness capability. These departures included: increasing airlift throughput capacity, incorporating limited airlift failure, and employing an air refueling scenario. The simulation models …
The Challenge Of Maintaining Or Replacing An Aging Airlift Fleet: A Cost/Capability Analysis For The Brazilian Air Force Mobility System, Julio C. Messias
The Challenge Of Maintaining Or Replacing An Aging Airlift Fleet: A Cost/Capability Analysis For The Brazilian Air Force Mobility System, Julio C. Messias
Theses and Dissertations
Despite the high Operational and Support costs incurred, the Brazilian Air Force's (BAF) declining budget has led to the establishment of conservative policies that favor short run solutions for a critical BAF airlift problem of operating an aging fleet. As a result of this policy, service life extensions of older airlift aircraft are the preferred solution. Using an equal airlift capacity approach to examine the Brazilian Air Force mobility system, this research performs a cost comparison analysis between two aircraft currently in operation at Brazilian's airlift command: C-130 Hercules and C-95 Bandeirante. To accomplish the cost analysis, this research develops …
An Ex Post Facto Analysis Of E-3 Maintenance Indicators In The 552d Air Control Wing Since Reorganization Under An Aircraft Generation Squadron Concept, Larry J. Stetz
Theses and Dissertations
Organizational restructuring sometimes occurs in the aircraft maintenance field, yet seldom are in-depth analyses performed after the fact to see if productivity improved. In December 1995, the 552D Air Control Wing restructured its flight line maintenance into an aircraft generation squadron concept. This study looked at before and after maintenance indicators to see if productivity improved. Maintenance data was collected from December 1993 to December 1997. Nineteen maintenance indicators were identified, and the key indicators were analyzed using means comparison and regression analysis to determine if efficiency and effectiveness had increased. The variables Mission Capable rate and Man-hours per Flying …
Cost-Benefit Analysis Of Leasing Versus Buying Air Force General Purpose Vehicles In The Continental United States, Robert J. Neal Jr.
Cost-Benefit Analysis Of Leasing Versus Buying Air Force General Purpose Vehicles In The Continental United States, Robert J. Neal Jr.
Theses and Dissertations
Given the increasingly aging vehicle fleet and declining vehicle budget, this research performed a cost-benefit analysis of leasing versus buying various Air Force general purpose vehicles for the entire continental United States (CONUS). In contrast to previous analyses, which have examined the leasing versus buying issue on a base-by-base basis, this analysis studies the issue from an Air Force-wide perspective using a cost-buying model. Costs and benefits are calculated for three purchasing options (Air Force ownership, GSA leasing, and commercial leasing) to determine and recommend the best alternative for the Air Force. Finally, a sensitivity analysis is to test the …
Closely Supervised Reactive Control Of An Uninhabited Aerial Vehicle, Roy G. Glassco
Closely Supervised Reactive Control Of An Uninhabited Aerial Vehicle, Roy G. Glassco
Theses and Dissertations
Closely Supervised Reactive Control is an alternative control method for uninhabited aerial vehicles that incorporates some of the benefits of both manual and autonomous operations. Utilizing an onboard camera, an operator can control a UAV by manually choosing desired targets. The flight path of the uninhabited vehicle is determined autonomously from the camera gimbal angles. The operator of the payload (i.e. camera), has close supervision of the aircraft. The aircraft, using an onboard computer, is given autonomous control to alter flight path to fly towards a target and at a specified range, loiter over the target. In the basic mode …
Parallel Digital Signal Processing On A Network Of Personal Computers Case Study: Space-Time Adaptive Processing, Fernando Silva
Parallel Digital Signal Processing On A Network Of Personal Computers Case Study: Space-Time Adaptive Processing, Fernando Silva
Theses and Dissertations
Network based parallel computing using personal computers is currently a popular choice for concurrent scientific computing. This work evaluates the capabilities and the performance of the AFIT Bimodal Cluster (ABC); a heterogeneous cluster of PCs connected by switched fast Ethernet and using MPICH 1.1 for interprocess communication for parallel digital signal processing using Space Time Adaptive Processing (STAP) as the case study. The MITRE RT_STAP Benchmark version 1.1 is ported and executed on the ABC, as well as on a cluster of six Sun SPARC workstations connected by a Myrinet network (the AFIT NOW), and on a IBM SP for …
Dual Channel Matched Filtering And Space-Time Adaptive Processing, Scott D. Berger
Dual Channel Matched Filtering And Space-Time Adaptive Processing, Scott D. Berger
Theses and Dissertations
We propose a dual channel matched filtering system that addresses two key challenges in the practical implementation of a single channel matched filtering system: secondary data support and computational cost. We demonstrated that the dual channel system requires half the secondary data to achieve nearly the same signal-to-interference plus noise ratio (SINR) as an equivalent single channel system. The key to the dual channel system is the block diagonalization of the interference plus noise correlation matrix with a fixed transformation. We investigated the application of this dual channel concept to the problem of space-time adaptive processing (STAP), referring to the …
Flow Separation Prevention On A Turbine Blade In Cascade At Low Reynolds Number, James P. Lake
Flow Separation Prevention On A Turbine Blade In Cascade At Low Reynolds Number, James P. Lake
Theses and Dissertations
The problem of flow separation from a low pressure turbine blade was investigated. The operating conditions under which the separation occurred were documented through measurement of surface pressure coefficients, boundary layer velocity and turbulence profiles, total pressure loss coefficient and wake velocity momentum deficit. Three different means for reducing the losses associated with the flow separation were also investigated. A boundary layer trip, dimples, and V-grooves were studied as passive means requiring no additional energy to reduce the separation losses. The boundary layer trip was only successful for an inlet and axial chord Reynolds number of 50k with a reduction …
Timed Safety Automata And Logic Conformance, Frank C. D. Young
Timed Safety Automata And Logic Conformance, Frank C. D. Young
Theses and Dissertations
Timed Logic Conformance (TLC) is used to verify the behavioral and timing properties of detailed digital circuits against abstract circuit specifications when both are modeled as Timed Safety Automata (TSA) with real-valued clocks. TLC is a bisimulation-style partial order relationship defined over TSA state space. In contrast to timed simulation, Calculus of Timed Refinement, and time-abstracted bisimulation, TLC defines when one system is an acceptable implementation of another by asymmetric action-matching requirements for specification inputs and implementation outputs. TLC intuitively and pragmatically supports writing abstract specifications and verifying them against implementations. TLC scales up by substituting verified specifications for implementations …
Wind Tunnel Investigation Of Joined Wing Configurations, Jennifer Corneille
Wind Tunnel Investigation Of Joined Wing Configurations, Jennifer Corneille
Theses and Dissertations
The Air Force Research Laboratory's Munitions Directorate is looking to extend the range of its small smart bomb. One proposed idea is to retrofit the bombs with a wing kit, particularly a joined wing configuration. A typical joined wing configuration is one where the wings are positioned in such a way that they form a diamond in both plan and front views. The purpose of this study is to conduct low speed wind tunnel testing of the joined wing configuration to help determine if the joined wing is more beneficial than a single wing configuration. Configurations with differing sweep angles …
A Performance Analysis Of A Low Earth Orbit Satellite System, Korkut A. Ercakar
A Performance Analysis Of A Low Earth Orbit Satellite System, Korkut A. Ercakar
Theses and Dissertations
This thesis provides a performance analysis of the TELEDESIC® Low Earth Orbit Satellite System. It analyzes the system's performance to meet the real-time communications constraints with a full satellite constellation. Computer simulation results are the sources to evaluate delays associated with packets transmitted from source to destination earth stations. The simulation is run at low, medium and high loading levels with two different, uniform and non-uniform, traffic distributions. The evaluated results are end-to-end packet delays and packet rejection rate. The results show that the TELEDESIC® satellite system network is capable of meeting the real-time communication requirements with delay values much …
Bistatic Radar Cross Section (Rcs) Characterization Of Complex Objects, Robert L. Eigel Jr.
Bistatic Radar Cross Section (Rcs) Characterization Of Complex Objects, Robert L. Eigel Jr.
Theses and Dissertations
This research addresses some phenomenological aspects of bistatic scattering from a complex object with an emphasis on specular, shadowing, dihedral, and cavity effects. Five targets are investigated for their simplicity and ability to highlight certain scattering phenomena. Direct measurements of scattered electromagnetic energy and simulation data is gathered for a frequency bandwidth of 6-18 GHz. Both ray tracing and scattering center approaches are used to describe the bistatic mechanisms. An appraisal of the effectiveness and utility of the monostatic-to-bistatic equivalence theorems (Kell's and Crispin's) and several commercial scattering prediction codes is also accomplished. Simulation data is generated from two different …
Close Formation Flight Control, Andrew W. Proud
Close Formation Flight Control, Andrew W. Proud
Theses and Dissertations
In this research the close formation flight control problem is addressed. The formation consists of a lead and wing aircraft, where the wing flies in close formation with the lead, such that the lead's vortices produce aerodynamic coupling effects, and a reduction in the formation's drag is achieved. A controller, i.e., a formation-hold autopilot for the wing aircraft, is designed such that the formation's geometry is maintained in the face of lead aircraft maneuvers. In the formation flight control system, the wing and lead aircraft dynamics are coupled due to kinematic effects, and, in the case of close formations, additional …
Positive Anisotropic Group Scattering Cross Sections For Radiation Transport, J. Mark Delgrande
Positive Anisotropic Group Scattering Cross Sections For Radiation Transport, J. Mark Delgrande
Theses and Dissertations
In solving the Boltzmann transport equation, most discrete ordinates codes calculate the source term by first approximating the scattering cross section using a Legendre polynomial expansion. Such expansions are insufficient when scattering is anisotropic and the Legendre expansion is truncated prematurely. This can lead to nonphysical negative cross sections, negative source terms and negative angular fluxes. While negative sources are problematic for standard discrete ordinates methods leading to poor convergence or convergence to incorrect results, they are of particular concern to exponential methods, causing such calculations to fail. We've developed and tested a new technique to solve this problem called …
Solving An Inverse Control Problem Using Predictive Methods, Chad J. Davis
Solving An Inverse Control Problem Using Predictive Methods, Chad J. Davis
Theses and Dissertations
Model Predictive Control is the class of control methods that optimizes a specified performance index in order to minimize the weighted future output deviations from a setpoint trajectory. This thesis applies MPC in the inverse sense -- known aircraft outputs are applied in the performance index as setpoints in an attempt to determine what control histories caused those outputs. Using this method, aircraft mishap investigators could then have a means of determining what the control surface deflections were throughout an incident since Flight Data Recorder data does not include control surface deflections. The actual Flight Data Recorder data from aircraft …
Variable Area Inlet For Vehicle Thermal Control, Thomas R. Layne, Milton E. Franke, Darrell B. Ridgedly
Variable Area Inlet For Vehicle Thermal Control, Thomas R. Layne, Milton E. Franke, Darrell B. Ridgedly
AFIT Patents
A variable area inlet structure for a vehicle utilizing ram air for coolant is described which comprises a variable area inlet device in the ram air inlet in the form of a butterfly valve, damper, shutter, or similar structure, a temperature sensor in thermal contact with a component within the vehicle to be cooled by ram air flow, a controller and actuator, responsive to the temperature sensor and operatively connected to the variable area device, for controlling the inlet area in response to the component temperature.
Output Control Of Vertical Microcavity Light Emitting Device, James A. Lott
Output Control Of Vertical Microcavity Light Emitting Device, James A. Lott
AFIT Patents
An improved intracavity sensor based output power control for microcavity light emitting devices. An improved phototransistor transducer is both configured and physically disposed so that it passively transmits the spurious optical energy output of the microcavity light emitting device while simultaneously generating a light determined electrical signal of easily used large magnitude that is nearly free of error. The base-collector region of the transistor is disposed with a quantum well absorbing layer and produces a signal responsive to a selected emission wavelength. The configuration of the optical energy communicating transducer is arranged so that it is improved in sensitivity and …
Concept Design And Optimization Of Msw Management System, James R. Palmer
Concept Design And Optimization Of Msw Management System, James R. Palmer
Theses and Dissertations
The maximum recovery of recyclables from municipal solid waste (MSW) using material recovery facility (MRF) technologies is determined. Two waste streams at Spangdahlem AB, Germany are analyzed; stationary container wastes and commingled recyclables. Three schemes are considered, one for each waste stream, and one for both. Multi-criteria decision making is the methodology. The criteria are recovery and annual benefit minus cost (B-C). Recovery is determined using the recovery factor transfer function of Diaz et al. (1982). Each technology, or unit operation, in a sequence is independent because particle size distribution of each waste component is considered. B-C is based on …
Strategic Effects Of Airpower And Complex Adaptive Agents: An Initial Investigation, Thomas R. Tighe
Strategic Effects Of Airpower And Complex Adaptive Agents: An Initial Investigation, Thomas R. Tighe
Theses and Dissertations
US airpower theory and doctrine depend on the concept that the destruction of a few key targets or centers of gravity can unravel the enemy's physical ability to wage war or break his will to prosecute the war. This synergistic decimation of the enemy's effectiveness and resistance to our political will is known as Strategic Effects. These strategic effects are very difficult to quantify and are not directly accounted for in current DoD computer models. Since these computer models are used to aid with decisions about force structure and budget priorities, many believe that the Air Force's greatest potential contribution …
Analysis Of Cost Growth In Us Air Force Base Support Function Contracts, James S. Romasz
Analysis Of Cost Growth In Us Air Force Base Support Function Contracts, James S. Romasz
Theses and Dissertations
The United States Air Force (USAF) has outsourced a significant portion of their activities defined as commercial activities and plans to aggressively outsource more in the future. The USAF outsources its commercial activities in the form of multi-year contracts to the private sector. Cost growth (either negative or positive) has been experienced by most of these contracts. This research effort performed a review of current literature and used statistical analysis to clarify the issue: what are the causes, and extent of cost growth in USAF base-support-function contracts?. From the literature, it can be concluded that changes to the statement of …
A New Sequential Goodness Of Fit Test For The Three-Parameter Gamma Distribution With Known Shape Based On Skewness And Kurtosis, Chil Ho Park
Theses and Dissertations
This research presents a new sequential goodness of fit test for the three-parameter gamma distribution with a known shape. The test is accomplished by employing two new tests, sample skewness and sample kurtosis, sequentially as test statistics. Unlike the typical goodness of fit test, using parameter estimation methods such as maximum likelihood estimation and minimum distance estimation, this test using the two test statistics above does not involve a substantial degree of computational complexity. Large Monte Carlo simulation has been used to determine critical values and overall significance levels for all combinations of the two tests, and to conduct extensive …
A New Sequential Goodness-Of-Fit-Test For The Three-Parameter Weibull Distribution With Known Shape Parameter Value Based On Skewness And Q-Statis G.O.F. Test Statistics, Tibet Memis
Theses and Dissertations
Due to its flexibility, the Weibull distribution has very wide applicability in a lot of disciplines and is very prevalent in reliability theory. Thus, a lot of statistical tests that generally have a substantial degree of computational complexity have been developed to determine if the data at hand can be represented with this distribution. This research presents a new omnibus goodness-of-fit test (G.O.F.) that has less computational complexity than the existing tests for the three-parameter Weibull distribution using a sequential application of two individual tests, sample skewness and Q-Statistic. A Monte Carlo procedure has been employed to generate critical values …
Expeditious Methods For Site Characterization And Risk Assessment At Department Of Defense Hazardous Waste Sites In The Republic Of Korea, Dean H. Hartman
Expeditious Methods For Site Characterization And Risk Assessment At Department Of Defense Hazardous Waste Sites In The Republic Of Korea, Dean H. Hartman
Theses and Dissertations
The overall goal of this research was to provide Department of Defense (DoD) decision-makers in the Republic of Korea (ROK) with preferred innovative site characterization technologies and risk assessment methods to meet their needs in obtaining hazardous waste site data and then prioritizing those sites for remediation based upon risk. The study examined the following: primary sources and types of existing contamination at DoD installations in the ROK; available site characterization data; criteria to be used in selecting innovative site characterization technologies; costs and capabilities of the innovative site characterization technologies; risk assessment or risk-based corrective action (RBCA) methods available …
Fatigue Response Of Repaired Thick Aluminum Panels With Bondline Flaws, David S. Conley
Fatigue Response Of Repaired Thick Aluminum Panels With Bondline Flaws, David S. Conley
Theses and Dissertations
his research investigated the fatigue response of precracked 558 x 177.8 x 6.35 mm (22.0 x 7.0 x 0.25 in) 2024-T351 aluminum panels repaired with single-sided partially bonded, unidirectional, eighteen ply boron/epoxy reinforcements. Disbonds were introduced into the bondline of each repair during the adhesion process using teflon inserts. Five different disbond configurations, with varying disbond locations and sizes, were tested. Each repaired panel was subjected to constant amplitude cyclic fatigue loading with a maximum stress of 120MPa. Results from the different configurations were compared against one another and against repaired panels with no debonds to assess the effect of …
Robust Eigenstructure Assignment Using Positive Definite Output Feedback Control, Adam G. Harris
Robust Eigenstructure Assignment Using Positive Definite Output Feedback Control, Adam G. Harris
Theses and Dissertations
This research investigates a method of eigenstructure assignment for the classes of controllers known as positive definite output feedback control. The research began with a closed loop system with output feedback control that utilizes a collocated actuator-sensor pair. It is shown that this system is robust because it is globally stable for positive definite feedback. Analytical analysis is then completed to determine gains that minimize a cost function that is the error between the desired and achievable (assuming positive definite output feedback) eigenstructure. Examples are given at the end of the thesis to validate the computer code and theory results.
Effects Of Pressure Gradients On Turbulent Boundary Layer Flow Over A Flat Plate With Riblets, Franklin L. Dement Jr.
Effects Of Pressure Gradients On Turbulent Boundary Layer Flow Over A Flat Plate With Riblets, Franklin L. Dement Jr.
Theses and Dissertations
The Air Force Institute of Technology Boundary Layer Research Facility test section was modified to create controlled non-zero streamwise pressure gradients. The capability of the modified facility to reproduce theoretical laminar boundary layer velocity profiles and to create a self-preserving flow with an adverse streamwise pressure gradient was verified with three-dimensional laser Doppler anemometry. The effects of streamwise adverse and favorable pressure gradients on turbulent boundary layer flow characteristics (velocity profiles, turbulence and skin friction) and vortex formation over a flat plate with riblets at low speed (U = 5 mIs) were studied. Normal and spanwise velocity profiles for both …