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Articles 4531 - 4560 of 5699
Full-Text Articles in Engineering
Manual Tracking Flight Control With Amplitude And Rate Constrained Dynamic Actuators, Russel B. Miller
Manual Tracking Flight Control With Amplitude And Rate Constrained Dynamic Actuators, Russel B. Miller
Theses and Dissertations
A new control methodology for manual flight control, viz., real-time tracking control, is developed. Amplitude and rate constrained dynamic actuators are considered. Optimal tracking control is made possible by the use of unique reference signal prediction strategies which extrapolate the reference signal over the optimization horizon. A receding horizon, linear-quadratic inner-loop controller is employed in conjunction with an outer-loop nonlinear element. The constraint effects mitigation strategy is to optimally track a modified reference signal which yields feasible actuator commands over the optimization horizon when the pilot demanded reference is too aggressive to be tracked by the inner-loop optimal control law. …
An Object-Oriented Discrete-Event Simulation System For Hierarchical Parallel Simulations, Kenneth W. Stauffer
An Object-Oriented Discrete-Event Simulation System For Hierarchical Parallel Simulations, Kenneth W. Stauffer
Theses and Dissertations
The purpose of this research is to design and implement an object-oriented discrete-event simulation system which supports hierarchically constructed players in a parallel or distributed environment. This system design considers modularity and portability so additional modules may be implemented to experiment with new algorithms for both partitioning and synchronization. A simulation system which meets these requirements was partially implemented on an eight-node Intel Hypercube in C. A desired goal was to maintain the functionality of the existing BattleSim application. Test cases used measure the performance and correct operation of the new simulation architecture using a BattleSim subclass. Test results prove …
Modeling And Simulation Of Optical Characteristics Of Microelectromechanical Mirror Arrays, Peter C. Roberts
Modeling And Simulation Of Optical Characteristics Of Microelectromechanical Mirror Arrays, Peter C. Roberts
Theses and Dissertations
MEMS (Micro-Electro-Mechanical Systems) micromirror devices can be used to control the phase of a propagating light wavefront, and in particular to correct aberrations that may be present in the wavefront, due to either atmospheric turbulence or any other type of fixed or time and space varying aberrations. In order to shorten the design cycle of MEMS micromirror devices, computer software is developed to create, from MEMS micromirror device design data, a numerical model of the MEMS device. The model is then used to compute the far field diffraction pattern of a wavefront reflected from the device, and to predict the …
A Comparative Analysis Of Two Alternatives To Chemical Aircraft Paint Stripping, George P. Joyce Ii
A Comparative Analysis Of Two Alternatives To Chemical Aircraft Paint Stripping, George P. Joyce Ii
Theses and Dissertations
The Air Force must periodically strip and paint its aircraft to prevent the damaging effects of corrosion. The paint removal process typically involves the use of toxic chemicals such as methylene chloride which are soon to be banned as a result of impending environmental regulations and increased costs associated with handling and disposing of such material. The Air Force must choose an alternative to methylene chloride chemical stripping which complies with environmental regulations and reduces costs. This thesis compares the life cycle costs and environmental impacts of two alternatives to chemical aircraft stripping. Plastic Media Blasting (PMB) and Modified Medium …
Study Of Desorption Of Contaminant From Synthetic Soil, Kung-Fu Hwang
Study Of Desorption Of Contaminant From Synthetic Soil, Kung-Fu Hwang
Theses and Dissertations
A better understanding of sorption and desorption processes could improve estimates of time and cost required for remedial activities, exposure times and health risk, and bioavailability. Conventional rate-limited sorption models do not accurately define the diffusion domain at the grain scale. Heyse (1994) proposed the multiple sites in series (MSS) model, which allows more general description of the geometry of the sorption domain than the classical spherical or discrete distributions. A version of this model was tested by deVenoge (1996). The model was able to accurately simulate sorption rate data, but could not estimate unique geometry parameters. This research is …
A Decision Support Model For Municipal Solid Waste Recycling At United States Air Force Installations, Gergory A. Williams
A Decision Support Model For Municipal Solid Waste Recycling At United States Air Force Installations, Gergory A. Williams
Theses and Dissertations
The United States Air Force requires each installation to operate a municipal solid waste recycling program. Two inherently conflicting objectives, waste material diversion and financial result, have been established for the program. Reducing landfill disposal is the primary objective, but the incentive for profit is strong because each installation can retain profits from the program. Installations can be divided into two distinct areas, commercial and residential, based on the waste stream composition and funding. Structuring of the recycling program is often done in an ad-hoc manner. A decision support model was developed to evaluate four methods for each area. The …
An Investigation Of Instantaneous Plume Rise From Rocket Exhaust, Paul F. Sand
An Investigation Of Instantaneous Plume Rise From Rocket Exhaust, Paul F. Sand
Theses and Dissertations
Rocket launches at Vandenburg Air Force Base and Cape Canaveral Air Station produce exhaust clouds containing several toxic by-products, including HC1 and A12O3. These clouds rise to atmospheric stabilization heights, and then start dispersing and diffusing through the air. Upon reaching the ground, concentration levels of the toxins may present a human health risk. To predict these risks and concentration levels, range officials use a computer program titled the Rocket Effluent Exhaust Diffusion Model (REEDM). The version currently in use has been shown to underpredict the stabilization height of the exhaust cloud. This thesis examines the theory and algorithms used …
Habitat Suitability Mapping Through Integration Of Multicriteria Evaluation Techniques With A Geographic Information System (Gis), Anthony A. Ference
Habitat Suitability Mapping Through Integration Of Multicriteria Evaluation Techniques With A Geographic Information System (Gis), Anthony A. Ference
Theses and Dissertations
The presence of an endangered species, the Pacific Pocket Mouse (PPM), in critical Marine Corps training areas aboard Camp Pendleton may adversely affect training activities that are crucial to meeting the Marine Corps' mission. Camp Pendleton must focus limited budgetary assets for live trapping surveys of the PPM in the areas of best habitat suitability and the purpose of this study was to develop a PPM habitat suitability map of Camp Pendleton. Suitability maps were developed by integrating expert opinion with the Camp Pendleton Geographic Information System (GIS) database.
Applying Probabilistic Risk Assessment And Decision Analysis Techniques To Avoid Excessive Remedial Investigation Costs, Alejandro Hinojos
Applying Probabilistic Risk Assessment And Decision Analysis Techniques To Avoid Excessive Remedial Investigation Costs, Alejandro Hinojos
Theses and Dissertations
The majority of remediation resources have been consumed by costly and lengthy remedial investigation studies to characterize the human health risk. Unable to deal directly with the uncertainty resulting from the convolution of the uncertainties in a multitude of variables, and heavily persuaded by the liabilities, decision makers and regulators have relied on conservative assumptions and more studies to take appropriate actions. The main objective of this research is to provide tools and techniques to aid risk analysts in determining whether it would be beneficial to gather additional information or whether the decision to take an appropriate action can be …
Economic Valuation Of Air Force Environmental Resources: A Contingent Valuation Case Study, Timothy P. Haynie
Economic Valuation Of Air Force Environmental Resources: A Contingent Valuation Case Study, Timothy P. Haynie
Theses and Dissertations
The Air Force spends $1 billion each year to preserve, maintain, and restore environmental resources under its control (Budget of the United States Government, 1994). Assessing the benefit of this spending is a central issue in federal environmental management. As federal environmental management moves from a "clean it up at any cost" mentality to one which carefully considers the costs and benefits of spending, a fundamental question arises: What value of environmental resources does our environmental spending provide? As in any rational economic exchange benefits must exceed costs; the value of an environmental resource which benefits from public spending must …
Determining The Optimum Strategy Of Techniques From The Municipal Solid Waste Management Hierarchy To Maximize Social Value, Camille M. Still
Determining The Optimum Strategy Of Techniques From The Municipal Solid Waste Management Hierarchy To Maximize Social Value, Camille M. Still
Theses and Dissertations
Environmental managers must make difficult decisions regarding how to manage solid waste generation and disposal. The primary waste management alternatives are source reduction, recycling, composting, incineration, and landfilling often, waste management policies are based entirely on technical considerations and ignore that actual disposal practices depend on individuals' attitudes and behaviors. This research formulated a decision analysis model that incorporates social value measures to determine the waste management strategy that maximizes the individuals' willingness to participate. The social values that are important and that were considered in the decision support model to assist with making decisions about solid waste management were …
Independent Verification And Validation Of The Hazardous Material Cost Trade-Off Analysis Tool Developed By The Human Systems Center At Brooks Air Force Base, Thomas S. Choi
Theses and Dissertations
The Air Force realizes that the life cycle cost (LCC) associated with hazardous materials is a significant cost in the acquisition of major weapon systems. In trying to mitigate the growth of environmental LCC for future weapon systems, the Air Force has developed a tool called the Hazardous Material Cost Trade-off Analysis Tool (HAZMAT CTAT). The HAZMAT CTAT estimates the LCC for weapon system hazardous materials, so that intelligent decisions can be made in the early stages of the acquisition process. The problem with implementing this program into the acquisition process is that an independent computer model evaluation has never …
An Activity Driver Based Analysis Of Hazardous Materials Usage At Wright-Patterson Afb, Charles D. Perham
An Activity Driver Based Analysis Of Hazardous Materials Usage At Wright-Patterson Afb, Charles D. Perham
Theses and Dissertations
As the Air Force has progressed and succeeded in the realm of pollution prevention, the opportunities for further progress have become more challenging. With the 'low-hanging fruit' now gone from the pollution prevention tree, new methods to identify opportunities must be adopted. This research effort applied a subset of activity based costing, activity driver analysis, to reveal pollution prevention opportunities in regards to hazardous materials usage. A sample of base organizations (civil engineering and aircraft maintenance), and a sample of the hazardous chemicals (Class C or most hazardous) used by those organizations were investigated to determine the drivers behind usage.
A Two-Phase Damped-Exponential Model For Speech Synthesis, H. Allan Arb
A Two-Phase Damped-Exponential Model For Speech Synthesis, H. Allan Arb
Theses and Dissertations
It is well known that there is room for improvement in the resultant quality of speech synthesizers in use today. This research focuses on the improvement of speech synthesis by analyzing various models for speech signals. An improvement in synthesis quality will benefit any system incorporating speech synthesis. Many synthesizers in use today use linear predictive coding (LPC) techniques and only use one set of vocal tract parameters per analysis frame or pitch period for pitch-synchronous synthesizers. This work is motivated by the two-phase analysis-synthesis model proposed by Krishnamurthy. In lieu of electroglottograph data for vocal tract model transition point …
Analysis Of Multimode Low-Probability-Of-Intercept (Lpi) Communications With Atmospheric Effects, Ala Ghordlo
Analysis Of Multimode Low-Probability-Of-Intercept (Lpi) Communications With Atmospheric Effects, Ala Ghordlo
Theses and Dissertations
This research expanded Low Probability of Intercept (LPI) communications analysis in two areas. First, multimode communication was included to account for ground to ground and air to ground links in addition to the standard air to air links traditionally used in LPI analysis. The propagation equations for the three modes of interest were derived and included in LPI analytic models in the form of a mode quality factor to account for multimode LPI scenarios. This new quality factor was used in studying several communication and interception link combinations. Variations due to differences between the communication and interception modes were presented …
Development Of Object-Based Teleoperator Control For Unstructured Applications, Hyunki Cho
Development Of Object-Based Teleoperator Control For Unstructured Applications, Hyunki Cho
Theses and Dissertations
For multi-fingered end effectors in unstructured applications, the main issues are control in the presence of uncertainties and providing grasp stability and object manipulability. The suggested concept in this thesis is object based teleoperator control which provides an intuitive way to control the robot in terms of the grasped object and reduces the operator's conceptual constraints. The general control law is developed using a hierarchical control structure, i.e., human interface I gross motion control level in teleoperation control and fine motion control/object grasp stability in autonomous control. The gross motion control is required to provide the position/orientation of the Super …
Application Of A Finite-Volume Time-Domain Maxwell Equation Solver To Three-Dimensional Objects, Frederick G. Harmon
Application Of A Finite-Volume Time-Domain Maxwell Equation Solver To Three-Dimensional Objects, Frederick G. Harmon
Theses and Dissertations
Concurrent engineering approaches for the disciplines of computational fluid dynamics (CFD) and electromagnetics (CEM) are necessary for designing future high-performance, low-observable aircraft. A characteristic-based finite-volume time-domain (FVTD) computational algorithm, developed for CFD and now applied to CEM, is implemented to analyze the radar cross section (RCS) of two three-dimensional objects, the ogive and cone-sphere. The FVTD formulation implements a Monotone Upstream-Centered Scheme for Conservation Laws (MUSCL) algorithm for the flux evaluation and a Runge-Kutta multi-stage scheme for the time integration. Developmental FVTD work for the thesis focused on algorithm development to analyze scattering and obtain RCS data for closed-surface perfect …
Multiple Model Adaptive Estimation And Control Redistribution For The Vista F-16, Robert W. Lewis Sr.
Multiple Model Adaptive Estimation And Control Redistribution For The Vista F-16, Robert W. Lewis Sr.
Theses and Dissertations
Performance characteristics of a Multiple Model Adaptive Estimation and Control Redistribution (MMAE/CR) algorithm are evaluated against single and double actuator and sensor failures. MMAE alone can compensate for sensor failures, whereas Control Redistribution compensates for actuator failures by redistributing commands, initially intended for failed actuators, to the unfailed actuators in such a way that the desired system response is achieved. Both failure detection and compensation capabilities are developed and analyzed through an extensive amount of simulation data, particularly addressing multiple failures. Simulations are performed utilizing the high fidelity, non-linear six degree of freedom Simulation Rapid Prototyping Facility for the VISTA …
Evaluation Of Hazardous Material Life Cycle Cost Tools For Use In Air Force Hazardous Material Pharmacies, Rowene J. Resler
Evaluation Of Hazardous Material Life Cycle Cost Tools For Use In Air Force Hazardous Material Pharmacies, Rowene J. Resler
Theses and Dissertations
This research focuses on evaluation of various tools that assist in the selection of hazardous material substitutes. Substitute material consideration is a function of the Hazardous Material Pharmacy (HMP) when a hazardous material is requested for purchase and use in a current base operation. The substitute material decision is complex, involving identification of potential substitutes and then comparison of factors, such as cost, performance, and environmental effects, between the potential substitute and the material being requested. Various tools such as life cycle cost models, databases, and other information services can provide assistance to HMPs making substitution decisions.
Evaluation Of Design Tools For Rapid Prototyping Of Parallel Signal Processing Algorithms, James C. Savage
Evaluation Of Design Tools For Rapid Prototyping Of Parallel Signal Processing Algorithms, James C. Savage
Theses and Dissertations
Digital signal processing (DSP) has become a popular method for handling not only signal processing, but communications, and control system applications. A DSP application of interest to the Air Force is high speed avionics processing. The real time computing requirements of avionics processing exceed the capabilities of current single chip DSP processors, and parallelization of multiple DSP processors is a solution to handle such requirements. Designing and implementing a parallel DSP algorithm has been a lengthy process often requiring different design tools and extensive programming experience. Through the use of integrated software development tools, rapid prototyping becomes possible by simulating …
Performance Analysis Of Preemption Algorithms In An Idnx Circuit Switch Communications Network, Eric C. Gumbs
Performance Analysis Of Preemption Algorithms In An Idnx Circuit Switch Communications Network, Eric C. Gumbs
Theses and Dissertations
Access to communication networks is increasing rapidly. The increase access to these networks results in delays and at times loss of data. At times of peak traffic or when trunks or nodes are down, very important customers' communications requirements are not met. One way to combat this problem is to prioritize the network and provide different levels of grade of service (GOS) for each priority. Call preemption provides an effective method of obtaining different levels of GOS. This research seeks to design the best circuit switch communications network preemption model for the DoD by analyzing previously developed preemption algorithms. Four …
Interference Suppression For Spread Spectrum Signals Using Adaptive Beamforming And Adaptive Temporal Filter, Wonjin Park
Interference Suppression For Spread Spectrum Signals Using Adaptive Beamforming And Adaptive Temporal Filter, Wonjin Park
Theses and Dissertations
Interference and jamming signals are a serious concern in an operational military communication environment. This thesis examines the utility and performance of combining adaptive temporal filtering with adaptive spatial filtering (i.e. adaptive beamforming) to improve the signal-to-jammer ratio (SJR) in the presence of narrowband and wideband interference. Adaptive temporal filters are used for narrowband interference suppression while adaptive beamforming is used to suppress wideband interference signals. A procedure is presented for the design and implementation of a linear constraints minimum variance generalized sidelobe canceler (LCMV-GSC) beamformer. The adaptive beamformer processes the desired signal with unity gain while simultaneously and adaptively …
Experimental Investigation Of Radar Cross Section Spatial Correlation Properties For A Point Scattering Target, John D. Shannon
Experimental Investigation Of Radar Cross Section Spatial Correlation Properties For A Point Scattering Target, John D. Shannon
Theses and Dissertations
This research investigates the spatial correlation of RCS. In pulsed radar systems, probability of detection for partially correlated signals depends on the autocovariance of the target's RCS. The RCS changes pulse to pulse due to spatial and time fluctuations. Spatial fluctuation are due to the motion of all scatterers relative to the radar (i.e. changing aspect angle). Time fluctuations are due to relative motion of scatterers to each other (i.e. wings flexing, engines spinning). Theory developed at AFIT [9] can generate autocovariance estimates from a distribution of scatterers. Theory based autocovariance estimates are compared to static measurement based autocovariance estimates …
Personnel Airdrop Risk Assessment Using Bootstrap Sampling, Wonsik Kim
Personnel Airdrop Risk Assessment Using Bootstrap Sampling, Wonsik Kim
Theses and Dissertations
Previous work on personnel airdrop problems involving jumpers has been (1) event-oriented entanglement rates, (2) number of canopy bumps, (3) landing injuries, and (4) deaths. The thesis expands this area of research by developing cumulative distribution functions of maximum possible chute entanglement risk for the C-17 using bootstrap techniques. By comparing the effects of various C-17 aircraft configurations on the entanglement CDF, this thesis shows that under certain configurations the risk of centerline entanglement for the C-17 is less than for the C-141.
Digital Rosetta Stone: A Conceptual Model For Maintaining Long-Term Access To Digital Documents, Steven B. Robertson
Digital Rosetta Stone: A Conceptual Model For Maintaining Long-Term Access To Digital Documents, Steven B. Robertson
Theses and Dissertations
Due to the rapid evolution of technology, future digital systems may not be able to read and/or interpret the digital recordings made by older systems, even if those recordings are still in good condition. This thesis addresses the problem of maintaining long-term access to digital documents and provides a methodology for overcoming access difficulties due to technological obsolescence. A review was conducted to determine the long-term access methods that have already been suggested by other researchers. These previously suggested methods are then combined with other ideas that were encountered and conceived while performing research for this project. The combination of …
Using Kriging To Interpolate Spatially Distributed Volumetric Medical Data, Stephen M. Matechik
Using Kriging To Interpolate Spatially Distributed Volumetric Medical Data, Stephen M. Matechik
Theses and Dissertations
Routine cases in diagnostic radiology require the interpolation of volumetric medical imaging data sets. Inaccurate renditions of interpolated volumes can lead to the misdiagnosis of a patient's condition. It is therefore essential that interpolated modality space estimates accurately portray patient space. Kriging is investigated in this research to interpolate medical imaging volumes. Kriging requires data to be spatially distributed. Therefore, magnetic resonance imaging (MRI) data is shown to exhibit spatially regionalized characteristics such that it can be modeled using regionalized variables and subsequently be interpolated using kriging. A comprehensive, automated, three-dimensional structural analysis of the MRI data is accomplished to …
Perceptual Fidelity For Digital Color Imagery, Curtis E. Martin
Perceptual Fidelity For Digital Color Imagery, Curtis E. Martin
Theses and Dissertations
The problem of measuring the fidelity of digital color images in a manner that corresponds to human perceptual assessments is addressed. Experiments are performed to validate human visual system (HVS) models, which provide access to a 'perceptual space' in which visual distortions may be measured, and then a model is proposed for assessing the perceptual fidelity of digital color image. Color Mach bands are produced in the first experiment, demonstrating that, as in the brightness channel, low spatial frequency attenuation occurs in the chromatic channels of the HVS. In the second experiment, a correlation between the chromatic channels of the …
Model Predictive Control Of Aerospace Systems, Derek W. Ebdon
Model Predictive Control Of Aerospace Systems, Derek W. Ebdon
Theses and Dissertations
The primary objective of this thesis is to explore the fault tolerance capabilities of a state space formulation of MPC. Subsequent to a simulated control surface failure on the F-18 High Alpha Research Vehicle (HARV), the MPC controller will attempt to maintain stability and nominal performance while tracking a setpoint. Secondary objectives include studying the effect of data sample rate and MPC horizon lengths on system performance. These objectives will be accomplished using Matlab to develop the MPC controller and Simulink to demonstrate its effectiveness through simulation.
Performance Analysis Of A Liquid Metal Heat Pipe Space Shuttle Experiment, Timothy J. Dickinson
Performance Analysis Of A Liquid Metal Heat Pipe Space Shuttle Experiment, Timothy J. Dickinson
Theses and Dissertations
Future spacecraft technologies require advanced high-temperature thermal control systems. Liquid metal heat pipes are considered ideally suited for such applications. However, their behavior during microgravity operation is not yet understood. This study investigated liquid metal heat pipe performance in such an environment. Three stainless steel/potassium heat pipes were flown on space shuttle mission STS-77 in May 1996. The objectives of the experiment were characterization of the frozen startup and restart transients, comparison of flight and ground test data to establish a performance baseline for analytical model validation, and assessment of three different heat pipe designs. Heat pipe performance was characterized …
Multidisciplinary And Multiobjective Optimization In Conceptual Design For Mixed-Stream Turbofan Engines, Luc J. J. P. Nadon
Multidisciplinary And Multiobjective Optimization In Conceptual Design For Mixed-Stream Turbofan Engines, Luc J. J. P. Nadon
Theses and Dissertations
Despite major advances in design tools such as engine cycle analysis software and computer aided design, conceptual gas turbine engine design is essentially a trial-and-error process based on the experience of engineers. Modern optimization concepts, such as multidisciplinary optimization (MDO), and multiobjective optimization (MOO), linked with sequential quadratic programming (SQP) methods and genetic algorithms (GA), were applied to the conceptual engine design process to automate the conceptual design phase. Robust integrated computer codes were created to find the optimal values of eight engine parameters in order to minimize fuel usage, aircraft cost and engine annulus area over a given mission. …