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Articles 5401 - 5430 of 5697
Full-Text Articles in Engineering
Propulsive Capability Of A Reel-In Tether With Safe Separation Between Payload And Orbiter, Jay H. Rothhaupt
Propulsive Capability Of A Reel-In Tether With Safe Separation Between Payload And Orbiter, Jay H. Rothhaupt
Theses and Dissertations
This study investigates the use of a massless reel-in tether for propulsion of a payload following deployment from an orbiter. The distance between the payload and orbiter at closest passage is addressed. A literature review revealed several tether concepts, extensive tether research, and numerous mathematical models. However, previous work in the area of reel-in tethers is limited to propulsion feasibility. The reel-in tether is operated following optimum ejection of the payload from the orbiter using a free arc and subsequent full arc. The free arc of zero tether tension provides initial separation. Switching to a full arc of continuously-maximum tension …
An Investigation Of Optimally Robust Structural Damping Through Fractional Order Feedback, Mark T. Leonard
An Investigation Of Optimally Robust Structural Damping Through Fractional Order Feedback, Mark T. Leonard
Theses and Dissertations
The purpose of this investigation was to determine if introducing fractional order states in a feedback system was beneficial to overall system performance. Fractional order differential equations have been used in the past primarily to model viscoelastic damping in structures. this study examined the use of fractional order differential equations in formulating a control algorithm with additional degrees of freedom. The algorithm presented is best suited for active structural damping. Including the fractional order time derivatives in the state allowed some additional flexibility in choosing relevant control parameters in the system. Optimization with respect to robustness was examined to determine …
Static Pressure Measurements Of A Low Power Arcjet, Kevin P. Talley
Static Pressure Measurements Of A Low Power Arcjet, Kevin P. Talley
Theses and Dissertations
The NASA Lewis 1.2 kilowatt arcjet has been used for a number of performance and lifetime studies. This design was modified to obtain static pressure measurements at several locations along the arcjet nozzle. These measurements were taken at various propellant flow rates over most of the operational envelope of the thruster. Measured static pressure distributions are considerably higher than predicted by ID models and are proportional to the arc power. A simple thermodynamic model is also compared to the data, and is shown to match the slope of the data while overpredicting the pressure.
Logic Programming In Digital Circuit Design, Joseph W. Eicher
Logic Programming In Digital Circuit Design, Joseph W. Eicher
Theses and Dissertations
The design of large, complex digital circuitry requires highly skilled engineers. Much of the time spent by these engineers in the design phase involves tasks that are repetitive, tedious, and slow. If these repetitive tasks are automated, the engineer can spend more time managing the design process and produce a better-quality design in less time. Logic programming can be used to automate design tasks, even those that require a high degree of skill. This thesis investigates several aspects of the digital circuit design process that involve pattern-matching paradigms suitable for encoding in the logic programming language Prolog.
Frequency Domain Speech Coding, Shane Switzer
Frequency Domain Speech Coding, Shane Switzer
Theses and Dissertations
The major goal of this research was to investigate speech coding techniques in an attempt to achieve high quality speech transmittable at 4800 bits per second. The approach taken to achieve this goal was to code the frequency domain representation of speech. Speech was represented by a sparse set of frequency components. Four frequency selections schemes were implemented, and the resulting frequency coefficients (magnitude and phase) were coded in an efficient manner for transmission. Specific techniques involved in the speech coder included: (1) a recurrent neural architecture to make a periodic/noiselike decision, (2) the use of variable length windows for …
Formal Verification Of Digital Logic, Stuart L. Labovitz
Formal Verification Of Digital Logic, Stuart L. Labovitz
Theses and Dissertations
The most widely used technique for checking the correctness of digital circuits designs is simulation. As the complexity of digital circuits has continued to grow, however, circuit designers have become unable to perform complete simulations of their integrated circuits. Formal hardware verification provides an alternative approach, performing a series of mathematical proofs in order to show that the construction of the circuit from its submodules will result in the intended overall circuit behavior. Papers by Barrow in 1983 and 1984 discuss a PROLOG-based hierarchical formal circuit verification system named VERIFY. AFIT VERIFY, a simple, experimental reverse-engineered version of Barrow's VERIFY …
Requirements Analysis For A Hardware, Discrete-Event, Simulation Engine Accelerator, Paul J. Taylor Jr.
Requirements Analysis For A Hardware, Discrete-Event, Simulation Engine Accelerator, Paul J. Taylor Jr.
Theses and Dissertations
An analysis of a general Discrete Event Simulation (DES), executing on the distributed architecture of an eight mode Intel PSC/2 hypercube, was performed. The most time consuming portions of the general DES algorithm were determined to be the functions associated with message passing of required simulation data between processing nodes of the hypercube architecture. A behavioral description, using the IEEE standard VHSIC Hardware Description and Design Language (VHDL), for a general DES hardware accelerator is presented. The behavioral description specifies the operational requirements for a DES coprocessor to augment the hypercube's execution of DES simulations. The DES coprocessor design implements …
Implementation Of An Object-Oriented Flight Simulator D.C. Electrical System On A Hypercube Architecture, Guy R. Booth
Implementation Of An Object-Oriented Flight Simulator D.C. Electrical System On A Hypercube Architecture, Guy R. Booth
Theses and Dissertations
The Software Engineering Institute developed an Object-Oriented Paradigm for Flight Simulators based on the concept of mapping the behavior of physical objects from an aircraft into an object-oriented software architecture. This mapping is a semi-formal method that maps objects to a hierarchy that has three logical layers: objects, systems, and executives. The paradigm was developed with the idea of implementing the derived simulation design on a parallel or distributed computer architecture, but no explicity design features are provided for implementing the design on a parallel computer. This research addresses the issue of determining what extensions (if any) are required to …
Parallel Implementation Of Vhdl Simulations On The Intel Ipsc/2 Hypercube, Ronald C. Comeau
Parallel Implementation Of Vhdl Simulations On The Intel Ipsc/2 Hypercube, Ronald C. Comeau
Theses and Dissertations
VHDL models are executed sequentially in current commercial simulators. As chip designs grow larger and more complex, simulations must run faster. One approach to increasing simulation speed is through parallel processors. This research transforms the behavioral and structural models created by Intermetrics' sequential VHDL simulator into models for parallel execution. The models are simulated on an Intel iPSC/2 hypercube with synchronization of the nodes being achieved by utilizing the Chandy Misra paradigm for discrete-event simulations. Three eight-bit adders, the ripple carry, the carry save, and the carry-lookahead, are each run through the parallel simulator. Simulation time is cut in at …
An Object-Oriented Database Implementation Of The Magic Vlsi Layout Design System, Timothy M. Jacobs
An Object-Oriented Database Implementation Of The Magic Vlsi Layout Design System, Timothy M. Jacobs
Theses and Dissertations
This thesis attempts to prove that the commercially available Object Store data management system provide the performance and functionality necessary to support a complex engineering design system. This is accomplished by modifying the Magic VLSI circuit layout design system to eliminate its current Unix file data management system and replace it with Object Store. The approach to this research effort includes a design recovery of the Magic system and identification of its ket data management functions. These functions are then modified to take advantage of the database management facilities of Object Store. Additional code is added to instrument performance measurement …
Proportional Plus Integral Control Of Aircraft For Automated Maneuvering Formation Flight, John L. Dargan
Proportional Plus Integral Control Of Aircraft For Automated Maneuvering Formation Flight, John L. Dargan
Theses and Dissertations
In this study an automated formation control system for a lead and wing aircraft flight is developed. The proposed formation control system is capable of controlling like or dissimilar aircraft in maneuvering formation flight. Thus, two versions of the C-130 aircraft, the C-130A and the C-130B, are modelled. The C-130B has superior performance characteristics to that of the C- 130A. The wing aircraft continuously measures lead aircraft position with an ideal on-board relative position sensor, maneuvering to maintain relative position. External formation guidance is assumed to be released in a single data burst, consisting of formation geometry and nominal separation …
A Rigorous Utd Analysis Of Electromagnetic Scattering From Resistive Strips And Resistive-Loaded Conducting Strips, Douglas H. Casanova
A Rigorous Utd Analysis Of Electromagnetic Scattering From Resistive Strips And Resistive-Loaded Conducting Strips, Douglas H. Casanova
Theses and Dissertations
This thesis investigates electromagnetic scattering from resistive strips and resistive-loaded conducting strips using a rigorous UTD formulation. The UTD diffraction coefficients are based on the Wiener-Hopf technique and Jones' method. Scattering predictions are performed for constant resistive strips, constant resistive-loaded conducting strips, tapered resistive strips, and tapered resistive-loaded conducting strips. All strip geometries have a total width of 4 lambda. Predictions are compared to method of moments (MM) and measurements to determine the validity of the UTD prediction. Overall, there is good agreement. For TMz polarization the only deviations that occur with MM are near edge-on when the degree of …
Application Of Nonlinear Qft To Flight Control Design For High Angle Of Attack Maneuvers With Thrust Vectoring, Steven J. Rasmussen
Application Of Nonlinear Qft To Flight Control Design For High Angle Of Attack Maneuvers With Thrust Vectoring, Steven J. Rasmussen
Theses and Dissertations
Nonlinear Quantitative Feedback Theory (QFT) is applied to the design of an flight Control system (FCS) to control maneuvers of an agile aircraft. To do this, maneuvers are chosen that are desirable during within visual range combat. Plant transfer functions are developed through the use of system identification, using the input/output time histories of the maneuvers. During the system identification process the q sub ij(o) are found directly and are constrained to be minimum phase. After identifying the plants, the cascaded multiple-input multiple-output QFT technique is used to design the FCS. During the design of the FCS, stability boundaries are …
Radar Scattering From Foamed Plastic Target Supports, Michael W. Chambers
Radar Scattering From Foamed Plastic Target Supports, Michael W. Chambers
Theses and Dissertations
This study investigates the scattering from foamed ranges to support all sizes of targets for radar cross section measurements. Two common foamed plastics, styrofoam and expanded bead polystyrene (EPS), are discussed. Two types of scattering are associated with foamed plastic, coherent and incoherent. The incoherent is normally the lowest, but has not been satisfactorily quantified. Coherent scattering is related to the shape of the target, and the emphasis of this study is on the coherent return. One goal was to predict the coherent RCS of an EPS column using the Uniform Theory of Diffraction (UTD). It was found that UTD …
Electrically Erasable Programmable Integrated Circuits For Replacement Of Obsolete Ttl Logic, Joseph V. Breen
Electrically Erasable Programmable Integrated Circuits For Replacement Of Obsolete Ttl Logic, Joseph V. Breen
Theses and Dissertations
Two microcircuits with electrically erasable programmable logic arrays, which use Fowler-Nordheim (F-N) tunneling for both programming and erasing, were designed to demonstrate the use of programmable logic for obsolete TTL logic replacement. Each microcircuit was fabricated in the Orbit 2-micron double-poly low noise analog CMOS process through MOSIS. Software to generate VHDL structural models from a pin list was developed and the logic of both designs was verified by simulation using the Zycad VHDL simulator. The first microcircuit included a simple programmable logic circuit and test cells that allowed measurement of the programming characteristics of the floating gate transistors. Test …
Application Of Silicon Micromachining To Thermal Dissipation Issues In Wafer Scale Integrated Circuits, Edward Cosnyka
Application Of Silicon Micromachining To Thermal Dissipation Issues In Wafer Scale Integrated Circuits, Edward Cosnyka
Theses and Dissertations
The purpose of this research effort was to investigate the feasibility of applying the silicon micromachining technique to thermal management as applied to integrated circuits and wafer scale integration techniques. Three silicon micromachined structures and an untextured reference wafer were compared as heat-dissipating surfaces. These four surfaces were realized using 3-inch diameter, single crystal silicon wafers. The following structures were micromachined in silicon wafers using wet chemical, anisotropic etching and photolithographic techniques: (1) randomly spaced and sized pyramids in (100)-oriented silicon, (2) deep vertical-wall grooves in (110)-oriented silicon, and (3) micro-fluid channels in (100)-oriented silicon. The heat- dissipating silicon wafers …
Simulation Of Finite-Precision Effects In Digital Filters, Perry L. Choate
Simulation Of Finite-Precision Effects In Digital Filters, Perry L. Choate
Theses and Dissertations
This thesis develops and demonstrates software that models finite- precision effects in digital filters. Coefficient quantization and internally generated roundoff noise effects are simulated by rounding coefficients and multiplier output values to (B+1) bits. Outputs include magnitude and phase responses that may be plotted to show results of coefficient quantization. The output noise power due to roundoff is calculated. Three types of digital filter structures are examined. The first type is direct form I implementation for FIR and IIR structures, second is direct form II, and third is cascading the canonic direct form II second-order sections for higher order filter …
A Time-Dependent Adaptive Filter For Cochannel Interference Reduction, Matthew H. Foster
A Time-Dependent Adaptive Filter For Cochannel Interference Reduction, Matthew H. Foster
Theses and Dissertations
This thesis presents a Time Dependent Adaptive Filter (TDAF) which exploits the cyclostationarity of digitally modulated communications signals and seeks to improve the Signal to Interference Ratio (SIR) and Signal to Noise Ratio (SNR) of such signals. The TDAF is embedded in a computer simulation of a simple communication system consisting of a data source, data formatter, pulse shaping filter, BPSK modulator, and demodulator. In the simulation the TDAF and a Time Independent Adaptive Filter (TIAF) attempt to extract the Signal of Interest (SOI) from noise or interference. the criteria of Mean Squared Error (MSE) is used as the primary …
Swatter (Space-Based Weapons Against Tactical Terrestrial-Based Resources): A Design For Integrating Space Into A Theater Level Wargame, Duane R. Cozadd
Swatter (Space-Based Weapons Against Tactical Terrestrial-Based Resources): A Design For Integrating Space Into A Theater Level Wargame, Duane R. Cozadd
Theses and Dissertations
This thesis provides the foundation to expand the newly developed theater level computerized wargame, SABER, at the Air Force Wargaming Center, Maxwell AFB, Alabama to include space conflict at the theater level of simulation. Building upon the recently completed SABER, this thesis effort expands the conceptual framework of the model by integrating the dynamics of space warfare into the current theater level model. This expansion forms a new game called SWATTER. This thesis adds the space units required to integrate the land and air battles with the possible interactions from space. This thesis expands the stochastic attrition processes to include …
Improving Stochastic Communication Network Performance: Reliability Vs. Throughput, Leonard J. Jansen
Improving Stochastic Communication Network Performance: Reliability Vs. Throughput, Leonard J. Jansen
Theses and Dissertations
This research investigated the measurement and improvement of two performance parameters, expected flow and reliability, for stochastic communication networks. There were three objectives of this research. The first was to measure the reliability of large stochastic networks. This was accomplished through an investigation into the current methodologies in the literature, with a subsequent selection and application of a factoring program developed by Page and Perry. The second objective was to develop a reliability improvement model given that a mathematical reliability expression did not exist. This was accomplished modeling a heuristic by Jain and Gopal, into a linear improvement model. Finally, …
Separation Of Cloud/No-Cloud Regions In Satellite Imagery Using A Variation Of Hierarchical Clustering Analysis, Charles J. Martin Jr.
Separation Of Cloud/No-Cloud Regions In Satellite Imagery Using A Variation Of Hierarchical Clustering Analysis, Charles J. Martin Jr.
Theses and Dissertations
This study investigated the usefulness of personal-computer-based software applying hierarchical clustering theory to try to separate cloud- covered regions from clear regions using Automated Picture Transmission imagery from the National Oceanographic and Atmospheric Administration's Television Infrared Observation Satellite. The algorithms were developed in Turbo Pascal, Version 6, and are part of the Training Software Image Processing program developed by a professor at the Air Force Institute of Technology. The goal of the project was to see if hierarchical clustering could provide better separation of cloud/no-cloud regions than an existing technique, histogram thresholding, while running on a personal computer. Results of …
An Analysis Of Tracking And Impact Predictions, Susanne V. Lefebvre
An Analysis Of Tracking And Impact Predictions, Susanne V. Lefebvre
Theses and Dissertations
The accuracy of the United States Space Command's early Tracking and Impact Predictions and its OPREP-3 report initiation procedure are analyzed. The study involves satellites which decayed between 1987 and 1990. Each of the early decay predictions are compared to the final prediction with the resulting time error compared to the accuracy level asserted by the Space Surveillance Center. The results of this study indicate that the accuracy of the decay predictions is usually, but not always, within the asserted accuracy level. The results also suggest the existence of a positive bias indicating that the early decay predictions are routinely …
Radar System Classification Using Neural Networks, David M. Cameron
Radar System Classification Using Neural Networks, David M. Cameron
Theses and Dissertations
This study investigated methods of improving the accuracy of neural networks in the classification of large numbers of classes. A literature search revealed that neural networks have been successful in the radar classification problem, and that many complex problems have been solved using systems of multiple neural networks. The experiments conducted were based on 32 classes of radar system data. The neural networks were modelled using a program called the Neural Graphics Analysis System. It was found that the accuracy of the individual neural networks could be increased by controlling the number of hidden nodes, the relative numbers of training …
A Dynamic Computer Graphics Model Of Satellite Orbits For Use In Instruction And Analysis, John P. Anton
A Dynamic Computer Graphics Model Of Satellite Orbits For Use In Instruction And Analysis, John P. Anton
Theses and Dissertations
A computer model of satellite orbits was developed to illustrate difficult orbital concepts. It was also designed to analyze the positions of a satellite constellation with respect to locations on the earth as an aid to analysts. A literature review revealed that existing methods relay on drawings, expensive computers, or are satellite system specific, but that it would be possible to develop such a tool for an IMB-compatible personal computer using the Pascal language. Model capabilities selected included (1) a menu driven user interface; (2) a screen display showing satellite locations, ground track, and an earth map in one of …
Preliminary Design Of A Model To Assess The Effect Of Space Surveillance Network (Ssn) Sensor Upgrades On Orbit Prediction Accuracies Relative To The U. S. Anti-Satellite (Asat) Mission, Daniel L. O'Brien
Theses and Dissertations
This study gives a basis for implementation of a model to assess the effect of proposed sensor upgrades to the Space Surveillance Network (SSN) to determine if more accurate orbital element set predictions by the Space Surveillance Center (SSC) can be obtained for U.S. anti-satellite (ASAT) targeting. Handoff orbital element set predictions to nearby ASAT facilities for single, low-orbit satellite passes over a single radar sensor are considered. Model development began with simulation of the selected satellites passing over the selected sensors producing baseline truth observations based on the NORAD simplified General Publications (SGP4) model. Sensor errors, in the form …
The Application Of Statistical Kriging To Improve Satellite Imagery Resolution, Donald W. Mcgee Jr.
The Application Of Statistical Kriging To Improve Satellite Imagery Resolution, Donald W. Mcgee Jr.
Theses and Dissertations
Imagery analysts are always looking for improved methods of analyzing digital satellite imagery. The resolution of satellite imagery can be improved by enlarging the images since the result will be a higher degree of discernable detail. Currently, nearest-neighbor, bilinear interpolation, and cubic convolution techniques are used for this purpose. The nearest-neighbor technique produces block-like images. The latter two methods produce sharp imagery, but the original information contained in the pixel values is changed in the process of convolving the image. These techniques cannot, therefore, be considered true representations of the original image. Kriging is a statistical technique which can be …
A Formal Definition Of The Object-Oriented Paradigm For Requirements Analysis, Andrew D. Boyd
A Formal Definition Of The Object-Oriented Paradigm For Requirements Analysis, Andrew D. Boyd
Theses and Dissertations
This paper develops a formal definition of the Object-Oriented paradigm for requirements analysis. The literature was surveyed for both formal and informal methods for conducting an Object-Oriented Requirements Analysis (OORA). The informal methods reviewed are: Bailin's, Shlaer and Mellor's, Booch's, and Coad and Yourdon's. The formal methods reviewed are: Bralick's, Z, and REFINE. None of the methods were found to be adequate for doing an OORA. A formal definition of an OORA, based on the concept of classes, is developed. The definition itself is presented as set and relation theory. A supporting graphical representation is also developed and presented. The …
Verification And Validation Of The Comprehensive Operational Support Evaluation Model For Space, Lawrence A. Cooper
Verification And Validation Of The Comprehensive Operational Support Evaluation Model For Space, Lawrence A. Cooper
Theses and Dissertations
This study details the verification and validation (V and V) of the Comprehensive Operational Support Evaluation Model for Space (COSEMS). COSEMS is an Ada-based simulation which models spacecraft constellation support concepts such as support from the ground and on-orbit support. While the model is intended for use in analyzing Strategic Defense System concepts, it can easily evaluate non-military satellite constellations. The V&V was confined to a subset of the over 200 subprograms which comprise COSEMS. This subset covered random number generation, reliability, orbital mechanics, and mission planning functions. The study used traces and comparison to other models to perform the …
Binaural Sound Localization Using Neural Networks, Rushby C. Craig
Binaural Sound Localization Using Neural Networks, Rushby C. Craig
Theses and Dissertations
The purpose of this study was to investigate the use of Artificial Neural Networks to localize sound sources from simulated, human binaural signals. Only sound sources originating from a circle on the horizontal plane were considered. Experiments were performed to examine the ability of the networks to localize using three-different feature sets. The feature sets used were: time-samples of the signals, mena Fast Fourier Transform magnitude and cross correlation data, and auto-correlation and cross correlation data. The two different types of sound source signals considered were tones and gaussian noise. The feature set which yielded the best results in terms …
Determination Of Bistatic Radar Clutter Power From Topographic Data, Clyde R. Heddings
Determination Of Bistatic Radar Clutter Power From Topographic Data, Clyde R. Heddings
Theses and Dissertations
The purpose of this research was to develop a procedure for estimating the average bistatic radar clutter power from a topographic map using rough surface scattering theory. First, the terrain in the radar target area was divided into sub regions having homogeneous characteristics. A joint Gaussian distribution for the surface heights was fitted from the information contained in the topographic map contour lines for each homogeneous area. From these distributions, the normalized radar cross section for each terrain area was determined. The clutter power for each range cell was then determined via a modified radar range equation. The procedure was …