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Articles 5341 - 5370 of 5596
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Application Of Finite Element Modeling And Analysis To The Design Of Positive Pressure Oxygen Masks, Bruce H. Bitterman
Application Of Finite Element Modeling And Analysis To The Design Of Positive Pressure Oxygen Masks, Bruce H. Bitterman
Theses and Dissertations
This study investigated tools and techniques for performing finite element analysis of the MBU-20/P pilot's oxygen mask. The problem which was investigated was the fit of the mask to the face at Positive Pressure Breathing (PPB) pressures. Deformed geometry of the mask and reaction forces on the face were calculated to provide a measure of the fit. The MBU-20/P mask was first digitized by 3-D digitizer. A computer program was written to translate the digitized coordinate data to a finite element format for two commercial packages. The packages targeted were SDRC I-DEAS and PDA PATRAN. Other supplementary programs were written …
A Comparison Of Fractional Order Time Derivative Models Of The Viscoelastic Stress Relations In Thermorheologically Complex Materials, Victor B. Chambers
A Comparison Of Fractional Order Time Derivative Models Of The Viscoelastic Stress Relations In Thermorheologically Complex Materials, Victor B. Chambers
Theses and Dissertations
The purpose of this thesis was to examine the viscoelastic behavior of thermorheologically complex materials, a typical example of which is a soft, rubbery material. Materials such as these are very useful in damping vibrations in structures, but the relaxation moduli of these materials change significantly with temperature and frequency. In the case of space structures applications where temperatures vary greatly and a stable platform is necessary, a method to predict this changing modulus is needed. The original approach was to validate a previously developed viscoelastic model, but the task expanded to include extending the model to materials with two …
A Comparative Study Of Numerical Versus Analytical Waverider Solutions, Gregory O. Stecklein
A Comparative Study Of Numerical Versus Analytical Waverider Solutions, Gregory O. Stecklein
Theses and Dissertations
The WL/FIMM explicit, Roe flux-splitting Euler algorithm is applied to the inviscid hypersonic flow over a parabolic-top waverider configuration optimized for Mach 10 at zero degrees angle of attack. An on-design grid refinement study is conducted to determine the asymptotic nature of the optimized flight parameter L/D. A parametric study of off-design conditions is conducted to determine flow perturbation effects on HSDT waverider theory. A validation of the Euler code is conducted through a comparison of the numerical data to analytical results derived by Rasmussen. The grid refinement study shows little effect on the inviscid calculation of the optimized parameter …
Finite Element Analysis Of A Riveted Repair On A Curved Composite Panel, Scott A. Hamilton
Finite Element Analysis Of A Riveted Repair On A Curved Composite Panel, Scott A. Hamilton
Theses and Dissertations
To analyze the current Aircraft Battle Damage Repair (ABDR) techniques, a finite element model (FEM) of a curved composite panel with a center cutout section was developed and verified against previously obtained modal test results. The FEM was modified using different methods to exhibit the effects of riveting on an aluminum patch to repair the section. The different methods were contrasted against each other and previously obtained modal test results. The panel, a (0/-45/+45/90) sub s layup of AS4/3501 graphite epoxy measuring 12 inches in height and 12.19 inches across its arc length with a 2 by 4 inch cutout …
An Algorithm For Robust Eigenstructure Assignment Using The Linear Quadratic Regulator, Thomas C. Huckabone
An Algorithm For Robust Eigenstructure Assignment Using The Linear Quadratic Regulator, Thomas C. Huckabone
Theses and Dissertations
The Linear Quadratic Regulator (LQR) can guarantee a robust closed loop eigenstructure for full state feedback. The algorithm developed here takes advantage of the stability guarantees of LQR to achieve an eigenstructure close to desired but within the allowable region of LQR. The algorithm selects the LQR weighting matrices, Q and R, that minimize the distance between the elements of the desired and LQR achievable eigenstructures. The minimization is accomplished by using a simplex based optimization routine. Specific weightings placed on the elements of the desired eigenstructure define the relative importance of each element. The algorithm is programmed in FORTRAN …
Failure Characteristics Of Scs-6/Ti-24al-11nb Composite With A Circular Hole At Room And Elevated Temperatures, Joseph E. Overbeck
Failure Characteristics Of Scs-6/Ti-24al-11nb Composite With A Circular Hole At Room And Elevated Temperatures, Joseph E. Overbeck
Theses and Dissertations
Off-axis loading of eight ply, unidirectional specimens with and without a circular hole determined the ultimate tensile strength of SCS-6/Ti- 24A1-11Nb composite at temperatures of 25°C and 650°C and fiber orientations of 0 degrees, 15 degrees, 45 degrees. Longitudinal moduli of the tested orientations compared closely to the rule of mixtures calculated values, and strengths compared closely to those predicted by the Tsai-Wu failure theory. The small diameter hole does not act as a stress concentrator, but merely reduces the material's strength in proportion to area loss. This result differs from those predicted by linear finite element analysis and orthotropic …
Design And Application Of An Object Oriented Graphical Database Management System For Synthetic Environments, John A. Brunderman
Design And Application Of An Object Oriented Graphical Database Management System For Synthetic Environments, John A. Brunderman
Theses and Dissertations
The Air Force Institute of Technology (AFIT) is investigating the use of synthetic environments for military applications under the sponsorship of Rome Laboratories (RL). Areas under investigation include mission planning, battle management and flight simulation. The work reported in this thesis focuses on the object-oriented design and implementation of the Graphical Database Management System (GDMS) used to support research in these areas. GDMS provides the data structures, file format and algorithms to manage and render hierarchical, three-dimensional, polygonal models. Flexibility and adaptability were key factors in its design. A secondary objective of this research was to demonstrate the functionality of …
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 …
Investigation Of The Influence Of Rotary Aerodynamics On The Study Of High Angle Of Attack Dynamics Of The F-15b Using Bifurcation Analysis, Ralph D. Fero
Theses and Dissertations
The purpose of this research was to use bifurcation analysis to investigate the effectiveness of rotary balance data in the prediction of aircraft spin behavior as both a stand alone representation of a model's aerodynamic data and in a conventional hybrid model. using the foundation of a previously developed model of the F-15B, the rotary balance aerodynamic force and moment data were implemented as a function of angle of attack, angle of sideslip, non-dimensional rotation steady state rate and the control surface deflections. Bifurcation diagrams were developed as a function of alpha vs. deflection angles of, the rudder, stabilator, and …
Perturbation Theory For Restricted Three-Body Orbits, David A. Ross
Perturbation Theory For Restricted Three-Body Orbits, David A. Ross
Theses and Dissertations
A perturbation theory for restricted three-body orbits, using a periodic trajectory as a reference solution, is investigated. The nearly- periodic equations of motions are derived by analogy to a linearization about an equilibrium point. In this case, the linearization produces a set of time- periodic equations of motion that, according to Floquet, are completely solved by a periodic trajectory. The four-dimensional phase space of the restricted three-body problem is the first surveyed for regions of periodic motion, via the surface of section phase plot. Upon extraction of a periodic orbit, nearly- periodic orbits are integrated. The integrated state vector is …
The Application Of Statistical Estimation Techniques To Terrain Modeling, Donald P. Duckett Jr.
The Application Of Statistical Estimation Techniques To Terrain Modeling, Donald P. Duckett Jr.
Theses and Dissertations
This thesis researches methods of generating accurate and realistic polygonal terrain models by reducing gridded sampled terrain elevation data such as DMA DTED. The terrain models generated should be applicable for use in flight simulators and other systems. Existing methods of terrain modeling are discussed, and limitations of these systems are presented. The geostatistical estimation technique known as kriging is presented as a method estimating terrain elevations at locations not provided in DMA DTED or other gridded terrain elevation data. Kriging is an optimal interpolation method based on statistical analysis of the data. It also provides a measure of accuracy, …
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.
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 …
A Standardized Software Reliability Measurement Methodology, Joseph J. Stanko
A Standardized Software Reliability Measurement Methodology, Joseph J. Stanko
Theses and Dissertations
Current Air Force practice is to perform Operational Test and Evaluation (OT and E) for each new weapons system. In support of this, Headquarters Air Force Operational Test and Evaluation Center (HQ AFOTEC) is responsible for measuring both suitability and effectiveness. While suitability is adequately measured, the current effort only addresses hardware effectiveness, or at best, system effectiveness. Since tools and metrics are in place for software suitability assessments related to OT and E (for example, software maintainability), there should be some effective way of measuring the operational effectiveness of software. Currently, HQ AFOTEC/LG5 has a data collection tool for …
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 …
Analysis Of A Decision Support System For Case Tool Selection And The Specification Of An Ada To Sql Abstract Interface, Tina M. Deangelis
Analysis Of A Decision Support System For Case Tool Selection And The Specification Of An Ada To Sql Abstract Interface, Tina M. Deangelis
Theses and Dissertations
Information overload has long been a problem in the fast moving technical field of software development. Yet quality information is needed to make informed decisions about buying software tools that help in software development. Computer Aided Software Engineering (CASE) tools help to coordinate and control information in large software developments. Many CASE tool purchases, however, are being based on ad hoc tool evaluation and selection methods which depend on biased vendor information. To capture specific knowledge about how to pick a tool for a given software development effort, a historical database that identifies important tool characteristics needed to be maintained …
An Event Driven State Based Interface For Synthetic Environments, Mark J. Gerken
An Event Driven State Based Interface For Synthetic Environments, Mark J. Gerken
Theses and Dissertations
Previous research at the Air Force Institute of Technology (AFIT) has produced synthetic environments using head mounted displays (HMDs) and hand measurement devices. This thesis is a continuation of AFIT synthetic environment research. Hand measurement data from a VPL DataGlove is combined with hand orientation and translational data to define a set of valid gestures. These gestures form the basis of an input language for class of finite automata known as finite state machines. Using the input symbols from this language, the user may define a finite state machine which associates a stream of input symbols with one or more …
Design And Implementation Of A Graphical User Interface And Database Management System For The Saber Wargame, Andrew M. Horton
Design And Implementation Of A Graphical User Interface And Database Management System For The Saber Wargame, Andrew M. Horton
Theses and Dissertations
Saber is a theater level, multi-sided, airpower employment computerized wargame that can be programmed to simulate any combat scenario. The model simulates theater level combat between air and land forces, and takes into account the effects of logistics, resupply, and both theater nuclear and chemical warfare. The major objective of the Saber model is to provide a suitable educational platform to allow users to apply basic, tactical employment concepts to multiple combat units, each having a specialized mission, and incorporating every branch of the armed services. This thesis documents a graphical user interface and data management system that has been …
Enhanced Animation Of Parallel Algorithms, Michael D. Lack
Enhanced Animation Of Parallel Algorithms, Michael D. Lack
Theses and Dissertations
Algorithm animation is a visualization method used to enhance understanding of the functioning of an algorithm or program. Visualization is used for many purposes, including education, algorithm research, performance analysis, and program debugging. This research, which follows from previous work, examines algorithm animation requirements for the various visualization purposes and extends the capabilities of an existing facilities, the AFIT algorithm Animation Research Facility (AAARF). The structure of AAARF is summarised and its visualization capabilities presented, analysed and compared with other similar packages. This research focuses on the parallel data requirements of the AAARF users, and the meaningful display of large …
Graph-Based Visualization Of Formal Specification And Domain Specific Languages, Randel K. Langloss
Graph-Based Visualization Of Formal Specification And Domain Specific Languages, Randel K. Langloss
Theses and Dissertations
This research develops and implements Visual Refine, a graph-based visualization system, for the Refine wide-spectrum formal specification language and environment developed and marketed by Reasoning Systems, Inc. Refine specifications are represented in the Refine object base as abstract syntax trees (AST). Using these AST representations, one-to-one mappings are defined between nodes of the AST and the graphical icons of Visual Refine. Visual Refine uses these mappings to implement a set of formal transformations. Each transformation is encapsulated within a Refine rule, and this set of rules form the Visual Refine transformation system. The Visual Refine transformation system, in conjunction with …
Improved Task Scheduling For Parallel Simulations, Andrew E. Mcnear
Improved Task Scheduling For Parallel Simulations, Andrew E. Mcnear
Theses and Dissertations
The objective of this investigation is to design, analyze, and validate the generation of optimal schedules for simulation systems. Improved performance in simulation execution times can greatly improve the return rate of information provided by such simulations resulting in reduced development costs of future computer/electronic systems. Optimal schedule generation of precedence-constrained task systems including iterative feedback systems such as VHDL or war gaming simulations for execution on a parallel computer is known to be N P-hard. Efficiently parallelizing such problems takes full advantage of present computer technology to achieve a significant reduction in the search times required. Unfortunately, the extreme …
A Spatially Partitioned Parallel Simulation Of Colliding Objects, Robert S. Moser
A Spatially Partitioned Parallel Simulation Of Colliding Objects, Robert S. Moser
Theses and Dissertations
This study investigated the application of a conservative synchronization paradigm to the classical, distributed pool balls simulation executed on an eight node, Intel iPSC/2 hypercube. Wieland's concept of spatial partitioning and limited data replication was used. Analysis has shown that 100% parallelization of execution is possible in a conservative environment via assignment of multiple sectors to nodes. Two conservative formulations for minimum safe time were derived. A tradeoff exists between scalability and efficiency. Optimum sectoring prediction has been shown possible through application of linear regression techniques. The results of this research reveal that a conservative approach to distributed, discrete event …
Three-Dimensional Medical Image Registration Using A Patient Space Correlation Technique, Patrick J. Rizzuto Jr.
Three-Dimensional Medical Image Registration Using A Patient Space Correlation Technique, Patrick J. Rizzuto Jr.
Theses and Dissertations
The routine clinical use of three-dimensional data provided by modern medical imaging procedures is often impeded by the difficulty in accurately correlating the resultant volume datasets. These data are frequently obtained at different times using the same modality, or images of the same patient are sometimes produced using more than one imaging modality. In order to analyze the similarities and differences between such images, it is necessary for the medical imaging data to be spatially aligned using a process known as image registration. This research investigated a structure-based image registration technique based upon simple, three-dimensional relationships among user identified landmarks. …
Design Of Style-V — A Translator To Convert Standard Vhdl Into A Stylized Form For Automated Microcode Generation, Dennis A. Rumbley
Design Of Style-V — A Translator To Convert Standard Vhdl Into A Stylized Form For Automated Microcode Generation, Dennis A. Rumbley
Theses and Dissertations
This thesis provides an analysis and preliminary design of Style V, a source-to-source computer language translator. Style-V converts IEEE standard VHDL into a special style of VHDL defined for a commercial tool, the Integrated Design Automation System (IDAS). Thirteen mappings between standard VHDL and the IDAS subset were identified. The mappings were analyzed using Domain Analysis and Modern Structured Analysis techniques. Four processes covering several of the mappings were completely analyzed. One mapping to convert CASE statements to IF statements was implemented. Since the IDAS restricts designs to bit logic, a method for representing multilevel logic with bit logic was …
Effect Of Spatial Locality Prefetching On Structural Locality, Dirk D. Schalch
Effect Of Spatial Locality Prefetching On Structural Locality, Dirk D. Schalch
Theses and Dissertations
The purpose of this research was to analyze the effect that spatial locality prefetching in cache memory has on the structural locality of program memory referencing behavior. To examine this, a software simulator was built to model a proposed two-level cache memory subsystem. The proposed subsystem was designed to use spatial locality prefetching to exploit the structural locality contained in executing computer workloads. New memory referencing models were developed to incorporate the combined use of structural locality and spatial locality prefetching. From these models, equations were derived to predict the hit rates for both caches. Combined with the state transition …
An Application Of The Object-Oriented Paradigm To A Flight Simulator, Dennis J. Simpson
An Application Of The Object-Oriented Paradigm To A Flight Simulator, Dennis J. Simpson
Theses and Dissertations
This thesis describes the object-oriented software development techniques that were used to analyze, design and implement a flight simulator. The objective of this thesis was to present a comprehensive object-oriented software development methodology and show how it was used in constructing an actual application. An extensive review of current object-oriented practices is presented along with the methods that were used to take the flight simulator from analysis to design and through to implementation. The description of the methodology concentrates upon the design and implementation phases of the object-oriented software lifecycle. Examples from the design of the flight simulator demonstrate how …
A Cache Design To Exploit Structural Locality, Curtis M. Winstead
A Cache Design To Exploit Structural Locality, Curtis M. Winstead
Theses and Dissertations
A design and VHDL implementation of a content-addressable memory (CAM) to exploit structural locality is the subject of this research. The concept of structural locality is that memory locations are referenced in the same order as they were previously referenced. Therefore, if memory locations that exhibit structural locality can be made available to the CPU (Center Processing Unit) through a fast data store, an increase in speed of the computer system can be realized. The CAM's purpose is to store memory references in the order they were used by the CPU and prefetch these locations to a smaller on- chip …
Parallelizing Serial Code For A Distributed Processing Environment With An Application To High Frequency Electromagnetic Scattering, Paul R. Work
Theses and Dissertations
This thesis investigates the parallelization of existing serial programs in computational electromagnetics for use in a parallel environment. Existing Algorithms for calculating the radar cross section of a object are covered, and a ray-tracing code is chosen for implementation on a parallel machine. Current parallel architectures are introduced and a suitable parallel machine is selected for the implementation of the chosen ray tracing algorithm. The standard techniques for the parallelization of serial code are discussed, including load balancing and decomposition considerations, and appropriate methods for the parallelization effort are selected. A load balancing algorithm is modified to increase the efficiency …
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 …