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1991

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Articles 91 - 120 of 1363

Full-Text Articles in Engineering

Feature Extraction For Pose Estimation. A Comparison Between Synthetic And Real Ir Imagery, Donald J. Willis Dec 1991

Feature Extraction For Pose Estimation. A Comparison Between Synthetic And Real Ir Imagery, Donald J. Willis

Theses and Dissertations

This research addressed the problem of pose estimation of three- dimensional objects given their two-dimensional IR imagery and corresponding synthetic (computer-generated) IR imagery. Features and techniques were investigated to find those which may be extendable from computer models to real- world IR imagery. GTSIG and SCNGEN were used to create the synthetic imagery. Silhouette and outline shape moments were explored as optimum features for the comparison. Employing back-propagation with momentum as the training paradigm, a two-hidden-layer neural network was able to determine the base-plane orientation of the synthetic imagery to within 7.5 degrees with better than 90% accuracy. (No conclusive …

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Experimental Investigation Of Trailing Edge Crenulation Effects On Losses In A Compressor Cascade, Steven J. Decook Dec 1991

Experimental Investigation Of Trailing Edge Crenulation Effects On Losses In A Compressor Cascade, Steven J. Decook

Theses and Dissertations

The effects of blade trailing edge crenulations on wake losses in a compressor cascade were investigated at the Air Force Institute of Technology. The cascade used NACA 64-A905 blades with a turning angle of about 30 to model last row stators of an axial flow compressor. Three blade configurations were used: unmodified blades, blades with large crenulations, and blades with small crenulations. Wake losses and mixing were evaluated in four flow conditions, generated by combinations of increased freestream turbulence and sidewall boundary layer removal. Injection of air perpendicular to the inlet flow increased freestream turbulence from about 0.15% to about …

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Improvement Of The Thermodynamic Model For A Flux-Difference-Splitting Algorithm For The Computation Of High Speed Flows, Mark E. Schieve Dec 1991

Improvement Of The Thermodynamic Model For A Flux-Difference-Splitting Algorithm For The Computation Of High Speed Flows, Mark E. Schieve

Theses and Dissertations

This study modifies the thermodynamic model of a previously existing first-order accurate Flux Difference Splitting (FDS) algorithm for planar, supersonic nozzles. The thermodynamic model is changed from a calorically and thermally perfect gas to a thermally perfect (imperfect) gas, where the flow field is frozen or non-reacting. The frozen flow and imperfect gas assumptions more nearly approximate the real behavior of a fluid in supersonic propulsive nozzles. The modified code can now account for specific heats that vary as a function of temperature. Using curve fittings of JANAF thermochemical data, the code can handle nine gas species, as well, to …

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Investigation Of A Flux-Difference-Splitting Numerical Method In Supersonic Nozzles, Danny P. Allen Dec 1991

Investigation Of A Flux-Difference-Splitting Numerical Method In Supersonic Nozzles, Danny P. Allen

Theses and Dissertations

This research investigated the effects of adding a second-order flux- difference-splitting (FDS) correction term to an existing computer code that is based on a first-order FDS algorithm. It was determined that the second-order algorithm did improve the accuracy of the code for a source flow analysis, but second-order behavior could not be confirmed by the error convergence patterns. It was also discovered that, when tested across an oblique shock wave, the second-order correction terms had minimal influence on the accuracy and shock capturing ability of the first-order accurate FDS method.

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Investigation Of The Effects Of Increased Order Compensators In Mixed H2/H∞ Optimization, Scott R. Wells Dec 1991

Investigation Of The Effects Of Increased Order Compensators In Mixed H2/H∞ Optimization, Scott R. Wells

Theses and Dissertations

The problem of minimizing the 2-norm of one transfer function subject to an infinity-norm bound on another transfer function is examined for increased order controllers. In particular, the theoretical results of the full order case are extended to the higher order case, and SISO and MIMO numerical examples are given for increasingly higher order compensators. Some of the key proofs for higher order compensators include: the global minimum 2-norm is unachievable under output feedback for certain levels of gamma regardless of compensator order; the solution to the mixed H2/H infinity problem lies on the boundary of the infinity-norm constraint for …

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A Top-Down Performance Analysis Of A Pegasus-Based Space Strike System, Douglas E. Collins Dec 1991

A Top-Down Performance Analysis Of A Pegasus-Based Space Strike System, Douglas E. Collins

Theses and Dissertations

The feasibility of using Pegasus launch vehicle as a conventional weapons platform is examined. Using a top-down approach, the analysis addresses the fundamental question of whether such a system should be considered for development. The measures of effectiveness considered are delivery range, probability of destroying the target, and responsiveness. Each of the measures is assessed at its top-level and analyzed only to the level of detail needed to address the fundamental question. The study indicates that attaining a high probability of destroying the target requires extremely precise control over the burnout conditions and that the system must be on constant …

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Ground Collision Avoidance Using A Variable Incidence Altitude Measurement System For The A-7 Aircraft, Thomas A. Hartung Dec 1991

Ground Collision Avoidance Using A Variable Incidence Altitude Measurement System For The A-7 Aircraft, Thomas A. Hartung

Theses and Dissertations

This study examines the use of a forward looking sensor in the implementation of an automatic terrain following system. The effect of the incidence angle is studied as well as methodologies to include dynamic motion in the pointing of the sensor beam. The methods examined include fixed angle with respect to the aircraft, dynamics driven by a simple gain, and dynamics directed to gather the terrain information a fixed time interval ahead of the aircraft. Incidence angles of 25, 50, 75, and 90 are examined. The terrain obstacles include a single parabolic hill, a step change is terrain, and a …

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Comparison Of Pointing Control Systems Utilizing Dahl And Coulomb Friction Model Compensation, Whitney J. Hulett Dec 1991

Comparison Of Pointing Control Systems Utilizing Dahl And Coulomb Friction Model Compensation, Whitney J. Hulett

Theses and Dissertations

Bearing friction can be accurately modeled using the Coulomb friction model, provided the bearing is running. In an application where the bearing is rotated only a very small amount, the bearing does not actually rotate. Instead, the bearing undergoes plastic deformation. A nonlinear friction model was developed by P. R. Dahl of the Aerospace Corporation in the late sixties which addresses this region of placticity or compliance zone. Two friction compensation schemes for a single axis position servomechanism were developed and compared in this study. The first compensator was an integral control regulator/estimator which used the Coulomb friction model. The …

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Fatigue Behavior And Failure Mechanisms Of Centrally Notched [0]8 And [0/902]S Silicon Carbide Reinforced Aluminosilicate Glass, William R. Moschelle Dec 1991

Fatigue Behavior And Failure Mechanisms Of Centrally Notched [0]8 And [0/902]S Silicon Carbide Reinforced Aluminosilicate Glass, William R. Moschelle

Theses and Dissertations

Unidirectional and bidirectional notched laminates of silicon carbides/1723 were fatigue tested under tensile-tensile loading with a load ratio of 0.1. The notch, a hole, was determined to have a significant effect on [0]8 specimens. Matrix cracking developed near the theoretical maximum stress concentration points on the hole propagating parallel to the fibers, in the load direction, followed by fiber breakage. [0/902]s specimens were found to be notched insensitive. Damage modes for this lay-up were transverse ply matrix cracking, delamination and fiber breakage in the longitudinal plies which led to specimen failure. Several existing analytical models were …

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Failure Characterization Of A Fiber Reinforced Ceramic Matrix Composite With Circular Holes, Daniel E. Bullock Dec 1991

Failure Characterization Of A Fiber Reinforced Ceramic Matrix Composite With Circular Holes, Daniel E. Bullock

Theses and Dissertations

The purpose of this study was to investigate the performance of a fiber reinforced ceramic matrix composite with circular holes. The specific objectives were to (1) determine the relationship between tensile failure stress and the ratio of hole diameter to specimen width, and (2) to examine the initiation and progression of damage. The ceramic matrix composite used was SiC/ 1723, composed of continuous silicon titanium carbide fibers in an aluminosilicate glass ceramic matrix. Uniaxial tensile tests were performed at room temperature on two different layups; unidirectional [0]8, and [0/90]2s symmetric. Each layup was tested at three diameter-to-width …

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Thermomechanical Fatigue Characterization Of An Angle Ply Metal Matrix Composite, Wade H. Vaught Dec 1991

Thermomechanical Fatigue Characterization Of An Angle Ply Metal Matrix Composite, Wade H. Vaught

Theses and Dissertations

An investigation was conducted to study the thermomechanical fatigue (TMF) response of a [±45]2s angle ply SCS-6/titanium-15-3 metal matrix composite (MMC). Load controlled in-phase TMF experiments were performed over the temperature range 149-427 C, with a cycle frequency of 0.02 Hz. Test equipment included a high temperature extensometer, quartz lamp radiative heaters controlled by a Micricon thermal control unit and TMF test control software, MATE263. Stress and strain hysteresis, total strain and stiffness were monitored to characterize material behavior. Large plastic deformations were observed in all specimens, with total failure strains ranging from 7 to 13 percent. It was …

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Thermal Nonequilibrium Effects On Turbine Cascade Aerodynamics, Jill L. R. Shaw Dec 1991

Thermal Nonequilibrium Effects On Turbine Cascade Aerodynamics, Jill L. R. Shaw

Theses and Dissertations

The AFIT Total Variation Diminishing Euler Code (ATEC) was modified to include a thermal nonequilibrium model to investigate high temperature effects associated with vibrational relaxation in a transonic turbine cascade. Incorporation of this model into ATEC and creating ANTEC (AFIT Nonequilibrium TVD Euler Code) was accomplished in three steps. Steady-state solutions obtained with ANTEC were compared with those obtained with ATEC for various inlet and exit conditions. The Courant-Friedrichs-Levy criterion was held constant to ATEC; however, it required variation for ANTEC. Blade temperature profiles, temperature difference contours in the vicinity of the trailing edge and the value of the ratio …

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A Comparative Study Of Numerical Versus Analytical Waverider Solutions, Gregory O. Stecklein Dec 1991

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 …

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Finite Element Analysis Of A Riveted Repair On A Curved Composite Panel, Scott A. Hamilton Dec 1991

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 …

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An Experimental Study Of A Sting-Mounted Circulation Control Wing, Steven J. Lacher Dec 1991

An Experimental Study Of A Sting-Mounted Circulation Control Wing, Steven J. Lacher

Theses and Dissertations

This wind tunnel study investigated the lift, drag, and pitching moment of a 20% thick, 8.5% camber, partial elliptical cross-section, single blowing slot, 2.325 aspect ratio, rectangular circulation control wing. The AFIT 5-foot wind tunnel was used. Lift and drag were referenced to the wind axis. The Reynolds number was 500,000 for all tests. Angle of attack was varied from -6 to 16 degrees and the effects of pulsed blowing were investigated. Effects of tripping the Coanda jet with a small flow barrier attached spanwise along the Coanda surface were also studied. Results indicate that there is a limit on …

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Experimental Investigation Into The Effects Of Riblets On Compressor Cascade Performance, James A. Rothenflue Dec 1991

Experimental Investigation Into The Effects Of Riblets On Compressor Cascade Performance, James A. Rothenflue

Theses and Dissertations

The effects of adding riblets to the blades of a subsonic, linear compressor cascade were investigated at the Air Force Institute of Technology. Three blade configurations were tested, including a set of unmodified NACA 64- A905 series blades, a set with riblets applied to the suction surface, and a set with riblets on the pressure surface. Performance was evaluated over a wide range of Reynolds numbers, and at low and high free stream turbulence levels. Cascade performance was evaluated in terms of total pressure loss coefficient, turning angle, and static pressure rise. No riblet configuration offered robust cascade performance improvements; …

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Robust Grasp Design Using Grasp Force Focus Positioning, Freddie D. Zayas Dec 1991

Robust Grasp Design Using Grasp Force Focus Positioning, Freddie D. Zayas

Theses and Dissertations

A three-finger precision grasp is used to rotate a cylindrical object about a threaded post. Three fingered grasps are unique in that the homogeneous solution for the contact forces produces a grasp force focus. Mapping of focus points which meet grasp stability and joint torque criteria results in a usable focus region. The effects of applied torque, contact location, and object position and orientation on usable regions are presented. Stability behavior about the region is also examined. Results are used to demonstrate a technique for robust grasp design. The versatility of robotic hands permit fine motion manipulation on a wide …

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An Algorithm For Robust Eigenstructure Assignment Using The Linear Quadratic Regulator, Thomas C. Huckabone Dec 1991

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 …

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Failure Characteristics Of Scs-6/Ti-24al-11nb Composite With A Circular Hole At Room And Elevated Temperatures, Joseph E. Overbeck Dec 1991

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 …

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Optimization Of Tangential Mass Injection For Minimizing Flow Separation In A Scramjet Inlet, Richard J. Kacik Dec 1991

Optimization Of Tangential Mass Injection For Minimizing Flow Separation In A Scramjet Inlet, Richard J. Kacik

Theses and Dissertations

With the reemergence of interest in air-breathing hypersonic propulsion, scramjet inlet efficiency has become an area of concern. The impingement of the engine cowl shock near the shoulder (expansion corner between forebody and combustor) may cause boundary layer separation which reduces inlet efficiency. Tangential mass injection (TMI) upstream of the shoulder has recently been tested to control this separation but without much parametric evaluation. To resolve this deficiency, a 2-D scramjet inlet model with variable length cowl, and TMI was built and tested in the WL Mach 6 High Reynolds Number Facility. Parameters varied were boundary layer thickness, TMI flow …

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Analysis Of The Effects Of Removing Nose Ballast From The F-15 Eagle, Richard L. Bennett Dec 1991

Analysis Of The Effects Of Removing Nose Ballast From The F-15 Eagle, Richard L. Bennett

Theses and Dissertations

This study investigated the results of removing lead ballast from the nose section of the F-15 Air Superiority fighter. The goal of the investigation was to determine if aircraft handling qualities remained acceptable with the ballast removed, and also to determine what improvements in aircraft nose pointing authority resulted. Actual F-15 weight reports were used to calculate the worst case aft center of gravity location shift due to the ballast removal. Several configurations with different center of gravity locations (based on various amounts of lead weights removed) were used for comparison to the baseline aircraft. Moments of inertia were calculated …

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Analysis Of An Advanced Fighter Aircraft Using Jet Flap Techniques And The Vortex Lattice Method, Steven P. Snyder Dec 1991

Analysis Of An Advanced Fighter Aircraft Using Jet Flap Techniques And The Vortex Lattice Method, Steven P. Snyder

Theses and Dissertations

A computer code using the vortex lattice method with modified boundary conditions was used to determine the induced aerodynamic characteristics of high aspect ratio, vectoring, exhaust nozzles located at the wing root of a canard configured fighter aircraft. Comparison with existing wind tunnel data verified results of the method. The exhaust was modeled as a singularly blown jet flap at deflection angles of -10, 0, 10, 20, 30, and 40 degrees. Jet momentum coefficients were based on gross engine thrust for maximum afterburner and military power settings at a Mach number of 0.6 and an altitude of 20,000 ft. Lift, …

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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 Dec 1991

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 …

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The Effect Of Angle Of Incidence And Reynolds Number On Heat Transfer In A Linear Turbine Cascade, Steven G. Meschwitz Dec 1991

The Effect Of Angle Of Incidence And Reynolds Number On Heat Transfer In A Linear Turbine Cascade, Steven G. Meschwitz

Theses and Dissertations

The AFIT linear Turbine Cascade Test Facility was used to study the effect of the small changes in the angle of incidence on turbine blade convective heat transfer. Other parameters studied were the model Reynolds number and the freestream turbulence level. Characterization tests, performed to determine the feasibility of the study were followed by a series of tests designed to separate the effects of the angle of incidence, Reynolds number, and freestream turbulence level on convective heat transfer. For any given freestream turbulence level or angle of incidence, there is an increase in the heat transfer coefficient for an increase …

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Analysis Of Suborbital Launch Trajectories For Satellite Delivery, Mark R. Goodell Dec 1991

Analysis Of Suborbital Launch Trajectories For Satellite Delivery, Mark R. Goodell

Theses and Dissertations

A computer simulation program was used to analyse performance of suborbital launch trajectories using a hypersonic NASP derived vehicle for satellite deployment. The trajectory investigated for this project involved satellite deployment as suborbital speeds. To deploy a satellite in this manner, a booster motor is used to insert the payload into orbit while the launch vehicle reenters and returns to earth. A simplified energy analysis was also formulated and used to determine the sensitivity of suborbital trajectory performance to specific design parameters. Results show that suborbital launch trajectories can increase the useful payload to orbit capacity over an identical vehicle …

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Propulsive Capability Of A Reel-In Tether With Safe Separation Between Payload And Orbiter, Jay H. Rothhaupt Dec 1991

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 …

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An Investigation Of Optimally Robust Structural Damping Through Fractional Order Feedback, Mark T. Leonard Dec 1991

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 …

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Static Pressure Measurements Of A Low Power Arcjet, Kevin P. Talley Dec 1991

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.

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Logic Programming In Digital Circuit Design, Joseph W. Eicher Dec 1991

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.

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Frequency Domain Speech Coding, Shane Switzer Dec 1991

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 …

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