Open Access. Powered by Scholars. Published by Universities.®

Engineering Commons™

Open Access. Powered by Scholars. Published by Universities.®

Aerospace Engineering

Institution
Keyword
Publication Year
Publication
Publication Type
File Type

Articles 10741 - 10770 of 11113

Full-Text Articles in Engineering

Multi-Input Multi-Output Flight Control System Design For The Yf-16 Using Nonlinear Qft And Pilot Compensation, Russell B. Miller Dec 1990

Multi-Input Multi-Output Flight Control System Design For The Yf-16 Using Nonlinear Qft And Pilot Compensation, Russell B. Miller

Theses and Dissertations

Nonlinear Quantitative Feedback Theory (QFT) and pilot compensation techniques are used to design a 2x2 flight control system for the YF-16 aircraft over a large range of plant uncertainty. The design is based on numerical input- output time histories generated with a FORTRAN implemented nonlinear simulation of the YF-16. The first step of the design process is the generation of a set of equivalent linear time-invariant (LTI) plant models to represent the actual nonlinear plant. It has been proven that the solution to the equivalent plant problem is guaranteed to solve the original nonlinear problem. Standard QFT techniques are then …

Go to article

Multidisciplinary Modeling And Design Of A Space Structure, Brian K. Cassiday, Lawrence L. Gatchet, John T. Tester, Stephen O. Gaines Ii, Mario N. Moya Dec 1990

Multidisciplinary Modeling And Design Of A Space Structure, Brian K. Cassiday, Lawrence L. Gatchet, John T. Tester, Stephen O. Gaines Ii, Mario N. Moya

Theses and Dissertations

A method is needed to simultaneously integrate several engineering disciplines into one complete model to determine the performance of the system as a whole during the design development. System engineering methodologies are particularly suited to this problem. These methods provide a structured approach to problem formulation and system parameter identification. Bond graphs are also well suited as bond graphs model power flow and energy relationships within subsystems, a characteristic inherent to all dynamic systems. The intent of this research was to demonstrate the use of concurrent engineering theory to systematically model a large flexible space structure involving several engineering disciplines. …

Go to article

Development Of An Image Registration Technique For Polar-Orbiting Satellites, Jerry L. Mehlberg Dec 1990

Development Of An Image Registration Technique For Polar-Orbiting Satellites, Jerry L. Mehlberg

Theses and Dissertations

In this thesis, a means to perform spatial registration (gridding) of meteorological satellite data is developed. It is applicable to Automatic Picture Transmission (APT) data from the TIROS-N series polar-orbiting satellites operated by the National Oceanic and Atmospheric Administration (NOAA). This technique does not require the use of ground control points. Registration is accomplished using an advanced orbital model to precisely compute the satellite's location based on NORAD two-line element sets and the time of the image. This technique is examined for accuracy and sensitivity to errors in the element set and satellite attitude control. This study involves over 70 …

Go to article

Model-Based Reasoning In The Detection Of Satellite Anomalies, Ralph W. Dries Dec 1990

Model-Based Reasoning In The Detection Of Satellite Anomalies, Ralph W. Dries

Theses and Dissertations

Automatic fault detection and recovery would be a mandatory requirement for a satellite where some degree of autonomy is required. This thesis reviews some AI techniques used for the detection of satellite anomalies, and concludes that the model-based reasoning paradigm is best suited for automated on-board fault detection because it can cope with situations not necessarily programmed into the knowledge base. Using the Scheme language and its SCOOPS object oriented extension, development of software is described that models the pitch control channel in the attitude and velocity control subsystem of a typical geo-stationary communications satellite. This model is used by …

Go to article

An Analysis Of The Effects Of Phenytoin In Treating Motion Sickness And The Effects Of Motion Sickness On The Human Electroencephalogram, Todd M. Banducci Dec 1990

An Analysis Of The Effects Of Phenytoin In Treating Motion Sickness And The Effects Of Motion Sickness On The Human Electroencephalogram, Todd M. Banducci

Theses and Dissertations

This research had two goals: to continue the ongoing research at AFIT to determine the efficacy of the anticonvulsant drug phenytoin in combating the onset and progression of motion sickness; and to note whether or not there is a discernable similarity in the brains of the test subjects to indicate a common point of origin (epicenter) and propagation pattern of the effects of motion sickness in the brain. Eight male DOD personnel were used as subjects to complete twelve trials. Four subjects completed the phenytoin verses placebo double-blind crossover experiment. These four subjects experienced a 99% mean increase in their …

Go to article

Improving Reliability In A Stochastic Communication Network, William L. Gaught Dec 1990

Improving Reliability In A Stochastic Communication Network, William L. Gaught

Theses and Dissertations

This research investigated the behavior of increasing the reliability of components in stochastic communication networks. A stochastic communication network is one in which the components, links and nodes, are not 100 percent reliable. In addition the reliability value, each component also has a capacity value that limits the flow through the component. The throughput in a stochastic communication network can be improved by increasing the capacity or the reliability of the individual components. A set of linear and nonlinear models was developed to determine the best investment strategy for increasing the reliability of individual components. Once the models were developed, …

Go to article

Measuring The Effectiveness Of Space: Satellite Weather Systems, Steven T. Wilson Dec 1990

Measuring The Effectiveness Of Space: Satellite Weather Systems, Steven T. Wilson

Theses and Dissertations

Using concepts from multivariate utility theory, basic orbital mechanics, and information regarding operational and planned meteorological satellites, this thesis develops a meaningful MOE to support high-level decision making regarding the allocation, acquisition, and operational deployment of space meteorological satellite (METSAT) assets. Satellite meteorological systems were chosen because of the ready availability of pertinent unclassified data. However, the methodology presented may be applied to any type of space system.

Go to article

An Aluminum Salvage Station For The External Tank (Asset), James N. Haislip Jr., William C. Raynes Jr., David L. Van Matte, Roger E. Linscott, Michael A. Skinner Dec 1990

An Aluminum Salvage Station For The External Tank (Asset), James N. Haislip Jr., William C. Raynes Jr., David L. Van Matte, Roger E. Linscott, Michael A. Skinner

Theses and Dissertations

The external tank is currently the only non-reusable portion of the National Space Transportation System. The tank has 98% of the energy required to be placed in orbit at the point it is jettisoned. The purpose of this study is to develop techniques which would transform this throw-away item into a source of construction material at low earth orbit. A simulation is developed to verify the reduction timelines and peak power requirements for manual and automated reduction. The required tools to accomplish the tasks of initial cutting, product transport, spray on foam insulation removal, and product storage are developed. A …

Go to article

Application Of Influence Diagrams In Identifying Soviet Satellite Missions, Cary C. Chun Dec 1990

Application Of Influence Diagrams In Identifying Soviet Satellite Missions, Cary C. Chun

Theses and Dissertations

This thesis investigates the feasibility of applying influence diagrams to capture expert knowledge and incorporate decision theory to construct a Soviet satellite mission prediction model. Before a Soviet launch occurs, formulations of the model's prior probability distribution allows the input of expert knowledge and any available information. As the predictive variables of the model become known, the information is used to successively refine the estimate of the probable mission, thereby, reducing the uncertainty in the model. Discretizing is used to approximate continuous variables as discrete variables which successfully allows the combination of both variable types in a single influence diagram …

Go to article

A Correlation And Forecasting Analysis On Lost Satellites, Kenneth R. Norton Dec 1990

A Correlation And Forecasting Analysis On Lost Satellites, Kenneth R. Norton

Theses and Dissertations

The relationship between the size of the United States Air Force Space Command's lost satellite lists and thirteen other variables is investigated. The thirteen variables contain the Space Surveillance Center crew's effort to work the lost list, solar activity, geomagnetic field strength, and the number of observations received each day from seven space track sensors. To identify the relationship of cause and effect between the lost lists and the thirteen variables, simple and multiple linear regressions are used on a data set that begins on 1 January 1988 and ends on 31 December 1988. Multiple linear regression and basic time-series …

Go to article

Proposed Design Of A Tactical Reconnaissance Satellite System, John D. T. Severance Dec 1990

Proposed Design Of A Tactical Reconnaissance Satellite System, John D. T. Severance

Theses and Dissertations

Tactical reconnaissance is a much needed wartime asset, yet with the deactivation of all active-duty RF-4C squadrons world-wide there appears to be a gap in this country's war-fighting capability. This study proposes a system which utilizes a constellation of small tactical satellites and mobile ground receiving stations that can fulfill the tactical reconnaissance mission. A literature review gives background information on resolution variables, the RF-4C, space reconnaissance, and sensing technologies. After defining system requirements and constraints, a basic system concept is determined. Three alternative systems, separated mostly by threat scenario, technology, and cost, are evaluated using Athey's Systematic Systems Approach. …

Go to article

Adaptive Filtering And Smoothing For Tracking A Hypersonic Aircraft From A Space Platform, Kenneth A. Gotski Dec 1990

Adaptive Filtering And Smoothing For Tracking A Hypersonic Aircraft From A Space Platform, Kenneth A. Gotski

Theses and Dissertations

This study took a previously developed six state Kalman filter (designed for space-based tracking of a hypersonic transatmospheric vehicle), tuned it, and performed a Monte Carlo analysis. Three multiple model adaptive filters were then developed, with sub-filters designed for quiescent periods and periods with apparent acceleration. Next, a smoother was developed using the six state filter as the forward filter and a form of that same filter as the backward filter. The smoother and all of the above filters were compared for their ability to most accurately estimate the transatmospheric vehicle's state, with special emphasis on the acceleration states. This …

Go to article

A Numerical Investigation Of The Series Reversion/Inversion And Series Reversion Of Lambert's Time Function, Michael P. Ward Dec 1990

A Numerical Investigation Of The Series Reversion/Inversion And Series Reversion Of Lambert's Time Function, Michael P. Ward

Theses and Dissertations

An expression for the semi-major axis as a function of time may be determined by performing a series reversion and inversion of Lambert's Time Function. Since the resulting series contains a singularity, it is desirable to perform only a reversion on the original series to obtain an expression for the inverse of the semi-major axis. Using a Lagrange expansion to obtain the coefficients for this series is very computer intensive. Therefore, alternative methods are presented. Also, each series was expanded into a continued fraction which provided greater accuracy than the series using the same number of coefficients. The accuracy was …

Go to article

Material Properties Of Silicon Carbide Fibers With Continuously Applied Sol-Gel Alumina Coatings, Christian C. Daehnick Dec 1990

Material Properties Of Silicon Carbide Fibers With Continuously Applied Sol-Gel Alumina Coatings, Christian C. Daehnick

Theses and Dissertations

An investigation was conducted to determine the effect of non-alpha- alumina coatings applied under varying conditions on some of the properties of silicon carbide fibers. Limited characterization of the coating by optical, scanning electron, and transmitted electron microscopy as well as energy- dispersive x-ray analysis was performed. Tensile tests were used to determine changes in elastic modulus, ultimate strength, and strain to failure of the coated fibers relative to uncoated fibers. The coatings were found to lower the mean value of the measured properties as their thickness increased, but the measurements were not accurate enough to determine if this corresponded …

Go to article

Analysis Of Periodic Orbits About The Martian Moons By Continuation Techniques, Frank Luria Dec 1990

Analysis Of Periodic Orbits About The Martian Moons By Continuation Techniques, Frank Luria

Theses and Dissertations

From a few known periodic orbits of Phobos and Deimos, continuation techniques were used to find entire families of stable orbits. These techniques involved varying a parameter, the Hamiltonian, of the system and analyzing how the orbital behavior changed with the parameter. Floquet multipliers, for stability analysis, were also computed. AUTO86, a continuation/bifurcation software package, was used in this study. Artificial energy dissipation had to be added to the conservative Hamiltonian system to enable use of AUTO.

Go to article

A Comparison Of The Optimization And Analysis Of Doubly Curved Shells Using Msc/Nastran And Astros, John R. Dewsnap Dec 1990

A Comparison Of The Optimization And Analysis Of Doubly Curved Shells Using Msc/Nastran And Astros, John R. Dewsnap

Theses and Dissertations

This study identified techniques and software available for the optimization of doubly curved shells and applied them in the context of a large nozzle shape. An optimality criteria scheme that can reduce solution time was evaluated and compared to the Method of Feasible Directions. MSC/NASTRAN and ASTROS were used to perform finite element analysis and optimization, and the results were compared to the theory. The programs give virtually identical results, and if plates and shells are carefully modeled, then stresses, displacements and modes are accurate to within ten percent. A Mindlin-type axisymmetric finite element was implemented in ASTROS that preserved …

Go to article

Use Of Grasp Force Focus Positioning To Enhance The Torque Resistance Capability Of Robotic Grasps, Stephen G. Edwards Dec 1990

Use Of Grasp Force Focus Positioning To Enhance The Torque Resistance Capability Of Robotic Grasps, Stephen G. Edwards

Theses and Dissertations

Three-point-contact grasps are unique in that the homogeneous solution for the contact forces always produces a grasp force focus. Careful positioning of this focus point in the grasp plane can help avoid two things; slipping at the contact points, and violation of joint torque limits. The focus placement method is explored theoretically by examining two types of grasps on cylinders; 1) fingertip grasps using three independently operated fingers, and 2) single-finger power grasps with one contact point on each of three links. Constraint maps are generated for various fingertip grasps in order to show how proper placement of the grasp …

Go to article

Autonomous Navigation Of A Satellite Cluster, Stephen C. Johnston Dec 1990

Autonomous Navigation Of A Satellite Cluster, Stephen C. Johnston

Theses and Dissertations

The relative position determination of a cluster of satellites operating in a low earth orbit is investigated. A U-D Covariance Factorization Kalman Filter is used for the on-board estimator with dynamics based on the Clohessy-Wiltshire equations. Measurements consist of range data between a single host satellite and the remaining cluster. Therefore only relative position and velocity states with respect to the host satellite can be determined. A 15 sample Monte Carlo simulation was conducted with clusters of 2, 5, and 10 satellites, respectively. Performance results consists of average error, average true error and filter covariance as a function of time.

Go to article

Nonlinear Analysis Of A Spinning Symmetric Satellite In An Elliptical Orbit, Michael Ulisse Dec 1990

Nonlinear Analysis Of A Spinning Symmetric Satellite In An Elliptical Orbit, Michael Ulisse

Theses and Dissertations

Controlled and uncontrolled equations of motion for a spinning symmetric satellite in an elliptical orbit are analysed using Floquet theory, Poincare maps, and continuation. The equations of motion for the uncontrolled system are derived via energy methods. A simple feedback controller design and one based on Floquet theory are presented. Parameters varied in the equations of motion include the spin about the symmetry axis of the satellite, the inertia ratio of the satellite, the eccentricity of the orbit, and the controller gains. Floquet analyses determine local stability and bifurcation points. Poincare maps exhibit some interesting and complex structure in the …

Go to article

Investigation Of Direct And Indirect Optimization Algorithms For Aerospace Structures, Harry Hopkins Iii Dec 1990

Investigation Of Direct And Indirect Optimization Algorithms For Aerospace Structures, Harry Hopkins Iii

Theses and Dissertations

This thesis investigated the performance of two direct and two indirect methods of structural optimization. A gradient calculator and overall design system was created with the finite element code FRAME. Three of the methods were employed using this system with the fourth being a commercial available code. The algorithms were applied to two different sized trusses using static constraints and were measured for accuracy, reliability, and efficiency. Results for the problems tested showed the Direct methods were sensitive to starting designs and their performance depended on the proper selection of internal parameters. They were also shown to have a high …

Go to article

Numerical Analysis Of An Axisymmetric Thrust Augmenting Ejector, Kenneth R. Gage Dec 1990

Numerical Analysis Of An Axisymmetric Thrust Augmenting Ejector, Kenneth R. Gage

Theses and Dissertations

Use of an ejector is an effective way to increase the thrust produced by a jet. In this thesis project an axisymmetric ejector concept which had been previously explored by experiment was numerically modeled. An existing axisymmetric, internal flow code based on the explicit MacCormack method was modified to incorporate primary nozzle structure and flow injection within the flowfield. Results were compared qualitatively and quantitatively with experimental results to verify the validity of the model. Internal flow structure, difficult to obtain in experiment, is easily examined. This code may be used for parametric analysis of such ejector performance parameters as …

Go to article

Analysis Of Hypersonic Blunt-Body Flows Using A Total Variation Diminishing Scheme And The Maccormack Scheme, Montgomery C. Hughson Dec 1990

Analysis Of Hypersonic Blunt-Body Flows Using A Total Variation Diminishing Scheme And The Maccormack Scheme, Montgomery C. Hughson

Theses and Dissertations

An explicit second-order accurate, total variation diminishing (TVD) scheme and the MacCormack scheme are applied to the Euler equations in axisymmetric form to study hypersonic blunt body flows. The modified flux approach of Harten, with modification by Yee, for two-dimensional flows is extended to treat axisymmetric flows. Calculated flow properties for the steady state, blunt body problem such as shock standoff distance, bow shock shape, surface pressure distribution and entropy jump conditions are compared to theory, results from the MacCormack scheme, and experimental data for Mach numbers of 3.0, 4.03, 5.06, 6.03 and 8.1. Additionally, the TVD and MacCormack schemes …

Go to article

Modeling And Analysis Of Orthotropic Plate With Circular Cutout And Adhesive Bonded Patch, Mark W. Hunter Dec 1990

Modeling And Analysis Of Orthotropic Plate With Circular Cutout And Adhesive Bonded Patch, Mark W. Hunter

Theses and Dissertations

The purpose of this study was to investigate a modeling technique to simply and adequately model an adhesive bonded patch on an orthotropic plate. This report is limited to linear material behavior. This thesis is also the basis for further work into nonlinear material range and three-dimensional stress states. To further advance aerospace battle damage repair techniques for composite repairs, a finite element model of an orthotropic plate with a hole and patch was constructed to investigate the accuracy of such a model. The fundamental problem in this model is the development of a simple and accurate method of modeling …

Go to article

Turbulence Scales In The Passage Of A Linear Turbine Cascade, James L. Acree Dec 1990

Turbulence Scales In The Passage Of A Linear Turbine Cascade, James L. Acree

Theses and Dissertations

Convective heat transfer in a turbine cascade is examined for turbulence effects. Turbulence in the free stream is varied by injection of air through a jet-grid device upstream of the cascade. Pressure and flow patterns on the blade surface, and flow velocity in two components, are examined to determine the effect of the jet-grid. Velocity and velocity fluctuation in two components are measured. Local turbulence scales through the cascade passage are determined, and local turbulent energy dissipation rate is determined. Results indicate injection of air through the jet-grid changes the angle of incidence, and therefore changes the surface pressures and …

Go to article

Vortex Bursting Over A Unit Area Aspect Ratio Delta Wing Using Vortex Paneling Methods, Donald A. Lorey Dec 1990

Vortex Bursting Over A Unit Area Aspect Ratio Delta Wing Using Vortex Paneling Methods, Donald A. Lorey

Theses and Dissertations

A unit aspect ratio delta wing is analyzes to determine if an unsteady vortex panel method can calculate the vortex bursting of the vortex developed along the leading edge. A two-dimensional vortex panel method is used to investigate wake splitting schemes of the vortex cores that comprise the vortex sheet, or wake. The worthier of the splitting methods is later implemented into the three-dimensional wake. The weighting values of the Kutta equations are investigated for the leading edges, and are determined to be problem specific. An alternative approach to management of the wake data is presented and implemented. The delta …

Go to article

A Comparison Of Molecular Vibration Modeling For Thermal Nonequilibrium Airflow, Kenneth J. Moran Dec 1990

A Comparison Of Molecular Vibration Modeling For Thermal Nonequilibrium Airflow, Kenneth J. Moran

Theses and Dissertations

The effects of thermal nonequilibrium on flows about blunt-bodies have not been studied numerically in isolation from chemical reactions. Typically, air is modeled as a perfect gas or as a chemically reacting mixture. In the former case, significant errors result at Mach numbers exceeding about 5. However, below Mach numbers around 8, the effects of chemical reactions are negligible. This study analyzes flow about a simple axisymmetric blunt-body at moderate hypersonic speeds (Mach numbers between 5-8). A first-order-accurate Roe scheme was used to compute solutions of the Euler equations assuming different gas models: perfect gas, thermal equilibrium, and thermal nonequilibrium. …

Go to article

Transverse Cracking In A Fiber Reinforced Ceramic Matrix Composite, Steven E. Bachmann Dec 1990

Transverse Cracking In A Fiber Reinforced Ceramic Matrix Composite, Steven E. Bachmann

Theses and Dissertations

The purpose of this study was to investigate the transverse cracking behavior of a fiber reinforced ceramic matrix composite. The major objectives were to determine the crack initiation stress and the minimum transverse crack spacing for different cross-ply lay-ups of SiC/1723, to provide explanation for the differences in the performance of the lay-ups, and to compare the test results to available theoretical models and to other composite systems. The thickness of the transverse ply was found to have a great effect on the transverse cracking behavior of laminates. The saturation crack spacing decreased as the transverse ply thickness was decreased. …

Go to article

Effect Of Riblets On Pressure Recovery In A Straight-Walled Diffuser, Michael K. Reagan Dec 1990

Effect Of Riblets On Pressure Recovery In A Straight-Walled Diffuser, Michael K. Reagan

Theses and Dissertations

The objective of this thesis was to investigate the effect of riblets on the pressure recovery in a straight-walled diffuser. Previous work has shown that riblets were effective in reducing the viscous drag over surfaces subjected to a turbulent boundary layer. More recently, riblets were shown to delay the flow separation within a subsonic, straight-walled diffuser by as much as 200%. The purpose of this investigation was to determine the effect on the pressure distribution within a diffuser that has had the flow separation point favorably altered by the application of riblets. Investigation results revealed that riblets not only delayed …

Go to article

Investigation Of Fatigue Damage Mechanisms In A Metal Matrix Composite Under Elevated Temperature, Barry D. Portner Dec 1990

Investigation Of Fatigue Damage Mechanisms In A Metal Matrix Composite Under Elevated Temperature, Barry D. Portner

Theses and Dissertations

This study investigated the fatigue damage initiation and progression in SCS-6/Ti-15-3 under an environment of fatigue loading at isothermal temperature. This program included two parts. First, an 808 Ultimate Tensile Strength system was set up to accommodate testing at two frequencies of 2.0 and 0.0208 cps at a constant temperature of 427° C. Second, at intervals during the load cycle process, the test specimens were characterized by establishing damage parameters based on changing modulus of elasticity, average strain, strain range, and ultimate tensile strength. Damage progression was documented in the form of failure of the fiber-matrix interface, matrix cracking, fiber …

Go to article

Development Of A Piezoelectric Polymer Film Pressure Transducer For Low Frequency And Dynamic Pressure Measurement, Ted H. Halley Dec 1990

Development Of A Piezoelectric Polymer Film Pressure Transducer For Low Frequency And Dynamic Pressure Measurement, Ted H. Halley

Theses and Dissertations

The purpose of this research was to investigate the characteristics of a small and inexpensive pressure transducer made from piezoelectric film. The pressure transducer was designed to be small and surface mountable so that the pressure distribution could be measured on an aerodynamic body. A charge reset technique was used to overcome the traditional limitations, low frequency measurements and charge decay, of a piezoelectric device.

Go to article

First Prev Next Last