Open Access. Powered by Scholars. Published by Universities.®
- Discipline
-
- Engineering (5730)
- Physical Sciences and Mathematics (2946)
- Aerospace Engineering (1673)
- Electrical and Computer Engineering (1342)
- Operations Research, Systems Engineering and Industrial Engineering (1244)
-
- Computer Sciences (1234)
- Business (993)
- Physics (919)
- Operational Research (609)
- Signal Processing (458)
- Civil and Environmental Engineering (422)
- Computer Engineering (414)
- Aviation (353)
- Electrical and Electronics (351)
- Social and Behavioral Sciences (349)
- Operations and Supply Chain Management (346)
- Materials Science and Engineering (335)
- Optics (330)
- Oceanography and Atmospheric Sciences and Meteorology (278)
- Navigation, Guidance, Control and Dynamics (252)
- Other Operations Research, Systems Engineering and Industrial Engineering (233)
- Human Resources Management (231)
- Systems Engineering (228)
- Atomic, Molecular and Optical Physics (198)
- Electromagnetics and Photonics (195)
- Aerodynamics and Fluid Mechanics (188)
- Environmental Sciences (188)
- Environmental Engineering (185)
- Nuclear Engineering (180)
- Applied Mathematics (178)
- Keyword
-
- #antcenter (380)
- #csra (134)
- Machine learning (93)
- Decision making (89)
- Algorithms (75)
-
- Global Positioning System (75)
- Image processing (73)
- Kalman filtering (65)
- Optimization (64)
- #afcec (62)
- Computer networks--Security measures (62)
- Drone aircraft (59)
- Computer security (57)
- Target acquisition (57)
- Neural networks (Computer science) (54)
- Software engineering (54)
- Additive manufacturing (52)
- Remote sensing (49)
- Flight control (48)
- Microelectromechanical systems (45)
- Computer vision (44)
- Artificial satellites (43)
- Decision support systems (43)
- #ctisr (42)
- Adaptive optics (42)
- Composite materials (42)
- Neural networks (41)
- Simulation (41)
- Wireless communication systems (41)
- Scheduling (40)
- Publication Year
- Publication
- Publication Type
- File Type
Articles 8731 - 8760 of 8785
Full-Text Articles in Entire DC Network
Investigation Of Fatigue Damage Mechanisms In A Metal Matrix Composite Under Elevated Temperature, Barry D. Portner
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 …
Effect Of Riblets On Pressure Recovery In A Straight-Walled Diffuser, Michael K. Reagan
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 …
Investigation Of Damage Mechanisms In A Cross-Ply Metal Matrix Composite Under Thermo-Mechanical Loading, Joel J. Schubbe
Investigation Of Damage Mechanisms In A Cross-Ply Metal Matrix Composite Under Thermo-Mechanical Loading, Joel J. Schubbe
Theses and Dissertations
Metal matrix composites (MMCs) are rapidly becoming strong candidates for high temperature and high stiffness structural applications such as the Advanced Tactical Fighter (ATF). This study systematically investigated the failure modes and associated damage in a cross-ply, [0/90]2s SCS6/Ti-15-3 metal matrix composite under in-phase and out-of-phase thermomechanic fatigue. Initiation and progression of fatigue damage were recorded and correlated to changes in Young's Modulus of the composite material. Experimental results show an internal stabilization of reaction zone size but degradation and separation from constituent materials under extended cyclic thermal loading. Critical to damage were transverse cracks initiating in the 90° …
Computational Investigation Of Circulation Control Turbulence Modeling, T. Bryan Scruggs
Computational Investigation Of Circulation Control Turbulence Modeling, T. Bryan Scruggs
Theses and Dissertations
A computational study of the turbulence model parameters and the effect on the flow field of a circulation control airfoil was conducted. A Beam- Warming algorithm with a modified Baldwin-Lomax turbulence model was used to solve the Navier-Stokes equations. A comparison between the effects of the Bradshaw constant on the flow field about the cylinder and the flow field about an airfoil were to be made. The lack of a steady 'converged' solution for the cylinder precluded the analysis of the flow field about a cylinder. For the airfoil, the separation point moves rearward and an enhanced vortex pattern is …
Finite Element Investigation Into The Dynamic Instability Characteristics Of Laminated Composite Panels, Walter W. Taylor Jr.
Finite Element Investigation Into The Dynamic Instability Characteristics Of Laminated Composite Panels, Walter W. Taylor Jr.
Theses and Dissertations
Dynamic instability of a laminated composite panel subjected to a transverse load is studied. Up to cubic variations in the thickness coordinate are included in the inplane displacement field, and only the constant component is kept in the transverse displacement. The transverse shear strains retain only linear displacement terms and vary parabolically through the thickness. The complete quadratic displacement functions are included in the inplane strains. A 36 degree of freedom shell element is used to obtain numerical results. The static snap through load vs displacement curve, as well as the critical collapse load, is examined by invoking the Riks …
Effects Of Specific Heat Ratio On A Simulated Chemical Laser Cavity Flow, Curt Dewayne Botts
Effects Of Specific Heat Ratio On A Simulated Chemical Laser Cavity Flow, Curt Dewayne Botts
Theses and Dissertations
Mixing of primary cold flow air and secondary helium to control the ratio of specific heats for the medium flowing through a simulated chemical laser nozzle/lasing cavity was accomplished. The effects of a range of mixture specific heat ratios on flowfield behavior were examined using static pressure ports in the test cavity. Schlieren photography and high speed filming aided description of the flow dynamics. Results indicated that boundary layer effects became evident in the nozzles as specific heat ratios increased. Large pressure fluctuations were observed in the cavity when helium was introduced into the flow to raise the specific heat …
Failure Mechanisms In A Quasi-Isotropic Ceramic Composite Laminate Under Tensile Fatigue Loading, Gregory D. Tracy
Failure Mechanisms In A Quasi-Isotropic Ceramic Composite Laminate Under Tensile Fatigue Loading, Gregory D. Tracy
Theses and Dissertations
A study was conducted to experimentally investigate the tensile fatigue damage mechanisms in a quasi-isotropic ceramic matrix composite (Corning's Nicalon/CASIII). The goals of this study were to (1) develop a grip fixture for a servo-hydraulic MTS test machine and (2) conduct a series of tests with (0/±45/90)s specimens subjected to tensile fatigue loading to study their fatigue damage growth mechanisms. Results showed that when the material was subjected to stresses below 90 MPa, it lasted over 1000000 cycles but when stressed at or above 90 MPa, it failed in less than 1000 cycles.
Fracture Toughness Of Unidirectional Fiber Reinforced Ceramic Composites In Mode Ii Utilizing Laser Interferometry, Joseph W. Truskowski
Fracture Toughness Of Unidirectional Fiber Reinforced Ceramic Composites In Mode Ii Utilizing Laser Interferometry, Joseph W. Truskowski
Theses and Dissertations
A laser interferometry technique to measure crack opening displacement was developed and applied to end notched flexure specimens of a Corning Glass Works 1723 glass matrix with silicon carbide fibers. The laser interferometer displacement gauge monitored the crack opening displacement (COD) at the location of a support while specimens were subjected to Mode II (forward shear) cracking at room temperature via three point bend tests on a standard Instron Compression machine. Vertical displacement was measured at the center of the test specimen using a linear variable differential transformer. Load verses displacement curves were generated for both the LVDT displacement and …
Material Properties Of Silicon Carbide Fibers With Continuously Applied Sol-Gel Alumina Coatings, Christian C. Daehnick
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 …
Skin Friction And Heat Transfer Predictions For Hypersonic Turbulent Flow Over An Ogive-Cylinder, Richard H. Byers
Skin Friction And Heat Transfer Predictions For Hypersonic Turbulent Flow Over An Ogive-Cylinder, Richard H. Byers
Theses and Dissertations
The WRDC/FIMG Parabolized Navier-Stokes (PNS) Code is used to numerically predict both laminar and turbulent hypersonic flows over an ogive- cylinder body at zero angle of attack. A parametric study is conducted to determine the effects of selected code input variables on heat transfer and skin friction predictions. Comparisons are made between the PNS predictions and experimental data from the WRDC/Mach 6 High Reynolds Number Test Facility. Various problems encountered while obtaining PNS starting and marching solutions and corrective steps taken are discussed. A mesh resolution study indicates the minimum radial grid density sufficient for obtaining reasonable heat transfer results. …
Damping Of Layered Beams With Mixed Boundary Conditions, Eugene T. Cottle
Damping Of Layered Beams With Mixed Boundary Conditions, Eugene T. Cottle
Theses and Dissertations
For many years, viscoelastic materials have been used in damping treatments to control vibration. In order to optimize a damping treatment for maximum damping, a design engineer must be able to predict frequencies of vibration of damped normal modes and loss factors as a function of the design parameters. Theoretical models of layered beams have been developed, but to date, exact solutions have assumed boundary conditions to be the same for all layers. In this thesis, equations of motion for a damped, layered beam are solved for the longitudinal displacement of both elastic layers, as well as the lateral displacement …
A Whole Word And Number Reading Machine Based On Two Dimensional Low Frequency Fourier Transforms, Mark A. O'Hair
A Whole Word And Number Reading Machine Based On Two Dimensional Low Frequency Fourier Transforms, Mark A. O'Hair
Theses and Dissertations
The Fourier transform is investigated as a means for developing an optical reader capable of reading a large vocabulary without segmenting the image of a word into individual characters. The reader is capable of reading printed and cursive font styles, is scale invariant, and is substantially insensitive to noise. The image of a particular word is treated as a single symbol; the two dimensional low frequency Fourier coefficients (assuming n coefficients are calculated) define the word's location on an n dimensional hypersphere of unit radius. The distance between individual locations (words) categorizes similar and dissimilar words. The smaller the distance, …
Estimation Of Evoked Fields Using A Time-Sequenced Adaptive Filter With The Modified P-Vector Algorithm, Jeffery A. Kepley
Estimation Of Evoked Fields Using A Time-Sequenced Adaptive Filter With The Modified P-Vector Algorithm, Jeffery A. Kepley
Theses and Dissertations
This thesis describes a time sequenced adaptive filter developed to estimate visually evoked fields (EF) using visually evoked potentials (EP). These non-stationary signals are buried in strong background noise. The two types of noise are magnetoencephalogram (MEG) and electronencephalogram (EEG). The filter implementation is based on the Ferrara Time Sequenced Adaptive (TSAF) using the Least-Mean-Square (LMS) algorithm and the Williams modified P-vector algorithm (mPa). This essentially results in two filters. A two stage filter structure is used in which the first stage removes the time-varying mean of the input signals. This allows the second stage to process zero-mean signals which …
An Evolution Operator Solution For A Nonlinear Beam Equation, Carl E. Crockett
An Evolution Operator Solution For A Nonlinear Beam Equation, Carl E. Crockett
Theses and Dissertations
A nonlinear partial differential equation, motivated by the transverse vibration of a beam, is shown to have a unique solution. The existence theory, which is in the setting of semigroups and evolution operators, is a composite and synthesis of theorems of Kato. The formulation of the problem and the verification that the formulation leads to a solution are new. The introductory chapter provides background on the topic generally. Chapter 2 provides detailed formulations for the constant coefficient case. Chapter 3 describes nonautonomous cases. The general theorem is presented here. In Chapter 4, a more general case is considered. Namely, Kelvin …
Analysis Of Parking Orbits For A Sts External Tank In Low Earth Orbit, James E. Cross
Analysis Of Parking Orbits For A Sts External Tank In Low Earth Orbit, James E. Cross
Theses and Dissertations
A study was conducted of a single external tank in low earth orbit. Criteria for a parking orbit are then defined. Various orbits are then selected by varying the semi-major axis, eccentricity, and inclination. The resulting equations of motion for each of the above orbits (including atmospheric drag and a 2x0 gravity model) are numerically integrated over a time span of 90 earth days. An examination was made of the lowest initial altitudes which allowed the external tank to remain in the orbit window.
Dynamic Analysis Of A Combat Aircraft With Control Surface Failure, Marc Roy
Dynamic Analysis Of A Combat Aircraft With Control Surface Failure, Marc Roy
Theses and Dissertations
An investigation was performed to analyze the dynamic stability characteristic of an aircraft which has sustained damage to a primary control surface. The analysis was performed using the existing functional form of actual wind tunnel data taken on an F-16 model. Two control schemes are used for trimming an F-16 that has sustained damage to its rudder. The first control scheme represent the basic aircraft, while the second allowed the horizontal tail ailerons to move independently from the flaperons. The investigation was conducted for one flight condition representative of the aircraft at cruise speed. Region in α/β (angle of attack)/(sideslip …
Minimum Orbits About The Planet Venus, Jeffrey J. Smith
Minimum Orbits About The Planet Venus, Jeffrey J. Smith
Theses and Dissertations
An investigation is conducted into low orbiting satellites around the planet Venus with drag limited lifetimes. It is possible to specify combinations of orbital elements which result in orbital lifetimes in excess of some desired value. These combinations can be assembled into Critical Curves and Critical surfaces. Critical Curves and Surfaces are defined as curves and surfaces in orbital element space above which initial element sets will result in orbits that meet or exceed lifetime requirements. A numerical method is implemented for finding these combinations, and three Critical Surfaces are examined. A decay threshold is selected for bounding satellite lifetime. …
Numerical Analysis Of Critical Inclinations About The Planet Mars, Kenneth J. Hyatt
Numerical Analysis Of Critical Inclinations About The Planet Mars, Kenneth J. Hyatt
Theses and Dissertations
This study investigated critical inclinations about the planet Mars. Averaged equations of motion were numerically integrated over a time span of ten Earth years for various inclinations, eccentricities, and perigee heights. Each orbit (i.e. set of initial conditions) produced a standard deviation of the variations in eccentricity (SDE) and inclination (SDI). These were calculated using a polynomial approximation to the variations. Surface plots of SDI and SDE vs the initial conditions are then examined to ascertain the critical inclinations.
Specification And Equivalence Verification Of Sequential Circuits Via Vhdl, Richard L. Miller
Specification And Equivalence Verification Of Sequential Circuits Via Vhdl, Richard L. Miller
Theses and Dissertations
This research presents a merger of the specification and design capabilities of the Very High Speed Integrated Circuit (VHSIC) Hardware Description Language (VHDL) with a known verification method (UC Berkeley's verify software) in order to solve the design and verification problem of sequential circuits. The fruits of this research are a behavioral VHDL model for sequential circuit specification, a structural VHDL model for sequential circuit design, and a method for comparing two circuits described using these VHDL models in order to demonstrate circuit equivalence. The behavioral and structural VHDL models were developed and tested within the Intermetric's VHDL software support …
Continuous Wave And Pulsed Solid State Laser Model, Matthew D. Rotondaro
Continuous Wave And Pulsed Solid State Laser Model, Matthew D. Rotondaro
Theses and Dissertations
A solid state laser is modeled for use on a personal computer. The model can accurately represent Nd:YAG and Nd:Glass lasers during both continuous wave and repetitively pulsed operation. The large number of input variables allow the user to make changes to the cavity, optical pump source, and the cooling system. The model calculates the energy, power, and divergence angle of the beam along with other variables. Because of its user-friendly interface, it is possible for someone with limited laser experience to obtain useful information.
On The Maximum Range Of Flying Wings, Peter J. Torvik
On The Maximum Range Of Flying Wings, Peter J. Torvik
AFIT Documents
The classical equations for determining the maximum range of aircraft with propeller and jet propulsion systems are reviewed, along with previous work conducted to determine the optimal division of aircraft volume between fuselage and wing components. That the jet powered flying wing configuration produces optimal range only for limited geometries is confirmed. The optimal range of aircraft employing high bypass jet engines is explored, and found to lead to a broader range of design parameters for which the flying wing design produces maximum range than is the case when a pure jet system is used.
Monte Carlo Simulation Of Atmospheric Neutron Transport At High Altitudes Using Mcnp, Donald R. Culp, David L. Monti, James R. Shoemaker, David Wesley, Kirk A. Mathews
Monte Carlo Simulation Of Atmospheric Neutron Transport At High Altitudes Using Mcnp, Donald R. Culp, David L. Monti, James R. Shoemaker, David Wesley, Kirk A. Mathews
AFIT Documents
Neutron transport calculations were performed using the Monte Carol code, MCNP. The transport problem considered has a point source at high altitude (40 km). Since atmospheric density decreases with altitude, two-dimensional effects (cylindrical coordinates) can be important. Results were compared to those obtained with the SMAUG-II computer code, which performs mass-integral scaling of approximate fits to one-dimensional spherical discrete ordinates solutions. These comparisons show the importance of two-dimensional computations. The report discusses practical issues of applying MCNP to this problem, without code modifications and includes example input files for MCNP and for SMAUG-II. Computational modelling of neutron transport in the …
An Abstract Data Model For The Idef0 Graphical Analysis Language, Gerald R. Morris, Thomas C. Hartrum, Mark A. Roth
An Abstract Data Model For The Idef0 Graphical Analysis Language, Gerald R. Morris, Thomas C. Hartrum, Mark A. Roth
AFIT Documents
IDEF0 is the United States Air Force's ICAM (Integrated Computer Aided Manufacturing) Definition Method Zero graphical analysis language, a subset of Ross' Structured Analysis (SA) language. The language is also an excellent methodology for performing a requirements-phase analysis for any software development project. We present an abstract data model for IDEF0 using entity-relationship diagrams. This model helps to mitigate some of the ambiguities inherent in IDEF0. The model is divided into two parts representing the analysis data (the essential data model) and the graphical data (the drawing data model). This dual modeling approach allows for the …
Pronated Escape System For Fighter Aircraft, Allen D. Disselkoen Jr., Robert F. Gargiulo, James E. Haywood, Keith H. Heise, Darrell H. Holcombe, Stuart C. Kramer, Gregory R. Miller, Jeffrey S. Nicholson, Curtis H. Spenny
Pronated Escape System For Fighter Aircraft, Allen D. Disselkoen Jr., Robert F. Gargiulo, James E. Haywood, Keith H. Heise, Darrell H. Holcombe, Stuart C. Kramer, Gregory R. Miller, Jeffrey S. Nicholson, Curtis H. Spenny
AFIT Patents
An improved aircraft ejection seat system is described which embodies a forward leaning position for an occupant of the aircraft providing enhanced acceleration tolerance for an occupant during ejection from the cockpit, comprising a platform supporting at a rearward end thereof a seat having a seat back and seat pan sized and configured for accommodating the occupant, a forwardly disposed cowling integral with and faired to the platform for providing windblast protection to the occupant, a solid or cushioned upright wall member disposed centrally of the platform and extending between the seat and cowling and supporting an inclined chest plate …
System For Boundary Layer Control Through Pulsed Heating Of A Strip Heater, Milton E. Franke, Lawrence Kudelka
System For Boundary Layer Control Through Pulsed Heating Of A Strip Heater, Milton E. Franke, Lawrence Kudelka
AFIT Patents
A system is described for controlling the transition of laminar/turbulent flow at a surface which comprises a thin narrow strip heater disposed adjacent the surface and extending substantially transversely of the flow of the air stream thereacross, the heater being resiliently held in tension on or in closely spaced relationship to the surface, and a power source operatively connected to the heater for applying pulsed voltage of preselected amplitude and frequency to the heater.
Air Force Institute Of Technology Contributions To Air Force Research And Development, Calendar Year 1987, Air Force Institute Of Technology
Air Force Institute Of Technology Contributions To Air Force Research And Development, Calendar Year 1987, Air Force Institute Of Technology
AFIT Documents
From the introduction:
The primary mission of the Air Force Institute of Technology (AFIT) is education, but research and consulting are essential integral elements in the process. This report highlights AFIT's contributions to Air Force research and development activities [in 1987].
Synthetic Aperture Multi-Telescope Tracker Apparatus, Richard A. Carreras, Salvatore J. Cusumano, Morton B. Jenks, Robert I. Suizu
Synthetic Aperture Multi-Telescope Tracker Apparatus, Richard A. Carreras, Salvatore J. Cusumano, Morton B. Jenks, Robert I. Suizu
AFIT Patents
A plurality of telescopes provide output return signals which are applied both directly and in sampled form to a photo-detector cell. The detected signals from the photo-detector will represent the constant and transient errors of the telescope system. A low pass filter insures that the tracker provides only the constant or D.C. component of the error, while a high pass filter insures that the existing measuring devices for each telescope beam provide only the transient or A.C. component of the error. The A.C. and D.C. error signals are summed together with the appropriate applied gains on each channel such that …
Air Force Institute Of Technology Contributions To Air Force Research And Development, Calendar Year 1986, Air Force Institute Of Technology
Air Force Institute Of Technology Contributions To Air Force Research And Development, Calendar Year 1986, Air Force Institute Of Technology
AFIT Documents
This report highlights AFIT's contributions to Air Force research and development activities in 1986.
Optically Phased Laser Transmitter, Janet S. Fender, Salvatore J. Cusumano, Robert R. Butts, Christopher R. Dehainaut
Optically Phased Laser Transmitter, Janet S. Fender, Salvatore J. Cusumano, Robert R. Butts, Christopher R. Dehainaut
AFIT Patents
An apparatus and technique are described for phasing the outputs of a multiplier telescope array used as a laser transmitter. The technique uses samples of the transmitted beams to control optical path lengths through the separate telescopes so that the beams add coherently at the receiver. The phasing concept is applicable both to systems which provide inputs to the multiple telescopes by dividing a single laser beam and to systems in which the inputs to the telescopes and multiple, phase-locked laser beams. The approach is also compatible with single line and multi-line lasers, and it does not entail stringent alignment …
Multiple Jet Blowing Around The Blunt Trailing Edge Of A Circulation Controlled Airfoil, John K. Harvell, Milton E. Franke
Multiple Jet Blowing Around The Blunt Trailing Edge Of A Circulation Controlled Airfoil, John K. Harvell, Milton E. Franke
AFIT Patents
A circulation controlled airfoil has a body structure with leading and trailing ends and upper and lower surfaces extending therebetween, and a cylindrical member disposed along the trailing end of the body structure between the upper and lower surfaces thereof so as to form a rounded, blunt trailing edge surface on the airfoil. A first blowing jet slot is defined between the outer surface of the cylindrical member and the trailing end of the body structure adjacent its upper surface. A second blowing jet slot is defined in a tubular wall of the cylindrical member. The latter member can be …