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Theses and Dissertations

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Articles 1741 - 1770 of 1780

Full-Text Articles in Aerospace Engineering

Bifurcation Analysis Of The Longitudinal Dynamics Of A Simple Powered Lifting Hypersonic Vehicle, Eric E. Fox Dec 1990

Bifurcation Analysis Of The Longitudinal Dynamics Of A Simple Powered Lifting Hypersonic Vehicle, Eric E. Fox

Theses and Dissertations

Bifurcation analysis was used to investigate the nonlinear behavior of a simple powered lifting hypersonic vehicle in circular orbit about a spherical nonrotating Earth with gradients in atmospheric density and pressure and an inverse square law for gravity. Vehicle motion is constrained to a vertical plane so only longitudinal dynamics were modeled. Bifurcation analysis was conducted using the AUTO software package. A simple five-state model with three different thrust laws was derived to describe an unaugmented vehicle whose geometric and aerodynamic characteristics follow those of the literature. A parameter representing a body flap deflection was used to conduct one set …

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Investigation Of Strain Characteristics Of Graphite Polyetherether Ketone Using A Nonlinear Analysis And Experimental Methods, Stephen C. Gould Dec 1990

Investigation Of Strain Characteristics Of Graphite Polyetherether Ketone Using A Nonlinear Analysis And Experimental Methods, Stephen C. Gould

Theses and Dissertations

A geometric nonlinear technique is incorporated in a current finite element program. This nonlinear program allows material nonlinearity for calculating the stresses, strains and failure of composites. The improved program uses an updated Langrangian to calculate the stresses and strains. In addition, it updates the fiber orientation due to displacement in order to calculate the updated stiffness matrix. This method is valuable for large strain values. The analytical data were compared to experimental data obtained from Graphite PolyEtherEther Ketone laminates. To obtain data two geometries were used. Digitized photographs were used to measure the angle change for large strains.

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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 …

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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 …

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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.

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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 …

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Robustness Of H2 And H∞ Design Techniques In The Design Of A Guided Missile Controller, Steven R. Kolbow Dec 1990

Robustness Of H2 And H∞ Design Techniques In The Design Of A Guided Missile Controller, Steven R. Kolbow

Theses and Dissertations

This work follows Capt. R.L. Riddle's 1989 thesis (ADA216147) which compared conventional, H2 and H∞ controlled guided missiles in simulated flyouts against an airborne target. The simulation results did not clearly demonstrate the H2 and H∞ controller advantages. In this study the missile model and simulation were refined. In addition to simulation runs, performance, noise attenuation, and μ (structural singular value) robustness analyses were conducted. Results showed areas where improvement was needed in the H2 and H∞ controllers used in the study. An H2 and H∞ controller redesign is recommended using the …

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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 …

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H2 And H∞ Optimization With A Restricted Region Of Stability, Michael J. Mares Dec 1990

H2 And H∞ Optimization With A Restricted Region Of Stability, Michael J. Mares

Theses and Dissertations

Many modern control design methods, such as H2 and H∞ optimization, guarantee that the closed-loop system will be stable. To make further use of this guarantee, the portion of the s-plane considered to be stable is restricted to a region left of a vertical line some distance alpha from the imaginary axis. This alpha shift was accomplished in the state space equations, so standard computational tools still work. now the system is not only guaranteed to be stable, but also has some guaranteed speed for the time response. The equations for guaranteeing some arbitrary damping ratio were also …

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Investigation Of The High Angle Of Attack Dynamics Of The F-15b Using Bifurcation Analysis, Robert J. Mcdonnell Dec 1990

Investigation Of The High Angle Of Attack Dynamics Of The F-15b Using Bifurcation Analysis, Robert J. Mcdonnell

Theses and Dissertations

Previous studies predicted the F-15B high angle of attack and flat spin behavior using bifurcation analysis. These studies varied control surface deflections to find equilibrium and periodic solutions. The purpose of this research was to use bifurcation analysis to predict the F-15B high angle attack and flat spin behavior as a result of variable thrust, asymmetric thrust, and thrust vectoring. Using a previously developed model of the F-15, bifurcation analysis and continuation methods were used to map out the equilibrium and periodic solutions of the model as a function of the thrust parameters. A baseline bifurcation diagram, as a function …

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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. …

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An Experimental Study Of A Sting-Mounted Single-Slot Circulation Control Wing, Michael E. Pelletier Dec 1990

An Experimental Study Of A Sting-Mounted Single-Slot Circulation Control Wing, Michael E. Pelletier

Theses and Dissertations

This wind tunnel study investigated the feasibility of using a sting and force balance to measure the aerodynamic forces and moments on a circulation control wing. A 20% this, 8.5% camber, single blowing slot, rectangular wing was designed, built, and tested in the AFIT 5-ft wind tunnel. Lift and drag coefficients were referenced to the stability axis. The Reynolds number for all tests was 950,000; angle of attack was varied from -6 to +6 degrees. Trends in the data were similar to two dimensional data, with the exception of high drag coefficients with increased blowing. Results show it is feasible …

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Impact Damage In Curved Graphite/Epoxy Panels With Clamped Edges, Ronald B. Perry Dec 1990

Impact Damage In Curved Graphite/Epoxy Panels With Clamped Edges, Ronald B. Perry

Theses and Dissertations

Graphite/epoxy curved cylindrical panels were impacted in the center by an impact machine capable of measuring load during the test. Load, deflection and strain as functions of time were measured for six symmetric layup configurations for impact energies of 0.5 to 4.5 ft-lb. Damage was produced in all panels for certain impact energies. The extent and location of damage was determined from C-scans and optical microscopy of panel cross-sections. The cross-sections indicated that both delamination and transverse cracking contribute to internal damage. An in-house nonlinear finite element code was used to predict the panel deflections and stresses. The analysis produced …

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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. …

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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 …

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Micromechanical Modeling Of The Fiber/Matrix Interface Region In A Metal Matrix Composite, David D. Robertson Dec 1990

Micromechanical Modeling Of The Fiber/Matrix Interface Region In A Metal Matrix Composite, David D. Robertson

Theses and Dissertations

In order to develop reasonable analytical models and to better understand how the integrity of the fiber/matrix interface in high temperature titanium based metal matrix composites effects the overall transverse normal characteristics, a parametric study of various fiber/matrix interface conditions was performed. Analysis methods included both a simplified one-dimensional mathematical model and a finite element analysis using MSC/NASTRAN. First, both strong and weak interfacial bonds were examined. Subsequently, to provide for partial bonding, a model that used an elastic-plastic interphases zone between the fiber and matrix was examined.

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A Linear Quadratic Regulator Weight Selection Algorithm For Robust Pole Assignment, Jeffrey D. Robinson Dec 1990

A Linear Quadratic Regulator Weight Selection Algorithm For Robust Pole Assignment, Jeffrey D. Robinson

Theses and Dissertations

An advantage of linear quadratic regulator (LQR) design is that it gives a robust system by guaranteeing stability margins. This property is used to develop an algorithm for placing robust poles. The algorithm chooses the positive semidefinite weighting matrix Q and positive definite weighting matrix R by attempting to place closed loop poles at a set of desired poles. If the desired poles lie outside the allowable LQR region, the algorithm finds the achievable poles inside the region that are closest to the desired poles. The solution requires using a gradient search technique to minimize a weighted eigenvalue difference cost …

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Modelling And Analysis Of Kernel Function And Development Of Equivalent Theodorsen Function For Three-Dimensional Aeroelastic Analysis, John K. Ryder Dec 1990

Modelling And Analysis Of Kernel Function And Development Of Equivalent Theodorsen Function For Three-Dimensional Aeroelastic Analysis, John K. Ryder

Theses and Dissertations

A fractional calculus model is developed for the kernal function under incompressible subsonic flow conditions for rectangular planform airfoils with small aspect ratio. A model valid for restricted regions of the kernel function for compressible subsonic flow conditions is also developed. Additionally, a method for numerically solving the pressure-downwash integral equation for rectangular planform wings of aspect ratio two through ten in incompressible flow is developed. An equivalent Theodorsen function for three- dimensional unsteady flow is developed, enabling the use of simpler two- dimensional aeroelastic equations of motion to fully capture the more complicated three-dimensional effects.

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Computational Investigation Of Circulation Control Turbulence Modeling, T. Bryan Scruggs Dec 1990

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 …

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Finite Element Investigation Into The Dynamic Instability Characteristics Of Laminated Composite Panels, Walter W. Taylor Jr. Dec 1990

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 …

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Effects Of Specific Heat Ratio On A Simulated Chemical Laser Cavity Flow, Curt Dewayne Botts Dec 1990

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 …

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Failure Mechanisms In A Quasi-Isotropic Ceramic Composite Laminate Under Tensile Fatigue Loading, Gregory D. Tracy Dec 1990

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.

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Fracture Toughness Of Unidirectional Fiber Reinforced Ceramic Composites In Mode Ii Utilizing Laser Interferometry, Joseph W. Truskowski Dec 1990

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 …

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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 …

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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 …

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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.

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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 …

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Skin Friction And Heat Transfer Predictions For Hypersonic Turbulent Flow Over An Ogive-Cylinder, Richard H. Byers Dec 1990

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. …

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Damping Of Layered Beams With Mixed Boundary Conditions, Eugene T. Cottle Dec 1990

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 …

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Investigation Of Damage Mechanisms In A Cross-Ply Metal Matrix Composite Under Thermo-Mechanical Loading, Joel J. Schubbe Dec 1990

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° …

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