Engineering Commons^™

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.

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° …

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 …

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 …

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 …

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 …

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 …

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 …

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 …

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.

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 …

Realistic Orbits About The Martian Moons, Samuel R. Bryant

Theses and Dissertations

Orbits about the Martian moons, Phobos and Deimos, previously found to be stable by the Poincare surface of section technique in a restricted three- body system, were investigated with non-zero eccentricity of the moons added to the dynamics of the planar four-body system (Mars, moon sun, artificial satellite). Although not strictly applicable to this case, the surface of section technique was used to verify whether or not the previously found stable orbits were realistic when a real world perturbation was added to the system dynamics. The surface of section technique involves the numerical integration of several orbits with the same …

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.

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 …

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.

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 …

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. …

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 …

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 …

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.

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.

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. …

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 …

Development Of A Perturbation Generator For Vortex Stability Studies, John Edward Riester Jr.

Mechanical & Aerospace Engineering Theses & Dissertations

Theory predicts vortex instability when subjected to certain types of disturbances. It was desired to build a device which could introduce controlled velocity perturbations into a trailing line vortex in order to study the effects on stability. A perturbation generator has been designed and manufactured which can be attached to the center-body of an airfoil type vortex generator. Details of design tests and manufacturing of the perturbation generator are presented. The device produced controlled perturbations with frequencies in excess of 250 Hz. Preliminary testing and evaluation of the perturbation generator performance was conducted in a 4 inch cylindrical pipe. Observations …

Integrated Control Of Thermally Distorted Large Space Antennas, Robert H. Tolson

Mechanical & Aerospace Engineering Theses & Dissertations

Studies on controlling the thermal distortion of large space antennae have generally investigated a single orbital position and have optimized actuator locations based on minimizing the RMS surface deviation from the original parabolic shape. One study showed the benefits of directly using far zone electric field characteristics as the performance measure; but, this approach resulted in a nonlinear programming problem. The objective of the current study is to develop an approach to designing a control system that (1) recognizes the time dependence of the distortion and (2) controls variables that are directly related to far field performance in a quadratic …

Dynamics And Control Of Two Suspension Mechanisms For Ground-Based Testing Of Space Structures, Joseph E. Wilson

Mechanical & Aerospace Engineering Theses & Dissertations

Two suspension systems which effectively simulate a gravity-free environment are presented. A single degree-of-freedom suspension system utilizing a specially profiled band mechanism in conjunction with a torsional spring is presented to show its feasibility and applicability for use as a ground-based testing device for flexible space structures. The second device, a two degree-of-freedom suspension system consisting of two springs and a folding linkage is presented to show the feasibility as a testing device for suspending space structures on earth.

Problems resulting in unwanted dynamic behavior due to deviations from the design parameters for both systems are addressed. A nonlinear controller …

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.

The Development And Application Of A Trapezoidal Shear Panel For Use In Finite Element Codes, Glenn P. Greiner

Master's Theses - Daytona Beach

This thesis documents the efforts of the writer and his colleagues over the past several years to improve the theoretical foundation of the arbitrary quadrilateral shear panel used in structural analysis codes to model aircraft structures. An equilibrium stress-based element with pure shear resultants on its sides was developed using the principle of complementary virtual work. The internal stress field was derived from a complete polynomial Airy stress function. The element was numerically tested as a pure stress element and a hybrid element to assess the deflection properties for highly distorted planar panels. Linear-stress and quadratic-displacement rods were used, as …

Extension Of A Noninteractive Reliability Model For Ceramic Matrix Composites, Stephen F. Duffy, Robert C. Wetherhold, Lalit K. Jain

Civil and Environmental Engineering Faculty Publications

In the next decade ceramic composites will increasingly be used as high-temperature components in advanced gas turbines. Ceramic components will allow an increase in the operating temperature of the gas stream (measured by the turbine entry temperature), thereby resulting in greater fuel economy in aerospace and automotive turbine applications. Since these materials will be produced from abundant nonstrategic materials, computational structural mechanics methods are evolving to keep pace with this technology. As a result, establishing protocols for sound design methodology, which is the subject of this technical note, is the focus of much current analytical research.

Our objective was to …

Control Of Vortical Separation On A Circular Cone, Nikos J. Mourtos

Faculty Publications

For conical bodies, at moderate angles of attack, the flow separates from the lee side, forming two vortices. Although the vortex lift contrihution is highly desirable, as the angle of attack increases, the vortex system becomes asymmetric, and eventually the vortices breakdown. Thus, some control of the separation process is necessary if the vortex lift is to be exploited at higher angles of attack. The theoretical model which is used in this analysis has three parts. First, the 'single line-vortex' model is used within the framework of 'slender-body theory' to compute the outer inviscid field for specified separation lines. Second, …