Aerospace Engineering Commons^™

Flight Control Design Using Mixed H2/Μ Optimization, Douglas D. Decker

Theses and Dissertations

This thesis examines the use of the mixed H2-Microns optimal control synthesis method in the design of a flight control system for the lateral-directional axes of the F-16 Variable Stability In-Flight Simulator Test Aircraft (VISTA). The method is designed to minimize the H2 norm (two-norm) for a given value of microns. This should provide adequate noise and disturbance rejection while maintaining robustness against several types of uncertainties in the system. This thesis finds that, for this problem, the two-norm is not an accurate representation of the outputs of interest. When the two-norm is broken up into its constituent parts an …

The Enhanced Performance Of An Integrated Navigation System In A Highly Dynamic Environment, Brian J. Bohenek

Theses and Dissertations

For the U.S. Air Force to maintain an accurate and reliable Navigation Reference System (NRS) with Carrier-Phase Global Positioning System (CPGPS) measurements, it must develop an accurate and robust NRS in the face of cycle slips caused by highly dynamic maneuvers. This research investigates the implementation of a double differencing between receivers-satellites scheme to improve the accuracy of current NRS models. The removal of the 'perfect Doppler velocity aiding measurements' (a very poor assumption of past research) was completed with stable and accurate results. The double differencing implemented showed improvement in the accuracy of the NRS. An investigation of two …

Fatigue Behavior Of A Cross-Ply Metal Matrix Composite At Elevated Temperature Under Strain Controlled Mode, Leon B. Dennis

Theses and Dissertations

This research extends the existing knowledge of cross-ply metal matrix composites (MMC) to include fatigue behavior under strain-controlled fully reversed loading. This study investigated fatigue life, failure modes and damage mechanisms of the SCS-6-Ti-15-3, [O-9O]_2s, MMC. The laminate was subjected to fully reversed fatigue at elevated temperature (427° C) at various strain levels. Stress, strain and modulus data were analyzed to characterize the macro-mechanical behavior of the composite. Microscopy and fractography were accomplished to identify and characterize the damage mechanisms at the microscopic level. Failure modes varied according to the maximum applied strain level showing either mixed mode …

Compressible Turbulence Measurements In A Supersonic Flow With Adverse Pressure Gradient, Jon W. Dotter

Theses and Dissertations

Mean flow and compressible turbulence measurements have been obtained upstream and within a shock boundary interaction and a compression ramp in Mach 3 flow. Compressible turbulence models have met with little success in the accurate prediction of high-speed flows involving complicated shock boundary interactions and adverse pressure gradients because of a crucial lack of experimental data. Data were collected using conventional Pitot and cone static probes, single overheat cross-wire anemometry, multiple overheat cross-wire anemometry, and flow visualization techniques. Direct measurements of the total Reynolds shear stress were obtained using a turbulence transformation. Results indicate that compressibility effects, as evidenced by …

Investigation Of Tension-Compression Fatigue Behavior Of A Unidirectional Metal Matrix Composite At Elevated Temperature, Darren L. Kraabel

Theses and Dissertations

This study investigated the fatigue behavior in a unidirectional metal matrix composite under tension-compression loading conditions. Stress-strain responses, modulus and strain trends were monitored to characterize damage. Fractography and microscopy were used to characterize failure modes. Fatigue life curves were plotted base on different parameters such as stress and strain. Tension-compression fatigue life was shorter than the obtained under tension-tension fatigue cycling. Creep, observed in tension-tension. fatigue cycling, and the effects of the compressive load on the plastic zone around the crack tip explain shorter life under tension-compression fatigue loading.

Performance Characterization Of A Highly-Offset Diffuser With And Without Blowing Vortex Generator Jets, Michael B. Senseney

Theses and Dissertations

The effect of blowing vortex generator jets (VGJs) on the performance of a highly-offset (s-duct) diffuser was investigated experimentally. VGJs are pitched, skewed jets which generate streamwise vortices as well as injecting high-momentum fluid into the boundary layer. Diffuser performance with and without VGJs was measured for an inlet Mach number of 0.6 (Re/x = 1.27x10⁷ per cm). Pitot static and hot-film instrumentation was used to measure flow properties at the diffuser inlet and exit planes. Without blowing, the flow on the lower surface of the diffuser was massively separated. Blowing at 0.48% mass flow ratio through three lower-surface …

Applications Of ℓ1 And Mixed H2/ℓ1 Optimization, Mark S. Spillman

Theses and Dissertations

This thesis explores the use of ℓ₁ and mixed H2/ℓ1 optimization methods to design flight control systems. ℓ₁ optimization is used to handle tracking issues in the design of digital compensators. Control deflection and rate limitations, overshoot and undershoot limitations and steady-state error requirements are discussed. Model-matching techniques which produce acceptable tracking results with lower order controllers are also examined. New numerical methods for continuous H2/L1 and discrete H2/ℓ1 optimization are presented. These methods are used to design an aircraft controller in continuous and discrete time and the results are compared.

Fatigue Behavior Of A Cross-Ply Ceramic Matrix Composite At Elevated Temperature Under Tension-Tension Loading, Craig D. Steiner

Theses and Dissertations

This study investigated the fatigue behavior and damage mechanisms of a [0-90]_4s SiC-MAS ceramic matrix composite under tension-tension loading at two elevated temperatures and two frequencies. Stress and strain hystereses, maximum and minimum strain, and modulus of elasticity were evaluated to characterize the material behavior. Microscopy and fractography were used to evaluate damage progression and mechanisms. Fatigue life was independent of frequency at both temperatures.

Analysis And Simulation Of Narrowband Gps Jamming Using Digital Excision Temporal Filtering, Gerald L. Falen

Theses and Dissertations

The purpose of this thesis is to investigate the performance of the Digital Excision Temporal Filter (DETF) to reject narrowband jammers used against the Global Positioning System (GPS). The DETF takes the Fast Fourier Transform (FFT) of the GPS signal and excises any FFT bins that are above a preselected threshold level. Then the excised signal is Inverse Fourier Transformed and fed to the GPS receiver. Several jammer types are simulated including Continuous Wave (CW), Pulse CW, Swept CW, Narrowband Spot Noise, and Wideband Barrage Noise jammers. Cases are also simulated using all but the Wideband Barrage Noise jammer at …

Computing Norad Mean Orbital Elements From A State Vector, Dwight E. Andersen

Theses and Dissertations

NORAD maintains and disseminates mean orbital elements on Earth-orbiting satellites in the form of Two-Line Element Sets (TLE). Five mathematical propagator models were developed for NORAD's use to predict the position and velocity using TLEs. This study investigated two approaches, Newton's method and direct iteration, to inverting this process by iterating to obtain NORAD-compatible mean orbital elements from a position and velocity state vector and the drag term. The Newton's iteration method was developed but not tested. The less computationally intensive direct iteration method was developed, coded in FORTRAN, and tested. The initial guess and subsequent corrections in the iterative …

Optimization Of A Nutation Damper Attached To A Spin-Stabilized Satellite, Brady P. Hauboldt

Theses and Dissertations

This study uses linearized equations of motion for a rigid body with an attached spring-mass-damper to maximize the decay rate of a satellite's coning motion. An analysis of the numerical eigenvalues is presented which leads to an optimal relationship between relevant parameters: damper placement, spring constant, damping coefficient, system moments of inertia, and damper mass fraction. The coupled system's eigenvalues do not provide truly critical damping, thus the real eigenvalue parts are minimized in order to achieve damping which requires the minimum amount of time. A comparison between this optimal design method and a classical method concludes a noticeable improvement …

A Methodology To Assess The Utility Of Future Space Systems, Bruce Rayno

Theses and Dissertations

This research identifies the assumptions and simplifications in the SPACECAST 2020 value model and assesses modifications. The model determines and prioritizes future space systems' utility toward controlling and exploiting space. This study shows that the assumption of using an additive utility function is valid. This research shows that the mission areas are mutually utility independent allowing the use of the multiplicative utility function. This research also uses the multilinear function, which requires utility independence implied in mutual utility independence. This study makes modifications to the 98 SPACECAST 2020 measure of merit scoring functions. These scoring functions all used the same …

An Integrated Gps-Ins-Baro And Radar Altimeter System For Aircraft Precision Approach Landings, Robert A. Gray

Theses and Dissertations

Currently, the Department of Defense (DoD) and the commercial airline industry are utilizing the Instrument Landing System (ILS) during aircraft landings for precision approaches. The replacement system for the aging ILS was thought to he the Microwave Landing System (MLS). Instead, use of the Global Positioning System (GPS) is now thought to be a viable replacement for ILS precision approaches. The majority of current precision landing research has exploited 'stand-alone' GPS receiver techniques. This thesis instead explores the possibilities of using an extended Kalman filter (EKF) that integrates an Inertial Navigation System (INS), GPS, Barometric Altimeter, Pseudolite and Radar Altimeter …

Flow Visualization Of A Turbulent Shear Flow Using An Optical Wavefront Sensor, Daniel W. Jewell

Theses and Dissertations

The research reported here investigated the use of a shearing interferometer (SI) wavefront sensor to determine the effects of shear-layer turbulence on an optical wavefront. A collimated helium-neon laser beam was propagated through a plane shear-layer produced by mixing helium and nitrogen at different velocities. Since the gases have different indices of refraction, the optical wavefront was distorted by different amounts by each gas. The SI measured the wavefront slope across the sampled area of the wavefront. The shear-layer was viewed from two orthogonal directions. This document contains shadow graphs, interference patterns imaged by each of the SI's six cameras, …

An Analysis Of The Kc-135 Three-Person Cockpit, Robert A. Deivert

Theses and Dissertations

In an effort to quantitatively determine the utility of mission effectiveness of the KC-135, this research used value-focused thinking to measure the impact of replacing the KC-135 navigator with upgraded avionics. A Value Model was developed as a hierarchy with fundamental objectives at the highest level and attributes at the lowest level. Weights were assigned to show the contribution each level had to the one above it. The attributes were given a score and an additive model was used to determine utility with and without a navigator. Break-even analysis and net present value calculations were done to show the costs …

An Experimental Investigation Of The Time-Dependent Separation Of Tangent Bodies In Supersonic Flow, Neal A. Mosbarger

Theses and Dissertations

An experimental, time-dependent separation of tangent bodies was performed in a supersonic wind tunnel (Mach 1.5 and 1.9) to investigate the significance of transient effects and the suitability of using steady-state assumptions to predict a dynamic even. The model configurations consisted of two bodies placed in a near tangent position. A stationary body, plate or ogive, was instrumented to obtain dynamic surface pressures, while a second body, a wedge attached to an air cylinder, was plunged in a constrained motion away from and towards the stationary model. Three-dimensional flow expansion around the edge of the wedge reduced the strength of …

An Experimental Investigation Of Sandwich Flat Panels Under Low Velocity Impact, Timberlyn M. Harrington

Theses and Dissertations

This study evaluated the failure modes and mechanisms associated with increasing face sheet thickness of flat sandwich panels under low velocity impact. The sandwich panels were fabricated using 1.27 cm thick, 145 kg-m³ (9 lb-ft³), 3.175 mm (1-8 in.) cell size Nomex honeycomb core, FM 300-2 film adhesive and AS4-3501-6 graphite-epoxy face sheets. The thickness of the core remained 1.27 cm, and the thickness of the adhesive remained 0.25 mm. The thickness of the face sheets varied using the following stacking sequences: [0-90]_s, [0-90]_2s, [0-90]_4s, [0-90]_8s, and [0-90]_{12s …}

A Gain Scheduling Optimization Method Using Genetic Algorithms, Robert C. Martin Iv

Theses and Dissertations

Gain scheduling. the traditional method of providing adaptive control to a nonlinear system, has long been an ad hoc design process. Until recently; little theoretical guidance directed this practitioners' art. For this reason a systematic study of this design process and its potential for optimization has never been accomplished. Additionally, the nonlinearities and the large search space involved in gain scheduling also precluded such an optimization study. Traditionally, the gain scheduling process has been some variation of a linear interpolation between discrete design points. By using powerful non-traditional optimization tools such as genetic algorithms there are ways of improving this …

Investigation Of Tension-Compression Fatigue Behavior Of A Notched Cross-Ply Metal Matrix Composite At Elevated Temperature, Matthew W. Yocum

Theses and Dissertations

This research extends the existing knowledge of MMC fatigue damage mechanisms by studying the tension-compression fatigue behavior of a notched cross-ply laminate MMC at elevated temperature. A [0-90]_2S SCS-6-Ti-15-3 laminate with a center hole was subjected to tension-compression fatigue at 427 °C (800 °F). Stress and strain data was taken to evaluate macro-mechanic behavior of the material. Microscopy and fractography were performed to characterize the damage on a micro-mechanical level. Crack initiation and progression was monitored using acetate face replicas. Four cracks were found to develop around the periphery of the hole, two of which became dominant and proceeded …

The Nuts & Bolts Of Cooperative Learning In Engineering, Nikos J. Mourtos

Faculty Publications

A great number of engineering students work alone. But in industry, teamwork is required most of the time. Incorporating Cooperative Learning (CL) into an engineering program gives students an opportunity to practice problem solving and communication skills in a "simulated" professional environment. The paper briefly discusses the motivation behind using CL in engineering courses. Then, the essential elements to make CL successful in the classroom are examined and examples of how these elements have been incorporated into engineering courses taught by the author are given. Problems that have been encountered along with possible fixes are also mentioned.

Analysis Of Modal Behavior At Frequency Cross-Over, Robert N. Costa Jr.

Theses and Dissertations

The existence of the mode crossing condition is detected and analyzed in the Active Control of Space Structures Model 4 (ACOSS4). The condition is studied for its contribution to the inability of previous algorithms to successfully optimize the structure and converge to a feasible solution. A new algorithm is developed to detect and correct for mode crossings. The existence of the mode crossing condition is verified in ACOSS4 and found not to have appreciably affected the solution. The structure is then successfully optimized using new analytic methods based on modal expansion. An unrelated error in the optimization algorithm previously used …

Numerical Design Of Advanced Multi-Element Airfoils, Donovan L. Mathias, Russell M. Cummings

Aerospace Engineering

The current study extends the application of computational fluid dynamics to three-dimensional high-lift systems. Structured, overset grids are used in conjunction with an incompressible Navier-Stokes flow solver to investigate flow over a two-element high-lift configuration. The computations were run in a fully turbulent mode using the one-equation Baldwin-Barth turbulence model. The geometry consisted of an unswept wing which spanned a wind tunnel test section. Flows over full and half-span Fowler flap configurations were computed. Grid resolution issues were investigated in two-dimensional studies of the flapped airfoil. Results of the full-span flap wing agreed well with experimental data and verified the …

The Professional Air Traffic Controllers Strike: A Retrospective Analysis, Steven E. Durnin

Master's Theses - Daytona Beach

The purpose of this study was to assess the opinions, beliefs, and perspectives of former air traffic controllers who were terminated from employment with the Federal Aviation Administration for participating in the Professional Air Traffic Controllers Organization (PATCO) strike of 1981. The study examines the perceptions of the former controllers to determine their feelings toward the justification for going on strike over 13 years ago. This is relevant in light of recent events including the lifting of the ban against rehiring PATCO controllers by the Clinton Administration.

The data collected for this study were obtained with an opinionnaire mailed via …

Simulation Of Active Control Of Asymmetric Flows Around Slender Pointed Forebodies, Hazem Sharaf El-Din

Mechanical & Aerospace Engineering Theses & Dissertations

At high angles of attack, the flowfield over slender forebodies becomes asymmetric with substantial side force, which may exceed the available control capability. The unsteady compressible Navier-Stokes equations are used to investigate the effectiveness of different active control methods to alleviate and possibly eliminate the flow asymmetry and the subsequent side force. Although the research work focuses on active control methods, a passive control method has been investigated. The implicit, Roe flux-difference splitting, finite volume scheme is used for the numerical computations. Both locally-conical and three-dimensional solutions of the Navier-Stokes equations are obtained.

The asymmetric flow over five-degree semi-apex angle …

A Numerical Analysis Of Smoothed Particle Hydrodynamics, David A. Fulk

Theses and Dissertations

This dissertation studies the numerical method of Smoothed Particle Hydrodynamics SPH as a technique for solving systems of conservation equations. The research starts with a detailed consistency analysis of the method. Higher dimensions and non-smooth functions are considered in addition to the smooth one dimensional case. A stability analysis is then performed. Using a linear technique, an instability is found. Solutions are proposed to resolve the instability. Also a total variation stability analysis is performed leading to a monotone form of SPH. The concepts of consistency and stability are then used in a convergence proof. This proof uses lemmas derived …

Computational Analysis Of Forebody Tangential Slot Blowing, Ken Gee, Roxana M. Agosta-Greenman, Yehia M. Rizk, Lewis B. Schiff, Russell M. Cummings

Aerospace Engineering

No abstract provided.

Numerical Analysis Of The Viscous Flow In A Supersonic Diffuser, Sa'ed A'Rafat

Master's Theses - Daytona Beach

The goal of a diffuser is to transform kinetic energy into potential energy with minimum losses in total pressure. Existing supersonic diffusers are based on compression through shock waves. This process is inherently inefficient because of the large losses caused by the shocks. We investigate by means of Computational Fluid Dynamics (CFD) the viscous flow in a supersonic diffuser designed by means of inviscid theory to produce a shock-free isentropic compression. The design is based on the combination of elementary flows. Two simple wave regions connected by a sink flow are used to take a uniform supersonic flow at one …

Numerical Simulation Of Dynamic-Stall Suppression By Tangential Blowing, Matthew C. Towne

Theses and Dissertations

The use of tangential blowing to suppress the dynamic stall of a pitching airfoil is investigated numerically. The laminar two-dimensional, compressible Navier-Stokes equations are solved time-accurately using a Beam- Warming algorithm. A slot is located at four different positions along the surface of a NACA 0015 airfoil and air is injected in a nearly tangential sense along the upper surface. Suction control is also employed at one of these slot locations to directly compare with tangential-blowing control. Solution sensitivity to grid refinement, time-step size, numerical smoothing, and initial conditions is investigated at a Reynolds number of 2.4 x 10exp 4. …

Investigation Of Wall Injectors For Supersonic Mixing Enhancement, Yaacov Haimovitch

Mechanical & Aerospace Engineering Theses & Dissertations

A comparative study of the interaction between wall mounted swept-ramp injectors and injector nozzle shape has been conducted in a constant area duct to explore techniques to enhance mixing in scramjet combustors. The scramjet combustors are currently being developed for propulsion systems applications on the envisioned hypersonic vehicles. Short combustor residence time, a requirement for fuel injection parallel to the main flow in the combustor, and an overall strong sensitivity of the vehicle performance to the propulsion system motivated the investigation. The swept-ramp injector investigated in this study produces vortex shedding and local separation downstream of the injector's nozzle exit, …

Investigation Of Computational And Spectral Analysis Methods For Aeroacoustic Wave Propagation, Florence Odile Vanel

Mechanical & Aerospace Engineering Theses & Dissertations

Most computational fluid dynamics (CFD) schemes are not adequately accurate for solving aeroacoustics problems, which have wave amplitudes several orders of magnitude smaller yet with frequencies larger than the flow field variations generating the sound. Hence, a computational aeroacoustics (CAA) algorithm should have minimal dispersion and dissipation features. A dispersion relation preserving (DRP) scheme is, therefore, applied to solve the linearized Euler equations in order to simulate the propagation of three types of waves, namely: acoustic, vorticity, and entropy waves. The scheme is derived using an optimization procedure to ensure that the numerical derivatives preserve the wave number and angular …