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Theses and Dissertations

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Articles 1501 - 1530 of 1780

Full-Text Articles in Aerospace Engineering

Effects Of Base Cavity Depth On A Free Spinning Wrap-Around Fin Missile Configuration, Jon A. Struck Dec 1995

Effects Of Base Cavity Depth On A Free Spinning Wrap-Around Fin Missile Configuration, Jon A. Struck

Theses and Dissertations

This study investigated the role base cavity depth plays in altering the overall subsonic aerodynamic forces on a free spinning axisymmetric body with wrap around fins. Wind tunnel usage allowed the forces to be monitored for varying base cavity depths and angles of attack. A base cavity depth analysis was also performed on a non-spinning axisymmetric body for comparison. Oil visualizations were conducted on the non-spinning configuration to further describe airflow patterns around the body and within the cavity. Results revealed that the aerodynamic forces, mostly drag, changed with increasing cavity depth but not to the extent previously believed. The …

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Experimental Investigation Of Non-Adiabatic Supersonic Slot Injection Into A Supersonic Cross-Flow, Kelly C. Tucker Dec 1995

Experimental Investigation Of Non-Adiabatic Supersonic Slot Injection Into A Supersonic Cross-Flow, Kelly C. Tucker

Theses and Dissertations

Turbulence and mean flow measurements were acquired downstream of a normal, supersonic (M=1.6), two-dimensional, slot injection into Mach 3.0 flow (Re/m = 15x106). Two non-adiabatic cases Ti/T∞ = 1.11 and Ti/T∞ = 0.93) were studied. Multiple overheat anemometry and conventional mean flow analysis, as well as shadowgraph and schlieren photography, were utilized to study the turbulent mixing layer. The mean flow data included the Pitot, cone-static, and Mach number profiles. The measured turbulence data included shear stresses, mass flux, total temperature turbulence intensities, and turbulent heat fluxes. The temperature and density variation …

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Compressible Turbulence Measurement In The Mixing Layer Of An Adiabatic Normal Slot Injection Into Supersonic Flow, Christopher D. Whitcomb Dec 1995

Compressible Turbulence Measurement In The Mixing Layer Of An Adiabatic Normal Slot Injection Into Supersonic Flow, Christopher D. Whitcomb

Theses and Dissertations

In this study mean flow and compressible turbulence measurements were taken at a station x = 72W downstream of the injection, where W is the injector throat width, of an adiabatic 2-D Mach 1.6 normal slot injection into a Mach 2.9 flow. Data were collected using a conventional Pitot probe, a cone-static probe, and multiple overheat cross-wire anemometry. In addition, schlieren and shadowgraph flow visualization was used to investigate the flow structure at both the injection point and at the downstream data collection point. From these measurements, mass flux component turbulence intensities of 8% to 10% were seen. The total …

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Fatigue Response Of Cracked Aluminum Panel With Partially Bonded Composite Patch, Jason J. Denney Dec 1995

Fatigue Response Of Cracked Aluminum Panel With Partially Bonded Composite Patch, Jason J. Denney

Theses and Dissertations

More and more aircraft, both commercial and military, are being called upon to fly well beyond their economic and structural service lives. Budget cuts and dwindling new aircraft development has forced the United States Air Force (USAF) to look toward more reliable structural repairs. One of these repair techniques, which was the subject of this study, is the repair of metallic aircraft structures using high strength composite materials. This study investigated the fatigue response of a precracked, 508x1 52x1 mm, 2024-T3 aluminum panel repaired with a partially bonded, unidirectional, three-ply boron/epoxy composite reinforcement with ply lengths of 68, 56 and …

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Numerical Study Of A Transpiration Cooled Rocket Nozzle, Jay A. Landis Dec 1995

Numerical Study Of A Transpiration Cooled Rocket Nozzle, Jay A. Landis

Theses and Dissertations

This study proved that transpiration cooling provides a better cooling scheme than regenerative cooling for long operating duration, liquid-fueled rocket engine nozzles. This proof was made on the basis of maximum wall temperature. This study compared transpiration cooling to regenerative cooling in the throat region of the Space Shuttle Main Engine Main Combustion Chamber. The study also analyzed the effects of porosity, solid thermal conductivity, and porous sphere size on a porous wall made of packed spheres. The transpiration cooled nozzle operated 35% cooler than a regeneratively cooled nozzle, but the temperature gradient at the hot gas surface was 72 …

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Applications Of Nonlinear Control Using The State-Dependent Riccati Equation, David K. Parrish Dec 1995

Applications Of Nonlinear Control Using The State-Dependent Riccati Equation, David K. Parrish

Theses and Dissertations

This thesis examines the relatively new theory of nonlinear control using state dependent coefficient factorizations to mimic linear state space systems. The control theory is a nonlinear quadratic approach, analogous to linear quadratic regulation. All implementations examined in this thesis are done strictly numerically. This thesis is meant to provide a proof of concept for both satellite control and for an artificial pancreas to regulate blood glucose levels in diabetics by automatic insulin injection. These simulations represent only a first step towards practical use of the NQR method, and do not address noise rejection or robustness issues.

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Full Lyapunov Exponent Placement In Reentry Trajectories, Michael H. Platt Dec 1995

Full Lyapunov Exponent Placement In Reentry Trajectories, Michael H. Platt

Theses and Dissertations

This study investigated the ability to control the chaotic reentry of a Delta-Clipper like vehicle by setting the values of initial arid final principal dynamical directions as well as the Lyapunov exponents. A model of the original controlled reentry vehicle was created through the use of the equations of motion in conjunction with an atmospheric model. A modified linear quadratic regulator allowed the set up of a boundary value problem which specified the Lyapunov exponents and determined the gain matrix as a function of time. The gain matrix can eventually be used in the control system of the vehicle.

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Sub-Optimal Control Of Rigid Spacecraft Reorientation Using Three Momentum Wheels, Gregory W. Schultz Dec 1995

Sub-Optimal Control Of Rigid Spacecraft Reorientation Using Three Momentum Wheels, Gregory W. Schultz

Theses and Dissertations

This thesis addresses sub-optimal employment of 3 momentum wheels for large angle reorientation of rigid spacecraft with minimal induced spacecraft motion during maneuvers. In addition to development of general theory for 3 wheel vehicles, simulation results for a vehicle using momentum wheels for secondary attitude control (GPS Block IIR) are compared to results for a vehicle using them for primary attitude control (the Hubble Space Telescope), to demonstrate practical applications and limitations. While the control laws were developed assuming no external perturbing torques on the vehicle, reorientation scenarios were run both in a torque free environment as well as an …

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A Differential Gps Aided Ins For Aircraft Landings, Ryan L. Britton Dec 1995

A Differential Gps Aided Ins For Aircraft Landings, Ryan L. Britton

Theses and Dissertations

The Department of Defense (DOD) and the commercial airline industry are in the process of replacing the instrument landing system (ILS) for aircraft precision approach landings. The use of differential Global Positioning System (DGPS) is thought to be a viable replacement for ILS precision approaches. This thesis explores the integration of an INS, DGPS, Barometric Altimeter, Pseudolite, and Radar Altimeter for a tanker type and a single engine aircraft precision approach. These devices are integrated using an extended Kalman filter (EKF). For the tanker type aircraft federal Aviation Administration (FAA) requirements for a Category I and a Category II precision …

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Velocity Determination For An Inverted Pseudolite Navigation Reference System, Jeffrey M. Hebert Dec 1995

Velocity Determination For An Inverted Pseudolite Navigation Reference System, Jeffrey M. Hebert

Theses and Dissertations

As navigation systems continue to improve in performance and features, the Air Force must develop better Navigation Reference Systems (NRS) to keep pace with technology. Specifically, with the advent of enhanced, integrated Global Positioning System (GPS) and Inertial Navigation System (INS) navigators, emphasis is placed on the measuring performance in the presence of GPS jamming. To meet these needs, a new NRS, dubbed the Sub-Meter Accuracy Reference System (SARS), is being developed by the 746th Test Squadron, Holloman AFB, New Mexico. SARS uses a unique, inverted GPS pseudolite positioning system to determine a reference trajectory. This research investigates two post …

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A Quantitative Feedback Theory Fcs Design For The Subsonic Envelope Of The Vista F-16 Including Configuration Variation And Aerodynamic Control Effector Failures, Vicent J. Cacciatore Dec 1995

A Quantitative Feedback Theory Fcs Design For The Subsonic Envelope Of The Vista F-16 Including Configuration Variation And Aerodynamic Control Effector Failures, Vicent J. Cacciatore

Theses and Dissertations

Fault tolerant flight control systems for combat aircraft are an alternative to excessively redundant aircraft designs or reconfigurable control laws. However, due to the range of flight conditions within a combat aircraft's operational flight envelope, the variety of its configurations, and the unavailability of an aerodynamic data base for damaged aircraft, designing fault tolerant systems is a complicated endeavor. Quantitative Feedback Theory is a robust control design technique especially well-suited to manage the structured parametric uncertainty inherent in this problem, and consequently is applied as the primary design tool for this research. Furthermore, realistic failure models are developed for the …

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Wing Flexure Compensation For Aircraft Attitude And Position Determination In An Inverted Carrier-Phase Positioning System, Bradley W. Mahlum Dec 1995

Wing Flexure Compensation For Aircraft Attitude And Position Determination In An Inverted Carrier-Phase Positioning System, Bradley W. Mahlum

Theses and Dissertations

In response to the ever increasing accuracies in inertial navigation systems, the U. S. Air Force must develop higher accuracy reference systems. These reference systems must also be small enough to be utilized in the testing of navigation systems onboard fighter aircraft. One such proposed system utilizes carrier-phase Global Positioning System (CPGPS) transmitters mounted on MM-9 pods with receivers on the ground. This research examines one possible method of utilizing this system to determine the attitude and position of the aircraft, given position estimates for the transmitter's locations. The transmitter positioning algorithm showed that the geometry will be problematic for …

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Optimal Formation Flight Control, Shawn B. Mccamish Dec 1995

Optimal Formation Flight Control, Shawn B. Mccamish

Theses and Dissertations

Automatic formation flight involves controlling multiple wing aircraft equipped with standard Mach-hold, altitude-hold, and heading-hold autopilots in order to maintain a desired position relative to a lead aircraft throughout formation maneuvers. Changes in the lead aircraft's states, including formation heading, velocity, altitude, and geometry changes, are treated as disturbance and are rejected by the formation flight control system. The work in this thesis is a continuation of five previous theses, dealing with the design of formation flight control systems. The goal of the optimal formation flight control design is to achieve robust formation maintenance in the face of formation maneuvers …

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Design Of Flight Control Laws For Aircraft With Flexible Wings Using Quantitative Feedback Theory, Christina L. Osmon Dec 1995

Design Of Flight Control Laws For Aircraft With Flexible Wings Using Quantitative Feedback Theory, Christina L. Osmon

Theses and Dissertations

Aircraft composed of lightweight composite materials are extremely enticing since their structural weight is greatly reduced. However, the control of these aircraft is complicated by the resultant flexibility of the wings. Two avenues of approach are possible; stiffen the wings thus losing some of the weight reduction benefits, or design the lateral/directional flight control system cognizant of the wing's flexibility. In this thesis the second approach is taken. The design of three lateral/directional flight control systems for the sub-sonic flight envelope of the F-18 is presented. The Quantitative Feedback Theory (QFT) robust control design technique is used. These designs incorporate …

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Multiple Model Adaptive Control Of The Vista F-16, Michael J. Stepaniak Dec 1995

Multiple Model Adaptive Control Of The Vista F-16, Michael J. Stepaniak

Theses and Dissertations

Multiple model adaptive control (MMAC) is investigated using the high-fidelity, nonlinear, six-degree-of-freedom Simulation Rapid-Prototyping Facility VISTA F-16. Detection of single actuator and sensor failures is considered, with an MMAC algorithm initially pursued which allows a controller specifically designed for each particular failure condition to replace the standard F-16 Block 40 flight control system (FCS) once the failure is detected. The synthesis of certain discrete-time LQG/PI controllers (those using control variables linearly dependent on state derivatives) is shown to be unattainable due to numerical difficulties. A novel control technique, termed control redistribution, is introduced which redistributes control commands (that would normally …

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Design And Analysis Of A Navigation System Using The Federated Filter, Stephen J. Delory Dec 1995

Design And Analysis Of A Navigation System Using The Federated Filter, Stephen J. Delory

Theses and Dissertations

The purpose of this paper was to design and analyse a federated filter design, to be used for retrofit of an Embedded GPS/INS (EGI) navigation unit into an existing Kalman filter-based air navigation system. A design was selected and simulations were conducted in the Distributed Kalman Filter Simulation software (DKFSIM). As well, a centralized Kalman filter design was simulated under identical conditions for comparison purposes. The federated filter was shown to be a feasible design, with accuracy in position and velocity very close to centralized Kalman filter values. The federated filter design also showed some attractive fault detection and isolation …

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Analysis Of Gravity-Gradient Satellite Attitude Inversion, Jules-Francois D. Desamours Dec 1995

Analysis Of Gravity-Gradient Satellite Attitude Inversion, Jules-Francois D. Desamours

Theses and Dissertations

The purpose of this research is to understand and describe the process by which the 1986 Polar BEAR gravity- gradient research satellite of John Hopkins University/Applied Physics Laboratory achieved an orbital attitude correction (re-inversion) from an inverted orientation through the utilization of its momentum wheel. Understanding this process provides an analytical foundation from which a universal attitude inversion process for other gravity-gradient satellites with similar anomalous motions may be sought and developed. The equations of motion for a gravity-gradient satellite with a momentum wheel are derived and implemented in FORTRAN for simulation of the dynamics of the spacecraft. Several re-inversion …

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Systems Analysis Of Gps Electrical Power System Redesign, Kevin J. Walker Dec 1995

Systems Analysis Of Gps Electrical Power System Redesign, Kevin J. Walker

Theses and Dissertations

A systematic analysis is applied to the electrical power subsystem of the Global Positioning Satellite (GPS) system. Results determined the most appropriate power source and conversion system Options. Photovoltaic solar arrays, the current power system, were not included in the analysis. The best electrical power subsystem options found in the analysis include a solar power source with either a dynamic or direct conversion technique, and a direct conversion nuclear source. The two solar options are designed, at a low level of detail, to provide the same level of power the current GPS photovoltaic solar array system provides. These two designs …

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Development And Testing Of A New Optimum Design Code For Hypersonic Wind Tunnel Nozzles, Including Boundary Layer, Turbulence, And Real Gas Effects, Ralph C. Tolle Nov 1995

Development And Testing Of A New Optimum Design Code For Hypersonic Wind Tunnel Nozzles, Including Boundary Layer, Turbulence, And Real Gas Effects, Ralph C. Tolle

Theses and Dissertations

A robust and efficient optimization code is developed and validated. The code is used to redesign an existing Mach 12 wind tunnel nozzle and utilizes response surface methodology (RSM) techniques. Explicit, globally second-order, flux-difference-splitting algorithms are used to solve the Navier-Stokes (NS) and Parabolized Navier-Stokes (PNS) flow solvers incorporated into the optimizer code. Either the Baldwin-Lomax or the Yang-Shih k-s turbulence model may be employed in the optimization code. First, 2-D/axisymmetric NS and PNS flow solvers are developed/modified and account for perfect gas/nonequilibrium chemically reacting flows. All solvers are validated against Computational Fluid Dynamics (CFD) and experimental data. The optimization …

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Nonlinear Geometric And Material Behavior Of Composite Shells With Large Strains, Scott A. Schimmels Aug 1995

Nonlinear Geometric And Material Behavior Of Composite Shells With Large Strains, Scott A. Schimmels

Theses and Dissertations

A two-dimensional, geometrically and materially nonlinear shell theory applicable to arbitrary geometries described by orthogonal curvilinear coordinates and encompassing large displacements, moderate rotations for large strain situations has been developed. Additionally, the theory includes Jacobian transformation matrices, based upon displacement parameters, for the Cauchy - 2nd Piola-Kirchhoff stress-state and the Cauchy (Almansi) - Green strain-state transformations, and a layered material approach is included for the elastoplastic analysis to allow for variation of plasticity through-the-thickness. Doubly curved 20, 28, and 36 degree-of-freedom finite elements are defined based on specialization of the theory to spherical coordinates. The computer program includes algorithms for …

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The Dependence Of The Time-Asymptotic Structure Of 3-D Vortex Breakdown On Boundary And Initial Conditions, Jeffrey C. Tromp Jul 1995

The Dependence Of The Time-Asymptotic Structure Of 3-D Vortex Breakdown On Boundary And Initial Conditions, Jeffrey C. Tromp

Theses and Dissertations

The three-dimensional, compressible Navier-Stokes equations are solved numerically to simulate vortex breakdown in tubes. Time integration is performed with an implicit Beam-Warming algorithm, which uses fourth-order compact operators to discretize spatial derivatives. Initial conditions are obtained by solving the steady, compressible, and axisymmetric form of the Navier-Stokes equations using Newton's method. Stability of the axisymmetric initial conditions is assessed through 3-D time integration. Unique axisymmetric solutions at a Reynolds number of 250 lose stability to 3-D disturbances at a critical value of vortex strength, resulting in 3-D and time-periodic flow. Axisymmetric solutions at a Reynolds number of 1000 contain regions …

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Effects Of Blowing Ratios On Heat Transfer To The Throat Region Of A Porous-Walled Nozzle, Fu-Jung Chen Jun 1995

Effects Of Blowing Ratios On Heat Transfer To The Throat Region Of A Porous-Walled Nozzle, Fu-Jung Chen

Theses and Dissertations

The effects of transpiration cooling on heat transfer in the throat region of a porous-walled nozzle were investigated. The experiments were performed in the AFIT low speed shock tube fitted with a Mach 2 nozzle. A blowing region was limited to the area from 1.3 cm prior to the throat to 1.2 cm downstream of the throat. The blowing ratios from -0.0002 (suction) to 0.0117 (blowing) of the main stream flow were studied. Heat flux data were taken from both sides of the nozzle. One side was transpiration cooled by secondary air injection through a porous wall, while the other …

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Multipoint Quadratic Approximation For Numerical Optimization, Michael A. Blaylock Mar 1995

Multipoint Quadratic Approximation For Numerical Optimization, Michael A. Blaylock

Theses and Dissertations

A quadratic approximation for nonlinear functions is developed in order to realize computational savings in solving numerical optimization problems. Function and gradient information accumulated from multiple design points during the iteration history is used in estimating the Hessian matrix. The approximate Hessian matrix is the available for a second order Taylor series approximation to the functions of interest. Several truss and frame models will be used to demonstrate the effectiveness of the new Multipoint Quadratic Approximation (MQA) in solving structural optimization problems.

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Compressible Turbulence Measurement In Low-Angle Injection Into A Supersonic Flow, Gregory J. Mccann Mar 1995

Compressible Turbulence Measurement In Low-Angle Injection Into A Supersonic Flow, Gregory J. Mccann

Theses and Dissertations

Mean flow and compressible turbulence measurements have been obtained at two stations downstream of low-angle supersonic injection into a Mach 3.0 flow (Re/m = 15 x 106). Data were collected using conventional Pitot and cone-static probes, single and multiple overheat cross-wire anemometry, and flow visualization techniques (shadowgraphs and schlierens). A direct measure of total Reynolds shear stress was accomplished using a turbulence transformation of the Reynolds-averaged Navier-Stokes equations. Results show compressibility effects, indicated by density fluctuations, to be large relative to the velocity fluctuations and on the same order in all three components. Compressibility appears to account for …

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A Decision Model For Environmental Assessment Of Process Waste Products, Kyle F. Byard Mar 1995

A Decision Model For Environmental Assessment Of Process Waste Products, Kyle F. Byard

Theses and Dissertations

Environmental managers must compare the potential impacts of waste products when deciding upon courses of action. The estimation and comparison of these impacts is a subjective process, and few methods of comprehensive, quantitative comparison of waste products currently exist. The intent of this study is to develop a decision methodology to evaluate the environmental impacts of waste products and to score them for comparison. The method will follow established system design principles and incorporate significant characteristics of the waste material. Scores derived to represent the environmental impacts of materials will then he analyzed employing statistical and probabilistic methods to assess …

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Analysis And Modeling Of An Airport Departure Process, Joseph E. Hebert Mar 1995

Analysis And Modeling Of An Airport Departure Process, Joseph E. Hebert

Theses and Dissertations

This study analyzes departure delays at a major airport using probability models to represent this non-homogeneous process. The models developed in this study expand on the Markovian models presently used by employing the method of stages to represent some of the model processes. This technique improves the user's ability to achieve a close fit for the service time probability distribution while maintaining the advantages of the Markovian model. The three types of models developed and compared all assume a Markovian system entry process. The first model uses an exponential distribution to model the service process. The second uses an Erlang …

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Performance Characterization Of A Highly-Offset Diffuser With And Without Blowing Vortex Generator Jets, Michael B. Senseney Dec 1994

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 …

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The Design And Analysis Of Integrated Navigation Systems Using Real Ins And Gps Data, Curtis D. Evans Dec 1994

The Design And Analysis Of Integrated Navigation Systems Using Real Ins And Gps Data, Curtis D. Evans

Theses and Dissertations

An extended Kalman filter (EKF) is used to combine the information obtained from a Global Positioning System (GPS) receiver and an Inertial Navigation System (INS) to provide a navigation solution. This research compares the results of an actual tightly-coupled GPS-INS integrated system with those obtained in computer simulation. Differences between the simulation and actual hardware results, such as navigation solutions and tuning values, are shown in the research. An analysis of various GPS models was studied to determine the best representation for a system truth model. Measurement updates and their effects upon position accuracies was considered and preliminary research was …

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An Experimental Study Of Planar Heterogeneous Supersonic Confined Jets, Frederick J. Tanis Jr. Dec 1994

An Experimental Study Of Planar Heterogeneous Supersonic Confined Jets, Frederick J. Tanis Jr.

Theses and Dissertations

The effects of varying the exit pressure of a supersonic helium jet exhausting coaxially with two parallel supersonic air streams into a constant area duct were investigated. The method used to evaluate the mass entrainment rate was to measure helium molar concentration profiles and mass flux across the duct using a binary gas probe then calculate the mass entrainment into the helium jet. In order to conduct this study a novel binary gas probe was developed which allowed helium concentration and mass flux data to be obtained during continuous traverses across the supersonic flowfield. High exit pressure ratio (EPR) led …

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Investigation Of Boundary Layer And Performance Effects Of Transpiration Cooling Through A Porous Plate In A Rocket Nozzle, David N. Keener Dec 1994

Investigation Of Boundary Layer And Performance Effects Of Transpiration Cooling Through A Porous Plate In A Rocket Nozzle, David N. Keener

Theses and Dissertations

This study used a range of low blowing ratios with air through an area of porous material in a Mach 2.0 nozzle to quantity the change in boundary layer thickness as a function of blowing ratio. Also, exit and wall Mach number profiles at each blowing ratio were collected to characterize performance losses as a result of blowing. Performance in terms of specific impulse was also studied. As expected, the boundary layer thickness increased and nozzle performance in terms of exit Mach number decreased with increasing blowing ratio.

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