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Air Force Institute of Technology

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Articles 1501 - 1530 of 1674

Full-Text Articles in Aerospace Engineering

Evaluation Of A Concentration Probe For Application In A Supersonic Flow Field, John S. Alsup Dec 1993

Evaluation Of A Concentration Probe For Application In A Supersonic Flow Field, John S. Alsup

Theses and Dissertations

Aspirating, concentration probes are used to measure binary gas concentrations in a supersonic flow. In the past, a tank discharge method has been used to calibrate concentration probes. An alternate calibration method has been developed and tested on a probe in a steady, subsonic/sonic flow. This study evaluated the calibration and performance of a concentration probe in a steady, supersonic flow over a range of mixture ratios of air and helium. The results of this study and a comparison of the two calibration methods are presented.

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A Numerical Study Of High-Speed Missile Configurations Using A Block- Structured Parallel Algorithm, Douglas C. Blake Dec 1993

A Numerical Study Of High-Speed Missile Configurations Using A Block- Structured Parallel Algorithm, Douglas C. Blake

Theses and Dissertations

A numerical analysis of the aerodynamic phenomena associated with the high-speed flight of a sharp-nosed, four-finned, high-fineness ratio missile using a block-structured, parallel computer algorithm is presented. The algorithm, PANS-3EM, utilizes a second-order-accurate, shock-capturing, Total Variation Diminishing scheme and incorporates a Baldwin-Lomax turbulence model. PANS-3EM allows for extreme flexibility in the choice of computational domain decomposition and computing machine of implementation. Developmental work consists of conceptualization and verification of the algorithm as well as parallel performance and scalability studies conducted on a variety of computing platforms. Using PANS-3EM, the aerodynamic characteristics of the missile are investigated. Drag and pitching moment …

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Wake Passage Effects On The Losses In A Linear Turbine Cascade, James A. Braunschneider Dec 1993

Wake Passage Effects On The Losses In A Linear Turbine Cascade, James A. Braunschneider

Theses and Dissertations

A linear turbine cascade was used to investigate the effects of wake passage due to stator-rotor interaction. The wakes were modeled by passing 1.98 mm (0.078 in) diameter bars upstream of a linear cascade blade row. Total pressure loss coefficients, mass averaged total pressure loss coefficients and velocities were used to characterize the effects of wake passage. Bar passing frequencies of 80, 160, 320 bars/sec were tested. These frequencies were tested, with the bars at 6.35 mm (0.25 in) intervals and at two Reynolds numbers, 341, 000 and 45,5000 Bar spacings of 12.7 mm (0.5 in), and 89 mm (3.5 …

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Off-Design Performance Of Crenulated Blades In A Linear Compressor Cascade, Michael J. Costello Dec 1993

Off-Design Performance Of Crenulated Blades In A Linear Compressor Cascade, Michael J. Costello

Theses and Dissertations

The effects of using compressor blades with a crenulated (notched) trailing edge in a low aspect ratio (AR= 1) linear compressor cascade at four incidence angles (-1.08°, +4.49°, +9.32° and +12.44°) were investigated. Blade performance and wake mixing characteristics for crenulated blades were compared with similar data for blades with a straight trailing edge. A seven-bladed cascade was operated with a flow Mach number of 0.4 and a blade chord Reynolds number of 4.1 (10)5. The diffusion factor ranged from 0.22 to 0. 42 and strong three-dimensional flow effects were present. Total pressure losses were measured with a …

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Development And Implementation Of A Scramjet Cycle Analysis Code With A Finite-Rate-Chemistry Combustion Model For Use On A Personal Computer, Clarence F. Chenault Dec 1993

Development And Implementation Of A Scramjet Cycle Analysis Code With A Finite-Rate-Chemistry Combustion Model For Use On A Personal Computer, Clarence F. Chenault

Theses and Dissertations

This study compared the performance of an equilibrium combustion model to a finite-rate-chemistry combustion model for a fixed geometry Scramjet flying at the flight conditions of Mach 12, 15, and 18 with a constant dynamic pressure of 50,000 Pa. An integrated PC-based code, developed specifically for this study, models the combustor as an equilibrium combustion process or as finite-rate-chemistry combustion process. This integrated program is based on two existing programs, Ramjet Performance Analysis (RJPA) and 3 STREAM. The effects of mixing schedule, combustor length, and combustor exit area were investigated. The results of this study indicate that inefficient mixing is …

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Analysis And Characteristics Of Compressor Stall Precursor Signals In Forward And Aft Swept High Speed Compressor, Bernard J. Frank Dec 1993

Analysis And Characteristics Of Compressor Stall Precursor Signals In Forward And Aft Swept High Speed Compressor, Bernard J. Frank

Theses and Dissertations

The stall characteristic of four single-stage transonic compressor rotors were investigated as they were throttled to stall. Forward-swept, backward-swept, and straight leading edge rotors were examined. Three methods of analysis (1) windowed power spectrum densities of pressure and spatial Fourier coefficients, (2) phase tracking analysis, and (3) system identification were used to identify the first appearance of modal waves and their accompanying frequencies in order to identify a stall warning time. A direct correlation between the amount of stall warning time and the shape of the compressor characteristic was found. Specifically, if the compressor characteristic had a significant period of …

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Exploring Qdes As A Tool For Determining Limits Of Achievable Performance In Aircraft Design, Mark F. Reidinger Dec 1993

Exploring Qdes As A Tool For Determining Limits Of Achievable Performance In Aircraft Design, Mark F. Reidinger

Theses and Dissertations

This thesis explores the usefulness of a computer aided control design software package called QDES in determining the limits of achievable aircraft performance as it relates to controller capability. Modern aircraft, particularly fighters, are being designed to be statically unstable to enhance their maneuverability and performance. It is possible that the aircraft, although physically capable of a certain level of performance due to its engine/ airframe combination, may be uncontrollable up to this level. This study sought to develop a methodology to use QDES to make a preliminary analysis of an aircraft design to determine if there exists a controller …

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Effects Of Crenulations On Three Dimensional Losses In A Linear Compressor Cascade, William L. Spacy Ii Dec 1993

Effects Of Crenulations On Three Dimensional Losses In A Linear Compressor Cascade, William L. Spacy Ii

Theses and Dissertations

An experimental investigation into the effect of compressor blade trailing edge geometry on three-dimensional flows in a linear cascade was conducted at the AFIT linear cascade test facility. Hot-wire/hot-film anemometry along with total pressure instrumentation was used to analyze crenulation generated vortices and their interaction with the three-dimensional flows in the cascade. The effects of this interaction on the performance parameters associated with the cascade were quantified. The results-indicate that wake mixing is better for crenulated trailing edges and that the precise geometry of the crenulations is critical to performance. One crenulation geometry was found to increase wake mixing while …

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Optimal Control Design Advantages Utilizing Two-Degree-Of-Freedom Controllers, Michael J. Stephens Dec 1993

Optimal Control Design Advantages Utilizing Two-Degree-Of-Freedom Controllers, Michael J. Stephens

Theses and Dissertations

The purpose of this study was to investigate and describe the differences between a one-degree-of-freedom (1-DOF) controller, in which a controller is placed in a single location in the control loop, and a two-degree- of-freedom (2-DOF) controller, in which two separate controllers are designed -- one in the feedback loop and the other as a prefilter in the forward loop. The approach involved summarizing the major rules governing loop shaping for performance and robustness in the 1-DOF case and then extending the concepts to the 2-DOF case. H2 optimization was utilized to perform several types of SISO examples and …

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A Numerical Determination Of Bifurcation Points For Low Reynolds Number Conical Flows, Larry K. Waters Dec 1993

A Numerical Determination Of Bifurcation Points For Low Reynolds Number Conical Flows, Larry K. Waters

Theses and Dissertations

It has long been established that supersonic flow over axisymmetric conical bodies at high angles of attack tend to develop a side force due to vortical asymmetry. One of the proposed reasons for the asymmetry is a bifurcation point in the solution of the Navier-Stokes equations. This study investigated the possible existence of a bifurcation point in the Navier-Stokes equations for subsonic flow. Newton's method, with gauss elimination, was used- to solve the steady-state, viscous, compressible Navier-Stokes equations in spherical coordinates assuming conical similarity.

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A Virtual Environment For Satellite Modeling And Orbital Analysis In A Distributed Interactive Simulation, Andrea A. Kunz Dec 1993

A Virtual Environment For Satellite Modeling And Orbital Analysis In A Distributed Interactive Simulation, Andrea A. Kunz

Theses and Dissertations

In response to the need for a more realistic, interactive, and immersive space simulation system, the Joint National Intelligence Defense Staff JNIDS has sponsored the development of the Satellite Modeler at the Air Force Institute of Technology AFIT. The Satellite Modeler SM is a virtual environment VE application that allows analyst-users to enter a virtual near- Earth space environment and visualize realistic satellite models performing accurate orbital motion. The Satellite Modeler provides manipulation functions that allow a user to interact with multiple satellite models and satellite constellations. The system affords the user multiple vantage points within the environment to view …

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Dynamic Response Of A Compressor Research Facility, Janet W. Grondin Dec 1993

Dynamic Response Of A Compressor Research Facility, Janet W. Grondin

Theses and Dissertations

The response of the Wright Laboratory Compressor Research Facility to a small amplitude, acoustic, sinusoidal disturbance was investigated. The fluid transmission line equations for laminar, one-dimensional flow in a circular duct were solved and verified through a laboratory experiment using a scale model of the facility. The resonant frequencies of the facility were determined for a variety of flow conditions. Techniques for analytically modeling end impedance and flow straightening elements were also studied. The fundamental frequency of the facility was determined to be between 5.5 and 6.5 Hz depending on the flow conditions and geometry configurations specified.

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Rendering Of Three-Dimensional Data Sets Derived From Finite-Difference And Spectral Methods, Paul A. Schubert Dec 1993

Rendering Of Three-Dimensional Data Sets Derived From Finite-Difference And Spectral Methods, Paul A. Schubert

Theses and Dissertations

The timely visualization of three-dimensional data sets and the advantages of using a spectral method solution versus a finite-difference method solution in rendering isosurfaces is described. The Beam-Warming numerical algorithm, which uses implicit-approximate-factorization, is used to generate the steady-state solutions for a model diffusion-convection problem. The Chebyshev collocation operator is used to evaluate the right-hand side of the Beam-Warming algorithm for the spectral solution. Comparing the model problem results with the exact solution, the spectral series solution is truncated to the same degree of accuracy as the finite-difference for comparison of rendering times. The rendering algorithm employs octrees to efficiently …

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Crew Scheduling Of Space Operations Squadrons (Sops), Marianne Idzi Nov 1993

Crew Scheduling Of Space Operations Squadrons (Sops), Marianne Idzi

Theses and Dissertations

The mission of Space Operations Squadrons is continuous support of military satellite systems. The scheduling problem associated with conducting continuous operations is threefold. The first problem is finding cyclical crew shift schedules that meet daily manning requirements, adhere to current regulations, contain a minimum number of workshift changes during consecutive duty days, and maximize the non-duty time allowed between duty shifts. The second problem is to establish a sea of criteria to evaluate alternative shift schedules. Finally, the third problem is to minimize the number of personnel required to meet the scheduling requirements stated in the first problem. This study …

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An Investigation Of Integrated Product Development Teams Of The F-22 Program, Gary F. Wagner, Randall L. White Sep 1993

An Investigation Of Integrated Product Development Teams Of The F-22 Program, Gary F. Wagner, Randall L. White

Theses and Dissertations

This study investigated Integrated Product Development (IPD) at the F-22 System Program Office (SPO). A literature review revealed the key IPD characteristics of organizational structure, communication, intense up-front planning, training, integrated management tools, and lessons learned. The research method was twenty-two personal interviews of SPO subjects selected from four IPD teams, the front office, and functional support divisions. Key findings included an emphasis on up-front planning to establish an organizational and contractual structure which empowered workers to develop their products. Also, constant communication with all other functions and teams was stressed while training was primarily done while transitioning to IPD. …

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Experimental And Analytical Analysis Of The Response Of A Smart Beam To Rate Feedback, Terance J. Hoffman Jun 1993

Experimental And Analytical Analysis Of The Response Of A Smart Beam To Rate Feedback, Terance J. Hoffman

Theses and Dissertations

A smart beam with embedded sensors and actuators was analyzed and tested. The smart beam studied was constructed from graphite and epoxy with piezoceramic actuators and NiTiNOL sensors embedded. It was mounted vertically and subjected to transverse dynamic loading at the free end. Analytic expressions for the open loop and closed loop response (using strain rate feedback control) of the beam (including internal damping) to external forcing were derived in detail. Experimental testing of the beam verified the accuracy of the predicted open loop response.

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A Comparison Of Computational And Experimental Data For A Subscale High Speed Propulsive Nozzle At Low Mach Numbers, Yonghee Hyun Jun 1993

A Comparison Of Computational And Experimental Data For A Subscale High Speed Propulsive Nozzle At Low Mach Numbers, Yonghee Hyun

Theses and Dissertations

This computational study of a hypersonic sub-scale nozzle/cowl configuration compares numerical solutions with experimental data for nozzle performance at off design conditions (subsonic through supersonic Mach numbers. A combination of Van Leer and Roe flux-splitting algorithms was used to solve the flow field. The explicit formulation assumed laminar planar flow and the perfect gas equation of state. A validation for the numerical algorithm was accomplished by comparing with experimental data for a variety of cases. Grid refinement, geometry, and operating conditions all influenced the comparison of the experimental and computational data. Generally, as the Mach number and nozzle pressure ratio …

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Development Of An Air-To-Air Refueling Automatic Flight Control System Using Quantitative Feedback Theory, Dennis W. Trosen Jun 1993

Development Of An Air-To-Air Refueling Automatic Flight Control System Using Quantitative Feedback Theory, Dennis W. Trosen

Theses and Dissertations

Quantitative Feedback Theory and the improved method Quantitative Feedback Theory are enhanced to include the rejection of disturbance at the system output. The enhanced Quantitative Feedback Theory and improved method Quantitative Feedback Theory processes are applied to the design of an automatic flight control system to regulate position of the C-135B fuel receiving aircraft relative to the tanker during air-to-air refueling. A simple feedback control system is developed that will achieve stable position regulation. State-space aircraft models &re generated. An inner loop autopilot is designed to reduce the plant cutoff frequency and provide the system inputs for the Quantitative Feedback …

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Hoph Bifurcation In Viscous, Low Speed Flows About An Airfoil With Structural Coupling, Mark J. Lutton Mar 1993

Hoph Bifurcation In Viscous, Low Speed Flows About An Airfoil With Structural Coupling, Mark J. Lutton

Theses and Dissertations

The locations of Hopf bifurcation points associated with the viscous, incompressible flow about a NACA 0012 airfoil with structural coupling are computed for very low Reynolds numbers (<2000). A semi-implicit, first-order-accurate time integration algorithm is employed to solve the stream function-vorticity form of the Navier-Stokes equations. The formulation models the inclusion of simple structural elements affixed to the airfoil and captures the resulting airfoil motion. The equations describing the airfoil motion are integrated in time using a fourth-order Runge-Kutta algorithm. The dissertation is divided into two parts. In part one, numerical experiments are performed in the laminar regime to determine if the structural model of the airfoil has an effect upon the location of the Hopf bifurcation point when compared with the fixed airfoil. Results are reported for a variety of structural characteristics, including variations of torsional and linear spring constants, inertial properties, structural coupling, and structural damping. The structure of the solution space is explored by means of phase plots. In part two, the Baldwin-Lomax turbulence model is implemented to model turbulent flow. A numerical effort is made to predict the onset of unsteady flow.

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Effect Of Transverse Vibration On The Capillary Limit Of A Wrapped Screen Wick Copper/Water Heat Pipe, Mark C. Charlton Dec 1992

Effect Of Transverse Vibration On The Capillary Limit Of A Wrapped Screen Wick Copper/Water Heat Pipe, Mark C. Charlton

Theses and Dissertations

The effect of transverse vibration on the capillary limit of a copper/water heat pipe with a tightly wrapped screen wick was investigated. The capillary limit was measured over a range of operating temperatures under static conditions. A bench-top shaker was used to provide vibration normal to the longitudinal axis of the pipe, and the capillary limit was measured at vibration frequencies of 30, 250, and 1000 Hz. At each of these frequencies, tests were run at vibration levels of 1.0, 2.5, and 5.0 G. The pipe was maintained at a zero degree inclination angle and power throughput was increased until …

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An Experimental Determination Of The Effects Of Blending Collocated And Non-Collocated Sensor Measurements To Control A Flexible Structure, Richard G. Cobb Dec 1992

An Experimental Determination Of The Effects Of Blending Collocated And Non-Collocated Sensor Measurements To Control A Flexible Structure, Richard G. Cobb

Theses and Dissertations

An experimental investigation was performed controlling a cantilevered beam in bending using proportional feedback on a blend of collocated and non-collocated sensor measurements using a single actuator. Exact transfer functions between the control input and the measurements were developed and compared to the finite element method. By analyzing the open loop pole-zero locations as a function of the measurement blending, insight into the closed loop behavior is obtained. Minimum phase behavior can be maintained for a range of the blending ratio. Results using blended control were compared to both proportional collocated feedback and compensated collocated feedback using LQG methods. The …

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Extended Lyapunov Exponents For Second Order Systems, Janice M. Horn Dec 1992

Extended Lyapunov Exponents For Second Order Systems, Janice M. Horn

Theses and Dissertations

It is shown that the concept of the Lyapunov exponent can be extended to include an imaginary part. A numerical technique used to calculate these extended Lyapunov exponents for second order systems is presented. There are two requirements to make this extension possible: the definition of a coordinate frame on the tangent space of the differential equation, and an extension of the classical limit, called the limit of the mean. An application of the technique to the van der Pol equation for the constant coefficient and periodic coefficient cases is given. The extended Lyapunov exponents found using this technique totally …

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An Approximate Solution For The Linearized Spinup Dynamics Of A Dual-Spin Spacecraft, David L. Kinney Dec 1992

An Approximate Solution For The Linearized Spinup Dynamics Of A Dual-Spin Spacecraft, David L. Kinney

Theses and Dissertations

An approximate solution is obtained for the linearized equations of motion for the spinup dynamics of a dual-spin spacecraft. The approximation is obtained from the WKB (Wentzel, Kramers, and Brillouin) method, which usually generates a divergent series. Comparison between the WKB solution and the numerically integrated solution are used to study the effects of spinup torque magnitude and the number of WKB terms used on the accuracy of the approximation. The WKB method generates accurate approximations for small spinup torques using as few as two terms in the series when no singularities are present in the WKB terms during the …

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An Electromagnetically-Controlled Precision Orbital Tracking Vehicle (Potv), Richard E. Lawrence Jr. Dec 1992

An Electromagnetically-Controlled Precision Orbital Tracking Vehicle (Potv), Richard E. Lawrence Jr.

Theses and Dissertations

A propulsion configuration it defined for a precision orbital tracking vehicle (POTV) that employs electrodynamic forces to control vehicle attitude and position with respect to another spacecraft. A pair of electrically powered thrusters assist the POTV in position control. The vehicle can maintain continuous standoff at close range from another spacecraft in any direction, has docking capability, and has gross orbital transfer capability. These capabilities and the specific design derived for the POTV have been defined by the requirements of a postulated space facility (ASSET) that salvages structural aluminum from the external fuel tank of the space shuttle. Precision control …

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Canonical Floquet Perturbation Theory, David J. Pohlen Dec 1992

Canonical Floquet Perturbation Theory, David J. Pohlen

Theses and Dissertations

Classical Floquet theory is examined in order to generate a canonical transformation to modal variables for periodic system This transformation is considered canonical if the periodic matrix of eigenvectors is symplectic at the initial time. Approaches for symplectic normalization of the eigenvectors had to be examined for each of the different Poincare eigenvalue cases. Particular attention was required in the degenerate case, which depended on the solution of a generalized eigenvector. Transformation techniques to ensure real modal variables and real periodic eigenvectors were also needed. Periodic trajectories in the restricted three-body case were then evaluated using the canonical Floquet solution. …

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Passive Damping Of A Solar Array, Mark A. Scharpen Dec 1992

Passive Damping Of A Solar Array, Mark A. Scharpen

Theses and Dissertations

This study was an attempt to conceptualize, design, build, and test a constrained layer damping device that uses mechanical advantage for the purpose of increasing the damping of transient vibration of a five-bay planar truss. The aluminum truss was clamped to a fixed support and simulated a solar array. A conventional constrained layer treatment was designed, built, and tested to serve as a benchmark for comparison. For the conventional treatment, Plunkett and Lee's segmented constraining layer technique was used. The improved device, two three-layer sandwich beams spanning the two bays nearest the built-in end, were supported several inches away from …

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Data Reduction With Least Squares Differential Correction Using Equinoctial Elements, Michael S. Wasson Dec 1992

Data Reduction With Least Squares Differential Correction Using Equinoctial Elements, Michael S. Wasson

Theses and Dissertations

This study investigates earth satellite orbit estimation on a track of range, azimuth, and elevation data from a single tracking station. The estimation routine is a least squares batch filter based solely on two-body orbital motion. Using equinoctial elements for the reference orbit avoids the numerical difficulties of the classical elements at eccentricities near zero and inclinations near zero or 90 degrees. Orbits for Mir, DMSP, Explorer, Cosmos, and GPS are investigated. The goal of this study is to reduce orbit information from observations (range, azimuth, and elevation) to an element set and a covariance matrix without considering perturbation effects. …

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Strategies For Optimal Control Design Of Normal Acceleration Command Following On The F-16, James C. Baird Dec 1992

Strategies For Optimal Control Design Of Normal Acceleration Command Following On The F-16, James C. Baird

Theses and Dissertations

Weight shapes and locations are investigated for H2, H∞, and the general mixed H2/H infinity optimization methodologies. The design model is normal acceleration command following for the F-16 (SISO) at Mach 0.6 and Sea Level, which yields a nonminimum phase and unstable plant. H2 design types include LQG, LQG/Sensitivity, and LQG/Tracking. Robustness and tracking are the objectives of the central H infinity process. Both H∞ optimal and suboptimal controllers are examined, with the suboptimal controller shown as the practical choice for this plant. The mixed H2/H∞ setup allows the tradeoff between …

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Nozzle/Cowl Optimization For A Hypersonic Vehicle On A Typical Trajectory, Michael J. Bonaparte Dec 1992

Nozzle/Cowl Optimization For A Hypersonic Vehicle On A Typical Trajectory, Michael J. Bonaparte

Theses and Dissertations

An investigation of the effects of simultaneous variation of the nozzle attachment and cowl deflection angle on the performance of a two- dimensional nozzle used on a hypersonic vehicle such as the National Aero-Space Plane (NASP) was performed using a two parameter optimization procedure. Total thrust optimization was accomplished using a Flux-Difference-Split (FDS) cods, a RAMJET Performance Analysis program, and an oblique shock wave solver program, at sixteen points on a 1000 psf dynamic pressure trajectory for Mach numbers from 10.0 to 25.0. A single parameter optimization of the total thrust using a variable nozzle attachment angle was accomplished first …

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Characterization Of Stall Inception In High-Speed Single-Stage Compressors, Keith M. Boyer Dec 1992

Characterization Of Stall Inception In High-Speed Single-Stage Compressors, Keith M. Boyer

Theses and Dissertations

Two single-stage, transonic compressor designs were tested under various undistorted operating conditions to characterize the process leading up to aerodynamic stall. The rig case was instrumented with eight high-response static pressure transducers equally spaced around the annulus for stall development detection. High-response measurements were low-pass filtered and both spatially and temporally analyzed using discrete Fourier techniques. At all speeds tested for both designs, stall inception was characterized by growth of a small amplitude' rotating wave. The waves did not grow significantly until just prior to the instability, when exponential growth into fully-developed rotating stall occurred very rapidly, within 6-10 rotor …

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