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Articles 69391 - 69420 of 77631

Full-Text Articles in Engineering

Baseline Experiments On Coulomb Damping Due To Rotational Slip, John P. Santacroce Dec 1992

Baseline Experiments On Coulomb Damping Due To Rotational Slip, John P. Santacroce

Theses and Dissertations

Two experimental pin-type joint models are developed to study the effects of Coulomb Damping due to rotational slip. Model One is an inverted beam allowed to pivot at one end as a pendulum. Model Two is a horizontally mounted beam allowed to pivot about its center. The equations of motion for the joint geometries, considering only macro-slip friction, are developed and solved. Theoretical and experimental results for the response of the models in vibration are presented showing energy dissipation versus clamping force for the joint(s).

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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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Investigation Of Fatigue Behavior In Notched Cross-Ply Titanium Metal Matrix Composite At Elevated Temperature, Robert P. Baker Dec 1992

Investigation Of Fatigue Behavior In Notched Cross-Ply Titanium Metal Matrix Composite At Elevated Temperature, Robert P. Baker

Theses and Dissertations

The objective of this research was to investigate the initiation and progression of damage which develops in notched (0/90)2S SCS-6/Ti-15-3 at elevated temperature. Testing consisted of a monotonic tensile test at 427°C followed by fatigue testing performed under load control with a stress ratio of 0.1 at a frequency of 10 Hz. A crack was defined to have initiated when it had attained a length greater than or equal to 0.124 mm. Crack initiation and progression was monitored by strain and modulus observations and visual inspection via telemicroscope. The cracks were recorded with edge and face replicas. Metallographic and …

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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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Stratified Plate Model For Composite Plate Analysis, Richard A. Coveno Dec 1992

Stratified Plate Model For Composite Plate Analysis, Richard A. Coveno

Theses and Dissertations

This study continues the investigation of the stratified plate model for the analysis of composites plates. The strata theory models a composite plate as a stack of isotropic matrix and orthotropic, fiber dominated layers. Energy methods are used to derive a set of partial differential equations and boundary conditions as a function of the displacement. An assumed displacement field, of a polynomial in z and a Sine/Cosine function in x and y, generates a solution to a simply supported composite plate with cross plies. A cylindrical bending example is also solved with a polynomial in z and Sine/Cosine function in …

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The Non-Linear Dynamics Of Composite Cylindrical Shells, James M. Greer Jr. Dec 1992

The Non-Linear Dynamics Of Composite Cylindrical Shells, James M. Greer Jr.

Theses and Dissertations

The non-linear dynamic behavior of suddenly loaded composite shells is the subject of this research. The objective of research is two-fold: (1) to characterize the apparently random physical behavior sometimes observed in the finite element analysis as either numerical instability, chaotic behavior, or both; and (2) to develop criteria for choosing time steps for the finite element model, referred to as DSHELL. This displacement based finite element code is capable of dynamic analysis of plates, arches, and cylindrical shells undergoing large displacements and moderately large rotations during deformation. DSHELL uses a 36-DOF isoparametric shell element to obtain numerical results. A …

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Effect Of Thickness And Ply Layup On The Collapse Characteristics Of Cylindrical Composite Shells With Large Cutouts, James C. Hatfield Dec 1992

Effect Of Thickness And Ply Layup On The Collapse Characteristics Of Cylindrical Composite Shells With Large Cutouts, James C. Hatfield

Theses and Dissertations

This study involved a numerical and experimental investigation of the geometric instability(collapse loads/displacements) of vertically unsupported graphite/epoxy cylindrical shell panels undergoing axial compression. Symmetric quasi-isotropic and cross-ply laminates, with and without 4 X4 centralized cutouts, were investigated for three thicknesses:8,16,and 24 plies. The experimental data was compared to results from SHELL, a geometrically nonlinear finite-element computer program which incorporates a parabolic transverse shear strain distribution through the thickness. Good correlation was obtained for shells with large cutouts between the SHELL numerical data and the experimental results. This research verified that the SHELL program will provide good predictions of the collapse …

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Experimental Investigation Of The Aerodynamics Of Independently Rotating Cylindrical Shells, Walter C. Howerton Dec 1992

Experimental Investigation Of The Aerodynamics Of Independently Rotating Cylindrical Shells, Walter C. Howerton

Theses and Dissertations

The purpose of this thesis was to investigate experimentally the aerodynamic forces on two adjacent, independently rotating cylinders in a cross- flow. This investigation involved a force measurement setup which had the two cylinders mounted on a common support shaft, extending beyond the span of the wind tunnel test section, and supported by spoke rings with strain gages in the vertical and horizontal directions. This setup proved capable of measuring aerodynamic forces. The lift on the independently rotating cylinders was found to increase as one cylinder's angular speed increased while the other's remained constant, and decrease as the relative angular …

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Optimal Control Of The Starfire Beam Director, Troy V. Lanier Dec 1992

Optimal Control Of The Starfire Beam Director, Troy V. Lanier

Theses and Dissertations

The Starfire Beam Director (SBD) is located at the Starfire Optical Range at Kirtland Air Force Base in Albuquerque, New Mexico. The SBD capabilities include tracking celestial objects and active or passive tracking of artificial satellites to support the Phillips Laboratory Ground Based Laser Acquisition, Tracking, and Pointing (GBL ATP) program. The pointing and tracking accuracy needed to support such experiments is micron rad to sub-grad level. To accomplish this goal requires precise pointing of the massive 6 ton 1 -meter clear aperture coelostat. The purpose of this thesis is to use optimal control design techniques to develop a controller …

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Vibration Suppression In Large Flexible Space Structures Using Active Control Techniques, Chad T. Matheson Dec 1992

Vibration Suppression In Large Flexible Space Structures Using Active Control Techniques, Chad T. Matheson

Theses and Dissertations

This report investigates the use of active vibration control techniques applied to the PACOSS Dynamic Test Article as an experimental structure. In the course of the research, a mathematical model of the lightly damped experimental structure was created based on experimental data. This model was used in the design of two classes of controllers. The first class is pure rate feedback of the structure's measured states such that global stability is insured. The second type of controller investigated was an optimal controller (LQG) that was created using the truncated mathematical model. The rate feedback controller showed significant improvements in the …

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The Influence Of Structural Optimization On The Aeroelastic Properties Of A Vertical Tail, David G. Miller Dec 1992

The Influence Of Structural Optimization On The Aeroelastic Properties Of A Vertical Tail, David G. Miller

Theses and Dissertations

The purpose of this thesis is to investigate the influence of structural optimization parameters on the structural and aeroelastic behavior of a vertical tail. The outside geometry of the tail is assumed fixed. The objective of the optimization is to reduce the structural member sizes so that the overall weight of the tail is minimized. The influence that design loads, design constraints, design variable linking has on the optimal design is observed examining several design cases. The static aeroelastic properties a flutter speeds of the various design cases are then compared. The doublet lattice method is used to calculate the …

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The Effects Of Viscosity On A Conically Derived Waverider, James A. Mundy Dec 1992

The Effects Of Viscosity On A Conically Derived Waverider, James A. Mundy

Theses and Dissertations

This study investigated the effects of the interaction between the viscous boundary layer and the shock wave produced by a Mach 10 inviscid optimized waverider. An implicit, Roe flux-splitting algorithm, developed by WL/FIMM, was used to solve the flow field. A validation for the inviscid version of the CFD algorithm was accomplished by comparing the numerical -data produced by the CFD code to the analytic results derived by Rasmussen, and by comparison to results of the explicit version of the same Roe flux-splitting code. The computational results compared favorably. The inviscid case studied using the implicit code produced results identical, …

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A Wind Tunnel Study Of Magnus Effects On A Differentially Rotating Missile, Karen A. Naselius Dec 1992

A Wind Tunnel Study Of Magnus Effects On A Differentially Rotating Missile, Karen A. Naselius

Theses and Dissertations

This study investigates magnus effects on a non-firmed missile model which had three axially rotating sections that span at different rates. Five spin cases are examined; the mid section spinning only; the front and rear sections spinning only; all section spinning at the same speed; all sections spinning in the same direction with the mid section spinning at an additional ten revolutions per second; and all sections spinning with the mid sections spinning the opposite direction at an additional ten revolutions per second. These five cases are tested at three different spin rates for two different wind tunnel velocities. Since …

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Fatigue Behavior Of A Cross-Ply Ceramic Matrix Composite Under Tension-Tension And Tension-Compression Loading, Frank A. Opalski Dec 1992

Fatigue Behavior Of A Cross-Ply Ceramic Matrix Composite Under Tension-Tension And Tension-Compression Loading, Frank A. Opalski

Theses and Dissertations

A study was conducted which investigated the behavior of a cross-ply [0/90]2S Nicalon/Calcium-Aluminosilicate (Nicalon/CAS) ceramic matrix composite at room temperature under tension-compression fatigue loading. Material behavior and damage was recorded by stress-strain curves, elastic modulus, hysteretic energy density, and acetate replication techniques. Tension-tension fatigue tests at a load ratio R of 0.1 (R = σmin/σmax) were completed which determined that 140 MPa was the maximum stress allowable in which cycle runout (1,000,000 cycles) would occur. Above this value, transverse crack density increased with respect to cycles and failure ultimately occurred. Tension-compression tests were then performed …

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Open And Filled Hole Static Tensile Strength Characterization Of Metal Matrix Composite Scs-9/Β21s, Jacob T. Roush Dec 1992

Open And Filled Hole Static Tensile Strength Characterization Of Metal Matrix Composite Scs-9/Β21s, Jacob T. Roush

Theses and Dissertations

SCS-9/β21s has a reduced gauge thickness, in comparison with other metal matrix composites, due to a smaller diameter fiber. This reduced gauge thickness makes it an attractive candidate for the skin of hypersonic vehicles. Tensile testing of (0/90)2s and (O/±45/90)s laminates was performed at room temperature, 482°C, and 650°C. Both notched and unnotched specimens were tested. Notched specimens, open and filled hole, had a width-to-diameter ratio of six. Materials 7075-T6 and Mar-m-246 were used as pins in the filled hole tensile testing. Analytical work was completed to predict material properties, elastic and plastic stress concentration factors, residual stresses, …

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Application Of The Program Profile For The Design Of Low-Speed, Low- Observable Configuration Airfoils, Gregory A. Sharp Dec 1992

Application Of The Program Profile For The Design Of Low-Speed, Low- Observable Configuration Airfoils, Gregory A. Sharp

Theses and Dissertations

This study investigated-the use of the program PROFILE for the design of low-speed, low-observable configuration airfoils. For our purposes, low- observable configuration is defined as being characterized by a small leading- edge radius of less than 1.18 percent chord and a thickness-to-chord ratio of 2. 5 to 5.5 percent. A methodology was developed whereby the input parameters to prescribe the velocity distribution over the airfoil could be determined by a power law relationship. This relationship enables the designer to develop symmetric airfoils with the desired thickness-to-chord and leading-edge radius within the stated constraints. The resulting symmetric airfoils compared very well …

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Helicopter Flight Control System Design Using The Linear Quadratic Regulator For Robust Eigenstructure Assignment, Dempsey D. Solomon Dec 1992

Helicopter Flight Control System Design Using The Linear Quadratic Regulator For Robust Eigenstructure Assignment, Dempsey D. Solomon

Theses and Dissertations

This thesis applied modern, multi-variable control design techniques, via a FORTRAN computer algorithm, to U.S. Army helicopter models in hovering flight conditions. Eigenstructure assignment and Linear Quadratic Regulator (LQR) theory are used to achieve enhanced closed loop performance and stability characteristics with full state feedback. The addition of cross coupling weights to the standard LQR performance index is specifically addressed. A desired eigenstructure is chosen with a goal of reduced pilot workload via performance qualities requirements. Cross coupling weighting is shown to provide greater flexibility in achieving a desired closed loop eigenstructure. While the addition of cross coupling weighting is …

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Computational And Experimental Investigation Into Fracture Of Brittle Fiber - Brittle Matrix Composite Systems, James P. Solti Dec 1992

Computational And Experimental Investigation Into Fracture Of Brittle Fiber - Brittle Matrix Composite Systems, James P. Solti

Theses and Dissertations

Experimental and computational analyses provided an improved understanding of quasi-static fracture in model composite systems. Constant displacement compression tests using borosilicate glass double cleavage drilled compression test templates provided qualitative assessments of localized toughening for crack growth near cylindrical inclusions. Large crack-tip stress fields induced interfacial slip and separation prior to arrival of the main crack. Debonding and the proliferation of secondary matrix cracks characterized the role of bridging fibers along weak interfaces. Strong residual normal compressive interfacial stresses diminished the influence of crack-tip stresses; however, slip was still observed. VHS tape and computer enhanced photos record a history of …

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An Experimental Investigation Of A Finite Circulation Control Wing, John M. Tallarovic Dec 1992

An Experimental Investigation Of A Finite Circulation Control Wing, John M. Tallarovic

Theses and Dissertations

This wind tunnel investigation examined the lift, drag, and pitching moment of a 20% thick, 8.5% camber, partial elliptical cross-section, single blowing slot, rectangular, circulation control wing. The aspect ratios tested were 3.71 and 3.99. Variables included three differently shaped trailing edge Coanda surfaces and steady blowing and pulsed blowing. The test Reynolds number, based on the chord was 500,000. The-angle of attack was varied from minus 6 degrees to the inception of stall. The maximum lift coefficient measured was 3. 17 with an equivalent drag coefficient of 1.85. Results also show a limit to increasing lift by increasing the …

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Behavior Of A Centrally Notched Cross-Ply And Unidirectional Ceramic Matrix Composite In Tension-Compression Fatigue, William A. Weidenaar Dec 1992

Behavior Of A Centrally Notched Cross-Ply And Unidirectional Ceramic Matrix Composite In Tension-Compression Fatigue, William A. Weidenaar

Theses and Dissertations

Centrally notched (hole), cross-ply, ((0/90)2)s, and unidirectional, (0)8 laminates of Silicon Carbide fiber-reinforced Aluminosilicate glass, SiC/1723, were fatigue tested under tension-compression loading with a load ratio of -1. Damage accumulated continuously for both lay- ups, leading to eventual failure and a reduced fatigue life. Critical damage in the cross-ply consisted of longitudinal cracks in the 90° plies growing and combining with transverse cracks to effectively eliminate the 90° plies' load carrying capability and allowing the specimen to buckle. Critical damage in the unidirectional lay-up consisted of longitudinal cracks which initiated at the shear stress concentration …

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Object-Oriented Analysis, Design, And Implementation Of The Saber Wargame, David S. Douglass Dec 1992

Object-Oriented Analysis, Design, And Implementation Of The Saber Wargame, David S. Douglass

Theses and Dissertations

Saber is a two-sided, air and land war game that simulates decisions made of commanders at the theater-level. It is being developed by the Air Force Institute of Technology for the Air Force Wargaming center at Maxwell AFB, Alabama. Saber models conventional, chemical, and nuclear warfare between aggregated air and land forces. It also portrays the effects of logistics, satellites, weather, terrain, and intelligence which add to the realism of the Saber war game. The Saber war game has three main components, the preprocessor. which is responsible for scenario development and pregame activities, the simulation. the guts of the war …

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A Vhdl Interpreter For Model-Based Diagnoses, David R. Griffin Dec 1992

A Vhdl Interpreter For Model-Based Diagnoses, David R. Griffin

Theses and Dissertations

Model-based reasoning permits diagnostic applications to be written without waiting for someone to become an 'expert' of the system. For model-based diagnostics, there must be a model to reason from. This thesis explores using a VHDL description of the system as that model. A system based around a VHDL interpreter was written specifically for a model-based diagnostic algorithm. Currently, the diagnostic system uses an algorithm by Dries. This algorithm was derived from Scarl's Full Consistency Algorithm. The system was designed to be modular so that different diagnostic techniques could be implemented. It is divided into three parts: a VHDL parser, …

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Design And Development Of A High-Speed Winograd Fast Fourier Transform Processor Board, James F. Herron Dec 1992

Design And Development Of A High-Speed Winograd Fast Fourier Transform Processor Board, James F. Herron

Theses and Dissertations

Since 1985, the Air Force Institute of Technology has pursued a project to develop a 4080-point Discrete Fourier Transform processor using the Winograd Fourier Transform Algorithm (WFTA) and Good-Thomas Prime Factoring Algorithm (PFA). In the first attempt to build a working system, this research effort designed and constructed, in part, a modified single processor architecture in order to demonstrate the proof of concept of the WFTA system design. This prototype architecture is simpler in implementation but uses the same principles and procedures as those of the 4080-point WFTA design. The design developed in this thesis was validated using the Very …

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Generalization And Parallelization Of Messy Genetic Algorithms And Communication In Parallel Genetic Algorithms, Laurence D. Merkle Dec 1992

Generalization And Parallelization Of Messy Genetic Algorithms And Communication In Parallel Genetic Algorithms, Laurence D. Merkle

Theses and Dissertations

Genetic algorithms (GA) are highly parallelizable, robust semi- optimization algorithms of polynomial complexity. The most commonly implemented GAs are 'simple' GAs (SGAs). Reproduction, crossover, and mutation operate on solution populations. Deceptive and GA-hard problems are provably difficult for simple GAs. Messy GAs (MGA) are designed to overcome these limitations. The MGA is generalized to solve permutation type optimization problems. Its performance is compared to another MGA's, an SGA's, and a permutation SGA's. Against a fully deceptive problem the generalized MGA (GMGA) consistently performs better than the simple GA. Against an NP-complete permutation problem, the GMGA performs better than the other …

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An Intelligent Real-Time System Architecture Implemented In Ada, Michael A. Whelan Dec 1992

An Intelligent Real-Time System Architecture Implemented In Ada, Michael A. Whelan

Theses and Dissertations

Conventional real-time systems are fully deterministic allowing for off-line, optimal, task scheduling under all circumstances. Real-time intelligent systems add non-deterministic task execution times and non- deterministic task sets for scheduling purposes. Non-deterministic task sets force intelligent real-time systems to trade-off execution time with solution quality during run-time and perform dynamic task scheduling. Four basic design considerations addressing those tradeoffs have been identified: control reasoning, focus of attention, parallelism, and algorithm efficacy. Non-real- time intelligent systems contain an environment sensor, a model of the environment, a reasoning process, and a large collection of procedural processes. Real-time intelligent systems add to these …

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Creating And Manipulating Formalized Software Architectures To Support A Domain-Oriented Application Composition System, Cynthia G. Anderson Dec 1992

Creating And Manipulating Formalized Software Architectures To Support A Domain-Oriented Application Composition System, Cynthia G. Anderson

Theses and Dissertations

This research investigated technology which enables sophisticated users to specify, generate, and maintain application software in domain-oriented terms. To realize this new technology, a development environment, called Architect, was designed and implemented. Using canonical formal specifications of domain objects, Architect rapidly composes these specifications into a software application and executes a prototype of that application as a means to demonstrate its correctness before any programming language specific code is generated. Architect depends upon the existence of a formal object base (or domain model) which was investigated by another student in related research. The research described in this thesis relied on …

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Parallel Simulation Of Structural Vhdl Circuits On Intel Hypercubes, Thomas A. Breeden Dec 1992

Parallel Simulation Of Structural Vhdl Circuits On Intel Hypercubes, Thomas A. Breeden

Theses and Dissertations

Many VLSI circuit designs are too large to be simulated with VHDL in a reasonable amount of time. One approach to reducing the simulation time is to distribute the simulation over several processors. This research creates an environment for designing and simulating structural VHDL circuits on the Intel iPSC/2 and iPSC/860 Hypercubes. Logic gates and system behaviors are partitioned among the processors, and signed changes are shared via event messages. Circuit simulations are run over the SPECTRUM parallel simulation testbed, and the null- message paradigm is used to avoid deadlock. Structural circuits ranging from forty to over one thousand logic …

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