Open Access. Powered by Scholars. Published by Universities.®

Digital Commons Network™

Open Access. Powered by Scholars. Published by Universities.®

Theses and Dissertations

Discipline
Institution
Keyword
Publication Year
File Type

Articles 64621 - 64650 of 74096

Full-Text Articles in Entire DC Network

Congress And Early Federalist Military Policy: An Examination Of Defense Related Roll Calls In The Second United States Congress, 1792-1793, Elbert S. Barker Iii Dec 1992

Congress And Early Federalist Military Policy: An Examination Of Defense Related Roll Calls In The Second United States Congress, 1792-1793, Elbert S. Barker Iii

Theses and Dissertations

The legislators of the Second United States House of Representatives faced a set of challenging military and political problems when they met in November 1791. The issue of what would be the primary means of the young nation's defense had not yet been determined. The old British and colonial precedents of a militia as the first line of defense were firmly rooted in the minds of most congressmen meeting in Philadelphia. Many of the legislators had been indelibly imprinted with a fear of a large standing army in peacetime from their own personal experiences in the pre-Revolutionary days. Many of …

Go to article

Improvements To Lqgi/Ltr Methodology For Plants With Lightly Damped Or Low Frequency Poles, An-Chi Ju Dec 1992

Improvements To Lqgi/Ltr Methodology For Plants With Lightly Damped Or Low Frequency Poles, An-Chi Ju

Theses and Dissertations

LQG/LTR design has a tendency to invert the plant's dynamics, which is undesirable if there are plant poles near the imaginary axis. In this study, Static Output Feedback (SOF) is applied to reassign plant poles before LQG/LTR is applied. Alternatively, Robust Eigenstructure Assignment (REA) was used to design the target loop transfer function with an ideal eigenstructure to avoid the undesirable cancellations. Both methods were applied to several aircraft design problems. Results showed that the methods can be effectively used so that the LQG/LTR design has improved stability and performance; however, it was found that each method had strengths and …

Go to article

Solution To A Multicriteria Aircraft Routing Problem Utilizing Parallel Search Techniques, James J. Grimm Iii Dec 1992

Solution To A Multicriteria Aircraft Routing Problem Utilizing Parallel Search Techniques, James J. Grimm Iii

Theses and Dissertations

Pilots select routes based on factors such as threats, fuel, time on target, distance, and refueling points. This is a time consuming task. This thesis presents the software engineering synthesis of a software tool, based on a parallelized A* search algorithm, to select routes. For simplicity only threats and distance are used. A centralized open list is used with one processor managing the list while the other processors perform the node expansions. This decomposition result in a dynamically load balanced system. A number of parameters are changed to study their impact on the execution time. The use of a branch …

Go to article

Ada Implementation Of An Object Data Repository, Stephen P. Perucca Dec 1992

Ada Implementation Of An Object Data Repository, Stephen P. Perucca

Theses and Dissertations

The many benefits of object-oriented software development such as encapsulation and extendibility have inspired numerous models of the object- oriented paradigm. Rumbaugh's Object Modeling Technique (OMT) is an object- oriented model that uses three submodels. The object, dynamic, and functional submodels of the OMT describe the data, behavioral, and processing aspects of a system by using entity-relationship, state-transition, and data flow models. Cross-links relate how the three submodels tie together. Two metamodels (models of models) of the OMT are developed using the OMT methodology and notation. The essential data elements of the OMT are abstracted into a data metamodel, and …

Go to article

Entity-Relationship Versus Object-Oriented Modeling And The Underlying Dbms, Kevin J. Routhier Dec 1992

Entity-Relationship Versus Object-Oriented Modeling And The Underlying Dbms, Kevin J. Routhier

Theses and Dissertations

Despite the impressive accomplishments in relational database research, greater support is needed for persistence of the new types of data encountered with object-oriented programming. The concept of object-orientation is not new in the realm of programming; however, its utilization in database management systems is still immature. Regardless of this fact, there is an urgency for object-oriented database technology. With this increase in demand for the next generation databases comes the need to examine object-oriented data modeling versus the conventional entity-relationship modeling of relational database design. This thesis objective is to analyze both paradigms to determine if object-oriented modeling can significantly …

Go to article

An Interactive Life Cycle Cost Forecasting Tool, Nicolas M. Habash Dec 1992

An Interactive Life Cycle Cost Forecasting Tool, Nicolas M. Habash

Theses and Dissertations

This thesis is about computing life cycle cost and culminates with a life cycle cost forecasting tool (software). The software is written in FORTRAN 77 and uses IMSL subroutine extensively for random number generation from various distributions. The algorithm can compute life cycle cost for the following types of cost elements: constant, stochastic, and cost estimating relationships (CERs). The use of a trapezoid approximation of payment allocation is allowed. Percent allocation of payments is also allowed and is recommended where the trapezoid fails to correctly represent the payment schedule. The CER algorithm handles cost data that was estimated in base …

Go to article

Solving Nonlinear Composite Material Problems Using The Automated Structural Optimization System (Astros), Robert Bolha Dec 1992

Solving Nonlinear Composite Material Problems Using The Automated Structural Optimization System (Astros), Robert Bolha

Theses and Dissertations

Most advanced composite materials have nonlinear stress versus strain curves--grossly so in the laminas shear direction. If linear approximations are used, overly conservative design will result. This thesis expands the usefulness of the Automated Structural Optimization System (ASTROS) finite element (FE) program by incorporating a newly developed capability to include material nonlinearities. By dividing a FE problem into several intervals, and incorporating the changing nature of the nonlinear material properties within each element, a good approximation of the laminate's actual stresses and strains can be obtained without the undue experimentation involved in testing every individual configuration. Each material property is …

Go to article

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 …

Go to article

Rewet Performance Of A Rectangular Grooved Heat Pipe Wick After Gravitationally Induced Dryout, Lowell S. Hawthorne Dec 1992

Rewet Performance Of A Rectangular Grooved Heat Pipe Wick After Gravitationally Induced Dryout, Lowell S. Hawthorne

Theses and Dissertations

The effects of increased acceleration forces on the transient dryout and rewet performance of an axial groove heat pipe wick were experimentally studied using inclination to simulate increased acceleration forces. Two durations of increased acceleration were investigated, one being less than the time required for the groove to reach steady-state dryout conditions, the other being sufficient to ensure the groove had reached steady-state dryout conditions. The groove's extent of dryout was found to be greater at increased levels of acceleration. The period of time required for the groove to rewet after an acceleration induced dryout increased as acceleration increased. The …

Go to article

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 …

Go to article

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. …

Go to article

A Study Of Heat Flux Induced Dryout In Capillary Grooves, Timothy J. Murphy Dec 1992

A Study Of Heat Flux Induced Dryout In Capillary Grooves, Timothy J. Murphy

Theses and Dissertations

This is an experimental study of ethanol flowing in the narrow grooves of a copper plate which is subjected to heat fluxes sufficient to evaporate more liquid than can be replaced by capillary pumping. Three groove geometries are used: square, rectangle, and trapezoid. The objective is to simulate aspects of liquid flow in heat pipes with axial grooves. In order to validate analytical models of capillary flow in grooves, the capillary limit, dryout front location, and dryout front movement in response to power draw downs are documented. The results show the rewet performance of the groove is dependent on geometry. …

Go to article

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).

Go to article

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 …

Go to article

Power Analysis In Flexible Automation, Nathan A. Titus Dec 1992

Power Analysis In Flexible Automation, Nathan A. Titus

Theses and Dissertations

The performance of an automation or robotic device can be measured in terms of its power efficiency. Screw theory is used to mathematically define the task instantaneously with two screws. The task wrench defines the effect of the device on its environment, and the task twist describes the motion of the device. The tasks can be separated into three task types: kinetic, manipulative, and reactive. Efficiency metrics are developed for each task type. The output power is strictly a function of the task screws, while device input power is shown to be a function of the task, the device Jacobian, …

Go to article

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. …

Go to article

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 …

Go to article

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 …

Go to article

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 …

Go to article

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 …

Go to article

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 …

Go to article

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 …

Go to article

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 …

Go to article

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 …

Go to article

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 …

Go to article

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 …

Go to article

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 …

Go to article

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, …

Go to article

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 …

Go to article

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 …

Go to article

First Prev Next Last