Digital Commons Network^™

Use Of The Genetic Algorithm In Positioning Sacrificial Anodes For Optimum Cathodic Protection, Chi-Cheng Tsao

Mechanical & Aerospace Engineering Theses & Dissertations

A systematic design methodology is developed in this thesis to automatically determine the best locations to place the anodes in order to obtain the maximum cathodic protection. The design methodology numerically solves a design optimization problem which selects the locations to place the anodes to maximize the difference between the minimum current density supplied by sacrificial anodes on the surface of the cathodic materials and its free corrosion current density. The numerical tools used in this design methodology are the finite element analysis and the genetic algorithm. The former analyzes the current density distribution in the field of concern and …

Development Of Vibration And Sensitivity Analysis Capability Using The Theory Of Structural Variations, Ting-Yu Rong

Mechanical & Aerospace Engineering Theses & Dissertations

In the author's previous work entitled "General Theorems of Topological Variations of Elastic Structures and the Method of Topological Variation," 1985, some interesting properties of skeletal structures have been discovered. These properties have been described as five theorems and synthesized as a theory, called the theory of structural variations (TSV). Based upon this theory, an innovative analysis tool, called the structural variation method (SVM), has been derived for static analysis of skeletal structures (one-dimensional finite element systems).

The objective of this dissertation research is to extend TSV and SVM from one-dimensional finite element systems to multi-dimensional ones and from statics …

An Experimental And Analytical Investigation Of The Iosipescu Shear Test For Composite Materials, Barry Stuart Spigel

Mechanical & Aerospace Engineering Theses & Dissertations

Mechanical properties of composite materials under shear loading are difficult to determine. The Iosipescu Shear test, originally proposed for metals, has in recent years been applied to composites. It has the advantages of small specimen size, simple loading and a reasonably uniform shear stress in the test section.

The purpose of this work is to study the validity of the Iosipescu test method for measuring the shear modulus and shear strength of composites. Finite element analyses indicate that optimum specimen geometry and load locations depend upon the degree of orthotropy of the composite. Test results for a quasi-isotropic graphite/epoxy laminate …

Numerical Solution Of Nonequilibrium Compressible Nozzle Turbulent Boundary Layers Using Laws Of The Wall And Wake, Ajit A. Prabhu

Mechanical & Aerospace Engineering Theses & Dissertations

Accurate prediction of the development of the boundary-layer thickness is essential in designing hypersonic wind tunnel nozzles using computational fluid dynamics (CFD). The nozzle boundary-layer thickness becomes extremely thin at the throat region. Immediately downstream of the throat, as the flow begins to expand, the boundary-layer thickness grows rapidly. Estimates of grid requirements for resolving the turbulent boundary layer in the throat region using a Navier-Stokes solver have shown that the number of grid points is typically an order of magnitude greater than what is needed to resolve the nozzle exit region. Approximately 80% of the total time taken to …

The Development Of A Method To Extract High Purity Oxygen From The Martian Atmosphere, Dongchuan Wu

Mechanical & Aerospace Engineering Theses & Dissertations

A glow-discharge in an ambient Mars atmosphere (total pressure of 5 torr, composed of 95% carbon dioxide) results in the dissociation of carbon dioxide molecules into carbon monoxide and oxygen. If the glow-discharge zone is maintained adjacent and close to a silver membrane, operated at temperatures above 400°C, atomic and molecular oxygen, produced by the glow-discharge, can be separated from the other species by atomic diffusion through the membrane to an ultrahigh vacuum region where the desorbed O₂ is then collected. Experiments have been conducted to study the behavior of the glow discharge in both molecular oxygen and carbon …

Investigation Of Wall Injectors For Supersonic Mixing Enhancement, Yaacov Haimovitch

Mechanical & Aerospace Engineering Theses & Dissertations

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

Stress Fields In Composites With A Variable Interphase Under Thermo-Mechanical Loadings, Nianfeng Chen

Mechanical & Aerospace Engineering Theses & Dissertations

An interphase in a composite material has a important role for the composite performance. It influences directly or indirectly the strength, fatigue performance and effective properties of the composite. Recently, interphase has drawn increasing attention in composite mechanics. To the best of our knowledge, however, no one seems to have considered the effect of the variable material prope1ty in the interphase on the stress field in the composite material. In this research, the stress fields are determined in the continuous fiber composite and the particulate composite by using the four concentric circular cylinders model and the four phase spheres model, …

Transient Simulations And Modelling Of Semi-Insulating Gaas Photoconductive Switches, Prasun Kumar Raha

Electrical & Computer Engineering Theses & Dissertations

The primary objective of this thesis is to develop a one-dimensional transient simulator for Photoconductive Semiconductor Switches (PCSS) taking into consideration the material characteristics, the internal physical effects, and the external circuit. Simulations have been performed to study the device behavior at different voltage levels for copper-doped silicon-compensated GaAs material, though other materials could easily be simulated by changing the parameters. The model includes hole transport, and the results demonstrate the effect of hole injection, with and without recombination centers. In addition to developing a one-dimensional transient simulator, the role of various physical effects, such as the field-dependence of trapping …

An Assessment Of Four-Hour Sample Durations Used To Determine Full-Shift Noise Exposures In A Foundry, Vince Marlo Fleming

Community & Environmental Health Theses & Dissertations

Full-shift sampling, usually eight hours, is traditionally performed to assess daily occupational noise exposure. This sampling approach is inefficient, and costly for repeated, long-term exposure evaluations. This study assessed the use of four-hour sample durations and subsequent data analysis to determine daily occupational noise exposures in a foundry. The four-hour sample durations were extracted from full-shift samples and analyzed on their ability to provide valid data for estimating mean daily noise exposure levels without significantly affecting sampling precision or accuracy. Results of this study indicate four-hour sample durations can be used successfully to estimate full-shift noise exposures provided certain criteria …

The Identification And Magnitude Estimation Of Occupational Stressors In The Industrial Hygiene Profession, Judith Hinch

Community & Environmental Health Theses & Dissertations

The industrial hygiene professional is responsible for the evaluation and control of hazards in the workplace. Job stress has been identified as a factor affecting the health, safety and productivity of workers and can be considered a workplace hazard.

This study involved the development of an instrument to identify and quantify sources of stress within a give profession. The industrial hygiene profession was chosen, though the method can be, and has been, used to evaluate stress in other groups of individuals. The method involved the identification of the most significant sources of stress by surveying a small number of the …

Analysis Of Random Structure-Acoustic Interaction Problems Using Coupled Boundary Element And Finite Element Methods, Carl S. Pates Iii

Mechanical & Aerospace Engineering Theses & Dissertations

A coupled boundary element(BEM)-finite element(FEM) approach is presented to accurately model structure-acoustic interaction systems. The boundary element method is first applied to interior, two and three-dimensional acoustic domains with complex geometry configurations. Boundary element results are very accurate when compared with limited exact solutions.

Structure-interaction problems are then analyzed with the coupled FEM-BEM method, where the finite element method models the structure and the boundary element method models the interior acoustic domain. The coupled analysis is compared with exact and experimental results for a simplistic model. Composite panels are analyzed and compared with isotropic results. The coupled method is then …

Flow Simulations About Steady-Complex And Unsteady Moving Configurations Using Structured-Overlapped And Unstructured Grids, James Charles Newman Iii

Mechanical & Aerospace Engineering Theses & Dissertations

The limiting factor in simulating flows past realistic configurations of interest has been the discretization of the physical domain on which the governing equations of fluid flow may be solved. In an attempt to circumvent this problem, many Computational Fluid Dynamic (CFD) methodologies that are based on different grid generation and domain decomposition techniques have been developed. However, due to the costs involved and expertise required, very few comparative studies between these methods have been performed. In the present work, the two CFD methodologies which show the most promise for treating complex three-dimensional configurations as well as unsteady moving boundary …

Diamond Thin Film Sensors For Hypersonic Flow Studies, Bhaskar Kumar Bulusu

Electrical & Computer Engineering Theses & Dissertations

Conventional metal film sensors can measure flow instabilities of the order of 60 kHz. The turbulence fluctuations in the hypersonic regime are of the order of 200- 400 kHz. To measure these fluctuations, sensors with an enhanced frequency response are required. Therefore, it is required to identify the parameters to enhance the frequency response. These include parameters such as the temperature sensitivity, the resistivity, the thermal conductivity, the diffusivity, specific heat capacity and the geometric size and shape of the film and the substrate. A selection of materials was then carried out to maximize the frequency response. Diamond was identified …

Implementation Of A Multiblock Sensitivity Analysis Method In Numerical Aerodynamic Shape Optimization, James Matthew Lacasse

Mechanical & Aerospace Engineering Theses & Dissertations

A multiblock sensitivity analysis method is applied in a numerical aerodynamic shape optimization technique. The Sensitivity Analysis Domain Decomposition (SADD) scheme which is implemented in this study was developed to reduce the computer memory requirements resulting from the aerodynamic sensitivity analysis equations, Discrete sensitivity analysis offers the ability to compute quasi-analytical derivatives in a more efficient manner than traditional finite-difference methods, which tend to be computationally expensive and prone to inaccuracies.

The direct optimization procedure couples CFD analysis based on the two-dimensional thin-layer Navier-Stokes equations with a gradient-based numerical optimization technique. The linking mechanism is the sensitivity equation derived from …

Transverse Stress Effects For Laminated Composite Beams In Bending, Christine Chatterton Schleicher

Mechanical & Aerospace Engineering Theses & Dissertations

A higher-order theory and an associated finite element formulation are developed for analysis of laminated planar beams in bending. The higher-order theory incorporates both transverse normal stress and transverse shear stress, and is developed using two approaches. The first approach is based on assuming the transverse normal strain distribution to be a cubic function through the beam thickness, while the second approach is based on assuming the transverse normal stress distribution to be a cubic function through the beam thickness. In both approaches, the transverse shear strain distribution is assumed to be a quadratic function through the beam thickness. Theoretical …

Circulation, Spring 1994, Center For Coastal Physical Oceanography, Old Dominion University

CCPO Circulation

Spring 1994 issue of CCPO Circulation featuring article "The MPC Project"

The Application Of Formal Principles Of Public Administration As Perceived By City Managers, Shelton P. Rhodes

Theses and Dissertations in Urban Services - Urban Management

The present study seeks to determine the extent to which formalist ideas in public administration are evident in the practice of managerial performance as perceived by city managers and assistant city managers in the three states of Arizona, Colorado, and Virginia. While numerous studies demonstrate how administrative practices vary in different socio-political environments, the International City Management Association contends that certain basic features of public management nevertheless should be widely applied in different settings.

The questions that are being posed in this study are: What are the perceived norms or standards that structure managerial performance of city managers and do …

A Direct Numerical Simulation Of Vortex Breakdown Induced Tail Buffet, Steven James Massey

Mechanical & Aerospace Engineering Theses & Dissertations

A simulation of tail buffet is presented for a delta wing-vertical tail configuration. Flow conditions are chosen such that the wing primary-vortex cores experience vortex breakdown and the resulting turbulent wake flow impinges on the vertical tail. The dimensions and material properties of the vertical tail are chosen such that the deflections are large enough to insure interaction with the flow, and the natural frequencies are high enough to facilitate a practical computational solution. This multidisciplinary problem is solved sequentially for the fiuid flow, the elastic deformations and the grid displacements. The fluid flow is simulated by time accurately solving …

Explicit And Iterative Lqg Controller Design, Min-Hung Hsiao

Mechanical & Aerospace Engineering Theses & Dissertations

This dissertation presents two new LQG controller designs, namely, explicit and iterative designs. For the explicit design, the explicit solutions to the corresponding Riccati equations of controller design for large structures with collocated rate sensors and actuators are derived. Numerically solving the Riccati equations for state feedback and state estimation is no longer required. Since the number of design parameters for either state feedback or state estimation equals the number of controlled modes, the performance of each mode can be easily adjusted. NASA's Spacecraft COntrol Laboratory Experiment (SCOLE) configuration is used to demonstrate the effectiveness of the explicit design.

For …

Unsteady Flow Simulations About Moving Boundary Configurations Using Dynamic Domain Decomposition Techniques, Guan-Wei Yen

Mechanical & Aerospace Engineering Theses & Dissertations

A computational method is developed to solve the coupled governing equations of an unsteady flowfield and those of rigid-body dynamics in six degrees-of-freedom (6-DOF). This method is capable of simulating the unsteady flowfields around multiple component configurations with at least one of the components in relative motion with respect to the others. Two of the important phenomena that such analyses can help us to understand are the unsteady aerodynamic interference and the boundary-induced component of such a flowfield. By hybridizing two dynamic domain decomposition techniques, the grid generation task is simplified, the computer memory requirement is reduced, and the governing …

Dynamic Task Scheduling For The Atamm Multicomputer Operating System Using Embedded Firmware On Microcontrollers, Sudhir Sastry

Electrical & Computer Engineering Theses & Dissertations

A dynamic task scheduling strategy for the distributed processing of large grain dataflow algorithms using embedded firmware on an ATAMM testbed consisting of interconnected microcontrollers is presented in this thesis. The ODU/NASA developed Algorithm to Architecture Mapping Model, ATAMM, uses marked graph models to specify data and control flow for the execution of iterative, deterministic large grain dataflow algorithms in a multicomputing environment. The testbed consists of a bank of four 68HC11 microcontrollers that communicate over a token bus. The token bus arbitration scheme used is contention free and well suited for real-time computing applications. The execution of data flow …

Optimal Active And Passive Control Design For A Slewing Piezoelectric Laminate Beam, Travis V. Dubois

Mechanical & Aerospace Engineering Theses & Dissertations

This thesis presents the development and experimental verification of a distributed parameter model for a slewing beam system with piezoelectric actuators and sensors. Also presented is the development of an optimal active control synergism which employs IMSC, (Independent Modal Space Control) and an optimally designed, viscoelastic damping treatment. The beam is pinned at the proximal end and patches of thin piezoelectric laminates are attached to its surface. Formulation is general enough to allow the patches to be located anywhere on the beam's surface. A viscoelastic material with a constraining layer covers the rest of the beam. The differential equation of …

Judging Statistical Significance: The Effects Of Standard Error Bar Formats And Visual Displays, Rebecca Wilson Miller

Psychology Theses & Dissertations

The present study examined various graphical displays for illustrating statistical significance. These displays were created following Dunlap and May's (1989) recommendation about representing statistical significance in figures with error bars derived from the pooled estimate of error variance. In the first experiment, 15 graduate students were asked to judge whether the relationships depicted in a series of graphs and tables were significant or nonsignificant. Four significance levels were combined factorially with three standard error bar formats, unidirectional opposite direction, unidirectional same direction, and bidirectional, and two displays, line graphs and bar graphs. A tabular display was also presented for comparison. …

Come Rain Or Come Shine, Teresa E. (Terry) Perrel

English Theses & Dissertations

This novella, set in 1946, explores the needs and wants of Cooley and Edna Godwin, who have been married almost twenty years. The title comes from a popular song of the time about the constancy of love. The story opens and closes with both the husband's and wife's perspectives, but the central body of the work takes on Edna's consciousness as she leaves home, South Norfolk, Virginia, to look for happiness in California. During her travels, she is forced to examine her prejudices, to question her myopic view of the world, and to recognize the nature of true love.

Three-Dimensional Aerodynamic Shape Optimization Using Discrete Sensitivity Analysis, Gregory Wayne Burgreen

Mechanical & Aerospace Engineering Theses & Dissertations

An aerodynamic shape optimization procedure based on discrete sensitivity analysis is extended to treat three-dimensional geometries. The function of sensitivity analysis is to directly couple computational fluid dynamics (CFD) with numerical optimization techniques, which facilitates the construction of efficient direct-design methods. The development of a practical three-dimensional design procedures entails many challenges, such as: (1) the demand for significant efficiency improvements over current design methods; (2) a general and flexible three-dimensional surface representation; and (3) the efficient solution of very large systems of linear algebraic equations. It is demonstrated that each of these challenges is overcome by: (1) employing fully …

High Energy Coupled Nucleon Tranpsort In One Dimension, Stanley L. Lamkin

Physics Theses & Dissertations

The problem of energetic nucleon transport through extended bulk matter is considered in the context of the 'straight ahead' approximation. The applicable form of the Boltzmann transport equation is derived and solved in one dimension. The production term for secondary generation nucleons due to nuclear fragmentation includes 'coupling' of the flux to other types of nucleon projectiles. A physically motivated perturbation series approach is developed to enhance solution convergence. The Boltzmann operator is inverted and the flux is computed using a numerical marching scheme. The secondary production integrals are optimized for second order accuracy using a set of analytical benchmarks. …

Optimization Of Electron-Beam Activated Gaas Switches, Raymond Jack Allen Iii

Electrical & Computer Engineering Theses & Dissertations

The use of electron induced luminescence (cathodoluminescence) in gallium arsenide offers the possibility to modulate the conductance of the material on a timescale of nanoseconds and with a pulse rate of MHz, through modulation of an electron-beam current. This ionization mechanism allows the utilization of semi-insulating GaAs in fast, high power closing and opening switches. The efficiency of the switches is determined by the hold-off voltage of the GaAs switches, and by the conversion efficiency of electron energy into (useful) photon energy. Studies of the dark-current and the electron-beam induced conductance in semi-insulating GaAs have been performed in order to …

Derivative Absorption Spectroscopy With Tunable Laser Diodes, Andrew D. Jackson

Electrical & Computer Engineering Theses & Dissertations

Derivative Absorption Spectroscopy using tunable diode lasers provides a non­ intrusive, sensitive, and convenient method for monitoring gaseous characteristics such as concentration, temperature, and flow velocity. In addition, the specie type can be identified, and if the equation of state is known, pressure may be deduced.

This technique was used on molecular oxygen, in which the rovibronic transitions of the A-band ( b ¹ ∑_g ⁺ ← X ³ ∑g ^- ; v^II = O, v^I = O) were probed. Phase sensitive detection with a lock-in amplifier provides the flexibility to examine lineshape derivatives; several such derivative …

Specialized Accreditation And Academic Libraries, Stuart L. Frazer

Libraries Faculty & Staff Publications

Discussion of academic libraries and the accrediting process focuses on an evaluation and comparison of library guidelines from 17 specialized accrediting bodies with guidelines from regional accreditors. Input versus output measures are discussed, and suggestions for improving the library's participation in the process are offered.

Estimation Of Diversity And Community Structure Through Restriction-Fragment-Length-Polymorphism Distribution Analysis Of Bacterial 16s Ribosomal-Rna Genes From A Microbial Mat At An Active, Hydrothermal Vent System, Loihi Seamount, Hawaii, Craig L. Moyer, Fred C. Dobbs, David M. Karl

OES Faculty Publications

PCR was used to amplify (eu)bacterial small-subunit (16S) rRNA genes from total-community genomic DNA. The source of total-community genomic DNA used for this culture-independent analysis was the microbial mats from a deep-sea, hydrothermal vent system, Pele's Vents, located at Loihi Seamount, Hawaii. Oligonucleotides complementary to conserved regions in the 16S rRNA-encoding DNA (rDNA) of bacteria were used to direct the synthesis of PCR products, which were then subcloned by blunt-end ligation into phagemid vector pBluescript II. Restriction fragment length polymorphism patterns, created by using tandem tetrameric restriction endonucleases, revealed the presence of 12 groups of 16S rRNA genes representing discrete …