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Shape Sensitivity Analysis And Optimization Of Skeletal Structures And Geometrically Nonlinear Solids, Ching-Hung Chuang

Mechanical & Aerospace Engineering Theses & Dissertations

Formulations and computational schemes for shape design sensitivity analysis and optimization have been developed for both skeletal structures and geometrically nonlinear elastic solids. The continuum approach, which is based on the weak variational form of the governing differential equation and the concept of the material derivative, plays a central role in such a development.

In the first part of this work, the eigenvalue and eigenvector sensitivity equations for skeletal structures are derived with respect to configuration variables of joint and support locations. This derivation is done by the domain method as well as the boundary method. The discrete approach for …

Monitoring Computer Systems: An Intelligent Approach, Myron Zhihong Xu

Computer Science Theses & Dissertations

Monitoring modern computer systems is increasingly difficult due to their peculiar characteristics. To cope with this situation, the dissertation develops an approach to intelligent monitoring. The resulting model consists of three major designs: representing targets, controlling data collection, and autonomously refining monitoring performance. The model explores a more declarative object-oriented model by introducing virtual objects to dynamically compose abstract representations, while it treats conventional hard-wired hierarchies and predefined object classes as primitive structures. Taking the representational framework as a reasoning bed, the design for controlling mechanisms adopts default reasoning backed up with ordered constraints, so that the amount of data …

A Computational Aerodynamic Design Optimization Method Using Sensitivity Analysis, Mohamed E. Eleshaky

Mechanical & Aerospace Engineering Theses & Dissertations

A new and efficient procedure for aerodynamic shape optimization is presented. The salient lineaments of this procedure are: (1) using a discrete sensitivity analysis approach to determine analytically the aerodynamic sensitivity coefficients; (2) obtaining the flowfield solution either by a computational fluid dynamics (CFD) analysis or, alternatively, by a flowfield extrapolation method which is based on a truncated Taylor's series; (3) defining the aerodynamic shape in such a way that it is not restricted to any class of surfaces and the optimizer automatically shapes the aerodynamic configuration to any arbitrary geometry; and (4) requiring no expertise other than that needed …

Neural Network Based Vowel Articulation Training Aid For The Deaf, Andrew E. Beck

Electrical & Computer Engineering Theses & Dissertations

Teaching the hearing-impaired to speak is both a challenging and rewarding task. Computer-based training aids are valuable teaching tools and complement the speech therapist in the speech training process. We have developed a computer based vowel articulation training aid designed to provide visual feedback for vowel production to the hearing-impaired user. This system transforms speech spectra from a multi-dimensional acoustic space to a two-dimensional phonetic space which is displayed on a computer monitor. The system signal processing includes feature extraction designed to mimic the properties of the human ear, and a transformation to a two-dimensional display space. The dimensionality transformation …

Characterization Of Trailing Line Vortices, Karla M. Mossi

Mechanical & Aerospace Engineering Theses & Dissertations

Mean velocity surveys were taken for axial or trailing line vortices produced behind a bi-wing vortex generator in a low-speed wind tunnel. Data were taken primarily with a seven-hole probe at a speed of 30m/s; but vortex steadiness was studied using smoke flow visualization over a speed range between 10 and 40 m/s. Various generator center body configurations were studied, with particular interest directed toward how a centerline jet and an asymmetric, unsteady circumferential flow influenced the mean velocity profiles. This study found that a centerline jet did not produce a well-behaved two-cell vortex over the parametric range available in …

The Effects Of Orthopaedic Surgery And Dorsal Rhizotomy On Selected Gait Characteristics Of Cerebral Palsy Children, Danielle M. Lanoue

Rehabilitation Sciences Theses & Dissertations

Surgical management of cerebral palsy children typically involves multiple orthopaedic surgeries in order to achieve and maintain the maximum functional level of ambulation. Orthopaedic intervention to address lower extremity spasticity often includes: muscle lengthenings, muscle releases and tendon transfers. The most recent advance in management of lower extremity spasticity has been through a neurosurgical approach; selective dorsal rhizotomy. The long term effects of dorsal rhizotomy are still being investigated. Through the use of instrumented gait analysis, the specific objective results of both of these types of surgeries can be investigated. The purpose of this retrospective study was to examine the …

Materially Nonlinear Finite Element Analyses Of Trusses And Slab-On-Grade Problems, Moayyad Moh'd Al-Nasra

Civil & Environmental Engineering Theses & Dissertations

The overall approach is to employ the finite-element method along with specified material models to account for material nonlinearity. This study includes two different applications: truss structures and slabs-on-grade.

Procedures for materially nonlinear analysis of truss structures, which apply for both determinate and indeterminate cases are proposed. The proposed procedures are simple and can handle a variety of different stress-strain functions, and the applied load does not have to be incremental. Proposed procedures results are verified with the output of NASTRAN.

A finite-element model for slab-on-grade is introduced. The concrete slab is represented by eight-node brick elements, and the joints …

Control Of Low-Speed Turbulent Separated Flow Over A Backward-Facing Ramp, John C. Lin

Mechanical & Aerospace Engineering Theses & Dissertations

The relative performance and flow phenomena associated with several devices for controlling turbulent separated flow were investigated at low speeds. Relative performance of the devices was examined for flow over a curved, backward-facing ramp in a wind tunnel, and the flow phenomena were examined in a water tunnel using dye-flow visualization. Surface static pressure measurements and oil-flow visualization results from the wind tunnel tests indicated that transverse grooves, longitudinal grooves, submerged vortex generators, vortex generator jets (VGJ’s), Viets’ fluidic flappers, elongated arches +a + a (positive angle of attack), and large-eddy breakup devices (LEBU’s) +a + a placed near the …

Reasoning By Analogy In A Multi-Level System Architecture For The Design Of Mechanisms, Ghassan F. Issa

Computer Science Theses & Dissertations

Since the first attempts to integrate AI technology and engineering design nearly two decades ago, few expert systems have been shown to demonstrate sufficient reasoning capabilities to solve real-world design problems. The complex nature of design, the lack of understanding of the design process, and the limitations of current expert system technology have all been shown to have adverse effects on the maturity of this research area. Therefore, our direction in this research concentrates on understanding the design process, investigating a novel area of research focusing on creative design, and incorporating the results into a system model feasible for production …

Biodegradation Of Crude Oil By Marine Higher Fungi, Brian J. Dyer

Biological Sciences Theses & Dissertations

Four experiments were performed to determine the ability of marine higher fungi to grow in and degrade crude oil. Eight species, previously determined to be hydrocarbonoclastic, were grown in artificial sea water medium (ASM) and southern Louisiana crude oil. The dry mycelial weights were measured and consumption of crude oil was measured gravimetrically. The two species with the best growth, Corollospora maritima and Zalerion maritimum, were grown in ASM containing crude oil spiked with three known hydrocarbons. To this was added glucose (0.15%) and incubated 49 days to test for possible cometabolism of hydrocarbons. Hydrocarbons remaining in the growth …

Hierarchical Flux-Based Thermal-Structural Finite Element Analysis Method, Sandra P. Polesky

Mechanical & Aerospace Engineering Theses & Dissertations

A hierarchical flux-based finite element method is developed for both one- and two-dimensional thermal-structural analyses. Derivation of the finite element equations is presented. The resulting finite element matrices associated with the flux-based formulation are evaluated in closed-form. The hierarchical finite elements include additional degrees of freedom in the approximation of the element variable distributions by the use of nodeless variables. The nodeless variables offer increased solution accuracy without the need for defining actual nodes and rediscretizing the finite element model. Thermal and structural responses obtained using the hierarchical flux-based method are compared with results obtained from a conventional linear finite …

Formant Estimation From Dctc's Using A Feedforward Neural Network, Shubhangi U. Kelkar

Electrical & Computer Engineering Theses & Dissertations

Formants are the natural frequencies of the human vocal tract. Existing methods for estimating formants from speech signals are computationally complex and subject to errors for certain type of speech sounds. This thesis describes a method for estimating vowel formant frequencies from Discrete Cosine Transform Coefficients (DCTC's), a form of cepstral coefficients, using a feedforward neural network with back-propagation training. Experimental results are based on a large multispeaker data base. The results are obtained for both a linear transformation and a feedforward neural network with a nonlinear hidden layer. In general, the neural network transformation is superior to the linear …

Development Of A Model Updating Technique For Controls-Structures Integrated Design Optimization, Angela Georges

Mechanical & Aerospace Engineering Theses & Dissertations

A model updating technique is developed with the intent of providing an efficient means of improving the accuracy of the modelling of the vibrational qualities of a large, flexible structure as it undergoes an integrated controls-structures design optimization. The proposed technique utilizes eigenvalue/eigenvector sensitivity information, two different model reduction methods which assign weights of importance to the vibrational modes of the structure, and modal switching based upon the modal weights determined by the model reduction methods. Issues associated with the numerical implementation of the proposed technique, such as discontinuities induced by modal switching, are also addressed.

The proposed model updating …

Modal Analysis Of Gyroscopically Coupled Sound-Structure Interaction Problems, Vijay B. Bokil

Mechanical & Aerospace Engineering Theses & Dissertations

In many practical situations we encounter sound-structure interaction between the fluid in a cavity and the flexible wall on the boundary. The aircraft cabin interacting with its fuselage and double-leaf partition walls interacting with the enclosed cavity are some of the typical examples. The vibratory behavior of the structure and the acoustical pressure inside the cavity are affected by this interaction.

In most of the cases, the governing differential equations for the coupled system can be shown to involve gyroscopic coupling. A special method has been applied to decouple the equations in terms of pairs of generalized coordinates and the …

Transfer Function Models And Control Of A Flexible Structure Using Piezoelectric Laminates, Joseph A. Colvin

Mechanical & Aerospace Engineering Theses & Dissertations

The development of piezoelectric polymer films has generated a great deal of excitement in the structural controls community because they are lightweight, durable, distributed in nature and have broad band frequency characteristics. The flurry of research inspired by piezoelectric films has primarily been dedicated to using them as distributed sensors, and to a lesser extent, as distributed actuators.

Active damping of structural vibrations using piezoelectric polymer films as sensors and actuators has primarily been directed toward taking advantage of their distributed nature and employing various types of distributed control theory. This approach does not easily yield insight into the dynamics …

An Experimental Method For Determining Membrane Penetration, Jong W. Choi, Isao Ishibashi

Civil & Environmental Engineering Faculty Publications

A new and simple experimental method is proposed for the determination of membrane penetration due to changes of the effective confining pressure in triaxial and hollow cylinder tests. The proposed method has advantages over existing methods in that it requires neither special devices nor questionable assumptions. It only requires a series of drained isotropic compression tests in a conventional triaxial device with plastic liners. The results from the proposed method are compared to those from several existing experimental and analytical methods.

Studies Of High Field Conduction In Diamond For Electron Beam Controlled Switching, R. P. Joshi, M. K. Kennedy, K. H. Schoenbach, W. W. Hofer

Bioelectrics Publications

Experimental studies on a vertical metal‐diamond‐silicon switch structure have been conducted for potential pulsed power applications. Both the dc current‐voltage characteristics and the transient switching response have been measured for a range of voltages. With a 1 μm diamond film, the switch has been seen to withstand electric fields up to 1.8 MV/cm. Our results show a polarity dependence which can be associated with current injection at the asymmetric contacts. Polarity effects were also observed in the presence of e‐beam excitation, and arise due to nonuniform carrier generation near the diamond‐silicon interface. Our switching transients were seen to follow …

Bistable Behavior Of The Dark Current In Copper-Doped Semi-Insulating Gallium Arsenide, R. A. Roush, K. H. Schoenbach, R. P. Brinkmann

Bioelectrics Publications

The dark current characteristics of gallium arsenide doped with silicon and compensated with diffused copper were found to have a pronounced region of current controlled negative differential conductivity (ndc) similar to the characteristics of a thyristor. The resistivity of the semi‐insulating semiconductor was measured to be 10⁵ Ω cm for applied voltages up to 2.2 kV, which corresponds to an average electric field of 38 kV/cm. At higher voltages, a transition to a stable high current state was observed with a current rate of rise exceeding 10¹¹ A/s. There is evidence of the formation of at least one …

U.S.S. New Ironsides: The Seagoing Ironclad In The Union Navy, William Howard Roberts

History Theses & Dissertations

Of the ironclads completed by the Union during the Civil War, only the U.S.S. New Ironsides was a seagoing, high-freeboard design. Her seagoing qualities and heavy battery made her uniquely valuable to the Union in combat. Although New Ironsides was highly successful and her high-freeboard design squarely in the European mainstream, she represented the last of her direct line in the U.S. Navy. The lessons learned from her construction and wartime service, which should have provided invaluable instruction for U.S. designers, were not followed up. By failing to develop the seagoing ironclad the United States forfeited the advantages it might …

Seismic Response Of Pipeline Systems In A Soil Liquefaction Environment, Hongzhi Zhang

Civil & Environmental Engineering Theses & Dissertations

This research is a study of the general seismic response behavior of buried pipeline systems during a soil liquefaction process. To aid the design of buried pipelines in a soil liquefaction environment, the purpose of this research is to provide the basic dynamic seismic response of different pipeline systems. Several important parameters such as pipe diameter, buried depth, additional mass and the size of the liquefiable soil zone have been introduced. The pipeline systems under study are cross-types, T-types and straight pipelines, with or without a manhole, buried in a soil liquefiable zone.

Time-varying soil spring constants are used for …

Energetic Protons And Deuterons Emitted Following Μ⁻ Capture By ³He Nuclei, W. J. Cummings, G. E. Dodge, S. S. Hanna, B. H. King, S. E. Kuhn, Y. M. Shin, R. Helmer, R. B. Schubank, N. R. Stevenson, U. Wienands, Y. K. Lee, G. R. Mason, B. E. King, K. S. Chung, J. M. Lee, D. P. Rosenzweig

Physics Faculty Publications

Spectra of energetic protons and deuterons emitted following negative muon capture from rest in ³He have been measured for the first time. Significant capture strength is observed at high energy transfers (mμ- E_v >60 MeV) for the two-body and three-body breakup channels, indicative of the importance of nucleon-nucleon correlations and meson exchange currents in the capture process. A simple plane wave impulse approximation calculation reproduces the proton spectrum reasonably well, but underpredicts the deuteron rate at the highest energies by a large factor.

Solution Uniqueness And Stability Criteria For A Model Of Growth Factor Production, J. A. Adam

Mathematics & Statistics Faculty Publications

Uniqueness and stability criteria are established for the steady states of a nonlinear model of growth factor production. A specific expression for the nonlinearity is chosen, containing three parameters which can be adjusted to fit a specific biological context, but much of the analysis applies to a general class of source terms that exhibit the same qualitative behavior.

Temperature And Suction Effects On The Instability Of An Infinite Swept Attachment Line, D. G. Lasseigne, T. L. Jackson, F. Q. Hu

Mathematics & Statistics Faculty Publications

It is known that the incompressible, infinite swept attachment line flow is unstable to streamwise disturbances that originate in the boundary layer when the cross-flow exceeds a critical magnitude. Furthermore, a small degree of suction at the surface has a significant stabilizing influence while a small degree of blowing has a considerable destabilizing influence. This paper investigates the stabilizing and destabilizing effects of, respectively, cooling or heating the plate and the competing or enhancing effects of suction or blowing. A nonorthogonal flow with respect to the attachment line is also considered by adding a component of shear to the mean …

Approaches To Control Of The Large Angle Magnetic Suspension Test Fixture, Mehran Ghofrani

Mechanical & Aerospace Engineering Theses & Dissertations

The Large Angle Magnetic Suspension Test Fixture is a five degree-of-freedom system, developed and built at NASA Langley Research Center. It is intended for study of control techniques in magnetic suspension systems with large angular capabilities. In this study, steps have been taken to prove the system in practice, using the existing hardware. A classical control approach, using dual phase advance compensators, is applied in simulation and hardware. A single decoupled degree-of-freedom of the system is stabilized and controlled in simulation. The procedure is then employed for all five degrees-of-freedom. The design and implementation of an analog and a digital …

Laureate, 1992, Old Dominion University

University Yearbooks

1992 yearbook of Old Dominion University

Bounds On Constraint Weight Parameters Of Hopfield Networks For Stability Of Optimization Problem Solutions, Gursel Serpen

Electrical & Computer Engineering Theses & Dissertations

The purpose of the presented research is to study the convergence characteristics of Hopfield network dynamics. The relation between constraint weight parameter values and the stability of solutions of constraint satisfaction and optimization problems mapped to Hopfield networks is investigated. A theoretical development relating constraint weight parameter values to solution stability is presented. The dependency of solution stability on constraint weight parameter values is shown employing an abstract optimization problem. A theorem defining bounds on the constraint weight parameter magnitudes for solution stability of constraint satisfaction and optimization problems is proved. Simulation analysis on a set of optimization and constraint …

Explicit Multistage Schemes For The Solution Of The Three-Dimensional Compressible Euler/Navier-Stokes Equations, Alaa Ahmed Elmiligui

Mechanical & Aerospace Engineering Theses & Dissertations

The objective of this study was to develop a high-resolution-explicit-multi-block numerical algorithm, suitable for efficient computation of the three-dimensional, time-dependent Euler and Navier-Stokes equations. The resulting algorithm has employed a finite volume approach, using MUSCL-type differencing to obtain state variables at cell interface. Variable interpolations were written in the $\kappa$-scheme formulation. Inviscid fluxes were calculated via Roe's flux-difference splitting, and van Leer's flux-vector splitting techniques, which are considered state of the art. The viscous terms were discretized using a second-order, central-difference operator.

Two classes of explicit time integration has been investigated for solving the compressible inviscid/viscous flow problems--two-stage predictor-corrector schemes, …

A Study To Determine Criteria Essential To Technology Education At The Secondary Education Level, Jason Edward Perry

OTS Master's Level Projects & Papers

To accomplish the purpose of this study, the following goals were used: 1. Determine the list of curriculum criteria essential to technology education programs at the secondary level; 2. Validate the list of curriculum criteria essential to technology education programs at the secondary level.

Effect Of Magnetic And Density Fluctuations On The Propagation Of Lower Hybrid Waves In Tokamaks, George Vahala, Linda L. Vahala, Paul T. Bonoli

Electrical & Computer Engineering Faculty Publications

Lower hybrid waves have been used extensively for plasma heating, current drive, and ramp-up as well as sawteeth stabilization, The wave kinetic equation for lower hybrid wave propagation is extended to include the effects of both magnetic and density fluctuations. This integral equation is then solved by Monte Carlo procedures for a toroidal plasma. It is shown that even for magnetic/density fluctuation levels on the order of 10^-4, there are significant magnetic fluctuation effects on the wave power deposition into the plasma. This effect is quite pronounced if the magnetic fluctuation spectrum is peaked within the plasma. For …

Charge-State Equilibrium And Nonequilibrium Modeling Of The Carbon-Pellet Plasma Interaction, A. G. Elcashlan, G. A. Gerdin, L. L. Vahala, P. B. Parks

Electrical & Computer Engineering Faculty Publications

Self-consistent equilibrium and nonequilibrium charge-state models are formulated for the spherical expansion of low-Z pellet vapor as an inviscid perfect gas of constant ratio of specific heats being heated volumetrically by the incident electrons of a thermonuclear plasma. The two models are found to be in agreement in the region where the ratio of the ionization length ζ_j to pellet radius r_p is less than unity, but a single parameter, such as the magnitude of this ratio on the sonic surface, is insufficient to determine whether an equilibrium model will be valid for all regions of the ablatant …