Engineering Commons^™

Long-Term Performance Of Old Dominion Technology Graduates, William D. Stanley, Alok K. Verma

Engineering Technology Faculty Publications

The long-term career patterns of Old Dominion University's engineering technology baccalaureate graduates have been studied extensively. Results from approximately 400 alumni have been analyzed. The results of the analysis are presented and conclusions are drawn from the trends. The results indicate that the career progress of engineering technology graduates over a nearly twenty-year period is substantial and that they are performing effectively in a variety of career patterns.

Mechanical Alloying Of Nitrogen Into Iron Powders, J. Rawers, D. Govier, D. C. Cook

Physics Faculty Publications

Mechanical alloying of nitrogen into bcc-fe powder is a very effective and efficient means of obtaining very high concentration of nitrogen in micron-size iron particles. Mechanical alloying increases the concentration of nitrogen in the iron powder far in excess of the bcc-Fe lattice low nitrogen solubility, however most of the infused nitrogen resides on the nano-size grain boundaries and in nano-size bct-fe that forms during mechanical alloying.

Surface Debye Temperature Measurement With Reflection High-Energy Electron Diffraction, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

Measurement of the surface mean-square atomic vibrational amplitude, or equivalently the surface Debye temperature, with reflection high-energy electron diffraction is discussed. Low-index surfaces of lead are used as examples. Particular details are given about the temperature-dependent diffraction pattern of Pb(100) in the Debye-Waller region. The use of reflection high-energy electron diffraction for measurement of the substrate surface temperature in thin-film deposition chambers is suggested. © 1996 American Institute of Physics.

Application Of Reanalysis Techniques For Pattern Design Of Spot Welds, Young San Kim

Mechanical & Aerospace Engineering Theses & Dissertations

Extensive benchmarking on competitive cars has shown that the durability of vehicles, assembly-induced variations, and assembly cost are directly related to the quality and number of spot welds. On most luxury cars, approximately 4,500 to 5,000 spot welds are found. On less expensive cars, the range is from 3,500 to 4,500. These cars usually inherit more noise, rattles, squeaks, and other quality-related problems. These problems have motivated the search for a new capability to systematically place welds in the most critical areas, with a minimum number of welds for car bodies, while satisfying all performance requirements (e.g., stiffness, stress distribution, …

Numerical Simulation Of Complex, Three-Dimensional, Turbulent-Free Jets, Robert V. Wilson

Mechanical & Aerospace Engineering Theses & Dissertations

Three-dimensional, incompressible turbulent jets with rectangular and elliptical cross-section are simulated with a finite-difference numerical method. The full Navier-Stokes equations are solved at low Reynoids numbers, whereas at high Reynolds numbers filtered forms of the equations are solved along with a sub-grid scale model to approximate the effects of the unresolved scales. A 2-N storage, third-order Runge-Kutta scheme is used for temporal discretization and a fourth-order compact scheme is used for spatial discretization. Although such methods are widely used in the simulation of compressible flows, the lack of an evolution equation for pressure or density presents particular difficulty in incompressible …

Dynamic Scale Genetic Algorithm: An Enhanced Genetic Search For Discrete Optimization, Bela Dange Joshi

Engineering Management & Systems Engineering Theses & Dissertations

The minimization of operations and support resources of reusable launch vehicles is a complex task, involving discrete optimization and the simulation domain. Genetic algorithms, offering a robust search strategy suitable for integer variables and the simulation domain, can be applied to minimize these resources. This research developed an enhanced genetic algorithm for problems with a linear objective function, the most common class of discrete optimization problems. The dynamic scale genetic algorithm developed here incorporates concepts of implicit enumeration to enhance search. This is achieved by utilizing problem specific information to refine the solution space over successive generations. The utility of …

The Modeling Of Structural-Acoustic Interaction Using Coupled Fe/Be Method And Control Of Interior Acoustic Pressure Using Piezoelectric Actuators, Yucheng Shi

Mechanical & Aerospace Engineering Theses & Dissertations

A coupled finite element (FE) and boundary element (BE) approach is presented to model full coupled structural/acoustic/piezoelectric systems. The dual reciprocity boundary element method is used so that the natural frequencies and mode shapes of the coupled system can be obtained, and to extend this approach to time dependent problems. The boundary element method is applied to interior acoustic domains, and the results are very accurate when compared with limited exact solutions. Structural--acoustic problems are then analyzed with the coupled finite element/boundary element method, where the finite element method models the structural domain and the boundary element method models the …

The Effects Of Risk Management Program Implementation On Worker Safety Knowledge, John C. Donnelly

Community & Environmental Health Theses & Dissertations

This study examined the effect of the implementation of a risk management program tool on worker safety knowledge in a composite building material fabrication facility whose workers suffered from an increasingly high injury (incidence) rate in recent years. Risk assessment codes (RACs) and job safety analyses (JSAs) were the primary tools used to introduce workers to the concept of risk. Because employee involvement is a crucial element in JSA development. employee input was frequently solicited throughout JSA development.

The study instrument consisted of a pre-test and post-test survey, to which an experimental and control group were subjected. The instrument was …

Text Independent Speaker Verification Using Binary-Pair Partitioned Neural Networks, Claude A. Norton Iii

Electrical & Computer Engineering Theses & Dissertations

A method is presented for the application of binary-pair partitioned neural networks to the task of speaker verification. This technique is based on a previously developed neural network classifier for speaker identification.

The main focus of this research was the development and testing of the algorithms necessary to extend the binary-pair partitioning approach from speaker identification to speaker verification. The method is based on the development of a user profile which is obtained from discriminative data provided by the binary-pair partitioned neural networks.

Experimental results are provided which demonstrate the viability of this approach, using the TIMIT speech corpus for …

System Dynamic Modeling Of Activity And Flow Relationships In Plant Layout Problems, Gary Allen Weaver

Engineering Management & Systems Engineering Theses & Dissertations

The problem of determining an optimal plant layout involves the distribution of machinery, service areas, and storage spaces. The solution is usually determined for a specific period of time and static in nature. Planning for the plant layout is normally performed at the onset of new construction, or major refurbishment of an existing facility. In addition, plant layouts are renewed when a significant productivity decrease is experienced over long periods of time and linked to material flow problems, and when an expanding company plans for major capital expenditures in equipment and space. Due to the dynamic nature of business the …

Finite Element Formulation Of A Three-Node Spatially Curved And Twisted Beam, Umesh Vishnu Padhye

Mechanical & Aerospace Engineering Theses & Dissertations

A three-node curved and twisted beam element is developed for linear analysis of structures modeled with curved and pre-twisted beams. A set of governing equations consisting of kinematic relations, constitutive relations, and equilibrium equations is derived. The beam element has three rotational and three displacement degrees of freedom at each node. The differential equations of kinematics are solved exactly for linearly varying longitudinal strains, constant transverse shear strains, linearly varying twist, and quadratically varying curvature changes to obtain the description of rotation and displacement modes. These rotation and displacement modes are then used as the basis functions for development of …

Experimental Investigation Of The Inlet Deflector Configuration Variation In The Flow Field At Mach 1.9, Kyu C. Hwang

Mechanical & Aerospace Engineering Theses & Dissertations

In recent years, active research has been conducted to study the technological feasibility of supersonic laminar flow control on the wing of the High Speed Civil Transport (HSCT). For this study, the F-16XL has been chosen due to its highly swept crank wing planform that closely resembles the HSCT configurations. During flights, it is discovered that the shock wave generated from the aircraft inlet introduces disturbances on the wing where the data acquisition is conducted. The flow field about a supersonic inlet is characterized by a complex three-dimensional pattern of shock waves generated by the geometrical configuration of a deflector …

Atomic Broadcast In Heterogeneous Distributed Systems, Osman Zeineldine

Computer Science Theses & Dissertations

Communication services have long been recognized as possessing a dominant effect on both performance and robustness of distributed systems. Distributed applications rely on a multitude of protocols for the support of these services. Of crucial importance are multicast protocols. Reliable multicast protocols enhance the efficiency and robustness of distributed systems. Numerous reliable multicast protocols have been proposed, each differing in the set of assumptions adopted, especially for the communication network. These assumptions make each protocol suitable for a specific environment. The presence of different distributed applications that run on different LANs and single distributed applications that span different LANs mandate …

An Experimental Investigation Of Wall Cooling Effects On Hypersonic Boundary Layer Stability In A Quiet Wind Tunnel, Alan E. Blanchard

Mechanical & Aerospace Engineering Theses & Dissertations

One of the primary reasons for developing quiet tunnels is for the investigation of high-speed boundary-layer stability and transition phenomena without the transition-promoting effects of acoustic radiation from tunnel walls. In this experiment, a flared-cone model under adiabatic- and cooled-wall conditions was placed in a calibrated, 'quiet' Mach 6 flow and the stability of the boundary layer was investigated using a prototype constant-voltage anemometer. The results were compared with linear-stability theory predictions and good agreement was found in the prediction of second-mode frequencies and growth. In addition, the same 'N=10' criterion used to predict boundary-layer transition in subsonic, transonic, and …

Buckling Analysis And Optimum Design Of Multidirectionally Stiffened Composite Curved Panel, Navin R. R. Jaunky

Mechanical & Aerospace Engineering Theses & Dissertations

Continuous filament grid-stiffened structure is a stiffening concept that combines structural efficiency and damage tolerance. However, buckle resistant design optimization of such structures using a finite element method is expensive and time consuming due to the number of design parameters that can be varied. An analytical optimization procedure which is simple, efficient and supports the preliminary design of grid-stiffened structures for application to combined loading cases is needed.

An analytical model for a general grid-stiffened curved panel is developed using an improved smeared theory with a first-order, shear-deformation theory to account for transverse shear flexibilities and local skin-stiffener interaction effects. …

Assessment Of High-Order Serendipity And Lagrangian Quadrilateral Membrane Elements, Timothy Scott Davis

Mechanical & Aerospace Engineering Theses & Dissertations

The development and implementation of high-order Lagrangian and serendipity quadrilateral elements including a biquartic Lagrangian element, a 16-node serendipity element, and a 17-node serendipity element are presented and assessed. This assessment includes an evaluation of the patch test, an element eigenvalue test to detect any zero-energy modes, and selected plane stress problems. The effects of using both full and reduced numerical integration procedures and optimum locations for stress recovery are discussed. All elements evaluated represent the three rigid-body modes without inducing strains, exhibit geometric isotropy, and pass the membrane patch test. The most promising high-order quadrilateral element proved to be …

A Two-Dimensional Model For Watershed Runoff And Pollutant Transport, Laura Jean Howard

Civil & Environmental Engineering Theses & Dissertations

A two-dimensional mathematical model is developed for the quantitative and qualitative analysis of watershed runoff for a given rainfall event. The runoff is routed through a receiving channel. The model is designed for use on a personal computer. Full documentation is included in the Appendix. The model is capable of accommodating downstream boundary conditions, temporally varied effective rainfall conditions, and spatially varied watershed conditions. Output takes the form of flow depths, discharges, and concentrations. The model was tested for quantity and quality using existing experimental data, and the results are presented herein.

Studies Of Mixing Processes In Gases And Effects On Combustion And Stability, Frank Paul Kozusko Jr.

Mathematics & Statistics Theses & Dissertations

Three physical models of laminar mixing of initially separated gases are studied. Two models study the effects of the mixing dynamics on the chemical reactions between the gases. The third model studies the structure and stability of a laminar mixing layer in a binary gas. The three models are:

1. Two ideal and incompressible gases representing fuel and oxidizer are initially at rest and separated across an infinite linear interface in a two dimensional system. Combustion, expected as the gases mix, will lead to a rapid rise in temperature in a localized area, i.e. ignition. The mixing of the gases …

Nonlinear Transient Thermal Analysis By The Force-Derivative Method, Narayani V. Balakrishnan

Mechanical & Aerospace Engineering Theses & Dissertations

The force-derivative method (FDM) represents a series of higher-order modal methods which offer an increasingly improved approximation of the higher modes neglected in the basic mode-displacement method (MDM). The FDM includes additional terms which involve the forcing function and derivatives of the forcing function with respect to time. The mode-acceleration method (MAM), extensively used in structural analysis, is a first-order form of the FDM which includes only one correction term that depends on the forcing function itself. The success of the FDM in many structural dynamic applications has prompted its application for solving transient thermal problems. The superior convergence of …

Dynamic Unstructured Method For Prescribed And Aerodynamically Determined Relative Moving Boundary Problems, Kamakhya Prasad Singh

Mechanical & Aerospace Engineering Theses & Dissertations

A new methodology is developed to simulate unsteady flows about prescribed and aerodynamically determined moving boundary problems. The method couples the fluid dynamics and rigid-body dynamics equations to capture the time-dependent interference between stationary and moving boundaries. The unsteady, compressible, inviscid (Euler) equations are solved on dynamic, unstructured grids by an explicit, finite-volume, upwind method. For efficiency, the grid adaptation is performed within a window around the moving object. The Eulerian equations of the rigid-body dynamics are solved by a Runge-Kutta method in a non-inertial frame of reference. The two-dimensional flow solver is validated by computing the flow past a …

Fault Tolerance In Critical Real-Time Systems, Balaji Tirukarneswaran

Electrical & Computer Engineering Theses & Dissertations

Critical real-time applications require work to be completed before a predefined deadline, else the consequences may be catastrophic. The anticipation of faults in such systems necessitates the need for fault tolerance. Fault tolerance can be achieved in many different ways. A real-time system designer may impose restrictions on any of the system performance measures such as the latency, throughput and number of processors, depending on the type of application. In this work, several different fault tolerant strategies for any given DFG (Data Flow Graph) are discussed. DFG models are developed using the strategies and the resulting worst case performances a.re …

Fault Tolerant Pipelined Adaptive Systems, Bhasker Reddy Allam

Electrical & Computer Engineering Theses & Dissertations

A fault tolerant pipelined architecture for high sampling rate adaptive filters is presented in this thesis. The architecture is based on the computational requirements of delayed LMS and lattice adaptive 61ters. It offers robust performance in the presence of single hardware faults, and software faults resulting from numerical instability. Two different architectures are proposed. One allows a graceful degradation in system performance in the event of a fault, and the other uses a module replacement strategy to recover from faults without decreasing performance. Analysis of the steady state error increase due to filter reconfiguration is presented. The reliability of the …

Numerical Investigation Of Shock-Induced Combustion Past Blunt Projectiles, Jagjit K. Ahuja

Mechanical & Aerospace Engineering Theses & Dissertations

A numerical study is conducted to simulate shock-induced combustion in premixed hydrogen-air mixtures at various free-stream conditions and parameters. Two-dimensional axisymmetric, reacting viscous flow over blunt projectiles is computed to study shock-induced combustion at Mach 5.11 and Mach 6.46 in hydrogen-air mixture. A seven-species, seven reactions finite rate hydrogen-air chemical reaction mechanism is used combined with a finite-difference, shock-fitting method to solve the complete set of Navier-Stokes and species conservation equations. In this approach, the bow shock represents a boundary of the computational domain and is treated as a discontinuity across which Rankine-Hugoniot conditions are applied. All interior details of …

Comparison Of System Identification Techniques For The Dexterous Orbital Servicing System (Doss), Allan Terrence Morris

Electrical & Computer Engineering Theses & Dissertations

The major contribution of system identification is the development of analytical models of a system. Many identification techniques can adequately describe the input and output map. One of the challenges of these techniques is to correctly infer from the measured data the characteristics of the individual, contributing components producing a more accurate system model.

In this thesis linear, dynamic, multivariable state-space models for three joints of the Dexterous Orbital Servicing System (DOSS) are identified. DOSS is a representative space station manipulator at the NASA Langley Research Center. The dynamic models of the manipulator will first be estimated by applying nonparametric …

Real-Time Communication In The Algorithm To Architecture Mapping Model, Somesh M. Varma

Electrical & Computer Engineering Theses & Dissertations

The objective of this thesis is to analyze schedules of communication resources to obtain deterministic and contention-free communication in the Algorithm To Architecture Mapping Model (ATAMM). In ATAMM, performance must be deterministic to guarantee meeting deadlines. It is difficult to achieve deterministic performance in the presence of contention during communication. This thesis develops new data-flow models to study and analyze different schedules of communication resources to achieve deterministic and contention-free communication. These models are the Synchronous Communication Marked Graph (SCMG) and the Asynchronous Communication Marked Graph (ACMG). The SCMG is based on message passing synchronous communication. It defines schedules for …

An Investigation Of The Speed And Power Limitations Of A Copper-Doped Gallium Arsenide Photoconductive Switch, David Clifton Stoudt

Electrical & Computer Engineering Theses & Dissertations

The processes of persistent photoconductivity followed by photo-quenching are demonstrated in copper-compensated, silicon-doped, semi-insulating gallium arsenide. These processes allow a switch to be developed that can be closed by the application of one laser pulse (λ = 1.06 μm) and opened by the application of a second laser pulse with a wavelength equal to twice that of the first laser (λ= 2.13 μm). Switch closure is primarily achieved by elevating electrons from a deep copper center which has been diffused into the material. The opening phase is a two-step process which relies initially on the absorption of the 2-μm laser …

Assumed-Stress Hybrid Beam Element For Nonlinear Elastic Stress Analysis, William Scott Carron

Mechanical & Aerospace Engineering Theses & Dissertations

An assumed-stress hybrid 2-node beam element is formulated using the Hellinger-Reissner variational principle. Independent approximations are made for the stresses and displacements. The stress field is assumed to be consistent with the force and moment equilibrium equations. The displacement field is assumed to be linear except that the transverse deflections vary quadratically using the rotational freedoms, The element is implemented in COMET and coupled with its corotational utilities. This enables an analyst to extend the element to problems involving geometric nonlinearities. Excellent performance of the element for nonlinear behaviors of both a stiffening and softening behavior is demonstrated.

Wing-Section Optimization For Supersonic Viscous Flow, Cem Cihan Item

Mechanical & Aerospace Engineering Theses & Dissertations

The recent interest in the High Speed Civil Transport (HSCT) has resulted in renewed research studies of optimized supersonic cruise transport configurations. Incorporation of flow viscosity effects in the design process of such a supersonic wing is currently under investigation. This may lead to more accurate problem formulations and, in tum, greater aerodynamic efficiency than can be obtained by the traditional, inviscid, linear theories. In this context, for a design code to be a candidate for a complex optimization problem, such as three-dimensional viscous supersonic wing design, it should be validated using simpler building-block shapes.

To optimize the shape of …

Development Of A Knowledge-Based System For Generating Process Plans Using Group Technology: A Study For Norfolk Naval Shipyard, William P. Keene Jr.

Engineering Management & Systems Engineering Theses & Dissertations

The purpose of this research was to study and analyze the Norfolk Naval Shipyard's manufacturing methods of determining part families and generating part process plans for parts in the machine shop. A knowledge-based decision support system was designed based on knowledge acquired from machinist experts and documented sources of the Norfolk Naval Shipyard. The system interprets specific part information provided by the user, categorizes parts into part families and generates process plans to manufacture the parts. The system was evaluated and tested for parts provided by Norfolk Naval Shipyard.

Aerodynamic Design Optimization With Consistently Discrete Sensitivity Derivatives Via The Incremental Iterative Method, Vamshi M. Korivi

Mechanical & Aerospace Engineering Theses & Dissertations

In this study which involves advanced fluid-flow codes, an incremental iterative formulation (also known as the "delta" or "correction" form), together with the well-known spatially split approximate-factorization algorithm, is presented for solving the large, sparse systems of linear equations that are associated with aerodynamic sensitivity analysis. For the smaller two dimensional problems, a direct method can be applied to solve these linear equations in either the standard or the incremental form, in which case the two are equivalent. However, iterative methods are needed for larger two-dimensional and three dimensional applications because direct methods require more computer memory than is currently …