Engineering Commons^™

Teamwork In The Workplace: A Discovery Of The Work Processes One Team Used To Meet Its Goals, Thomas Andrew Hassler

Engineering Management & Systems Engineering Theses & Dissertations

A century-old disagreement in academia surrounds the question of whether individuals acting alone accomplish all work or whether workers can truly act in concert to meet management's production requirements. Total Quality Management (TQM) is a powerful force today in the industrial world, and the formation of teams to solve short-term problems is one of its fundamental techniques. This dissertation focuses on a particular TQM team with the purpose of understanding the processes it used to meet its goals. This ten-member team functioned for about one year and was assigned goals leading to improved accelerator reliability. The investigator was a member …

Vibration Control With Piezoelectric Actuation Applied To Nonlinear Panel Flutter Suppression, Zhihong Lai

Mechanical & Aerospace Engineering Theses & Dissertations

Panel flutter is a large-deflection limit-cycle motion excited by the airflow, which is only on one side of a panel. The objective of this research is to analytically study the panel flutter limit-cycle suppression using nonlinear vibration control techniques with piezoelectric actuation. It is well known that piezoelectric materials are characterized by their ability to produce an electrical charge when subjected to a mechanical strain. The converse piezoelectric effect can be utilized to actuate a panel by applying an electrical field. Piezoelectric actuators are driven by feedback controllers, and control the panel dynamics. For a simply supported panel with piezoelectric …

Multigrid Acceleration Of Time-Dependent Solutions Of Navier-Stokes Equations, Sarafa Oladele Ibraheem

Mechanical & Aerospace Engineering Theses & Dissertations

Recent progress in Computational Fluid Dynamics is encouraging scientists to look at fine details of flow physics of problems in which natural unsteady phenomena have hitherto been neglected. The acceleration methods that have proven very successful in steady state computations can be explored for time dependent computations. In this work, an efficient multigrid methods is developed to solve the time-dependent Euler and Navier-Stokes equations. The Beam-Warming ADI method is used as the base algorithm for time stepping calculations. Application of the developed algorithm proved very efficient in selected steady and unsteady test problems. For instance, the inherent unsteadiness present in …

Impact Of Field-Dependent Electronic Trapping Across Coulomb Repulsive Potentials On Low Frequency Charge Oscillations, R. P. Joshi, K. H. Schoenbach, P. K. Raha

Bioelectrics Publications

We have performed Monte Carlo simulations to obtain the field dependence of electronic trapping across repulsive potentials in GaAs. Such repulsive centers are associated with deep level impurities having multiply charged states. Our results reveal a field‐dependent maxima in the electronic capture coefficient, and the overall shape is seen to depend on the background electron density due to the effects of screening. Based on the Monte Carlo calculations, we have examined the stability of compensated semiconductors containing such repulsive centers. Our analysis indicates a potential for low frequency charge oscillations which is in keeping with available experimental data.

Reflection High-Energy Electron-Diffraction Study Of Surface Disorder And Anomalous Expansion Of Pb(100), D. Tang, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

The temperature-dependent surface structural behavior of Pb(100) is studied using reflection high-energy electron diffraction. Anomalous surface expansion for temperatures between room temperature to about 500 K is observed. A high density of surface vacancies appears at temperatures above ~ 500 K. © 1994 The American Physical Society.

The World Wide Web And Technology Transfer At Nasa Langley Research Center, Michael L. Nelson, David J. Bianco

Computer Science Faculty Publications

NASA Langley Research Center (LaRC) began using the World Wide Web (WWW) in the summer of 1993, becoming the first NASA installation to provide a Center-wide home page. This coincided with a reorganization of LaRC to provide a more concentrated focus on technology transfer to both aerospace and non-aerospace industry. Use of the WWW and NCSA Mosaic not only provides automated information dissemination, but also allows for the implementation, evolution and integration of many technology transfer applications. This paper describes several of these innovative applications, including the on-line presentation of the entire Technology Opportunities Showcase (TOPS), an industrial partnering showcase …

World Wide Web Implementation Of The Langley Technical Report Server, Michael L. Nelson, Gretchen L. Gottlich, David J. Bianco

Computer Science Faculty Publications

On January 14, 1993, NASA Langley Research Center (LaRC) made approximately 130 formal, 'unclassified, unlimited' technical reports available via the anonymous FTP Langley Technical Report Server (LTRS). LaRC was the first organization to provide a significant number of aerospace technical reports for open electronic dissemination. LTRS has been successful in its first 18 months of operation, with over 11,000 reports distributed and has helped lay the foundation for electronic document distribution for NASA. The availability of World Wide Web (WWW) technology has revolutionized the Internet-based information community. This paper describes the transition of LTRS from a centralized FTP site to …

Electronic Document Distribution: Design Of The Anonymous Ftp Langley Technical Report Server, Michael L. Nelson, Gretchen L. Gottlich

Computer Science Faculty Publications

An experimental electronic dissemination project, the Langley Technical Report Server (LTRS), has been undertaken to determine the feasibility of delivering Langley technical reports directly to the desktops of researchers worldwide. During the first six months, over 4700 accesses occurred and over 2400 technical reports were distributed. This usage indicates the high level of interest that researchers have in performing literature searches and retrieving technical reports at their desktops. The initial system was developed with existing resources and technology. The reports are stored as files on an inexpensive UNIX workstation and are accessible over the Internet. This project will serve as …

A Strategy For Electronic Dissemination Of Nasa Langley Technical Publications, Donna G. Roper, Mary K. Mccaskill, Scott D. Holland, Joanne L. Walsh, Michael L. Nelson, Susan L. Adkins, Manjula Y. Ambur, Bryan A. Campbell

Computer Science Faculty Publications

To demonstrate NASA Langley Research Center's relevance and to transfer technology to external customers in a timely and efficient manner, Langley has formed a working group to study and recommend a course of action for the electronic dissemination of technical reports (EDTR). The working group identified electronic report requirements (e.g., accessibility, file format, search requirements) of customers in U.S. industry through numerous site visits and personal contacts. Internal surveys were also used to determine commonalities in document preparation methods. From these surveys, a set of requirements for an electronic dissemination system was developed. Two candidate systems were identified and evaluated …

Landfill Leachate Production And Gas Generation Numerical Model, John Edward Riester Jr.

Civil & Environmental Engineering Theses & Dissertations

Numerous processes occur in landfills which lend themselves to modeling. Many of the processes are mutually interdependent. An unsteady numerical model is developed combining the major processes. The three-dimensional moisture transport equations and boundary conditions are solved using an implicit finite difference scheme. The boundaries are determined through a two-dimensional runoff model for the landfill surface and a one-dimensional leachate liner flow model at the bottom of the landfill. The runoff model accounts for evapotranspiration, runoff, infiltration, and leachate recirculation. Richard's equation is solved for saturated and unsaturated vertical flows and Darcy's Equation is solved for lateral flow between adjacent …

Finite Element Analysis For Nonlinear Flutter Suppression Of Composite Panels At Elevated Temperatures Using Piezoelectric Materials, Run Chen Zhou

Mechanical & Aerospace Engineering Theses & Dissertations

Nonlinear coupled finite element equations of motion are derived for composite panels with embedded piezoelectric layers subjected to aerodynamic, thermal loads and applied electric fields. The nonlinear equations of motion describe the coupling between a structure and an electrical network through the piezoelectric effect. The von Karman large-deflection strain-displacement relations, quasi-steady first-order piston theory aerodynamics, quasi-steady thermal stress theory and linear piezoelectricity theory are used to formulate the nonlinear coupled panel flutter finite element equations of motion in nodal displacements. The governing equations, which are referred to actuator and sensor equations, form a basis for piezoelectric actuation and sensing. Following …

Materials Recovery Facilities In The United States Virgin Islands: A Regional Facilities Location Model Study, Lloyd O. Prince Jr.

Engineering Management & Systems Engineering Theses & Dissertations

Continental municipalities have derived many benefits from the economies of scale associated with a regional approach to facilities location and management planning. Centralized solid waste processing facilities is an example. Island communities, however, surrounded by miles of ocean, are constrained to a fragmented approach to the facilities location solution. This research was conducted to determine if the regional paradigm suggested in the literature is applicable to a set of island communities connected by an ocean transportation infrastructure. A linear programming (LP) model, constraints and data requirements were developed and applied to a network of islands. A series of hypothetical material …

Emissions Studies For A Natural Gas-Fired Internal Combustion Engine, Carlos M. Buitrago

Mechanical & Aerospace Engineering Theses & Dissertations

Since 1991, a University owned truck has been operating with natural gas. In order to improve emissions performance a different fuel management strategy was developed. With the help of Siemens Automotive in Newport News, VA, a liquid fuel injector was modified to handle natural gas. The basic engine was tested to determine the benefits in emissions that the multi-point injection system can have over the single point injection system that had been used previously. Pre-catalyst, raw exhaust-gas data for the more important pollutants were taken and analyzed in both systems under different loads and intake manifold pressures. In addition, to …

Simulation Of Vertical Tail Buffet In Internal Vortex Breakdown Flows, Mark William Flanagan

Mechanical & Aerospace Engineering Theses & Dissertations

Computational simulation of vertical tail buffet in an internal vortex breakdown flow is considered. The fiuid-flow problem is formulated using the full, compressible, unsteady Navier-Stokes equations which are solved using an implicit, flux-difference splitting, finite volume scheme. The fluid-flow problem is solved in a configured circular duct using quasi-axisymmetric assumptions to simplify the flow equations. A plate is placed transverse to the incoming flow. Solution of the flow in the duct is performed with and without a rigid plate, and with and without an elastic plate. The elastic response of the plate is calculated assuming that it is a cantilever …

Accurate Evaluation Of Homogeneous And Nonhomogeneous Gas Emissivities, Kam-Pui Lee

Mechanical & Aerospace Engineering Theses & Dissertations

Spectral transmittance and total band absorptance of selected infrared bands of carbon dioxide and water vapor are calculated by using the line-by-line and quasi-random band models and these are compared with available experimental results to establish the validity of the quasi-random band model. Various wide-band model correlations (such as Edwards and Balakrishnan, Tien and Lowder, and Felske and Tien) are employed to calculate the total band absorptance and total emissivity of these two gases under homogeneous and nonhomogeneous conditions. These results are compared with available experimental results under identical conditions. From these comparisons. it is found that the quasi-random band …

A New Adjoint Variable Method For The Sensitivity Analysis Of Dynamic Responses, Krishnamoorthy Ramesh

Mechanical & Aerospace Engineering Theses & Dissertations

A new adjoint variable method has been formulated for finding the sensitivity derivatives of dynamic system responses. Though the method can be based on any step-by-step time marching scheme, the Wilson Theta Method has been chosen as the basis of the new formulation . Wilson Theta Method is an implicit numerical integration scheme for finding the dynamic system responses. The new formulation uses the differential form of equations of motion as given by the Wilson Theta Method in its formulation of the adjoint equation. The conventional methods used for finding the sensitivity derivatives, namely, the direct differentiation technique, the central …

Computation Of The Aerodynamic Characteristics Of A Subsonic Transport Aircraft Using A Panel Method, Lillianne Plaster Whitelock Troeger

Mechanical & Aerospace Engineering Theses & Dissertations

An advanced low-order panel method, VSAERO, is applied to a full-configuration transport aircraft. Wing pressure distributions as well as lift, drag, and pitching moment coefficients calculated for the full computational configuration are compared with experimental data. In addition, partial configurations are evaluated computationally to determine the relevance of certain complex aircraft components to the computations. It is shown that the wing-surface pressure distributions and pitching moment coefficient are well predicted by VSAERO. The lift coefficient is consistently overpredicted by the code.

An Evaluation Of The Implementation Of Total Quality Management In A Service Organization, Charles Stanford Stevens

Engineering Management & Systems Engineering Theses & Dissertations

This research consists of a formative evaluation designed to identify the steps necessary to revitalize a formerly successful Total Quality Management (TQM) process at a U.S. Navy engineering and logistics support organization. The research also developed a methodology to account for the fact that the investigator is a well-informed insider who served as one of the principle change agents for the TQM implementation.

The research is based on the researcher's observation that the major cause for the waning implementation was due to senior management and leadership issues and the organization-wide processes with which they interface. The investigation consisted of an …

Cyclo-Static Scheduling Of Large Grain Dataflow Algorithms On A Local Area Atamm Multicomputing Testbed, Sudeepto Roy

Electrical & Computer Engineering Theses & Dissertations

A strategy for cyclo-statically scheduling deterministic large grain dataflow (LGDF) algorithms for distributed execution on loosely coupled multicomputer architectures is presented in this research. The computational paradigm used is the ODU/NASA developed Algorithm To Architecture Mapping Model (ATAMM), which consists of marked graphs and Gantt chart representations that model the iterative execution of deterministic LGDF algorithms for different values of throughput and computation time. It is postulated that the behavior of these algorithms could be represented by the aggregate execution of an ensemble of cyclically shifted threads of a specific node sequence. Assuming the existence of one or more such …

Acoustic Correlates Of Vowel Perception As Determined From Synthesis Experiments With Multi-Tone Stimuli, Zhongjiang Zhang

Electrical & Computer Engineering Theses & Dissertations

An essential requirement of speech signal processing is to extract information (features or parameters) from the speech signal which encode the information carried by the signal. The objective of this thesis work was to examine and evaluate two feature sets as acoustic correlates for vowel perception. They are formants and DCTCs. Formants are the frequencies of spectral peaks of the speech signal. DCTCs are the Discrete Cosine Transform Coefficients of the magnitude spectrum and are thus features which encode the global spectral shape of speech signal.

There are different opinions regarding which feature set is a more accurate representation for …

Simultaneous Aerodynamic Analysis And Design Optimization, Satish Venkatasubra Mani

Mechanical & Aerospace Engineering Theses & Dissertations

An efficient approach for simultaneous aerodynamic analysis and design optimization is presented. Using this approach, the expensive procedure of performing complete steady— state flow analyses at every design-optimization step is avoided, thus addressing the challenge of incorporating computational fluid dynamics software into efficient gradient—based optimization techniques for aerodynamic design. An adjoint—variable method is introduced to nullify the effect of an increased number of design variables in this problem formulation. This approach is successfully tested on two quasi—one—dimensional nozzle—flow problems: a fully supersonic flow, and also a transonic flow with a normal shock. The algorithm is implemented using the direct Newton—iteration …

Numerical Simulation Of Two-Dimensional, Spatially Developing Mixing Layers, Robert V. Wilson

Mechanical & Aerospace Engineering Theses & Dissertations

Numerical simulation of a forced, two-dimensional, spatially-developing mixing layer using a control-volume formulation is performed. Three classes of forcing functions are used at the inlet boundary which are; (i) steady boundary conditions, (ii) combinations of the fundamental, first subharmonic, and second subharmonic modes from linear inviscid stability theory, and (iii) a broad spectrum of modes whose velocity power spectrum and transverse turbulence intensity relationship is taken from experiment. The results show that shear layer rollup occurs for time-dependent inlet boundary conditions and that the resulting vortex dynamics are determined from the subharmonic content of the inlet boundary conditions. It is …

Boundary Layer Influences On The Subsonic Near-Wake Of A Family Of Three-Dimensional Bluff Bodies, Charles Willliam Alcorn

Mechanical & Aerospace Engineering Theses & Dissertations

A study is reported on subsonic bluff body near-wake flows. It has been determined that one family of bluff bodies, namely slanted-base ogive cylinders, can experience either a closed recirculating near-wake, or a longitudinal vortex near-wake depending on the base slant-angle and the Reynolds number. This suggests a dependence of near-wake parameters on the state of the boundary layer ahead of separation. This report addresses the influence of the boundary layer on the near-wake of slanted-base bluff bodies. Experiments were conducted in two facilities, the 6-inch Magnetic Suspension and Balance System (MSBS) at NASA Langley Research Center and the Old …

A Multivariate Quality Control Approach For Automated Manufacturing Systems, Hisham Naim Ashur

Engineering Management & Systems Engineering Theses & Dissertations

In today's competitive manufacturing environment, effective and practical statistical quality control approaches are essential. A successful process control approach needs to provide on line real time monitoring of quality related characteristics.

No longer acceptable is an approach that analyzes quality related data only after the product is produced. A statistical process control approach that monitors the process during production and that reports trouble spots before bad products are made is necessary in an automated manufacturing environment.

An automated manufacturing environment is characterized by high volume production runs and short production cycles. Traditional statistical process control approaches are not capable of …

Absorption Imaging Studies On Intrinsic Gaas, John Samuel Kenney

Electrical & Computer Engineering Theses & Dissertations

A diagnostic technique has been developed which allows recording of the temporal and spatial development of electric field structures in GaAs photoconductive switches. The optical method is based on the Franz-Keldysh effect. Measurements were performed with a Nd:YAG activation laser and a GaAs laser diode as the probe laser. At low applied voltages a 100 atm wide region of high electric field is seen at the cathode only. With increasing voltage strong domain like structures emerge at the anode also. A calibration measurement shows that the electric fields in these domains are well above 50 kV/cm. At a threshold voltage, …

Development Of A Knowledge Based System For Wastewater Pipeline Failure Risk Assessment, Adam Mayanzani Ngaliga

Engineering Management & Systems Engineering Theses & Dissertations

The purpose of this thesis was to study and analyze the wastewater pipeline failure risk assessment process, and then design and develop an effective and efficient wastewater pipeline risk assessment tool for the Hampton Roads Sanitation District, in Virginia, U.S.A. A knowledge based system was developed using an expert system building shell (Xi-Plus).

The system design is based on the knowledge elicited from the experts and literature in sanitary pipeline failure risk evaluation. The knowledge base contains both heuristics and procedural rules. The system interprets the information provided by the user and reasons from that information to reach conclusions on …

Boundary Value Problems In Rectilinearly Anisotropic Thermoelastic Solids, Gilbert Kerr

Mathematics & Statistics Theses & Dissertations

The boundary value problems which are considered are the type that arise due to the presence of a Griffith crack (or cracks) in an anisotropic thermoelastic solid. The thermoelastic field, in such materials, when the infinitesimal theory is employed, is governed by a set of elliptic partial differential equations. The general solution of these equations is expressed in terms of arbitrary analytic functions whose real parts, in turn, are expressed in terms of Fourier type integrals or Fourier series. Integral transform techniques are then used to determine the stress intensity factors (and other pertinent information) for various crack geometries. In …

Studies On Nonequilibrium Phenomena In Supersonic Chemically Reacting Flows, Rajnish Chandrasekhar

Mechanical & Aerospace Engineering Theses & Dissertations

This study deals with a systematic investigation of nonequilibrium processes in supersonic combustion. The two-dimensional, elliptic Navier-Stokes equations are used to investigate supersonic flows with nonequilibrium chemistry and thermodynamics, coupled with radiation, for hydrogen-air systems. The explicit, unsplit MacCormack finite-difference scheme is used to advance the governing equations in time, until convergence is achieved.

For a basic understanding of the flow physics, premixed flows undergoing finite rate chemical reactions are investigated. Results obtained for specific conditions indicate that the radiative interactions vary substantially, depending on reactions involving HO$\sb2$ and NO species, and that this can have a noticeable influence on …

Fiber Enhanced Viscoelastic Damping Polymers And Their Application To Passive Vibration Control, Houchun Xia

Mechanical & Aerospace Engineering Theses & Dissertations

A new composite damping material is investigated, which consists of a viscoelastic matrix and high elastic modulus fiber inclusions. This fiber enhanced viscoelastic damping polymer is intended to be applied to light-weight flexible structures as surface treatment for passive vibration control. A desirable packing geometry for the composite material is proposed, which is expected to produce maximum shear strain in the viscoelastic damping matrix. Subsequently, a micromechanical model is established in which the effect of fiber segment length and relative motion between neighboring fibers are taken into account. Based on this model, closed form expressions for the effective storage and …

Light Injection From An Active Cladding To The Core Of A Fiber Optic Fluorosensor, Alvin Leon Bryant

Electrical & Computer Engineering Theses & Dissertations

A fluorosensor works on the basis of light injection from the clad into the core of an optical fiber. The sensitivity of such a sensor depends on the efficiency of light injection. Conditions necessary for a high injection efficiency are experimentally determined. The refractive index difference between the core and the clad,ⁿcore ^-nclad, must be maximized to achieve a high injection efficiency. Since an air clad has the least refractive index, a bare core fiber will have a maximum efficiency. Standard optical fibers used for communication employ a minimum value for ⁿcore ^-nclad, in order …