Engineering Commons^™

Dynamic Analysis Of An Earth-Orbiting Satellite Deploying Hinged Appendages, Kevin Fielding Oakes

Mechanical & Aerospace Engineering Theses & Dissertations

The planar liberational dynamics of an arbitrary spacecraft with deployable hinged appendages is presented here both analytically and numerically. The system model consists of a central rigid satellite moving about the earth in a circular orbit at a uniform orbital rate. Attached to the satellite are two unfolding rigid booms with specified mass and length. Tip masses are included at the ends of each boom and deployment is driven by torsional springs at both frictionless hinge points. The equations of motion are developed for both a single- and double-appendage model through the use of Lagrange's equations. The formulation accounts for …

Erosion Of Yellow Brass And Type 304 Stainless Steel In A Gas Blown Spark Gap, Rakasi Madhava Reddy

Mechanical & Aerospace Engineering Theses & Dissertations

Erosion rates of yellow brass and type 304 stainless steel electrodes were studied in air under pulse discharge conditions at a voltage of 100 kV, a current of 20 kA, and pulse durations of 70 ns. Anodes and cathodes, configured vertically, were fitted with removable hemispherical tips having a diameter of 0.95 cm and a mass of 3 gm. Tests were conducted inside a low speed, high pressure wind tunnel at pressures of 30 and 50 psig and air velocities ranging from 0 to 36 nm/s.

Erosion was studied gravimetrically for several flow velocities. As many as 60,000 discharges were …

Deterministic Linear Predictors For Bit Rate Improvement, Dhanvant H. Goradia

Electrical & Computer Engineering Theses & Dissertations

This thesis addresses the application of deterministic linear predictor s for telemetry based systems. Deterministic linear predictors are considered as a viable alternative to block transform coding in order to achieve bit rate reduction. A method of calculating the predictor coefficients of a deterministic linear predictor is presented. The system model is developed parametrically with respect to the bandwidth, polynomial order, signal class and predictor length. Two classes of signals, deterministic and random are analyzed and bounds on the performance of the deterministic linear predictor are established. A family of six pole Butterworth filters are used as presample filters in …

A Non-Linear Vortex Panel Method For Wings With Edge Separation, Vijay Kalburgi

Mechanical & Aerospace Engineering Theses & Dissertations

A global nodal vortex panel method is developed to predict steady aerodynamic loads on rectangular lifting surfaces with side edge separation. The lifting surface and free shear layers are modeled by bound and free vortex sheets respectively, which are then discretized into triangular bound and free vortex panels respectively. On each triangular panel, a linear distribution of vorticity is defined in terms of the global components of vorticity at its nodes. The velocity field induced by any triangular vortex panel is obtained in closed form. The vortex core of the side edge vortex is modeled by a concentrated core of …

An Evaluation Of A Taylor-Galerkin Algorithm For High Speed Inviscid Flows Using Quadrilateral And Triangular Elements, Kim S. Bey

Mechanical & Aerospace Engineering Theses & Dissertations

The Taylor-Galerkin finite element algorithm is used to obtain solutions to the two-dimensional compressible Euler equations. The mathematical formulation of the algorithm is presented for a typical scalar equation. The derivation results in element equations which are assembled over the entire solution domain to obtain the system of equations that are solved explicitly. The algorithm has the unique feature that the finite element matrices can be evaluated in closed form, avoiding expensive numerical integration. Aspects of vector programming strategies and mesh generation important to an effective analysis procedure are also described. Solutions to supersonic flow problems with exact solutions are …

Investigation Of Vscous/Inviscid Interaction In Transonic Flow Over Airfoils With Suction, Chadra S. Vemuru

Mechanical & Aerospace Engineering Theses & Dissertations

The viscous/inviscid interaction over transonic airfoils with and without suction is studied. The streamline angle at the edge of the boundary layer is used to couple the viscous and inviscid flows. The potential flow equations are solved for the inviscid flow field. In the shock region the Euler equations are solved using the method of integral relations. For this the potential flow solution is used as the initial and boundary conditions. An integral method is used to solve the laminar boundary-layer equations. Since both methods are integral methods, a continuous interaction is allowed between the outer inviscid flow region and …

Silicon-On-Insulator Technology By Crystallization On Quartz Substrates, Helmut Baumgart

Electrical & Computer Engineering Faculty Publications

The purpose of the novel zone-melting recrystallization process (ZMR) is to produce single crystalline Si films on Si02 of high crystalline perfection, which are suitable for device fabrication and subsequent industrial applications. However, silicon films grown on amorphous insulating substrates without seeding contain regularly spaced subgrain boundaries as their predominant growth defect and to a lesser degree twin boundaries and some grain boundaries. Detailed materials studies have revealed the core structure of these extended defects and the fundamental mechanisms responsible for subgrain boundary formation. The nature and origin of subgrain boundaries is reviewed and a model for polygonization of the …

Faceting At The Silicon (100) Crystal-Melt Interface: Theory And Experiment, Uzi Landman, W.D. Luedtke, R.N. Barnett, C.L. Cleveland, M.W. Ribarsky, Emil Arnold, S. Ramesh, H. Baumgart, A. Martinez, B. Khan

Electrical & Computer Engineering Faculty Publications

Molecular-dynamics simulations and in situ experimental observations of the melting and equilibrium structure of the crystalline Si(100)-melt interface are described. The equilibrium interface is structured, exhibiting facets established on (111) planes.

An Investigation To Improve Linear Predictive Vocoder Pulse/Noise Excitation Models, Elizabeth Annella Martina Effer

Electrical & Computer Engineering Theses & Dissertations

The quality of synthetic speech from Linear Predictive (LP) vocoders is known to be degraded due to the lack of detail in the commonly used pulse/noise excitation model. In this investigation, it was hypothesized that this degradation is due to the lack of precise timing information in the pulses and to the constraint that each short-time segment of excitation be either an impulse train or white noise. Accordingly, more complex excitation models were implemented using precise timing from peaks in the residual and a mixture of pulses and noise. Since the LP residual is known to be the perfect excitation …

Design Of Multivariable Feedback Control Systems Via Spectral Assignment, Mohsen Marefat

Electrical & Computer Engineering Theses & Dissertations

During the past 15 year s significant advances have been made towards developing viable synthesis- techniques for multivariable feedback control systems. The entire aggregate of this theoretical work has been reviewed and consolidated. Diverse notations have been standardized into a single system. A two-step design philosophy for spectral assignment has been developed which first meets stability and time response requirements by assigning eigenvalues and eigenvector s and then provides for attainment of secondary objectives without significant deviation from the initial assignment. Finally, a computer-aided design package has been created to streamline the process of mathematical calculation and to allow users …

Solar-Assisted Heat Pumps For Low-Temperature Industrial Process Heat Applications, Kamran Fouladi-Semnani

Mechanical & Aerospace Engineering Theses & Dissertations

In recent years, solar energy has been investigated as an alternative to· the fossil fuel based systems for industrial process heat (IPH) applications. Published results in literature indicate that roughly seven percent of total U.S. IPH requirement is in the temperature range of 40-90 °C. The present study, sponsored by Tennessee Valley Authority (TVA), examines the potential of series solar-assisted heat pumps (SAHP) for low-temperature IPH spectrum in the TVA region.

A design method based on utilizability technique is employed to determine the long-term thermal performance of the SAHP system. The transient simulation methodology is also employed to determine the …

Eigenvalue And Eigenvector Design Sensitivity Analysis For Nonlinear Beam Vibrations, Jian-Zhong Yuan

Mechanical & Aerospace Engineering Theses & Dissertations

A beam with immovable ends under large amplitude oscillations is axially subjected to an amplitude-dependent stretching force which is induced by the geometrical nonlinearity. The design sensitivity analysis for such a beam is investigated in this study.

Two variational formulations based on different approximations of nonlinear stretching force are studied firstly. The analytical equations of design sensitivity analysis for these nonlinear eigenproblems are then derived. Finally, a computational scheme using finite element method is developed to calculate the design sensitivity derivatives of the eigenvalue and eigenvector numerically. Numerical examples associated with the nonlinear eigenvalue and eigenvector analysis, as well as …

Design Of A Modulation System Simulator, Vincent Carl Dale

Computational Modeling & Simulation Engineering Theses & Dissertations

The development of a Modulation System Simulator is described. The Modulation System Simulator is used to investigate the performance, in the presence of noise, of various analog and digital modulation systems. The methods of modulation studied using this simulator are amplitude modulation, frequency modulation, pulse amplitude modulation, pulse code modulation, amplitude shift keying modulation, and frequency shift keying modulation. For each of these modulation systems a mathematical model is devised and then analyzed to predict the performance of each modulation system in the presence of noise. The results of this theoretical analysis are then compared with the experimental results obtained …

High Performance Switching Circuits For Vlsi, Ali Reza Feizi

Electrical & Computer Engineering Theses & Dissertations

Interconnection topology and device performance are of major concern in the design of LSI/VLSI systems, Pass networks are very suitable in this regard because of low power consumption, high density, and simple interconnection topology. A special type of pass networks called Binary Tree Structured (BTS) pass networks uses almost minimum number of transistors for the design of switching circuits. An algorithmic procedure is developed here for BTS pass networks which is very efficient in terms of both execution time and memory space. Based on these networks, the necessary and sufficient conditions are derived for the design of multiple-output pass networks. …

Effect Of Grain Characteristics On Liquefaction Potential—In Search Of Standard Sand For Cyclic Strength, Isao Ishibashi

Civil & Environmental Engineering Faculty Publications

Since the original Monterey 0 sand, which had been used for cyclic triaxial testing system calibration, is not available any more, the search for an alternative sand was started. In order to provide useful information for the above purpose, liquefaction potentials were evaluated for Monterey 0 and 0/30 sands and for ASTM Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or 50-mm Cube) (C 109) Ottawa sands from various sources. The results clearly indicated that the liquefaction potential was very sensitive to slight changes in material properties (mean grain size, coefficient of uniformity, sphericity, and volume decrease …

Analog Computer Simulation With Automatic Scaling By Digital Computer, Mark Anthony Motter

Electrical & Computer Engineering Theses & Dissertations

A computer-aided design approach for the simplification of analog computer simulation is presented. The simulation configuration consists of an EAI 2000 analog computer with serial communications link to a PDP — 11/24 digital computer. Under control of the PDP-11, the analog simulations are realized with appropriate time and magnitude scaling which adjusts the range of the simulation coefficients and prevents overloads of the analog components. The analog computer hardware configuration accommodates both stable plants up to eighth order and closed-loop systems up to tenth order. Cascade compensation is provided for the closed-loop systems.

The plant may be described by either …

Removing Fluoride From Drinking Water By Organic Polymers, Eleni Davou Achilleos

Civil & Environmental Engineering Theses & Dissertations

Fluoride is a substance that can provide beneficial or detrimental effects depending on the total amount ingested. Naturally occurring high fluoride concentrations exist in many drinking water supplies. The fluoride removal methods developed in the past have been found to be either impractical and/or not cost effective.

The purpose of this study was to determine whether organic polymers can effectively remove fluoride. The water used in this study contained naturally occurring fluoride concentrations between 4.5 to 5.5 mg/1 and it was collected from the City of Franklin, Virginia, water supply system. Laboratory jar test procedures, which simulated a conventional water …

The Unification And Decomposition Of Processing Structures Using Lattice Theoretic Methods, David L. Livingston

Electrical & Computer Engineering Theses & Dissertations

The purpose of this dissertation is to demonstrate that lattice theoretic methods can be used to decompose and unify computational structures over a variety of processing systems. The unification arguments provide a better understanding of the intricacies of the development of processing system decomposition. Since abstract algebraic techniques are used, the decomposition process is systematized which makes it conducive to the use of computers as tools for decomposition. A general algorithm using the lattice theoretic method is developed to examine the structures and therefore decomposition properties of integer and polynomial rings. Two fundamental representations, the Sino-correspondence and the weighted radix …

Analyses Of Quasi-Isotropic Composite Plates Under Quasi-Static Point Loads Simulating Low-Velocity Impact Phenomena, Ajit Dhundiraj Kelkar

Mechanical & Aerospace Engineering Theses & Dissertations

Composite laminates have high strength to density ratios that make them attractive for use in aircraft structures. However, the damage tolerance of these materials is limited because they have very low ultimate strains, no plastic deformation range, and no usable strength in the thickness direction. These limitations are very obvious when laminates are subjected to impact loads. Due to these impact loads, laminates suffer visible and invisible damage. To improve the material performance in impact requires a better understanding of the deformation and damage mechanics under impact type loads.

In thin composite laminates, the first level of visible damage occurs …

Color Display Of Vowel Spectra As A Training Aid For The Deaf, Amir Jalali Jagharghi

Electrical & Computer Engineering Theses & Dissertations

The objective of this research was to develop a transformation for mapping speech parameters to color parameter. This transformation is done in real-time, and the resulting color parameter are continuously displayed on a color monitor. This visual speech display is to be used as a speech articulation training aid for the deaf. The conversion of speech acoustic signals into speech parameter was accomplished using special -purpose electronics. The real-time conversion of speech parameter to display parameter was controlled by an 8086/8088 microprocessor operating in an S-100 bus structure. The coefficients of the Karhunen-Loeve series expansion of speech power spectra were …

Test Derivation For Cmos Iterative Logic Arrays, Ravi Sharma

Electrical & Computer Engineering Theses & Dissertations

Testability criteria for stuck-open (s-op) faults in one-dimensional unilateral iterative logic arrays (ILA) of CMOS combinational cells are considered in this thesis. A functional fault model to represents-op faults i~ an ILA cell is given. The procedure to detect as-op fault needs a pair of test vectors. The first is used to set up the initial conditions required to test the fault and the second is the test which distinguishes between the good and the bad circuit. Based on this approach necessary and sufficient conditions are given for the testability of as-op fault in a CMOS ILA cell. These conditions …

Selecting Non-Point Source Pollution Treatment Practices Using Linear Optimization, John Gardy Garland Iii

Civil & Environmental Engineering Theses & Dissertations

This paper provides a case study application of a linear optimization program as a water quality management tool. The optimization program seeks to minimize the cost of nonpoint source pollution control by selecting the best combination of pollution control management practices for Hampton, Virginia. The management practice options are grass swale roadways, porous pavers, ponds, detention basins and fertilizer management education. Management practice selection is limited by constraints on land-use and water quality. Pollutants evaluated are total nitrogen, total phosphorus, suspended solids, fecal coliforms and biochemical oxygen demand (five-day). The value in the water quality constraints for pollution loading on …

Structural Self-Shadowing And Its Effects On The Thermal-Structural Behavior Of Orbiting Trusses, Jack Mahaney

Mechanical & Aerospace Engineering Theses & Dissertations

The determination of structural shadowing is described. The computation of environmental heat loads for slender structural members in earth orbit is described, and two methods for finite element thermal analysis are described . The effects of self-shadowing on the thermal structural behavior of single truss members and two different trusses are presented. In each case the shadowing produces a noticeable effect on the temperature distributions on truss members, and on the deformations of the trusses.

Analysis And Optimal Design Of Wind Tunnel Balances, Sung-Ling Twu

Mechanical & Aerospace Engineering Theses & Dissertations

The problem of finding the optimal cross-sectional shape of the elastic cage in wind tunnel balance is formulated and solved numerically. A mathematical model to implement the boundary condition associated with the elastic rigid connection into the finite element method is discussed. Numerical results show that the rigid connection at the end of the elastic cage has significant effect on the stress distribution.

The finite dimensional approach for a three dimensional design sensitivity analysis is derived. Using both the free and rigid boundary conditions, numerical examples are performed and comparisons of the accuracy of design sensitivity analysis between the proposed …

Unsteady Transonic Flow Over Slender Bodies, Cevdet Aydun

Mechanical & Aerospace Engineering Theses & Dissertations

The unsteady transonic small disturbance equation for an oscillating slender body is obtained from the full potential equation in cylindrical coordinates by means of a perturbation analysis. The time-dependent body-boundary condition is reduced into a simpler form by matching the outer and inner flows. Also, a time-dependent pressure coefficient over the slender body is derived by means of a matching principle. The simplified form of the body-boundary condition is incorporated into the difference equations at the body axis. This application allows use of the cylindrical coordinate system for the problem. By prescribing several different body-boundary conditions, various modes of body …

Analytic Forms Of Bidirectional Reflectance Functions For Application To Earth Radiation Budget Studies, Natividad Manalo Smith

Mechanical & Aerospace Engineering Theses & Dissertations

Reflected solar radiative fluxes emerging from the Earth's top of the atmosphere are inferred from satellite broadband radiance measurements by applying bidirectional reflectance functions (BDRFs) to account for the anisotropy of the radiation field. BDRFs are dependent upon the viewing geometry (i.e. solar zenith angle, view zenith angle, and relative azimuth angle), the amount and type of cloud cover, the condition of the intervening atmosphere, and the reflectance characteristics of the underlying surface. A set of operational Earth Radiation Budget Experiment (ERBE) BDRFs is available which was developed from the Nimbus 7 ERB (Earth Radiation Budget) scanner data for a …

Computer Aided Simulation Of A Heating, Ventilating, And Air Conditioning System In A Building, Sunil Shrikrishna Kulkarni

Mechanical & Aerospace Engineering Theses & Dissertations

The Godwin Life Science Building on the Old Dominion University campus presents an interesting problem in terms of energy conservation. The building is the maximum energy resource consumer on the campus, having a criterion value of 234 KBtu/sq.ft-year (2657 MJoules/sq. rneter-year). A Simplified Energy Analysis Method (ASEAM) loads and systems computer program was used to simulate the building and its heating, ventilating, and air conditioning (HVAC) plant in order to understand the building's high annual energy resource consumption rate, and to devise ways to overcome it. The main goal was to assess and propose energy conservation improvements to the existing …

Long-Term System Performance Of A Direct Expansion Solar Assisted Heat Pump, Majid Abazeri

Mechanical & Aerospace Engineering Theses & Dissertations

The long-term thermal performance of a direct expansion solar assisted heat pump is determined from the transient system simulation of the system. The system employs a bare collector which also acts as the heat pump evaporator. Of particular interest in this study is the

configuration in which the compressor and the collector area are properly matched from the long-term thermal performance viewpoint. This matching is achieved through continuous as well as two step compressor capacity modulation. In addition to examining the effects of compressor capacity modulation, the effects of various system parameters such as collector area„ storage volume, load temperature, …

The Direct Summation Of Totally Self-Checking Checkers, Stefean Andrew Fedyschyn

Electrical & Computer Engineering Theses & Dissertations

A new technique for reducing the complexity of designing Totally Self-Checking (TSC) checkers for m-out-of-n codes is presented. The method is based on the partitioning of the input variables into r classes, then partitioning the code groups generated into Z output partitions. Comparison with earlier results reveals improvements in design simplicity and logic and testing complexity.

This thesis also presents a new method of TSC checker design where a j-level m₁/n₁ code and a k-level m₂/n₂ code TSC checker are directly summed to form a max [j,k]-level (m₁ + m₂) / …

Groundwater Management By Linear Programming, Seungho Song

Civil & Environmental Engineering Theses & Dissertations

Three hydraulic optimization models are developed. These models combine the finite difference equations of two-dimensional groundwater flow in composite aquifers with various linear programming techniques. The hydraulic submodel employed in these hydraulic optimization models is so versatile that it accounts for time varying pumpage, leaky artesian conditions, a variety of boundary conditions, induced infiltrations from streams or rivers, and conversion from artesian to water table conditions. The objective of submodel 1 is to maximize the total hydraulic head from pumping wells at the end of a study period. The objective of submodel 2 is the same as submodel 1, but …