Digital Commons Network^™

The Effect Of Grinding On The Sorption Capacity Of Activated Carbon, John Garrett Dempsey

Civil & Environmental Engineering Theses & Dissertations

The current procedure employed to design full scale activated carbon contacting systems is presented in detail and followed by a review of the more important process controls and operating parameters. Inherent limitations of the design procedure are identified, with the need to be able to accurately predict carbon sorption capacity from bench scale analysis determined to be the most important. Some of the more recent models developed to predict activated carbon sorption capacity were analyzed leading to the realization that even the most sophisticated dynamic models were based upon sorption capacities determined from classical isotherm procedures. The validity of the …

Three-Dimensional Elastic-Plastic Finite Element Analysis Of Fatique Crack Growth And Closure, Rahmatollah G. Chermahini

Mechanical & Aerospace Engineering Theses & Dissertations

The purpose of this study was to develop a three-dimensional, elastic-plastic, finite element analysis to investigate crack extension and closure under cyclic loading. The initial study concentrated on the behavior of a straight through crack in a finite-thickness plate subjected to tensile loading (middle-crack tension specimen). The finite element model was composed of 8-noded (linear-strain) isoparametric elements. In the analysis, the material was assumed to be elastic-perfectly plastic. Zienkiewicz's "initial-stress" method, von Mises' yield criterion, and Drucker's normality condition, under small-strain assumptions, were used to account for plasticity. The three-dimensional analysis is capable of extending the crack and changing boundary …

An Analytical And Experimental Study Of Clearance And Bearing-Bypass Load Effects In Composite Bolted Joints, Rajiv Vikas Arun Naik

Mechanical & Aerospace Engineering Theses & Dissertations

A combined analytical and experimental study is conducted to determine the effects of clearance and bearing-bypass loading for mechanically fastened joints in composites. A simple method of analysis is developed to account for the nonlinear effects of bolt-hole clearance. The nonlinear load-contact variations for clearance-fit fasteners are also measured using specially instrumented fasteners. For a quasi-isotropic graphite/epoxy laminate, results show that the contact arc as well as the peak stresses around the hole and their locations are strongly influenced by the clearance. After a slight initial nonlinearity, the peak stresses vary linearly with applied load. The typical clearance levels are …

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.

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 …

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 …

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 …

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 …

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 …

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 …

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) / …

Studies On The Interference Of Wings And Propeller Slipstreams, Ramadas K. Prabhu

Mechanical & Aerospace Engineering Theses & Dissertations

The small disturbance potential flow theory is applied to determine the lift of an airfoil in a nonuniform parallel stream. The given stream is replaced by an equivalent stream with a certain number of velocity discontinuities, and the influence of these discontinuities is obtained by the method of images. Next, this method is extended to the problem of an airfoil in a nonuniform stream of smooth velocity profile. This model allows perturbation velocity potential in a rotational undisturbed stream. A comparison of these results with numerical solutions of Euler equations indicates that, although approximate, the present method provides useful information …

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

Mechanical & Aerospace Engineering Theses & Dissertations

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

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

Block Transform Coding Of Presample Filtered Data, Thomas A. Shull

Electrical & Computer Engineering Theses & Dissertations

This dissertation addresses the application of non-adaptive transform coding for bit rate reduction of presampled filtered data. Transform coding is examined as an alternative to conventional pulse code modulation (PCM) for multi-source, fixed rate data acquisition systems. Typical bandlimiting presample filters introduce redundancy into the sequence of data samples. Linear transformation of successive N-length blocks of the data sequence and subsequent binary coding of the resulting components is shown to lead to reduced average bit rate for the same less distortion as PCM.

Four Butterworth filters, two corresponding to eight bit PCM systems, and two corresponding to ten bit PCM …

Design Of Efficient Algorithms Through Minimization Of Data Transfers, Yong Mo Chong

Electrical & Computer Engineering Theses & Dissertations

This thesis explores the time optimal implementation of computational graphs on a finite register machine. The implementation fully exploits the machine architecture, especially, the number of registers. The derived algorithms allow one to obtain time efficient implementations of a given graph in machines with a known number of registers.

These optimization procedures are applied to digital signal processing graphs. It is shown that the regular structure of these graphs allows one to identify computational kernels which, when used repeatedly, can cover the entire graph. The l- and r-register implementations of Hadamard and Fast Fourier Transforms using various computational kernels are …

On The Space Shuttle Wing Thermal-Structural Analysis, Kumar Krishna Tamma

Mechanical & Aerospace Engineering Theses & Dissertations

A finite element approach for efficient thermal-structural analysis of structures with thermal protection systems (TPS) is described. The approach is applied to Space Shuttle wing structure configurations subjected to reentry heating. New two and three-dimensional finite elements are developed to model heat transfer in the TPS and supporting structure. A typical TPS/Structural element predicts transient nonlinear temperature variations through the TPS thickness and detailed structural temperatures at the TPS/Structure interface. The accuracy of the TPS/Structure approach in two and three-dimensions is evaluated by comparisons with the conventional approach for various configurations of the wing structure. The results indicate that the …

Stability Analysis Of Closed Surge Tanks By Phase-Plane Method, Mostafa A. Sabbah

Civil & Environmental Engineering Theses & Dissertations

The governing equations describing water level oscillations in a closed surge tank with compressed air at the top of the tank are a set of nonlinear ordinary differential equations if the hydraulic system is analyzed as a lumped system. These oscillations are stable or unstable depending on the parameters of the plant and the type and magnitude of the disturbance.

The present available stability criterion has been developed by linearizing the governing equations and is, therefore, valid only for small disturbances.

In the research reported herein, the governing equations are normalized to reduce the number of parameters from nine to …

Improved Finite Element Methodology For Integrated Thermal-Structural Analysis, Pramote Dechaumphai

Mechanical & Aerospace Engineering Theses & Dissertations

An integrated thermal-structural finite element approach for efficient coupling of thermal and structural analysis is presented. New thermal finite elements which yield exact nodal and element temperatures for one-dimensional linear steady-state heat transfer problems are developed. A nodeless variable formulation is used to establish improved thermal finite elements for one-dimensional nonlinear transient and two-dimensional linear transient heat transfer problems. The thermal finite elements provide detailed temperature distributions without using additional element nodes and permit a common discretization with lower order congruent structural finite elements. The accuracy of the integrated approach is evaluated by comparisons with analytical solutions and conventional finite …

Electrical And Structural Properties Of P-N Junctions In Cw Laser Annealed Silicon, M. Maier, D. Bimberg, G. Fernholz, H. Baumgart, F. Phillipp

Electrical & Computer Engineering Faculty Publications

Depth profiles of the electrical quality of ion implanted and cw laser annealed p-n junctions in silicon are obtained for the first time by secondary ion mass spectroscopy. A comparison with the crystallographic properties of the surface and the junction as observed by Nomarski optical microscopy as well as cross-sectional and plan view transmission electron microscopy is made. Samples containing slip dislocations show better insulation and a lower reverse bias current across the p-n junction as compared to samples with a perfect surface in agreement with current-voltage characteristics. Small dislocation loops located at the junction are found to degrade the …

Seeded Oscillatory Growth Of Si Over Sio² By Cw Laser Irradiation, G.K. Celler, L. E. Trimble, K.K. Ng, H.J. Leamy, H. Baumgart

Electrical & Computer Engineering Faculty Publications

Extensive seeded epitaxial growth of crystalline Si over SiO₂ was achieved by an oscillatory regrowth method applied to rectangular Si pads recessed into a thick SiO₂ film. Narrow (≃5 μm) via holes linked the pads with the bulk (100) Si substrate. Oriented single crystals propagated as far as 500 μm from the seeding area, following the long term advance of a scanned focused laser beam.

Water Wave Refraction With Non-Linear Theory, Im Sang Oh

OES Theses and Dissertations

Two different kinds of wave refraction models are formulated in the present study using Stokes' third order wave theory. One type of model is utilized in a parametric study employing several different topographies. Wave trajectories obtained from this model, when obtained by using first and third order wave theory with and without the consideration of energy dissipation, show considerable differences. These differences are examined in more detail for a bottom of constant slope: (1) An approximate 10% difference occurs between the refraction coefficients obtained using the first and the third order wave theory. (2) Considerably different ray trajectories are detected …

Mining The Deep Seabed Implications For International Law And American Foreign Policy, Steven H. Fitzgerald

Graduate Program in International Studies Theses & Dissertations

Whether or not the United States may someday face a mineral shortage, the need for a coherent, unified minerals policy is critical to national objectives and national security. Deep-sea mining may be the answer to American (and world) mineral needs in the twenty-first century. However, there are numerous problems which must be dealt with and resolved in the near future, in order to enable the U.S. (and the world community) to take advantage of vast undersea resources. Deep-sea mining requires the development of technology, tremendous capital investments, and years of labor before production can begin. U.S. policy makers must decide …

Effects Of Multiple Scattering And Surface Albedo On The Photochemistry Of The Troposphere, Tommy Reinhold Robert Augustsson

Mechanical & Aerospace Engineering Theses & Dissertations

A one-dimensional photochemical model of the troposphere containing the species of the nitrogen, oxygen, carbon, hydrogen, and sulfur families has been developed and used to investigate the vertical profiles and the natural (including atmospheric chemical reactions) and anthropogenic sources and sinks of these species. The species continuity equations are solved numerically applying prescribed boundary conditions. The vertical flux is simulated by use of the parameterized eddy diffusion coefficients. Heterogeneous losses (e.g. rainout, gas-to-particle chemistry, and dry deposition), are parameterized to make calculated profiles consistent with measurements. The photochemical model is coupled to a radiative transfer model that calculates the radiation …

Sound Absorption In N2-H2o Gas Mixtures At Room Temperature And Low Frequency/Pressure Ratios, William Axam Griffin

Mechanical & Aerospace Engineering Theses & Dissertations

This study was motivated by a need to obtain standard values of nitrogen's contribution to sound absorption in the Earth's atmosphere. Specific goals included accurate measurements of sound absorption in nitrogen - water vapor mixtures at room temperature and low frequency/pressure ratios, the determination of the N₂ vibrational relaxation peak location, (f/P)_max, on the f/P axis as a function of humidity, h, and critical evaluation of all results.

The free decay technique was used in a resonance tube to obtain ten sets of sound absorption data in N₂-H₂O gas mixtures and requisite companion …

Usage And Limitations Of Characteristic Vector Analysis Of Remote Sensing Multispectral Data For The Identification And Quantification Of Water Quality Parameters, Theodore A. Talay

Civil & Environmental Engineering Theses & Dissertations

Recent applications of the technique of characteristic vector analysis to remote-sensing water color data has met with varying degrees of success. It is apparent from these experiments that a more thorough understanding of the informational capability of characteristic vector analysis is needed.

A Method Of Modeling Multirate Two-Dimensional Recursive Digital Filters Author, Albert P. Gerheim

Electrical & Computer Engineering Theses & Dissertations

This dissertation presents a method of modeling two dimensional sampled data systems with two sampling rates in each dimension. This methodology is applied to the problem of synthesizing two dimensional velocity filters using one dimensional prototypes and multirate concepts.

The modeling method includes the replacement of scalar z-transforms of signals by vectors of polynomials, and the replacement of scalar z-transforms of impulse responses by matrices of polynomials.

The synthesis of velocity filters is accomplished through the use of coordinate transformations in the z-transform domain which skew the ω₁ -ω₂ axes on the unit bidisc. The filters synthesized using …

Slip Dislocation Formation During Continuous Wave Laser Annealing Of Silicon, Helmut Baumgart

Electrical & Computer Engineering Faculty Publications

High-voltage electron microscopy (HVEM) has been used for the investigation of the defect structure in cw laser-annealed silicon. We report for the first time a (HVEM) analysis of the formation processes involved in the nucleation and glide of slip dislocations during epitaxial regrowth by cw laser annealing of ion-implantation damaged silicon layers. Based on the combined optical and HVEM observations a model of the dislocation generation and glide processes is presented.

Sound Absorption In N2-H2O Gas Mixtures At Elevated Temperatures, Roger W. Meredith

Physics Theses & Dissertations

Sound absorption measurements were conducted in N₂ -H₂O gas mixtures at 297, 343, and 387 Kelvin to determine the location of the vibrational relaxation peak of nitrogen on the frequency/pressure, (f/P), axis as a function of humidity and temperature. At low humidities the best fit of the data is to a linear relationship between (f/P)_max and humidity (h) yields a slope of 1 .84 X 10⁴ Hz/ atm mole fraction at all three temperatures. The slope is the same as that reported by Zuckerwar and Griffin (2.00 X 10⁴ Hz/atm mole fraction) but is …

High Resolution Laser Absorption Spectroscopy Of Ozone Near 1129.4 Cm-1, Lawrence N. Majorana

Physics Theses & Dissertations

A Beer's Law experiment was performed with a tunable laser to determine self broadened line shape parameters of one infrared absorption ozone line in the v1 band for ten pressures from 0.26 to 6.29 Torr at 285K. SO₂ line positions were used for wavelength calibration. Line shapes were iteratively fitted to the Voigt function at a Doppler width of 29.54 MHz (HWHM) resulting in values for the integrated line• strength, ( S), of (0.144 +/- 0.007 ) x ·10^-20 cm-1/molecule cm-2, line center frequency, (υ_ο) of 1129.426 cm-1 and the Lorentzian contributions to half width, (α …

An Apparatus For Measuring The Thermal Conductivity Of Cast Insulation Materials, Christine A. Wilkins, Robert L. Ash

Mechanical & Aerospace Engineering Faculty Publications

A steady-state apparatus has been developed for measuring the thermal conductivity of cast materials. The design has employed a novel thermal symmetry arrangement which can permit total electrical isolation of the test material from its surroundings. © 1980 American Institute of Physics