Engineering Commons^™

Analysis And Design Sensitivity Computations Of Nonlinear Free And Forced Vibrations Of Stepped Beams, Yong Xiang Xue

Mechanical & Aerospace Engineering Theses & Dissertations

A finite element method is developed in this thesis for analyzing stepped beams under nonlinear free and forced vibrations. A new assumption is made to improve an existing finite element procedure for treating beams of nonuniform cross sections. The geometric nonlinearity results from the nonlinear, strain-displacement relation due to large deflection of a beam.

Based on an improved finite element procedure a computational method is then established for design sensitivity analyses of nonlinear eigenproblems pertaining to the free and forced nonlinear vibrations of beams. It is found that the equation for computing the design sensitivity of eigenvector is linear and …

Analysis And Optimal Design Of Pyramidal Truss Core Panels, Mark A. Wiseman

Mechanical & Aerospace Engineering Theses & Dissertations

The Pyramidal Truss Core Panel has been developed to save weight in applications normally devoted to solid plates. Present design formulas use classical beam theory with engineering assumptions made for moment of inertia and shear modulus determinations. Analysis with the SUPERSAP finite element code indicates that the present theory provides good prediction for the plate stresses but may be inadequate for the core stress and deflection determination. Two optimization routines are presented. The first procedure uses a batch file to execute separate programs with SUPERSAP used as the analysis code. The second combines a FORTRAN program used for analysis with …

Topology And Grid Adaption For High-Speed Flow Computations, Jamshid Samareh Abolhassani

Mechanical & Aerospace Engineering Theses & Dissertations

This study investigates the effects of grid topology and grid adaption on numerical solutions of the Navier-Stokes equations. In the first part of this study, a general procedure is presented for computation of high-speed flow over complex three-dimensional configurations. This includes the grid generation and solution algorithm for Navier-Stokes equations in a general three-dimensional curvilinear coordinate system. The flow field is simulated on the surface of a Butler wing in a uniform stream. Results are presented for Mach number 3.5 and a Reynolds number of 2,000,000. The O-type and H-type grids have been used for this study, and the results …

The Influence Of Transverse Magnetic Fields On The Current-Voltage Characteristics Of Glow Discharges, Thomas J. Powers

Electrical & Computer Engineering Theses & Dissertations

In low pressure discharges, operated in electronegative gas mixtures to the right of the Paschen curve minimum, the discharge resistance can be increased by application of transverse magnetic fields. In this range of operation, both the mean free path and the larmor radius are small compared to the discharge dimensions. The relationship between the electric field and the magnetic field is therefore controlled by electron- molecule collisional processes. Specifically, the magnetically induced increase in the discharge resistance is caused by a downward shift of the electron energy distribution which leads to an increase in attachment and a reduction in ionization. …

Computation Of 2-D And 3-D Natural Convection Heat Transfer In Closed And Vented Cavities, T. O. Mohieldin

Mechanical & Aerospace Engineering Theses & Dissertations

The natural convective heat transfer in closed and vented cavities has been studied numerically, using the primitive variables formulation. A two-and three-dimensional enclosure, and a two-dimensional Trombe Wall channel geometries are considered. The flow has been assumed to remain Laminar, and Boussinesq approximation is invoked for solving the governing equations, The finite-difference method used in this study, is based on the SIMPLER algorithm which uses a combination of central and upwind differencing scheme to obtain stable numerical results.

For both geometries, namely the closed and vented cavities, the fundamental nature of the fluid dynamic and heat transfer characteristics is revealed …

Direct Simulation Of Hypersonic Transitional Flows Over Blunt Slender Bodies, Vincent Cuda Jr.

Mechanical & Aerospace Engineering Theses & Dissertations

Hypersonic transitional flow has been studied using the Direct Simulation Monte Carlo method. The cylindrically blunted wedge and spherically blunted cone were examined for body half angles of 0°, 5° and 10°, at a flight velocity of 7.5 km/s, zero angle of incidence and altitudes of 70 to 100 km. Those geometries and flow conditions are important considerations for hypersonic vehicles currently under design. Surface chemistry was examined for diffuse, finite-catalytic surfaces. Nonequilibrium chemistry and nonequilibrium thermodynamics were considered for both configurations at all altitudes.

Numerical simulations showed that rarefied gas effects, such as surface temperature jump and velocity slip, …

Structural Sensitivity Analysis On A Parallel Computer, Niu Kian Teck

Civil & Environmental Engineering Theses & Dissertations

Substructuring formulation using adjoint variable approach has been developed for design sensitivity analysis and optimization of large scale structures. In this study, the procedure for statics and sensitivity analysis are re-examined to propose a programming scheme which can be implemented either in a sequential or parallel environment. The computational times of the substructuring formulation using a single processor versus multi-processors are compared to see the effectiveness of the formulation in the concurrent computing environment.

Software Tools For Performance Evaluation Of Concurrent Processing, Rodrogo A. Obando

Electrical & Computer Engineering Theses & Dissertations

The development and use of software tools for performance evaluation of concurrent processing is presented in this thesis. The particular concurrent processing architecture proposed by Stoughton and Mielke is investigated. The modelling of this architecture is based on Petri net theory and it can be studied making use of circuit theory. Computation of lower bounds for Time Between Outputs (TBO) and Time Between Input and Output (TBIO) can be accomplished by using principles of circuit theory, among others. This new modelling needs to be deeply evaluated and studied. This evaluation and study is accomplished with the tools developed and presented …

The Effects Of Nonlinear Damping On The Large Deflection Response Of Structures Subjected To Random Excitation, Chunchu Bhavani Prasad

Mechanical & Aerospace Engineering Theses & Dissertations

Effects of both nonlinear damping and large deflection stiffness are included in the theoretical analysis in an attempt to explain the experimental phenomena of aircraft panels excited at high sound pressure levels; that is the broadening of the strain response peak and the increase in modal frequency. Beams and symmetrically laminated plates subjected to acoustic excitation are considered in the analyses. The excitations are ergodic and Gaussian with zero mean. A polynomial containing both linear and nonlinear damping terms is considered as a damping model. Galerkin's method is used to derive modal equations. Direct equivalent linearization is used to solve …

A Numerical Study Of Three-Dimensional Vortex Breakdown, Robert Edward Spall

Mechanical & Aerospace Engineering Theses & Dissertations

A numerical simulation of vortex breakdown using the time-dependent Navier-Stokes equations was performed. Unlike previous studies, the numerical algorithm, formulated in terms of the velocity and vorticity, was not restricted to axisymmetric flows. Prototype vortices were parameterized in terms of their Reynolds number and Rossby number. Two cases were studied extensively. In one case, a vortex was imbedded in a uniform free stream. In the other case, the axial velocity of the free stream was decelerated in the streamwise direction. For both cases breakdown occurred when the Rossby number was below a critical value. Vortex lines, particle traces and velocity …

Experimental Study Of Shock Wave Interference Heating On A Cylindrical Leading Edge, Allan R. Wieting

Mechanical & Aerospace Engineering Theses & Dissertations

An experimental study of shock wave interference heating on a cylindrical leading edge representative of the cowl of a rectangular hypersonic engine inlet at Mach numbers of 6.3, 6.5, and 8.0 is presented. Stream Reynolds numbers ranged from 0.5 x 10⁶ to 4.9 x 10⁶ per foot and stream total temperature ranged from 2100 °R to 3400 °R. The model consisted of a 3-inch-diameter cylinder and a shock generation wedge articulated to angles of 10, 12.5, and 15 degrees. The primary goal of this study was to obtain a fundamental understanding of the fluid mechanics of shock wave …

Finite Element Methodology For Nonlinear Free And Harmonic Forced Vibrations Of Beam And Plate Structures, Kamolphan Decha-Umphai

Mechanical & Aerospace Engineering Theses & Dissertations

The literature and experiments have shown that nonlinear vibrations produce significant effects in structural analysis, especially the frequency-amplitude-force relation and the analysis of strain. An analysis was developed to predict both the frequency-amplitude-force relation and strains of beam and plate structures. Two finite element methods were developed, namely, the iterative single-mode method (method I) and the multiple-mode method (method II). The harmonic force matrix was developed to analyze nonlinear forced vibrations. Nonlinear free vibration was a special case of the general forced vibration by setting the harmonic force matrix equal to zero. The harmonic force matrix represents the external applied …

Experimental Parametric Study Of A True Airspeed Sensor, Adel R. Ibrahim

Mechanical & Aerospace Engineering Theses & Dissertations

The results of an experimental parametric study of a true airspeed sensor are presented. The objective of this study was primarily to investigate experimentally the parameters that effect the frequency response of the true airspeed sensor. A secondary objective was to identify the sensor configuration which achieved the best performance. The model used to conduct these experiments basically consisted of swirl generator and vortex tube sections and pick-up signal system. A regression analysis was performed on the experimental results to obtain the effect of each parameter individually on the frequency response. The most significant parameters were selected by the regression …

Coupled Bending-Torsion Steady-State Response Of Pretwisted, Nonuniform Rotating Beams Using A Transfer-Matrix Method, Carl E. Gray Jr.

Mechanical & Aerospace Engineering Theses & Dissertations

Using the Newtonian method, the equations of motion are developed for the coupled bending-torsion steady-state response of beams rotating at constant angular velocity in a fixed plane. The resulting equations are valid to first order strain-displacement relationships for a long beam with all other nonlinear terms retained. In addition, the equations are valid for beams with the mass centroidal axis offset (eccentric) from the elastic axis, nonuniform mass and section properties, and variable twist. The solution of these coupled, nonlinear, nonhomogeneous, differential equations is obtained by modifying a Hunter linear second-order transfer-matrix solution procedure to solve the nonlinear differential equations …

Implementation And Performance Analysis Of Numerical Algorithms On The Mpp, Flex/32, And Cray/2, Raad A. Fatoohi

Electrical & Computer Engineering Theses & Dissertations

This dissertation presents the results of the implementation of a number of numerical algorithms on three parallel/vector computers. The object of this research is to determine how well, or poorly, a number of numerical algorithms would map onto three different architectures and to analyze the performance of these architectures using these algorithms. These algorithms are: a relaxation scheme for the solution of the Cauchy-Riemann equations, an ADI method for the solution of the diffusion equation, and a compact difference scheme for the solution of two-dimensional Navier-Stokes equations. The computers were chosen so as to encompass a variety of architectures. They …

Comment On "Orientation, Alignment, And Hyperfine Effects On Dissociation Of Diatomic Molecules To Open Shell Atoms", Mark D. Havey, Linda L. Vahala

Electrical & Computer Engineering Faculty Publications

A recent paper in this journal [Y. B. Band e t a l., J. Chem. Phys. 8 4, 3762 (1986)] reported parameters describing orientation and alignment produced, in an axial recoil limit, by one photondissociation of diatomic molecules. Reported also were values, applicable to the resonance transitions of the alkali atoms, for orientation and alignment depolarization coefficients. Most of the numerical values reported for the coefficients were incorrect, in some cases by as much as a factor of 2. We report a tabulation of correct depolarization coefficients applicable to the resonance transitions of common alkali isotopes. Further, the coefficients …

An Investigation Of Overvoltage Effects On A Gas-Blown Spark Gap, Michael Steven Mazzola

Electrical & Computer Engineering Theses & Dissertations

This experimental investigation addresses the anomalous overvoltage breakdown and subsequent recovery characteristics observed in gas-blown spark gaps. Previous investigations have reported a two-stage recovery process in self-break, pulse-charged, gas-blown spark gape in which the spark gap recovers first to an intermediate breakdown strength before recovering to the undisturbed breakdown voltage. The recovery process has been explained in terms of two different characteristic times. The first is that required to obtain initial recovery in which the spark gap regains its intrinsic breakdown strength. The second time is that required to obtain final recovery in which the pulse-charged spark gap regains the …

A Frequency Domain Digital Signal Processor For Laser Velocimeter Systems, Andreas Evangelos Savvakis

Electrical & Computer Engineering Theses & Dissertations

A new signal processor for laser velocimeter systems is proposed. The proposed processor incorporates automatic initialization, real time operation, and can efficiently process input signals comprised of as low as 150 photons, with mean oscillation frequency up to 100 MHZ, and input turbulence from 0 to 20%. A bank of digital bandpass filters is employed for the energy spectrum estimation of the input signal. A deterministic model is developed to describe the relationship between the filter output energies and the input signal parameters. The input frequency is estimated by linearly weighting the filter output energies. A spline function approximation approach …

Calibration Of Old Dominion University Low-Speed Wind Tunnel, Nicolaos P. Sargianos

Mechanical & Aerospace Engineering Theses & Dissertations

No Abstract.

Wind Streamline Ambiguity Removal Of Microwave Scatterometer Data, Hans W. Zaepfel

Electrical & Computer Engineering Theses & Dissertations

There is a class of satellite microwave scatterometers that return oceanographic information which includes wind vectors with directional ambiguity. The first part of the ambiguity removal process is to reduce the data to a directional ambiguity of 180°. This thesis shows that wind direction change contains the information required for streamline ambiguity removal and that syntactic pattern recognition techniques can be used to locate the areas of wind direction change. Spreading the information along the areas of wind direction change results in the removal of the streamline ambiguity. The algorithm is implemented and the results are presented showing that it …

Chemoviscosity Modeling Of Thermosetting Resins, Jia-Mo Bai

Mechanical & Aerospace Engineering Theses & Dissertations

A new analytical model for simulating chemoviscosity of thermosetting resin has been formulated. The model is developed by modifying the well-established Williams-Landel-Ferry (WLF) theory in polymer rheology for thermoplastic materials. By introducing a relationship between the glass transition temperature Tg (t) and the degree of cure a(t) of the resin system under cure, the WLF theory can be modified to account for the factor of reaction time. Temperature-dependent functions of the modified WLF theory constants C₁(T) and C₂(T) were determined from the isothermal cure data. Theoretical predictions of the model for the resin under dynamic …

Optimal Cure Cycle Design Of A Resin-Fiber Composite Laminate, Jeenson Sheen

Mechanical & Aerospace Engineering Theses & Dissertations

High performance polymeric composites have been experiencing increasing usage in the aerospace and automobile industries. Such materials are commonly composed of long or chopped fibers embedded in the thermosetting resin matrix. Changes in physical and chemical properties of such composite materials during the cure process are rather complex. Thus, it is not a trivial task to properly design a cure cycle (temperature and pressure profiles) for a cure process. The material should be cured uniformly and completely with the lowest void content; the temperature inside the laminate must not exceed some maximum value; and the cure process should be completed …

An Experimental And Analytical Investigation Of Incompressible Fluid Flow Through A Distensible Tube System, Steven C. Wells

Mechanical & Aerospace Engineering Theses & Dissertations

An analysis was made of pressure and flow in a novel elastic tube system which has been used to theorize certain aspects of renal hemodynamic cs. Validation of the theory could alter the treatment of certain heart and kidney disorders. In an attempt to better understand a system flow anomaly under steady driving head conditions, experiments were performed, and a mathematical model was developed. The development of the model incorporated a set of nonlinear differential and algebraic equations. Using a finite-difference analysis as the method for obtaining a numerical solution, various pressures and flows were obtained. Results for the steady-state …

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 …

A Quantitative Approach To Simulation And Analysis Of Storm Water Systems, John Nathan Paine

Civil & Environmental Engineering Theses & Dissertations

A generalized package of hydrologic and hydraulic models and programs is developed for the quantitative analysis of watersheds and drainage networks. The package is microcomputer based and is available to interested parties. Full documentation is included in the Appendix. The approach applies a lengthy historical rainfall record to the system in continuous simulation. One of the most powerful operational hydraulic routing models available is adopted into the package. Output takes the form of statistical predictions of flood stages, discharges, storage requirements, and rainfall analyses for various return-periods. Computer runs are completely summarized. The package was applied to a 969-acre watershed …

Laser Pump And Probe Excited State Absorption Measurements, Shawpin Jong

Electrical & Computer Engineering Theses & Dissertations

A pump and probe technique was used to investigate triplet-triplet excited state absorption in solutions of the scintillators 2,5 diphenyloxazole (PPO) and 2,1 naphthyl,5 phenylzole (a-NPO) in several solvents.

KrF excimer radiation (248 nm) was used to pump the samples under investigation as well as a tunable dye laser which was used as the probe. Time-resolution was obtained by changing the optical path difference between the pump and probe beams.

Transient excited state absorption was measured in a wide spectral region between 330 nm and 600 nm, showing a peak at 400 nm for PPO solutions, and two …

Convective Heat Transfer From Circular Cylinders Located Within Perforated Cylindrical Shrouds, Kamran Daryabeigi

Mechanical & Aerospace Engineering Theses & Dissertations

The influence of perforated cylindrical shrouds on the convective heat transfer to circular cylinders in transverse flow has been studied experimentally. Geometries studied were similar to those used in industrial platinum resistance thermometers. The influence of Reynolds number, ventilation factor (ratio of the open area to the total surface area of shroud), radius ratio (ratio of shroud's inside radius to bare cylinder's radius), and shroud orientation with respect to flow were studied.

The experiments showed that perforated shrouds with ventilation factors in the range 0.1 to 0.4 and radius ratios in the range 1.1 to 2.1 could enhance the convective …

An Investigation Of High Strength To Weight Corrugated Compression Panels With Non-Load Carrying Webs, Charles Thomas Lee Mills

Mechanical & Aerospace Engineering Theses & Dissertations

An investigation of the weight saving potential of corrugated compression panel concepts using curved elements and non-load carrying webs was performed. The concepts investigated were corrugated panels with flat and curved caps with beaded webs. These concepts utilize a beaded web that carries negligible axial load but is very stiff in the transverse direction. Therefore the web substantially stabilizes the load carrying caps to produce a high weight-strength efficient structure.

The optimum geometry parameters were determined using an iterative solution method employing simplified buckling assumptions. The results were checked with a non-linear optimization program coupled to a rigorous buckling analysis. …