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Full-Text Articles in Physics

Simulation Of Active Control Of Asymmetric Flows Around Slender Pointed Forebodies, Hazem Sharaf El-Din Oct 1994

Simulation Of Active Control Of Asymmetric Flows Around Slender Pointed Forebodies, Hazem Sharaf El-Din

Mechanical & Aerospace Engineering Theses & Dissertations

At high angles of attack, the flowfield over slender forebodies becomes asymmetric with substantial side force, which may exceed the available control capability. The unsteady compressible Navier-Stokes equations are used to investigate the effectiveness of different active control methods to alleviate and possibly eliminate the flow asymmetry and the subsequent side force. Although the research work focuses on active control methods, a passive control method has been investigated. The implicit, Roe flux-difference splitting, finite volume scheme is used for the numerical computations. Both locally-conical and three-dimensional solutions of the Navier-Stokes equations are obtained.

The asymmetric flow over five-degree semi-apex angle ...


Dosimetry Of High-Energy Heavy-Ion Beams Using Energy-Dependent Green's Functions, Sang Yull Chun Oct 1994

Dosimetry Of High-Energy Heavy-Ion Beams Using Energy-Dependent Green's Functions, Sang Yull Chun

Physics Theses & Dissertations

A theoretical description of the transport of high-charge and high-energy (HZE) ion bombardment of biological tissue is developed. The energy-dependent Green’s functions and particle fluxes are obtained for two boundary distributions - the monoenergetic and the Gaussian. Approximate energy-dependent Green’s functions for the collision terms are obtained for computational simplicity. As an application of the energy-dependent Green’s function method, dosimetric quantities, such as dose, dose-equivalent, and average quality factor, for 600A MeV56Fe , 517A MeV 40Ar, and 625A MeV 20Ne ion beams incident on a water target are obtained and compared with the values obtained ...


Flow Simulations About Steady-Complex And Unsteady Moving Configurations Using Structured-Overlapped And Unstructured Grids, James Charles Newman Iii Apr 1994

Flow Simulations About Steady-Complex And Unsteady Moving Configurations Using Structured-Overlapped And Unstructured Grids, James Charles Newman Iii

Mechanical & Aerospace Engineering Theses & Dissertations

The limiting factor in simulating flows past realistic configurations of interest has been the discretization of the physical domain on which the governing equations of fluid flow may be solved. In an attempt to circumvent this problem, many Computational Fluid Dynamic (CFD) methodologies that are based on different grid generation and domain decomposition techniques have been developed. However, due to the costs involved and expertise required, very few comparative studies between these methods have been performed. In the present work, the two CFD methodologies which show the most promise for treating complex three-dimensional configurations as well as unsteady moving boundary ...


High Energy Coupled Nucleon Tranpsort In One Dimension, Stanley L. Lamkin Apr 1994

High Energy Coupled Nucleon Tranpsort In One Dimension, Stanley L. Lamkin

Physics Theses & Dissertations

The problem of energetic nucleon transport through extended bulk matter is considered in the context of the 'straight ahead' approximation. The applicable form of the Boltzmann transport equation is derived and solved in one dimension. The production term for secondary generation nucleons due to nuclear fragmentation includes 'coupling' of the flux to other types of nucleon projectiles. A physically motivated perturbation series approach is developed to enhance solution convergence. The Boltzmann operator is inverted and the flux is computed using a numerical marching scheme. The secondary production integrals are optimized for second order accuracy using a set of analytical benchmarks ...


Prediction Of The Stochastic Behavior Of Nonlinear Systems By Deterministic Models As A Classical Time-Passage Probabilistic Problem, L. M. Ivanov, A. D. Kirwan Jr., O. V. Melnichenko Jan 1994

Prediction Of The Stochastic Behavior Of Nonlinear Systems By Deterministic Models As A Classical Time-Passage Probabilistic Problem, L. M. Ivanov, A. D. Kirwan Jr., O. V. Melnichenko

CCPO Publications

Assuming that the behaviour of a nonlinear stochastic system can be described by a Markovian diffusion approximation and that the evolution equations can be reduced to a system of ordinary differential equations, a method for the calculation of prediction time is developed. In this approach, the prediction time depends upon the accuracy of prediction, the intensity of turbulence, the accuracy of the initial conditions, the physics contained in the mathematical model, the measurement errors, and the number of prediction variables. A numerical application to zonal channel flow illustrates the theory. Some possible generalizations of the theory are also discussed.


Reflection High-Energy Electron-Diffraction Study Of Surface Disorder And Anomalous Expansion Of Pb(100), D. Tang, H. E. Elsayed-Ali Jan 1994

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.


A Fast Numerical Solution Of Scattering By A Cylinder: Spectral Method For The Boundary Integral Equations, Fang Q. Hu Jan 1994

A Fast Numerical Solution Of Scattering By A Cylinder: Spectral Method For The Boundary Integral Equations, Fang Q. Hu

Mathematics & Statistics Faculty Publications

It is known that the exact analytic solutions of wave scattering by a circular cylinder, when they exist, are not in a closed form but in infinite series which converge slowly for high frequency waves. In this paper, a fast numerical solution is presented for the scattering problem in which the boundary integral equations, reformulated from the Helmholtz equation, are solved using a Fourier spectral method. It is shown that the special geometry considered here allows the implementation of the spectral method to be simple and very efficient. The present method differs from previous approaches in that the singularities of ...


Multigrid Acceleration Of Time-Dependent Solutions Of Navier-Stokes Equations, Sarafa Oladele Ibraheem Jan 1994

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 ...