768 Matching Results

Search Results

Advanced search parameters have been applied.

in subjects: "Iterative Methods"

open access

A domain decomposition algorithm for solving large elliptic problems

AN algorithm which efficiently solves large systems of equations arising from the discretization of a single second-order elliptic partial differential equation is discussed. The global domain is partitioned into not necessarily disjoint subdomains which are traversed using the Schwarz Alternating Procedure. On each subdomain the multigrid method is used to advance the solution. The algorithm has the potential to decrease solution time when data is stored across multiple levels of a memory hier… more

Date: January 1, 1991

Creator: Nolan, M.P.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Heat transfer in oscillatory flow. Progress report, January 1983-December 1983

Progress is reported in work with a water tunnel facility and wind tunnel facilities used to study heat transfer in oscillatory flow. Work on both facilities include construction and modifications of the facilities themselves, instrumentation and data acquisition, and experimental measurements. A computer code was developed for the calculation of steady and unsteady heat transfer over the attached portion of the boundary layer. The equations of momentum and energy were recast in their finite-di… more

Date: January 1, 1983

Creator: Telionis, D. P. & Diller, T. E.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Mathematical modeling of the behavior of geothermal systems under exploitation

Analytical and numerical methods have been used in this investigation to model the behavior of geothermal systems under exploitation. The work is divided into three parts: (1) development of a numerical code, (2) theoretical studies of geothermal systems, and (3) field applications. A new single-phase three-dimensional simulator, capable of solving heat and mass flow problems in a saturated, heterogeneous porous or fractured medium has been developed. The simulator uses the integrated finite di… more

Date: January 1, 1982

Creator: Bodvarsson, G.S.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Overview of image reconstruction

Image reconstruction (or computerized tomography, etc.) is any process whereby a function, f, on R/sup n/ is estimated from empirical data pertaining to its integrals, ..integral..f(x) dx, for some collection of hyperplanes of dimension k < n. The paper begins with background information on how image reconstruction problems have arisen in practice, and describes some of the application areas of past or current interest; these include radioastronomy, optics, radiology and nuclear medicine, elect… more

Date: April 1, 1980

Creator: Marr, R.B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Implementing sparse matrix techniques in the ERATO code

The ERATO code computes the stability of an equilibrium with respect to the linear MHD equation. The ERATO code is divided into 5 programs (ERATO1 through ERATO5). This report documents some minor changes made in ERATO3 and a major reorganization of ERATO4. The changes were made to reduce drastically the amount of secondary storage needed by the codes and at the same time improve the efficiency of ERATO4. The ultimate goal is to allow the successful completion of runs with finer meshes than are… more

Date: April 1, 1980

Creator: Scott, D.S.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Unconditionally stable diffusion-acceleration of the transport equation

The standard iterative procedure for solving fixed-source discrete-ordinates problems converges very slowly for problems in optically large regions with scattering ratios c near unity. The diffusion-synthetic acceleration method has been proposed to make use of the fact that for this class of problems the diffusion equation is often an accurate approximation to the transport equation. However, stability difficulties have historically hampered the implementation of this method for general transp… more

Date: January 1, 1982

Creator: Larsen, E.W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Parallel supercomputing: Advanced methods, algorithms and software for large-scale problems

Research has continued with excellent progress and new results on methodology and algorithms. We have also made supporting benchmark application studies on representative parallel computing architectures. Results from these research studies have been reported at scientific meetings, as technical reports and as journal publications. A list of pertinent presentations and publications is attached. The work on parallel element-by-element techniques and domain decomposition schemes has developed wel… more

Date: April 1, 1992

Creator: Carey, G.F. & Young, D.M.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Fast Algorithms for transport models

The first two years of this project were mainly focused on developing fast algorithms for the solution of the equations arising from models of single group isotropic transport of neutrally charged particles in slab geometry. In this context, the equation governing transport is an integral-differential equation involving one space variable and one angle variable. This paper discusses the solution of the equations.

Date: April 1992

Creator: Manteuffel, T.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Simulation of synchrotron motion with rf noise

The theoretical formulation is described that is behind an algorithm for synchrotron phase-space tracking with rf noise and some preliminary simulation results of bunch diffusion under rf noise obtained by actual tracking.

Date: August 1, 1986

Creator: Leemann, B.T.; Forest, E. & Chattopadhyay, S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Discretization on a general staggered grid

A discretization scheme on a general staggered grid is described. This discretization is used in conjunction with an arbitrary Lagrangean-Eulerian method that allows use of a fixed Eulerian grid, a Lagrangean grid, or an adaptive grid. 11 refs.

Date: January 1, 1991

Creator: Sulsky, D.L. (New Mexico Univ., Albuquerque, NM (United States). Dept. of Mathematics and Statistics) & Brackbill, J.U. (Los Alamos National Lab., NM (United States))

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Structural transformation of nickel hydroxide films during anodic oxidation

The transformation of anodically formed nickel hydroxide/oxy-hydroxide electrodes has been investigated. A mechanism is proposed for the anodic oxidation reaction, in which the reaction interface between the reduced and oxidized phases of the electrode evolves in a nodular topography that leads to inefficient utilization of the active electrode material. In the proposed nodular transformation model for the anodic oxidation reaction, nickel hydroxide is oxidized to nickel oxy-hydroxide in the re… more

Date: May 1, 1992

Creator: Crocker, R. W. & Muller, R. H.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Ripple: A New Model for Incompressible Flows with Free Surfaces

A new free surface flow model, RIPPLE, is summarized. RIPPLE obtains finite difference solutions for incompressible flow problems having strong surface tension forces at free surfaces of arbitrarily complex topology. The key innovation is the Continuum Surface Force (CSF) model which represents surface tension as a (strongly) localized volume force. Other features include a high-order momentum advection model, a volume-of-fluid free surface treatment, and an efficient two-step projection soluti… more

Date: January 1, 1991

Creator: Kothe, D.B. & Mjolsness, R.C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

STMVOC User's Guide

This report contains instructions for using the STMVOC numerical simulator. This code, which was developed at Lawrence Berkeley Laboratory, is an extension of the TOUGH geothermal code for use in problems involving subsurface contamination by nonaqueous phase liquids (NAPLs). The code is used for modeling the nonisothermal transport of air, water, and an organic chemical in three fluid phases. A discussion of the physical processes included in the simulator is given along with a brief outline o… more

Date: June 1, 1991

Creator: Falta, R.W. & Pruess, K.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Mathematical software for ODEs

No Description Available.

Date: January 1, 1989

Creator: Shampine, L. F.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Current diffusion in rail-gun conductors

A method has been developed to analyze one- and two-dimensional, nonlinear current diffusion in rail-gun conductors. A nonlinear current-diffusion equation that accounts for the temperature dependence of electrical conductivity has been developed from Maxwell's equations. A finite-difference heat-transfer computer program was adapted to solve the current-diffusion and thermal-diffusion problems for rail-gun conductors in one and two dimensions. The nonlinear current-diffusion equation was also … more

Date: June 1, 1982

Creator: Kerrisk, J.F.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Diagnosis of nonlinear systems using time series analysis

Diagnosis and analysis techniques for linear systems have been developed and refined to a high degree of precision. In contrast, techniques for the analysis of data from nonlinear systems are in the early stages of development. This paper describes a time series technique for the analysis of data from nonlinear systems. The input and response time series resulting from excitation of the nonlinear system are embedded in a state space. The form of the embedding is optimized using local canonical … more

Date: January 1, 1991

Creator: Hunter, N.F. Jr.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Hydrogen mixing in a closed containment compartment based on a 1-D model with convective effects. Final report

A transient one-dimensional finite-difference model was developed to determine the hydrogen concentration variation with position in a closed containment compartment due to radiolysis following a LOCA. The model includes mixing due to molecular and eddy diffusion and natural convection. For representative compartments, the maximum hydrogen concentration difference between the bottom and top of the compartment never exceeds 0.25 volume percent when all three mixing mechanisms are considered for … more

Date: January 1, 1980

Creator: Willcutt, G. J. E., Jr.; Gido, R. G. & Koestel, A.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Acceleration of the inner iteration of the DOT-IV transport code using a new source correction scheme

A detailed description of the steady-state Boltzmann transport equation is given. Then the discrete ordinates method of solving the transport equation is described. The conventional rebalance method, the source correction scheme of rebalance, and a new source correction scheme involving a correction equation with a modified flow term are derived. Difference equations for each version of the source correction scheme are presented. The different versions of the source correction scheme and the co… more

Date: July 1, 1980

Creator: Aull, J.E.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Automatic Differentiation Applied to Unsaturated Flow - ADOL-C Case Study

We have experimented with many variants of the code dual.c for two-dimensional unsaturated flow in a porous medium. The goal has been to speed up the evaluation of derivatives required for a Newton iteration. We have primarily investigated the use of ADOL-C, a C++ tool for automatic differentiation and have come to the following conclusions: three colors suffice for computing the nonlinear portion of the Jacobian. That speeds up the Jacobian evaluation in the original code by a factor of two. T… more

Date: April 1, 1992

Creator: Corliss, G.; Griewank, A.; Wright, S. & Robey, T.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Limited-angle 3-D reconstructions using Fourier transform iterations and Radon transform iterations

The principles of limited-angle reconstruction of space-limited objects using the concepts of allowed cone and missing cone in Fourier space are discussed. The distortion of a point source resulting from setting the Fourier components in the missing cone to zero was calculated mathematically, and its bearing on the convergence of an iteration scheme involving Fourier transforms was analyzed in detail. It was found that the convergence rate is fairly insensitive to the position of the point sour… more

Date: December 1, 1979

Creator: Tam, K.C. & Perez-Mendez, V.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Three-dimensional calculations of fields and loading for loop and folded waveguide ICRF antennas

The ANT and ORION codes have been combined and used to study the loading of various antenna geometries with simple three-dimensional (3-D) effects. Both codes use a slab model with periodic Fourier analysis for modeling the toroidal and poloidal directions. The ANT code is used to prescribe current sets in a vacuum region where the field solutions are obtained analytically of each Fourier mode and matching conditions are used at poloidal/toroidal current sheet locations. Multiple current sheets… more

Date: January 1, 1991

Creator: Carter, M. D.; Baity, F. W.; Batchelor, D. B.; Hoffman, D. J.; Jaeger, E. F.; Swain, D. W. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Application of the implicit TENSOR code to studies of containment of undergound nuclear tests

The TENSOR code, a two-dimensional finite-difference code, has been used extensively for the solution of stress wave propagation problems in materials, particularly those associated with the containment of underground nuclear test. These problems are typically characterized by shock waves at early times and by nearly incompressible flow at later times. To address this type of problem more economically, an implicit Newmark time integration has been implemented. Implicit differencing requires the… more

Date: February 1, 1982

Creator: Burton, D.E.; Bryan, J.B.; Lettis, L.A. Jr. & Rambo, J.T.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Pulsations of delta Scuti stars

A general review of the pulsating {delta} Scuti variables is given including the observed light curves and positions of the stars in the Hertzsprung-Russell diagram. Theoretical interpretations from evolution and pulsation calculations give their masses, radii, luminosities, and even their approximate internal compositions. Three models of these stars are discussed and used to study the nonlinear hydrodynamic behavior of these stars. The hydrodynamic equations and the Stellingwerf method for ob… more

Date: January 1, 1989

Creator: Cox, A. N.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

On adaptive grid computations of variable stars

We show that the use of an implicit adaptive-grid technique is an efficient and up-to-date approach for the calculations of radial oscillations in variable stars. We chose as an illustrative example the radiative envelope of an RR Lyrae variable. For the hydrostatic initial model we compare the Lagrangean ratioed zoning with an adaptive-grid rezoning. We show that the adaptive-grid yields an optimal distribution of the mesh points in the sense that the relevant physical features, the H{minus} a… more

Date: January 1, 1991

Creator: Cox, A.N.; Deupree, R.G. & Gehmeyr, M.

Item Type: Article

Partner: UNT Libraries Government Documents Department