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in subjects: "Lagrangian Function"

open access

Simulation of Alfven wave-resonant particle interaction

New numerical simulations are presented on the self-consistent dynamics of energetic particles and a set of unstable discrete shear Alfven modes in a tokamak. Our code developed for these simulations has been previously tested in the simulations of the bump-on-tail instability model. The code has a Hamiltonian structure for the mode-particle coupling, with the superimposed wave damping, particle source and classical relaxation processes. In the alpha particle-Alfven wave problem, we observe a t… more

Date: July 1, 1995

Creator: Berk, H.L.; Breizman, B.N. & Pekker, M.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

A Regularized Galerkin Boundary Element Method (RGBEM) for Simulating Potential Flow About Zero Thickness Bodies

The prediction of potential flow about zero thickness membranes by the boundary element method constitutes an integral component of the Lagrangian vortex-boundary element simulation of flow about parachutes. To this end, the vortex loop (or the panel) method has been used, for some time now, in the aerospace industry with relative success [1, 2]. Vortex loops (with constant circulation) are equivalent to boundary elements with piecewise constant variation of the potential jump. In this case, ex… more

Date: October 1, 1999

Creator: Gharakhani, Adrin & Wolfe, Walter P.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Shock-recovery experiments of sandstone under dry and water-saturated conditions

Shock-recovery experiments have been performed on Berea Sandstone under dry and water-saturated conditions using a single-stage light-gas gun. Stress levels in the range between 3.1 and 9.8 GPa were achieved by impacting projectiles in a recovery fixture. The microstructural damage of the shocked samples were analyzed with scanning electron microscopy (SEM), laser particle analysis and X-ray computed micro tomography (XCMT). The dry samples show strongly and irregularly fragmented quartz grains… more

Date: September 3, 1999

Creator: Hiltl, M; Nellis, W J; Swift, R P; Hagelberg, C R & Carney, T C

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

A Model for Molten Fuel-Coolant Interaction during Melt Slumping in a Nuclear Reactor

This paper describes a simple fuel melt slumping model to replace the current parametric model in SCDAP/RELAP5. Specifically, a fuel-coolant interaction (FCI) model is developed to analyze the slumping molten fuel, molten fuel breakup, heat transfer to coolant, relocation of the molten droplets, size of the partially solidified particles that settle to the bottom of the lower plenum, and melt-plenum interaction, if any. Considering our objectives, the molten fuel jet breakup model, and fuel dro… more

Date: October 1, 1999

Creator: Siefken, L. J. & Sohal, M. S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Numerical simulations of turbulent dispersion around buildings via a lagrangian stochastic particle model

This paper describes a numerical modeling approach that can be used to provide estimates of air concentrations due to emissions at industrial sites or other sites where buildings may have an important impact on the dispersion patterns. The procedure consists of two sequential steps: (i) Prediction of mean flow and turbulence fields via a turbulent flow model; and, (ii) Employment of the calculated flow and Turbulence fields to drive a Lagrangian Stochastic Particle Model. Two flow scenarios in … more

Date: July 1, 1995

Creator: Lee, R.L. & Naeslund, E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Numerical Analysis of Spherically Convergent Rayleigh-Taylor Experiments on the Nova Laser

In the frame of a CEA/US DOE collaboration, convergent experiments have been done on the Nova laser. Numerical simulations with our 2D Lagrangian code FCI2 led the analysis and correctly reproduced the experimental data. From single mode 2D perturbations, ablation front Rayleigh-Taylor instability growth is computed. Moderate and high convergence ratios are addressed. The shrinking of the wavelength plays a prominent role for small convergence ratio and weakly nonlinear hydrodynamics.

Date: August 23, 1999

Creator: Cherfils, C.; Galmiche, D.; Glendinning, S. G.; Laffite, S.; Remington, B. A. & Wallace, R. J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The large-N{sub c} renormalization group

In this talk, we review how effective theories of mesons and baryons become exactly soluble in the large-N{sub c}, limit. We start with a generic hadron Lagrangian constrained only by certain well-known large-N{sub c}, selection rules. The bare vertices of the theory are dressed by an infinite class of UV divergent Feynman diagrams at leading order in 1/N{sub c}. We show how all these leading-order dia, grams can be summed exactly using semiclassical techniques. The saddle-point field configura… more

Date: May 1, 1995

Creator: Dorey, Nicholas & Mattis, Michael P.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Periodic Boundary Conditions in the ALEGRA Finite Element Code

This document describes the implementation of periodic boundary conditions in the ALEGRA finite element code. ALEGRA is an arbitrary Lagrangian-Eulerian multi-physics code with both explicit and implicit numerical algorithms. The periodic boundary implementation requires a consistent set of boundary input sets which are used to describe virtual periodic regions. The implementation is noninvasive to the majority of the ALEGRA coding and is based on the distributed memory parallel framework in AL… more

Date: November 1, 1999

Creator: AIDUN,JOHN B.; ROBINSON,ALLEN C. & WEATHERBY,JOE R.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Investigation of particle/gas flow characteristics in pipelines.

Gas-solid flows occur frequently in many industrial processes and systems, such as in pulverized coal transport pipelines and portions of fluid catalytic cracking (FCC) risers. Many of these systems have been modeled and optimized over the years by ''engineering know-how,'' which has been derived from the operating experience with the unit. However, it is being recognized that a more detailed, analytic tool is necessary to improve the efficiency of these systems due to heightened industrial com… more

Date: July 14, 1999

Creator: Golchert, B. M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

VMD, the WZW Lagrangian and ChPT:The Third Mixing Angle

We show that the Hidden Local Symmetry Model, supplemented with well-known procedures for breaking flavor SU(3) and nonet symmetry, provides all the information contained in the standard Chiral Perturbation Theory (ChPT) Lagrangian L{sup (0)} + L{sup (1)}. This allows to rely on radiative decays of light mesons (VP{gamma} and P{gamma}{gamma}) in order to extract some numerical information of relevance to ChPT: a value for {Lambda}{sub 1} = 0.20 {+-} 0.04, a quark mass ratio of {approx_equal} 21… more

Date: March 31, 1999

Creator: O'Connell, Heath B

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

JAC3D -- A three-dimensional finite element computer program for the nonlinear quasi-static response of solids with the conjugate gradient method; Yucca Mountain Site Characterization Project

JAC3D is a three-dimensional finite element program designed to solve quasi-static nonlinear mechanics problems. A set of continuum equations describes the nonlinear mechanics involving large rotation and strain. A nonlinear conjugate gradient method is used to solve the equation. The method is implemented in a three-dimensional setting with various methods for accelerating convergence. Sliding interface logic is also implemented. An eight-node Lagrangian uniform strain element is used with hou… more

Date: February 1, 1993

Creator: Biffle, J. H.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Modeling Atmospheric Deposition from a Cesium Release in Spain using a Stochastic Transport Model

This paper discusses the incorporation of dry and wet deposition into a stochastic particle transport model (the Lagrangian Particle Dispersion Model, LPDM (Uliasz 1993)).

Date: October 7, 1999

Creator: Buckley, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Particle Transport in Parallel-Plate Reactors

A major cause of semiconductor yield degradation is contaminant particles that deposit on wafers while they reside in processing tools during integrated circuit manufacturing. This report presents numerical models for assessing particle transport and deposition in a parallel-plate geometry characteristic of a wide range of single-wafer processing tools: uniform downward flow exiting a perforated-plate showerhead separated by a gap from a circular wafer resting on a parallel susceptor. Particles… more

Date: August 1, 1999

Creator: Rader, D.J. & Geller, A.S.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

One-loop corrections to the D3 brane action.

We calculate one-loop corrections to the effective Lagrangian for the D3 brane. We perform the gauge-fixing of the {kappa}-symmetric Born-Infeld D3 brane action in the flat background using Killing gauge. The linearized supersymmetry of the gauge-fixed action coincides with that of the N = 4 Yang-Mills theory. We use the helicity amplitude and unitarity technique to calculate the one-loop amplitudes at order {alpha}{sup 4}. The counterterms and the finite 1-loop corrections are of the form ({pa… more

Date: June 30, 1999

Creator: Shmakova, Marina

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Relabeling symmetries in hydrodynamics and magnetohydrodynamics

Lagrangian symmetries and concomitant generalized Bianchi identities associated with the relabeling of fluid elements are found for hydrodynamics and magnetohydrodynamics (MHD). In hydrodynamics relabeling results in Ertel`s theorem of conservation of potential vorticity, while in MHD it yields the conservation of cross helicity. The symmetries of the reduction from Lagrangian (material) to Eulerian variables are used to construct the Casimir invariants of the Hamiltonian formalism.

Date: April 1, 1996

Creator: Padhye, N. & Morrison, P.J.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

A new parallel algorithm for contact detection in finite element methods

In finite-element, transient dynamics simulations, physical objects are typically modeled as Lagrangian meshes because the meshes can move and deform with the objects as they undergo stress. In many simulations, such as computations of impacts or explosions, portions of the deforming mesh come in contact with each other as the simulation progresses. These contacts must be detected and the forces they impart to the mesh must be computed at each timestep to accurately capture the physics of inter… more

Date: March 1, 1996

Creator: Hendrickson, B.; Plimpton, S.; Attaway, S.; Vaughan, C. & Gardner, D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Application and validation of direct numerical simulation for ICF implosion stability analysis

We have recently been applying a powerful computational tool, direct numerical simulation (DNS), to evaluate the stability of imploding inertial confinement fusion (ICF) capsules designed for the National Ignition Facility. In DNS, we explicitly calculate the evolution of realistic surface perturbations far into their nonlinear regimes, using a 2D Lagrangian radiation-hydrodynamics code. Because the mesh may become greatly distorted during the calculation, requiring frequent application of an a… more

Date: July 1, 1996

Creator: Hoffman, N. M.; Swenson, F. J. & Varnum, W. S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Discrete anomaly and dynamical mass in 2+1 dimension U(1){sub v} {times} U(1){sub A} model

The authors note that in (2+1)-dimensional gauge theories with even number of massless fermions, there is anomalous Z{sub 2} symmetry if theory is regularized in a parity-invariant way. They then consider a parity invariant U(1){sub v} {times} U(1){sub A} model, which induces a mutual Chern-Simons term in the effective action due to Z{sub 2} anomaly. The effect of the discrete anomaly is studied in the induced spin and in the dynamical fermion mass.

Date: December 31, 1995

Creator: Hong, D.K.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Signals from flavor changing scalar interactions in extended models

If on the one hand many predictions of the Standard Model seem to be in remarkable agreement with experiments, on the other hand the full consistency of the model needs still to be proved. In particular, given our present ignorance of the Higgs sector of the theory, extensions of the Standard Model scalar sector are worth considering. The simplest extension of adding one extra SU(2) doublet of scalar fields, i.e. the Two Higgs Doublet Model, generally introduces Flavor Changing Scalar Neutral C… more

Date: January 19, 1996

Creator: Reina, L.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

A Hybrid Vortex Method for Two-Dimensional Flow Over Tube Bundles

A hybrid vortex method is presented for computing flows about objects that accurately resolves the boundary layer details while keeping the number of free vortices at a reasonable level. The method uses a wall layer model close to the body surface and discrete vortex blobs in the free wake. Details of the wall layer implementation are presented, and results of sample calculations are compared with known analytical solutions and with calculations from other vortex codes. These results show that … more

Date: November 13, 1998

Creator: Strickland, J.H. & Wolfe, W.P.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Min-max redundancy resolution for a mobile manipulator

We have considered the problem of determining the values of the joint variables of a mobile manipulator with many redundant degrees of freedom that will minimize an objective function when the position and orientation of the end of the manipulator are given. The objective function is the weighted sum of three components: distance, torque, and reach. Each of the three components is a max or min. We have converted the min-max optimization problem into a nonlinear programming problem and used the … more

Date: February 1, 1996

Creator: Reister, D.B.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Diffusive mesh relaxation in ALE finite element numerical simulations

The theory for a diffusive mesh relaxation algorithm is developed for use in three-dimensional Arbitary Lagrange/Eulerian (ALE) finite element simulation techniques. This mesh relaxer is derived by a variational principle for an unstructured 3D grid using finite elements, and incorporates hourglass controls in the numerical implementation. The diffusive coefficients are based on the geometric properties of the existing mesh, and are chosen so as to allow for a smooth grid that retains the gener… more

Date: June 1, 1996

Creator: Dube, Eveline I.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Accurate, finite-volume methods for 3D MHD on unstructured Lagrangian meshes

Previous 2D methods for magnetohydrodynamics (MHD) have contributed both to development of core code capability and to physics applications relevant to AGEX pulsed-power experiments. This strategy is being extended to 3D by development of a modular extension of an ASCI code. Extension to 3D not only increases complexity by problem size, but also introduces new physics, such as magnetic helicity transport. The authors have developed a method which incorporates all known conservation properties i… more

Date: October 1, 1998

Creator: Barnes, D. C. & Rousculp, C. L.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Brittle damage models in DYNA2D

DYNA2D is an explicit Lagrangian finite element code used to model dynamic events where stress wave interactions influence the overall response of the system. DYNA2D is often used to model penetration problems involving ductile-to-ductile impacts; however, with the advent of the use of ceramics in the armor-anti-armor community and the need to model damage to laser optics components, good brittle damage models are now needed in DYNA2D. This report will detail the implementation of four brittle … more

Date: September 1, 1997

Creator: Faux, D. R.

Item Type: Report

Partner: UNT Libraries Government Documents Department