The method of discrete ordinates is commonly used to solve the Boltzmann radiation transport equation for applications ranging from simulations of fires to weapons effects. The equations are most efficiently solved by sweeping the radiation flux across the computational grid. For unstructured grids this poses several interesting challenges, particularly when implemented on distributed-memory parallel machines where the grid geometry is spread across processors. We describe an asynchronous, parallel, message-passing algorithm that performs sweeps simultaneously from many directions across unstructured grids. We identify key factors that limit the algorithm's parallel scalability and discuss two enhancements we have made to the basic algorithm: one to prioritize the work within a processor's subdomain and the other to better decompose the unstructured grid across processors. Performance results are given for the basic and enhanced algorithms implemented within a radiation solver running on hundreds of processors of Sandia's Intel Tflops machine and DEC-Alpha CPlant cluster.

No abstract

We present a turbulent combustion code for modeling heat transfer in fires that arise in accident scenarios. The code is a component of a multi-mechanics framework and is based on a domain-decomposition, message-passing approach to parallel computing. The turbulent combustion code is based on a vertex-centered, finite-volume scheme for 3D unstructured meshes. The multi-mechanics nature of the frameworks allows us to couple to a conduction heat transfer code for conjugate heat transfer problems or a participating media radiation code for radiation transport in soot-laden flows. We describe our numerical methods, our approach to parallel computing, and the multi-mechanics frameworks. We demonstrate parallel performance using some example verification problems.

NTIS price codes Printed copy A03 Microfiche copy AO 1. DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

ALEGRA is an arbitrary Lagrangian-Eulerian finite element code that emphasizes large distortion and shock propagation. This document describes the user input language for the code.

A number of physics problems can be modeled by a set of N elements, which have pair-wise interactions with one another. The use of such elements for the evolution of vorticity in fluid flows and the calculation of the velocity field from the evolving vorticity field is well known. Fast multipole methods for fluid flow problems have been developed in the past to reduce computational effort to something less than O(N 2 ). In this paper we develop a fast multipole solver with application to both 3-D radiation problems (calculation of the heat flux from the evolving temperature field in an absorbing medium) and 3-D fluid flow. This is accomplished by using a more general kernel for the associated volume integrals. This kernel also encompasses other applications such as gravitational fields, electrostatics, scattering, etc. The present algorithm has been designed to have a very high "parallel efficiency" when used on massively parallel computers. This feature comes at the expense of computational effort, which is less than O(N 2 ) but greater than O(N) or O(NlnN).

This report provides a review of the open literature relating to numerical methods for simulating deep penetration events. The objective of this review is to provide recommendations for future development of the ALEGRA shock physics code to support earth penetrating weapon applications. While this report focuses on coupled EulerianLagrangian methods, a number of complementary methods are also discussed which warrant further investigation. Several recommendations are made for development activities within ALEGRA to support earth penetrating weapon applications in the short, intermediate, and long term.

No abstract