Publications

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Co-design has been identified as a key strategy for achieving Exascale computing in this decade. This paper describes the need for co-design in High Performance Computing related research in embedded computing the development of hardware/software co-simulation methods.

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Los Alamos and Sandia National Laboratories have formed a new high performance computing center, the Alliance for Computing at the Extreme Scale (ACES). The two labs will jointly architect, develop, procure and operate capability systems for DOE's Advanced Simulation and Computing Program. This presentation will discuss a petascale production capability system, Cielo, that will be deployed in late 2010, and a new partnership with Cray on advanced interconnect technologies.

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There is considerable interest in achieving a 1000 fold increase in supercomputing power in the next decade, but the challenges are formidable. In this paper, the authors discuss some of the driving science and security applications that require Exascale computing (a million, trillion operations per second). Key architectural challenges include power, memory, interconnection networks and resilience. The paper summarizes ongoing research aimed at overcoming these hurdles. Topics of interest are architecture aware and scalable algorithms, system simulation, 3D integration, new approaches to system-directed resilience and new benchmarks. Although significant progress is being made, a broader international program is needed.

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Two years ago, researchers at Sandia National Laboratories showed that a massively parallel computer with 1024 processors could solve scientific problems more than 1000 times faster than a single processor. Since then, interest in massively parallel processing has increased dramatically. This review paper discusses some of the applications of this emerging technology to important problems at Sandia. Particular attention is given here to the impact of massively parallel systems on applications related to national defense. New concepts in heterogenous programming and load balancing for MIMD computers are drastically increasing synthetic aperture radar (SAR) and SDI modeling capabilities. Also, researchers are showing that the current generation of massively parallel MIMD and SIMD computers are highly competitive with a CRAY on hydrodynamic and structural mechanics codes that are optimized for vector processors.

A two-dimensional model of melt progression, oxidation and natural convection in reactor core debris beds has been developed. Three fields are considered in the model: vapor, melt and solid. Conservation equations are solved for the species of interest in each field. Momentum equations that are based on Darcy's law are solved for the vapor and the melt and a simplified model is used to calculate the motion of the solid as it settles downward. An energy equation is included that accounts for melting/freezing, convection, conduction, oxidation and decay heating. Key results from a sensitivity study include: (1) gas velocities increase rapidly at the onset of oxidation and subsequently decrease when the bed becomes steam-starved; (2) natural convection flows are sensitive to radial variations in the decay heat; (3) raising the pressure in the bed and the upper plenum increases the amount of steam that is available for oxidation and leads to much higher temperatures and gas velocities; (4) reducing the average particle diameter decreases the permeability and significantly lowers gas velocities; and (5) solutions are sensitive to conditions in the upper plenum and consequently, melt progression models discussed here must be coupled to a mechanistic code, such as MELPROG or SCDAP, in order to analyze specific accident sequences. 33 refs., 20 figs.