Publications

Results 8751–8800 of 9,998

Search results

Jump to search filters

Sustaining knowledge in the neutron generator community and benchmarking study

Huff, Tameka B.; Turgeon, Jennifer T.; Baldonado, Esther B.; Stubblefield, W.A.; Kennedy, Bryan C.; Saba, Antony S.

In 2004, the Responsive Neutron Generator Product Deployment department embarked upon a partnership with the Systems Engineering and Analysis knowledge management (KM) team to develop knowledge management systems for the neutron generator (NG) community. This partnership continues today. The most recent challenge was to improve the current KM system (KMS) development approach by identifying a process that will allow staff members to capture knowledge as they learn it. This 'as-you-go' approach will lead to a sustainable KM process for the NG community. This paper presents a historical overview of NG KMSs, as well as research conducted to move toward sustainable KM.

More Details
TYPE SAND Report YEAR 2008
DOIOSTI

Parallel job scheduling policies to improve fairness : a case study

Leung, Vitus J.

Balancing fairness, user performance, and system performance is a critical concern when developing and installing parallel schedulers. Sandia uses a customized scheduler to manage many of their parallel machines. A primary function of the scheduler is to ensure that the machines have good utilization and that users are treated in a 'fair' manner. A separate compute process allocator (CPA) ensures that the jobs on the machines are not too fragmented in order to maximize throughput. Until recently, there has been no established technique to measure the fairness of parallel job schedulers. This paper introduces a 'hybrid' fairness metric that is similar to recently proposed metrics. The metric uses the Sandia version of a 'fairshare' queuing priority as the basis for fairness. The hybrid fairness metric is used to evaluate a Sandia workload. Using these results, multiple scheduling strategies are introduced to improve performance while satisfying user and system performance constraints.

More Details
TYPE SAND Report YEAR 2008
DOIOSTI

Dissipation-induced heteroclinic orbits in tippe tops

Proposed for publication in SIAM Review.

Romero, L.A.

This paper demonstrates that the conditions for the existence of a dissipation-induced heteroclinic orbit between the inverted and noninverted states of a tippe top are determined by a complex version of the equations for a simple harmonic oscillator: the modified Maxwell-Bloch equations. A standard linear analysis reveals that the modified Maxwell-Bloch equations describe the spectral instability of the noninverted state and Lyapunov stability of the inverted state. Standard nonlinear analysis based on the energy momentum method gives necessary and sufficient conditions for the existence of a dissipation-induced connecting orbit between these relative equilibria.

More Details
TYPE Journal Article YEAR 2008
OSTI

ALEGRA: An arbitrary Lagrangian-Eulerian multimaterial, multiphysics code

46th AIAA Aerospace Sciences Meeting and Exhibit

Robinson, Allen C.; Brunner, Thomas A.; Carroll, Susan; Richarddrake; Garasi, Christopher J.; Gardiner, Thomas; Haill, Thomas; Hanshaw, Heath; Hensinger, David; Labreche, Duane; Lemke, Raymond; Love, Edward; Luchini, Christopher; Mosso, Stewart; Niederhaus, John; Ober, Curtis C.; Petney, Sharon; Rider, William J.; Scovazzi, Guglielmo; Strack, O.E.; Summers, Randall; Trucano, Timothy; Weirs, V.G.; Wong, Michael; Voth, Thomas

ALEGRA is an arbitrary Lagrangian-Eulerian (multiphysics) computer code developed at Sandia National Laboratories since 1990. The code contains a variety of physics options including magnetics, radiation, and multimaterial flow. The code has been developed for nearly two decades, but recent work has dramatically improved the code's accuracy and robustness. These improvements include techniques applied to the basic Lagrangian differencing, artificial viscosity and the remap step of the method including an important improvement in the basic conservation of energy in the scheme. We will discuss the various algorithmic improvements and their impact on the results for important applications. Included in these applications are magnetic implosions, ceramic fracture modeling, and electromagnetic launch. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc.

More Details
TYPE Conference YEAR 2008
ScopusOSTI

Peridynamics with LAMMPS : a user guide

Parks, Michael L.; Plimpton, Steven J.; Lehoucq, Richard B.; Silling, Stewart A.

Peridynamics is a nonlocal formulation of continuum mechanics. The discrete peridynamic model has the same computational structure as a molecular dynamic model. This document details the implementation of a discrete peridynamic model within the LAMMPS molecular dynamic code. This document provides a brief overview of the peridynamic model of a continuum, then discusses how the peridynamic model is discretized, and overviews the LAMMPS implementation. A nontrivial example problem is also included.

More Details
TYPE SAND Report YEAR 2008
DOIOSTI
Results 8751–8800 of 9,998
Results 8751–8800 of 9,998