A publication of the Office of Advanced Simulation & Computing, NNSA Defense Programs
NA-ASC-500-07—Issue 4
September 2007
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New Model for Tantalum Developed under ASC Multiscale Modeling Effort
More than 10 years ago, an effort began to develop improved, physically based models of material constitutive behavior for use in integrated multiphysics codes. The challenge has been that the models are needed for programmatic applications in regimes of pressure, strain-rate, and temperature, where relevant experimental data are scarce or nearly impossible to obtain. Building upon the ASCI paradigm at the time, a multiscale modeling strategy was developed to bring together and leverage material modeling activities from a variety of length scales. This technique uses new and improved computational simulations involving detailed physics to enable the development of better macroscopic models for the integrated codes.
Lawrence Livermore National Laboratory has just completed a milestone for the Physics & Engineering Models (PEM) element of the ASC Program that utilized the multiscale modeling methodology to develop a new strength model for tantalum. This effort involved combining theoretical developments with modeling and simulation efforts involving quantum molecular dynamics, classical molecular dynamics, dislocation dynamics, and integrated continuum simulations. Dislocation dynamics is a relatively new simulation capability, using the Livermore parallel code ParaDiS, where the motion, generation, and interaction of dislocations (crystallographic irregularities) are modeled as a way to predict realistic single crystal behavior. The new model has been successfully used to run large-scale, multiphysics programmatic simulations.
The development of the new tantalum strength model using the multiscale modeling methodology has truly been enabled through ASC model developments and modern platforms. Calculations required for this milestone involved utilizing one-third of the BlueGene/L machine to perform dislocation dynamics simulations requiring more than 200 million CPU-hours—equivalent to running a 1985 Cray Y-MP from the great ice age of 20,000 years ago until now. Additional molecular dynamics simulations required more than 10 million CPU-hours.
Four snapshots in time of a ParaDiS dislocation dynamics simulation, where complexity
of the problem continuously increases as dislocations multiply and interact.
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