FLAG

Ejecta source and transport modeling in the FLAG hydrocode. We present the ongoing development and implementation of an ejecta model in the FLAG hydrocode. Ejecta is the term given to particulate matter that is produced at the free surface of a material subject to extreme shock loading. Following shock propagation into a material and reflection at its free surface, conditions may be sufficient to induce phase changes, damage, or fragmentation at the surface. The dynamics of the fragmentation may be such that a “cloud” of particulate matter forms and propagates away from the material. Modeling such phenomena in a continuum hydrodynamics code challenges the assumptions underlying the numerical approximations made in the hydrodynamics. The representative scales for the particulate matter are often much smaller than the representative scales for the bulk material producing the ejecta. However, this scale separation allows for statistical descriptions of ejecta that are compatible with continuum mechanics. Earlier work documents an initial effort in modeling ejecta in the FLAG hydrocode. The FLAG hydrocode computes continuum mechanics solutions for fluid and solid materials in an Arbitrary-Eulerian-Lagrangian (ALE) framework. To model ejecta in FLAG, a hybrid particle-continuum representation was defined that allows for coupling with continuum materials on large (bulk) scales. Numerical models were developed and implemented for particle production (sourcing) as well as for solving the particle equations of motion. The numerics were shown to conserve mass, momentum and energy, and preliminary results were given for modeling drag and volume effects. This work documents recent advances in source and transport models. Spatial and temporal dependencies have been added to the source models to account for geometric free-surface variations, mesh dependence, and shock loading. More physically relevant drag models have been implemented that include Reynolds number effects. These will be presented along with test results verifying the models. A FLAG model of an actual ejecta experiment will also be presented.

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  1. Fung, J.; Harrison, A.K.; Chitanvis, S.; Margulies, J.: Ejecta source and transport modeling in the FLAG hydrocode (2013)