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Thursday, April 18th 2019

3:35 pm:

Computational physicists are commonly faced with the task of resolving discrepancies between the predictions of a complex, integrated multi-physics numerical simulation and corresponding experimental datasets. Such efforts commonly require a slow iterative procedure. However, a different approach is available in cases where the multi-physics system of interest admits closed-form analytic solutions. In this situation, the ambiguity is broken into separate consideration of theory-simulation comparisons (issues of verification) and theory-data comparisons (issues of validation). We demonstrate this with the specific example of a fluid- instability based ejecta source model (“RMI+SSVD”) under development at Los Alamos National Laboratory and implemented in FLAG, a Los Alamos continuum mechanics code. For a specific (but wide-ranging) class of explosively driven metal coupon experiments, the ejecta model prediction inherently reduces to a one-dimensional vacuum kinematics problem. This enables us to compute, purely analytically, piezoelectric ejecta mass measurements suitable for “apples-to-apples” comparisons to both simulated and measured datasets. Thus, studying the solution to a very simple yet overlooked problem yields rich and concrete insights into performance of the model, its strengths and shortcomings, as well as strategies for improving it. These conclusions are made quantitative through the introduction of a straightforward yet rigorous “compatibility score” metric incorporating published measurement uncertainties on relevant experimental parameters.

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