Publications

Over the past few years, the CTH multiphysics hydrocode has overhauled its software quality and testing processes, implementing current best practices in software quality and building a robust V&V test suite comprised of traditional hydrocode verification problems, including ASC Tri-Lab Test Suite and Enhanced Tri-Lab Test Suite problems, as well as validation problems for some of CTH’s most frequently used equations of state, materials models, and other key capabilities. Substantial progress towards building this new test suite was made in FY19 and FY20. In FY21, the test suite has been expanded to include verification and validation tests of the Steinberg-Guinan-Lund (ST) viscoplastic model and the Johnson Cook (JFRAC) fracture model. Additionally, two new verification tests were added, covering hydrodynamics and high explosive (HE) modeling capabilities: the Kidder Gaussian density problem and the Escape of HE Products (EHEP) problem from the Tri-Lab Test Suite. This report discusses each of these test problems in detail. Verification test results are compared to analytic solutions. Validation test results are compared to experimental data. Wherever possible, convergence or mesh refinement studies are included. Additionally, while implementing the Kidder verification problem, a bug was identified that affects the use of tables to initialize pressure or density in 1D or 2D calculations. A brief discussion of the bug and its fix is included. CTH demonstrates good performance overall on the new test suite problems. Simulation results showed good agreement with analytic solutions for the Kidder problem, with convergence rates ranging between 1.8 and sub-linear, and relatively good agreement for the EHEP problem, though convergence rates for pressure and density were nearly 0. The ST and JFRAC strain rate loading verification tests show good agreement with analytic solutions. Likewise, CTH simulation results show good agreement with experimental validation data, including Taylor rod impact testing, for the materials tested. Future V&V work will focus on adding 2D and 3D versions of existing verification tests as well as adding validation tests of other frequently used capabilities such as other fracture models.

The CTH multiphysics hydrocode is used in a wide variety of important calculations. An essential part of ensuring hydrocode accuracy and credibility is thorough code verification and validation (V&V). In the past, CTH V&V work (particularly verification) has not been consistently well documented. In FY19, we have made substantial progress towards addressing this need. In this report, we present a new CTH V&V test suite composed of traditional hydrocode verification problems used by similar ASC codes as well as validation problems for some of the most frequently used materials models and capabilities in CTH. For the verification problems, we present not only results and computed errors, but also convergence rates. Validation problems include mesh refinement studies, providing evidence that results are converging. CTH performs well overall on the new V&V test suite, though the test suite itself still only covers a fraction of CTH capabilities. Accuracy and convergence rates for traditional verification problems such as Sedov, Noh, and the 1D Riemann problems are comparable to similar ASC codes. Likewise, CTH simulation results show good agreement with experimental validation data for the AVAVE, EPPVM, and Johnson-Cook strength models as well as for the Mie-Griineisen EOS for the materials tested. Future V&V work will add testing for other frequently used material models and code capabilities, helping to provide confidence in simulation results for critical analyses. ACKNOWLEDGEMENTS The authors would like to thank Brian Carnes, Jim Cox, and Kevin Dowding for helpful discussions. We would also like to acknowledge the valuable resources published by Los Alamos National Laboratory, such as the code verification tool ExactPack 1 , which was used in this work to calculate and plot analytic solutions, and the Standardized Definitions for Code Verification Problems 2 , which was helpful in implementing the ASC Tri-Lab Test Suite problems. Finally, we wish to thank Kim Mish, Angel Urbina, and Walter Witkowski for supporting this work. 1 R. Singleton Jr, D. M. Israel, S. W. Doebling, C. N. Woods, A. Kaul, J. W. Walter Jr, and M. L. Rogers, Exactpack documentation, tech. rep., Los Alamos National Lab. (LANL), Los Alamos, NM (United States), 2016. 2 J. Kamm, S Doebling, D. Israel, and R. Singleton, Standardized definitions for code verification test problems, tech. rep., LA-UR-14-20418 (Rev. 2), 2014.

Abstract not provided.