CTH is a family of codes developed at Sandia N_onal Laboratories for modelling complex " multi-dimensional, multi-material problems that are characterized by large de/Ormationsand/or strong shocks. A two-s_p, second-order accurateEulerian solution algorithm is used to solve themass, momen-_...._'_ C_[ mm, and energy conservation equations. CTH includes models for material strength, fracture, porous t_ "-_ materials, and high explosive detonation and initiation. [/ft.,' !.,., or rate-dependent models of material strength have been added recently. The formulations _U0 of Johno_3n-Cook,Vise°pla_c Zerilli-Annstrong, and Steinberg-Guina_|-Lundare standard options within CTI-LThese _ _ models rely on the use of an internal state variable (typically the equivalent plastic strain) to account for the histoq dependence of material response. The implementation of internal state variable models will be O _ T [ discussed and several sample calculations will be presented. Comparison with experimental data will be made among the various material strength models. The advancements made in modelling material response have signiticanfly improved the ability of CrH to model complex large-deformation, plasticflow dominated phenomena. The detonation of energetic material under shock loading conditions has been an area of great interest. A recently developed model of reactive burn for high explosives 0-lE) has been added to CTH. This model along with newly developed tabular equations-of-state for the HE reaction by-products has been compared to one-and two-dimensional explosive detonation experiments. These comparisons indicate excellent agreement of CTH predictions with experimental results. The new reactive bum model coupled _cg ___ g _ _ _ _ with the adw,pces in equation-of-state modeling make it possible to predict multi-dimensional bum phe-_. _-_ _ _ 8 _: _ _, _" nomena without modifying the model parameters for different dimensionality. Most current bum models 2. _o _, _ _ _ _., ,, = ct __g"g'_ _ o _ 8 _.__ do not accurately predict both one-dimensional plate acceleration experiments and two-dimensional cylin-_-_"._ _ _. _ _. :" b_" = der expansion experiments simultaneously. Our implementation is significant because it represents the _ _ o _ _ _ _ _ "first time a multi-dimensional model has been used to successfully predict multi-dimensional detonation _ o .., o ,_ _ _ _ z effects without requiringa modification of the model parameters.

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.

ALEGRA is an arbitrary Lagrangian-Eulerian finite element code that emphasizes large distortion and shock propagation. This document describes the user input language for the code.

SUMMARYArbitrary Lagrangian-Eulerian (ALE) methods are commonly used for challenging problems in hydrodynamics. Among the most challenging matters are the approximations in the presence of multiple materials. The ALE code ALEGRA has used a constant volume method for computing the impact of multiple materials on both the Lagrangian step and the remap step of the method. Here, we describe modifications to these methods that provide greater modeling fidelity and better numerical and computational performance. In the Lagrangian step, the effects of differences in material response were not included in the constant volume method, but have been included in the new method. The new methodology can produce unstable results unless the changes in the variable states are carefully controlled. Both the stability analysis and the control of the instability are described. In the standard (Van Leer) method for the remap, the numerical approximation did not account for the presence of a material interface directly. The new methodology uses different, more stable and more dissipative numerical approximations in and near material interfaces. In addition, the standard numerical method, which is second-order accurate, has been replaced by a more accurate method, which is third-order accurate in one dimension. Published in

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