Further Developments in a Load History Generator To Couple Epic and Ls-Dyna

Abstract eng:
Numerical simulation of blast-structure-fragment interaction is a multidisciplinary application that combines some of the most challenging problems in computational mechanics today, including numerical modeling of material failure, fracture and fragmentation; development of robust algorithms for rapidly evolving dynamic contact; models for burning, deflagration and detonation of energetic materials; methods for coupling loads from the blast wave and detonation products to structures; and calculation of the large deformations and damage to the structure as a result of these loads. Because of the many challenging facets associated with this problem no single numerical code is well-suited for simulation of this entire suite of phenomena. The EPIC code, for example, contains algorithms that allow very realistic simulation of weapons effects, but its geometry primitives, boundary condition and setup options are not well-suited for performing general purpose finite element computations, as is typically required in a realistic structural model. A recent addition to EPIC is a particle algorithm combined with element-particle conversion to permit more realistic modeling of large deformations that occur in weapons effects modeling. The LS-DYNA code, on the other hand, is a general-purpose Lagrangian finite element code well-suited for simulation of large-scale deformation that occurs when a structure is subjected to impact or impulsive loadings, but does not have many of the specialpurpose algorithms for weapons modeling contained in EPIC. In this work, we have exploited the advantages of these two codes by developing a load history generator for coupling the air blast, ground shock and fragmentation loading calculated from EPIC to a structural model generated for LSDYNA. The history generator was developed to be as seamless and user-friendly as possible to enable ease of use. Mesh and geometry information for the structure are read directly into the EPIC code from LS-DYNA input. Particular attention has been placed on high fidelity tracking of loads imparted to the structural surface (typically composed of shell elements coming from LS-DYNA) by explosive products and geomaterials (typically composed of particles from EPIC). A partitioning algorithm is used to automatically subdivide the load surface, passed from LS-DYNA to EPIC as a side set, into a number of segments. The partition is weighted so that regions expected to receive the highest pressures are segmented into the smallest areas. Loads on surfaces of each segment are calculated in EPIC and the output, in the form of load curves, is passed back to an include file that can be read directly by LS-DYNA. Example calculations are shown which illustrate the advantages of this approach.

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