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Modeling explosive-solid interactions with meshless particles in a Lagrangian framework allows for robust computations in complex geometric situations where modeling explosives with elements could be problematic. The EPIC code originally used a single-bucket scheme to find the "neighbor" particles for the meshless algorithm. The efficiency of the bucketing scheme is O(N), where N is the number of particles, but there is a constant multiplicative factor which is proportional to the average number of particles per bucket (P). When the explosive particles expand, they can cause the bucket size to be an order of magnitude larger than what would be necessary for the majority of the particles, which drives up P and causes the computational time to become unworkably large. The computational time is reduced by adding a second set of buckets to sort the smaller particles. This paper shows the algorithm used to determine the size of the smaller buckets so as to approximately minimize computational search time, and also shows some simulations that were made possible due to those faster search times (30-70 times faster than a single-bucket search). [ABSTRACT FROM AUTHOR]

This article presents an algorithm to automatically convert distorted hexahedral elements into meshless particles during dynamic deformation. With this approach the initial mesh is composed only of elements, and the particles are generated only as needed when the elements become highly distorted. This allows the mildly distorted regions of the problem to be accurately and efficiently represented with finite elements, and the highly distorted regions to be robustly represented with meshless particles. This algorithm is an extension of a previous algorithm that converts distorted tetrahedral elements into particles. The algorithm for hexahedral elements is more complex because the faces of these elements are not planar, as they are for tetrahedral elements. Examples of high-velocity impact are included to demonstrate the capabilities of this algorithm. [ABSTRACT FROM AUTHOR]

The simulation of high-velocity impact and penetration is inhibited by complex material behavior and large deformations. Lagrangian formulations best model complex materials because history-dependent variables and material boundaries are not advected. However, Lagrangian finite elements are limited by large deformations. Recently, meshfree particle methods have been used to avoid such limitations, and have demonstrated greater accuracy than traditional erosion methods (wherein deformed elements are removed). Though the variable connectivity of particles enables them to model large deformations, it requires more computational effort than (fixed-connectivity) elements. Therefore, an algorithm was designed to convert deformed elements to particles, thus providing the ability to model large deformations where needed, while maintaining the efficiency of elements elsewhere. This combination is essential in three dimensions, where problem size demands efficiency. In this paper, the conversion algorithm is demonstrated for several three-dimensional simulations of high-velocity impact and penetration. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]