Simulation of the penetration of a sequence of bombs into granitic rock

Abstract

This computational study was undertaken to investigate the penetration efficiency of a sequence of penetrating bombs into granitic hard rock. The main objective of the study was to ascertain the feasibility of using several bombs - all precision-guided to the same target point and detonated a few tens of milliseconds apart - to defeat a Hard and Deeply Buried Target (HDBT) that cannot be defeated using conventional means. Several simulations were performed in support of this objective, including a sequence of six consecutive bombs traveling with a velocity of 300 m/s, with each bomb being made to penetrate into the crater produced by its predecessor. The simulations were performed using GEODYN - a parallel Eulerian hydrocode with adaptive mesh refinement capabilities - and a constitutive model for granite that was calibrated using ground motion data from several underground explosions. The cumulative penetration depth from all six bombs was 5.7 m, with the first bomb penetrating as much as 2.1 m and the last one penetrating as little as 0.4 m. The general trend of decreasing penetration depth with each successive bomb was shown to be primarily attributed to crater geometry and to accumulation of high strength steel in the bottom of the crater. Shock conditioning of the rock was shown to have a favorable effect on penetration.