A practical numerical simulation approach for explosions in large-scale complex urban environments

Abstract

In recent years, terrorist attacks and accidental explosions in urban environments have occurred frequently, causing severe damage, even collapse, of building structures, and have become a major concern of modern society. The need to design and evaluate the blast resistance of building structures is rising markedly. The utmost requirement is the determination of blast loads acting on building structures, i.e., the reflected overpressure of blast waves. To better keep the balance between computational efficiency and prediction accuracy of complex blast wave propagation and its interactions with buildings, a practical numerical simulation approach integrating multiple existing techniques including the multi-stage method, graded mesh, mapping, and un-refinement technique is proposed based on ANSYS/AUTODYN. Firstly, the propagation of blast waves is simplified into three stages, i.e., propagation in the free air from the explosion center to ground zero, propagation after the ground reflection, and interaction with building structures. These three stages are modeled by 1D uniform meshes and 2D/3D graded meshes with increasing mesh sizes. Then, the mapping technique, including mesh un-refinement, is adopted to transfer the predicted results at the previous stage into the next stage. The corresponding meshing strategy against the scaled distances Z (\(Z = R / \root 3 \of {W}\), where R is the distance between the detonation point and the target surface, W is the equivalent charge weight of TNT) for each stage is recommended through mesh sensitivity analyses. Finally, the proposed approach and mesh sizes are validated against four series of explosive tests for a single house, an intersection, and two city blocks by comparing with both the overpressures and impulses of blast waves. Additionally, two solvers, i.e., Euler FCT and Euler multi-material, are compared. The former solver is recommended due to its greater efficiency and accuracy. The present work could provide a helpful reference for the blast-resistant design and evaluation of urban building structures.