Replacing Detonation by Compressed Balloon Approaches in Finite Element Models

Pierre Legrand,S Kerampran,M Arrigoni

doi:10.1155/2020/1497632

Abstract

The evaluation of blast effects from malicious or accidental detonation of an explosive device is really challenging especially on large buildings. Indeed, the time and space scales of the explosion together with the chemical reactions and fluid mechanics make the numerical model really difficult to achieve acceptable structural design. Nevertheless, finite element methods and especially Arbitrary Lagrangian Eulerian (ALE) have been extensively used in the past few decades with some simplifications. Among them, the replacement of the explosive event by a compressed balloon of detonation products has been proven useful in numerous different situations. Unfortunately, the ALE algorithm does not achieve a proper energy balance through the numerical integration of the discrete scheme; this important drawback is not compensated by the use of the classical compressed balloon approach. The paper focuses on increasing the radius of the equivalent ideal gas balloon in order to achieve better energy balance and thus better results at later stages of the blast wave propagation.

Highlights

Ese gases will expand and react with the surrounding air and create a blast wave propagating outwards in the air for a few milliseconds, a possible fireball, and high pressure and temperature gradients
In order to evaluate the β-methods which could be used for civil engineering application, all data are extracted from the radial structured mesh at a scaled mesh size of 5 mm·kg− 1/3
Based on the initial work of Brode and the latest papers, a compressed balloon has been studied to replace the detonation process of high explosive in numerical simulations of blast waves impacting structures. e previous models did not account for the numerical damping acting in every finite element explicit scheme. e main goal of this paper was to address this issue

Summary

Introduction

Ese gases will expand and react with the surrounding air and create a blast wave propagating outwards in the air for a few milliseconds, a possible fireball, and high pressure and temperature gradients. Structural components will be impacted by the blast wave and may collapse over a few seconds. All those phenomena come with different space scales from the cm of the explosive sources to the dozens of meters of the structure. In spite of neglecting the chemical detonation and so close-in effects (afterburning, fireball) the proposed method leads to proper time-history pressure curves and adequate structural design. The overpressure is no more than ten times the ambient pressure and, close to the charge, the scaled distance is less than ten times the explosive diameter and so the point source assumption is no longer appropriate. Only simple geometries for both the charge and the structure can be considered (spherical charge and plan wall)

Results

Discussion

Conclusion