Modelling of complex blast

Abstract

There is an extensive hierarchy of models for the prediction of free-field blast wave propagation and loading. As one begins to move to more complex scenarios (e.g. near-field blast, non-ideal explosives, internal blast or buried charges), there is a need for more detailed understanding and modelling. In this article, we discuss a range of sub-models for the components of complex blast which can be used in hydrocode modelling of the loading of targets or structures. Many explosives are fuel-rich and thus have the capacity to undergo secondary combustion after detonation (afterburn). Even in the free field, this mechanism affects the wave profile and we illustrate the errors associated with simpler models, even for the case of detonation of a sphere of 2,4,6-trinitrotoluene (TNT) in the free field. We identify why these effects should be accounted for in any analysis of later time reflections in more complex targets and discuss how the effects of complex blast are also important in assessing human injury. We also report some engineering models which we have developed based on parameter studies using hydrocode models. The effects of any casing surrounding the explosive charge also influence the loading on a target, both by taking energy out of the blast wave and by accelerating fragments which produce a heterogeneous loading on a structure. Some blast mitigation concepts also make use of the transfer of energy to powder, liquid or foam surrounds. Buried charges can also behave in a similar manner to powder-based blast mitigants and lead to fast moving fingers of solid material which can produce localised loadings on structures. We identify how recent studies in these areas are influencing complex blast calculations.