Summary
Recent interest in blast propagation in urban environments has demonstrated a need for a fast running model to approximate the modifications to the blast environment caused by the interaction with buildings. A series of first principles calculations was completed which provides a data base for describing the interaction of buildings with blast waves of various yields. Using this data base, ARA has developed a fast running model to describe this interaction.
The interaction of a blast wave with a structure involves complex flow phenomena. Modeling of this interaction with a fast running PC based method presents some interesting challenges. Reflection of a planar shock from the front face of a rectangular structure with a normal angle of incidence can be handled fairly well with the application of the Rankine-Hugoniot (R-H) relations to get the peak reflected pressure. Knowledge of the building dimensions determines the rarefaction wave propagation from each edge of the building. The R-H relations can then be applied to obtain the stagnation pressure behind the incident wave. If we simply change the incident wave to a curved front, impinging the structure at an angle other than 90 degrees, the problem becomes more complex.
The model described in this paper provides not only the load as a function of time at any point on any surface of a rectangular structure from an arbitrary blast wave, it also provides the pressure waveform in the “shadow” of the building. This model is based on results of first principles, high resolution CFD calculations, supported by experimental data and the TNT standard. The model accounts for the effects of vortices forming and shedding from the edges of the building and follows the shock around multiple corners.
Examples and comparisons of the results of the model with first principle calculations are presented for several shock strengths and building orientations.
This work was funded by the Defense Threat Reduction Agency (DTRA).