Distribution A: For Public Release
1
A Fast Running Model for Accurate Time-
Dependent Post-Shock Gas Flow
Keywords: Confined Airblast, Explosive effects, Blast Model, Numerical Analysis
Pietro Gheorghiu
1
, Joseph Abraham
2
, Casey Meakin
3
, Simon Fu
4
1
Karagozian & Case, Inc., 700 N. Brand Blvd., Suite 700, Glendale, CA 91203, USA (gheorghiu@kcse.com)
2
Karagozian & Case, Inc., 700 N. Brand Blvd., Suite 700, Glendale, CA 91203, USA (abraham@kcse.com)
3
Karagozian & Case, Inc., 700 N. Brand Blvd., Suite 700, Glendale, CA 91203, USA (meakin@kcse.com)
4
Karagozian & Case, Inc., 700 N. Brand Blvd., Suite 700, Glendale, CA 91203, USA (simon@kcse.com)
Abstract
The gas pressure and heat resulting from a munition detonated within a structure often contributes
significantly to the damage imparted to a target. Therefore, an accurate prediction of weapon
effects under these circumstances requires modeling the pressure and thermal loads acting on
structural members which will depend on the process by which gas pressure is equilibrated
throughout the interior of the structure by sound waves and advection as well as conductive and
radiative heat transport. Although fast-running models (FRMs) exist to treat these processes, their
formulations are incomplete. A common approach involves modeling the interior structure of
buildings as a network of locally equilibrated rooms or compartments connected by vents (e.g.,
ducts, open doorways, breach holes, etc.) through which gases can flow and pressure can
eventually equilibrate globally. While this approach is computationally efficient and allows for
various levels of fidelity with regards to calculating the flow rate driven by differential pressure
between rooms, the assumption of instantaneous equilibration within a room or compartment can
significantly undermine accuracy for a large number of scenarios of interest. Examples which are
poorly handled by these approximations include breach holes which span a significant fraction of
a wall as well as structures containing large rooms or hallways for which the sound crossing time
can be significant. In order to address these issues, a mass, energy, and momentum conserving
gas-flow model has been developed which employs a set of orthogonal planforms to represent sub-
room structure and provides a means to capture the finite sound and gas flow speeds that drive
equilibration. The model is fast running, unconditionally stable, and employs an implicit
integration scheme to handle the stiff equation set. The model can evaluate complex high explosive
compositions, afterburn energy, dynamic energy release rates, dynamic breach/vent openings,
dynamic increases in room volume, and room vent activation based on sound crossing time.
Results are provided which demonstrate the calculational efficiency of the model as well as
