PLOT OF THE MONTH

Urban Bomb Explosion
Helotes, TX

Contributed by:
J. Keith Clutter
Analytical and Computational Engineering, Inc.

J. Keith Clutter is the President of Analytical & Computational Engineering, Inc. (ACE). ACE is a small, dynamic company focused on the development and implementation of analytical and computational engineering models for predicting industrial explosions. They have expertise in fluid mechanics, combustion, aerodynamics, explosions and blasts.

The plot of the month is an animation showing the simulated evolution of pressure contours produced during a 2000-pound car bomb explosion in a large urban setting. As depicted in the animation, the blast does not decay and is focused1 in areas where there are alleys and streets (numbered notes are on the left sidebar). Animations play a key role in interpreting blast and explosion simulation data. They enable users to view pressure contours, pressure time histories, and other critical data from the model.

These results were calculated with a Computational fluid dynamics (CFD) code developed by ACE, called Computational Explosion & Blast Assessment Model (CEBAM). At the front of this modeling method is a GUI preprocessor used to set up problems. Tecplot is bundled with CEBAM for post-processing and data presentation. The data generated by CEBAM is quickly loaded and plotted in Tecplot using the Quick Macro Panel.

The main focus at ACE is developing simulation tools for predicting industrial explosions. Their goal is to determine the most likely blast scenario - either reconstructing explosion incidents or predicting potential explosions. Scenarios include various reactive flow systems (chemical reactions) involving condensed phase explosives (TNT, ANFO, C-4) and gas phase explosions (hydrocarbons like propane and methane mixed with air). This includes external and internal vapor cloud explosions (inside and outside buildings) and vessel explosions (storage tanks).

Risk, safety or process engineers from petrochemical companies, government agencies, engineering services companies, and risk assessment companies use CEBAM to determine risk from potential accidental explosions or terrorist attacks. Using the results from CEBAM they design retrofits for buildings and other facilities. Actual cases where CEBAM has been used include boiler explosions, gas well explosions, terrorist bombings, and industrial explosions at petrochemical facilities.

ACE is leading the way in applying state-of-the-art CFD techniques in simulating these occurrences. Using the latest in explosion modeling methodology they systematically evaluate various candidate explosion scenarios against actual observed damage. Using CFD to solve such problems is essential. CFD incorporates key effects such as blast focusing,1 shielding,2 component failure,3 venting4 and cloud migration.5 The results include applied load signal6 and the amount of fuel combusted versus the amount of structural damage created. The results can be coupled with a structural response model to predict how structural elements will deform or break.

To generate accurate models, CEBAM solves the full set of governing equations for fluid dynamics. The equations are solved on a finite volume mesh that represents both the domain and physical objects. The ignition source, congested zones and clouds are defined, and various species such as reactants7 and combustion products8 are represented in the model. CEBAM can also apply boundary conditions to buildings and structures.

The ability to assess many indicators10 and accurately characterize them within the model make CEBAM an excellent tool for realistically recreating blasts and their aftermath. Objects such as buildings, doors and wall panels can be given full failure criteria.9 Both pressure magnitude and impulse are recorded on these objects over time - which is the key to properly representing blast propagation, venting, and how structures and components will respond. The qualitative results from CEBAM are readily comparable to real-life data - the output looks very much like post-incident photos.