Modeling Brain Blasts

Traumatic brain injury (TBI) is often called the signature injury of the war in Iraq. Medical experts have yet to determine exactly what causes the condition, but the violent waves of air pressure emitted by an improvised explosive device (IED) or a rocket-propelled grenade are most likely to blame. These pressure waves travel close to the speed of sound and can rattle the brain's soft tissue, causing permanent, yet invisible, damage. In an effort to better understand how the waves shake soldiers' brains, researchers at the Naval Research Laboratory (NRL), in Washington, DC, developed a computer simulation that models the motion of a propagating blast wave using data gathered from laboratory experiments with sensor-studded mannequins. The simulation gives us the full 3D flow field, velocities, and pressure distributions surrounding the head and the helmet. Initial testing has already revealed some compelling results. The NRL researchers are collaborating with a team of researchers at Allen-Vanguard Technologies, in Canada.

The group placed Marine Corps ballistic helmets on mannequins equipped with pressure sensors and accelerometers, and these modified mannequins were placed at various orientations and distances from controlled explosions. The researchers collected data from more than 40 different blast scenarios and integrated the data into their computer simulation. The simulation uses a set of well-established flow-modeling algorithms for simulating reacting and compressible flow to create a 3D simulation of the pressure wave that would be experienced by a real soldier. These [algorithms] have been used in the past, but we are combining them in a new way to make software for this particular problem. The calculations are done in two steps. First, the algorithms are used to model the initial blast to get a realistic blast profile from the explosion. This includes the chemistry, so we can get the strength of the pressure waves and the velocity field. Second, as the wave approaches the mannequin, this information is fed into a compressible flow simulation that produces a more complex 3D simulation of the head-helmet geometry. This combined approach makes the calculations more realistic and efficient.

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http://www.technologyreview.com/computing/21712/?a=f