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June 14, 2007, 08:13 AM ET
Repeating 9/11 in a Computer
No one wants to relive the terrorist attacks of September 11, 2001. Researchers at Purdue University, however, have found a valid scientific reason to recreate them. They have made an animation of American Airlines Flight 11 slamming into the north tower of the World Trade Center. The animation shows the effects of the impact on the steel structure of the building, the dispersal of jet fuel and flame, and the wreckage of the plane.
"I think the main question in the minds of the public is whether the impact destroyed the tower, or whether it was the fire," says Christoph M. Hoffmann, the director of the Rosen Center for Advanced Computing at Purdue and one of the designers of the simulation. His answer: It was the fire.
The Purdue animation shows that the force of the initial hit damaged or destroyed 14 to 17 steel support columns on the 95th, 96th, and 97th floors. "But even with 17 columns knocked out, the building would have stood," Mr. Hoffman says. "The subsequent fire could have reached high enough temperatures to melt steel" and take down the entire structure.
Data on the force of the impact came from published FEMA reports, as well as airplane-manufacturer studies of crashes. And to model jet-fuel dispersal, Mr. Hoffman and his colleagues shot soda cans out of a steel pipe and into a wall, providing a splatter pattern to map into the simulation.
The number of support columns damaged in the Purdue simulation is higher than in other reconstructions. "Impact is a chaotic process, and you can never reproduce everything," Mr. Hoffman says, noting that all recreations rest on assumptions that leave room for disagreement. His work, he says, matches up well with photographs of the actual tower damage right after impact, giving him confidence this model is on target. --Scott Carlson and Josh Fischman
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