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Updated 10:00 AM October 15, 2007
 

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Reversing shipwreck simulations helps identify dangerous waves

Big waves in fierce storms have long been the focus of ship designers in simulations testing new vessels.

But a new computer program and method of analysis by University researchers makes it easy to see that a series of smaller waves — a situation much more likely to occur — could be just as dangerous.

"Like the Edmund Fitzgerald that sank in Michigan in 1975, many of the casualties occur in circumstances that aren't completely understood, and, therefore, they are difficult to design for," says Armin Troesch, professor of naval architecture and marine engineering. "This analysis method and program gives ship designers a clearer picture of what they're up against."

Troesch and doctoral candidate Laura Alford presented a paper on their findings Oct. 2 at the International Symposium on Practical Design of Ships and Other Floating Structures.

Today's ship design computer modeling programs are based on cause and effect. A scientist tells the computer what type of environmental conditions to simulate, asking, in essence, "What would waves like this do to this ship?" The computer answers with how the boat is likely to perform.

Alford and Troesch's method goes backward, from effect to cause. To use their program, a scientist enters a particular ship response, perhaps the worst case scenario. The question this time is more like, "What are the possible wave configurations that could make this ship experience the worst case scenario?" The computer answers with a list of water conditions.

What struck the researchers was that quite often the biggest ship response is not caused by the biggest waves. Wave height is only one contributing factor. Others are wave grouping, wave period and wave direction.

"This is about operational conditions and what you can be safely sailing in," Alford says. "The safe wave height might be lower than we thought."

This new method is much faster than current simulations, which subject the virtual ship to random waves. To pinpoint the worst-case scenario, a ship designer sifts through months of data.

Alford and Troesch's program and method of analysis takes about an hour and it gives multiple possible wave configurations that could have statistically caused the end result.

"There's an outcry in the shipping industry for advanced ship concepts, including designs with more than one hull," Troesch says. Since ships are so large and expensive to build, prototypes are uncommon. This new method is meant to be used in the early stages of design to rule out problematic architectures and help spur innovation.

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