It's strange stuff.
Place a magnet next to the puddle of coffee-like fluid and, Shazam! it's instant pudding. Remove the magnet and Presto! it's a puddle again.
"Magnetorheological" fluid has been around since the '40s, but only recently has the oil with micron-sized iron chunks suspended in it been harnessed -- and then just for small-scale applications like truck-seat shock absorbers and exercise equipment.
When Bill Spencer looked at the quirky liquid, however, he saw a solution to a much bigger problem. A trade magazine article about the truck-seat system suggested to the ND civil engineering professor a novel way to earthquake-proof buildings. Whatever keeps a trucker from vibrating, he reasoned, ought to take the shake out of a quake -- if it were scaled up.
"Essentially it's the same problem," Spencer says. "In one instance you're trying to isolate the truck seat from road vibration; in the other you're trying to isolate a building and its contents from quaking ground."
The Lord Corporation, manufacturer of the truck-seat shock absorber, was delighted with Spencer's insight and agreed to underwrite research on the system's feasibility. Using a full-scale Lord prototype, Spencer and Michael Sain, Notre Dame's Freimann Professor of Electrical Engineering, have been experimenting to develop a mathematical model for optimizing its performance. Spencer believes the system will be superior to both the "passive" quakeproofing method -- the U.S. norm, which relies on economical shock absorbers like those found on cars -- and "active" systems now widely used in Japan. The active systems rapidly move heavy masses back and forth to cancel out earthquake vibrations.
A system with magnetorheological fluid would represent a hybrid.
"It offers the best of both worlds," Spencer says. "The system is very reliable because it has only one moving part and is battery powered. Since earthquakes frequently cut off normal electric service, this is an important advantage over active systems, which need large amounts of power to move the heavy masses."
Even if the system fails in its active mode, Spencer points out, it will still work as a passive shock absorber.
For more information, see Notre Dame's Structural Dynamics and Control/Earthquake Engineering Laboratory home page at http://www.nd.edu/~quake/