Texas A&M aerospace engineer Dr. Othon Rediniotis said propellers generate wakes that are visible behind the ship. Satellites can be used to identify and track a ship based on its wake. Submarines also generate wakes that can be seen on the ocean's surface.

Aquatic animals don't leave a large wake because they move more efficiently through the water. This makes them less detectable, Rediniotis said. The U.S. military wants to develop vessels that mimic this movement to reduce the "wake signatures" that can give away the presence and identity of its ships.

"The military wants at least small vehicles to maneuver more like fish do rather than like clunky submarines," he said. "Right now, the vehicles are slow in maneuvering because they move using propellers and slow control surfaces and are not using body motion to propel themselves."

Texas A&M engineers are using wires made of Shape Memory Alloys (SMAs) -- materials that dramatically expand or shrink with temperature change but return to their original shape after the temperature returns to normal -- to mimic the motion of a fish's muscles. When heated, the wire's length shrinks as much as 8 percent. By using springs and attaching the wires to a metal skeleton, engineers can cause the vehicle to flex back and forth -- similar to a fish's body -- by alternately heating and cooling the wires.

"In a sense, we're using the Shape Memory Alloys as muscles," Rediniotis said.

In one prototype vehicle, batteries provided the heat energy needed to cause the wire to contract. But researchers found that batteries big enough to power the vehicle would take up too much room -- room that would be needed for supplies, payloads or personnel in a real-life situation.

The latest version uses fuel as a heat source. Fuel provides a lot of energy but takes up a relatively small amount of space, Rediniotis said. The wire is embedded within channels filled with ethylene glycol, or antifreeze. The fuel heats the ethylene glycol, and therefore the SMA wire, causing the wire to contract. The surrounding water cools the wire in the underwater vehicle and returns it to its normal length.

A similar project is being done at the Massachusetts Institute of Technology, but instead of using SMAs to propel their vehicle, MIT researchers are using conventional motors.

In addition to its use by the military, Rediniotis said, the SMA technology developed for these vehicles could be used for other applications, such as unmanned vehicles to inspect offshore drilling hardware, ocean floor mapping and other types of oceanographic studies.

This project is funded by the Office of Naval Research and Aeroprobe Corp. Dr. Dimitris Lagoudas, a professor in Texas A&M's aerospace engineering department, is the co-investigator for the project.

Related website:

Dr. Dimitris Lagoudas faculty page

[Contact: Dr. Othon Rediniotis, Mark Evans]

19-Nov-2001