From the tiniest guppy to the giant blue whale, aquatic animals all can maneuver through water and do so without being easily detected -- an ability the U.S. Navy has asked Texas A&M University engineers to copy to make U.S. ships and submarines more efficient and undetectable. 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.