The ease with which a manta ray can zoom
through the water has offered scientists and
engineers an incredibly challenging task: They
want to see if they can build a mechanical
substitute for one of nature's best performers.
An underwater robot that could travel great
distances at high speed while consuming very
little energy could be useful for a wide range
of projects, from carrying scientific
instruments into the ocean deep to measuring
pollutants in bays and waterways to, of course,
unobtrusively delivering explosives to a distant
target.
That's a long range goal, but first they have to
figure out how the ray works its magic.
CLICK FOR VIDEO: The Mechanical Manta
Ray
"We want to learn from the biology," Hilary
Bart-Smith, associate professor of mechanical
and aerospace engineering at the University of
Virginia, said in a telephone interview. "We
want to see how rays have found the optimal
solution for underwater propulsion, or if there
is another solution out there that could be
even better."
Bart-Smith leads an
interdisciplinary project
involving scientists and
engineers at four universities
whose collective effort has
resulted in a mechanical
version of a cownose ray that
looks remarkably lifelike as it
swims through the water in
the University of Virginia's
swimming pool. At this stage,
it's no match for the real
thing, but it will serve as an
instrument in an ongoing
effort to learn from the
Batoidea ray, a collection of
500 species in 13 families
including stingrays and
mantas.
This project is still in its early
stages. The mechanical ray is
controlled, for now, by a
joystick linked to the robot
through a tether, so it can
only reach a maximum depth
of 10 feet. The ultimate goal,
of course, is to build a robot
that performs at least as well
as a real ray and can be controlled remotely,
even at 10,000 foot depths, where some rays
live.
But studying rays in their natural environment
can be a bit tricky. They can deliver a real
punch, as Captain John Smith learned in 1608
when he was stung near Chesapeake Bay so
severely that his crew thought he was going to
die.
Marine biologist Frank Fish (that's really his
name) of West Chester University in
Pennsylvania, a member of the team, traveled
to the remote Micronesian island of Yap to
videotape rays in their natural habitat.
He has also studied rays in his lab as they
swam down a channel through water
containing particles highlighted by a laser, thus
showing some of the fluid dynamics at work.
The rays move forward through the water by
flexing their pectoral fins, commonly referred
to as "wings" because that's what they look
like. But how they do that is still something of
a mystery. An aircraft uses propulsion to drive
itself forward, creating lift as air passes over
its wings. A ray flaps its wings up and down --
but has no visible means of forward thrust.
Tetsuya Iwasaki, an expert on animal
locomotion at the University of California, Los
Angeles, has been addressing that question.
Animals, including humans, are propelled by a
linear series of electrical pulses from the brain
that cause us to put one foot in front of the
other, a pretty simple solution to a complex
problem. But rays flap their wings up and
down to produce forward thrust and maintain
proper depth instead of sinking to the bottom
of the ocean.
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