Sea lions may inspire ‘strokes’ of genius – Science Nation


[nat/music] Miles O’Brien:
It’s a drizzly morning at the National Zoo, but here at the sea lion
exhibit it’s not too early play. Megan Leftwich:
At heart, I’m a fluid dynamicist.
I’m interested in how animals interact with the water or air
around them to generate forces. Miles O’Brien:
Mechanical engineer Megan Leftwich and her team have set up their cameras
and settled in for a stake-out, waiting and watching
for a passing sea lion to do what they call
“the clap.” Megan Leftwich:
It’ll take its arms out on its side
and clap them into its belly, and when it does that,
it grabs all the water between the two and pushes
the water towards its feet, and that makes it go
in the other direction. Miles O’Brien:
With support from the National
Science Foundation, Leftwich and her students are
using motion capture techniques to record data on the sea lions’
unique style of swimming. Megan Leftwich:
So, what we do is we use two cameras at 90-degree angle
to each other, and then we calibrate
those cameras to each other. So, we know pixel 452 on one
is pixel 229 on the other. Miles O’Brien:
Fish and marine mammals swim by swishing their tails.
Sea lions do it with their arms. Those front flippers
might look like fins, but anatomically
they are more like hands. Megan Leftwich:
That was really what got me thinking like, “Ooh, that’s a really
different way to generate thrust
under water.” And so, it’s really
that “differentness” about sea lions
that made me think, “Let’s look more
deeply into that.” Is that a paradigm that,
you know, as an engineer, we could build into future
underwater vehicles? Miles O’Brien:
Today, most state-of-the-art underwater drones rely on rear
propulsion to move around. But, imagine one that would
swim like a sea lion. Megan Leftwich:
The idea is if it we understand this different
type of propulsion, perhaps we could build
that into a capability for unmanned
underwater vehicles, and, to really do that, we need
to understand the physics that underpins
that type of motion. Miles O’Brien:
Back in the lab, they use software tools to crunch through
all the imagery and generate an accurate
3D model of a flipper. Aditya Kulkarni:
So, this product is a scaled-up version of what we are
printing right now. Miles O’Brien:
They 3D print test articles, starting with
rudimentary cross sections and eventually working up
to something that looks like the real thing.
They test them in a wind tunnel to evaluate their
aerodynamic properties. They use talcum powder
mixed with oil to visualize the flow of air
over the leading and trailing edges. Aditya Kulkarni:
And, a stream of air goes over the flipper, and we can actually measure
what lift and drag the object
is producing. Miles O’Brien:
They also test silicone flippers in a water flume. Eli Kashi:
What we do is we take this 3D printed skeleton.
It’s meant to mimic the wrist and then the elbow
and joints on a sea lion, and we mount this into a mold,
pour silicone in and come up
with the finished flipper. [nat/sound] Miles O’Brien:
The silicone flipper is 65% the size of a real one. Eli Kashi:
I oscillate them back and forth, and I see what the wake
is behind the flipper. Miles O’Brien:
They use dye to visualize how the water moves
in swirls and eddies. Another technique uses
a laser and glass beads. Eli Kashi:
And, I’m going to be able to tell the kind of propulsion
and the kind of thrust that’s produced through
this method of swimming. Miles O’Brien:
Leftwich stresses that she and her team
are working on basic research. Any underwater vehicles
built based on these principles will be the work of other
engineers further down the road and probably won’t look
much like a sea lion. Megan Leftwich:
The idea is not to replicate the sea lion. It’s to understand the sea lion
and be inspired by that, by the physics
that make the sea lion work. Miles O’Brien:
Looking to nature for engineering insights…
building a better understanding of how these most agile
of swimmers move. For Science Nation,
I’m Miles O’Brien. Miles O’Brien, reporting.

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