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Can You Dig the RoboClam?

Anchor technology hasn't changed too much since Blackbeard's heyday. They're really not much more than gigantic hunks of steel with hooks. Now, scientists are working on building a smart, robotic anchor inspired by a clam that buries itself into the seabed.

Burrowing is something that the clams figured out the best way to do long ago. The Atlantic razor clam in particular is one of the planet's best burrowers.
Image: Arne Hückelheim via Wikimedia

"It has a digging efficiency that is more than ten times any existing technology," said Kerstin Nordstrom, a researcher at the University of Maryland.

Razor clams are one of the best tunnelers in the animal kingdom, able to move though earth at a speedy centimeter a second. Nordstrom and the rest of her research team have been studying how the aquatic critter is so good at burying itself.

What makes it so efficient is a subtle way the clam squeezes its shell when it's surrounded by sand. By making itself ever so slightly narrower, it changes the way the sand behaves around it. Instead of acting like a solid wall on all sides, grains of sand cascade down and flow around more like a liquid than a solid.
Image courtesy of Nordstrom

"All the clam has to do is dig through a liquid-like material rather than a sold-like material, which makes for a much more efficient digging mechanism," Nordstrom said.
Photo: Donna Coveney, Amos Winter (MIT GEAR Lab)

A team at MIT built a machine to mimic the way the clam digs through the underwater sand. Dubbed "RoboClam," it resembles the grips of a pair of pliers more than a mollusk, but it works the same way. A rod pushes the lighter-sized machine down into the seabed while its two "handles" are opened up. It quickly closes, stirring up the nearby sand both to the side and in front of it. The rod pushes the machine down smoothly thorough the now liquid like sand while the handles open up again for another round.

Submarine companies are one of the main sponsors of the research. Tiny watercraft like unmanned subs don't have a lot of space on board for big batteries, so they need a way to get the most bang for their buck.

Nordstrom used MRI machines to take detailed pictures of simulated sand around the RoboClam to test their predictions. They ran the device in a special fish tank full of transparent beads that mimicked the behavior of the sand grains. The MRI machine took photo slices through the tanks, watching how the beads flowed around the opening and closing clam.

"This is really a confirmation of models so we can further optimize future systems," Nordstrom said.

With their theories now better supported by experiment, the MIT team is already working on RoboClam 2.


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