MIT researchers find whiskers slaloming motion help harbor seals track prey

CAMBRIDGE, Mass. – Engineers at MIT have fabricated and tested a large-scale model of a harbor seal’s uniquely shaped whiskers, which are shaped with an elliptical cross-section varying in size along its span, to help scientists determine if the pinnipeds ability to track prey is due to antennae-like whiskers.

According to an article published by MIT News Office a team of researched found a seal’s whiskers oscillate in response to the turbulence left by a moving object. By using the fabricated whiskers the researchers observed once the whisker enters the wake left by a passing object it starts vibrating at the same frequency as the wake’s passing vortices.

This slaloming provides the seal with clues of the objects size, shape and path.

Former graduate student Heather Beem used 3-D printing techniques to reproduce the seal’s wavy morphology at a much larger scale, in order to measure its response to various wakes. She tested the whisker’s vibration properties in a 30-meter-long tank of water with a moving track suspended above the water.

Beem found the wavy pattern of the whisker’s geometry created much weaker vortices, enabling the whisker to move silently, with very little vibration, through the water.
The whisker’s morphology, the researchers found, might help the seal block out its own disturbance as it moves through water.

“It’s like having the ability to stick your head out of a car window, and have there be no noise, so that your ears don’t ring: It’s a quieting effect,” said Michael Triantafyllou, the William I. Koch Professor in MIT’s Department of Mechanical Engineering.

To test how a whisker reacts to external stimuli, Beem attached a large, long circular cylinder ahead of the whisker. Beem found that the whisker, when following the cylinder, vibrated significantly, moving in a slaloming pattern among the wake vortices. As she varied the speed of the moving track, the whisker quickly adapted, vibrating at precisely the frequency of the cylinder’s changing vortices, according to the news release.

“The geometry of the whisker allows for this phenomenon of being able to move very silently through the water if the water’s calm, and extract energy from the fish’s wake in order to vibrate a lot,” Beem said. “Now we have an idea of how it’s possible that seals can find fish that they can’t see.”

Triantafyllou says artificial whiskers may be useful as low-power sensors for underwater vehicles.

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