Sunday, 18 October 2015

3D-printed seal whisker helps scientists understand how they use them to hunt

OCTOBER 16, 2015

by John Hopton

Seals' impressive ability to track prey has long intrigued marine biologists, so Engineers at MIT wanted to investigate how seals can be such master hunters.

Seals can follow the path of prey that passed by up to 30 seconds before, due to the antennae-like qualities of their whiskers. Engineers at MIT fabricated and tested a large-scale model of a harbor seal’s whisker in order to investigate how this talent works.

Each whisker is wavy rather than straight, with an elliptical cross-section that varies in size along its span.

“It’s marvelous to see this intricate pattern, it’s not just a straight antenna — it’s a perfect sinusoid,” said Michael Triantafyllou, the William I. Koch Professor in MIT’s Department of Mechanical Engineering. Together with former graduate student Heather Beem, whose PhD thesis formed the basis of the work, he published the results of the study in the Journal of Fluid Mechanics.

Whereas most long, thin rods tend to create large vortices, or eddies, as they move through water, Beem found that the wavy pattern of the whisker’s geometry created much weaker vortices, enabling the whisker to move silently. This, the researchers suggest, may help the seal block out its own disturbance as it moves.

“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,” Triantafyllou said.

Whiskers that ‘slalom’ like a skier

With minimal water disturbance assured, the seals can follow the wake left by the prey because of a ‘slaloming’ motion in the whiskers, the scientists found.

The team observed that once their own synthetic whisker entered the wake left by a passing object, it started to vibrate at the same frequency as the wake’s passing vortices. Close inspection showed that the whiskers ‘slalom’ among the vortices, like a skier zigzagging between flags.

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