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Seal Whisker Geometry Could Inspire Stronger Underwater Structures

ByLydia-Rose KesichNOVA NextNOVA Next

Turbine blades as silent as owl wings. Smartphone displays as vibrant as butterfly scales. Drones as maneuverable as bats.

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Nature has solved most engineering problems at one point or another, and studying these solutions can improve technologies and provide us with new ones. The most famous of these is Velcro—wildly useful, worth over $1 billion, and inspired by sticky burdock seeds—but the ideas keep coming. Research published by Cleveland, Ohio, engineers this month explains how a seal’s whiskers could teach us how to build bridge struts and oil wells that last longer underwater.

“There’s a lot that we can learn if we just take a moment to look at nature,” said Aidan Rinehart, an author of the Cleveland University paper. Rinehart is a classically trained engineer, but as a student he attended a lecture about building jet engine blades textured like whale skin and decided to pursue biologically inspired design. Now Rinehart is figuring out how seals manage to detect predators and prey with their whiskers while neatly avoiding problems that plague our own underwater technology.

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Seals have undulating whiskers that allow them to hunt even when blindfolded and ear-muffed.

When water flows around an irregular structure, it forms a lazy zigzag wake that makes the structure rattle. These vibrations damage almost everything we put in the water, from the columns of wind turbines to the risers on oil rigs, and they cost us a fortune—British Petroleum estimates that countering the damage eats up 10% of their multi-billion dollar budget for deep-sea projects.

A seal’s underwater acrobatics should cause its whiskers to vibrate so intensely that outside disturbances would be undetectable, but they don’t. If we understood why, we might be able to build underwater structures that work better and last longer.

A seal whisker is shaped like a ripe bean-pod—a slightly flattened cylinder with smooth, regular bulges up and down the length. If you sliced it in two at the center of a bulge, the cross-section would be an ellipse; if you sliced it at a narrow place the cross-section would be a circle. The current theory is that these undulations each make their own small wake, instead of the single, powerful wake left by smooth whisker. Not only are the smaller wakes weaker, but they go in all different directions, so they can’t align to move the whisker. Sea lions, which have smooth whiskers, can’t navigate with their whiskers alone, but seals with undulating whiskers can hunt even when blindfolded and ear-muffed by researchers.

By holding its whiskers perfectly steady, the seal can detect tiny swirls of turbulence that would otherwise be invisible. As a fish swims, a defined current unfolds in its wake, undulating through the water like a cracked whip. To a seal, this trail is as easy to follow as the track a snake leaves in the dust. “It’s like a signature,” said MIT’s Michael Triantafyllou. “They can tell what it is at a distance.”

Triantafyllou is one of the pioneers of biologically-inspired marine engineering, and Rinehart cites his work both in his recent paper and in conversation. Research by Triantafyllou, Rinehart, and many others supports the idea that the undulations in seal whiskers are the key to their remarkable stability, but that wasn’t enough information to start building multi-million dollar bridges and drilling platforms. Rinehart’s recent paper focuses on finding the exact parameters of the whisker so they can be applied to human technologies—the kind of fiddly measurement work that is vital, but not usually very exciting.

But Rinehart found something thrilling in his measurements. The proportions of the whisker, produced by millions of years of natural selection, were precisely what several different groups of engineers had calculated to be ideal for reducing vibration. Evolution and human problem solving had collided at the same solution.

“There’s this small aspect of this really complex geometry that’s found in nature, and it just so happens to match—it’s dumfounding,” Rinehart said. “There’s some really amazing things happening in nature, and we don’t even really know most of the time.”

“The ideas never stop coming,” Triantafyllou said. “The question is not whether there are such applications, it’s whether we have the knowledge and understanding to do something about it.”

Photo credit: Marcel Burkhard / Wikimedia Commons (CC BY-SA 2.0 DE)

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