Magazine article Oceanus

Seal Whiskers Inspire Marine Technology: By Closely Observing Nature, Biomimetic Engineer Designs a New Sensor

Magazine article Oceanus

Seal Whiskers Inspire Marine Technology: By Closely Observing Nature, Biomimetic Engineer Designs a New Sensor

Article excerpt

The night approaches quickly. A harbor seal plunges into the water, diving deep as the sunlight recedes. Through the dark, turbid waters, she searches for fish. Suddenly, the whiskers on her right cheek begin vibrating. And she's off.

Like many other animals, seals can use their whiskers to touch objects to determine their size, shape, and distance away. But the fish that our seal set out to catch hadn't touched her whiskers.

Could seals also use their whiskers to "feel" the surrounding water patterns to track fish that swim by? In the early 2000s, marine biologists at the University of Rostock in Germany began to explore that theory. They conducted experiments in which they placed a blindfold and earmuffs on a seal. The animal nonetheless was able not only to detect the presence of moving objects, but also to track them long after any visible traces of their passage had disappeared. It became increasingly clear to the researchers that seals have an uncanny ability to use even the faintest signals in the water to paint a picture of their dark, watery surroundings.

This finding intrigued engineers in my research group on the other side of the Atlantic in the Towing Tank Laboratory at the Massachusetts Institute of Technology. Could we learn a few tricks from seals to overcome the challenges we face in designing underwater vehicles with better navigation and sensing capabilities?

Fluid dynamics and biomimetics

When news of the Rostock seal biologists' work reached our research group, it stimulated new thinking about two main lines of inquiry we were pursuing. The first concerns vibrations in large offshore structures such as oil drilling platforms. The steady flow of currents around these structures induces significant, prolonged vibrations that lead to structural fatigue. For the past three decades, my Ph.D. advisor, Professor Michael Triantafyllou, has led studies uncovering the basic physics of flow around riser legs and cables in offshore structures and, more fundamentally, around circular cylinders.

Our group has also pioneered the field of marine biomimedcs: the science of using features observed in nature to inform the design of new marine technologies. One example is RoboTuna, an underwater vehicle our lab developed that employs motions observed in efficiently swimming fish. This research not only allowed us to design improved underwater propulsion systems, it also enabled us to uncover some fundamental physics of fish swimming that we wouldn't have been able to obtain through observation alone.

We jumped at the opportunity to combine our interests in vibrations and bio-inspired design and pursue research on seal whiskers. We had two goals in mind: The first was to uncover how the basic physics of fluid flow around cylindrical structures--seals' whiskers--enables them to sense their environment. The second was to use what we discovered to engineer a new technology: a flow sensor that can track a fading hydrodynamic trail.

Such a sensor installed on autonomous underwater vehicles (AUVs) would improve the vehicles' ability to navigate. Rather than relying as they do now just on reflected sound waves--listening like a bat to calculate their positions and detect objects--the vehicles could use another sensor to "feel" their way to moving objects.

Why look to nature?

My dad is an aquatic biologist, and when I was younger, he took my siblings and me tromping through streams to collect water samples for testing. I was excited to be surrounded by the natural world, with all of my senses heightened. The fresh air, the crisp water around my legs, and the slimy rocks were all pointing to the myriad unknowns out there to be discovered.

As time went on, I began learning about many things happening in nature that at first glance didn't seem possible: a blind fish called the Mexican tetra, for example, that somehow can navigate through caves, or sea turtles that traverse thousands of miles across the open ocean to reach their nesting sites with pinpoint accuracy. …

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