Sea Lion Inspired Research for Underwater Stealth Robotics

Sea Lion Inspired Research for Underwater Stealth Robotics

17 August 2015 | Greogre Washigton University |

Sea lion has a unique way of moving through the ocean. This highly maneuverable aquatic mammal produces thrust primarily with its fore flippers – the ones it has where you have hands. Despite being fast, efficient and agile, this sea lion swimming technique is quite different from the way other large fish and marine mammals move through the water. Sea lions produce high levels of thrust while leaving little traceable wake structure.

Inspired by Nature – how Nature solves the problems and how we can use  this into future technologies, Prof. Megan Leftwich led Researcher’s team from the Greogre Washigton University, USA are cracking sea lions’ high-thrust and low-wake swimming technique. Professor Megan Leftwich and her research team are building a robotic flipper based on the sea lions flipper.

(This video is the highlights the work that SEAS Professor Megan Leftwich and her research team conduct in the hopes of building a robotic flipper based on the sea lion flipper.  In the video, Leftwich explains how the sea lion’s unique way of swimming inspired her research.)

How does sea lions’ motion differ from others?

The sea lion relies predominantly on its foreflippers for thrust production. Thrust is the force that accelerates the animal in the forward direction. The large flippers move through the water in a clapping motion that ends with each flipper pressed against the animal’s torso.

This flipper-based motion differs significantly from other large fish and marine mammals, which typically have a dominant oscillation frequency. For fish, that means they flap their tails side to side continually. Aquatic mammals flap up and down. In both, every flap takes about the same amount of time. Instead, in sea lions, each clap of the flipper is followed by a prolonged glide — particularly unusual for large, high-thrust-producing swimmers. The smooth swim is assisted by the animal’s low drag coefficient, meaning it glides through the water easily without much resistance slowing it down.

(In this GW-produced video, Dr. Leftwich gives a fuller explanation of her efforts to study nature’s solutions to propulsion challenges.)


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Ten tracked points on the sea lion’s foreflipper. (Image: Megan Leftwich)

Researchers collected lots of HD footage of sea lion movements from California zoo to understand sea lion hydrodynamics – that is, the physics of how their swimming motion disrupts the surrounding water and to characterize the Kinematics means how their bodies move.  But video is only a two-dimensional representation of what really happened in space.  That’s why to analyze the motion of sea lion in 3D; they used digital linear transformation, a method used to track three-dimensional motion that was developed by Ty Hedrick of UNC to track hummingbird and hawk moth flying.

Individual points on a sea lion’s flipper are digitally located in each frame of the video (120 frames per second). Those locations are tracked from frame to frame, creating a surface that represents the motion of the sea lion’s foreflipper while swimming. Through this process, team created a digital foreflipper that can be programmed to move like a real sea lion.

Robotic Sea Lion Flipper

BY using collected data they created a robotic sea lion foreflipper prototype model.

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The robotic flipper will be used to measure the reaction of the water to the sea lion’s clapping motion. (Image: Megan Leftwich)

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3D geometry for sea lion foreflipper based on laser scanning. (Image: Megan Leftwich)

And With this robo-foreflipper, they can investigate, and hopefully understand, the unique way that sea lions move the water while performing their one-of-a-kind swimming motion. Eventually they might see this technique incorporated into an engineered underwater vehicle that could be used to search for underwater mines, or shipwrecks, or unexplored caves – anything that requires stealth, agility and speed in the water.

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