Submersible robot surfs water currents
video:
Example trajectory of CARL surfing a vortex ring for propulsion. In response to sensed acceleration, CARL autonomously executed a short burst maneuver to become entrained into the material boundary of a vortex ring. Afterwards, CARL advected passively across the tank with the vortex ring. The trajectory of CARL is indicated by the white line, with the short maneuver highlighted in red. Velocity vectors and vorticity from PIV measurements are overlaid to indicate the vortex ring.
view moreCredit: John O. Dabiri and Peter Gunnarson
An autonomous underwater vehicle can propel itself efficiently by using the energy in nearby water currents. Underwater and aerial vehicles must make their way through a complex environment of gusts and currents, fighting against many flows as they attempt to stay on course. Peter Gunnarson and John O. Dabiri designed an underwater robot that makes use of these flows to cut down on the energy needed to travel, “surfing” vortices to make its way to its destination. The palm-sized robot, CARL, was equipped with an onboard inertial measurement unit, ten motors to allow movement in all three axes, and a simple but effective algorithm: if the magnitude of the acceleration in the crossflow-direction exceeded a threshold, CARL would swim in the same direction as the acceleration. The robot was tested in a 1.5 m deep and 5 m long tank, in which vortex rings were generated by pulsing a wall-mounted thruster. Using the algorithm, CARL was able to surf the vortex from one end of the tank to another using one-fifth of the energy as a robot without the same programming. According to the authors, CARL’s success surfing a prototypical flow structure, suggests that with further elaboration, a similar technique could be used to allow autonomous vehicles to improve their efficiencies significantly by interacting with background flows.
Journal
PNAS Nexus
Article Title
Surfing vortex rings for energy-efficient propulsion
Article Publication Date
25-Feb-2025
High speed video of CARL swimming into and surfing the vortex ring. Particle streaks are shown in the reference frame of the vortex ring to visualize the boundary and shape of the vortex ring. Video is played at 20% or 1/5th real-time speed.
The palm-sized robot, CARL.
CARL schematics.
CARL schematics.
Images are combined from a video to show CARL's motion while surfing the vortex ring.
Credit
John O. Dabiri and Peter Gunnarson
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