CARL schematics. Credit: 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. Their work is published in PNAS Nexus.
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. Credit: John O. Dabiri and Peter Gunnarson
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.
CARL swimming. Credit: John O. Dabiri and Peter Gunnarson
More information: Peter Gunnarson et al. Surfing vortex rings for energy-efficient propulsion, PNAS Nexus (2025). academic.oup.com/pnasnexus/art … 93/pnasnexus/pgaf031
Provided by PNAS Nexus
