Submersible Robot Rides Water Currents

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.