Underwater vehicle uses a balloon to dart like an octopus

The octopus-inspired device, inflated and ready to go

When you inflate a balloon and then release it without tying the valve shut, it certainly shoots away quickly. Octopi utilize the same basic principle, although they suck in and then rapidly expel water. An international team of scientists have now replicated that system in a soft-bodied miniature underwater vehicle, which could pave the way for very quickly-accelerating full-size submersibles.

The 30-cm (11.8-in)-long model was created by researchers from the University of Southampton, MIT and the Singapore-MIT Alliance for Research and Technology.

It features a rigid 3D-printed polycarbonate skeleton, which is mostly covered by an outer elastic balloon-type envelope. Water is pumped into that balloon by an external pump, inflating it. When the model is then released from the pump, that water rushes out of the balloon, rapidly propelling the model forward.

Fins at the rear of the device allow it to travel in a straight line, while the skeleton beneath the balloon keeps it from deflating to the point that it becomes limp and unstreamlined. It can be seen in action, in the following video.

While it at first glance might appear to be a glorified toy, the scientists claim that with its ability to accelerate by over 10 body lengths in under a second, the vehicle's performance is unmatched by any other submersible.

"Man-made underwater vehicle are designed to be as streamlined as possible, but with the exception of torpedoes, which use massive amounts of propellent, none of these vehicles achieve speeds of even a single body length per second," said Southampton's Dr. Gabriel Weymouth, lead author of the study. "Rigid bodies always lose energy to the surrounding water, but the rapidly shrinking form of the robot actually uses the water to help propel its ultra-fast escape, resulting in 53 per cent energy efficiency, which is better than the upper estimates for fast-starting fish."

Ultimately, it's conceivable that technology based on the same principle may find its way into the design of proper ROVs (remote operated vehicles), AUVs (autonomous underwater vehicles) or other submersibles. In fact, Germany's Fraunhofer Institute for Manufacturing Engineering and Automation is developing its own miniature octopus-inspired propulsion system, which also works by drawing in and then expelling water.

A paper on the Southampton/MIT device was recently published in the journal Bioinspiration and Biomimetics.

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