A flexible underwater robot with the ability to propel itself through the water quite similar to the Aurelia aurita jellyfish—nature’s most efficient swimmer—has been developed by researchers from the University of Southampton and the University of Edinburgh.
Published in Science Robotics, the results of the study show that the newly developed underwater robot can swim as fast and efficiently as the jellyfish and squid, on which its design is based. This could possibly pave the way for new possibilities for underwater exploration with its soft exterior and lightweight design.
The fascination for organisms such as squid, jellyfish and octopuses has been growing enormously because they are quite unique in that their lack of supportive skeletal structure does not prevent them from outstanding feats of swimming.
Dr Francesco Giorgio-Serchi, Study Co-Author, Lecturer, and Chancellor’s Fellow, School of Engineering, University of Edinburgh
Using the “cost of transport,” efficiencies of species across biology are compared, and this measure reveals the jellyfish is nature’s most efficient animal and easily beats running and flying animals as well as bony fish.
The new robot was created at the University of Southampton and is the first-ever submersible to show the advantages of leveraging resonance for underwater propulsion. Resonance denotes huge vibrations that appear when a force is applied at the optimal frequency, such as pushing a child on a swing. This enables the robot to use minimal power yet produce large water jets to thrust itself forward.
The simple yet effective mechanism involves a rubber membrane that incorporates eight 3D-printed flexible ribs, which collectively form a “propulsive bell.” A small piston located at the top half of the robot repeatedly taps this bell such that it expands and then springs back.
This simulates the swimming technique of a jellyfish and generates the jets of fluid needed to propel the robot through the water. If the piston works with the accurate frequency—the natural resonance for the components—the robot can propel at one body length per second and parallel the efficiency of the Aurelia aurita jellyfish.
The most recent investigations reveal that the new robot is 10–20 times more efficient compared to standard small underwater vehicles driven by propellers. Such an improved efficiency, together with the extra advantages of the robot’s soft, flexible exterior, would render it perfect for working near sensitive environments like a coral reef, archaeological sites, or even in waters crowded with swimmers.
Thierry Bujard, co-author of the study and a Master’s student in Naval Architecture at the University of Southampton, designed and developed the robot within a few months.
Previous attempts to propel underwater robots with jetting systems have involved pushing water through a rigid tube but we wanted to take it further so we brought in elasticity and resonance to mimic biology. I was really surprised by the results, I was confident that the design would work but the efficiency of the robot was much greater than I expected.
Thierry Bujard, Master’s Student in Naval Architecture, University of Southampton
According to Dr Gabriel Weymouth, Associate Professor in the University’s School of Engineering, who supervised the project, “The great thing about using resonance is that we can achieve large vibrations of the propulsive bell with a very small amount of power; we just need to poke it out of shape and let the elasticity and inertia do the rest. This has allowed us to unlock the efficiency of propulsion used by sea creatures that use jets to swim.”
The last decade has seen a surge in research into flexible and biologically-inspired robots, such as Boston Dynamic’s ‘Big Dog’, because they can be much more versatile than standard industry robots. This research demonstrates that these concepts can also be applied to underwater robotics.
Dr Gabriel Weymouth, Associate Professor, School of Engineering, University of Southampton
“There are still many challenges and exciting possibilities to explore with soft underwater robotic technologies. We are now looking to extend the concept behind this robot to a fully manoeuvrable and autonomous underwater vehicle capable of sensing and navigating its environment,” added Dr Weymouth.
Bujard, T., et al. (2021) A resonant squid-inspired robot unlocks biological propulsive efficiency. Science Robotics. doi.org/10.1126/scirobotics.abd297.