Submarine robot for shallow waters

A new type of swimming robot developed by researchers at Bath University could lead to improved submersible devices for applications such as the inspection of oil rigs.



Conventional submarine robots are powered by propellers that are heavy, inefficient and can get tangled in weeds.



In contrast, Gymnobot, created by researchers from the Ocean Technologies Lab in Bath’s department of mechanical engineering, is powered by a fin that runs the length of the underside of its rigid body. The fin undulates to make a wave in the water to propel the robot forward.



The researchers believe the design, inspired by the Amazonian knifefish, will be more energy efficient than conventional propellers and allow the robot to navigate shallow water near the seashore.



It is proposed that one application for the Gymnobot could be for filming and studying the diverse marine life near the seashore. Conventional submersible robots would have difficulty manoeuvring because the shallow water, with its complex environment of rocks and marine plants, can tangle a propeller.



William Megill, lecturer in biomimetics at Bath, explained: ‘The knifefish has a ventral fin that runs the length of its body and makes a wave in the water that enables it to easily swim backwards or forwards in the water.



‘Gymnobot mimics this fin and creates a wave in the water that drives it forwards. This form of propulsion is potentially much more efficient than a conventional propeller and is easier to control in shallow water near the shore.’



Keri Collins, a postgraduate student who developed the Gymnobot as part of her PhD, added: ‘We hope to observe how the water flows around the fin in later stages of the project. In particular, we want to look at the creation and development of vortices around the fin.



‘Some fish create vortices when flicking their tails one way but then destroy them when their tails flick back the other way. By destroying the vortex they are effectively reusing the energy in that swirling bit of water. The less energy left in the wake when the fish has passed, the less energy that is wasted.



‘It will be particularly interesting to see how thrust is affected by changing the wave of the fin from a constant amplitude to one that is tapered at one end.’



The lab was recently awarded a grant to work with six other European institutions to create a similar robot that reacts to water flow and is able to swim against currents.



In addition to studying biodiversity near the shore and in fast-flowing rivers, robots such as Gymnobot could also be used for detecting pollution in the environment or for inspecting structures such as oil rigs.



The project was funded by BMT Defence Services and the EPSRC.