Water 'tractor beam' could help confine oil spills

Australian researchers develop wave manipulation technique to control objects on water's surface

Researchers at the Australian National University (ANU) have developed a “tractor beam on water” that could confine oil spills, manipulate floating objects or explain rips at the beach.

The group, found that they can control water flow patterns with wave generators to move floating objects. Dr Horst Punzmann, from the Research School of Physics and Engineering, said: “We have figured out a way of creating waves that can force a floating object to move against the direction of the wave. No one could have guessed this result.”

The technique could enable the control of objects and substances adrift on water in a way they have never had before, resembling sci-fi tractor beams that draw in objects, said the researchers.

The team used a ping-pong ball in a wave tank to work out the size and frequency of the waves required to move the ball in whichever direction they want. Advanced particle tracking tools, developed by the team, revealed that the waves generate currents on the surface of the water.

Professor Michael Shats, from the Physics of Fluids Laboratory of the Australian National University, said:  “We found that above a certain height, complex three dimensional waves generate flow patterns on the surface of the water. The tractor beam is just one of the patterns. They can be inward flows, outward flows or vortices. We've got a new tool, a new concept here to engineer surface flows with. ”

The team also experimented with different shaped plungers to generate different swirling flow patterns.

Punzmann said that current mathematical theory was unable to explain the results of the experiment. He said: “It’s one of the great unresolved problems, yet anyone in the bathtub can reproduce it. We were very surprised no one had described it before.”