Physicists create water tractor beam

Aug 10, 2014
Dr. Horst Punzmann and professor Michael Shats demonstrate their water tractor beam. Credit: Stuart Hay, ANU

Physicists at The Australian National University (ANU) have created a tractor beam on water, providing a radical new technique that could confine oil spills, manipulate floating objects or explain rips at the beach.

The group, led by Professor Michael Shats discovered they can control with simple wave generators, enabling them to move floating objects at will.

"We have figured out a way of creating that can force a floating object to move against the direction of the wave," said Dr Horst Punzmann, from the Research School of Physics and Engineering, who led the project.

"No one could have guessed this result," he said.

The new technique gives scientists a way of controlling things adrift on water in a way they have never had before, resembling sci-fi tractor beams that draw in objects.

Using a ping-pong ball in a wave tank, the group worked out the size and frequency of the waves required to move the ball in whichever direction they want.

Advanced particle tracking tools, developed by team members Dr Nicolas Francois and Dr Hua Xia, revealed that the waves generate currents on the surface of the water.

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Physicists at the Australian National University have created a tractor beam in water. Using a simple wave generator they can create water currents which could be used to confine oil spills, manipulate floating objects or explain rips at the beach. Credit: ANU Multimedia Team

"We found that above a certain height, these complex three-dimensional waves generate flow patterns on the surface of the water," Professor Shats said. "The is just one of the patterns, they can be inward flows, outward flows or vortices."

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

As yet no mathematical theory can explain these experiments, Dr Punzmann 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."

Explore further: Researchers build acoustic tractor beam

More information: Generation and reversal of surface flows by propagating waves, Nature Physics, DOI: 10.1038/nphys3041
On Arxiv: arxiv.org/abs/1407.0745

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User comments : 13

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Jag_Pop
1.1 / 5 (8) Aug 10, 2014
(faceslap)...this isn't news, is it?!

Article offers this:
----------------------
"We have figured out a way of creating waves that can force a floating object to move against the direction of the wave," said Dr Horst Punzmann, from the Research School of Physics and Engineering, who led the project.

"No one could have guessed this result," he said.
----------------------

Well *I* thought of it years ago. Actually, I *read* about it years ago. It had me ponder "reversing" waves as gravity itself.

Maybe I will have better luck later finding the specific article, but the article I read a few (?) years ago described why boats experience drag in shallow water. I own a canoe so I have felt this first hand. The article illustrated that the wake of a boat could reflect off the shallow bottom and the trough of the reflected wave could then drag on the stern.

But you knew that already, right? So why is this article news?
NIS_0
2 / 5 (2) Aug 10, 2014
Replace the water with dark matter and then it's a party.
clay_ferguson
5 / 5 (5) Aug 10, 2014
@Jag_Pop, I think the article is news because they are controlling the object's position, rather elegantly and precisely, rather than just saying some phenomenon is theoretically possible.
Nik_2213
not rated yet Aug 10, 2014
http://www.ship-squat.com/ documents the 'wake of boat' thing, but that is barely related to this wave-shaping effect. A nearer step might be the non-linear way convergent wave groups may interact to throw up a ship-smashing 'rogue'.

( This process is different to the more predictable 'wind against current' monsters of eg the Agulhas Current. )
Urgelt
not rated yet Aug 11, 2014
Hmm. Hmm.

So, I wonder if we put a wave-producing plunger on an America's Cup yacht, we could generate useful wave patterns to move the boat faster.

Two plungers! Four!

I'd say five, but I don't think there's a toilet on those yachts. Four should do it. :P
Pexeso
not rated yet Aug 11, 2014
Well, this experiment just ads another piece into similarity of the vacuum and water surface behavior. The tractor beams with sound and light were prepared and used many times already.
antialias_physorg
not rated yet Aug 11, 2014
As yet no mathematical theory can explain these experiments

It would be interesting to do this experiment in a smoke chamber. Maybe it's an interplay between turbulent waves and turbulent air?

(alternatively one could check whether the effect also happens with a flat object)
swordsman
4 / 5 (1) Aug 11, 2014
This explains the slow surface currents generated by high frequency acoustic waves in water.
Watebba
not rated yet Aug 11, 2014
no mathematical theory can explain these experiments
The theory for 3D acoustic tractor beam already exists and I don't think the transition from 3D to 2D would be very difficult. Maybe they just should read the articles of another physicists instead of doing of journalism.
Isaacsname
1 / 5 (1) Aug 13, 2014
Interesting

I've been able to generate square waves on a water surface
ChrisMD123
not rated yet Aug 13, 2014
Never leave spacedock without it.
mdarr
not rated yet Aug 13, 2014
So can the necessary waves be generated in open water or is the phenomena to delicate to be replicated with other waves around? If so then this does get really useful. Sounds like we have enough of a mathematical description that the engineers can use it while the physicists figure out the theory behind it.
mercury rising
not rated yet Aug 18, 2014
chemicals and radioactive isotopes can be directed toward ports of intended depopulation. Now we can attrit the enemy much more easily. Within a couple generations they will be gone.