A new paper
from researchers at the Australian National University is making waves in physics this month; the group claims to have developed a “tractor beam” of sorts. However, as is usual for claims of science-fiction technology made real, there’s a catch—it won’t be useful for pulling in rogue spaceships, but it might one day find applications helping guide the path of steamships. The report details the creation of never-before-seen flow patterns using waves on the surface of water in a shallow tank that, paradoxically, draw objects toward the wave source.
Counter-spiraling whirlpools create an axis along which floating objects will be drawn in. The water is ejected laterally, in the chaotic squiggly region.
The new technique relies on mechanically-driven buoys that oscillate up and down at a certain frequency to create stable whorl-like patterns of flow, which draw in surface particles from a particular direction. By changing the shape, size, and oscillation speed of the buoys, the team managed to create a variety of flow patterns, one of which displayed the unique pulling effect described in the paper. The most effective “tractor beam” arrangement used a cylindrical oscillator, oriented like a floating log, to make standing waves. While plane waves (below, left) can only move objects away from the source, under the right circumstances they can reflect off the boundaries of the tank to create peaked, three-dimensional waves (below, right), which lead to the unprecedented phenomenon.
Plane waves extend to the edges of the container laterally, but the more exotic waves created in this experiment are described as fully three-dimensional.
Further experiments with different buoy shapes led to the creation of unexpected and interesting flow dynamics, which may lead to advances in the study of fluid vortexes, but only the cylindrical oscillator produced the reported pulling effect. And while it is difficult to imagine finding a large body of water with conditions suitable to recreate the experiment, the paper's authors hope that the work may someday see use in the containment of oil spills and other surface contaminants.
Bizarre flow dynamics emerge when a conical “plunger” is used.
All images credit H. Punzmann, et al, Australian National University.