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Fluid dynamics

Getting through a drowning machine


People adrift in fast-moving rivers can get caught and even drown in hydraulic jumps — turbulence that forms when a shallow, fast-moving waterway spills into a slower and deeper section. By creating a small hydraulic jump in the lab, researchers have determined the factors that affect how long different objects remain caught in these 'drowning machines.'

Pinaki Chakraborty and his colleagues at the University of Illinois in Urbana observed the time it took objects of different shapes and buoyancies, such as a ball and a bottle, to emerge from the jump. Using these data, they calculated that light objects remain in the rolling eddy for several minutes, whereas denser items — including humans — should be expelled after only seconds. Because object buoyancy affected residence time, the authors suggest that public-safety agencies test the best strategy for people to use if they fall into a drowning machine: remaining still, and thus more buoyant, or swimming with the current to emerge from the jump sooner.

Proc. Natl Acad. Sci. USA doi:10.1073/pnas.1015183108 (2011)

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Getting through a drowning machine. Nature 472, 9 (2011).

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