Daffodils inspire improved structural stability

SEOUL, May 10 (UPI) -- New research proves the shape of a daffodil stem reduces drag and oscillating sideways forces -- forces that can prove catastropic for poorly designed buildings or bridges.

The simple flower is inspiring the design of more stable antennae, towers and other tall structures.

When wind blows sideways across an elongated structure, vortices roll off either side. The action, called vortex shedding, can impart oscillating sideways forces on the structure or object.

One example of the phenomenon, called von Kármán vortex shedding, is when one sticks an arm out the window of a moving car. Forces periodically move the arm up and down.

Testing by researchers in South Korea proved the daffodil stem -- with its twisted, helix-like shape and elliptical cross section -- eliminates these sideways forces.

In 1940, the Tacoma Narrows Bridge -- a pair of twin suspension bridges spanning Puget Sound's Tacoma Narrows strait in Washington state -- collapsed when von Kármán vortex shedding caused the bridge to vibrate at its resonant frequency.

"This vortex shedding triggered the twisting mode of the bridge, and finally the bridge collapsed," Haecheon Choi of Seoul National University explained in a news release.

Researchers looked to nature for a design that could prevent a similar catastrophic structural failure. The shape of the daffodil stem ultimately proved most effective at curbing von Kármán vortex shedding.

Tested against a variety of air flows, the stem's shape consistently reduced drag and vortex shedding.

The findings -- detailed in the journal Physics of Fluids -- may not prove practical for bridge design, but they could inspire design of more stable lampposts, antennae, chimneys, sky-scrapers or even golf clubs.