How Flowers Help Us Understand Why Bridges Collapse

The catastrophic collapse of Washington State’s Tacoma Narrows Bridge in 1940 launched intensive research into the aerodynamics of bridge design. Now a team of South Korean scientists have identified a geometric structure that can better withstand the complicated aerodynamic forces at play—and they found their inspiration in the shape of a daffodil stem.

When wind flows across a long object, like a daffodil stem, it sheds little eddies of wind along each side, with a small vortex of low pressure forming in the wake. The technical term is “von Karman vortex shedding.” Stick your arm out the window of a moving car and you can feel those oscillating side forces in action. You can also see the effect simply by dropping a sheet of paper to the floor. It will sway…

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