Flexibility reduces drag: daffodil
The flowers of daffodils twist in the wind, reducing drag because of their torsional flexibility due to stem noncircularity.
|Biomimetic Application Ideas|
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"Daffodil flowers extend laterally from the long axes of their stems; as a result, wind on a flower exerts torsional as well as flexural stress on the stem. Stems respond by twisting, and thus flowers reorient to face downwind in moderate winds, in the process reducing their drag by ∼30%. This repositioning is facilitated by the stems' relatively low torsional stiffness. Daffodil stems have a ratio of flexural to torsional stiffness of 13.27 ± 0.96 (SD), compared with 8.33 ± 3.20 (SD) for tulip stems, which bear flowers as symmetrical extensions of their long axes, and compared with 1.5 for isotropic, incompressible, circular cylinders." (Etnier and Vogel 2000:29)
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist
Application Ideas: Incorporating materials with torsional flexibility into building designs and structures, particularly in coastal cities prone to wind storms and hurricanes; microstructures on wind turbine blades that allow them to continue functioning in high winds; wind turbine towers that flex with the wind; more aerodynamic cars, semi trailers and cabs, with structures that 'twist' to reduce drag.
Industrial Sector(s) interested in this strategy: Architecture, construction, structural engineering, wind energy, automotive, transportation
Biology Department, Duke University