James Hanna likes to have fun with his engineering views of physics.
So when he and his colleague Jemal Guven visited their friend Martin Michael Müller in France on a rainy, dreary day, the three intellects decided to stay in. Guven, absent-mindedly switching between channels on the television, stumbled upon a documentary on whirling dervishes, best described as a Sufi religious order, who commemorate the teachings of 13th century Persian mystic and poet Rumi through spinning at a fixed speed in their floor length skirts.
"Their skirts showed these very striking, long-lived patterns," Hanna, the engineer, recalled.
The film caused physicists Guven and Müller to think about structures with conical symmetry, or those shapes that can be defined as a series of straight lines emanating from a single point. By contrast, Hanna, the engineer with a physicist's background, thought about rotating flexible structures, namely strings or sheets.
The three put their thoughts together and the whirling dervishes became the inspiration for a technical paper appearing in the Nov. 27 of the New Journal of Physics, published by the Institute of Physics and the German Physical Society. They gave their work the slightly bemusing title of "Whirling skirts and rotating cones."
The three authors reflect an international collaboration. Hanna is on the faculty of Virginia Tech's Department of Engineering Science and Mechanics, while Guven hails from the nuclear sciences institute of the National Autonomous University of Mexico, and Müller is part of the BioPhysStat research group at the University of Lorraine, France.
In terms of the impact of their work, it widens the scientist's understanding of the dynamics of flexible objects and of pattern formation in rotating systems. They may also "shed some light on the previously known instabilities of turbine disks and hard disks," Hanna said.
"Rotating systems often break axisymmetry. Were it not so, there would be no hurricanes," Hanna explained. "There are steadier examples. The skirts of the whirling dervish carry cusped wave patterns which seem to defy gravity and common sense." A YouTube video of the Whirling Dervishes in action can be viewed here: https://www.youtube.com/watch?v=L_Cf-ZxDfZA
Watching the swirling skirts, the three linked their patterns to the presence of the Coriolis force, the reason why objects deflect on the Earth. They realized the Coriolis force was essential in the creation of the different patterns, and were subsequently able to develop a set of mathematical equations that govern how fixed or free-flowing cone-shaped structures behave when rotating.
According to the Institute of Physics, the simple equations the three developed were able to reproduce the sharp peaks and gentle troughs that appear along the flowing surface of the dervishes' skirts.
The three are presenting their findings this week at the 66th Annual Meeting of the American Physical Society of Fluid Dynamics. http://meetings.aps.org/Meeting/DFD13/Session/R14.8
Hanna joined Virginia Tech in the fall of 2013 after working for three and a half years as a postdoctoral research associate in the Department of Physics at the University of Massachusetts, Amherst. He has focused on the dynamics of strings and other flexible bodies, and the design of thin sheet structures by inhomogeneous swelling and buckling.
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