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W. G. Pritchard Lab Seminar: 11:15 AM - 12:15 PM, 216 McAllister Bldg

	            **Monday November 28, 2005**
	
All bent out of shape: buckling instabilities of fluid sheets and threads

Neil Ribe

Institut du Physique du Globe de Paris
University of Paris VI

Abstract:

The periodic buckling of sheets and filaments of viscous fluid falling 
onto a surface is a common fluid mechanical instability with applications 
from geophysics to food processing. Two geometries are of particular 
interest: the "folding" of a two-dimensional sheet, and the "coiling" of 
a round filament. Both cases, however, exhibit the same fundamental 
dynamics, with four distinct regimes (viscous, gravitational, inertio-
gravitational, and inertial), depending on how the viscous forces that 
resist bending are balanced. The most interesting behavior occurs during 
the gravitational-to-inertial transition, where multiple states with 
different frequencies can exist at a fixed fall height within a certain 
range. These points will be demonstrated using an asymptotic "thin 
filament" model for coiling, as well as recent laboratory experiments for 
both folding and coiling.

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