BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY:Forms and Patterns of Viscous and Elastic Threads - Neil Ribe (CNR S (Centre national de la recherche scientifique)\; Université Paris Sacla y\; CNRS (Centre national de la recherche scientifique)) DTSTART:20170926T100000Z DTEND:20170926T110000Z UID:TALK81661@talks.cam.ac.uk CONTACT:INI IT DESCRIPTION:Some of the most beautiful and easy-to-produce instabilities i n fluid mechanics
are those that occur when a thin stream of viscous fl uid like honey falls steadily
from a certain height onto a solid surfac e. In addition to the familiar '\;liquid rope
coiling'\; effect\, one can observe periodic folding with or without rotation of the
foldi ng plane\; periodic collapse and rebuilding of the hollow cylinder formed by a
primary coiling instability\; and '\;liquid supercoiling'\;\ , in which the cylinder as a
whole undergoes steady secondary folding a nd rotation. Using a combination of
laboratory experiments\, analytical theory\, and numerical simulation\, I and my
colleagues have determine d a phase diagram for these states in the space of
dimensionless fall h eight and flow rate\, and have identified the dimensionless
parameter t hat controls which state or states are observed under given
conditions. We have also studied pattern formation in the closely related '\;fluid
mechanical sewing machine&rsquo\; (FMSM)\, wherein a viscous thread fa lling onto a
moving belt generates a wealth of complicated '\;stitch '\; patterns including
meanders\, alternating loops\, and doubly per iodic patterns. We have determined
experimentally and numerically the p hase diagram for these patterns in the
space of dimensionless fall heig ht and belt speed\, and have formulated a simple
reduced (three degrees of freedom) model that successfully predicts the patterns
in the limit of negligible inertia. In closing\, I shall compare the observed FMSM
patterns with those of the &lsquo\;elastic sewing machine&rsquo\; in which a normal elastic
thread falls onto a moving belt.

LOCATION:Seminar Room 2\, Newton Institute END:VEVENT END:VCALENDAR