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SUMMARY:Fazle Hussain and Jie Yao (Texas Tech University - USA)
DTSTART:20211029T150000Z
DTEND:20211029T160000Z
DTSTAMP:20260423T022924Z
UID:GEOTOP-A/6
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/GEOTOP-A/6/"
 >Dynamics of viscous vortex knots and links</a>\nby Fazle Hussain and Jie 
 Yao (Texas Tech University - USA) as part of GEOTOP-A seminar\n\n\nAbstrac
 t\nReconnection is the process by which two approaching vortices cut and c
 onnect to each other. As a topologically changing event\, it has been a su
 bject of considerable fundamental interest for decades – not only in (cl
 assical) viscous flows but also in quantum fluids\, as well as in numerous
  other fields\, such as plasmas\, polymers\, DNAs\, and so on. For viscous
  fluid flows\, reconnection is believed to play a significant role in vari
 ous important phenomena\, such as turbulence cascade\, fine-scale mixing\,
  and aerodynamic noise generation. We first delineate the underlying mecha
 nism involved in vortex reconnection and its apparent role in turbulence c
 ascade. Then we address the helicity dynamics involved in viscous reconnec
 tion occurring in evolutions of a trefoil knotted vortex and a Hopf-link. 
 For both cases\, we find that the global helicity <i>H</i> gradually decre
 ases before reconnection but sharply increases during reconnection – thi
 s effect increases with increasing vortex Reynolds number (<i>Re≡circula
 tion/viscousity</i>). This suggests that <i>H</i> for viscous flows is not
  conserved as <i>Re→∞</i>. Both positive and negative helical structur
 es are simultaneously generated before and during reconnection\, and their
  different decay rates due to asymmetric reconnection appears to cause suc
 h an increase of <i>H</i> during reconnection. By examining the topologica
 l aspects of the helicity dynamics\, we find that different from <i>H</i>\
 , the sum of linking and writhing numbers (i.e.\, <i>Lk+Wr</i>) continuous
 ly drop during reconnection. Our results suggest that the twist\, which in
 creases with <i>Re</i>\, plays a more important role in helicity dynamics 
 than recognized before\, particularly at high <i>Re</i>.\n
LOCATION:https://researchseminars.org/talk/GEOTOP-A/6/
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