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SUMMARY:Waves\, channels and levees in geophysical mass flows - Prof. Nico
  Gray
DTSTART:20220824T111500
DTEND:20220824T120000
DTSTAMP:20260916T061410Z
UID:5267b788d172016f83724f96310bc314d8f16de7e7aaa163e6eab475
CATEGORIES:Conferences - Seminars
DESCRIPTION:Nico Gray is a Professor of Applied Mathematics in the Departm
 ent of Mathematics at the University of Manchester\, UK. He is an expert 
 on granular flows and the particle segregation that takes place within the
 m. This has applications to a wide range of industrial processes\, as well
  as to geophysical flows such as snow avalanches and debris flows. Nico ho
 lds a BSc in Mathematics from the University of Manchester\, a PhD in Sea 
 Ice Dynamics from the University of Cambridge and a Habilitation in Contin
 uum Mechanics and Geophysical Mechanics from the Technical University of D
 armstadt in Germany.  \n\nWaves\, channels and levees in geophysical mass
  flows\n\nProf. Nico Gray\, University of Manchester\n \n\n\nAbstract: Ge
 ophysical mass flows often break down into large amplitude wave pulses and
 /or spontaneously form channels with static levees in the arrest zone\, en
 hancing overall run-out. This talk reviews recent depth-averaged models th
 at capture the formation of (i) rollwaves\, (ii) erosion-deposition waves 
 (which exchange mass with the underlying substrate) and (iii) channel and 
 levee formation within a single framework. The key is the inclusion of fri
 ctional hysteresis\, which allows static and moving zones to coexist\, as 
 well as depth-averaged viscous terms that incorporate further details of t
 he granular rheology. As well as being able to compute time-dependent spat
 ially evolving solutions numerically\, the resulting model allows steady-s
 tate solutions to be constructed for the height\, width and depth-averaged
  velocity profile across a leveed channel\, which are in good quantitative
  agreement with small scale analogue experiments using monodisperse dry sa
 nd. Colour change experiments are also used to show that erosion-depositio
 n waves really do propagate downslope as a wave\, rather than a coherent b
 ody of grains\, and that the presence of the substrate gives them surprisi
 ng mobility over very long distances. Photos and videos of the similar eff
 ects at field scale will be shown to emphasize the importance of these ide
 as for a wide range of geophysical mass flows. There are\, however\, stil
 l many open challenges in how to generalize these results to multiphase mi
 xtures with broad grain size distributions.\n\nNote - The illustrative pic
 ture is taken from\nRocha\, F.M.\, Johnson\, C.G. & Gray\, J.M.N.T. 2019 S
 elf-channelisation and levee formation in monodisperse granular flows. J. 
 Fluid Mech. 876\, 591–641.\n\n\n\n
LOCATION:GC B1 10 https://plan.epfl.ch/?room==GC%20B1%2010
STATUS:CONFIRMED
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