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SUMMARY:New results on wind driven waves and negative tsunami waves at coa
 stlines - Hunt\, J (University College London and Trinity College)
DTSTART:20140717T150000Z
DTEND:20140717T160000Z
UID:TALK53421@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Wind driven waves on the surfaces of water bodies have great p
 ractical importance on all scales (H. Jeffreys in 1926 illustrated his fam
 ous paper with photographs of ripples on the Newnham duck pond in Cambridg
 e and huge waves on the Atlantic ocean). Despite 50 years of intense resea
 rch\, there is still disagreement about how idealised mathematical models 
 apply to real air flow over real waves. In this lecture the model of Miles
  (1957) and Lighthill (1962) for inviscid shear flow over a growing monoch
 romatic wave is explained in terms of critical layer dynamics\, but is sho
 wn to be invalid for viscous\, turbulent flow when the growth rate is asym
 ptotically small. But analytical viscous turbulent shear flow models\, als
 o with critical layers\, are valid in this limit and agree more closely wi
 th experimental wind profile data. But the former type of model (suitably 
 adjusted) is widely used by oceanographers and meteorologists. However for
  real wind-driven waves both the critical-layer and sheltering mechanisms 
 are significant and affect how waves travel in groups with characteristic 
 asymmetry of the wave-shapes on the windward and leeward sides of the grou
 p. (Sajjadi et al. 2013). \n\nThe second part of the lecture concerns rece
 nt long tsunami-like waves\, especially waves where the leading part of th
 e wave is depressed\, which was a characteristic feature of the tsunamis t
 hat approached the coast-lines of SEAsia in 2004 and Japan in 2011. As suc
 h waves travel from the source region\, a non-linear Kortweg-de Vries mode
 l of R. Grimshaw\, K.W. Lam and J.C.R. Hunt (2014) shows how when a depres
 sion wave is followed by an elevation (a 'breather) there is a transition 
 at a location which can be estimated when the peak elevation catches up wi
 th the peak depression and nearly doubles in height before it then decreas
 es and travels in front of the depression. In situations where the depress
 ion reaches the beach\, recent modelling and laboratory studies show how t
 he depression deepens\, leading to a back flow and drying out of the beach
 \, before there is a transition when the following much amplified elevatio
 n (in which the total momentum of the wave is maintained) surges up the be
 ach and moves some kilometres inland\, which corresponds with recent and p
 ast observations (Klettner et al. 2012). \n
LOCATION:Seminar Room 1\, Newton Institute
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