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SUMMARY:Rocking the boat: The physics of kayaks\, canoes and rowing - Grah
 am Benham\, BP Institute
DTSTART:20200213T113000Z
DTEND:20200213T123000Z
UID:TALK137230@talks.cam.ac.uk
CONTACT:Catherine Pearson
DESCRIPTION:In this talk I will present two topics related to the physics 
 of boat sports: The first explains the shape of a kayak - and why it's dif
 ferent to a dolphin. The second explains how to beat Olympic records by ch
 oosing the correct water depth!\n\nMore than a century ago\, J.H. Michell 
 derived an integral formula for the wave drag on a moving body\, using the
  approximation of a slender body in an irrotational\, inviscid fluid (Mich
 ell 1898). The major shortcoming of this formula is that\, due to the reve
 rsibility of the steady potential flow formulation\, it predicts no differ
 ence in the wave drag when an object with front-back asymmetry moves forwa
 rds or backwards. However\, anyone who has tried to row a dinghy in the wr
 ong direction would argue differently!  In the first part of my talk\, I w
 ill discuss recent experimental observations investigating the effects of 
 body asymmetry on wave drag\, and show that these effects can be replicate
 d by modifying Michell's theory to include the growth of a symmetry-breaki
 ng boundary layer. I will demonstrate that asymmetry can have either a pos
 itive or a negative effect on drag\, depending on the depth of motion and 
 the Froude number\, explaining the difference in shape between a kayak and
  a dolphin.\n\nAnother factor which strongly affects the wave drag is the 
 water depth. Olympic race courses have a minimum depth requirement of 3m\,
  but with boats as long as 18m\, rowers are likely to generate waves in bo
 th the deep (dispersive) and shallow (non-dispersive) regimes at various m
 oments during a race. Entering from deep to shallow water is accompanied b
 y a focusing of the wave drag near the shallow wave speed - and hence the 
 emergence of co-existing fast and slow solution branches. In the second ha
 lf of my talk\, I will describe the non-linear dynamics of such motion\, i
 ncluding sketches of possible bifurcation patterns and hysteresis routes d
 uring a race. I will demonstrate the existence of both dead and anti-dead 
 regions of shallow water - and how they may be responsible for recent Olym
 pic records.
LOCATION:Open Plan Area\, BP Institute\, Madingley Rise CB3 0EZ
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