Bruce Winterbon wrote: > > Various questions about the Kelvin wave angle: > > I looked in a book _Fluid Dynamics for Physicists_, by T E Faber. > As John Winters suggested, it's geometric. It depends on the "dispersion > relation" for gravity waves, i.e. wavelength being proportional to the > square of the frequency. This is true when wave amplitude is small, water > is deep, and wave length is large enough (much greater than an inch or so ( > a few cm.)) that viscosity can be neglected. Also, as John said, it's based > on a point source: the object creating the wave is very small. In practise, > the waves created by each point on the hull add together. My guess is that > finite wave amplitude is the major reason for departure from the ideal angle. Don't have access to any fluid dynamics books so I'm stuck with my physical intuition ... which tells me that other properties of a fluid are involved here also -- not just viscosity, per se. What I'm thinking about is that it is the visco-elastic restoring forces which affect gravity wave propagation, and those will be a function of the medium. Tightly coupled molecules should respond to a wave disturbance differently than ones that are not tightly coupled, giving lesser amplitude for a given disturbance, but greater speed of gravity wave propagation ... and that might give a different "ideal angle" for the bow wave. Hmmmmm ... "more tightly coupled" may just translate into "more viscous." Maybe I'm all wet! If the oceans were made of alcohol, gravity waves would travel at a lesser speed, and could the bow wave angle be different than it is in water? (I assume the viscoelastic resotoring forces in sea water are pretty close to those in fresh water, though the density is some 3 % different.) This discussion may be more than most Paddlewisers want to know ... -- Dave Kruger Astoria, OR *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced/forwarded outside PaddleWise without author's permission Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Tue Oct 10 2000 - 05:55:47 PDT
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