Research in Nonlinear Water Waves.
Quarterly letter progress rept. 1 Jan-31 Mar 89,
CALIFORNIA INST OF TECH PASADENA DEPT OF APPLIED MATHEMATICS
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The major effort has been work on the calculation of wind drift effects on the properties of finite amplitude capillary gravity waves. The code is extended to the case when the wave is not too steep and the wind drift layer is thin compared with the height of the wave. Results have been obtained showing the effect of the wind drift layer on the properties of finite amplitude waves of permanent form. These are currently being validated to compare with the theory of Banner Phillips which models the wind drift layer by a quasi-one-dimensional sheet. The construction of a boundary integral type code is being evaluated which will enable the calculation of the effect of the wind drift layer on steep waves. A remarkable result is the stability of the waves when there is a wind drift layer. It appears that infinitesimal waves may be spontaneously unstable in the presence of a thin drift layer of sufficient strength. First results indicate that capillary gravity waves in a narrow band of around 2 cm wavelength are unstable for a wind drift layer corresponding to a wind speed of around 15 knots. This appears to be a complete new mechanism for the generation of waves by wind, since it is independent of the air motion once the wind drift layer is set up by viscous or turbulent stresses. jhd
- Fluid Mechanics