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A laboratory study of the minimum wind speed for wind wave generation

Published online by Cambridge University Press:  21 April 2006

Kimmo K. Kahma
Affiliation:
National Water Research Institute, Canada Centre for Inland Waters, Burlington, Ontario, Canada, L7R 4A6 Present address: Institute of Marine Research, PO Box 33, SF-00931, Helsinki, Finland
Mark A. Donelan
Affiliation:
National Water Research Institute, Canada Centre for Inland Waters, Burlington, Ontario, Canada, L7R 4A6

Abstract

The minimum wind speed for wind wave generation has been investigated in a laboratory wind-wave flume using a sensitive slope gauge to measure the initial wavelets about 10 μm high. The growth at very low wind speeds was higher than predicted by the viscous shear-flow instability theory. Assuming that the growth is exponential, the inception wind speed at which the growth rate becomes positive can be defined. It occurred at (friction velocity) u* ≈ 2 cm/s, somewhat lower than the u* ≈ 4–5 cm/s predicted by shear-flow instability theory. However, the observed growth rates were close to the theory at higher wind speeds when the waves were higher than 1 mm. The effect of temperature on the wind speed at which the waves become readily visible is shown to be appreciable and in keeping with the temperature dependent viscous damping. Other sources of growth are discussed. Our estimates show that the Phillips resonance mechanism might be sufficiently effective to generate the observed growth at very low wind speeds.

Type
Research Article
Copyright
© 1988 Cambridge University Press

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