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Response of gravity water waves to wind excitation

Published online by Cambridge University Press:  28 March 2006

James B. Bole  and
En Yun Hsu
James B. Bole
Affiliation:
Department of Civil Engineering, Stanford University, Stanford, California Present address: Chevron Oil Field Research Company, La Habra, California.
En Yun Hsu
Affiliation:
Department of Civil Engineering, Stanford University, Stanford, California
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Abstract

The primary objective of this work was to study the response of gravity water waves to wind excitation and, in particular, the applicability of the Miles inviscid shear-flow theory of gravity wave growth, by conducting experiments in a laboratory wind-wave channel under conditions approximating the assumptions of the mathematical model. Mechanically generated wave profiles subjected to wind action were measured with capacitance wire sensors and wave energy was calculated at seven stations spaced at 10ft. intervals along the channel test section. Waves varied in length from about 2·5 to 6·5 ft. and maximum wind speeds ranged from 12 to 44 ft./sec. Vertical mean air velocity profiles were taken at six stations in the channel, fitted near the air-water interface with semi-logarithmic profiles, and used in a stepwise computation of theoretical wave growth. The results show that the measured wave energy growth is exponential but considerably larger than the growth predictions of Miles's theory. Derived experimental values of the phase-shifted pressure component β are greater than theoretical values by a factor varying from 1 to 10, with a mean of about 3. Wind mean velocity profiles appear to be closely logarithmic near the air-water interface. Wind-generated ripples superposed on mechanically generated waves created a rough water surface with standard deviation larger, in all cases, than the respective critical-layer thickness.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 35 , Issue 4 , 10 March 1969 , pp. 657 - 675
Copyright
© 1969 Cambridge University Press

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