The suppression of wind-generated waves by a surface film

Abstract

In the presence of a surface-active agent waves generated on the surface of a liquid by a wind may be stabilized. This problem is explored, and in particular the critical wind velocity is calculated for wave inception in the presence of such a film.The dominant parameter associated with the surface layer is the surface elasticity χ the ‘inextensible film’ of Lamb is obtained as a limit as χ → ∞. Such a value is hypothetical as for real films χ is not large, being in the range 0 to 80 dyne/cm approximately. Nevertheless, we show that damping exceeding that of the inextensible film can be obtained for short wavelengths, and that the critical wind speed for capillary ripples can be increased by a factor of ten in the presence of a film of experimentally attainable characteristics.The reason for the effectiveness of films of low χ is that the damping in the liquid is related to χ and the wavelength λ in such a way that for small λ, damping is a maximum for small χ.