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It is known that organic and mineral films appear in microwave radar or optical aircraft/satellite images as the areas of reduced intensity due to suppression of short wind gravity-capillary waves (GCW) - slicks. The suppression of GCW with wavelengths ranged from some millimeters to decimeters can be characterized in terms of film elasticity. Hence, marine slicks in radar/optical images can be quantitatively described if the film elasticity is known. The elastic properties of monomolecular films have been thoroughly studied, while the problem for thick films, particularly for crude oil films remains poorly investigated. The latter are characterized by strong inhomogeneity in thickness. This paper is focused on laboratory analysis of GCW attenuation due to non-uniform films. The damping of GCW was measured in laboratory using a method of parametric excitation of standing GCW in a vertically oscillating cuvette mounted on a vibration table. Laboratory measurements were performed for highly inhomogeneous films of pure dodecyl alcohol. When the surfactant concentration exceeded the values corresponding to the saturated monomolecular layer, the surfactant excess was concentrated in non-spreading drops (lenses) of macroscopic thickness of 1-3 mm. The GCW attenuation coefficient was studied for GCW frequencies of 10 to 20 Hz and for different sizes and number of lenses. It was found that the attenuation coefficient increased with the relative area of the lenses. A physical explanation of this effect was proposed based on the “lens-wall” model, when assuming that the lenses reduced the area of the monomolecular film and, accordingly, increased the wave attenuation. Theoretical analysis of wave damping based on a “lens-wall” hypothesis has demonstrated good consistence with the experiment. The effective elasticity of a two phase film -a monomolecular layer with a lens phase- is introduced, which replaces the two-phase film with an effective monomolecular film.
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