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.
It is well known that marginal ice zones are characterized by different forms of initial stages of ice such as, e.g., grease and fragmented ice which act as surface wave absorbers and thus affect microwave radar backscattering. As a result, mapping of boundaries between solid ice and open water areas using radar may become rather complicated. Another aspect of the problem of wind wave damping due initial stages of ice is that the areas of strong wave damping due to ice can be erroneously interpreted as surface pollutions in radar imagery. Studies of wave damping due to ice floes are still insufficient, and relations between the floe geometry and wave damping are poorly established. The motivation of this study is to improve our understanding of the process of wave damping due to ice floes for elaboration of physical models of wave damping. New wave tank experiments were carried out to investigate the damping of regular mechanically generated waves and of irregular wind waves due to drifting floe imitators (washing sponges) as well as for the case of stationary, non moving floes. Dependencies of the damping coefficient on wave frequencies for regular and wind waves for different floe sizes and different areas occupied by the floes were obtained. One of the most interesting results was that the damping coefficient indicated a local maximum when the floe size was about half the wave length. A physical interpretation of the results was given, based on the analysis of floe movement under the action of the orbital wave motion taking into account the floe added mass.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.