11:45 〜 12:00
[ACG39-11] 波浪存在下における氷盤形成の水槽実験
キーワード：波浪・海氷相互作用、室内実験、蓮葉氷
Arctic sea ice is rapidly reducing, and an increasing trend of the wave height in the Arctic sea has been reported. Therefore, there is an increasing demand for improved modeling of wave-ice interactions. When seawater is frozen under wave effects, frazil crystals consolidate to form circular floes called pancake ice. The floe size is an important parameter in the sea ice thermodynamics and wave attenuation, but the knowledge of the relation between wave parameters and floe sizes is very limited. Shen et al.'s (2001, 2004) theory and experiments suggest that the floe size is limited by the tensile failure due to wave orbital motion. This leads to the scaling law D/L ∝ a-0.5, where D, L, and a are floe diameter, wavelength, and wave amplitude, respectively. However, the experimental data to support their theory is rather limited. To deepen the understanding of wave-ice interaction processes under controlled conditions, we conducted laboratory experiments using a newly built wave tank (8m x 1.5m x 1.0m with 0.6m water depth) with a freezing facility.
The experiments were conducted with freshwater, supposing that the difference in material and thermodynamic properties from seawater would not qualitatively alter the processes. To reproduce the ice floe formation processes in our wave tank, we cooled the water while monochromatic waves of various periods and amplitudes are continuously produced. Due to continuous agitation by waves, ice formed as numerous thin pieces of 1~5 cm size, and the pieces consolidated to form floes with raised ridges similar to observed pancake ice. The sizes of the floes were relatively uniform in each case. Representative floe sizes were objectively estimated from ridges detected by image processing.
The floes were larger with longer waves and smaller with larger wave amplitudes, both of which were consistent with Shen's model. However, the floe sizes normalized with wavelength showed stronger dependence on wave amplitudes. This result suggests a need for a new model of ice floe formation. Also, the results imply the presence of upper and lower limits of a for floes to form. These results, together with the experimental results of wave attenuation by the ice floes, will be useful for a simple description and understanding of wave-ice interactions in the marginal ice zone.
The experiments were conducted with freshwater, supposing that the difference in material and thermodynamic properties from seawater would not qualitatively alter the processes. To reproduce the ice floe formation processes in our wave tank, we cooled the water while monochromatic waves of various periods and amplitudes are continuously produced. Due to continuous agitation by waves, ice formed as numerous thin pieces of 1~5 cm size, and the pieces consolidated to form floes with raised ridges similar to observed pancake ice. The sizes of the floes were relatively uniform in each case. Representative floe sizes were objectively estimated from ridges detected by image processing.
The floes were larger with longer waves and smaller with larger wave amplitudes, both of which were consistent with Shen's model. However, the floe sizes normalized with wavelength showed stronger dependence on wave amplitudes. This result suggests a need for a new model of ice floe formation. Also, the results imply the presence of upper and lower limits of a for floes to form. These results, together with the experimental results of wave attenuation by the ice floes, will be useful for a simple description and understanding of wave-ice interactions in the marginal ice zone.