Effective viscosity of grease ice in linearized gravity waves

Grease ice is an agglomeration of disc-shaped ice crystals, named frazil
ice, which forms in turbulent waters of the Polar Oceans and in rivers as
well. It has been recognized that the properties of grease ice to damp
surface gravity waves could be explained in terms of the effective
viscosity of the ice slurry.
This presentation is devoted to the study of the dynamics of a suspension
of disc-shaped particles in a gravity wave field. For dilute suspensions,
depending on the strength and frequency of the external wave flow, two
orientation regimes of the particles are predicted: a preferential
orientation regime with the particles rotating in coherent fashion with
the wave field, and a random orientation regime in which the particles
oscillate
around their initial orientation while diffusing under the effect of
Brownian motion. For both motion regimes, the effective viscosity has been
derived as a function of the wave frequency, wave amplitude and aspect
ratio of the particles. Model predictions have been compared with wave
attenuation
data in frazil ice layers grown in wave tanks