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 paper 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.Comment: 13 pages, 3 eps figures included; one more section on inertia effect