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Summary of Working Paper No. 43-1996

I.6.2 : Behavior of Ice Floe in Restricted Waters

By Dr. Hajime Yamaguchi, Department of Naval Architecture and Ocean Engineering, Graduate School of Engineering, University of Tokyo, Japan.

A new model named "Distributed Mass / Discrete Floe model", is proposed for practical computations of mesoscale pack ice rheology. This model possesses the advantages of both the continuum and the discrete element ones: it can express the discrete nature of pack ice which is difficult for a continuum model to treat, and can realize much shorter computation time than a discrete element model. The pack ice is divided into ice floe bunches in which the floes, assumed to be distributed uniformly, are modeled as inelastic circular disks or rectangles floating on the water. The ice interaction forces are formulated from the relation between the impulse on the bunch and the variation of the bunch momentum. The ocean flow is calculated by a multi layer model simultaneously with the ice floe movement.

In a circulation water channel, drift tests of physical model floes were performed in order to investigate the characteristics of their motion and interaction with the structure. The floe motion near the structure depends on the floe shape. Disk floes show a lateral motion in front of the structure. They flow out from both sides of the structure and the number of floes in front of the structure decreases with time. On the other hand, rectangle floes scarcely expand laterally. The number of the floes in front of the structure remains almost constant with respect to time. These experiments indicate that when the motion of pack ice is simulated around a structure, it is important to choose the floe shape. The disk floe motion and the rectangle floe motion can be regarded as the two extreme cases of pack ice motions. An actual pack ice motion may be between these two extreme cases.

Some computations using Distributed Mass / Discrete Floe (DMDF) model were made. Simulation results were compared with the circulating water channel experiments and the sea ice motion in the southern part of the Okhotsk. The DMDF predicted the circulating water channel drift tests quite closely. The DMDF results also compared quite well with the sea ice motion.