The paper describes numerical simulations of ship transit through pressured ice conditions. The numerical model solves the equations of the conservation of mass and linear momentum together with constitutive equations representing plastic yield. That yield envelope is based on a cohesive Mohr-Coulomb criterion with a tension cut-off. The numerical solution employs a hybrid Lagrangian-Eulerian formulation. Pressured ice conditions are constructed by allowing a shear stress (e.g. representing wind drag) to compress an ice cover of initial uniform thickness against a straight land boundary. A ship is then introduced and moves parallel to the land boundary at constant velocity. The geometry of the Canadian Coast Guard vessel, CCGS Louis S. St- Laurent, is used in the tests. The results give the total force on the ship under a range of confining ice pressures. The distributions of ice concentration, thickness and pressures are also obtained. The simulation results show that both the velocity of the ship, and magnitude of confining pressure have significant effects on ice force. The results also examine the dependence of ice forces on ship velocity and ice thickness.
Pressured ice conditions are widely acknowledged as a major threat to the performance and safety of ships. There are abundant reports of ship besetting under such conditions. The expression pressured ice is used to describe the convergence of the ice cover and the build-up of compressive stresses in a general imprecise sense. Aside from a number of anecdotal reports, there is no specific information on the manner in which different vessel classes can withstand or navigate through such pressured ice conditions. Navigating pressured ice relies entirely on the experience of mariners. The present study aims at developing means of quantifying the resistance experienced by a ship transiting through pressured ice.
