ABSTRACT

A new theory called the pressure decrease theory related to the increase of ship ice resistance with speed in level ice is introduced in this paper. It is assumed that there is a water flow induced by the relative movement of the ship hull surface with the ice pieces in the boundary layer between the hull and the ice layer, when the ice pieces are submerged. A decrease of pressure with increasing speed can then occur in the boundary layer. This phenomenon is analyzed using the Bernoulli equation and the equation of continuity of the flow. The decrease of pressure with speed in the boundary layer will increase Ice resistance with speed by increasing the frictional forces between the hull surface and the ice pieces. The theory is compared with full scale and model scale ice resistance data.

INTRODUCTION

In this paper the ice submerging component of ship ice resistance in level ice is studied theoretically ship ice resistance is defined to be the time average of the horizontal forces due to mechanical breaking of the ice cover and hydrodynamical phenomena associated with displacement of ice and water. Ship Ice resistance can be thought to arise in two zones breaking of the level ice field and turning of the broken ice pieces takes place at the waterline level of the ship hull, and submerging the broken ice pieces takes place In the underwater part of the ship's hull (see Kamarainen, 1993a). Two kinds of forces act between the hull surface and the ice Normal forces, and tangential forces due to friction between the hull surface and the ice pieces. Crushing of the ice edge, and bending and shearing of the ice edge into ice pieces cause normal and frictional forces between the hull and the ice pieces at the waterline level.

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