Theoretical Investigation on the Effect of Fluid Flow Between the Hull of a Ship and Ice Floes on Ice Resistance in Level Ice

Abstract

The icebreaking capability of a ship in level ice is a very important concept for the designers of ice-going ships. Theincrease of ice resistance with speed is both due to the increase in the resistance forces with speed in the ice-breakingphase, which takes place at the waterline level, and in the sliding phase when the broken ice floes are submerged.The resistance of a ship in level ice as a result of the decrease in pressure between the hull surface and an ice floewhen the ice floe is submerged is studied in this thesis. Three basic phenomena have been presented in the literature toexplain the origin of the change of the pressure in the gap between the hull and an ice floe in the sliding phase: theventilation phenomenon; the acceleration of water flow in the gap between the ice floe and the hull surface, and theflow of water to and from the gap as a result of changes in the geometry of the hull along the trajectory of an ice floesliding against the hull. The research objective of this study was to study the effect of the last two phenomena on iceresistance in the sliding phase and to develop a calculation tool for this purpose. The CFD code Iceflo based on thehydrodynamic lubrication theory was written to calculate the flow in the gap between the hull surface and an ice floe.The following main conclusions can be drawn. The low-pressure phenomenon in the gap between the hull surface andice floes may be caused by the inertia forces under favourable conditions or by changes in the height of the gapbetween the hull surface and the ice floes, or both. The force resulting from the pressure decrease in the gap betweenthe hull surface and ice floes may be several times the force resulting from the static lift of the ice floes. Thisphenomenon has to be taken into account e.g. in friction panel tests. The resistance caused by the low pressure in thegap is higher than the resistance resulting from viscous forces in the gap. An inclined cylindrical bow form can beconsidered to be the optimal hull form for an icebreaking ship, concerning the low-pressure phenomenon.