Experimental and theoretical investigation of the icebreaking cycle in two dimensions

The transient response of a floating ice sheet to an advancing icebreaker is investigated experimentally in two dimensions. The maximum forces encountered by the vessel during the icebreaking cycle and the lengths of the broken slabs show a clear velocity dependence. Only a slight variation with speed is found in the average forces. Measurements with presawn and unbroken ice sheets are compared: The inertia of the floating ice sheet and the surrounding fluid is found to have a significant effect on the forces encountered by the advancing vessel.;A second force peak at the end of the icebreaking cycle appears in 34 cases of the 87 recorded test runs in level ice. This force peak is found to be related to the deceleration of the rotation of the broken slab at the end of the icebreaking cycle. The fluid on top of the slab is ejected from the narrowing gap between the bow plate of the advancing vessel and the rotating ice slab, thus causing the second force peak.;The response of the ice sheet and the flow around the advancing vessel is simulated with a numerical model. The theory behind the investigation is based on the assumption of unsteady potential flow, together with a relatively complicated boundary condition written for the ice sheet - fluid surface.;Before the flexural failure takes place in the ice sheet, the deflections are small and the boundary conditions are satisfied on the reference position of the sheet. After the failure, the displacements become large and the boundary conditions are satisfied on the moving boundary. A mixed Eulerian-Lagrangian formulation together with a time-dependent coordinate mapping is used to describe the large motion of the rotating slab. Two nonlinear load functions are developed to describe the contact force due to the advancement of the vessel and the response of the ice sheet and of the broken ice slab.;The numerical model describes the overall response of the floating ice sheet fairly well. Smaller details show more differences between the theory and experiments, indicating areas for further research.