Physical modelling of ship/ice interaction: Report 2. Parametric model study of ships ramming multi-year ice floes

The report describes the second and final phase of a joint research project between Canada and Finland. The objective of the work was to experimentally investigate the mechanics of a ship ramming a massive ice floe. In the first phase, models of the vessel M.V. Arctic were tested and compared with full scale data. While the model/full scale agreement was encouraging, concern was raised about the influence of ship size, bow form, ice strength scaling and other parameters on the ramming forces and ship hull response. In the second phase, described herein, these questions were addressed by testing a model of a very large vessel (150 000 tonne) and a model of the M.V. Canmar Kigoriak (6 700 tonne). Both models consisted of multiple segments connected to a flexible backbone. Ramming forces and vessel dynamic response were measured. Altogether 107 tests were conducted with these models. The results of the tests are summarised in this report. The main result of the project is the understanding of the ramming process and the ways in which the ship and ice parameters influence the vessel response. The main engineering concern is the maximum bending moment that may occur in the hull girder. It is shown that two separate processes take place during ramming. These can be called initial impact phase and beaching phase. There are cases in which only quasi-static beaching is important, especially for a large ship striking a square ice edge. Dynamically amplified interaction forces of the initial impact phase in some cases may be nearly 50 % larger, and the resulting bending moments may be nearly 100 % larger than those of the quasi-static case. The main factors contributing to dynamics of interaction forces are vessel size, bow form, size of previous imprint and ice strength. Velocity linearly influences force and bending moment, but does not affect the degree of dynamic amplification. The results have implications to both design and operation of Arctic vessels.