An improved numerical method for calculation of icebreaking force is proposed in this paper. First, the dynamic bending failure criterion is introduced considering the loading rate, which is of great significance to the icebreaking process. The parametric expression of the dimensionless coefficient (λt) related to velocity is determined by dimensional analysis. The approximate numerical expression of λt is obtained at last. Second, the secondary fracture is introduced. The secondary fracture has an enormous influence on the period of ice loads. A time-domain analysis curve of icebreaking force is obtained based on the tests carried out by Tianjin University. The approximate expression of the icebreaking force in the whole fracture process is determined at last. The direct sailing and the turning motions of the Swedish icebreaker, Tor Viking II, are simulated in level ice. The numerical simulation results are compared with full-scale trial data and semi-empirical formulas to validate its rationality.
In recent years, global warming is melting the ice sheet in the Arctic Ocean increasingly. The complete opening of the Arctic Route is just around the corner. This newly opened route will inevitably exert a significant influence on the international ocean transportation pattern. The icebreaker is a service ship used to break ice, open channels and guide ships in the ice region. In view of the risk of working environment and the specificity of missions, the research on icebreaking mechanism, motion trajectory and ice loads of the icebreaker appears to be particularly important, which is directly related to its safety and efficiency.
At present, the study of the icebreaker has been widely concerned by scholars around the world, and the computing method for icebreaking force in level ice is becoming a research hotspot. Wang (2001) used a new ice loads model to simulate the icebreaking process of conical structure in level ice. The model simplified the icebreaking process as three continuum processes of crushing, bending and rubble formation. A model for establishing the time history of ice loads during the ice-hull interaction was developed based on a geometric grid method. Liu, Lau and Williams (2006) separated ice forces into three independent components. The breaking, buoyancy and clearing forces, representing individual processes identified during the ship-ice interaction, were calculated separately and summed as the total ice forces. Su, Riska and Moan (2011) introduced a numerical model to investigate both global and local ice loads on the ship hull. This model was partly based on empirical data. The interdependence between ice loads and ship motions was considered, as well as the variations in the thickness and strength properties of ice. Tan, Riska and Moan (2013) concluded that the dependency of ice resistance on hull speed was observed to be linear as was predicted by Lindqvist's semi-empirical formulas. Liu, Xue, Lu and Cheng (2018) calculated ice loads and simulate the ship-ice interaction process by using the peridynamics method.