Accurate prediction of the continuous icebreaking process in level ice is crucial for the design of ice-going ships. Physical simulations are performed as ice model tests in ice test basins, it is one of the most precise simulation methods. The model tests were carried out in the Small Ice Model Basin (SIMB) of CSSRC with a model divided into different segments. To research the resistance characteristics and its composition, a quasi-two-dimensional bow model based on the Waas-Bow concept was designed. Tests were performed in level ice and presawn ice sheets. The total ice resistance of the bow was measured by a 6-component scale, while the forces acting on each segment were determined by 3-component load cells. This test setup allowed determination and comparison of the ice resistance components. The ice breaking and clearing process was observed and documented by underwater video cameras placed on the basin bottom and used for ship-ice interaction analysis. Based on the model tests, the influences advancing velocity during the continuous icebreaking process were determined, the composition of ice resistance is analyzed, and the ice failure modes and ice floe motions are studied.
When assessing the performance of ships operating in the ice, the total resistance in ice, Rit is the most important criterion for the icebreaking ability. The in-depth study of the ice resistance is most important for the hull design and optimization of ice-going vessels. It will determine the power to be installed and, together with the propeller-ice-interaction, the speed and thus the icebreaking capability of the vessels.
When navigating in an almost uniform ice cover or giant floes a vessel breaks the ice predominantly by bending but crushing at the stem and the shoulder could also be involved. In the further course of the process, the ice floes are turned, submerged and slide all along the ship hull. Ideally, the ice floes are pushed under the surrounding ice cover by the shape of the ship's hull. One of the main contributions of the total ice resistance in level ice is the breaking resistance (Puntigliano, 2003), it can account for more than 40% of the total resistance. In a first attempt the total ice resistance was divided into two main components, breaking of the ice sheet and submersion of the ice floe. The breaking component includes the resistance due to crushing and bending, and the submersion component is including the friction when ice floes are sliding along the hull (Lindqvist, 1989). By observing the process of ice breaking, the total resistance acting on the ship hull can be further subdivided into the following categories: breaking, rotary, submersion, and sliding force (Valanto P, 2001). In order to investigate the mechanism of ice resistance in depth, experimental and numerical means are indispensable. Model tests in level ice and pre-sawn ice were carried out in the ice basin of Korea Institute of Marine Engineering (KRISO), and the empirical formula of non-dimensional coefficients were obtained (Jeong, etc.,2010). The ship type and traffic profile have a large influence on ice resistance. The effect of bow shapes on ice-breaking process was studied at HSVA, by Daniela Myland. She found a correlation between bow shape parameters, the total resistance and breaking pattern. Based on her analysis she refined the Lindqvist formula. (Daniela Myland, etc.,2016). There are also several numerical simulation methods used to calculate the process of ship-ice interaction. Wang idealized the ice-breaking process as a cycle of contact-bending failure, and proposes a numerical method in the time domain (Wang, 2001). Biao Su divided the ice breaking process into two parts: icebreaking force and the ice forces induced in the displacing progress and established a three-degree-of-freedom coupling equation between the ice load and the ship motion, which was in good agreement with the experimental data of AHTS/IB(Biao Su, 2011). The discrete element method has unique advantages due to the transformation from continuum to discrete segment during the interaction between ice and structure (Ji,2018). Lau simulated the nonlinear large deformation and fracture process in the interaction between flat ice and cone type structures, and wrote the three-dimensional discrete element program DEMICE 3D (Lau et al., 2011). Ji introduced GPU-based high-performance computing methods into discrete element numerical simulation, which significantly improved the calculation scale and efficiency of DEM method, and applied it to the research of icebreakers (Ji et al., 2016).
