Breaking characteristics of ice cover and dynamic ice load on upward–downward conical structure based on DEM simulations

Abstract

In ice-covered regions, the upward–downward ice-breaking cones are applied widely to reduce the ice load on the vertical jacket offshore platforms. The ice load is affected by the diameter of cone at the water level. In particular, the sea ice can impact on the vertical portion of the platform which is beyond the covered area of the upward–downward cone under the extreme low or high water level. In this study, the discrete element method (DEM) with the bond and failure model is adopted to simulate the breaking process of sea ice acting on conical structure and vertical pile considering the changing of water level. The ice load and ice failure mode simulated with the DEM is compared well with the field data measured in the Bohai Sea. The DEM results indicate that the bending failure of ice cover occurs when it acts on the upward or downward cone. For both of the upward and downward cones, the ice load increases with the increase in the cone diameter at water level, but the ice load on upward cone is larger than that on downward cone. Meanwhile, the breaking length of ice cover on upward cone is smaller than that on the downward cone. The ice load and the breaking length of ice cover are analyzed based on the DEM results and the field observation in the Bohai Sea. When the ice cover impacts on the junction of upward–downward cone, the ice cover can be broken by a local crushing failure, but it has little effect on the maximum of the ice load. The interaction between ice cover and vertical pile is also simulated with DEM under the extreme low or high water levels. The sea ice breaks with crushing failure mode, and the ice load is obviously larger than that of conical structure. The ice loads and failure modes of ice cover are compared when the ice cover impacts on the vertical pile, upward cone, downward cone and their junction portion considering the influence of water level.