Ice, Caused By The Dynamic Ice Force Of The Flexible Upright Structure Vibration

When an ice sheet moves against a flexible vertical structure, it may fail either by buckling or by crushing. Then the structure may be destroyed by the ice force. As many oil platforms are to be erected at the oceans coved with ice. more and more problems appear. Since 1960s ice researcher had begun to study the problems of ice-structures interaction. Now the research of sea-ice had been an independent subject, that is ice mechanics. Because the dynamic ice force is a cyclic load and induces structure' vibration and fatigue, it is more serious. The sea ice is a high temperature material comparatively and there is a character of ductile to brittle, so it is complicated to research ice force.Firstly this paper reviews the research about ice-structure interaction home and overseas and the results attained. Then this paper discussed the dynamic ice force when the ice interacted with vertical structure. After that a full-scale test system was introduced at JZ9-3 platform and JZ20-2 MSW platform in Liaodong Bay. And a test about ice compression at several load speeds was finished in laboratory. Based on the ice character of compression failure and the test data at the oil platforms in Bohai. the dynamic ice force curves of the ice sheets failure are compared at different ice speeds . The results illustrate that three ice force modes with the increase of ice speed, and the different modes can induce three vibration forms of the structure, that is quasi-static, steady-static and random vibration. Furthermore the mechanisms of these three ice force modes are analyzed. It is demonstrated that with the increase of ice speed, the loading rates increase near the ice field, and it can make ice fail in three modes, plastic failure, ductile-brittle transitions failure and brittle failure. The explanations are given to describe the process of cyclic ice formation. The fourth chapter analyses the ice brittle failure when the ice sheets crushed the vertical structure at high speed by fracture mechanics.Lastly, the fifth chapter gives the numeric evolution model about the ice strength relation to strain rate. Because its strength is very sensitive to strain rate, sea ice displays different mechanics behavior and strength features in different -anges of strain rates. In different section of strain rate, sea ice has a different constitutive model, so the evolution model of sea ice should be described in divided sections. This paper calculated the sea ice strength relation to its strain rate from the Liaodong Bay sea ice. The result indicated that this evolution model is effective because the calculation is consistent with the experimental value very well.