A Temperature-Gradient-Dependent Elastic-Plastic Material Model of Iceberg and its Application on the Simulation of FPSO-Iceberg Collision

Abstract

An accurate constitutive material model of iceberg ice is important for the finite element simulation of ship-iceberg collision process. A temperature-gradient-dependent elastic-plastic material model of iceberg ice, proposed by the authors in reference [5], is adopted in this paper. The model behaves linear elastic before reaching the ‘Tsai-Wu’-type yield surface, which are a series of concentric elliptical curves with different sizes. Increasing temperature leads to small curves which means the strength of iceberg is weak. Upon reaching yield surface, the iceberg model response is perfectly plastic. A failure criteria based on accumulated plastic strain and hydrostatic pressure is adopted. In order to reflect the change of temperature with depth of iceberg, three typical types of iceberg temperature profiles are assumed in the model. According to these profiles, iceberg ice element located at different depth has different temperature. Therefore, mechanical property of iceberg differs along depth. The iceberg model is implemented as a user-defined subroutine in the commercial explicit finite element code LS-DYNA. Collisions between FPSO side and iceberg are simulated. Four typical shapes of iceberg (sphere, prism, cone and cube) with three temperature profiles are applied. Also, different temperature ranges are assumed in each simulation case. The influence of temperature profile, temperature range and iceberg shape on relative strength between iceberg and side structure are analyzed. The energy dissipation ratio of side structure and iceberg in collision process is examined. Moreover, energy dissipation of the component structures of FPSO side is analyzed. The simulation results show that the iceberg model can be used to demonstrate the influence of temperature on collision process between FPSO-iceberg.