Numerical Study On Ship Collision With Level Ice Based On Nonlinear Finite Element Method

Due to the rising global average temperature, the melting speed of ice in Arctic region has been accelerating, Arctic ocean transportation, oil and gas exploration have become possible, which makes ocean transportation, energy development and utilization in Arctic region currently a hot issue. Ships which are suitable for Arctic voyages will be of great significance to Arctic transport and energy exploration. However, ships will inevitably collide with ice in the Arctic voyage, and the mechanism of ship-ice collision is not yet fully studied nowadays. Therefore, it is urgently needed to carry out prediction research on the ice load of polar ships.There are many methods to study ice load of ships, such as experimental method, numerical method and empirical method. Among these commonly used methods, Finite Element Method(FEM), one of the numerical methods, has been widely applied in the field of collision and is validated by a lot of cases.In this thesis, ship‘s dynamic structure response during collision with level ice is studied by using the commercial software LS-DYNA based on nonlinear explicit finite element method. The deformation of ship and ice, magnitude of ice force and energy changes of ship and ice, etc., are obtained. Some meaningful conclusions are drawn from these data.Firstly, domestic and abroad prediction methods and literatures of ice load on ships are introduced, including research achievements and trends of experimental method, numerical method and empirical method.Secondly, the basic theories and key technology of FEM applied in numerical simulation of collision problem are summarized. The developments of nonlinear explicit FEM and basic functions of the commercial software LS-DYNA are introduced. The 3D element algorithms used in this thesis, i.e., the Lagrange and ALE formulations and their control equations, are elaborated. The dynamic control equation and the solving method, the control method of explicit integral time step and the numerical method of collision are introduced. The yield criterion of the material used in this thesis is discussed.Thirdly, the extrusion test of cone ice is simulated using LS-DYNA. In this simulation, isotropic elastic plastic with failure model it selected as the ice material model. By changing the strain-rate and size of the ice specimen, the numerical simulation results are obtained and compared with the test data. It is shown that the simulation results are in good agreement with the test results, which demonstrates that the ice material model selected in this thesis can be used for numerical simulation of the collisions between ship and ice.In addition, by establishing the 3D finite element models of a bulk carrier and level ice, front collision between the ship with a certain initial speed and infinite level ice is simulated. The deformation and the energy change of ship and ice, the ice load on the ship are obtained. The influences of the initial ship speed and level ice thickness on the impact load of ship-level ice collision are analyzed. The results have a certain reference value for analyzing the ship structure performance during collision with level ice.Finally, by establishing the 3D finite element models of an icebreaker and level ice, combined with the method of fluid-structure interaction, the ice force and the energy changes of level ice when the icebreaker is breaking ice in the continuous mode is analyzed. The influences of the ship speed and level ice thickness on ice breaking process are obtained. The numerical results in simulation of ice breaking process of the icebreakers with wedge bow and spoon bow are compared, and reasonable suggestions are given on icebreaker‘s line design.