Numerical Simulation Of Ship Collision With Rafted Ice Based On Cohesive Element Method

With the gradual transfer of shipping and drilling activities to the Arctic,the marine activities in the polar ice area are gradually increasing.The special environment of the polar region has special requirements and standards for the safe navigation of ships.The research on the structural safety of polar ships in various ice conditions has attracted more and more attention.The rafted ice is gradually formed through extrusion,crushing and stacking,and there are many pores in it,which is an extreme existence in a variety of polar ice conditions.In the previous structural safety analysis,regardless of the number of overlapping layers,the thickness of overlapping ice is treated as twice the maximum thickness of single layer ice,and most of them think that the material of natural ice is uniform,without considering the influence of porosity.Therefore,combined with the characteristics of rafted ice,it is of great significance to establish the interaction model between ship and rafted ice.Based on the nonlinear finite element software,the interaction between ship and rafted ice is studied,and the ice load data of ship hull are obtained.The specific contents are as follows:According to the HSVA inverted cone ice breaking test,the random porosity is applied to the flat ice modeling,the simulation results and test data are compared to verify the reliability of the random porosity ice material model,and the application of cohesive element method in ice material is improved.It is found that the random porosity will make the cracks of flat ice propagate along the pores and produce many branches.The number of cracks is large and the cracks propagate far,which reduces the average value of ice load.According to the measured data of Arctic sea ice,the values of parameters in the formula are determined,and the limit thickness and maximum overlapping length of single-layer flat ice constituting rafted ice and the relationship between overlapping length and single-layer ice thickness under the action of wind and current are obtained.According to the uniaxial compression strength of fresh water ice cuboid cut at 45 ° after secondary freezing,the corresponding rafted ice parameters in numerical simulation are obtained.Based on the finite element model of inclined plate and the cohesive element numerical model of rafted ice with random porosity,the ice load of rafted ice during the collision between inclined plate and ship hull is studied.In the nonlinear finite element software,the collision process between inclined plates with different inclination angles and rafted ice at different speeds is simulated.It is found that the greater the inclination angle and speed,the greater the ice load in X direction.The ice load is sensitive to the change of tilt angle.Finally,according to the interaction scene between icebreaker and rafted ice,the influence of overlapping part in the process of ship collision is analyzed.Considering the influence of ship speed and the number of overlapping layers,it is found that the faster the sailing speed of the ice breaker,the farther and faster the crack propagation,and it is easier to produce large ice fragments.The increase of the number of overlapping layers will greatly increase the ice load in X and Z directions.