Research On Calculation Method Of Polar Icebreaker's Level Ice Resistance

Ice resistance is the main resistance of polar ships in ice covered waters.It is important to forecast the ice resistance in the early stage of polar ship design.This present thesis focuses on a nonlinear finite element model for simulating ship-ice interaction,which is to study the ice breaking resistance of "Icebreaker Research Vessel”while continuously breaking level ice.Total ice resistance model is partly based on empirical method therefore it's a semi-numerical algorithm.In the simulation,the icebreaker is set as a rigid body with a single degree of freedom while the thickness and material properties of level ice are assumed to be constant.In order to determine the failure mode of ice sheet,two contact model of cylindrical structure,frustum structure to level ice are established respectively.The simulation results show that the level ice is mainly crushed when in contact with relatively vertical structure and the plastic strain can be used as failure criterion.When level ice is in contact with small inclination angle structure,bending fracture failure is dominated and the maximum normal stress is recommended in this paper.In order to study the effect of hydrostatic support in ship-ice contact,two models are established respectively,one considers hydrostatic support with non-linear spring element while the other neglects hydrostatic support.The calculation results show it is hydrostatic support that makes the ship's influence on the level ice mainly concentrate in the vicinity of ship hull,which is signif cant to the damage process of level ice.The hydrostatic support cannot be negligible in ship-ice continuous contact.The ice breaking resistance time history curve oscillates violently and the values generally increases with the growth of calculation time.After the bow's entering the level ice,the values trend to stabilize.The ice breaking resistance can be characterized by average value of the time history curve,which shows a positive correlation with ship speed,ice thickness and fracture stress.Five empirical methods for forecasting ice resistance is summarized.Compared with Lindqvist and Jeong formula,the ice breaking resistance calculated by nonlinear FEM shows the same magnitude and close value.Compared with Riska,Lindqvist,Jeong formula,the ice resistance calculated by semi-numerical model has the least relative error to Lindqvist formula which is less than 20%and a slightly larger relative error to the other two methods.The water resistance of ships is calculated by equivalent plate theory.Among the total resistance,the proportion of water resistance is very small which is less than 2%,and the proportion of ice breaking resistance is up to 43-49%.