Study On Local Ultimate Strength Of Polar Ships Under Ice Impact Load And Ice Fragmentation

With global warming,the ice in the Arctic sea area is melting year by year,and the opening of the Arctic shipping route is possible.Besides,the Arctic region is rich in oil and gas resources,so the development of the Arctic region has become a hot topic at present.In recent years,various countries have introduced various policies to develop the Arctic one after another,and the construction of China’s "Ice Silk Road" has also started,which means that there will be a large number of ships sailing to the Arctic.Since there is still a large amount of sea ice in the Arctic sea area,the interaction with ships is inevitable,and the lowest temperature in the Arctic region measured by Russia is about-68℃,so the ships sailing in the polar region first face a complex ice load environment and extreme temperature environment.The research shows that low temperature environment can improve the yield strength and ultimate strength of steel.If this research result is directly applied to the design of polar ships,unpredictable risks may arise.Therefore,the ultimate strength of ship structure under low temperature environment is studied and analyzed in this thesis by combining experimental data,empirical formula,ultimate strength theory and finite element numerical simulation.The research results will provide a certain reference for the design of ships sailing in polar regions.Specific research contents are as follows:1)The ultimate strength theory and dynamic constitutive model of steel are studied.According to the requirements of the code,AH32 steel was selected as the main material of polar ships.Combined with the experimental data of others,the finite element method was used to conduct the numerical simulation of the finite element tensile experiment of AH32 steel.By comparing the test results with the simulation results,the rationality of the Cowper-Symonds constitutive model of AH32 steel was verified.2)The ultimate strength of the collision between box beam and sea ice is studied in low temperature environment.The finite element software LS-DYNA is used to model the box beam-ice calculation model.Combined with the research on sea ice material at home and abroad,the properties of sea ice material and the sea ice constitutive model are determined.Combined with the above steel dynamic constitutive model,the numerical simulation analysis of the collision between box beam and sea ice is carried out to explore the influence of ambient temperature(20℃,0℃,-30℃,-60℃),speed and ice thickness on the ultimate strength of box beam.3)Analysis of ultimate strength of ship structure under collision load based on S-ALE fluid-structure coupling method.The three-dimensional modeling of the whole ship was completed in Patran software,and the three-dimensional model of sea ice was established by Hypermesh software,which was finally imported into LS-DYNA software.Based on the S-ALE fluid-structure coupling theory,the virtual grid flow field was established in LS-DYNA,and the material properties,contact algorithm and boundary conditions were set.By comparing the collision force between ship ice under the action of flow field,the results show that the S-ALE fluid-structure coupling method is more close to the real situation.Finally,finite element numerical simulation is carried out to analyze the influence of ambient temperature,speed and ice thickness on the ultimate strength of the ship structure under collision load.4)The hull collision damage model was derived,and the hull model with initial defects was processed in Hypermesh.The compressive ice load and uniform distribution pressure in the bow and shoulder area of the ship were calculated by IACS "Polar Ship Requirements".The Grasshopper plug-in in Rhino software was used to complete the construction of the three-dimensional crushed ice model.Based on LS-DYNA nonlinear finite element analysis and supported by S-ALE fluid-structure coupling theory and ultimate strength theory,the hull model with initial defects was analyzed and studied.By changing the ambient temperature and the average thickness of the sea ice model,the structural damage deformation,collision force and residual ultimate strength of the bow and shoulder area were explored.