Research On Ice Impact Loads On Marine Ranch Platform Based On Cohesive Element Method

In recent years,with the continuous development of marine resources and the continuous development of marine economy,the demand for aquaculture in offshore waters has also become increasingly high.The marine ranch cage platform used for aquaculture in the Bohai Sea and other waters in China is not only affected by fluid loads,but also threatened by the collision load of sea ice,which often poses a threat to its stability and safety.Therefore,establishing a marine ranch cage platform for aquaculture in frozen coastal waters requires consideration of the hazards brought by sea ice loads.In order to accurately predict the impact load of sea ice and ensure the stability and safety of the cage platform structure,it is very necessary to analyze and study the ice load on the platform through the numerical simulation of the impact of sea ice and marine ranch cage platform by finite element method.Therefore,based on the frozen sea area of Bohai Sea,this thesis simply the "Ocean Farm 1" marine ranch cage platform,build the finite element model of the ice-marine ranch cage platform collision based on the cohesive element model,and study the ice impact load of the marine ranch cage platform based on the cohesive element method.The finite element method is used to build a model to simulate the interaction between sea ice and marine structures,so as to predict the ice load and consider the harm of sea ice collision.It has important research significance for the stability and security of marine structures such as marine ranch cage platform,and has important practical value for the establishment of marine ranch for aquaculture and other maritime activities in the ice sea areas such as Bohai Sea.The work content of this thesis is as follows:(1)Introduce the physical properties,mechanical properties and main failure forms of sea ice,introduce the elastic-plastic constitutive model of annual ice homogenization,and explain the origin and principle of cohesive element method.Based on the study of sea ice and cohesive element by domestic and foreign scholars,the sea ice material and cohesive element material as well as related parameters are determined,which provides a theoretical basis for the subsequent numerical simulation.(2)Based on the "Ocean Farm 1" marine ranch cage platform,the hexagonal multi-column ocean ranch cage platform is constructed.Based on the cohesive element method,the finite element simulation software LS-DYNA is used to construct the finite element model of sea ice-marine ranch cage platform for numerical simulation of collision,and conduct sensitivity research on sea ice grids.The numerical results of ice load,energy change,sea ice compression failure and cohesive element failure and so on during the collision process are analyzed to study the anti-ice performance of the marine ranch platform.(3)The sensitivity of parameters is studied based on the basic collision condition of sea ice-cage platform.The influence of the variation of cohesive element parameters(TSL curve form,fracture stress,fracture energy release rate)and sea ice parameters(ice thickness,failure strain,stress-strain curve form and strain rate curve)on the ice load is studied.(4)The collision model is simplified.The ice-column collision process under the influence of flow field is simulated by combining the S-ALE fluid-structure interaction method with the cohesive element method.The buoyancy form of sea ice and column in the cohesive element method is realized by the fluid-structure interaction method.Studying the influence of the flow field grid size,water depth and ice velocity on the numerical simulation,the numerical calculation results of the S-ALE fluid-structure interaction buoyancy form and the buoyancy form with rigid plate at the bottom of the layer ice are compared,and the difference between the two buoyancy forms is analyzed,and the influence of the flow field on the collision is studied.