考虑粘结-破碎的块体海冰离散单元方法研究及应用

The sea ice and the ice load is the main influence factors for the offshore structural in cold regions. The Discrete element mothed (DEM) is good on simulate the dynamic process of ice breaking. In DEM simulation, the shape of the discrete element particle cannot be neglected, and the block particle model is the closest shape for the trash ice. First, this project establishes the block sea ice particle element, for this particle model the more precise contact model and the hydrodynamic force are considered in the simulation. Based on this block particle model the level ice, trash ice and pressure ridge are established. Second, the cohesive-break model is modelling for the block sea ice model. Account for macroscopic crack, which is also affected by the temperature, velocity and so on. And last, based on the block discrete element model, the interaction for ice interact with the different offshore structures are simulated, the comparison for simulation result and the experiment data, field data is analyzed to improve and correct the simulation model. This study will contribute to the development of DEM during its application in offshore engineering of cold regions, and also provide significant scientific foundation for the design of ice-resistant hull structures and the navigation security in ice-covered fields.

海冰是寒区海洋工程结构设计需要着重考虑的因素。离散单元法可以充分反映海冰的离散特性，是海冰数值模拟研究的重要工具。离散单元法中颗粒单元的几何形态对计算结果影响较大，而块体单元最接近真实海冰破碎后的冰块形态，是目前海冰模拟的理想单元形态。为此，本项目首先将构建块体海冰单元，改进单元间接触力模型及水动力计算模型，并构建平整冰、碎冰、冰脊等冰型；其次考虑海冰温度、冰速等因素对海冰破碎的影响，构建块体海冰单元的粘结-破碎模型，实现对海冰裂纹发展及破碎过程的模拟；最后基于块体海冰单元构建的不同冰型，模拟海冰与不同海洋结构物碰撞并发生破碎的动力过程，并将模拟结果与现场实测数据进行对比分析以实现对数值模型的改进和修正。本项目研究不仅可以促进离散单元法在寒区海洋工程中的发展和完善，还可为新型抗冰结构设计提供理论参考和依据。

离散单元法是海冰数值模拟的重要方法之一。特别是模拟海冰的裂纹以及破碎的物理过程有着显著的优点。海冰破碎后形成的冰块大小形状各异，因此为了模拟冰块这种特点，本项目通过闵可夫斯基和运算得到扩展型多面体海冰单元，同时为了准确模拟海冰的力学性质，针对块体单元的特点构建了海冰单元间的接触力模型，并考虑了冰块的浮力、拖曳力、附加质量等。构建了基于多面体海冰单元的平整冰模型，通过在海冰单元之间建立粘结-破碎模型，使块体海冰单元可以在初始时粘结在一起进而形成平整冰模型，并在外力作用下产生裂纹并破碎。为了验证块体海冰单元的合理性，基于这种非规则块体海冰单元模型分别模拟了海冰的三点弯曲实验以及平整冰与窄锥结构相互作用过程。对比发现数值模拟结果与实验结果以及现场观测数拒较为吻合，本项目构建的块体海冰单元模型可以准确的模拟海冰破碎的物理力学过程。