极地航行船舶与海冰碰撞破损状态的数值和实验研究

Because of the particularity of the environmental loads in the polar region, the polar ships are likely to encounter the collisions of the icebergs, which may damage the hull，induce flooding and threaten the safety of the ship. Assessment of the collision and damage between icebergs and polar ships is therefore considered to be one of the key issues in the future development of safe ships. Nowadays the study on the local deformation and damage of the ship as well as the icebergs are still in lack, neither the flooding induced. To solve this problem, Nonlinear Finite Element Analysis (NLFEA), Discrete Element Method (DEM) and Smooth Particle Hydrodynamics (SPH) are combined to simulate the whole process of the collision, damage and flooding. At the early stage, NLFEA is aodopted and the user defined subroutine is combined in the common commercial software to simulate the collision of the large icebergs and ships, which focuses on the local deformation and the energy loss; at the middle stage, DEM is applied to simulate the collision between the small ices and the ship, which corcerns the crack propagtion and breakup of the ice; at the late stage, SPH is used to study the flooding of the sea water and the cracked ices, which pays attentions to the large deformation the free surface or the splashing. On the other hand, model tests will be conducted in a small water tank. The numerical results are validated against the experimental data, which aims to reveal the mechanical mechanism behind this complicated physical problem. Finally a whole dynamic analysis method will be developed for the ship-iceberg collision, which will lay a foundation for the safty asscssment of polar ships.

由于极地环境载荷的特殊性，极地航行船舶可能遭遇海冰碰撞，甚至破舱进水而威胁人员和财产，故对船舶-海冰碰撞破损的计算评估是关系船舶生命力的重要课题之一。目前对船舶和海冰的局部变形和破损等内部动力学问题研究不足，对碰撞导致破舱入水的研究也尚匮乏。鉴于此本研究拟采用非线性有限元分析（NLFEA）、离散元（DEM）和光滑粒子法（SPH）模拟船舶-海冰碰撞、破损和进水全过程。在碰撞前期采用NLFEA二次开发通用软件模拟船舶与层冰撞击，关注局部变形和能量损失等；在碰撞中期采用DEM模拟船舶与碎冰碰撞，关注海冰的裂纹扩展和破碎等过程；在碰撞末期采用SPH模拟离散海冰和海水向破舱内的涌入，关注自由液面大变形和破碎等强非线性运动。同时进行海水与海冰混杂破舱入水机理性模型实验，将计算结果与实验数据对比以验证模型有效性。最终建立一套船舶与海冰碰撞及破损的完整动力学分析方法，为极地航行船舶安全性评估提供支撑。

由于极地环境载荷的特殊性，极地航行船舶可能遭遇海冰碰撞，甚至破舱进水而威胁人员和财产，故对船舶-海冰碰撞破损的计算评估是关系船舶生命力的重要课题之一。目前对船舶和海冰的局部变形和破损等内部动力学问题研究不足，对碰撞导致破舱入水的研究也尚匮乏。鉴于此本研究根据冰船相互碰撞的不同阶段和不同特征，分别采用非线性有限元法（NLFEM）、离散元（DEM）、光滑粒子法（SPH）和计算流体力学-离散元（CFD-DEM）耦合方法模拟船舶-海冰碰撞、破损和进水全过程。在碰撞前期采用NLFEM，基于Drucker-Prager本构方程，考虑静水压力影响、粘聚力软化、多重失效面并结合自定义破坏准则编写冰材料的本构模型，成功嵌入ls-dyna软件中，完成二次开发并形成新求解器，完成船舶与层冰撞击，关注局部变形和能量损失等；在碰撞中期采用DEM，考虑冰晶结构、冰温、盐度和加载速率对海冰力学性质的影响，建立具有粘接-破碎功能的海冰离散元模型，采用单元不同的排列方式表征冰内晶体结构，模拟船舶与碎冰碰撞，关注海冰的裂纹扩展和破碎等过程；在碰撞末期发生破舱入水后，一方面采用改进的三维弱可压流体SPH方法在模拟船舶破舱进水问题；另一方面采用CFD-DEM耦合方法模拟离散海冰和海水向破舱内的涌入，关注自由液面大变形和破碎等强非线性运动。同时制作带有破口的舱段模型，分别应用非冻结模型冰和模型冰模拟海水与海冰混杂下破舱入水的机理性模型实验，研究发现碎冰的存在一定程度上会减弱船舱进水的速度。随着碎冰密集度以及碎冰尺寸的增大，这一阻碍作用愈发明显。最终建立了一套船舶与海冰碰撞及破损的完整动力学分析方法，为极地航行船舶安全性评估提供支撑。