复杂载荷下裂纹SIF计算的子模型技术

对船舶与海洋工程结构物进行疲劳评估,首先要通过子模型技术解决复杂应力场中裂纹应力强度因子(SIF)的计算问题。针对子模型技术实现过程繁杂且效率较低的问题,分别提出"逐周分层法","转换矩阵法"及"映射划分法"并基于VBA及APDL语言编写插件MPCarrangerV1.0,FEMcoortransferV1.0及CrackmapperV1.0,解决从Patran整体有限元模型到Ansys子模型时壳体单元间MPC创建低效、不同坐标系间节点位置转换困难及裂纹自由划分的局限性问题。基于DNV及ABS相关规范,以某B型LNG燃料舱的疲劳热点为例,对改进的子模型技术进行验证,结果表明经改进的子模型技术可成功施加合理边界条件并实现SIF的求解,可为子模型技术快速实现复杂载荷下裂纹SIF的准确计算提供参考。

Research on the sub-modeling technique of SIF calculation of cracks under complex loads

Accurate calculation of the stress intensity factors(SIF)of cracks under complex loads must be done firstly using sub-modeling technique in order to evaluate the fatigue behaviour of navel architecture and ocean engineering structures based on fracture mechanics.In view of the complicated and low efficiency problems in adopting sub-modeling technique,the Circumferentially-layering method,Transition matrix method and Crack mapping method are respectively proposed in order to improve the process of creating sub-models in Ansys based on the overall FEM model in MSC.Patran.Plug-ins MPC_arranger_V 1.0,FEM_coor_transfer_V 1.0 and Crack_mapper_V1.0 are respectively writen in VBA or APDL to accelerate the MPC creation between shell and solid elements,nodes location conversion between different coordinate systems and crack meshing improvement.Based on the related DNV and ABS rules,taking the fatigue hotspot of a B-type LNG fuel tank as an example,the rationality verification of the above methods was performed.The results showed that the plugins can greatly and reasonably improve the efficiency of sub-modeling technique.The methods proposed in this article could provide a reference for rapid realization of sub-modeling technique in accurate calculation of the SIF of cracks under complex loads.