海洋平台结构系统弹塑性整体计算的裂纹柱壳新单元

柱壳是船舶与海洋工程结构物中主要结构构件。由于波浪等载荷的交变作用，疲劳裂纹损伤是这类结构物中一种常见且对安全性危害极大的损伤形式，因此裂纹损伤柱壳的研究一直是一个关注的课题。通常，对于韧性良好的结构物材料，在裂纹扩展前，裂纹前端可能出现较大范围的塑性，其相应的分析称为弹塑性断裂分析。另一方面，裂纹损伤构件在载荷作用下的演变与整体结构系统的关系密切，因此，包含裂纹损伤的结构整体系统计算是必要的，而目前一般的有限元方法由于裂纹存在和非线性的特殊原因，进行这样的计算工作量非常大，因此有必要开发未知量少且能反映弹塑性裂纹影响的新的结构单元。针对周向壁穿裂纹损伤柱壳，利用Sanders弹塑性裂纹解析解，通过增量运算，实现载荷和位移的增量显式表达，建立了弹塑性裂纹的单元增量刚度方程，为裂纹损伤结构系统的整体计算奠定了必要的理论基础。

A New Cracked Cylinder Element to Predict Elastic-plastic Behavior of Offshore Structural Systems

Cylindrical shells are a sort of main structural members in naval architecture and offshore structures． Due to heavy cyclic wave loads，fatigue cracks as a kind of common and dangerous damage to safety may occur in the construction．Therefore the research on the cracked cylindrical shell is always a hot SUbject．In general，some material with suficient ductility is used for these structures， then it is possible that there is a large plastic area around the crack front before the crack growths． Thus it is necessary that elastic-plastic analysis of fracture is applied in this case． On the other hand，the evolution of the cracked cylindrical members under loading is closely related to the structural system ，which contains the members．Thus elastic-plastic analysis of the structural system containing the cracked members as a whole is required．However such a calculation by means of the ordinary finite element method is a task of enormous efforts due to the crack existence and nonlinearity．Therefore it is necessary to develop a new structural element considering influences of the elasticplastic crack with the least unknowns．In this paper，incremental derivation is performed to Sanders elastic-plastic analytical solutions for circumferential through-cracked cylindrical shells． The explicit relationships between nodal force and displacement are obtained． The relevant element stiffness equation in tangential incremental form is established．The new element provides the ability to predict the elastic-plastic behavior of structural system with cracks on a necessary theoretical base．