薄壁筒壳是箭体的主承力结构，初始几何缺陷对其承载性能影响巨大，因而考虑缺陷影响的高效分析方法与优化设计对确保该类结构的安全性能、有效提升其承载能力意义重大。本申请将以申请人近年来围绕板壳力学问题提出的辛叠加解析方法为基础，突破传统理论方法难以精确求解高阶偏微分方程复杂边值问题的挑战，结合初始后屈曲理论，建立含缺陷筒壳的高精度后屈曲求解方法：辛叠加-Koiter方法。基于筒壳实测缺陷和辛叠加-Koiter方法，发展最不利缺陷的快速搜索技术，实现筒壳实际承载力下限的快速预测。构建网格加筋筒壳低缺陷敏感度高效分层优化设计框架，克服单次后屈曲分析耗时长导致优化效率低的难题，获得低缺陷敏感度的鲁棒性筒壳设计。通过本研究，预期在获取理论创新成果的同时，力争将其服务于我国重型运载火箭的贮箱结构设计。

Thin-walled cylindrical shells serve as the primary load-carrying structures of the launch vehicles, with initial geometric imperfections having a remarkable impact on their mechanical behavior. Accordingly, the efficient analysis method and optimal design incorporating the imperfection effects are of great significance for ensuring the structural safety and effectively promoting the load-carrying capacity. In this proposal, based on the symplectic superposition method, which was established by the applicant for plate and shell problems, and the initial post-buckling theory, a highly accurate post-buckling solution method, i.e., the symplectic superposition-Koiter method, will be established for the cylindrical shells with imperfections. The challenge in using classical theoretical methods, which cannot accurately solve the complex boundary value problems of high-order partial differential equations, will be well addressed. A fast technique for seeking the worst imperfection will be developed based on the experimentally measured imperfections of a cylindrical shell and the symplectic superposition-Koiter method, by which fast prediction of the actual lower-bound bearing capacity will be realized. A highly efficient layered optimization framework toward low imperfection-sensitive grid-stiffened cylindrical shells will be constructed. By overcoming the difficulty of inefficient optimization caused by the time-consuming post-buckling analysis in a single calculation, the robust design of cylindrical shells with low imperfection-sensitivity will be obtained. Through the present study, we aim to obtain some innovative theoretical achievements and use them to serve for the structural design of the fuel tanks in Chinese heavy-lift launch vehicles.