考虑形位公差的薄壁筒壳折减因子预测方法研究

缺陷敏感性是薄壁筒壳结构设计所面临的主要问题之一，通常利用折减因子来量化筒壳结构的缺陷敏感性程度。然而现有缺陷敏感性分析方法大多以预测筒壳折减因子下限为目的，未考虑不同形位公差水平对筒壳折减因子的影响。针对此问题，本文提出了一种考虑形位公差的薄壁筒壳折减因子预测方法。该方法基于多点最不利扰动载荷法进行最不利缺陷搜索，获得筒壳不同形位公差下的折减因子下限值，从而确定考虑形位公差的薄壁筒壳折减因子参考值，并利用不完全折减刚度法对计算过程进行加速。算例结果表明本文提出的筒壳折减因子预测方法可在保证安全可靠的前提下，有效提高折减因子预测精度，消除筒壳结构设计过程中不必要的安全裕度，对结构减重有积极意义。未来可基于本方法展开我国新一代航天结构薄壁筒壳折减因子设计规范的研究工作，进一步提高我国航天筒壳结构设计的精细化和轻量化水平。

Research on knockdown factor determination method of thin-walled cylinder considering geometric tolerances

Imperfection sensitivity is one of the main problems faced in the design of thin-walled cylindrical shell structures. A knockdown factor is usually used to quantify the degree of sensitivity to imperfections in the cylindrical shell structure. However, most of the existing imperfection sensitivity analysis methods aimed at predicting the lower limit of the shell knockdown factor, and did not consider the influence of different geometric tolerance levels on the shell knockdown factor. Aiming at this problem, this paper proposes a method to determine the knockdown factor of thin-walled cylindrical shells considering the geometric tolerances. The method is based on the worst perturbation load method of multiple points to search for the worst imperfection modes, and obtains the lower limit of the knockdown factor under different geometric tolerances of the cylindrical shell, thereby determining the knockdown factor of the thin-walled cylindrical shell considering the geometric tolerance, and the incomplete reduced stiffness method is used to accelerate the calculation process. The results of the calculation examples show that the knockdown factor determination method proposed in this paper can effectively improve the prediction accuracy of the knockdown factor and eliminating unnecessary safety margins under the premise of ensuring safety and reliability, which has positive effect on structural weight savings. Based on this method, the research on the new knockdown factor design criteria of aerospace structure thin-walled cylindrical shells can be carried out, and can further improve the design of aerospace shell structure and the level of refinement and light-weight.