This study is aimed at providing a numerical derivation of the shell knockdown factors of isogrid-stiffened cylinders under axial compressive loads. The present work uses two different analysis models such as the detailed model with modeling of numerous stiffeners and the equivalent model without modeling of stiffeners for isogrid-stiffened cylinders. The single perturbation load approach is used to represent the geometrically initial imperfection of the cylinder. Postbuckling analyses using the displacement control method are conducted to calculate the global buckling loads of a cylinder. The shell knockdown factor is numerically derived using the obtained global buckling loads without and with the initial imperfection of the isogrid-stiffened cylinder. The equivalent model is more efficient than the detailed model in terms of modeling time and computation time. The present knockdown factor function in terms of the shell thickness ratio (radius to thickness) for the isogrid-stiffened cylinder is significantly higher than NASA’s knockdown factor function; therefore, it is believed that the present knockdown factor function can facilitate in developing lightweight launch vehicle structures using isogrid-stiffened cylinders.

中文翻译：

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不同壳厚比的等强度圆柱的屈曲击倒因子的数值推导

这项研究的目的是提供在轴向压缩载荷下等强度加筋气缸壳击穿系数的数值推导。本工作使用两种不同的分析模型，例如带有多个加劲肋的模型的详细模型和不带等筋加劲圆柱体的加劲器的等效模型。单一摄动载荷方法用于表示圆柱体的几何初始缺陷。使用位移控制方法进行后屈曲分析，以计算气缸的整体屈曲载荷。使用获得的整体屈曲载荷，在没有等斜刚度圆柱体的初始缺陷和没有初始缺陷的情况下，通过数值推导得出壳的击穿系数。就建模时间和计算时间而言，等效模型比详细模型更有效。以等厚刚度圆柱体的壳厚度比（半径与厚度）表示的当前击倒因子函数明显高于NASA的击倒因子函数；因此，可以相信，目前的击倒因子功能可以促进使用等强度加筋圆柱体开发轻型运载火箭结构。