Derivations of Knockdown Factors for Cylindrical Structures Considering Different Initial Imperfection Models and Thickness Ratios

Sim, Chang-Hoon; Kim, Han-Il; Lee, Ye-Lin; Park, Jae-Sang; Lee, Keejoo

doi:10.1007/s42405-018-0069-4

Cited by 14 publications

(11 citation statements)

References 9 publications

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“…Therefore, the SPLA is used to represent the geometrically initial imperfection of both the detailed and equivalent models for the isogrid-stiffened cylinders. The SPLA is represented using the following three-step process [28,29], which differs slightly from the original modeling [30].…”

Section: Analysis Techniquesmentioning

confidence: 99%

“…Firstly, an assumed perturbation load (Q) in the radial direction is applied to the middle of the cylinder (Figure 6(a), [24][25][26][27][28][29][30]). In the present work, for the detailed model of the isogrid-stiffened cylinder, the radial perturbation load is applied to the intersection point between the axial stiffener of a grid panel and the cylinder's middle line, as shown in Figure 6(b); however, the application point of the radial perturbation load for the equivalent model is considered to be the same point as in the detailed model.…”

Section: Analysis Techniquesmentioning

confidence: 99%

“…International Journal of Aerospace Engineering cylinder by modifying the nodal coordinates of the cylinder's finite element model [28,29]. This modeling can represent a cylinder with geometrically initial imperfection in a stress-free state, which provides realistic modeling of the initial imperfections of thin-shell structures [24][25][26][27].…”

Section: Analysis Techniquesmentioning

confidence: 99%

“…The geometrically initial imperfection of the cylinder is modeled using the single perturbation load approach (SPLA), which is considered one of the best methods to represent the most realistic and worst initial imperfections of shell structures [24][25][26][27]. In this study, a slightly modified modeling technique for the SPLA [28,29] to the original modeling technique [30] is used.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Numerical Derivation of Buckling Knockdown Factors for Isogrid-Stiffened Cylinders with Various Shell Thickness Ratios

Kim

Sim

Park

et al. 2020

International Journal of Aerospace Engineering

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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.

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Section: Analysis Techniquesmentioning

confidence: 99%

Section: Analysis Techniquesmentioning

confidence: 99%

Section: Analysis Techniquesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Numerical Derivation of Buckling Knockdown Factors for Isogrid-Stiffened Cylinders with Various Shell Thickness Ratios

Kim

Sim

Park

et al. 2020

International Journal of Aerospace Engineering

Self Cite

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“…25 In order to investigate the outstanding load-carrying capacity of hierarchical stiffened panels, numerical and experimental studies have been carried out by Quinn et al, [30][31][32] and corresponding design guidelines of hierarchical stiffened panels were also given by Houston et al 33 Wang et al 21 developed a novel hierarchical stiffened shell reinforced by orthogrid major stiffeners and triangle minor stiffeners and Zhao et al 24 developed a novel one reinforced by triangle major and minor stiffeners, which both improved the bucking loads of stiffened shells significantly. Under the same weight, the hierarchical stiffened shell was verified to have low imperfection sensitivity in comparison to the traditional stiffened shell by Wang et al 22 and Sim et al 34,35 Additionally, the thermal buckling capacity of hierarchical stiffened structures was discussed by Wang et al 36 Although the hierarchical stiffened shell achieves higher load-carrying capacity than the traditional stiffened shell, its optimization problem is more complicated. Generally, the optimization of hierarchical stiffened shells faces two major challenges.…”

Section: Introductionmentioning

confidence: 99%

Buckling surrogate-based optimization framework for hierarchical stiffened composite shells by enhanced variance reduction method

Tian

Zhang

et al. 2019

Journal of Reinforced Plastics and Composites

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The surrogate-based optimization of hierarchical stiffened composite shells against buckling is a typical multimodal and multivariables optimization problem. To improve the computational efficiency and global optimizing ability of the surrogate-based optimization of hierarchical stiffened composite shells, an enhanced variance reduction method based on Latinized partially stratified sampling and multifidelity analysis methods is proposed in this paper and then integrated into the surrogate-based optimization framework. In the offline step of the optimization framework, candidate pairing strategies of design variables are generated by Latinized partially stratified sampling and compared by performing priori optimizations based on the low-fidelity analysis method, and the optimal pairing strategy is therefore determined. On the basis of the optimal pairing strategy, the surrogate-based optimization is carried out using the highfidelity analysis method in the online step. With less computational cost in the offline step, the proposed enhanced variance reduction method overcomes the limitation of Latinized partially stratified sampling that the optimal pairing strategy is not obvious in complex problems. Then, extensive optimization examples are carried out to verify the efficiency and effectiveness of the proposed optimization framework. Given an approximate computational cost, the optimal buckling result of the proposed framework using enhanced variance reduction method increases by 18.2% than that of the traditional framework based on Latin hypercube sampling. In particular, the advantage of enhanced variance reduction method in the space-filling ability is highlighted in comparison to Latin hypercube sampling. When achieving an approximate global optimal solution, the proposed framework reduces the total computational cost by 76.3% than the traditional framework. Finally, the numerical implementation of asymptotic homogenization method is used herein for the accurate prediction of effective stiffness coefficients of the initial design and optimal results. Through comparison, it is concluded that the high axial stiffness and bending stiffness are the main mechanism for the high loadcarrying capacity of optimal results.

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Toward the robust establishment of variable-fidelity surrogate models for hierarchical stiffened shells by two-step adaptive updating approach

Tian

et al. 2019

Struct Multidisc Optim

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Derivations of Knockdown Factors for Cylindrical Structures Considering Different Initial Imperfection Models and Thickness Ratios

Cited by 14 publications

References 9 publications

Numerical Derivation of Buckling Knockdown Factors for Isogrid-Stiffened Cylinders with Various Shell Thickness Ratios

Numerical Derivation of Buckling Knockdown Factors for Isogrid-Stiffened Cylinders with Various Shell Thickness Ratios

Buckling surrogate-based optimization framework for hierarchical stiffened composite shells by enhanced variance reduction method

Toward the robust establishment of variable-fidelity surrogate models for hierarchical stiffened shells by two-step adaptive updating approach

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