Chang-Hoon Sim, Han-Il Kim, Jae-Sang Park and Keejoo Lee
The purpose of this paper is to derive knockdown factor functions in terms of a shell thickness ratio (i.e. the ratio of radius to thickness) for conventional orthogrid and…
Abstract
Purpose
The purpose of this paper is to derive knockdown factor functions in terms of a shell thickness ratio (i.e. the ratio of radius to thickness) for conventional orthogrid and hybrid-grid stiffened cylinders for the lightweight design of space launch vehicles.
Design/methodology/approach
The shell knockdown factors of grid-stiffened cylinders under axial compressive loads are derived numerically considering various shell thickness ratios. Two grid systems using stiffeners – conventional orthogrid and hybrid-grid systems – are used for the grid-stiffened cylinders. The hybrid-grid stiffened cylinder uses major and minor stiffeners having two different cross-sectional areas. For modeling grid-stiffened cylinders with various thickness ratios, the effective thickness (teff) of the cylinders is kept constant, and the radius of the cylinder is varied. Thickness ratios of 100, 192 and 300 are considered for the orthogrid stiffened cylinder, and 100, 160, 200 and 300 for the hybrid-grid stiffened cylinder. Postbuckling analyses of grid-stiffened cylinders are conducted using a commercial nonlinear finite element analysis code, ABAQUS, to derive the shell knockdown factor. The single perturbation load approach is applied to represent the geometrical initial imperfection of a cylinder. Knockdown factors are derived for both the conventional orthogrid and hybrid-grid stiffened cylinders for different shell thickness ratios. Knockdown factor functions in terms of shell thickness ratio are obtained by curve fitting with the derived shell knockdown factors for the two grid-stiffened cylinders.
Findings
For the two grid-stiffened cylinders, the derived shell knockdown factors are all higher than the previous NASA’s shell knockdown factors for various shell thickness ratios, ranging from 100 to 400. Therefore, the shell knockdown factors derived in this study may facilitate in the development of lightweight structures of space launch vehicles from the aspect of buckling design. For different shell thickness ratios of up to 500, the knockdown factor of the hybrid-grid stiffened cylinder is higher than that of the conventional orthogrid stiffened cylinder. Therefore, it is concluded that the hybrid-grid stiffened cylinder is more efficient than the conventional orthogrid-stiffened cylinder from the perspective of buckling design.
Practical implications
The obtained knockdown factor functions may provide the design criteria for lightweight cylindrical structures of space launch vehicles.
Originality/value
Derivation of shell knockdown factors of hybrid-grid stiffened cylinders considering various shell thickness ratios is attempted for the first time in this study.
Details
Keywords
SeungGeon Hong, Kang Hyouk Lee and Il Han Park
The purpose of this paper is to propose dot sensitivity analysis of ferromagnetic materials for topology optimization in an axi-symmetric magnetostatic system.
Abstract
Purpose
The purpose of this paper is to propose dot sensitivity analysis of ferromagnetic materials for topology optimization in an axi-symmetric magnetostatic system.
Design/methodology/approach
The dot sensitivity formula for the axi-symmetric system is derived as a closed form using the continuum shape sensitivity formula. The dot sensitivity method is combined with the level set method to perform topology optimization.
Findings
Derived dot sensitivity analysis can generate a ferromagnetic ring torus in a vacant region. Thus, an initial design is not needed for the design material. Two design problems are tested to demonstrate the usefulness of dot sensitivity.
Originality/value
By simultaneously using the shape sensitivity and dot sensitivity, in axi-symmetric magnetic system, the design space is expanded and it includes the interface and the inside of the vacant region. This property can reduce the possibility of local optimum convergence.
Details
Keywords
During the 1920s and 1930s in the colonial city of Seoul, a group of women called the New Women and the Modern Girls expressed their modern identities by wearing different…
Abstract
Purpose
During the 1920s and 1930s in the colonial city of Seoul, a group of women called the New Women and the Modern Girls expressed their modern identities by wearing different clothing, hairstyles and make-up; visiting cafés; viewing Western movies; and consuming other foreign merchandise. While these women were admired by many women as being pioneers of modernity, they were severely criticized by others under the pretext that they indulged their vanity without considering the economy of their families and their colonized nation. These criticisms continue in twenty-first century Korea. Based on the striking similarity between the two eras, an understanding of the consumption and the criticisms of the Modern Girls could provide a historical context for understanding women's experiences in the consumer culture of twenty-first century Korea. The paper aims to discuss these issues.
Design/methodology/approach
As secondary sources, literature published in both English and Korean was included. Primary data were obtained from articles in Korean newspapers, magazines and print advertisements from the 1920s and 1930s.
Findings
The New Women and Modern Girls expressed their modern identities by consuming various fashion goods, including Western-style clothes, make-up and various accessories, adopting Western hairstyles and frequenting modern cafés, theaters and department stores. However, their behaviors escaped the boundaries of the “wise mother, good wife” ideology, and they were severely criticized by those adhering to the neo-Confucianism and Korean nationalist ideology that was deeply rooted in Korean society. Thus, the reputations of the Modern Girls were tainted and the individuals were stigmatized.
Originality/value
This research illuminates the negative aspects of self-expressive consumption, showing how individualistic, identity-driven consumption can be stigmatized in the collectivistic culture of Korea that is rooted in neo-Confucian nationalism.