• Bulletin of the Korean Chemical Society
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• v.26 no.12
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• pp.1965-1968
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• 2005

Extended H$\ddot{u}$ckel molecular calculations have been used to analyze how the magnitude of exchange coupling is influenced by the structural distortions in a series of dinuclear six-coordinate copper(II) complexes bridged by the planar bis-bidentate oxalate anion. Copper(II) ions have distorted octahedral surroundings, one being axially elongated and the other compressed. The magnetic interaction is strong in the former complexes and very weak in the latter. This is interpreted as resulting from a switching of magnetic spin orbitals due to the structural distortions (bond elongation or compression) of the copper sites.

• Journal of the Korean Ceramic Society
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• v.28 no.6
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• pp.437-442
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• 1991

Temperature and atmosphere dependence of electrical conduction of the metal Cu, Ag, Au films, vaccum evaporated on glass, was investigated. The structural changes of the metal films were examined by SEM and high temperature XRD. The electrical resistance slightly increased with initial temperature increase up to the inflection point and decreased to minimum value, after this rapidly increased with further temperature increased below minimum. These phenomena were caused by the thermally induced film failure as a result of the mass transport. The temperature for the film failure increased in the order of O2, Air, Vacuum, N2, Ar in Cu, Ag films and Air, Vacuum, N2, Ar in Au film. The increase of resistance at the lower temperature range was attributed to the lattice distortion by disordered crystal structure, while the decreasing resistance was attributed to the removal of structural defects and film densification.

• Journal of Korean Association for Spatial Structures
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• v.19 no.4
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• pp.35-44
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• 2019

Recently, the occurrence frequency of earthquake has increased in Korea, and many cultural assets have been damaged. Cheomseongdae is a valuable cultural assets that must be preserved historically and culturally. But, the masonry structure such as Chemseongdae is vulnerable to lateral forces. Therefore, in this study, structural modeling and dynamic analysis are performed to reflect the ground state and structural form of Cheomseongdae. Also, discrete element analysis technique is applied and dynamic behavior characteristics are analyzed according to earthquake load. For this purpose, displacements and stresses according to locations are reviewed and then swelling and distortion are analyzed.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.531-536
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• 2001

The structural shape optimization is a useful tool for engineers to determine the shape of a structure. During the optimization process, relocations of nodes happen successively. However, excessive movement of nodes often results in the mesh distortion and eventually deteriorates the accuracy of the optimum solution. To overcome this problem, an efficient method for the shape optimization has been developed. The method starts from the design domain which is large enough to hold the possible shape of the structure. The design domain has pre-defined uniform fine meshes. At every cycle, the method judges whether all the elements are inside of the structure or not. Elements inside of the structure are assigned with real material properties, however elements outside of the structure are assigned with nearly zero values. The performance of the method is evaluated through various examples.

• Laser Solutions
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• v.1 no.1
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• pp.11-17
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• 1998

The electron beam welding system has the advantages of the high power density, narrow welding section, and small thermal distortion of a workpiece. Recently, the electron beam welding system is widely used to the airplane engineering, nuclear power plant, and automobile industry. In the present paper, the structural analyses on the vacuum chamber of the electron beam welding system are performed by the F.E.M. analysis. The stiffening characteristics on the geometric shape, stiffener height and stiffener span are investigated. The deflection of the stiffened vacuum chamber under pressure is minimized by longitudinal and transverse stiffeners which are continuous in both direction.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.836-840
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• 2006

Design optimization of layered plates bonding process is conducted to achieve high product quality by considering uncertainties in a manufacturing process. During the cooling process of the sequential sub-processes, different thermal expansion coefficients lead to residual stress and displacement. thus resulting in defects on the surface of the adherent. So robust process optimization is performed to minimize the residual stress mean and variation of the assembly while constraining the distortion as well as the instantaneous maximum stress to the allowable limits. In robust process optimization, the dimension reduction (DR) method is employed to quantify both reliability and quality of the layered plate bonding. Using this method. the average and standard deviation is estimated. Response surface is constructed using the statistical data obtained by the DRM for robust objectives and constraints. from which the optimum solution is obtained.

• Structural Engineering and Mechanics
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• v.9 no.6
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• pp.541-555
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• 2000

Pultruded cross-sections are always thin-walled due to constraints in the manufacturing process. Thus, the buckling strength determines the overall strength of the member. The elastic buckling of pultruded angle sections subjected to direct compression is studied. The lateral-torsional buckling, very likely to appear in thin-walled cross-sections, is investigated. Plate theory is used to allow for cross-sectional distortion. Shear effects and bending-twisting coupling are accounted for in the analysis because of their significant role. A simplified approach for determining the maximum load of equal leg angle sections under compression is presented. The analytical results obtained in this study are compared to the manufacturer's design guidelines for compression members as well as with the design specifications for steel structural members. Experimental results are obtained for various length specimens of pultruded angle sections. The results presented in this paper correspond to actual pultruded equal leg angle sections being used in civil engineering structures.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.10a
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• pp.120-128
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• 2002

In order to analyze shell structures more accurately and effectively, a hybrid 4-node quadrilateral shell element is formulated. The element includes the frilling degrees of freedom and the independent parameter terms of the stress resultants are appropriately selected to overcome some of the shortcomings of the standard 4-node quadrilateral elements. In order to show the accuracy and convergent characteristics of the proposed shell element, three numerical examples are analyzed and the results are compared with the existed. As a result of this study, following conclusions are obtained. (1)Analysis results by the proposed element are less sensitive to the element geometric distortion. (2)The proposed element does not produce any spurious zero-energy modes

• Computational Structural Engineering
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• v.5 no.2
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• pp.105-118
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• 1992

Static performance was compared for the triangular plate elements through some numerical experiments. Four Kirchhoff elements and six Mindlin elements were selected for the comparison. Numerical tests were executed for the problems of rectangular plates with regular and distorted meshes, rhombic plates, circular plates and cantilever plates. Among the Kirchhoff 9 DOF elements, the discrete Kirchhoff theory element was the best. Element distortion and the aspect ratio were shown to have negligible effects on the displacement behaviour. The Specht's element resulted in better results than the Bergan's but it was sensitive to the aspect ratio. The element based on the hybrid stress method also resulted in good results but it assumed to be less reliable. Among the linear Mindlin elements, the discrete shear triangle was the best in view of reliability, accuracy and convergence. Since the thin plate behaviour of it was as good as the DKT element, it can be used effectively in the finite element code regardless of the thickness. As a quadratic Mindlin element, the MITC7 element resulted in best results in almost all cases considered. The results were at least as good as those of doubly refined meshes of linear elements.

• Computational Structural Engineering : An International Journal
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• v.3 no.1
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• pp.19-29
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• 2003

In the present study, finite element linear buckling analysis is performed for grid-stiffened composite plates. A hybrid element with drilling degrees of freedom is employed to reduce the effect of the sensitivity of mesh distortion and to match the degrees of freedom between skins and stiffeners. The preliminary static stress distribution is analyzed for the determination of accurate load distribution. Parametric study of grid structures is performed and three types of buckling modes are observed. The maximum limit of buckling load was found at the local skin-buckling mode. In order to maximize buckling loads, stiffened panels need to be designed to be buckled in skin-buckling mode.