• Journal of Welding and Joining
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• v.32 no.4
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• pp.69-74
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• 2014

Welding distortions of large steel structures had mainly been estimated with some simplified formula obtained by lots of experience and numerical analyses for small steel structures. However, the large structures would have different characteristics of distortion with welding because of their own stiffness coming from the size itself. Therefore, in order to find some measures for preventing welding distortion of large structure, it is requite in advance to precisely analysis thermal stress and distortion during welding of the structure. Numerical analysis for larger structure has been known to take large amount of calculation time and have a poor convergency problem during the thermo-elasto-plastic calculation. In this study, a hybrid method is proposed to analysis the thermal stress and distortion of a large steel plate with the finite element analysis by incorporating with temperature distribution of the plate calculated by an analytical solution. The proposed method revealed that the thermo-mechanical analysis for welding of the large structure could be performed with a good convergence and produced precise results with much reduced time consumption.

• Journal of the Korean institute of surface engineering
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• v.52 no.1
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• pp.6-15
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• 2019

Metal-halide perovskite (MHP) solar cell is a promising candidate for next-generation flexible devices and the BIPV (Building-integrated photovoltaics) because it can exhibit high power conversion efficiencies over 23%, good bendability and low processing cost. However, MHP solar cells are commonly fabricated by the spin coating that is not a reliable method to produce large-scale commercial solar cells. A shear coating can be one of the potential candidates for the large-scale deposition method of MHP films. In this work, the influences of the process parameters such as solvents of precursor solution, substrate temperature, concentrations of precursor solution, and annealing time on the thin film growth of MHP were investigated for the shear coating process. This study presents the possibility of the shear coating process for large-scaled perovskite film fabrication and reveals the role of process condition in the thin film growth of perovskites.

• Computational Structural Engineering
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• v.2 no.3
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• pp.97-103
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• 1989

In this study, a usefulness of the iterative solution procedures is reviewed for the elasto-plastic large deflection analysis of imperfect plates by finite element method. Three typical solution techniques such as simple incremental(SI) method, Newton-Raphson(NR) method and modified Newton-Raphson (mNR) method are compared. It is concluded that for thin plates which are given rise to the large deflection, iteration for the convergence of the unbalance force should be performed and in this case mNR method is more useful than NR method since the computing time of the former becomes to be a half of the latter, in which the accuracy of the result remains same. For thick plates or thin plates with large initial deflection, however, the use of SI method is quite better since the unbalance force may be negligible.

• Geomechanics and Engineering
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• v.21 no.6
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• pp.527-536
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• 2020

An elastic-plastic solution for cavity expansion problem considering strength degradation, undrained condition and initial anisotropic in-situ stress is established based on the Tresca yield criterion and cavity expansion theory. Assumptions of large-strain for plastic region and small-strain for elastic region are adopted, respectively. The initial in-situ stress state of natural soil mass may be anisotropic caused by consolidation history, and the strength degradation of soil mass is caused by structural damage of soil mass in the process of loading analysis (cavity expansion process). Finally, the published solutions are conducted to verify the suitability of this elastic-plastic solution, and the parametric studies are investigated in order to the significance of this study for in-situ soil test.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.18 no.36
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• pp.133-141
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• 1995

One of the problems brought up in the effective execution of genetic algorithms is that if they come under any influences according as the population size is large or small. In the case of small population size the opportunities of premature convergence are increased when the greatly powerful or no good individual is generated during search of the solution space. And searching the solution space in the case of large population size, the difficulties under the execution cause to searching all for one by one individual in every generation applied is limited, this gives the many interruptions to the convergence of final solution. Now this paper gives a suggestion to set up the adaptive population size which could compute the more correct solution and simplify the development of computation performance.

• Geomechanics and Engineering
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• v.19 no.2
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• pp.141-151
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• 2019

A novel theoretical solution is presented for created (zero initial radius) cavity expansion problem based on CamClay model and considers the effect of initial anisotropic in-situ stress and drained conditions. Here the strain of this theoretical solution is small deformation in elastic region and large deformation in plastic region. The works for cylindrical and spherical cavities expanding in drained condition from zero initial radius are investigated. Most of the conventional solutions were based on the isotropic and undrained condition, however, the initial stress state of natural soil mass is anisotropy by soil deposition history, and drained cavity expansion calculation is closer to actual engineering in permeable soil mass. Finally, the parametric study is presented in order to the engineering significance of this work.

• Korean Journal of Mathematics
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• v.4 no.1
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• pp.39-43
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• 1996

Large-time asymptotic behavior of the solutions of interacting population reaction-diffusion systems are considered. Polynomial stability was proved.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.242-242
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• 2012

Transparent oxide semiconductors are increasingly becoming one of good candidates for high efficient channel materials of thin film transistors (TFTs) in large-area display industries. Compare to the conventional hydrogenated amorphous silicon channel layers, solution processed ZnO-TFTs can be simply fabricated at low temperature by just using a spin coating method without vacuum deposition, thus providing low manufacturing cost. Furthermore, solution based oxide TFT exhibits excellent transparency and enables to apply flexible devices. For this reason, this process has been attracting much attention as one fabrication method for oxide channel layer in thin-film transistors (TFTs). But, poor electrical characteristic of these solution based oxide materials still remains one of issuable problems due to oxygen vacancy formed by breaking weak chemical bonds during fabrication. These electrical properties are expected due to the generation of a large number of conducting carriers, resulting in huge electron scattering effect. Therefore, we study a novel technique to effectively improve the electron mobility by applying environmental annealing treatments with various gases to the solution based Li-doped ZnO TFTs. This technique was systematically designed to vary a different lithium ratio in order to confirm the electrical tendency of Li-doped ZnO TFTs. The observations of Scanning Electron Microscopy, Atomic Force Microscopy, and X-ray Photoelectron Spectroscopy were performed to investigate structural properties and elemental composition of our samples. In addition, I-V characteristics were carried out by using Keithley 4,200-Semiconductor Characterization System (4,200-SCS) with 4-probe system.

• Structural Engineering and Mechanics
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• v.35 no.2
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• pp.205-215
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• 2010

Recently, earthquake proof technology has been widely applied to both new and existing structures and bridges. The analysis of bridge systems equipped with structural control devices, which possess large degrees of freedom and nonlinear characteristics, is a result in time-consuming task. Therefore, a piecewise exact solution is proposed in this study to simplify the seismic mitigation analysis process for bridge systems equipped with sliding-type isolators. In this study, the simplified system having two degrees of freedom, to reasonably represent the large number of degrees of freedom of a bridge, and is modeled to obtain a piecewise exact solution for system responses during earthquakes. Simultaneously, we used the nonlinear finite element computer program to analyze the bridge responses and verify the accuracy of the proposed piecewise exact solution for bridge systems equipped with sliding-type isolators. The conclusions derived by comparing the results obtained from the piecewise exact solution and nonlinear finite element analysis reveal that the proposed solution not only simplifies the calculation process but also provides highly accurate seismic responses of isolated bridges under earthquakes.

• Structural Engineering and Mechanics
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• v.11 no.2
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• pp.185-197
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• 2001

This paper presents the effect of axial stretching on large amplitude free vibration of an extensible suspended cable supported at the same level. The model formulation developed in this study is based on the virtual work-energy functional of cables which involves strain energy due to axial stretching and work done by external forces. The difference in the Euler equations between equilibrium and motion states is considered. The resulting equations govern the horizontal and vertical motion of the cables, and are coupled and highly nonlinear. The solution for the nonlinear static equilibrium configuration is determined by the shooting method while the solution for the large amplitude free vibration is obtained by using the second-order central finite difference scheme with time integration. Numerical examples are given to demonstrate the vibration behaviour of extensible suspended cables.