• Journal of the Korean Mathematical Society
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• v.37 no.2
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• pp.193-223
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• 2000

In the late 1970's, M. Kuranishi proposed to control the moduli of the germ of a normal Stein space by deformations of the CR structure on the boundary. I this paper, we will see that it is naturally accomplished by considering stably embeddable deformations of CR structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.1
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• pp.124-132
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• 1997

This paper describes an experimental and numerical study on growing ductile crack-tip behaviors. The hybrid experimental and numerical method by means of a computer image processign technique, was applied to the analysis of both base metal and weld metal CT specimens. In the weld metal specimen, the initial crack-tip was placed in front of fusion line, and the crack orientation was perpendicular to it. Finite element analysis of crack growth behaviors in both base and weld matal specimens made of A533B Class 1 steel were also performed to examine the effects of weldment on near crack-tip fields. a series of experimental studies on crack-tip behaviors have clearly shown the qualitative effects of material properties, especially a hardening exponent. The experimental and numerical results have also shown that weldment does not affect displacement and strain fields near a crack-tip while a stress field is influenced by the difference between yield stresses of both base and weld metals.

• Solar Energy
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• v.17 no.1
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• pp.35-46
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• 1997

In this study comparison of experiment results with the computed results of linear theory and nonlinear theory using singularity method was obtainable. Specially singularity points like sources and vortexes on hydrofoil and freestreamline were distributed to analyze two dimensional flow field of supercavitating cascade using nonlinear theory, and governing equations of flow field were derived and hydraulic characteristics of cascade were calculated by numerical analysis of the governing equations. The results compared linear theory and nonlinear theory with the experiment results of the study are as follows: The tolerances of nonlinear theory were larger than those of linear theory in case of ${\alpha}<10^{\circ}$. Moreover the computational range of attack angles could be expanded from ${\alpha}=10^{\circ}$ to ${\alpha}=25^{\circ}$, the flow field of supercavitating cascade could be analyzed in the condition which the wake thickness and the length of cavity are a variable. The shapes of cavity were changed sensitively according to various variable such as attack angles, pitches and wake thickness, and the pressure distribution of hydrofoil surface was identical almost disregarding wake thickness but changed largely according to attack angle and the length of cavity. Lift coefficient and drag coefficient were reduced according to increasing of wake thickness but the influences of wake thickness were very little in the situation of small pitch and long cavity.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04a
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• pp.353-358
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• 1998

The strain localization is a discontinuous phenomenon that addresses the formation of jumps of the field variables across a singularity surface. It has become widely accepted that the localization may occur as the result of discontinuous bifurcation which corresponds to the loss of ellipticity of the governing differential equations for elasto-plastic continua. In this paper, condition for strain localization in concrete based on bifurcation theory is studied and localization tensor analysis algorithm is employed to determine the directions of localization of deformations in concrete. By applying a plasticity model of concrete into the algorithm, localization analysis is performed concrete under uniaxial tension, pure shear and uniaxial compression.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.7189-7195
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• 2015

The method of moments (MoM) is implemented to simulate scattering from a PEC (perfectly electric conductor) cylinder in the TE(transversw electric) EFIE (Electric Field Integral Equation) approach. The procedure expresses the singularity integral and the hypersingularity integral in terms of an analytic function and employs a singularity isolation process coupled with numerical technique along the discretized segment to evaluate the self terms. It is known that, in the MoM technique, the choice of base functions and test functions is very important for the accuracy and convergence of the numerical analysis. Thus, in this paper, three conditions, obtained from the combination of basis functions and test functions, are adopted to get the induced currents on the PEC surface. These currents are compared to the analytical one in the relative rms current error to get the condition that shows fast convergence rate. The fast order of convergence of the current error, 2.528, is obtained under the combination of pulse basis function/delta test function.

• Journal of KSNVE
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• v.5 no.3
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• pp.337-344
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• 1995

A BEM program is developed for the performance analysis of axisymmetric mufflers. In the program the sub-region method is used to deal with singularity or inner boundary. The program is applied to typical axisymmjetric mufflers such as simple expansion, extended tube, perforated tube and absorptive expansion sufflers. The transmission losses of the mufflers are calculated by the program and compared with experiments. It is found that the prediction is in a good agreement with measurement, except for the absorptive muffler with parallel lining.

• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.286-289
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• 2008

Mass of generator is one of the most important characteristic value especially direct drive type wind turbine. This paper introduce how to decease mass of generator rotor frame without declining generator performance. To obtain optimal design of rotor frame, sensitivity analysis using Taguchi method and RSM(response surface method) are have been performed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.1
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• pp.206-214
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• 1998

When a crack meets bimaterial interface stress singularity depends on the elastic constants of the adjacent materials. In the present study we are going to describe the finite element formulation for problems with a crack to be embedded in the stiffer material$({\mu}_2/{\mu}_1)$. The cubic isoparametric singular element, represented by adequately shifting the mid-side nodes adjacent to the crack tip is constructed to enclose the crack tip. An alternative method to obtain the optimal position of the mid-side nodes of cubic isoparametric elements is presented. In addition, a proper definition for the stress intensity factors of a crack normal to bimaterial interface is provided. It is based upon near a tip displacement solutions. Models for numerical analysis are two dimensional elastic bodies with a through crack under plain strain. The results obtained are compared with the previous solutions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.179-189
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• 1991

Composite materials are generally treated as anisotropic or an orthotropic materials. Unlike isotropic materials, the orthotropic materials can divided three groups depending upon the relationship of the four material constants or depending upon the characteristic roots of orthotropic materials. In particular, the fundamental solutions of two dimensional BEM for composite materials (orthotropic or anisotropic material) generally have a singularity in the conventional method when the characteristic roots are equal. In consideration of this singularity in the conventional method when the characteristic roots are equal. In consideration of this singular problems, in this paper, the fundamental solutions of BEM are systematically analysed for orthotropic materials. And the stress and displacement fields for a crack in an orthotropic materials are singular when the characteristic roots of orthotropic materials are equal. Therefore, these fields for a crack in an orthotropic materials are analysed by the analogous method to isotropic materials when the characteristic roots are equal.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.4
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• pp.673-678
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• 1997

Stress wave propagations in an elastic half space to a normal point force of ramp type in time are analyzed. The governing equations are transformed by applying the Laplace and Hankel transforms with respect to time and radial distance. The inversion of Laplace transforms are performed by employing the Cagniard-de Hoop method, where the Rayleigh waves at surface are obtained by including the residue terms. The stress waves computed at the location very cose to the surface are shown to be almost identical to the surface waves obtained by the residue method except the Rayleigh wavefront. It is found that at the surface, the stresses are dominated by the Rayleigh waves, whose amplitudes increase linearly with time when time is very large. It is also found that in the interior part, the radial stress has a logarithmic singularity at the shear wavefront, while tangential stress shows no singularity.