• 한국정밀공학회지
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• 제30권11호
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• pp.1203-1210
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• 2013

Korea's first Naro-Science small class satellite was launched by Naro launcher in 2013. The structure of the satellite is mostly composed of aluminum honeycomb and frame. The honeycomb structure is homogenized with asymptotic homogenization method and its mechanical properties were used for the numerical analysis. There have been some difficulties to modeling the honeycomb sandwich panels for FEA. In the present study, the mechanical characteristics of the sandwich panel composite were numerically computed and used for the simulation. This methodology makes it easy to overcome the weakness of modeling of complicated sandwich panels. Both an experiment of vibration test and numerical analyses were conducted simultaneously. The analysis results from the current homogenization were compared with that of experiment. It shows a good agreement on the dynamic responses and certified the reliability of the present methodology when manipulate sandwich panel structure.

• Multiscale and Multiphysics Mechanics
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• 제1권1호
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• pp.15-33
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• 2016

In this paper, an asymptotic method is employed to formulate nano- or micro-beams based on strain gradient elasticity. Although a basic theory for the strain gradient elasticity has been well established in literature, a systematic approach is relatively rare because of its complexity and ambiguity of higher-order elasticity coefficients. In order to systematically identify the strain gradient effect, an asymptotic approach is adopted by introducing the small parameter which represents the beam geometric slenderness and/or the internal atomistic characteristic. The approach allows us to systematically split the two-dimensional strain gradient elasticity into the microscopic one-dimensional through-the-thickness analysis and the macroscopic one-dimensional beam analysis. The first-order beam problem turns out to be different from the classical elasticity in terms of the bending stiffness, which comes from the through-the-thickness strain gradient effect. This subsequently affects the second-order transverse shear stress in which the surface shear stress exists. It is demonstrated that a careful derivation of a first strain gradient elasticity embraces "Gurtin-Murdoch traction" as the surface effect of a one-dimensional Euler-Bernoulli-like beam model.

• 충청수학회지
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• 제21권3호
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• pp.413-426
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• 2008

An asymptotic solution of a fourth order critically damped nonlinear differential system has been found by means of extended Krylov-Bogoliubov-Mitropolskii (KBM) method. The solutions obtained by this method agree with those obtained by numerical method. The method is illustrated by an example.

• 정보처리학회논문지A
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• 제10A권1호
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• pp.59-68
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• 2003

3 차원 산포 볼륨 데이터의 모델링(3-D Scattered Data Modeling)은 지질구조 조사, 환경가시화, 초음파 검사 등의 분야에 사용된다. 이러한 분야에 사용되는 데이터는 마칭큐브 알고리즘에서 사용하는 규칙적인 데이터와는 다르게 일반적으로 불규칙적으로 흩어진 데이터이다. 이 논문에서는 우선 불규칙적으로 흩어진 데이터에 적합한 사면체를 영역(domain)으로 하는 볼륨 모델링 기법에 대하여 고찰한다. 다음에 사면체 영역 결정에 애매성이 발생하였을 때 점근선 판정기(asymptotic decider critrion)로 애매성을 해결하는 방법을 제안하고 수식을 구한다. 마지막으로 제안한 방법을 이용하여 간단한 가시화 시스템을 구현하여 구 판정기(sphere criterion)와 비교한다. 사면체의 영역을 결정하는데 있어서 구 판 정기는 점의 좌표만을 이용하나 점근선 판정기는 점의 좌표와 그 점이 가지고 있는 함수 값을 이용하므로 보다 정확한 영역 분할이 가능하다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제15권3호
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• pp.201-222
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• 2011

In the present work, the mathematical model of wire coating in a straight annular die is developed for unsteady second grade fluid in the form of partial differential equation. The Optimal Homotopy Asymptotic Method (OHAM) is applied for obtaining the solution of the model problem. This method provides us a suitable way to control the convergence of the series solution using the auxiliary constants which are optimally determined.

• 한국기계가공학회지
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• 제20권2호
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• pp.72-79
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• 2021

The present paper aims to set forth a two-dimensional theory for the dynamics of plates that is valid over a large range of excitation. To construct a dynamic plate theory within the long-wavelength approximation, two dimensional-reduction procedures must be used for analyzing the low- and high-frequency behaviors under the dynamic variational-asymptotic method. Moreover, a separate and logically independent step for the short-wavelength regime is introduced into the present approach to avoid violation of the positive definiteness of the derived energy functional and to facilitate qualitative description of the three-dimensional dispersion curve in the short-wavelength regime. Two examples are presented to demonstrate the capabilities and accuracy of all of the formulas derived herein by using various dispersion curves through comparison with the three-dimensional finite element method.

• 충청수학회지
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• 제19권1호
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• pp.49-56
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• 2006

A convergence behavior is under investigation near a simple real zero for the k-fold pseudo-Olver's method defined by extending the classical Olver's method. The order of convergence is shown to be at least k+3. The asymptotic error constant is explicitly given in terms of k and the corresponding simple zero. Various numerical examples with a proposed zero-finding algorithm are successfully confirmed with the use of symbolic and computational ability of Mathematica.

• 한국시뮬레이션학회논문지
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• 제9권3호
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• pp.43-51
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• 2000

In regression model, we estimate the unknown parameters by using various methods. There are the least squares method which is the most general, the least absolute deviation method, the regression quantile method and the asymmetric least squares method. In this paper, we will compare each others with two cases: firstly the theoretical comparison in the asymptotic sense and then the practical comparison using Monte Carlo simulation for a small sample size.

• Journal of the Korean Statistical Society
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• 제30권3호
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• pp.419-433
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• 2001

In this paper we introduce a method of improving efficiency of the moment estimator of Dekkers, Einmahl and de Haan(1989) for the extreme value index $\beta$. a new estimator of $\beta$ is proposed by adding the third moment ot the original moment estimator which is composed of the first two moments of the log-transformed sample data. We establish asymptotic normality of the new estimator and examine and adaptive procedure for the new estimator. The resulting adaptive estimator proves to be asymptotically better than the moment estimator particularly for $\beta$<0.

• 대한수학회보
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• 제55권3호
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• pp.735-747
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• 2018

This paper deals with the asymptotic behavior of solutions to the generalized MHD and Hall-MHD systems. Firstly, the upper bound for the generalized MHD and Hall-MHD systems is investigated in $L^2$ space. Then, the effect of the Hall term is analyzed. Finally, we optimize the upper bound of decay and obtain their algebraic lower bound for the generalized MHD system by using Fourier splitting method.