• 충청수학회지
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• 제23권3호
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• pp.435-442
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• 2010

This paper is concerned with algorithm for calculating one-sided best simultaneous approximation, in the case of continuous functions. we will apply any subgradient algorithm. In other words, we consider the algotithms from a mathematical, rather then computational, point of view.

• 복합신소재구조학회 논문집
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• 제6권1호
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• pp.6-13
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• 2015

In this paper we present the result of investigations pertaining to the buckling strength of Zelkova Serrata (Elm-like) tree column with entasis at the Muryangsujeon in Buseoksa-Temple, Korea. Wooden columns with entasis had been used in the construction of ancient architectural buildings in Korea. It was not known why did they design columns with entasis of the buildings. It is just presumed that the reason may be the compensation of optical illusion, aesthetics, and/or structural safety. The question is not answered even today and it may not be possible to answer clearly and easily. In the paper, the buckling analyses are conducted on both of the wooden column with entasis and the prismatic wooden column by the successive approximations technique and the finite element methods, respectively. The results of analyses are compared and discussed.

• 전산구조공학
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• 제6권4호
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• pp.57-66
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• 1993

적분형 르장드르 다항식과 가상균열확장법을 사용한 p-version균열모델이 선형 탄성파괴력학에서 응력확대계수를 산정할 수 있도록 제안되었다. 이 모델의 큰 장점은 소수의 요소를 사용하기 때문에 입력재료를 최소화 할 수 있고 균열선단 부근에서 높은 정확도와 빠른 수검율을 얻을 수 있다는 것이다. 이 연구를 통해 얻어진 두 가지 결론은 다음과 같다. 첫째, 변형에너지의 정해인 극한치가 수검구간에 있는 연속된 3개의 p-version 유한요소 결과로 부터 확정 할 수 있다는 것이다. 둘째, 인장력을 받는 균열판 해석에서 p-version의 수검율은 균등 또는 유사균등 요소분할에 근거를 둔 h-version모델에 비해 거의 2배 가량 빠름을 알 수 있다.

• 대한전자공학회논문지
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• 제19권6호
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• pp.55-61
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• 1982

집적 광학에서 응용되는, 주기가 거의 선형으로 변하는 도파로 격자 필터의 파장에 따른 응답을 격자의 길이가 유한함을 고려하여 수식적으로 구하였다. 이 필터가 광대역 필터로서 설계되는 보편적인 경우에 대해서는 관련된 포물주면 함수를 변수의 위상에 따라 점근 근사를 취함으로써 파장에 따른 응답을 간단한 함수들로써 나타냈다. 또한 구한 결파식들이 기존 근사식들을 특별한 경우로 포함하는 일반적인 식임을 보였다. 마지막으로, 수식적인 해에 의한 결과와 RunRe-Kutta 수치 계산법에 의한 정확한 해를 비교하여 서로 잘 일치함을 확인하였다. An analytic solution for the spectral response of linearly-chirped grating filter is derived, which takes the finite physical length of filter into account. In the usual case of broad-band linearly-chirped grating filter the analytic solution is expressed in terms of elementary functions, by approximating asymptotically the involved parabolic cylinder functions over different ranges of its argument. It is also shown that derived results are general enough to include previously-available approximations as particular cases, and that they agree well with the numerical solutions based upon the Runge-Kutta method.

• 한국전산응용수학회:학술대회논문집
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• 한국전산응용수학회 2003년도 KSCAM 학술발표회 프로그램 및 초록집
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• pp.6-6
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• 2003

In this work we consider the mathematical formulation and numerical resolution of the linear feedback control problem for Boussinesq equations. The controlled Boussinesq equations is given by $$\frac{{\partial}u}{{\partial}t}-{\nu}{\Delta}u+(u{\cdot}{\nabla}u+{\nabla}p={\beta}{\theta}g+f+F\;\;in\;(0,\;T){\times}\;{\Omega}$$, $${\nabla}{\cdot}u=0\;\;in\;(0,\;T){\times}{\Omega}$$, $$u|_{{\partial}{\Omega}=0,\;u(0,x)=\;u_0(x)$$ $$\frac{{\partial}{\theta}}{{\partial}t}-k{\Delta}{\theta}+(u{\cdot}){\theta}={\tau}+T,\;\;in(0,\;T){\times}{\Omega}$$ $${\theta}|_{{\partial}{\Omega}=0,\;\;{\theta}(0,X)={\theta}_0(X)$$, where $\Omega$ is a bounded open set in $R^{n}$, n=2 or 3 with a $C^{\infty}$ boundary ${\partial}{\Omega}$. The control is achieved by means of a linear feedback law relating the body forces to the velocity and temperature field, i.e., $$f=-{\gamma}_1(u-U),\;\;{\tau}=-{\gamma}_2({\theta}-{\Theta}}$$ where (U,$\Theta$) are target velocity and temperature. We show that the unsteady solutions to Boussinesq equations are stabilizable by internal controllers with exponential decaying property. In order to compute (approximations to) solution, semi discrete-in-time and full space-time discrete approximations are also studied. We prove that the difference between the solution of the discrete problem and the target solution decay to zero exponentially for sufficiently small time step.

• 대한기계학회논문집A
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• 제22권2호
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• pp.278-288
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• 1998

An efficient and useful method to improve the local stress field in a displacement-formulated finite element solution has been proposed using the theory of conjugate approximations for a stress field and the Loubignac's iterative method for a displacement field. Validity of the proposed method has been tested through three test examples, to improve the stress field and displacement field in the whole domain and the local regions. As a result of analysis on the test examples, it is found that the stress field in the local regions are approximated to those in the whole domain within a few iterations which have satisfied the original finite element equilibrium equation. In addition, it is found that the local stress field are by far better approximated to the exact stress field than the displacement-based stress field with the reduction of the finite-element mesh-size.

• 한국항해학회지
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• 제9권2호
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• pp.43-63
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• 1985

As a circular cylinder has a comparatively simple shape and becomes a basic problem for flows around other various shapes of bodies, the problem of two-dimensional viscous flow around the circular cylinder has been investigated, both theoretically and experimentally. But not a few problems are left unsolved. It is well known that the calculations are successfully made with the approximations of Stokes or Oseen for very low Reynolds numbers, but as Reynolds number is increased, Oseen's approximations as well as Stokes's ones become more and more remote from the exact solution of the Navier-Stokes equations. Therefore, in this paper, the authors transform the Navier-Stokes equations into the finite difference equations in the steady two-dimensional viscous flow at Reynolds number up to 45, and then solve the solution of the Navier-Stokes equations numerically. Also, the authors examine the accuracy of the solution by means of flow visualization with aluminum powder. The main results are as follows; (1) The critical Reynolds number at which twin vortices begin to form in the rear of the circular cylinder is found to be 6 in the experiment and 4 in the numerical solution. (2) As Reynolds number is increased, it is proved that the ratio of the length of the twin vortices to the diameter is grown almost linearly, both experimentally and numerically. (3) Separation angle is also increased according to reynolds number. But it is found that it would converge into 101.3 degrees, both experimentally and numerically.

• 비파괴검사학회지
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• 제20권2호
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• pp.102-109
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• 2000

본 논문에서는 체적형 결함과 균열형 결함에 대한초음파산란 현상을 모델링하기 위한 두가지 이론을 설명하였다. 동탄성 Kirchhoff 근사 (EKA)와 기하학적 회절이론 (GTD)이 각각 원주형 기공과 반무한 균열에 적용되었다. 이 두 이론은 고주파수 근사법으로 알려져 있다. 모델 결함들에 평면파가 입사하는 경우의 2차원 동탄성 산란 문제를 고려하였으며 산란장을 반사계수와 회절계수의 항으로 구하였다. 원거리에서 산란파의 변위에 대한 입사파 변위의 비를 관찰 방향의 함수로 구했으며 그 결과를 경계요소법과 비교하였다.

• 한국의류학회지
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• 제30권8호
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• pp.1242-1252
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• 2006

Many applications in computer graphics require complex, highly detailed models. However, to control processing time, it is often desirable to use approximations in place of excessively detailed models. Therefore, we have developed the notion of an optimal matrix to simplify the model surface which can then rapidly obtain high quality 2D patterns by flattening the 3D surface. Firstly, the woman's 3D body was modeled based on Size Korea data. Secondly, the 3D model was divided by shell and block for the pattern draft. Thirdly, each block was flattened by the grid and bridge method. Finally, we select the optimal matrix and demonstrate it's efficiency and quality. The proposed approach accommodates surfaces with darts, which are commonly utilized in the clothing industry to reduce the deformation of surface forming and flattening. The resulting optimal matrix could be an initiation of standardization for pattern flattening. This can facilitate much better approximations, in both efficiency and exactness.

• 지구물리와물리탐사
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• 제1권3호
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• pp.155-160
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• 1998

확장된 Born 근사법을 사용하는 2.5차원 EM 모델링 알고리듬을 이용하여 2차원 역산에 근거한 EM 토모그래피 기법을 개발하였다. 역산법은 평활화 제한을 가한 감쇠최소자승법을 사용하였으며, 측정값은 2차 자기장의 수직성분으로 제한하였다. 적분방정식법에 근거한 3차원 EM 모델링 프로그램을 이용하여 단순한 형태를 갖는 모형에 대한 이론 자료를 계산하고, 이 자료를 측정값으로 EM 토모피래피 영상을 획득하였다. 거의 모든 경우에 EM 토모그래피 영상은 이상체의 위치는 비교적 정확히 추정하였으나, 전도도는 실제 값보다 상당히 낮게 추정하였다. 해상도 분석결과 수직해상도가 수평해상도에 비하여 월등히 뛰어난 것으로 나타났다.