• 한국통신학회논문지
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• 제13권3호
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• pp.255-259
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• 1988

무한히 긴 도체 스트립라인으로 이루어직 격자위에 TM파가 입사될 때 전류분포를 계산한다. 이런 구조에 모먼트법을 적용하면 행렬식이 매우 커져서 큰 컴퓨터 용량과 많은 계산시간이 필요하게 된다. 격자들의 경계조건과 산란파를 스펙트럴 영역으로 변환하고 격자들의 주기적 구조를 이용하여 Flouquet모드를 적용하며 산란파는 급수형태로 변형될 수 있다. 적합한 전개함수를 선정하여 급수형태의 식을 행렬로 변형하면 도체 스트립에 발생된 전류분포를 계산할 수 있다. 입사파의 각도 변화와 스트립의 폭과 간격의 변화에 따른 전류분포를 계산하다.

• 한국전자파학회논문지
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• 제15권5호
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• pp.499-508
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• 2004

마이크로스트립 구조체를 해석하는데 있어, 행렬 요소를 해석적으로 계산할 수 있는 효율적인 모멘트법이 제안된다. 본 논문의 모멘트법에서는 공간영역 그린함수로 Bessel 함수의 반 무한구간 정적분에 관한 공식에 근거하여 유도된 새로운 형태의 closed-form 그린함수를 사용한다. 본 논문의 모멘트법을 사용할 경우 기존의 모멘트법의 사용에 비해, 계산량 및 계산 속도와 같은 수치계산 효율 측면에서 약 4배 정도로 개선됨을 알 수 있었다. 본 논문이 제안하는 방법의 타당성을 확인하기 위하여 몇 가지 수치해석 결과를 제시한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.209-212
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• 2002

Since Berkhoff proposed the mild-slope equation in 1972, it has widely been used for calculation of shallow water wave transformation. Recently, it was extended to give an extended mild-slope equation, which includes the bottom slope squared term and bottom curvature term so as to be capable of modeling wave transformation on rapidly varying topography. These equations were derived by integrating the Laplace equation vertically. In the present study, we develop a finite element model to solve the Laplace equation directly while keeping the same computational efficiency as the mild-slope equation. This model assumes the vertical variation of wave potential as a cosine hyperbolic function as done in the derivation of the mild-slope equation, and the Galerkin method is used to discretize . The computational domain was discretized with proper finite elements, while the radiation condition at infinity was treated by introducing the concept of an infinite element. The upper boundary condition can be either free surface or a solid structure. The applicability of the developed model was verified through example analyses of two-dimensional wave reflection and transmission. .

• 대한기계학회논문집A
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• 제21권10호
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• pp.1598-1608
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• 1997

Based on the application of te theory of conjugate approximations and the Loubignac's iterative method in a local region, a method to improve the stress filed in a displacement-formulated finite element solution has been proposed. The validity of the proposed method has been tested through two examples : a thick cylinder under internal pressure loading and an infinite plate with a central circular hole subjected to uniaxial tension. As a result of analysis of the examples, it was found that the stress field obtained for the local region model by the proposed method approximates well for the whole domain model. In addition, it was found that because of a significant decrease in the computing time to obtain the improved stress field, the proposed method is efficient and useful for the detailed stress analysis in local regions.

• The Journal of the Acoustical Society of Korea
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• 제13권2E호
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• pp.83-91
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• 1994

쐐기형 영역에서 전파되는 음향파는 다음 3가지 성분으로 분류할 수 있다 : 직접 전달 경로에 의한 성분, 경계면으로 부터의 반사에 의한 상(image) 성분 그리고 정점에 의한 산란 성분, 2개의 평면으로 경계가 구성된 쐐기(또는 봉우리) 영역에서 점원에 의한 3차원적인 시간 조화 장(field)에 대한 Helmholtz 방정식의 새로운 해를 구하였으며, 그 해는 위의 3가지 성분을 모두 내포하고 있다. 이 해는 정상모우드 들의 무한 급수로 이루어졌으며 각 모우드 계수는 Gegenbauer polynomial을 포함하는 유한적분으로 주어진다. 위의 해석해를 사용하여 봉우리 영역에서 음파의 분포를 계산하였다.

• 대한전자공학회논문지TC
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• 제37권11호
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• pp.23-31
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• 2000

평면형 구조에서 공간영역 그린함수를 구하기 위해서는 무한 Sommerfeld 적분을 계산하여야 한다. 무한 적분을 짧은 시간에 계산하기 위한 복소 영상법(complex image method)과 2단계 근사화법(two-level method)은 전원점과 관측점 사이의 거리가 가까운 경우에는 정확하지만, 거리가 멀어지면 오차가 커지게 된 다. 본 논문에서는 실수축 상의 적분경로에서 파수영역 그린함수를 근사화 함으로써 코플래너 도파로 구조에서 기존의 결과에 비해 정확한 closed-form 그린함수를 구하는 방법을 제시하였다.

• 설비공학논문집
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• 제9권1호
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• pp.43-54
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• 1997

This paper presents an approximate analytical solution to a two-region one-dimensional model for the charging process of stratified thermal storage tanks with variable inlet temperature in the presence of momentum-induced mixing. Based on the superposition principle, an arbitrary-varying inlet temperature is decomposed into inherent discontinuous steps and continuous intervals approximated as a finite number of piecewise linear functions. This approximation allows the temperature of the upper perfectly-mixed layer to be expressed in terms of constant, linear and exponential functions with respect to time. Applying the Laplace transform technique to the model equation for the lower thermocline layer subject to each of three representative interfacial conditions yields compact-form solutions, a linear combination of which constitutes the final temperature profile. A systematic method for deriving solutions to the plug-flow problem having polynomial-type boundary conditions is also established. The effect of adiabatic exit boundary on solution behaviors proves to be negligible under the actual working conditions, which justifies the assumption of semi-infinite domain introduced in the solution procedure. Finally, the approximate solution is validated by comparing it with an exact solution obtained for a specific variation of inlet temperature. Excellent agreements between them suffice to show the necessity and utility of this work.

• 대한전기학회논문지:전력기술부문A
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• 제54권6호
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• pp.306-314
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• 2005

In this paper, a new approach that is based on EEAC & only with network solutions for CS&S in the transient stability assessment is developed. The proposed CS&S algorithm in conjunction with EEAC to include the capability of performing on-line TSA without TDS is used to calculate the critical clearing time for stability index. In this algorithm, all generators are represented by classical models and all loads are represented by constant impedance load models. The accelerating & synchronizing power coefficient as an index is determined at its disturbance through solving network equation directly. As mentioned above, a new index for generator is generally used to determine the critical generators group. The generator rotor angle is fixed for non-critical generators group, but has equal angle increments for critical generators group. Finally, the critical clearing time is calculated from the power-angle relationship of equivalent OMIB system. The proposed CS&S algorithm currently being implemented is applied to the KEPCO system. The CS&S result was remarkably similar to TSAT program and SIME. Therefore, it was found to be suitable for a fast & highly efficient CS&S algorithm in TSA. The time of CS&S for the 139 contingencies using proposed CS&S algorithm takes less than 3 seconds on Pentium 4, 3GHz Desktop.

• 대한전기학회논문지:전력기술부문A
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• 제50권5호
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• pp.225-233
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• 2001

SIME(SIngle Machine Equivalent) method has been recognized as a useful tool to determine transient stability of power systems. In this paper, SIME method is used to develop the KEPCO transient stability assessment (TSA) tool. A new screening algorithm that can be implemented in SIME method is proposed. The salient feature of the proposed screening algorithm is as follows. First, critical generators are identified by a new index in the early stage of the time domain simulation. Thus, computational time required to find OMIB(One Machine Infinite Bus) can be reduced significantly. Second, clustering critical machines can be performed even in very stable cases. It enables to be avoid extra calculation of time trajectory that is needed in SIME for classifying the stable cases. Finally, using power-angle trajectory and subdividing contingency classification have improved the screening capability. This algorithm is applied to the fast TSA of the KEPCO system.

• Journal of KIEE
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• 제11권1호
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• pp.55-61
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• 2001

SIME(Single Machine Equivalent) method has been recognized as a useful tool to determine transient stability of power system. In this paper, SIME method is used to develop the KEPCO transient stability assessment (TSA) tool. A new screening algorithm that can be generators are identified by a new index in the early stage of the time domain simulation. Thus, computational time require to find OMIB(One Machine Infinite Bus) can be reduced significantly. Second, clustering critical machines can be performed even in very stable cases. It enables to be avoid extra calculation of time trajectory that is needed in SIME for classifying the stable cases. This algorithm is applied to the fast TSA of the KEPCO system in the year of 2010.