• 한국철도학회논문집
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• 제16권5호
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• pp.372-378
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• 2013

이 논문에서는 도시철도의 최대수요전력 산출을 위한 근사모델을 제시한다. 전류 벡터 반복법을 활용하여 변전소의 최대수요전력을 계산할 경우에 기존의 방법으로는 수 많은 반복 조류계산이 필요하기 때문에 계산시간 제약으로 인해 실시간 적용이 어렵다는 문제가 있다. 본 논문에서는 모든 조건이 동일한 상태에서 전원 임피던스의 변화에 따른 변전소 최대수요 전력을 빠르게 산출하는 근사모델을 제시한다. 제시된 근사 모델에 의한 산출결과가 기존 모델과 거의 유사한 정확성을 보임을 시뮬레이션을 통해 예시한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.386-391
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• 2001

This paper presents a new two-point approximation method based on the exponential intervening variable. To avoid the lack of definition of the conventional exponential intervening variables due to zero- or negative-valued design variables the shifting level into each exponential intervening variable is introduced. Then a new quadratic approximation, whose Hessian matrix has only diagonal elements of different values, is proposed in terms of these intervening variables. These diagonal elements are computed in a closed form, which correct the typical error in the approximate gradient of the TANA series due to the lack of definition of exponential type intervening variables and their incomplete second-order terms. Also, a correction coefficient is multiplied to the pre-determined quadratic term to match the value of approximate function with that of the original function at the previous point. Finally, the authors developed a sequential approximate optimizer, solved several typical design problems used in the literature and compared these optimization results with those of TANA-3. These comparisons show that the proposed method gives more efficient and reliable results than TANA-3.

• Structural Engineering and Mechanics
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• 제30권1호
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• pp.37-66
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• 2008

This paper focuses on the nonlinear vibrations of stay cables and evaluates the dynamic characteristics of stay cables by using the nonlinear enhanced MECS approach and the approximate approach. The nonlinear enhanced MECS approach is that both the girder-tower vibrations and the cable vibrations including parametric cable vibrations are simultaneously considered in the numerical analysis of cable-stayed bridges. Cable finite element method is used to simulate the responses including the parametric vibrations of stay cables. The approximate approach is based on the assumption that cable vibrations have a small effect on girder-tower vibrations, and analyzes the local cable vibrations after obtaining the girder-tower responses. Under the periodic excitations or the moderate ground motion, the differences of the responses of stay cables between these two approaches are evaluated in detail. The effect of cable vibrations on the girder and towers are also discussed. As a result, the dynamic characteristics of the parametric vibrations in stay cables can be evaluated by using the approximate approach or the nonlinear enhanced MECS approach. Since the different axial force fluctuant of stay cables in both ends of one girder causes the difference response values between two approach, it had better use the nonlinear enhanced MECS approach to perform the dynamic analyses of cable-stayed bridges.

• 전산구조공학
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• 제11권1호
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• pp.171-178
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• 1998

점탄성감쇠기가 장치된 건물은 감쇠력과 강성이 증가하며 부가되는 감쇠력에 의하여 비고전적 감쇠시스템이 된다. 이러한 경우 비감쇠시스템에서 구한 고유값을 이용하여 감쇠행렬을 대각행렬로 변환할 수 없으므로 일반적으로 운동방정식을 2n크기 행렬의 1차 미분방정식 형태로 변환하여 해석하게 된다. 이러한 방법은 일반적인 고전적 감쇠시스템에 비해 복잡하므로 감쇠행렬의 비대각항을 무시하고 해석하는 방법이 이용되기도 한다. 본 논문에서는 이러한 근사적인 방법의 타당성과 이론적 근거를 검증하고 정해와 근사해법을 이용하여 3층 전단건물의 진동특성을 구하여 비교하였다. 결과에 따르면 부가되는 감쇠력이 작을 때는 근사해와 정해가 매우 근접하나 감쇠력이 커질수록 그 오차가 커지는 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제21권2호
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• pp.137-150
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• 2005

Dynamic analysis of dam-reservoir-foundation system is usually carried out by employing a simplified and approximate one-dimensional model to account for fluid-foundation interaction. The approximation introduced on this basis is examined thoroughly in this paper by comparing the method with the rigorous approach. It is concluded that the errors due to approximate method could be very significant both for horizontal and vertical ground motions.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1990년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 26-27 Oct. 1990
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• pp.406-410
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• 1990

This paper presents an approximate analysis of the serial production lines using decomposition technique. A serial production line consists of a series of unreliable machines separated by finite buffers. The serial production line is evaluated by approximation method, the results of which are compared with those examined by the discrete time event simulation, based on this approximation method, a gradient technique is proposed, which improves the efficiency of an operation of production line through the re-allocation of buffers.

• Journal of the Korean Data and Information Science Society
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• 제26권2호
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• pp.517-524
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• 2015

Unlabeled examples are easier and less expensive to be obtained than labeled examples. In this paper semisupervised approach is used to utilize such examples in an effort to enhance the predictive performance of nonlinear quantile regression problems. We propose a semisupervised quantile regression method named semisupervised support vector quantile regression, which is based on support vector machine. A generalized approximate cross validation method is used to choose the hyper-parameters that affect the performance of estimator. The experimental results confirm the successful performance of the proposed S2SVQR.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
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• pp.271-278
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• 2002

Structural optimization using improved higer-order convex approximation is proposed in this paper. The proposed method is a generalization of the convex approximation method. The order of the approximation function for each constraint is automatically adjusted in the optimization process. And also the order of each design variable is differently adjusted. This self-adjusted capability makes the approximate constraint values conservative enough to maintain the optimum design point of the approximate problem in feasible region. The efficiency of proposed algorithm, compared with conventional algorithm is successfully demonstrated in the Three-bar Truss example.

• Journal of the Korean Data and Information Science Society
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• 제25권3호
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• pp.643-653
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• 2014

In this paper, we propose some estimators for the extreme value distribution based on the interval method and mid-point approximation method from the progressive Type-I interval censored sample. Because log-likelihood function is a non-linear function, we use a Taylor series expansion to derive approximate likelihood equations. We compare the proposed estimators in terms of the mean squared error by using the Monte Carlo simulation.

• 대한전기학회논문지
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• 제37권4호
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• pp.232-239
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• 1988

The approximate overdetermined method is proposed for high resolution spectral estimation in case of short data record length or narrow band signal. And a new recursive AR parameter estimation is derived in the form of fast algorithm. For ARMA spectral estimation, two stage procedure is used in estimating ARMA parameters. First AR parameters are estimated by using the modified Yule-Walker equations, and then MA parameters are implicitly estimated by estimating numerator spectral(NS) coefficients.