• 한국정보통신학회논문지
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• 제3권1호
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• pp.209-221
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• 1999

실시간 스케줄가능성 분석을 위한 여러 가지 방법들이 제안되었지만, 이들은 프로세스의 모든 상태공간을 추적하거나 고정 우선 순위 스케줄링 방법을 사용하기 때문에 시간 및 공간에 대한 복잡성의 증가를 야기한다. 따라서 상태공간의 수를 줄임으로써 보다 빠른 시간에 스케줄가능성을 판단하는 방법이 필요하다. 본 논문에서는 프로세스 대수의 전이규칙을 이용하여 번역시간에 결정될 수 있는 프로세스의 최소 수행시간, 주기, 마감시간, 동기화 시간을 고려하여 실시간 프로세스가 마감시간을 지키는가를 판단하는 개선된 알고리즘을 제안 및 구현한다. 구현 결과를 통하여 모든 상태 공간을 검색하지 않고도 스케줄가능성을 판단하는 효과적인 성능을 보였다.

• Nuclear Engineering and Technology
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• 제43권6호
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• pp.531-546
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• 2011

The backward differentiation formula (BDF) method is applied to a three-dimensional reactor kinetics calculation for efficient yet accurate transient analysis with adaptive time step control. The coarse mesh finite difference (CMFD) formulation is used for an efficient implementation of the BDF method that does not require excessive memory to store old information from previous time steps. An iterative scheme to update the nodal coupling coefficients through higher order local nodal solutions is established in order to make it possible to store only node average fluxes of the previous five time points. An adaptive time step control method is derived using two order solutions, the fifth and the fourth order BDF solutions, which provide an estimate of the solution error at the current time point. The performance of the BDF- and CMFD-based spatial kinetics calculation and the adaptive time step control scheme is examined with the NEACRP control rod ejection and rod withdrawal benchmark problems. The accuracy is first assessed by comparing the BDF-based results with those of the Crank-Nicholson method with an exponential transform. The effectiveness of the adaptive time step control is then assessed in terms of the possible computing time reduction in producing sufficiently accurate solutions that meet the desired solution fidelity.

• Nuclear Engineering and Technology
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• 제50권7호
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• pp.1043-1050
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• 2018

For an efficient Monte Carlo (MC) burnup analysis, an accurate high-order depletion scheme to consider the nonlinear flux variation in a coarse burnup-step interval is crucial accompanied with an accurate depletion equation solver. In a Seoul National University MC code, McCARD, the high-order depletion schemes of the quadratic depletion method (QDM) and the linear extrapolation/quadratic interpolation (LEQI) method and a depletion equation solver by the Chebyshev rational approximation method (CRAM) have been newly implemented in addition to the existing constant extrapolation/backward extrapolation (CEBE) method using the matrix exponential method (MEM) solver with substeps. In this paper, the quadratic extrapolation/quadratic interpolation (QEQI) method is proposed as a new high-order depletion scheme. In order to examine the effectiveness of the newly-implemented depletion modules in McCARD, four problems in the VERA depletion benchmarks are solved by CEBE/MEM, CEBE/CRAM, LEQI/MEM, QEQI/MEM, and QDM for gadolinium isotopes. From the comparisons, it is shown that the QEQI/MEM predicts ${k_{inf}}^{\prime}s$ most accurately among the test cases. In addition, statistical uncertainty propagation analyses for a VERA pin cell problem are conducted by the sensitivity and uncertainty and the stochastic sampling methods.

• 한국산학기술학회논문지
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• 제20권2호
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• pp.404-411
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• 2019

곡교천 유역의 홍수-유출 특성을 파악하는 연구를 수행하기 위하여 HEC-HMS 모형을 적용하였다. 이 유역은 일부 소유역에서 대규모 농업용 저수지가 있어 소유역으로부터 발생한 초기 유출이 저수지에 의해서 상당량 저류되는 특징을 갖고 있다. 이러한 현상을 반영하기 위하여 3가지 침투모의 방법을 사용하였으며, 방법 1은 기존의 유출곡선지수법, 방법 2는 방법 1에 표면법 기능을 추가한 방법, 방법 3은 초기 및 일정손실율 방법이다. 모형은 3가지 방법으로 손실계산, Clark의 단위도법으로 강우의 직접유출 변환, 지수함수적 감소법으로 기저유량, Muskingum 법으로 하도추적 하는 과정을 포함한다. 모형에서 최적화 기법을 시행착오법과 병행하여 최적화 변수를 도출하였다. NSE, RAR, and PBIAS 등의 평가지표를 사용하여 모형의 보정을 수행하였다. 유출체적, 첨두유량, 첨두발생시각 등에 대하여 모의치와 실측치를 비교한 결과 초기손실을 반영할 수 있도록 설계된 방법2와 3에서 우수한 결과를 나타낸 반면, 그렇지 못한 방법 1은 모의치와 실측치의 차이가 큰 것으로 나타났다. 복합 강우인 경우에 방법 3은 방법 2에 비하여 좋은 결과를 나타내지 못하였다. 결론적으로 방법 2가 단일 강우나 복합강우 모두 좋은 결과를 주는 것으로 나타났다. 본 연구의 결과는 정책입안자가 홍수관리대책을 수립하는 데 유용한 도구로서 사용되어 질 수 있을 것으로 판단된다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 Proceedings of the Korea Automatic Control Conference, 11th (KACC); Pohang, Korea; 24-26 Oct. 1996
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• pp.16-19
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• 1996

In this paper, a sliding mode control scheme that guarantees the smoothness of the control signal and the exponential error convergence is proposed for robot manipulators. The proposed method inserts a low pass filter (LPF) in front of the plant, and the virtual controller is designed for the virtual plant - the combination of the LPF and the robot manipulator. The virtual control signal contains high frequency components because of a switching function. The real control signal, however, always shows a smooth curve since it is an output of the LPF. In addition to the smoothness of the control signal is always assured, the overall system is in the sliding mode at all times, that is, its performance is always invariant under the existence of parameter uncertainties and external disturbances. The closed-loop system is shown to be globally exponentially stable.

• International Journal of Control, Automation, and Systems
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• 제1권1호
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• pp.19-27
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• 2003

It is well known that one can easily design a high-gain adaptive output feedback control for a class of nonlinear systems which satisfy a certain condition called output feedback exponential passivity (OFEP). The designed high-gain adaptive controller has simple structure and high robustness with regard to bounded disturbances and unknown order of the controlled system. However, from the viewpoint of practical application, it is important to consider a robust control scheme for controlled systems for which some of the assumptions of output feedback stabilization are not valid. In this paper, we design a robust high-gain adaptive output feedback control for the OFEP nonlinear systems with uncertain nonlinearities and/or disturbances. The effectiveness of the proposed method is shown by numerical simulations.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.1413-1415
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• 2004

This paper proposes a SVM(Support Vector Machine) training algorithm to control a service robot with voice command. The service robot with a stereo vision system and dual manipulators of four degrees of freedom implements a User-Dependent Voice Control System. The training of SVM algorithm that is one of the statistical learning theories leads to a QP(quadratic programming) problem. In this paper, we present an efficient SVM speech recognition scheme especially based on less learning data comparing with conventional approaches. SVM discriminator decides rejection or acceptance of user's extracted voice features by the MFCC(Mel Frequency Cepstrum Coefficient). Among several SVM kernels, the exponential RBF function gives the best classification and the accurate user recognition. The numerical simulation and the experiment verified the usefulness of the proposed algorithm.

• Journal of the Korean Data and Information Science Society
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• 제4권
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• pp.65-74
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• 1993

Suppose that we have two populations(or systems), say ${\Pi}_{1}\;and\;{\Pi}_{2}$, to be tested. A random sample of size n from each population is taken and the test for each system will be terminated when the first r failures among n random samples are observed. This kind of test is caned the type-II censored (or item-censored) testing without replacement. Under this scheme we consider the problem of estimating the unknown parameters of interests and the reliability for a given time t for each population.

• 산업공학
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• 제17권spc호
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• pp.152-159
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• 2004

The Purpose of this paper is to propose performance evaluation schemes of flexible manufacturing cell using a generalized stochastic Petri net. In the competitive and global manufacturing environment, to evaluate the feasibility and manufacturability of a product in the product design stage is highly required. Through this process, all the possible problems which may occur in the manufacturing stage can be fixed in early stage. The scheme of generalized stochastic Petri net utilizing both immediate and exponential distributed transitions are applied to model a manufacturing cell with flexible machines, material handler, transporter and buffers. Performance analyses are performed based on behavioral, structural and quantitative properties. A flexible manufacturing cell is evaluated using a Petri net simulator.

• Journal of electromagnetic engineering and science
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• 제7권4호
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• pp.195-200
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• 2007

Doubly-selective channel estimator for orthogonal frequency division multiplexing(OFDM) systems is proposed in this paper. Based on the generalized complex exponential basis expansion model(GCE-BEM), we describe the time-variant channel with time-invariant coefficients over multiple OFDM blocks. The time variation of the channel destroys the orthogonality between subcarriers, and the resulting channel matrix in the frequency domain is no longer diagonal, but the main interference comes from the near subcarriers. Based on this, we propose a channel estimator with low pilot ratio. We first develop a least-square(LS) estimator under the assumption that only the maximum Doppler frequency and the channel order are known at the receiver, and then verify that the correlation matrix of inter-channel interference(ICI) is a scaled identity matrix based on which we derive an optimal pilot insertion scheme for the LS estimator in the sense of minimum mean square error. The proposed estimator has the advantages of low pilot ratio and robustness against inter-carrier interference.