• 한국수소및신에너지학회논문집
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• 제22권3호
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• pp.305-312
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• 2011

The use of a separator to control stack temperature in a molten carbonate fuel cell was studied by numerical simulation using a computational fluid dynamics code. The stack model assumed steady-state and constant-load operation of a co-flow stack with an external reformer at atmospheric pressure. Representing a conventional cell type, separators with two flow paths, one each for the anode and cathode gas, were simulated under conditions in which the cathode gas was composed of either air and carbon dioxide (case I) or oxygen and carbon dioxide (case II). The results showed that the average cell potential in case II was higher than that in case I due to the higher partial pressures of oxygen and carbon dioxide in the cathode gas. This result indicates that the amount of heat released during the electrochemical reactions was less for case II than for case I under the same load. However, simulated results showed that the maximum stack temperature in case I was lower than that in case II due to a reduction in the total flow rate of the cathode gas. To control the stack temperature and retain a high cell potential, we proposed the use of a separator with three flow paths (case III); two flow paths for the electrodes and a path in the center of the separator for the flow of nitrogen for cooling. The simulated results for case III showed that the average cell potential was similar to that in case II, indicating that the amount of heat released in the stack was similar to that in case II, and that the maximum stack temperature was the lowest of the three cases due to the nitrogen gas flow in the center of the separator. In summary, the simulated results showed that the use of a separator with three flow paths enabled temperature control in a co-flow stack with an external reformer at atmospheric pressure.

• 한국과학교육학회지
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• 제22권4호
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• pp.837-850
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• 2002

학생들의 인지발달을 촉진시켜 학습효과를 높이려고 개발된 CASE 프로그램의 효과를 조사했다. 중학교 1학년(841명) 학생들이 연구에 참가하였으며, 같은 분량의 시간동안 실험반에서는 교육과정에 따른 과학 교과 수업과 '생각하는 과학' 활동을 병행하였고, 통제반에서는 과학교과 수업만을 수행하였다. 연구 초기에 논리적 사고력 검사(SRT II)를 이용하여 집단의 동질성을 비교하고, 2년 동안 실험반에 CASE 프로그램을 처치한 후 이질동형검사도구인 SRT VII을 이용하여 처치별, 성별, 인지수준별 인지가속에 대한 효과를 조사했다. CASE 프로그램에 의한 중학생들의 인지발달 가속 효과는 중간검사에서는 보이지 않았으나, 사후검사에서 상당히 큰 것으로 확인되었다. 성별에 따라 CASE 프로그램의 효과를 비교한 결과 남 여 중학생들 모두에게 유의미한 인지가속이 이루어진 것으로 나타났다. 남학생들 보다 여학생들의 인지수준이 더 발달된 것으로 밝혀졌으나, 처치와 성별간 상호작용 효과는 나타나지 않았다. 학생들의 사전 인지수준에 따라 CASE 프로그램의 효과를 분석한 결과, 모든 인지수준에서 처치효과가 뚜렷하게 있었으나 특별한 경향성은 나타나지 않아다. 특히 초기 구체적 조작기(ES=1.10)와 전조작기 (ES=1.07), 그리고 구체적조작 후기(ES=1.01) 학생들에게 상당히 큰 효과가 있었다. 이상과 같은 CASE 프로그램의 성공적인 결과는 현행 우리나라 과학교육과정 개정과 교육방법 개선에 시사하는 바가 많다.

• 한국컴퓨터산업학회논문지
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• 제10권1호
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• pp.21-28
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• 2009

역할-기반 접근 제어 정책의 경우 조직의 보안 정책을 보다 효율적이고 일관성 있게 관리할 수 있지만 각 역할의 계층에 의하여 권한의 상속이 결정된다. 이 경우, 하위 개념의 역할은 상위 개념의 역할이 가지는 권한을 수행 하여야 하는 경우에 적절히 대처할 수 없고 하위 개념의 역할에 필요한 새로운 권한을 추가해야만 하고 추가되는 권한은 관리자의 권한 제거 작업 이전까지 하위 역할에 귀속되는 문제가 발생한다. 따라서 본 논문에서는 이러한 문제를 해결하기 위하여 역할이 가지는 권한의 일시적인 위임을 통하여 이를 해결하고자 한다. 이를 위하여 권한의 위임을 수행하기 위한 정책과 새로운 역할-권한 관계의 정의, 권한 위임을 위한 새로운 프로토콜을 제시하였다.

• International Journal of Control, Automation, and Systems
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• 제4권2호
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• pp.146-154
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• 2006

In this paper, we propose direct and indirect adaptive fuzzy sliding mode control approaches for a class of nonaffine nonlinear systems. In the direct case, we use the implicit function theory to prove the existence of an ideal implicit feedback linearization controller, and hence approximate it to attain the desired performances. In the indirect case, we exploit the linear structure of a Takagi-Sugeno fuzzy system with constant conclusion to establish an affine-in-control model, and therefore design an indirect adaptive fuzzy controller. In both cases, the adaptation laws of the adjustable parameters are deduced from the stability analysis, in the sense of Lyapunov, to get a more accurate approximation level. In addition to their robustness, the design of the proposed approaches does not require the upper bounds of both external disturbances and approximation errors. To show the efficiency of the proposed controllers, a simulation example is presented.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1989년도 한국자동제어학술회의논문집; Seoul, Korea; 27-28 Oct. 1989
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• pp.1069-1074
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• 1989

A discrete-time learning control for robotic manipulators is studied using its pulse transfer function. Firstly, discrete-time learning stability condition which is applicable to single-input two-outputs systems is derived. Secondly, stability of learning algorithm with position signal is studied. In this case, when sampling period is small, the algorithm is not stable because of an unstable zero of the system. Thirdly, stability of algorithm with position and velocity signals is studied. In this case, we can stabilize the learning control system which is unstable in learning with only position signal. Finally, simulation results on the trajectory control of robotic manipulators using the discrete-time learning control are shown. This simulation results agree well with the analytical ones.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.346-346
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• 2000

We proposed a method of second-order iterative learning control with feedback, which shows an enhancement of convergence speed and robustness to the disturbances in our previous study. In this paper, we show that the proposed second-order iterative learning control algorithm with feedback is more effective and has better convergence performance than the algorithm without feedback in the case of the existence of initial condition errors. And the convergence woof of the proposed algorithm in the case of the existence of initial condition error is given in detail, and the effectiveness of the Proposed algorithm is shown by simulation results.

• International Journal of Aeronautical and Space Sciences
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• 제4권1호
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• pp.99-109
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• 2003

Attitude control law synthesis for the three-axis attitude maneuver of a flexible spacecraft model is presented in this study. The basic idea is motivated by previous works for the extension into a more general case. The new case includes gravitational gradient torque which has significant effect on a wide range of low earth orbit missions. As the first step, the fully nonlinear dynamic equations of motion are derived including gravitational gradient. The control law design based upon the Lyapunov approach is attempted. The Lyapunov function consists of a weighted combination of system kinetic and potential energy. Then, a set of stabilizing control law is derived from the basic Lyapunov stability theory. The new control law is therefore in a general form partially validating the previous work in some sense.

• 동아시아식생활학회지
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• 제10권5호
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• pp.403-410
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• 2000

In order to investigate the possibility of lwo fat meat products, beef patties were prepared with gums such as carrageenan, methyl cellulose, and xanthangum. The quality characteristics of beef patties were examined. Moisture contents of raw and cooked patties of control were lower than those of patties containing gums, and fat content was higher than those of containing gums. There was no significant difference in the protein contents of patties. In case of L-value(lightness) of raw patty, the control was higher than those patties containing gums. a-(redness) and b-value(yellowness) among patties were not significantly different. Cooking yield, fat retention, and water holding capacity of beef patties containing gums were higher than control beef patty, but salt soluble protein and gel strength were not significantly different. Significant difference did not exist among beef patties in hardness, but the chewiness and gumminess of patties containing gums were higher than control. In case of sensory evaluation, there was no significant difference among patties in aroma and palatability. Texture of control was higher than patties containing gums, and juiciness of control was higher than patties containing carrageenan.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.364-367
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• 2008

Many different types of network equipments are deployed in a large-scale IP network. In this operating environment, network service providers suffer from difficulty in controlling various equipments simultaneously in case network faults happen in their overall or regional network due to physical link failure or abnormal traffic. This paper presents a policy-based methodology to control many different types of network equipments at the same time in abnormal cases. The key idea is that NMS(Network Management System) keeps vendor-neutral control policies in normal times and that when an abnormal case occurs in network, NMS transforms the selected policy into vendor-specific control commands and enforces them to various equipments simultaneously.

• 동력기계공학회지
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• 제8권3호
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• pp.58-66
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• 2004

The sway motion control problem of a container hanging on the trolly is considered in the paper. In the container crane control problem, suppressing the residual swing motion of the container at the end of acceleration, deceleration or the case of that the unexpected disturbance input exists is main issue. For this problem, in general, many trolley motion control strategies are introduced and applied. In this paper, we introduce and synthesize a swing motion control system in which a small auxiliary mass is installed on the spreader made by ourselves. In this control system, the actuator reacting against the auxiliary mass applies inertial control forces to the container to reduce the swing motion in the desired manner. Especially, we apply the $H_{\infty}$ based gain-scheduling control technique the anti-sway control system design problem of the controlled plant. In this control system, the controller dynamics are adjusted in real-time according to time-varying plant parameters. And the simulation result shows that the proposed control strategy is shown to be useful to the case of time-varying system and, robust to disturbances like winds and initial sway motion.