• Journal of computational fluids engineering
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• v.17 no.1
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• pp.86-93
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• 2012

A numerical investigation is conducted to search for the optimal flow rate for a rotating-disk chemical vapor decomposition reactor operating at a high temperature and a low pressure. The flow of a gas mixture supplied into the reactor is modeled by a laminar flow of an ideal gas obeying the kinetic theory. The axisymmetric two-dimensional flow in the reactor is simulated by employing a CFD package FLUENT. With operating pressure and temperature fixed, numerical computations are performed by varying rotation rate and flow rate. Examination of the structures of flow and thermal fields leads to a flow regime diagram illustrating that there are a stable plug-like flow regime and a few unfavorable flow regimes induced by mass unbalance or buoyancy. The criterion for sustaining a plug-like flow regime is discussed based on a theoretical scaling argument. Interpretation of the flow regime map suggests that a favorable flow is attainable with a minimum flow rate at the smallest rotation rate guaranteeing the dominance of rotation effects over buoyancy.

• Proceedings of the KIEE Conference
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• 1998.07b
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• pp.515-518
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• 1998

This paper proposes a new hybrid algorithm for auto-tuning fuzzy controllers improving the performance. The presented algorithm estimates automatically the optimal values of membership functions, fuzzy rules, and scaling factors for fuzzy controllers, using a genetic-MGM algorithm. The object of the proposed algorithm is to promote search efficiency by a genetic and modified gradient optimization techniques. The proposed genetic and MGM algorithm is based on both the standard genetic algorithm and a gradient method. If a maximum point don't be changed around an optimal value at the end of performance during given generation, the genetic-MGM algorithm searches for an optimal value using the initial value which has maximum point by converting the genetic algorithms into the MGM(Modified Gradient Method) algorithms that reduced the number of variables. Using this algorithm is not only that the computing time is faster than genetic algorithm as reducing the number of variables, but also that can overcome the disadvantage of genetic algorithms. Simulation results verify the validity of the presented method.

• Journal of the Institute of Convergence Signal Processing
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• v.3 no.3
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• pp.36-40
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• 2002

In this paper, we proposed a digital watermarking method based on the edge-wavelet transform to protect digital contents copyrights. We find out the optimal watermark insertion region and the proper amount of watermark in order to satisfy robustness and imperceptibility against various attacks such as noise, compression, collusion, clipping, scaling. Especially through this experiment, we could find out the adequate location of watermark insertion and proper amount of watermark and it is also viewed to satisfy robustness and imperceptibility in the lower frequency region with small watermark quantity.

• 전기의세계
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• v.18 no.6
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• pp.9-22
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• 1969

This thesis has suggested a method of applying the Maximum Principle of Pontryagin to the optimal control of distributive electrical networks. In general, electrical networks consist of branches, nodes, sources and loads. The effective values of steady state currents and voltages are independent of time but only expressed as the functions of position. Moreover, most of the node voltages and branch currents are not predetermined, that is, initially unknown, and their inherent loop characteristics satisfy only Kirchhoff's current and voltage laws. The Maximum Principle, however, needs the initial fixed values of all state variables for its standand way of application. In spite of this inconsistency this thesis has undertaken to suggest a new approach to the successful solution of the above mentioned networks by introducing scaling factors and a state variable change technique which transform the boundary-value unknown problem into the boundary-value partially fixed and partially free problem. For the examples of applying the method suggested, the control problems for minimizing copper quantity in a distribution line have been solved with voltage drop constraint imposed on. In the case of uniform load distribution it has been shown that the optimal wire diameter of the distribution line is reciprocally proportional to the root of distance. For the same load pattern as above the wire diameter giving the minimum copper loss in the distribution line has been shown to be reciprocally proportional to distance.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2000.04a
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• pp.691-694
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• 2000

기존 LAN 환경에서 인터넷을 이용한 멀티미디어 실시간 전송과 같은 QoS 보장형 서비스에 대한 요구가 증대되면서, 고속의 ATM 기술을 LAN에 적용하는 기술들이 등장하였다. LANE(LAN Emulation)은 그러한 기술 대안들 중에서 campus network와 enterprise network에 많이 보급되고 있는 기술이다. 그러나 이러한 급격한 LANE 도입에 비하여 이의 효과적인 운용에 대한 연구는 많지 않은 실정이다. 본 논문에서는 LANE을 도입한 campus network의 최적 운영방안에 대하여 논한다. Broadcast 데이터 트래픽 관리에서 발생하는 규모성(Scalability) 문제로 인하여 전체 LANE망은 여러 개의 ELAN으로 나뉘어 관리된다. 이 때 하나의 ELAN은 마치 단위 LAN로써, Broadcast 데이터의 전송범위를 제한한다. 즉, 서로 다른 ELAN에 속하는 노드간에는 Broadcast 방식으로 데이터를 전송할 수 없게 된다. 그런데, IPX 등을 사용하는 대화형 시뮬레이션 게임 등과 같은 응용프로그램에서는 Broadcast 방식이 이용되므로, 서로 다른 ELAN에 속하는 노드간의 데이터 전송은 불가능하게 되거나 별도의 복잡한 과정을 개입시켜야 하는 비용이 발생한다. 따라서 규모성 문제해결을 위한 ELAN 구성(configuration)에는 위와 같은 비용이 수반된다. 본 연구에서는 LANE망을 여러 개의 ELAN으로 분할하는 경우에 블로킹(blocking) 되는 Broadcast 트래픽 규모를 해당 ELAN 구성의 비용으로 간주한다. 이 경우에 규모성을 고려한 ELAN의 최적 구현방안(optimal configuration)은 ELAN 구성을 위한 기술적 제약하에서 블로킹되는 Broadcast 트래픽을 최소화시키는 문제로 요약된다. 이는 다시 그래프 분할문제(graph partition problem)의 변형된 형태로 모형화 될 수 있다. 본 논문에서는 이러한 사항들을 고려하여 제시된 수리적 모형을 대상으로, genetic algorithm을 이용하여 최적 ELAN 구성을 위한 여러 파라미터들의 효과를 살펴보고, 이러한 결과들이 LANE 운영과 관련하여 가지는 함축적인 의미를 고찰한다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1391-1407
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• 1990

In this paper, optimization procedures are presented considering the static and dynamic constraints for laminated composite plate and hybrid laminated composite plate subject to concentrated load on center of the plates. Design variables for this problem are ply angle or ply thickness. Deflection, natural frequency and specific damping capacity are considered as constraints. Using a recursive linear programming method, the nonlinear optimization problems are solved. By introducing the design scaling factor, the number of iterations is reduced significantly. Composite plates could be designed optimally combined with FEM analysis under various conditions. In the optimization procedure, verification for both analysis and design of the laminated composite plates are compared with the results of the others. Various design results are presented for the laminated composite plates and hybrid laminated composite plates.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.2
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• pp.145-152
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• 1999

This paper presents an optimal design method for fuzzy logic controllers using genetic algorithms. In general, the design of fuzzy logic controllers has difficulties in the acquisition of exper's knowledge and relies to a great extent on empirical and heuristic knowledge which, in many cases, cannot be objectively justified. So, the performance of the controller can be degraded in the case of plant parameter variations or unpredictable incident which the designer may have ignored, and parameters of the fuzzy logic controller obtained by expert's control action may not be global. To solve these problems, the proposed method using genetic algorithms in this paper, can tune the parameters of fuzzy logic controller including scaling factors and determine the appropriate number of fuzzy reles systematically and automatically. We provide the second drder dead time plant and inverted pendulum system to evaluate the feasibility and generality of our proposed method. Comparison shows that the proposed controller can producd higher accuracy and a smaller number of fuzzy rules than manually tuned fuzzy logic controller.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.49 no.11
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• pp.599-609
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• 2000

The new design methodology of a hybrid fuzzy controller by means of the genetic algorithms is presented. First, a hybrid fuzzy controller(HFC) related to the optimal estimation of control parameters is proposed. The control input for the system in the HFC combined PID controller with fuzzy controller is a convex combination of the FLC's output and PID's output by a fuzzy variable, namely, membership function of weighting coefficient. Second, an auto-tuning algorithms utilizing the simplified reasoning method and genetic algorithms is presented to automatically improve the performance of hybrid fuzzy controller. Especially, in order to auto-tune scaling factors and PID parameters of HFC using GA, three kinds of estimation modes such as basic, contraction, and expansion mode are effectively utilized. The proposed HFC is evaluated and discussed to show applicability and superiority with the and of three representative processes.

• Current Optics and Photonics
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• v.2 no.4
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• pp.356-360
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• 2018

We demonstrate continuous-wave operation of an all-fiber thulium-holmium codoped laser operating at a wavelength of 1706.3 nm. To realize laser operation in the short-wavelength region of the emission-band edge of thulium in silica fiber, we employ fiber Bragg gratings having resonant reflection at a wavelength around 1700 nm as a wavelength-selective mirror in an all-fiber cavity scheme. We first examine the performance of the laser by adjusting the central wavelength of the in-band pump source. Although a pump source possessing a longer wavelength is observed to provide reduced laser threshold power and increased slope efficiency, because of the characteristics of spectral response in the gain fiber, we find that the optimal pump wavelength is 1565 nm to obtain maximum laser output power for a given system. We further explore the properties of the laser by varying the fiber gain length from 1 m to 1.4 m, for the purpose of power scaling. It is revealed that the laser shows optimal performance in terms of output power and slope efficiency at a gain length of 1.3 m, where we obtain a maximum output power of 249 mW for an applied pump power of 2.1 W. A maximum slope efficiency is also estimated to be 23% under these conditions.

• Journal of Institute of Control, Robotics and Systems
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• v.1 no.1
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• pp.63-70
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• 1995

퍼지논리제어기는 산업응용에 광범위하게 연구되고 있으며, 계속적으로 사용되고 있다. 그러나 퍼지집합의 조정을 통해 최적규칙을 구축하기 위하여, 시행착오에 의한 매우 능숙한 기술이 요구된다. 이 논문에서는 첫째로, 퍼지논리제어기와 기존의 PID 제어기로 구성된 하이브리드 퍼지제어기를 제안한다. 즉, 시스템의 제어 입력은 퍼지변수로서, 과도상태에서의 FLC출력과 정상상태에서의 PID 출력의 컨벡스(convex) 결합이다. 둘째로, 간략추론법과 개선된 컴플렉스방법을 이용한 강력한 자동동조알고리즘이 퍼지논리제어기의 성능을 자동적으로 개선하기 위하여 사용된다. 이방법은 오차변화율및 제어출력의 제한조건에 의하여, 언어제어규칙, 퍼지계수(scaling factor), PID계수, 하이브리드 퍼지논리제어기의 하중계수의 최적값을 자동적으로 추정한다. 시뮬레이션은 시간지연 플랜트및 하수처리시스템의 활성오니공정과 같은 비선형 플랜트에서 실행되고, 시스템의 성능은 평가지수 ITAE로 평가된다.