• 한국압력기기공학회 논문집
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• 제10권1호
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• pp.1-6
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• 2014

PID(Proportional, Integral, Derivative) controller is one of the most used process controllers in nuclear power plants. The optimized parameter setting of process controller contributes to the stable operation and efficiency in the operating nuclear power plants. PID parameter setting is tuned when new process control system is established or process control system is changed. It is a burdensome work for I&C(Instrument and Control) engineers to tune the PID controller because it requires a lot of experience and knowledge. When the plant is in operation, inadequate PID parameter setting can be the cause of the unstable process of the plant. Therefore the results of PID parameter setting should be compared, simulated, verified and finally optimized. The practical PID tuning methods used in process controller are tuning operation calculation(Ziegler-Nicholes, Minimum TIAE, Lambda, IMC), exclusive tuning program based on computer and Matlab application. This paper introduces the various tuning methods and suggests an optimized PID tuning process in the operating nuclear power plants.

• Steel and Composite Structures
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• 제15권4호
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• pp.357-377
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• 2013

In order to study the degradation and damage behaviors of steel frame welded connections, two series of tests in references with different connection constructions were carried out subjected to various cyclic loading patterns. Hysteretic curves, degradation and damage behaviours and fatigue properties of specimens were firstly studied. Typical failure modes and probable damage reasons were discussed. Then, various damage index models with variables of dissipative energy, cumulative displacement and combined energy and displacement were summarized and applied for all experimental specimens. The damage developing curves of ten damage index models for each connection were obtained. Finally, the predicted and evaluated capacities of damage index models were compared in order to describe the degraded performance and failure modes. The characteristics of each damage index model were discussed in depth, and then their distributive laws were summarized. The tests and analysis results showed that the loading histories significantly affected the distributive shapes of damage index models. Different models had their own ranges of application. The selected parameters of damage index models had great effect on the developing trends of damage curves. The model with only displacement variable was recommended because of a more simple form and no integral calculation, which was easier to be formulated and embedded in application programs.

• Ocean Systems Engineering
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• 제1권4호
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• pp.355-372
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• 2011

Based on the fully nonlinear velocity potential theory, the liquid sloshing in a three dimensional tank under random excitation is studied. The governing Laplace equation with fully nonlinear boundary conditions on the moving free surface is solved using the indirect desingularized boundary integral equation method (DBIEM). The fourth-order predictor-corrector Adams-Bashforth-Moulton scheme (ABM4) and mixed Eulerian-Lagrangian (MEL) method are used for the time-stepping integration of the free surface boundary conditions. A smoothing scheme, B-spline curve, is applied to both the longitudinal and transverse directions of the tank to eliminate the possible saw-tooth instabilities. When the tank is undergoing one dimensional regular motion of small amplitude, the calculated results are found to be in very good agreement with linear analytical solution. In the simulation, the normal standing waves, travelling waves and bores are observed. The extensive calculation has been made for the tank undergoing specified random oscillation. The nonlinear effect of random sloshing wave is studied and the effect of peak frequency used for the generation of random oscillation is investigated. It is found that, even as the peak value of spectrum for oscillation becomes smaller, the maximum wave elevation on the side wall becomes bigger when the peak frequency is closer to the natural frequency.

• 한국멀티미디어학회논문지
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• 제13권9호
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• pp.1314-1321
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• 2010

본 논문에서는 도로에서 주행 중인 차량검출 알고리즘에 대하여 연구한다. 카메라에서 입력된 영상으로부터 차량을 검출하기위해 먼저 분할 및 합병(split & merge)방법을 적용하여 영상을 분할하고 그 다음 분할된 영역을 해석하여 차량이 위치할 가능성이 높은 영역을 집중적으로 탐색하여 차량을 실시간으로 검출하는 알고리즘을 연구한다. 전방차량의 후면을 검출하기 위하여 수직/수평 성분을 특정으로 하였으며 적분영상을 이용하여 계산시간을 줄일 수 있는 Haar-like방법을 적용하였으며 분류기로는 SVM을 사용하였다. 제안된 방법의 성능을 평가하기 위해 350개의 영상을 사용하여 분류기를 학습하였으며 또한 학습에 사용하지 않은 비학습영상 150개를 사용하여 인식률을 구하였다. 실험결과 비학습영상에 대해 95.00%의 인식률을 얻었다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1994년도 Proceedings of the Korea Automatic Control Conference, 9th (KACC) ; Taejeon, Korea; 17-20 Oct. 1994
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• pp.405-410
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• 1994

The purpose of this paper is to present the details of design procedure of a nonlinear regulator by Riemannian geometric approach and to applied it to the case of a double-effect evaporator. A nonlinear geometric model is proposed on a direct sum space of a state vector and a control vector as well as in the previous parers by the authors. The geometric model is derived by replacing the orthogonal straight coordinate axes of a linear system on the direct sum space with the curvilinear coordinate axes. The integral manifold of the geometric model becomes homeomorphic to that of fictitious linear system. For the geometric model a nonlinear regulator with a performance index is designed renewedly by the procedure of optimization. The construction method of the curvilinear coordinate axes on which the nonlinear system behaves as a linear system is discussed. To apply the above regulator theory to double-effect evaporators especially to the pilot plant at the University of Alberta, a suitable nonlinear model is determined by the plant dynamics. The optimal control law is derived through the calculation of the homeomorphism. As a result it is confirmed that the regulator is effective and superior to that of the conventional control.

• 한국통신학회논문지
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• 제18권11호
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• pp.1669-1676
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• 1993

본 논문에서는 도체 상자에 부착된 선형 모노폴(thin-straight monopole) 안테나를 wire-grid방법을 적용하여 안테나 및 도체상자를 모델링하였고, 효율적인 계산을 위해 Pocklington 적분 방정식과 모멘트 방법(Moment Method)을 사용하여, 안테나의 특성 변화를 계산하였다. 안테나 및 모델링된 도체상자에 이용된 기저함수는 PWS(Piecewise Sinusoidal)함수이고, 도체상자의 모서리에 흐르는 전류를 효과적으로 표현하기 위해, 접합기저함수(Junction Basis Function)를 사용하였다. 특히, 모서리의 꼭지점에서 전류의 연속 조건을 만족하기 위해, 접합기저 함수가 중복되도록 하였다. 안테나 및 도체상자에 흐르는 전류분포를 계산하여, 입력 임피던스 및 복사패턴을 구하였고, 기존의 결과 데이터와 비교하였다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
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• pp.337-344
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• 2000

A modified k-$\epsilon$ model is proposed for calculation of transitional boundary layer flows. In order to develop the eddy viscosity model for the problem, the flow is divided into three regions; namely, pre-transition region, transition region and fully turbulent region. The pre-transition eddy-viscosity is formulated by extending the mixing Length concept. In the transition region, the eddy-viscosity model employs two length scales, i.e., pre-transition length scale and turbulent length scale pertaining to the regions upstream and the downstream, respectively, and a university model of stream-wise intermittency variation is used as a function bridging the pre-transition region and the fully turbulent region. The proposed model is applied to calculate three benchmark cases of the transitional boundary layer flows with different free-stream turbulent intensity ( $1\%{\~}6\%$ ) under zero-pressure gradient. It was found that the profiles of mom velocity and turbulent intensity, local maximum of velocity fluctuations, their locations as well as the stream-wise variation of integral properties such as skin friction, shape factor and maximum velocity fluctuations are very satisfactorily Predicted throughout the flow regions.

• 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.

• 대한기계학회논문집A
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• 제24권3호
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• pp.645-652
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• 2000

A method for shape design sensitivity analysis is proposed utilizing commercial software ANSYS for thermal conduction problems. While the sensitivity formula is derived analytically by introduing adjoint variable concept, sensitivity calculation in practice as well as the primal and adjoint solution of thermal conduction is performed using the ANSYS very easily. Since the formula always takes boundary integral form, sensitivity evaluation in ANSYS requires a little more addition of post-processing routine which involves evaluation of boundary variable from the obtained solution. Though the BEM has been used as a better tool for this purpose, the present study shows it can also be calculated using any kind of analysis code such as ANSYS since the formula is based on analytic nature. Therefore the present study provides a new and efficient way of optimization which was not possible before using commercial software. The usefulness of the method is illustrated via a weight minimization problem of thermal diffuser.

• 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.