• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1989년도 한국자동제어학술회의논문집; Seoul, Korea; 27-28 Oct. 1989
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• pp.682-686
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• 1989

A new sufficient condition for the convergency of an iterative adaptive control algorithm is presented, in which a parameter estimator of the system together with an inverse system model to generate the control signal at each iteration. Also the result is extended to discrete time domain and a similar sufficient condition is derived.

• Journal of applied mathematics & informatics
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• 제29권3_4호
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• pp.909-920
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• 2011

A regularized Newton method for nonlinear ill-posed problems is considered. In each Newton step an implicit iterative method with an appropriate stopping rule is proposed and analyzed. Under certain assumptions on the nonlinear operator, the convergence of the algorithm is proved and the algorithm is stable if the discrepancy principle is used to terminate the outer iteration. Numerical experiment shows the effectiveness of the method.

• 에너지공학
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• 제10권3호
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• pp.183-187
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• 2001

Impedance imaging for binary mixture is a kind of nonlinear inverse problem, which is usually solved iteratively by the Newton-Raphson method. Then, the ill-posedness of Hessian matrix often requires the use of a regularization method to stabilize the solution. In this study, the Levenberg-Marquredt regularization method is introduced for the binary-mixture system with various resistivity contrasts (1:2∼1:1000). Several mixture distribution are tested and the results show that the Newton-Raphson iteration combined with the Levenberg-Marquardt regularization can reconstruct reasonably good images.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제7권1호
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• pp.7-14
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• 2003

The main concern of this paper is to develop a new class of quasi-newton methods. These methods are intended for use whenever memory space is a major concern and, hence, they are usually referred to as limited memory methods. The methods developed in this work are sensitive to the choice of the memory parameter ${\eta}$ that defines the amount of past information stored within the Hessian (or its inverse) approximation, at each iteration. The results of the numerical experiments made, compared to different choices of these parameters, indicate that these methods improve the performance of limited memory quasi-Newton methods.

• 전산구조공학
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• 제11권1호
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• pp.205-216
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• 1998

본 논문에서는 중복근을 갖는 비비례 감쇠시스템의 고유치 해석 방법을 제안하였다. 2차 고유치 문제의 행렬 조합을 통한 선형 방정식에 수정된 Newton-Raphson기법과 고유벡터의 직교성을 적용하여 제안방법의 알고리즘을 유도하였다. 벡터 반복법 또는 부분공간 반복법과 같은 기존의 반복법에서는 수렴성을 향상시키기 위해 변위법을 적용하였으며, 이 값이 시스템의 고유치에 근사하게 되면 행렬분해 과정에서 특이성이 발생한다. 그러나 제안방법은 구하고자 하는 고유치가 중복근이 아닐 경우에, 변위값이 시스템의 고유치 일지라도 항상 정칙성을 유지하며, 이것을 해석적으로 증명하였다. 제안방법은 수정된 Newton-Raphson기법을 이용하기 때문에 초기값을 필요로 한다. 제안방법의 초기값으로는 반복법의 중간결과나 근사법의 결과를 사용할 수 있다. 이들 방법중 Lanczon방법이 가장 효율적으로 좋은 초기값을 제공하기 때문에 Lanczon방법의 결과를 제안방법의 초기값으로 사용하였다. 제안방법의 효율성을 증명하기 위하여 두가지 예제 구조물에 대해 해석시간 및 수렴성을 가장 많이 사용하고 있는 부분공간 반복법과 Lanczon방법의 결과와 비교하였다.

• 대한기계학회논문집A
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• 제28권5호
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• pp.632-639
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• 2004

In this paper, an inverse problem of glass forming process is studied to determine a number of unknown heat transfer coefficients which are imposed as boundary conditions. An analysis program for transient heat conduction of axi-symmetric dimension is developed to simulate the forming and cooling process. The analysis is repeated until it attains periodic state, which requires at least 30 cycles of iteration. Measurements are made for the temperatures at several available time and positions of glass and moulds in operation. Heat removal by the cooling water from the plunger is also recorded. An optimization problem is formulated to determine heat transfer coefficients which minimize the difference between the measured data and analysis results. Significant time savings are achieved in finite difference based sensitivity computation during the optimization by employing distributed computing technique. The analysis results by the optimum heat transfer coefficients are found to agree well with the measured data.

• 한국전자파학회논문지
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• 제16권11호
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• pp.1123-1130
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• 2005

본 논문에서는 PAPR 저감 기법인 SPW(Sub-block Phase Weighting) 기법에서 PAPR(Peak-to-Average Power Ratio)이 저감되도록 조절한 부가 정보를 처리하는 방법을 제안한다. SPW기법은 입력 데이터를 여러 개의 서브블록으로 나누고 위상 회전 벡터를 곱해주는 것으로 피크 전력을 줄여준다. SPW 기법은 부반송파 수와 변조방식, 서브 블록의 수가 PTS 기법과 같을 때 서로 유사한 점을 지니고 있지만, 오직 한 개의 IFFT(Inverse Fast Fourier Transform)를 사용한다는 점에서 기존의 PTS(Partial Transmit Sequence)나 SLM(Selected Mapping) 기법과는 다르다. SPW기법은 비록 PAPR을 효율적으로 줄일 수 있지만 계산 복잡도 문제는 여전히 존재한다. 본 논문에서는 위상 조절을 위 한 방법으로서 flipping 알고리즘과 full iteration 알고리즘을 사용하였다. 컴퓨터 시뮬레이션을 통하여 제안 방식의 특성을 분석하고 성능을 검토하였다.

• 한국강구조학회 논문집
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• 제18권5호
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• pp.575-584
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• 2006

본 연구에서는 압축력을 받는 적층복합 I형 박벽보의 좌굴해석을 위한 전단변형을 고려한 유한요소 모델을 제안한다. 직교좌표계에 근거로 변위장은 1차 전단변형을 고려한 보 이론을 사용하여 정의된다. 유도된 요소는 휨 전단변형과 ? 비틂에 의한 영향을 고려한다. 지배방정식을 풀기 위하여 본 유한요소에서는 2절점, 3절점, 4절점의 세 가지 보요소를 제안하였다. 선형 좌굴문제를 풀기 위하여 이동기법을 의한 역방향 반복법을 사용하였다. 적층복합 I형 박벽보의 좌굴거동에 전단 유연성과 파이버 방향성의 중요도를 조사하기 위하여 매개변수 해석을 수행하였다. 본 연구의 전단변형을 고려한 모델은 다른 연구자의 수치해석 결과와 유한요소해에 잘 일치하는 것을 확인하였다.

• Journal of Radiation Protection and Research
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• 제42권4호
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• pp.212-221
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• 2017

Background: This study aims to calculate detector positions as a design of a radioactive source localizing radiation portal monitor (RPM) system using an improved genetic algorithm. Materials and Methods: To calculate of detector positions for a source localizing RPM system optimization problem is defined. To solve the problem, a modified iterative genetic algorithm (MIGA) is developed. In general, a genetic algorithm (GA) finds a globally optimal solution with a high probability, but it is not perfect at all times. To increase the probability to find globally optimal solution rather, a MIGA is designed by supplementing the iteration, competition, and verification with GA. For an optimization problem that is defined to find detector positions that maximizes differences of detector signals, a localization method is derived by modifying the inverse radiation transport model, and realistic parameter information is suggested. Results and Discussion: To compare the MIGA and GA, both algorithms are implemented in a MATLAB environment. The performance of the GA and MIGA and that of the procedures supplemented in the MIGA are analyzed by computer simulations. The results show that the iteration, competition, and verification procedures help to search for globally optimal solutions. Further, the MIGA is more robust against falling into local minima and finds a more reliably optimal result than the GA. Conclusion: The positions of the detectors on an RPM for radioactive source localization are optimized using the MIGA. To increase the contrast of the measurements from each detector, a relationship between the source and the detectors is derived by modifying the inverse transport model. Realistic parameters are utilized for accurate simulations. Furthermore, the MIGA is developed to achieve a reliable solution. By utilizing results of this study, an RPM for radioactive source localization has been designed and will be fabricated soon.

• 대한자원환경지질학회:학술대회논문집
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• 대한자원환경지질학회 2002년도 춘계 공동학술발표회
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• pp.167-169
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• 2002

The extended Born, or localized nonlinear approximation of integral equation (IE) solution has been applied to inverting single-hole electromagnetic (EM) data using a cylindrically symmetric model. The extended Born approximation is less accurate than a full solution but much superior to the simple Born approximation. When applied to the cylindrically symmetric model with a vertical magnetic dipole source, however, the accuracy of the extended Born approximation is greatly improved because the electric field is scalar and continuous everywhere. One of the most important steps in the inversion is the selection of a proper regularization parameter for stability. Occam's inversion (Constable et al., 1987) is an excellent method for obtaining a stable inverse solution. It is extremely slow when combined with a differential equation method because many forward simulations are needed but suitable for the extended Born solution because the Green's functions, the most time consuming part in IE methods, are repeatedly re-usable throughout the inversion. In addition, the If formulation also readily contains a sensitivity matrix, which can be revised at each iteration at little expense. The inversion algorithm developed in this study is quite stable and fast even if the optimum regularization parameter Is sought at each iteration step. Tn this paper we show inversion results using synthetic data obtained from a finite-element method and field data as well.