• 전자공학회논문지SC
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• 제48권4호
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• pp.17-24
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• 2011

본 논문에서는 알 수 없는 주파수를 가지는 주기적인 외란이 존재하는 광디스크 드라이브에 대하여 주파수 적응 알고리즘과 출력 제어기를 추가하여 외란을 제거하는 제어기법을 제안한다. 여기서 IMP(internal model principal)에 기반을 두는 주파수 적응 알고리즘은 주기적인 외란의 주파수를 알아내는 역할을 한다. 전체 시스템의 안정도 및 외란제거 성능은 특이섭동이론(singular perturbation theory)으로 증명된다. 본 논문의 기여는 주파수 범위에 따른 설계의 제약이 없다는 점과 모델 불확실성이 존재할 때도 외란을 제거할 수 있다는 점을 들 수 있다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1998년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Spring 1998
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• pp.93-99
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• 1998

Mathematical model can be obtained by physical law or engineering theory. However it is always incomplete expression of the real system. In active controls to suppress vibration due to earthquake or wind load, modeling errors can often cause the problems of instability and performance degradation. In this paper, robust optimal controller design method using H$\infty$ control theory is developed for the systems which have uncertain natural frequency and design constraints. Numerical results show that the proposed H$\infty$ controller can avoid the performance degradation due to several errors and has better performance than conventional LQR method.

• 동굴
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• 제65호
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• pp.1-10
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• 2004

Joint reflects the structure of the earth. And in many cases joints controls the developments of stream directions. In this studying area three joint sets are represented. One is concentrated to the north and the other is deviated $50^{circ}-60^{circ}$ from north to east and west. It is uncertain that the master joint set is a fault line, but the presence of the structural line is evident from the joint strike frequency. The Spearman's $\Upsilon$ between joint patterns and the stream directions is about 0.73.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.467-471
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• 2014

The natural frequencies of a mechanical system are determined by the system parameters such as masses and stiffness of the system. Since material irregularities and manufacturing tolerances always exist in most of practical engineering situations, the system parameters always have uncertainties. As the uncertainties of the parameters increase, the uncertainties of the system natural frequencies also increases. Then, the reliability of the system deteriorates. So, the uncertainty of the system natural frequencies should be analyzed accurately and considered in the design of the system. In order to analyze the uncertainty of the system natural frequencies employing most of existing uncertainty analysis methods, the probability distributions of the uncertain system parameters should be identified. In most practical situations, however, identification of the probability distributions is almost impossible because of limited time and cost. For that case, the reliability should be estimated based on finite samples of the system parameters. In this paper, sample based reliability estimation method employing extreme value theory was proposed. Using the proposed estimation method, sample based reliability design of the system natural frequencies was conducted.

• 한국산업정보학회논문지
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• 제16권4호
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• pp.99-105
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• 2011

본 논문은 다물체 복합시스템 인자의 변위에 강인한 중앙집중식 연속반복학습제어기(Repetitive Controller, RC)를 설계하는 방법을 소개하고자 한다. 이때 사용되는 불확실 인자들은 확률분포함수에 의해 무작위로 설정되게 된다. 분포함수를 직접 적용하는 대신, 본 제어기는 설정된 확률함수로부터 생성된 모형을 기본으로 설계하였다. 이러한 중앙집중식 복수모형 설계기법으로 엄의의 분포함수로 구성된 수많은 불확실 인자들을 다룰 수 있다. 그러므로, 제어기는 반복영역에서 수렴성을 보장하는 비용함수를 주파수영역에서 최소화함으로써 유도할 수 있다. 다물체 복합시스템에서 중앙집중식 복수모형설계 기법을 단수모형 설계기법과 함께 제안하였다.

• 대한전자공학회논문지SD
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• 제43권12호
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• pp.8-14
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• 2006

본 논문에서는 노이즈에 둔감한 4*4 밴드패스 이산 코사인 (MF-DCT) 초점 값 연산자를 제안하였다. 제안된 연산자는 DCT 결과 중 중간 주파수 성분을 사용하는 8*8 MDCT 연산자를 노이즈에 둔감하도록 4 형태로 개선한 것으로써 연산자를 180도 회전하여도 같은 구조를 같도록 하였다. 이 연산자는 샘플링 주파수의 절반 부분지 주파수를 통과시키는 밴드패스 필터와 같이 동작하여 초점 정보를 가지고 있지 않는 저주파 신호와 노이즈에 의해 많은 영향을 받는 고주파 신호를 억제함으로써 노이즈에 둔감한 특성을 가진다. 또한 밴드패스 필터를 통과한 성분의 에너지를 초점 값으로 사용함으로써 초점 합의 선형성을 보장받게 된다. 실험 결과에서는 MF-DCT 연산자의 가우시안 노이즈 및 임펄시브 노이즈 특성을 살펴보기 위해 기존의 초점 값 연산자들과의 Autofocusing Uncertain Measure (AUM)비교를 통해 우수성을 검증하였다.

• Wind and Structures
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• 제10권4호
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• pp.347-366
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• 2007

Guyed masts subjected to turbulent winds exhibit complex vibrations featuring many vibration modes, each of which contributes to various structural responses in differing degrees. This dynamic behaviour is further complicated by nonlinear guy cable properties. While previous studies have indicated that conventional frequency domain methods can reliably reproduce load effects within the mast, the system linearization required to perform such an analysis makes it difficult to relate these results directly to corresponding guy forces. As a result, the estimation of peak load effects arising jointly from the structural action of the mast and guys, such as leg loads produced as a result of guy reactions and mast bending moments, is uncertain. A numerical study was therefore undertaken to study peak load effects in a 295 m tall guyed mast acted on by simulated turbulent wind. Responses calculated explicitly from nonlinear time domain finite element analyses were compared with approximate methods in the frequency domain for estimating peak values of selected responses, including guy tension, mast axial loads and mast leg loads. It was found that these peak dynamic load effects could be accurately estimated from frequency domain analysis results by employing simple, slightly conservative assumptions regarding the correlation of related effects.

• 제어로봇시스템학회논문지
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• 제5권1호
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• pp.39-46
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• 1999

Disturbances acting on the track-following servo system of an optical disk drive inherently contain significant periodic components that cause tracking errors of a periodic nature. Such disturbances can be effectively rejected by employing a repetitive controller, which must be implemented carefully in consideration of system stability. Plant uncertainty makes it difficult to design a repetitive controller that will improve tracking performance yet preserve system stability. In this paper, we examine the problem of designing a repetitive controller for an optical disk drive track-following servo system with uncertain plant coefficients. We propose a graphical design technique based on the frequency domain analysis of linear interval systems. This design method results in a repetitive controller that will maintain system stability against all admissible plant uncertainties. We show simulation and experimental results to verify the validity of the proposed design method.

• 전기학회논문지
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• 제59권1호
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• pp.168-175
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• 2010

The issue of rejecting periodic disturbances arises in various applications dealing with rotating machinery. A new method using DIDF (Dual-Input Describing Function) is presented for the rejection of periodic disturbances with uncertain frequency. This can be added to an existing feedback control system without altering the closed-loop system stability. The objective is to design a nonlinear compensator to secure specified oscillation amplitude and frequency which are the same as disturbances. We suggest two procedures to determine coefficients for DIDF's synthesis. The structure of the proposed DIDF is so simple that we can easily synthesize. A number of computer simulations were carried out to demonstrate the salient feature of the proposed DIDF compared to the conventional ones(that is, adaptive algorithms).

• 한국해양공학회지
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• 제17권6호
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• pp.58-64
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• 2003

The performance of vibration-based damage detection methods is dependent upon the accuracy of modal parameters measured from structures of interest. Vibration monitoring, performed on a structure under uncertain temperature conditions, results in the uncertainty in model parameters of the structure. In this study, an experiment on the effect of various temperatures on modal characteristics of steel plate-girders is presented. First, the model plate-girder used for the experiment is described. Second, natural frequencies measured from the structure, using two different excitation sources, are described. Third, natural frequencies measured from the structure, under various temperatures, are described. Finally, the relationship between measurement temperature and natural frequency is analyzed.