• 대한전자공학회논문지
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• 제26권3호
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• pp.160-166
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• 1989

공간영역 예측기의 계수를 계산하기 위한 적응 알고리듬이 제안되었다. 제안된 방법은 LMS 알고리듬을 사용하여 TDL(tapped-delay-line)과 ESC(escalator) 구조를 갖는 공간영역 예측기의 계수를 계산한다. 기종존의 일반적인 예측기와 다른점은 순방향과 역방향 예측 오차의 평균 자승값의 합을 최소화하며 예측기의 계수를 계산함으로 향상된 선형예측 공간 스펙트럼을 얻을 수 있다. 제안된 방법을 선형으로 배열된 센서에 의하여 얻어진 협대역신호의 입사각 추정문제에 적용시켜 기존의 적응예측 알고리듬과 컴퓨터 시뮬레이션을 통하여 성능을 비교하였다.

• Geomechanics and Engineering
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• 제6권6호
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• pp.531-544
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• 2014

Studies of earthquakes over the last 50 years and the examination of dynamic soil behavior reveal that soil behavior is highly nonlinear and hysteretic even at small strains. Nonlinear behavior of soils during a seismic event has a predominant role in current site response analysis approaches. Common approaches to ground response analysis include linear, equivalent linear and nonlinear methods. These methods of ground response analysis may also be categorized into time domain and frequency domain concepts. Simplicity in developing analytical relations and accuracy in considering soils' dynamic properties dependency to loading frequency are benefits of frequency domain analysis. On the other hand, nonlinear methods are complicated and time consuming mainly because of their step by step integrations in time intervals. In part Ι of this paper, governing equations for seismic response analysis of surcharged and layered soils were developed using fundamental of wave propagation theory based on transfer function and boundary conditions. In this part, nonlinear seismic ground response is analyzed using extended HFTD method. The extended HFTD method benefits Newton-Raphson procedure which applies regular iterations and follows soils' fundamental stress-strain curve until convergence is achieved. The nonlinear HFTD approach developed here are applied to some examples presented in this part of the paper. Case studies are carried in which effects of some influencing parameters on the response are investigated. Results show that the current approach is sufficiently accurate, efficient, and fast converging. Discussions on the results obtained are presented throughout this part of the paper.

• 대한조선학회논문집
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• 제31권2호
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• pp.65-77
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• 1994

본 논문은 SWATH선의 히브 및 피치 제어에 대한 LQ이론의 상세한 응용과정을 제시한다. 부가질량과 감쇄계수를 상하동요 고유주기에서의 값으로 근사함으로써 선형 시불변 2차 연립 미분방정식이 주파수 응답 모델로부터 유도된다. 파기진력은 사인파들의 합으로서 모델링 된다. 좋은 과도응답(transient response)과 적절한 제어핀 운동을 얻기 위하여 상태 및 제어 가중행렬의 체계적인 선택과정이 제시된다. 본 논문의 제어기 설계과정의 타당성이 시간영역 및 주파수 영역에서의 시뮬레이션과 전달함수행렬의 특이값 선도에 의해 철저히 조사되어 진다. 최종 설계된 제어시스템은 본 연구의 응용이 성공적이었음을 나타내는 좋은 전체 성능을 보여준다.

• Structural Engineering and Mechanics
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• 제85권5호
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• pp.607-620
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• 2023

The classical optimal control (COC) method has been widely used for linear quadratic regulator (LQR) problems of structural control. However, the equation of motion of the structure is incorporated into the optimization model as the constraint condition for the LQR problem, which needs to be solved through the Riccati equation under certain assumptions. In this study, an explicit optimal control (EOC) method is proposed based on the explicit time-domain method (ETDM). By use of the explicit formulation of structural responses, the LQR problem with the constraint of equation of motion can be transformed into an unconstrained optimization problem, and therefore the control law can be derived directly without solving the Riccati equation. To further optimize the weighting parameters adopted in the control law using the gradient-based optimization algorithm, the sensitivities of structural responses and control forces with respect to the weighting parameters are derived analytically based on the explicit expressions of dynamic responses of the controlled structure. Two numerical examples are investigated to demonstrate the feasibility of the EOC method and the optimization scheme for weighting parameters involved in the control law.

• 대한수학교육학회지:수학교육학연구
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• 제20권1호
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• pp.85-102
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• 2010

선형계획법은 일정한 조건아래 여러 가지 가능성 중에서 최적의 경우를 찾아낼 때에 유용하다. 본 연구에서는 수학적 맥락과 학교수학의 맥락에서 선형계획법을 분석하고, 인식론적 관점에서 선형계획법의 학습 과정을 살펴봄으로써, 가설 학습 경로를 탐색하였다. 수학적 맥락과 학교수학의 맥락의 차이는 주어진 영역이 실현 가능한지 또는 유계인지를 다루는가의 여부, 주어진 영역 속의 점 중에서 제한된 개수의 점만을 대입해도 최적해를 구할 수 있다는 정리의 정당화를 다루는가의 여부에 있었다. 그리고 학생들이 정의역이 제한된 경우에 이원일차함수의 최댓값과 최솟값이 무엇인지를 이해하지 못할 가능성이 있었다. 이 세 가지 측면을 인식론적 관점에서 고려하여 가설 학습 경로를 4단계 즉, 주어진 일차식이 함수식임을 이해하는 단계, 부등식 영역과 일차식을 목적함수와 관련시킴으로써 부등식 영역을 직선으로 분할하는 단계, 직선의 그래프와 k의 범위를 관계시켜 y절편의 개념을 구성하는 단계, 주어진 영역에서 최적해의 존재가능성을 확인하는 단계로 구성하였다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
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• pp.132-139
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• 2000

This paper presents a new hybrid approach for nonlinear dynamic analysis of the soil-structure interaction system in the time domain. It employs, in a practical manner, a linear SSI program and a general-purpose nonlinear finite element program. In order to demonstrate the validity and applicability of the proposed method, seismic response analyses are carried out for a free-field problem and a 2-D subway station. The results indicate that the proposed methodology gives reasonable solution for the linear/nonlinear SSI problem utilizing a general-purpose finite element program. Some further studies will endorse the applicability of the method to various soil-structure interaction problems.

• Ocean Systems Engineering
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• 제2권2호
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• pp.147-158
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• 2012

A time-domain simulation of a land-based Oscillating Water Column (OWC) with various irregular waves as a form of PM spectrum is performed by using a two-dimensional fully nonlinear numerical wave tank (NWT) based on the potential theory, mixed Eulerian-Lagrangian (MEL) approach, and boundary element method. The nonlinear free-surface condition inside the OWC chamber was specially devised to describe both the pneumatic effect of the time-varying pressure and the viscous energy loss due to water column motions. The quadratic models for pneumatic pressure and viscous loss are applied to the air and free surface inside the chamber, and their numerical results are compared with those with equivalent linear ones. Various wave spectra are applied to the OWC system to predict the efficiency of wave-energy take-off for various wave conditions. The cases of regular and irregular waves are also compared.

• 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.

• 한국항공운항학회지
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• 제14권1호
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• pp.22-27
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• 2006

The linear and nonlinear aeroelastic analyses of a flat plate wing with flaperon have been performed by using frequency-domain and time-domain analyses. Natural modes from free vibration analysis and a doublet-hybrid method (DHM) are used for the computation of subsonic unsteady aerodynamic forces. The flaperon hinge is represented by a free-play spring and is linearized by the described function method. The linear and nonlinear flutter analyses indicate that flapping mode of the flaperon, the hinge stiffness and free-play of hinge have significant effects on the aeroelastic characteristics. From the nonlinear flutter analysis, different modes like stable and unstable limit-cycle-oscillation are observed in same flutter velocity depending on initial conditions.

• The Journal of the Acoustical Society of Korea
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• 제22권3E호
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• pp.101-109
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• 2003

A multi-mode harmonic transform coding (MMHTC) for speech and music signals is proposed. Its structure is organized as a linear prediction model with an input of harmonic and transform-based excitation. The proposed coder also utilizes harmonic prediction and an improved quantizer of excitation signal. To efficiently quantize the excitation of music signals, the modulated lapped transform(MLT) is introduced. In other words, the coder combines both the time domain (linear prediction) and the frequency domain technique to achieve the best perceptual quality. The proposed coder showed better speech quality than that of the 8 kbps QCELP coder at a bit-rate of 4 kbps.