• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.3
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• pp.45-50
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• 2004

The design of reaction wheel control logic is critical to achieve the spacecraft attitude stabilization and performance requirements for the successful mission. Due to various uncertainties on orbit there exist limitation to obtain the model parameters through the ground tests and to design the associated control logic. Thus, the model parameter correction using on-orbit data is essential to the control performance on orbit. This paper performs the system identification using KOMPSAT-1 telemetry data and extracts the model parameters of the reaction wheel. Moreover, the reaction wheel is remodeled and compared with the ground test results.

• Tunnel and Underground Space
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• v.32 no.1
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• pp.20-29
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• 2022

The existence of underground cavity should be considered in the assessment of georisk such as ground subsidence. Even if the shear strength of the ground around the cavity is known, it is difficult to accurately analyze the safety around the cavity due to the uncertainties related to geometric conditions such as the cavity size. In this paper, stability chart representing dimensionless stability constants was proposed based on the ground strength and geometric conditions. Numerical analysis had been carried out accounting for the stability constants such as the ground strength, the adhesion and friction angles, and the size and depth of the underground cavity. The proposed charts can help estimating the stability of ground with underground circular cavity.

• Journal of IKEEE
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• v.1 no.1 s.1
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• pp.19-30
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• 1997

In this paper we design the optimal satellite-tracking antenna $H{\infty}$ control system using genetic algorithms. To do this, we give gain and dynamics parameters to the weighting functions and apply genetic algorithms with reference model to the optimal determination of weighting functions and design parameter ${\gamma}$ that are given by Glover-Doyle algorithm which can design $H{\infty}$ controller in the state space. These weighting functions and design parameter ${\gamma}$ are optimized simultaneously in the search domain guaranteeing the robust stability of closed-loop system. The effectiveness of this satellite-tracking antenna $H{\infty}$ control system is verified by computer simulation.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.119-126
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• 2002

A reliability analysis is performed to investigate the influence of the uncertainty from few in-situ samples and inherent heterogeneity of the ground on the probability of failure for a rock cut slope. The results are compared with those of deterministic slope stability analysis. The random variables used are unit weight of the rock, the angle of potential slope of failure, and cohesion and internal friction angle of joints. It was found that the rock slope in which the factor of safety satisfied the minimum safety factor in the deterministic analysis has high probability of failure in the reliability analysis when the weak geological strata are involved in the cut slope. The probability of failure of rock slope is most sensitive to the mean and standard deviation of cohesion in rock joint among the random soil parameters included in the reliability analysis. Sensitivities of the mean values are larger than those of standard deviations, which means that accurate estimation of the mean for the in-situ geotechnical properties is important.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.6
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• pp.761-767
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• 2007

In centralized control system, complicated control systems including sensors, power supply and dampers should be required to satisfy the target response of large-scale structures. The practical applications of the centralized control system, however, is very difficult due to high order finite element model of structures, uncertainty of models, and limitations of the excitation system. In this study, the decentralized response-dependent MR damper of which magnetic field is automatically modulated according to the displacement or velocity transferred to the damper without any sensing and computing systems. this decentralized response-dependent MR damper are investigated according to the ranges of relative magnitude between the control force of MR damper and the story shear force of structures by nonlinear time history analysis. Finally, its performance is compared with centralized LQR algorithm which is used in general centralized control theory for a three story building structure.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.208-217
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• 1998

본 연구에서는 ER 브레이크와 ER클러치를 피드백작동기로 사용하여 이송테이블의 위치 추적제어를 수행하였다. 이를 위해 먼저 아라빅 검(arabic gum)계통의 ER유체를 자체조성한 후 전기장에 대한 빙햄(Bingham)모델을 실험적으로 도출하였다. 빙햄모델에 근거하여 평판형의 ER브레이크와 실린더형의 ER클러치를 설계 제작하였으며, 계단입력(step input)전기장에 따른 출력토오크특성을 통하여 이들 작동기의 동적모델을 얻었다. 이들 작동기와 연계된 이송테이블시스템의 운동지배방정식을 유도한 후 위치추적제어를 위한 슬라이딩모드제어기를 설계하였다. 제어기 설계시 이송해이블의 부하질량 변화에 대한 시스템 불확실성과 마찰력을 고려하여 제어성능의 강건성을 보장하도록 하였다. 제안된 제어시스템의 제어영역(control bandwidth)을 주파수 영역에서 고찰한 후 여러 레적에 대한 위치추적제어 실험을 수행하였다.

• Journal of the Korean Institute of Intelligent Systems
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• v.12 no.1
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• pp.33-38
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• 2002

In this paper, a Two-Degree-of-Freedom-Controller(TDFC) for DC motors based on inverse dynamics and the fuzzy technique is presented. The proposed controller includes the inverse dynamic model of a DC motor system, a prefilter and a fuzzy compensator. The model of the system is characterized by a nonlinear equation with coulomb friction. The prefilter eliminates high frequency effects occurring when the inverse dynamic model is implemented. The fuzzy compensator is designed for tracking the change of the reference input and simultaneously regulating the error between the reference input and the system output which can be caused by disturbances. The optimal parameters of both the model and the compensator are identified by a real-coded genetic algorithm. An experimental work on a DC motor system is carried out to verify the performance of the proposed controller.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.2 s.42
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• pp.37-46
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• 2005

To date, many viable smart base isolation systems have been proposed and investigated. In this study, a novel friction pendulum system (FPS) and an MR damper are employed as the isolator and supplemental damping device, respectively, of the smart base isolation system. A fuzzy logic controller (FLC) is used to modulate the MR damper because the FLC has an inherent robustness and ability to handle non linearities and uncertainties. A genetic algorithm (GA) is used for optimization of the FLC. The main purpose of employing a GA is to determine appropriate fuzzy control rules as well to adjust parameters of the membership functions. To this end, a GA with a local improvement mechanism is applied. This method is efficient in improving local portions of chromosomes. Neuro fuzzy models are used to represent dynamic behavior of the MR damper and FPS. Effectiveness of the proposed method for optimal design of the FLC is judged based on computed responses to several historical earthquakes. It has been shown that the proposed method can find optimal fuzzy rules and the GA optimized FLC outperforms not only a passive control strategy but also a human designed FLC and a conventional semi active control algorithm.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.37 no.1
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• pp.10-18
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• 2000

This paper proposes a fuzzy logic cross-coupled controller using a new contouring modeling for a two-axis servo system. The general decoupled control approach may result in degraded contouring performance due to such factors as mismatch of axial dynamics and axial loop gains. In practice, such systems contain many uncertainties. The cross-coupled controller utilizes all axis position error information simultaneously to produce accurate contours. However, the conventional cross-coupled controllers cannot overcome friction, backlash, and parameter variations. Also since, it is difficult to obtain an accurate mathematical model of multi-axis system, here we investigate a fuzzy logic cross-coupled controller of servo system. In addition, new contouring error vector computation method is presented. The experimental results are presented to illustrate the performance of the proposed algorithm.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.5
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• pp.489-494
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• 2013

This study aims to understand the mode characteristics of a droplet under a periodic forced vibration. To predict the resonance frequency of a droplet, theoretical and experimental approaches were employed. A high-speed camera was used to capture the various deformation characteristics of a droplet-mode shape, detachment, separated secondary droplet, and skewed deformation. The comparison between the theoretical and the experimental approaches shows a ~10% discrepancy in the prediction of the resonance frequency, which appears to be caused by the effect of contact line friction, nonlinear wall adhesion, and experimental uncertainty. Owing to contact-line pinning and smaller amplitude, the droplet shape becomes symmetric and the size of each lobe at the resonance frequency exceeds that at the neighbor, which is out of resonance.