• 한국전산유체공학회지
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• 제11권3호
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• pp.59-63
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• 2006

Accurate prediction of a supersonic missile base drag continues to defy even well-rounded CFD codes. In an effort to address the accuracy and predictability of the base drags, the influence of grid system and competitive turbulence models on the base drag is analyzed. Characteristics of some turbulence models is reviewed through incompressible turbulent flow over a flat plate, and performance for the base drag prediction of several turbulence models such as Baldwin-Loman(B-L), Spalart-Allmaras(S-A), k-$\varepsilon$, k-$\omega$ model is assessed. When compressibility correction is injected into the S-A model, prediction accuracy of the base drag is enhanced. The NSWC wind tunnel test data are utilized for comparison of CFD and semi-empirical codes on the accuracy of base drag predictability: they are about equal, but CFD tends to perform better. It is also found that, as angle of attack of a missile with control fins increases, even the best CFD analysis tool we have lacks the accuracy needed for the base drag prediction.

• 드라이브 ㆍ 컨트롤
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• 제14권2호
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• pp.9-15
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• 2017

The steering systems of all-terrain cranes have been developed with various control strategies for the stability and drivability. To optimally control the input steering angle, an accurate mathematical model that represents the actual crane dynamics is required. The derivation of an accurate mathematical model to optimally control the steering angle, however, is difficult since the steering-control strategy generally varies with the magnitude of the crane's longitudinal velocity, and the postures of the crane's working parts vary while it is being driven. To address this problem, this paper proposes an automatic steering-control algorithm that is based on the MPC (model predictive control) with a disturbance observer for all-terrain cranes. The designed disturbance observer of this study was used to estimate the error between the base steering model and the actual crane. A model predictive controller was used for the computation of the optimal steering angle, along with the use of the base steering model with an estimated uncertainty. Performance evaluations of the designed control algorithms were conducted based on a curved-path scenario in the Matlab/Simulink environment. The performance-evaluation results show a sound reference-path-tracking performance despite the large uncertainties.

• Earthquakes and Structures
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• 제12권3호
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• pp.285-296
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• 2017

Base isolation is a quite practical control strategy for enhancing the response of structural systems induced by strong ground motions. Due to the dynamic effects of base isolation systems, reduction in the interstory drifts of the superstructure is often achieved at the expense of high base displacement level, which may lead to instability of the structure or non-practical designs for the base isolators. To reduce the base displacement, several hybrid structural control strategies have been studied over the past decades. This study investigates a particular strategy that employs Tuned Mass Dampers (TMDs) for improving the performance of base-isolated structures and unlike previous studies, specifically focuses on the effectiveness of this hybrid control strategy in structures that are equipped with nonlinear base isolation systems. To consider the nonlinearities of base isolation systems, a Bouc-Wen model is selected and nonlinear dynamic OpenSees models are used to perform several time-history simulations in time and frequency domains. Through these numerical simulations, the effects of several parameters such as the fundamental period of the structure, dynamic properties of the TMD and isolation systems and properties of the input ground motion on the behaviour of TMD-structure-base isolation systems are examined. The results of this study provide a better insight into the performance of linear shear-story structures with nonlinear base isolators and show that there are many scenarios in which TMDs can still improve the performance of these systems.

• 대한전기학회논문지
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• 제39권7호
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• pp.720-728
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• 1990

A learning control method is proposed in this paper, using a knowledge base which contains control rules, data, and patterns of the past experience of a plant. The knowledge for plant control is retrieved from measurement data during operation and continually modified after control performance evaluation. A control method is proposed using tinually modified after control performance evaluation. A control method is proposed using fuzzy model of the plant and a recursive statistic decision method of fuzzy subset for control rule generation. Also, the resulting knowledge-based control algorithm has been applied to aprocess and its performance improvement and proper generation of appropriate control rules have been verified.

• 한국정밀공학회지
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• 제18권10호
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• pp.45-52
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• 2001

This paper presents a study on the position tracking control of a robot system on the uncertain elastic base. The elastic bathe is a nonholonomic system but it can be changed into holonomic system, which is much easier to analyze, by modeling an elastic base as a virtual robot that has passive joints. Also, Jacobian operators, which represent the overall robot system including base movement, are defined and applied to the changed model. However, because base movements are not known, the exact Jacobian operators can＇t be estimated. The control algorithm proposed is that uses only Jacobians of a real robot as approximate Jacobian operators. Therefore the approximate Jacobian operators compensate the measured errors from external sensors. The proposed control strategy is evaluated by the simulation and experiment of a single-axis robot system on the elastic base.

• 융합보안논문지
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• 제2권2호
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• pp.49-58
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• 2002

역할기반 접근통제는 추상적 기본 개념의 임의적 접근통제나 강제적 접근통제에 비하여 응용 개념의 역할에 기반한 접근통제 모델이다. 모델은 BLP 모델에서 출발한 커널 단위의 액세스 제어의 제한적 기능과 달리 다양한 컴퓨터 네트워크 보안분야에 있어서 유연성과 적용성을 제공한다. 본 논문에서는 기존의 역할기반 접근통제 기본 모델인 $RBAC_0$ 모델에 주체 및 객체의 역할을 추가로 고려한 역할 계층을 포함하는 확장된 역할기반 접근통제 ($ERBAC_0$ : Exteded $RBAC_0$ 모델을 제안하였다. 제안된 $ERBAC_0$ 모델은 기존의 $RBAC_0$ 모델에 비하여 주체 및 객체 수준에서의 역할을 계층적으로 정교하게 할당하고, 할당된 역할에 기반하여 접근통제 서비스를 보다 유연하게 제공할 수 있다.

• 정보보호학회논문지
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• 제9권1호
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• pp.47-56
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• 1999

역할기반 접근통제는 사용자의 역할에 기반을 둔 접근통제 방법으로 기존의 임의적 접근통제나 강제적 접근통제에 비하여 다양한 컴퓨터.네트워크 보안분야에 있어서 유연성과 적용성을 제공한다. 본 논문에서는 Ravi S. Sandhu가 최초로 제안한 역할기반 접근통제 기본 모델인 RBAC$_{0}$ 모델에 주체 및 객체의 역할을 추가로 고려하여 확장된 역할기반 접근통제(ERBAC$_{0}$:Extended RBAC$_{0}$) 모델을 새롭게 제안하였다. 제안된 ERBAC$_{0}$ 모델은 기존의 RBAC$_{0}$ 모델에 비하여 주체 및 객체 수준에서의 역할기반 접근통제를 보다 정교하게 제공할 수 있다.

• 전자공학회논문지
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• 제50권8호
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• pp.245-249
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• 2013

In this paper, we propose two rate control algorithms for multi-view extension of HEVC with two rate control algorithms adopted in HEVC and analyze the multi-view rate control performance. The proposed multi-view rate controls are designed on HEVC-based multi-view video coding (MV-HEVC) platform with consideration of high-level syntax, inter-view prediction, etc. not only for the base view but also for the extended views using the rate control algorithms based on URQ (Unified Rate-Quantization) and R-lambda model adopted in HEVC. The proposed multi-view rate controls also contain view-wise target bit allocation for providing the compatibility to the base view. By allocating the target bitrates for each view, the proposed multi-view rate control based on URQ model achieved about 1.83% of average bitrate accuracy and 1.73dB of average PSNR degradation. In addition, about 2.97% of average bitrate accuracy and 0.31dB of average PSNR degradation are achieved with the proposed multi-view rate control based on R-lambda model.

• 산업경영시스템학회지
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• 제12권19호
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• pp.89-98
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• 1989

This research addresses the most sophisticated level of complexity of current electronic data processing(EDP) technology realtime, distributed data base(DDB) system. The major objective is to develop guidelines for the control and audit of these sophisticated system, since the control and audit philosophies, control features, and audit techniques applicable to traditional EDP systems are no longer fully appropriate for, or relevant to, these stat-of-art systems. An attempt is made to develop an internally consistent audit and control Conceptual Framework summarizing and integrating the material developed in this research, which then leads into the analysis of the control and audit model.

• 대한기계학회논문집A
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• 제35권5호
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• pp.533-541
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• 2011

본 연구에서는 공압형 인공근육으로 이루어진 회전관절의 동적 특성을 파악하기 위해서 두 개의 공압형 인공근육으로 이루어진 상극구동 시스템의 주파수 응답특성실험을 수행하였다. 인공근육의 작동범위에서 수행한 주파수 응답결과에 최적으로 근사할 수 있는 선형모델을 추정하고 이를 이용하여 회전관절의 움직임을 정밀하게 제어할 수 있는 모델에 기초한 제어법칙을 제시하였다. 사각파, 정현파 기준궤적에 대한 회전관절의 추종실험을 수행한 결과 선형 추정모델에 의한 보상효과와 피드벡 이득에 의한 추종오차 제거효과를 통해서 우수한 궤적 추정성능을 보였다.