• Structural Engineering and Mechanics
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• 제29권5호
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• pp.489-504
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• 2008

In piezoelectric flexible structures, the contribution of vibration modes to the dynamic response of system may change with the location of piezoelectric actuator patches, which means that the ability of actuators to control vibration modes should be taken into account in the development of modal reduction model. The spatial $H_2$ norm of modes, which serves as a measure of the intensity of modes to system dynamical response, is used to pick up the modes included in the reduction model. Based on the reduction model, the paper develops the state-space representation for uncertain flexible tructures with piezoelectric material as non-collocated actuators/sensors in the modal space, taking into account uncertainties due to modal parameters variation and unmodeled residual modes. In order to suppress the vibration of the structure, a dynamic output feedback control law is designed by imultaneously considering the conflicting performance specifications, such as robust stability, transient response requirement, disturbance rejection, actuator saturation constraints. Based on linear matrix inequality, the vibration control design is converted into a linear convex optimization problem. The simulation results show how the influence of vibration modes on the dynamical response of structure varies with the location of piezoelectric actuators, why the uncertainties should be considered in the reductiom model to avoid exciting high-frequency modes in the non-collcated vibration control, and the possiblity that the conflicting performance specifications are dealt with simultaneously.

• Structural Engineering and Mechanics
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• 제55권1호
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• pp.229-244
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• 2015

H-infinity norm relates to the maximum in the frequency response function and H-infinity control method focuses on the case that the vibration is excited at the fundamental frequency, while 2-norm relates to the output energy of systems with the input of pulses or white noises and 2-norm control method weighs the overall vibration performance of systems. The trade-off between the performance in frequency-domain and that in time-domain may be achieved by integrating two indices in the mixed vibration control method. Based on the linear fractional state space representation in the modal space for a piezoelectric flexible structure with uncertain modal parameters and un-modeled residual high-frequency modes, a mixed dynamic output feedback control design method is proposed to suppress the structural vibration. Using the linear matrix inequality (LMI) technique, the initial populations are generated by the designing of robust control laws with different H-infinity performance indices before the robust 2-norm performance index of the closed-loop system is included in the fitness function of optimization. A flexible beam structure with a piezoelectric sensor and a piezoelectric actuator are used as the subject for numerical studies. Compared with the velocity feedback control method, the numerical simulation results show the effectiveness of the proposed method.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.316-323
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• 1997

This paper compares input shaping techniques for controlling residual vibration of flexible structures. Input shaping generates vibration-reducing shaped commands through convolution of an impulse sequence with the desired command. Both feedforward and feedback control approaches with/without input shaper for uncertain dynamical systems are investigated to evaluate the control performances. The control objective is to achieve a fast settling time and robustness to plant uncertainty, to eliminate residual vibrations. It is shown by a series of simulation that a properly designed feedback controller with input shaper performs well, as compared with open-loop controller with input shaper.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국내학술편); Seoul National University, Seoul; 20-22 Oct. 1993
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• pp.937-942
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• 1993

This paper extends the authors' prior work on the regulation of flexible space structures via partial feedback linearization (PFL) methods to articulated systems. Recursive relations introduced by Jain and Rodriguez are central to the efficient formulation of models via Poincare's form of Lagrange's equations. Such models provide for easy construction of feedback linearizing control laws. Adaptation is shown to be an effective way of reducing sensitivity to uncertain parameters. An application to a flexible platform with mobile remote manipulator system is highlighted.

• 대한기계학회논문집A
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• 제20권5호
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• pp.1498-1507
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• 1996

This paper presents a robust control of a smart flexible structure featured by a piezofilm actuator characterizing its light weght and quick response time. A mathematical governing equation for the proposed structure is derived by employing Hamilton's principle and a state space control model is subsequentrly obtained through modal analysis. Uncertain system parameters such as frequency variation are included in the control model. A sliding mode control theroy thich has inherent robustness to systme uncertainties is adopted to design a tracking controller for the peizofilm actuator. Using the output informaiton from the tip deflection sensor, a full-order observer is constructed ot estimate state variables for the system. Tracking performances for desired trajectories of sinusoidal amd step functions are evaluated by undertaking both simulation and experimental works.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.55-55
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• 2015

Today, engineers are facing new set of challenges that are quite different from the conventional ones. Information technologies are rapidly commoditizing while the paths beyond the current roadmaps became uncertain as various technologies have been pushed to their limits. Along with these changes in IT ecosystems, grand challenges such as global security, health, sustainability, and energy increasingly require trans-disciplinary solutions that go beyond the traditional arenas in STEM (Science, Technology, Engineering and Mathematics). Addressing these needs is shifting engineering education and research to a new paradigm where the emphasis is placed on the consilience for holistic and system level understanding and the convergence of technology with AHSD (arts, humanities, social science, and design). At the center of this evolutionary convergence, nanotechnologies are enabling novel functionalities such as bio-compatibility, flexibility, low power, and sustainability while on a mission to meet scalability and low cost for smart electronics, u-health, sensing networks, and self-sustainable energy systems. This talk introduces the efforts of convergence based on the emerging nano technology tool sets in the newly launched School of Integrated Technology and the Yonsei Institute of Convergence Technology at Yonsei International Campus. While the conventional devices have largely depended upon the inherent material properties, the newer devices are enabled by nanoscale dimensions and structures in increasingly standardized and scalable fabrication platform. Localized surface plasmon resonance in 0 dimensional nano particles and structures leads to subwavelength confinement and enhanced near-field interactions enabling novel field of metal photonics for sensing and integrated photonic applications [1,2]. Unique properties offered by 1 dimensional nanowires and 2 dimensional materials and structures can enable novel electronic, photonic, nano-bio, and biomimetic applications [3-5]. These novel functionalities offered by the emerging nanotechnologies are continuously finding pathways to be part of smart systems to improve the overall quality of life.

• Wind and Structures
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• 제27권3호
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• pp.175-186
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• 2018

With the continuous increase of span lengths, modern bridges are becoming much more flexible and more prone to flutter under wind excitations. A reasonable probabilistic flutter analysis of long-span bridges involving random and uncertain variables may have to be taken into consideration. This paper presents a method for estimating the reliability index and failure probability due to flutter, which considers the very important variables including the extreme wind velocity at bridge site, damping ratio, mathematical modeling, and flutter derivatives. The Aizhai Bridge in China is selected as an example to demonstrate the numerical procedure for the flutter reliability analysis. In the presented method, the joint probability density function of wind speed and wind direction at the deck level of the bridge is first established. Then, based on the fundamental theories of structural reliability, the reliability index and failure probability due to flutter of the Aizhai Bridge is investigated by applying the Monte Carlo method and the first order reliability method (FORM). The probabilistic flutter analysis can provide a guideline in the design of long-span bridges and the results show that the structural damping and flutter derivatives have significant effects on the flutter reliability, more accurate and reliable data of which is needed.

• 한국터널지하공간학회 논문집
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• 제7권1호
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• pp.73-88
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• 2005

본 논문에서는 현재 암반 지하 구조물의 설계에 있어 사용되고 있는 접근법인 정량적 암반분류시스템, 시공중 암반 거동에 근거한 분류시스템 그리고 일반적인 정성적 설계 절차의 특징 및 장단점을 살펴보았으며, 이러한 설계 기법의 단점을 해결하기 위하여 제안된 오스트리아 터널 설계 가이드라인을 소개하고 국내의 경우와 비교하였다. 그 결과 기술적으로 안전하고 경제적인 터널 건설을 위해서는 불확실한 지반조건 및 환경조건에 매우 유연하게 대처할 수 있는 설계 및 시공 기술이 필요하다고 판단되며, 오스트리아 터널 설계 가이드라인에서 이와 관련된 기준을 제시하고 있다. 따라서 국내에서도 안전하고 경제적인 터널 건설을 위하여 시공중 계측 자료를 충분히 활용하여 실제 지반 조건을 예측하고 불확실한 지반 조건에 유연하게 대처할 수 있는 설계 및 시공 기술을 적용하는 것이 바람직하다고 사료된다.

• 중소기업연구
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• 제39권2호
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• pp.139-160
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• 2017

오늘날 기업을 둘러싸고 있는 환경의 변화는 매우 불확실하여 기업들이 경쟁력을 제고시키고 수익성을 개선하기 위해선 사내 기업가정신이 활성화되어야 할 필요성이 있다. 특히, 한국이나 중국과 같이 신흥시장에 속해 있는 국가들에 있어 중소기업들의 기업가정신 실천은 경제적 혁신과 기업의 경쟁력 제고를 위해 매우 중요한 과제로 제시되고 있다. 이에 본 연구는 한국과 중국의 중소기업들을 대상으로 Hornsby et al.(2002)이 제시한 사내 기업가정신의 활성화를 위한 5가지 환경적 요인들이 기업가정신 활동에 미치는 영향에 대해 살펴보았다. 설문조사를 통해 한국과 중국의 중소기업 300개 업체로부터 받은 자료를 분석한 결과, 기존의 서구의 대기업들을 대상으로 연구되어졌던 조직환경이 한국과 중국과 같은 신흥시장에 속해 있는 국가의 중소기업들에서도 동일하게 사내 기업가정신에 유의한 긍정적 영향을 미치는 것으로 나타났다. 다만, 사내 기업가정신의 실천은 혁신이나 전략 재구축과 같은 다양한 형태로 나타날 수 있는데 그 형태에 따라 각기 조직환경이 미치는 영향력에 있어서도 다소 차이가 있는 것으로 나타났다. 또한 비교적 동일한 문화권에 속해 있는 한국과 중국의 중소기업들은 조직환경에 있어 통계적으로 유의한 차이를 대체로 보이지 않는 것으로 나타났다. 뿐만 아니라 이들 요인들이 미치는 영향력에 있어서도 많은 경우 통계적으로 유의한 차이를 보이지 않는 것으로 나타났다. 그러나 한국의 중소기업들이 중국에 비해 유연한 조직구조나 직무자율성은 사내 기업가정신을 실천하는데 있어 보다 강점이 있는 것으로 나타났다. 본 연구의 이러한 결과는 향후 국내 중소기업들이 경쟁력 제고와 혁신을 위해서 그리고 중국 중소기업들에 비해 비교우위를 갖기 위해서 어떠한 노력들을 더 경주해야 하는지에 대한 시사점을 제공한다.

• 대한지리학회지
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• 제30권3호
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• pp.296-310
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• 1995

본 연구는 퍼지이론을 공간분석에 적용하기 위한 이론적인 배경을 고찰하고, 퍼지 분류법의 특성에 대해 살펴본 것이다. 이를 위해 필자는 공간정보의 모호성에 대해 살펴보 고, 퍼지공간분석의 전제를 설정한 다음 퍼지분류법을 소개하였다. 그리고 퍼지분류법의 특 성을 명확히 하기 위해 경상남도 읍급이상 도시의 산업별 고용비율을 대상으로 퍼지분류를 행한 후, 퍼지분류와 전통적인 군집분석의 결과를 비교하였다. 그 결과, 공간정보의 모호성 은 구체성의 부족, 인간행태, 인내치문제, 분류기준의 부족 등에 의해 발생하는데 기존의 공 간분석기법으로는 공간의 모호성을 반영할 수 없으므로 퍼지기법을 도입한 퍼지공간분석의 필요성이 있음을 확인하였다. 퍼지분류법 중, 퍼지이산분류는 계산절차는 상대적으로 간단하 나 분류결과가 집단간의 점이성을 고려하지 못하며, 퍼지중첩분류는 분류집단간의 점이성은 고려하나 분류결과가 지나치게 많아 적절한 분류수준을 선택하기 어렵고 결과해석이 상대적 으로 난해하다는 문제점이 있음이 밝혀졌다, 또 경남의 도시기능분류는 분류기법에 따라 다 르게 이루어졌지만 창원, 울산, 마산, 진해, 김해, 양산, 웅상, 장승포, 신현으로 구성된 제조 업 군집과 단독군집 충무의 존재가 세 가지 분류 모두에서 공통적으로 확인되었다.