• Structural Engineering and Mechanics
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• 제46권2호
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• pp.153-177
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• 2013

Pendulums can be used as passive vibration control devices in several structures and machines. In the present work, the nonlinear behavior of a pendulum-tower system is studied. The tower is modeled as a bar with variable cross-section with concentrated masses. First, the vibration modes and frequencies of the tower are obtained analytically. The primary structure and absorber together constitute a coupled system which is discretized as a two degrees of freedom nonlinear system, using the normalized eigenfunctions and the Rayleigh-Ritz method. The analysis shows the influence of the geometric nonlinearity of the pendulum absorber on the response of the tower. A parametric analysis also shows that, with an appropriate choice of the absorber parameters, a pendulum can decrease the vibration amplitudes of the tower in the main resonance region. The results also show that the pendulum nonlinearity cannot be neglected in this type of problem, leading to multiplicity of solutions, dynamic jumps and instability. In order to improve the effectiveness of the control during the transient response, a hybrid control system is suggested. The added control force is implemented as a non-linear variable stiffness device based on position and velocity feedback. The obtained results show that this strategy of nonlinear control is attractive, has a good potential and can be used to minimize the response of slender structures under various types of excitation.

• Journal of international Conference on Electrical Machines and Systems
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• 제2권1호
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• pp.97-103
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• 2013

This paper describes the characteristics of Electronic Throttle Controller (ETC) module in BLDC motor without the hall sensor for detecting a rotor position. The proposed ETC control system, which is mainly consisted of a BLDC motor, a throttle plate, a return spring and reduction gear, has a position sensor with an analogue voltage output on the throttle valve instead of BLDC motor for detecting the rotor position. So the additional commutation information is necessarily needed to control the ETC module. For this, the estimation method is applied. In order to improve and obtain the high resolution for the position control, it is generally needed to change the gear ratio of the module or the electrical switching method etc. In this paper, the 3-phase switching between successive commutations is adapted instead of the 2-phase switching that is conventionally used. In addition, the position control with a variable PI gain is applied to improve a dynamic response during a transient period and reduce vibration at a stop in case of matching position reference. The mentioned method can be used to estimate the commutation state and operate the high-precision position control for the ETC module and the high response characteristics. The validity of the proposed method is examined through the experimental results.

• Korea-Australia Rheology Journal
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• 제14권2호
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• pp.57-62
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• 2002

The sensitivity of the final filament to the ongoing sinusoidal disturbances has been Investigated in the viscoelastic spinning using frequency response method. Amplification ratios or gains of the spinline cross-sectional area at the take-up to any disturbances show resonant peaks along the frequency regime, where the frequencies at theme points directly correspond to the imaginary parts of the successive leading eigenvalues from the linear stability analysis. As shown in Jung et al. (1999) and Lee et al (2001), the sensitivity results on the effect of various process conditions such as spinline cooling and fluid viscoelasticity, obtained by dynamic transient simulation have been corroborated in this study. That is, increasing spinline cooling makes the system less sensitive to disturbances, thus stabilizes the spinning. Also, an increasing viscoelasticity for extension-thickening fluids decreases the sensitivity of the spinning. i.e., stabilizing the system, where, as it increases the sensitivity of the spinning of extension-thinning fluids. Furthermore, it has been found in the present study that the inertia force as one of secondary forces causes the system to be more stabile or less sensitive to process disturbances.

• 한국조명전기설비학회지:조명전기설비
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• 제9권1호
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• pp.37-46
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• 1995

최근의 전력계통은 대규모 복잡화 되어가고 장거리 대용량 송전이 증대함에 따라 안정도 해석에서 부하특성을 고려한 해석은 중요한 과제이다. 본 논문은 전력계통의 유도부하가 전력계통의 전압에 미치는 영향을 조사 분석한 논문으로 그 주요내용은 부하모선에 연결된 부하중에서 유도 전동기 부하의 비율이 크거나 유도전동기 부하의 관성정수가 적은 경우가 전압 불안정 현상에 미치는 영향이 크며, 유도전동기 부하가 클 경우는 그 부하가 연결된 회로의 일부 개로시 즉 단순한 계통의 회로 변경시에도 전압불안정 현상을 일으킬 수 있다. 이 전압 불안정 현상은 부하의 응동특성에 따라 계통에 적정용량의 전력용 콘덴서를 투입함으로써 방지할 수 있다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1993년도 춘계학술대회논문집; 한국과학연구소, 21 May 1993
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• pp.147-147
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• 1993

All types of dynamic excitation, periodical, pulse or transient in vertical, horizontal or all three directions can be effectively reduced by vibration isolation systems. Typical elements for vibration isolation control are spring units consisting of a group of helical compression springs. In all cases of shock, transient or random excitation energy absorbing dampers have to be added to the spring units in order to reduce system response in the frequency range near the natural frequency of the isolation system. The same isolation system of spring units and viscos-dampers has been used since 1979 for passive protection of buildings and structures has been proved to by very advantageous for vibration and structure borne noise control. Not only because of high vertical flexibility of the spring units, compared for example with typical rubber or neoprene mounts out also because of the horizontal of flexibility, which can be adapted by modifying the spring dimensions to nearly every requirement. It is just normal to use the same basic elements for passive isolation as for active isolation.

• Nuclear Engineering and Technology
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• 제55권9호
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• pp.3472-3484
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• 2023

The objective of this research is to assess the seismic performance of different types of electrical cabinets in nuclear power plants. The cabinets under investigation are: (a) Case 1: a short single cabinet; (b) Case 2: a tall single cabinet; (c) Case 3: separated cabinets; and (d) Case 4: a combined cabinet with coupling effects. To accurately capture the real behavior of the cabinet, three-dimensional finite element models are developed using ANSYS with connection non-linearity. Frequency domain decomposition (FDD) is used to determine the dynamic properties of the cabinets from shaking table testing data, and these results are utilized to validate the numerical model. The close match between the experimental and numerical results obtained from the modal analysis demonstrates the accuracy of the numerical model. Subsequently, transient structural analysis is performed on the validated models to explore seismic performance. The results show that the acceleration response of the combined cabinet is lower than the single cabinet and the separated cabinet. This observation suggests that top anchors used to combine two different types of cabinets play a crucial role in assessing the efficiency and seismic resistance of electrical cabinets in a nuclear power plant.

• Journal of Mechanical Science and Technology
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• 제20권2호
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• pp.251-261
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• 2006

The objective of this work is to apply artificial neural networks for solving inverse problems in the structural optimization of a fiber optic pressure sensor. For the sensor under investigation to achieve a desired accuracy, the change in the distance between the tips of the two fibers due to the applied pressure should not interfere with the phase change due to the change in the density of the air between the two fibers. Therefore, accurate dynamic analysis and structural optimization of the sensor is essential to ensure the accuracy of the measurements provided by the sensor. To this end, a normal mode analysis and a transient response analysis of the sensor were performed by combining commercial finite element analysis package, MSC/NASTRAN, and MATLAB. Furthermore, a parametric study on the design of the sensor was performed to minimize the size of the sensor while fulfilling a number of constraints. In performing the parametric study, the need for a relationship between the design parameters and the response of the sensor was fulfilled by using a neural network. The whole process of the dynamic analysis using commercial finite element analysis package and the parameter optimization of the sensor were automated within the MATLAB environment.

• 한국철도학회논문집
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• 제17권2호
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• pp.100-105
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• 2014

해중철도 부근에서 테러나 사고에 의해 수중폭발이 발생하였을 경우, 함체에 치명적인 손상을 가할 수 있으므로, 충분한 강도를 확보해야 한다. 본 연구에서는 설계 목적으로 해중철도 인근에서 수중폭발이 발생한 경우, 경험에 기초한 공식을 이용하여 충격압을 추정하고, 충격압에 의한 해중철도의 응답을 해석할 수 있는 간이 해석 방법을 제안하였다. 해중철도 함체를 탄성 지지된 보로 이상화하고, 초기 최대 충격압이 작용하는 보에 대해 정적 유한요소해석을 실시한 후, 동하중 계수와 조합함으로 최대 변위 및 굽힘 모멘트를 계산한다. 간이해석 결과는 상용 유한요소해석 소프트웨어를 이용한, 시간에 따른 과도응답해석 결과와 비교하여 양호한 일치를 보임을 확인하였다.

• 수산해양기술연구
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• 제26권1호
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• pp.81-87
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• 1990

본 논문에서는, 문헌[1]에서 보였던 적분형 서어보계의 구성문제를 목표입력이 선형자유계의 출력으로 얻어지는 경우로 일반화하여 확대계수를 얻고 쌍선형변환법에 의해 폐류우프계를 구성하는 설계법을 제안했다. 본 설계법의 유효성을 확인하기 위해, 전기 서어보기구의 각도 제어에 관한 응용 예를 보였다. 실제적인 서어보 시스템의 설계문제에 있어, 그 폐루우프계의 특성근을 정확한 위치에 배치하기보다는 오히려 어떤 요구하는 과도응답이 얻어질 수 있게 하는 영역내에 배치하면 된다는 의미에서 보면, 본 서어보계 구성법은 그 실제적인 의미가 크다고 할 수 있다.

• 디지털융복합연구
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• 제13권1호
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• pp.269-274
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• 2015

IT 산업의 발달로 AOI 장비의 보급이 확산되고 있으며, 장비의 사용되는 카메라의 높은 해상도를 요구하고 있다. 높은 해상도를 얻기 위해 카메라의 중량이 증가되고 있으며, 그로 인해 진동변위가 커지게 되어 촬상에 문제가 생기고 제어 또한 어려워지고 있다. 본 연구에서는 유한요소 해석프로그램인 NX/NASTRAN을 이용하여 카메라가 관성에 의한 충격력을 받을 때의 과도응답분석을 해 보았다. 또한 Laser Interferometer 측정 결과와의 상관관계 분석을 통하여 향후 AOI의 구조 개선 시, 유한요소해석으로 설계의 신뢰성을 검증할 수 있도록 하기 위한 해석모델을 개발하였다.