• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.8 s.101
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• pp.968-974
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• 2005

An analytical method for the hydroelastic vibration of a vessel composed of an upper annular plate and a lower circular plate is developed by the Rayleigh-Ritz method. The two plates are clamped along a rigid cylindrical vessel wall. It is assumed that the fluid bounded by a rigid cylindrical vessel is incompressible and non-viscous. The wet mode shape of the plates is assumed as a combination of the dry mode shapes of the plates. The fluid motion is described by using the fluid displacement potential and determined by using the compatibility conditions along the fluid interface with the plate. Minimizing the Rayleigh quotient based on the energy conservation gives an eigenvalue problem. It is found that the theoretical results can predict well the fluid-coupled natural frequencies comparing with the finite element analysis result.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05d
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• pp.373-379
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• 1996

모든 물체는 물체를 구성하는 재료의 성질과 구조의 형식에 따라 각각의 고유주기를 갖고 있으며, 구조물을 구성하는 재료는 시간의 경과와 더불어 경년열화 과정을 거치므로 구조물의 고유주기는 조금씩 길어지는 경향을 갖는다. 그러므로 구조물의 건설 당시에 동적특성을 파악해 놓았다면 구조물에 문제가 발생했을 시의 동적특성을 측정하여 구조물의 손상 여부를 판단하는 중요한 열쇠가 된다. 본 연구는 자연적으로 발생하는 진동 또는 인간이 사회생활을 영위하면서 항상 발생하고 있는 지반의 미소한 외력인 상시미동을 이용하여 구조물의 동적특성을 측정하고 구조해석을 통한 해석결과와 비교 분석하여 구조물의 진동특성을 파악하는 편리한 도구로써 상시미동이라는 진동측정방법의 실용성을 확인하였으며, 고유진동수의 변화추이는 구조물의 건전성을 평가하는 새로운 지표가 될 수 있음을 제안하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.921-925
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• 2003

An analytical method for the free vibration of single circular plate submerged in a fluid-filled rigid cylindrical vessel was developed by the Rayleigh-Ritz method based on the Fourier-Bessel series expansion. It was assumed that the plate is clamped at an offcentered location of the cylinder, and the non-viscous incompressible fluid contained in the cylinder is bisected by the plate. It was found that the theoretical results can predict well the fluid-coupled natural frequencies with excellent accuracy comparing with the finite element analysis results. The offcentered distance effect on the natural frequencies was also observed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.4 s.74
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• pp.399-406
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• 2006

The natural frequencies of Al square plates with a brass inclusion were analyzed by the rule of mixtures. The rule of mixtures is the method to derive natural frequency mutiplying effective inplane wane speed and nondimensional frequency parameters. Numerical models were Al square plates with an inclusion with cantilever type, 2 clamped edge-2 free edge type, 3 clamped edge-1 free edge type and fully clamped edge type. In cantilever type plates, 2 clamped edge-2 free edge type plates and 3 clamped edge-1 free edge plates with an inclusion, good agreement within 10% obtained from rule of mixtures' results and numerical analysis results within inclusion area ratio 1/9. It was found that the natural frequencies of the cantilever type, 2 clamped edge-2 free edge type and 3 clamped edge-1 free edge type plates with an inclusion decrease as the size of inclusion increases when inclusion is located center of plates. And when the density of inclusion is less than the plates, natural frequency of plates with an inclusion increases as the size of inclusion increases.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.2
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• pp.149-159
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• 1999

본 연구에서는 고유진동수를 사용하여 균열의 위치와 크기를 발견하는 비파괴 균열발견모델을 유도하고 Euler-Bernoulli 보를 대상으로 이 모델의 적합성을 검증하였다. 먼저, 균열위치예측모델과 균열크기예측모델로 이루어진 균열발견체계를 제시하였는데, 균열위치예측모델은 모드민감도와 고유진동수 사이의 선형적인 관계로부터 간접적으로 유도되었으며 균열크기예측모델은 균열발생에 의한 변형에너지의 손실을 진동특성치의 변화와 비교하는 동적 파괴역학적 방법으로부터 유도되었다. 다음으로, 기존에 발표된 양단-자유보에 대한 진동모드 실험결과를 사용하여 균열위치와 균열크기를 예측하고 평가하므로 균열발견모델의 적합성과 적용성을 실험적으로 검토하였다. 대부분의 손상시나리오에서 균열위치와 균열크기 예측치는 실제값과 근사하게 일치하였다.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.3
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• pp.62-73
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• 2001

The interest in evaluation of structural intensity arises for practical reasons, because net energy flow distribution offers information of energy transmission path, positions of sources, and sinks of vibration energy. In this paper, structural intensity analysis of local ship structures using finite element method(FEM) is carried out. The purpose of this analysis is to evaluate the relative accuracy according to mesh fineness. The structural intensity of unstiffened and stiffened plates varying their mesh fineness is analyzed and the results are compared with those obtained by the assumed mode method. As results, the proper mesh size in qualitative/quantitative structural intensity analysis of plate structures is proposed. In addition, the propagation phenomenon of vibration energy is investigated for the thickness-varying flat plate, L-type plate, and box-girder structures.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.421-426
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• 2009

This paper presents vibration analysis of maskless exposure module in Printed Circuit Board (PCB) manufacturing system. In order to complete exposure process in PCB, masking type module has been widely used in electronics industries. However, masking process confronts some limitations of application due to higher production cost for masking as well as lower printing resolution. Therefore, maskless exposure module is started to be in the spotlight for flexible production system to meet the needs of fabrication in variable patterns at low cost. Since maskless exposure process adopts direct patterning to PCB, vibration problems become more critical compared to conventional masking type process. Moreover, movements of exposure engine as well as stage generate vibration sources in the system. Thus, it is imperative to analyze the vibration characteristics for the maskless exposure module to improve the quality and accuracy of PCB. In this study, vibration analysis using the Finite Element Analysis is conducted to identify the critical structural parts deteriorating vibration performance. Also, Experimental investigations are conducted by single/dual encoder measurement process under the operating module speed. Measurement points of vibration are selected by three places, which are base of stage, exposure engine and top of stage, to check the effect of vibration from the exposure engine. Comparisons between analysis results and experimental measurement are conducted to confirm the accuracy of analysis results including the developed FE model. Finally, this studies show feasibility of optimal design using the developed FE analysis model.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.12
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• pp.1322-1328
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• 2009

This paper presents vibration analysis of maskless exposure module in printed circuit board(PCB) manufacturing system. In order to complete exposure process in PCB, masking type module has been widely used in electronics industries. However, masking process confronts some limitations of application due to higher production cost for masking as well as lower printing resolution. Therefore, maskless exposure module is started to be in the spotlight for flexible production system to meet the needs of fabrication in variable patterns at low cost. Since maskless exposure process adopts direct patterning to PCB, vibration problems become more critical compared to conventional masking type process. Moreover, movements of exposure engine as well as stage generate vibration sources in the system. Thus, it is imperative to analyze the vibration characteristics for the maskless exposure module to improve the quality and accuracy of PCB. In this study, vibration analysis using the finite element analysis is conducted to identify the critical structural parts deteriorating vibration performance. Also, Experimental investigations are conducted by single/dual encoder measurement process under the operating module speed. Measurement points of vibration are selected by three places, which are base of stage, exposure engine and top of stage, to check the effect of vibration from the exposure engine. Comparisons between analysis results and experimental measurement are conducted to confirm the accuracy of analysis results including the developed FE model. Finally, this studies show feasibility of optimal design using the developed FE analysis model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1994.10a
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• pp.300-305
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• 1994

차실 음향 공동의 특성을 유한요소법에 의해 해석하고자 할 때, 과거에는 차실 음향공동과 트렁크 음향공동과의 상호연성을 고려하지 않고, 두 공동의 경계면을 강체 경계조건으로 생각하여 해석 대상 모델을 차실 음향 공동만으로 국한시켰다. 이러한 해석 방법을 통해서는, 차실과 트렁크 공동이 완전히 밀폐되어 있지 않고 단지 뒷좌석에 의해 두 공동이 구별되어지는 차종에 대해서는 실험과 근접하는 유한요소해석 결과를 얻을 수 없다. 그러므로 차실 공동과 트렁크 공동의 경계면을 가상의 탄성벽 경계조건으로 생각하여 그 탄성벽을 통한 두 공동의 상호 연성을 고려하는 유한요소 모델을 구현하여야 한다. 실제로 트렁크가 차실에 미치는 연성효과를 고려하여 유한요소해석을 수행할 경우 차실의 고유진동수와 고유모드에 미치는 영향이 상당히 큰 것을 확인할 수 있었다. 이하 본 내용에서는 차실과 트렁크 공동, 그 사이의 탄성벽을 이론적으로 해석 가능한 1차원으로 모델링하여 실험 결과와 근접하는 3차원 유한요소 모델링 기법을 제시한다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1994.10a
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• pp.187-191
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• 1994

기계구조물내의 균열은 고하중상태에서 갑작스러운 파괴의 주요 원인의 하나로서 이러한 균열의 조기탐지를 위해 기존의 비파괴검사 방법 이외에, 최근 진동측정 및 진동분석을 이용하는 방법이 경제성 및 그 효용성으로 인하여 깊게 연구되고 있다. 이러한 진동특성의 변화를 이용하여 균열을 탐지하는 방법이 많은 학자들에 의해 연구되어졌으며, 현재까지의 연구결과중 균열의 크기 및 위치를 동시에 탐지할 수 있는 방법중에서 비교적 단순, 정확하다고 판단되는 방법으로는 임의의 두 지점에서의 진폭측정을 이용한 Rizos(1)의 방법과 고유진동수 및 모우드형 측정을 이용한 Kam & Lee(2)의 방법이 있으나 이들 방법은 두가지 이상의 진동특성치를 요구하고 있다. 본 연구의 목적은 진동특성치중 고유진동수만을 이용하여 단순부재에서 균열의 크기 및 위치를 수치적으로 예측할 수 있는 새로운 해석기법을 제시하고, 기존 방법 사용시의 결과와 비교 검토하여 그 유용성을 판단하는데 있다.