• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.4 s.109
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• pp.346-354
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• 2006

This study shows that the system performance of a positioning system composed of a piezoelectric actuator-driven flexure guide depends largely on the preload applied on the flexure guide and the driving input amplitude. We used a flexure guided system that had an original resonant frequency of 54 Hz. Our experiment showed that we could increase the driving bandwidth above the original resonant frequency, for a case involving a large preload and a small input amplitude. Results show that there is a specific 'separation frequency' where the response of the moving mass of the flexure system decouples from the response of the piezoelectric actuator, and this specific separation frequency can be selected by a proper choice of the preload and the input amplitude. To find the separation frequency, sine sweep tests were performed. To confirm the increased system bandwidth frequency, open-loop sine tracking experiments were performed. Test results show that the system responds very well up to 130 Hz frequency higher than the original natural frequency (54 Hz).

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.2
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• pp.77-86
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• 1999

In the previous $paper^{(1),(2)}$, a geometrically non-linear finite element formulation of spatial cables subjected to self-weights and support motions was presented using multiple noded cable elements and how to determine the initial equililbrium state of cables was addressed. In this paper, in order to perform dynamic non-linear analysis of ocean cables subjected to support motions and earthquakes, a numerical method to calculate Morison forces and incorporate effects of earthquake motions is presented based on the Newmark method. Challenging example problems are presented in order to investigate dynamic non-linear behaviors of ocean cables subjected to support motions and earthquake loadings.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.4
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• pp.459-467
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• 2004

This paper presents an efficient reanalysis algorithm, named PRAS (Partial Reanalysis algorithm using Adaptable Substructuring), for the partially changed structures. The algorithm recalculates directly any displacement or member force under consideration in real time without a full reanalysis in spite of local changes in member stiffness or connectivity_ The key procedures consists of 1) partitioning the whole structure into the changed part and the unchanged part, 2) condensing the internal degrees of freedom and forming the unchanged part substructure, 3) assembling and solving the new stiffness matrix from the unchanged part substructure and the changed members.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.296-297
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• 2007

PMN-PZT 단층 및 다층 후막을 알루미나 기판위에 켄티레버 형태로 제작하여, 외부의 미소 진동에 의한 마이크로 발전 특성을 고찰하였다. 미소 변위에 의한 마이크로 발전 특성은 켄티레버의 무게(load), 진동수, 켄티레버의 길이 등에 밀접한 영향을 미치므로 이에 준한 요소를 고려하여 여러 가지 변수로 실험하였다. 연구 결과 서로 다른 소재의 기판과 발전체의 계면 분리 현상, 전극과 발전체의 분리 현상, 소결 온도 등이 소재 측면의 문제점으로 크게 대두되었으며, $5{\times}20mm$ 기판위에 형성된 발전체의 특성은 $1.1k{\Omega}{\sim}1M{\Omega}$의 부하에 따른 전압변동이 0.01V에서 3.6V로 큰 차이가 났다. 켄티레버의 로드의 변화에 대한 피크 전압은 $1.9{\sim}{\pm}2.8V$로 조사되었으며, 출력은 $0.45{\sim}4{\mu}W$로 측정되었다. 그러나 이런 외부 조건 보다 압전체의 공진 특성과 진동수는 가장 중요한 요인으로 나타났으며, 몇몇 문제가 해결될 경우 마이크로 발전소자로의 활용 가능성이 있는 것으로 조사되었다.

• Tunnel and Underground Space
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• v.15 no.3 s.56
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• pp.185-194
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• 2005

Recently, the surrounding rock mass is understood as the major support system for the tunnel constructed in the rock mass. Generally, the rock mass contains many discontinuity planes such as joints, and thus, the tunnel behavior in the rock mass is governed by the characteristics of the discontinuity planes. In this study, the behavior of tunnel in jointed rock mass is studied by model tests and numerical analyses. The results shows that the behavior of tunnel depends on the different initial stress conditions, in case that the tunnel is excavated in the ground without any joints. When a joint is located near the tunnel, the pound stress and displacement tend to increase between the tunnel and the joint.

• Journal of the Earthquake Engineering Society of Korea
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• v.2 no.1
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• pp.47-62
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• 1998

The laminated elastomeric bearing and the lead-rubber bearing were designed to isolate one bay-two story steel frame which is designed for only gravity load. The seismic performance is evaluated for the designed steel frame before and after application of these seismic isolators between the super structure and the foundation. These isolators can improve the seismic capacity of the steel frame. Especially, by inserting the lead plug into the center of the laminated elastomeric bearing, the initial stiffness of th bearing can be increased, thus rather large lateral displacement can be prevented under the frequent service lateral load. During the strong earthquake, yielding of the lead can increase the capacity of the energy dissipation.

• Elastomers and Composites
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• v.45 no.4
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• pp.291-297
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• 2010

Strut insulator in a vehicle is an important part to prevent noise and vibration which is created for driving on the road. Most of the viscoelastic-mounts are made of rubber and natural rubber is the key ingredient. These rubber products show well performance for the initial time, but they will degrade after they are exposed to a high temperature circumstance and a cyclic load. NVH performance and comfort in a vehicle were decreased by these degradation of the rubber. In this study, spring displacement in a vehicle was measured to make a profile in the simulation test performed with an acceleration sensor. In addition, acceleration level, rubber permanent deformation and hardness of the rubber were measured according to drive distance and vehicle model.

• Tunnel and Underground Space
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• v.30 no.6
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• pp.551-558
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• 2020

This note presents the calculation of nominal area for rock core specimen under direct shear testing condition. The initial nominal area was assumed as ellipsoid, and the equations for calculating the nominal area are derived. The normalized shear displacement and normalized nominal area have an identical relationship regardless of the ellipsoid shape. New testing constants and the generalized method were suggested to calculate the decrease of the nominal area. The method was applied to calculate the direct shear testing data and the changes of result were discussed.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.210-210
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• 2021

Delft Dashboard는 유동모델을 위한 오픈소스 프로그램으로 로컬 및 글로벌 데이터 세트를 사용하여 다수의 입력 매개변수를 신속하게 생성, 편집하고 모델 내 입력을 시각화하도록 설계된 그래픽 사용자 인터페이스(GUI) 이다. 특히 Delft Dashboard에 제공하는 개방경계조건을 이용하면 격자영역을 인식하여 개방경계를 자동으로 분배 및 지정하고, 각 개방경계 위치에서 분조별 조석조화상수 값도 산출되므로 유동 모델의 편의성을 증대시킬 수 있지만 상황에 따라 적합하게 경계를 분배하여 개방경계로 지정하는 것이 중요하다. 본 연구에서는 Delft Dashboard에서 제공하는 개방경계조건 중 TPXO 8.0을 이용한 Delft-3D 해수유동 수치모의를 수행하여 개방경계조건이 결과에 미치는 영향을 분석하였다. TPXO 8.0의 경우 격자영역에서 개방경계조건을 설정할 때 사용자가 경계조건에 포함될 격자 수를 지정하면 전체 격자경계에서 격자 수에 해당하는 만큼 경계를 나누어 개방경계를 지정하고 각 개방경계 위치에서의 분조별 조석조화상수값을 산출한다. 특히 격자 수에 따라 개방경계로 지정되는 정도에 따른 영향을 분석하기 위하여 인위적으로 경계를 다양하게 분배하여 개방경계를 지정한 후 수치모의에 적용하였다. 수치모의는 동해안 고리원전 인근을 대상으로 격자 생성 후 Delft Dashboard TPXO 8.0을 이용하여 전술된대로 다양한 개방경계조건을 생성하였고 이를 Delft-3D내 적용하여 해수유동 모의를 수행하였다. 각 개방경계 조건별 초기 수면 변위 분석 및 인근 조위관측소의 관측값의 비교를 통해 개방경계조건이 모의결과에 미치는 영향을 분석하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5B
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• pp.551-555
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• 2006

In this study, new dispersion-correction terms are added to a leap-frog finite difference scheme for the linear shallow-water equations with the purpose of considering dispersion effects of the linear Boussinesq equations for propagation of tsunamis. The numerical model developed in this study is tested to the problem that the initial free surface displacement is a Gaussian hump over a constant water depth, and the predicted numerical results are compared with analytical solutions. The results of the present numerical model are accurate in comparison with those of existing models.