• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.3 s.55
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• pp.33-42
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• 2007

In this study, for research on an improvement of the seismic safety of an EDG system, a small scale EDG system was manufactured. For the isolation system, the Coil Spring-Viscous Damper systems were selected. For the shaking table test, 3 kinds of seismic motions were selected which had different frequency contents. In this study, the isolation effects were different and they depended on the input seismic motion. In the case of an NRC earthquake which had low fiequency contents, the isolation effects of the horizontal direction were 20%. But for the seismic motions which had high fiequency contents, the isolation effects were $50{\sim}70%$. In the case of the vertical direction, poor isolation effects were observed. It was because the design properties and the real properties of the isolation system were a little different.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.6
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• pp.498-503
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• 2012

Independent component analysis (ICA) technique based on statistical independency of the signals is known as suitable to identify the source signals by measuring and separating mixed signals through transfer paths and has successfully applied in the field of medical care, communications and so forth. In this study, the ICA technique is introduced for the identification of excitation sources from measured vibration signals of structures, which can be done by evaluating negentropy of centered and whitened vibration signals and correlation of separated signals. To validate the method, numerical analyses are carried out for a plate and a cylinder structure. The results show that the method can be applied efficiently to source identification of complex structures. Nevertheless, additional studies would be required to complement problems of occasional inaccuracy.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1953-1959
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• 2011

Subway stations have a characteristic that the facilities in the ceiling should be checked, replaced and expanded frequently. The new installation of supports (steel anchors) for new facilities and workers moving-around in the ceiling result in the damage in the ceiling finish material and concrete structure which also result in construction cost increase. In addition, the noise, vibration and dust generated during the work harm the station environment. There are civil complaints on these which give difficulty to ceiling works. Accordingly, this study suggests a ceiling frame construction method that considers the convenience, economy and efficiency of ceiling work by improving the support installation method for facilities in ceiling.

• The Journal of the Acoustical Society of Korea
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• v.12 no.4
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• pp.39-46
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• 1993

조화집중이동하중을 받는 무한보에서의 음향방사에 대한 연구는 선박, 비행기, 타이어 트레드 밴느 등과 같은 계의 설계시 계의 구조물로부터 발생하는 소음에 대한 해결방안을 제시해 준다. 구조물 표면에 발생하는 음향파워는 svktnqusghks방법을 이용하여 보의 전길이에 분포된 음향 인텐시티를 적분하여 구한다. 보의 표면에서 발생하는 음향파원는 미하수, 장력, 감쇠계수, 기초강성계수, 그리고 파수비에 의해서 결정된다. 각 인자에 따른 음향파워에 대한 정성적인 분석을 수행하기 위해 심프슨 적분방법을 이용하여 수치적분을 하였다. 무한보에 작용하는 유체하중에 3다라 진동에너지가 음향에너지로 변환되는 비율이 달라진다. 밀도가 큰 유체는 등가감쇠로 작용하여 보로부터 방사된 음향에너지는 빠르게 감소된다. 하중의 이동에 의하여 도플러이동효과가 발생하여 무한보의 공진부근에서의 음향파워 파크가 분리되고 보의 기초감쇠의 영향으로 음향에너지는 감소된다.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.113-114
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• 2016

본 논문에서는 오일 쿨러용 컴프레셔의 속도 맥동에 의한 영향을 분석하고 이를 저감하기 위한 알고리즘을 제안한다. 일반적으로 공작기계의 공작물 가공부위에서 발생하는 열 변형 오차를 줄이기 위해 오일 쿨러용 컴프레셔가 사용된다. 하지만 싱글 로터리 구조의 컴프레셔에서 발생하는 기계적인 진동은 배관의 피로파괴와 소음을 야기하므로 반드시 저감시켜야 한다. 따라서 본 논문에서는 싱글 로터리 컴프레셔의 운전 시 발생하는 속도 맥동의 영향을 최소화할 수 있는 실시간 보상기법을 제안한다. 제안된 기법은 특정 맥동 성분을 저감할 수 있는 비례공진제어기를 적용하여 속도 맥동의 주파수 성분을 검출하여 이를 최소화 하는 방향으로 보상신호를 주입하는 방식이다. 시뮬레이션과 실험을 통해 제안하는 기법의 효용성을 검증한다.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.3
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• pp.105-110
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• 2011

Recently, a deep mixture method as a soil improvement method of marine soft ground, which causes less noise and vibration than other methods, are widely used. In this study, for DCM(Deep Cement Mixing) method, one of the deep mixture method, optimum mixing ratio of clay-cement was suggested using uniaxial compression tests on specimens with various mixing ratio of claycement. In addition, the stability of a caisson on tangent circle-type and wall-type DCM treated ground was evaluated using centrifuge tests. As a result, optimum mixing ratio of clay-cement was 28.5% and the stability of the caisson on DCM treated ground was confirmed. However, the lateral displacement of the caisson on the wall-type DCM treated ground was 7% less and the settlement of that was 39% less than the case of the tangent-circle-type DCM method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.71-81
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• 2008

This paper proposes a spectral element which can represent dynamic responses in high frequency domain such as Lamb waves on a thin plate. A two layer beam model under 2-D plane strain condition is introduced to simulate high-frequency dynamic responses induced by piezoelectric layer (PZT layer) bonded on a base plate. In the two layer beam model, a PZT layer is assumed to be rigidly bonded on a base beam. Mindlin-Herrmann and Timoshenko beam theories are employed to represent the first symmetric and anti-symmetric Lamb wave modes on a base plate, respectively. The Bernoulli beam theory and 1-D linear piezoelectricity are used to model the electro-mechanical behavior of a PZT layer. The equations of motions of a two layer beam model are derived through Hamilton's principle. The necessary boundary conditions associated with electro mechanical properties of a PZT layer are formulated in the context of dual functions of a PZT layer as an actuator and a sensor. General spectral shape functions of response field and the associated boundary conditions are formulated through equations of motions converted into frequency domain. A detailed spectrum element formulation for composing the dynamic stiffness matrix of a two layer beam model is presented as well. The validity of the proposed spectral element is demonstrated through comparison results with the conventional 2-D FEM and the previously developed spectral elements.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.2
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• pp.123-130
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• 2014

An ultrasonic magnetostrictive transducer-based phased-array system for imaging defects in plate structures is newly proposed. In that most ultrasonic phased array systems rely on piezoelectric transducers or electromagnetic acoustic transducers, this system has its own unique feature of employing magnetostrictive transducers. Interest in using a phased array system using magnetostrictive transducers has been recently reported for pipe inspection but no such system has been developed for plate inspection. In this investigation, we aim to propose a phased array system using OL-MPTs (Omnidirectional Lamb wave Magnetostrictive Patch Transducers) for plate inspection. The developed system consists of a multi-channel function generator, power amplifiers, preamplifiers and a data acquisition unit. In the process of its development, each of the units must be checked and in doing so, we suggest types of ultrasonic wave experiments that should be carried out. Finally, the phased system using a transducer array composed of eight OL-MPTs is newly configured and is applied for actual crack detection experiments.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.668-674
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• 2001

An experimental study was performed for two types of co-axial cylindrical shell structures in order to establish the relationship between in-air dynamic characteristics and in-water ones and to observe hydrodynamic mass effects on their mode shapes when submerged. The outer cylinders are prepared with two kinds to get more insights on the fluid-structure interaction phenomena: one is flexible, which means that the outer cylinder has almost same stiffness as the inner one, and the other is a rigid one whose stiffness is more than ten times of the inner one's(it might be regarded as the scaled-down model of the reactor internals). The finite element. analyses were also implemented to support the experimental results. The results show that the natural frequencies of a co-axial cylindrical shell structure in water are remarkably lower than those in air due to the fluid mass effects. In case of the flexible-to-flexible cylinders, there exist in-phase and out-of-phase mode shapes and they are affected by the annular gap between the. co-axial cylinders. For the in-phase mode the in-water natural frequency decreases exponentially as the gap increases, while it slightly increases in case of the out-of-phase mode due to the squeezing effect of the gap fluid. In the flexible-to-rigid case, the normalized natural frequency(in-water frequency/in-air one) of the inner cylinder(core barrel model) ranges between in-phase and out-of-phase mode frequencies of the flexible-to-flexible co-axial cylindrical structure having identical dimensions. Also the normalized natural frequency of the inner cylinder of the flexible-to-rigid one moves from near of the in-phase mode frequency into the out-of-phase mode value of the flexible-to-flexible case as circumferential mode number(n) increases.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.5
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• pp.567-577
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• 2016

The hutches which are installed in the beamline are largely classified into two, i.e XPP (X-ray pump probe) and CXI (Coherent X-ray image). Laser room is installed on the hutch and provides laser to XPP and CXI simultaneously. And two hutches have heavy crane to install some optics equipments. Safety and reliability of hutch structures should be taken into account for the precise operating of the laser facilities, so vibration analysis is essential to do this. The main purpose of vibration analysis is to install hutch structures with large stiffness. We have changed materials specification several times to install hutch structures having strong stiffness. Now hutch structures were installed and checked vibration status at laser room and XPP hutch. The results of laser table and robot arm satisfy vibration criteria. This paper explains about the design and vibration analysis of hutch structures.