• 한국소음진동공학회논문집
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• 제15권8호
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• pp.988-995
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• 2005

Vibration has been severly increased at the branch pipe of main steam header since the commercial operation of nuclear power plant. Intense broad band disturbance flow at the discontinuous region such as elbow, valve, and header generates the acoustical pulsation which is propagated through the piping system. The pulsation becomes the source of low frequency vibration at piping system. If it coincide with natural frequency of the pipe system, excessive vibration is made. High level vibration due to the pressure pulsation related to high dynamic stress, and ultimately, to failure probability affects fatally the reliability and confidence of plant piping system. This paper discusses vibration effect for the branch pipe system due to acoustical pulsations by broad band disturbance flow at the large main steam header in 700 MW nuclear power plant. The exciting sources and response of the piping system are investigated by using on-site measurements and analytical approaches. It is identified that excessive vibration is caused by acoustical pulsations of 1.3 Hz, 4.4 Hz and 6.6 Hz transmitted from main steam balance header, which are coincided with fundamental natural frequencies of the piping structure. The energy absorbing restraints with additional stiffness and damping factor were installed to reduce excessive vibration.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.780-785
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• 2005

Vibration has been severly increased at the branch pipe of main steam header since the commercial operation of a nuclear power plant. Intense broad band disturbance flow at the discontinuous region such as elbow, valve or heather generates the acoustical pulsation which is propagated through the piping system. The pulsation becomes the source of low frequency vibration at piping system. If it coincide with natural frequency of the pipe system, excessive vibration is made. High level vibration due to the pressure pulsation related to high dynamic stress, and ultimately, to failure probability affects fatally the reliability and confidence of plant piping system. This paper discusses vibration effect for the branch pipe system due to acoustical pulsations by broad band disturbance flow at the large main steam header in 7nn nuclear power plant. The exciting sources and response or the piping system are investigated by using on site measurements and analytical approaches. It is identified that excessive vibration is caused by acoustical pulsations of 1.3Hz, 4.4Hz and 6.6Hz transferred from main steam header, which are coincided with fundamental natural frequencies of the piping structure. The energy absorbing restraints with additional stiffness were installed to reduce excessive vibration.

• 한국지반공학회논문집
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• 제32권8호
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• pp.5-14
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• 2016

싱크홀 발생의 주요 원인인 하수관거 배면의 공동 탐지를 위해 비파괴검사 방법 중 하나인 충격반향법을 적용한 실내 모형 실험을 수행하였다. 콘크리트 하수관의 모의를 위해 얇은 두께의 콘크리트 평판 시험체를 제작하였고 주변지반은 모래로 조성하였으며 공동의 모사를 위해 스티로폼 박스를 모래에 매립하였다. 콘크리트 판 배면이 공동인 경우와 완전히 모래에 밀착된 경우로 나누어 실험이 진행되었으며 일정한 타격 강도의 유지를 위해 새롭게 제작된 타격 장치를 사용하여 획득 자료의 신뢰성을 높였다. 측정된 반사파는 고속 푸리에 변환과 국소 푸리에 변환을 사용하여 주파수 특성 및 시간 특성을 분석하였다. 그 결과, 푸리에 스펙트럼의 형상으로는 공동의 유무를 판별할 수 없는 것으로 나타났다. 본 연구에서는 공진 시간이라고 명한 새로운 지표를 제안하였다. 이는 공진 주파수가 일정 강도를 초과하는 지속 시간으로 정의하였다. 공진 시간은 공동의 유무를 효과적으로 예측하는 것으로 나타났다. 나아가 공동유무를 구분할 수 있는 공진 시간을 제시하였다. 실제 현장 조건에서의 검증과 보다 광범위한 적용성의 확보를 위해 다양한 지반 조건에 대한 추가 실험과 실제 하수관에 대한 현장 실험 등을 진행할 예정이다.

• 과학교육연구지
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• 제37권1호
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• pp.233-243
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• 2013

이 연구의 목적은 기주의 길이와 공명주파수의 관계를 정량 분석할 수 있는 교육용 실험기구를 개발하는 것이다. 일회용 플라스틱 주사기와 분자모형 조립용 플라스틱 구를 이용하여 '머리' 달린 기주 공명 장치를 제작하고 상용화된 소프트웨어를 이용하여 PC 실험시스템을 구성하였다. 연구 결과, PC 실험시스템은 전문가용 장비를 대신할 수 있는 것으로 나타났다. 주사기로 만든 이 실험기구는 '관'이 아닌 '헬름홀쯔 공명기'인 것으로 증명되었다. 실험으로 얻은 자료가 소리공명현상을 증명할 수 있는 것으로 나타났다. 결론적으로, 이 주사기 공명기는 중고등학생을 위한 영재교육이나 대학 음향실험용으로 사용가능한 실험장치이다.

• 동력기계공학회지
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• 제9권2호
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• pp.19-25
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• 2005

Empirical experiments have been undertaken to investigate the effects of Intake Pulsating Flow on volumetric efficiency in a diesel engine. Waves occurs in the manifolds of engine owing to the periodic nature of the induction and exhaust processes caused by piston motion. During induction process, as waves travel both directions, they are reflected and interacted each other and pressure waves are transmitted through it. Hence, the flow become more complex and unsteady flow. These pressure waves act upon intake pulsating flow and affects on volumetric efficiency. In this paper the effects of change in length of induction pipes and wide range of engine speed on volumetric efficiency was examined and evaluated. It was found that volumetric efficiency was affected by intake pulsating flow with engine speed and the pipe length. The results obtained were considered by adopting a theory of wave action.

• 한국정밀공학회지
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• 제28권2호
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• pp.185-192
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• 2011

This study deals with a basic proposal to prove the safety for the exhausted fittings of the hydrogen fuel cell vehicle. First, this study was approached to numerical analysis solving to close the exact boundary condition (Axial, Bending, Lateral) and the second, this study produced the Lateral movement equipment for the vibration. For the numerical analysis, This study was considered with the exact solution of Lateral movement and the resonance effect for durability sample according to fitting positions. The second, This study was made for special equipment for displacement/gas leak and the frequency because the domestic samples were comparing with foreign fitting and foreign fitting for the hydrogen fuel cell vehicle. The result of this study was satisfied with domestic fittings for the basic reference but it need more test because of other situation for hydrogen fuel cell vehicle.

• Structural Engineering and Mechanics
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• 제86권6호
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• pp.751-764
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• 2023

In practical engineering such as aerial refueling pipes, the boundary of the fluid-conveying pipe is difficult to be completely immovable. Pipes under movable and immovable boundaries are controlled by different dominant nonlinear factors, where the boundary mobility will affect the nonlinear dynamic characteristics, which should be focused on for adopting different strategies for vibration suppression and control. The nonlinear dynamic instability characteristics of functionally graded fluid-conveying pipes lying on a viscoelastic foundation under movable and immovable boundary conditions are systematically studied for the first time. Nonlinear factors involving nonlinear inertia and nonlinear curvature for pipes with a movable boundary as well as tensile hardening and nonlinear curvature for pipes with an immovable boundary are comprehensively considered during the derivation of the governing equations of the principal parametric resonance. The stability boundary and amplitude-frequency bifurcation diagrams are obtained by employing the two-step perturbation- incremental harmonic balance method (TSP-IHBM). Results show that the movability of the boundary of the pipe has a great influence on the vibration amplitude, bifurcation topology, and the physical meanings of the stability boundary due to different dominant nonlinear factors. This research has guidance significance for nonlinear dynamic design of fluid-conveying pipe with avoiding in the instability regions.

• 한국음향학회지
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• 제16권6호
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• pp.68-75
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• 1997

본 연구에서는 맥동류에 의한 파이프 계의 진동응답을 고찰하기 위해 전달행렬법을 사용하였다. 유속과 압력을 시간과 위치의 함수로 다루어 유체와 파이프간의 상호작용을 파동방정식으로 정립하고, 각 파동방정식으로부터 전달행렬을 직접 유도하였다. 맥동류로부터 유발되는 파이프 계의 동적응답은 맥동으로부터 발생하는 변동유속과 압력에 의존되는 것으로 나타났으며, 공진 근처에서 맥놀이 현상이 관찰되었다. 파이프 계의 동적거동은 파이프 내부의 유동양상과 동일한 응답특성을 나타내고, 내부 유동유체에 의해 결정된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.699-705
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• 2013

This paper presents vibration testing, control, and finite element analysis of a piping system, which is subjected to the changes in fluid levels. Nuclear power plants typically employ a cooling system that uses sea water. These systems are subjected to dynamic characteristic changes caused by sea-level variations, which introduces failures of cooling system components. Therefore in this study, analytical and experimental studies were performed to understand the effect of sea-level changes on the dynamic characteristics of piping systems. It was shown that, as the sea-level increases, pipe's natural frequencies decreases in relation to its mode shape. A 1/14 scale model was also built to compare the results obtained by the analytical study. A good agreement between experiment and analytical studies were observed. Finally, an on-line resonant frequency identification system was proposed and developed, which utilizes piezoelectric transducers as sensors and actuators, in order to avoid catastrophic failure of piping systems.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.1077-1082
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• 2004

It is well known that the pipe will be unstable if the fluid velocity is higher than critical velocity. But even if the velocity of the fluid below the critical velocity, resonance will be caused by pulsation of the fluid. So, many people has studied about the piping system vibration due to a fluid pulsation. But almost guess that fluid has only one hamonic pulsation. Actually, like this case is rare quite. So, in this paper, we consider the vibration analysis of a pipe conveying fluid with several harmonic pulsations and compare the result which considers one hamonic pulsation with the result which considers several harmonic pulsations. And we verify the result in time domain again.