• Journal of KSNVE
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• v.6 no.6
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• pp.709-715
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• 1996

In recent years, the piping vibration in many Power Plants is being increased by the aged generating facilities due to a long time use. Generally, the pressure fluctuations associated with the flow-induced excitations in this case are broadband in nature. Mainly, the dominant sources of vibration are a vortex-shedding, plane waves and boundary layer turbulence. The peak level of the spectrum is proportional to the dynamic head. A severe disturbance in pipeline results in the generation of intense broadband internal sound waves which can propagate through the piping system. The characteristic frequencies of operating loads of 20%, 57%, 70%, 100% are 4 - 6 Hz and coincide with the results from impact hammering test and FEM analysis. We chose the wire energy absorbing rope restraint as a vibration reduction method after reviewing the various conditions such as site, installing space and economic cost etc. After installation, the vibration level was reduced about 54% in velocity.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.334-336
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• 2010

가정용 인버터 에어컨에 사용되는 싱글 피스톤 압축기는 가격은 저렴한 장점이 있지만, 한 회전 당 냉매를 1회 압축, 토출하므로 이에 따른 부하변동이 심해 진동이 심하다는 단점이 있다. 싱글 피스톤 압축기는 고속운전 시에는 관성에 의해 진동이 작지만, 에어컨의 효율을 높이기 위해 압축기를 저속으로 운전할 경우 진동이 심해, 소음 증대와 배관 소손의 문제점이 발생 한다. 이러한 문제를 해결하기 위해 싱글 피스톤 압축기 내의 BLDC 모터가 냉매를 압축, 토출 하는 시점을 검출하여, 인버터가 부하변동을 보상하여 저속 운전 시에도 소음 및 진동을 저감하는 제어 기술을 개발하였다. 부하 토크 변동 보상 기술을 적용하여 기존 35Hz가 최저 운전 주파수였던 싱글 피스톤 압축기를 15Hz까지 낮추어 운전이 가능하므로 에어컨의 저전력 고효율 운전이 가능하다.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.4
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• pp.307-314
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• 2004

A circumferential guided wave method was developed to detect the axial crack on the bent feeder pipe. Dispersion curves of circumferential guided waves were calculated as a function of curvature of the pipe. In the case of thin plate, i.e. infinite curvature, as the frequency increases, the $S_0$ and $A_0$ mode coincide and eventually become Rayleigh wave mode. In the case of pipe, however, as the curvature increases, the lowest modes do not coincide even in the high frequencies. Based on the analysis, a rocking technique using angle beam transducer was applied to detect an axial defect in the bent region of PHWR feeder pipe. Based on the analysis of experimenal data for artificial notches, the vibration modes of each signal were identified. It was found that the notches with the depth of )0% of wall thickness can be detected with the method.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.10a
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• pp.345.2-345
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• 1999

• Journal of the Korean Institute of Gas
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• v.15 no.4
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• pp.15-20
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• 2011

This study presents the behavior characteristics of buried three-layered pipeline subjected to pile driving loads corresponding to its cover depth. The analysis considered the driving energy caused by 7 tonf of ram weight and 1.2m of stroke with 20m distance from buried pipeline for all the analysis cases. A cover depth of pipe is varied 0.6m to 3.8m for this research. Vibration Velocity and stress are investigated at the center section in longitudinal direction. With same distance from pile, attenuation ratio of vibration velocity for increment of cover depth has shown an increasing trend. Also, Stress attenuation ratio of inner pipe is increased with cover depth.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.5
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• pp.385-393
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• 2013

In this paper, the mechanism identification and the avoidance measures on the phenomena of transient acoustic vibration amplified at the water-supply piping system to regulate the steam temperature of the boiler reheater in 500MW class supercritical power plant are presented. The pressure pulsation waves induced by the impeller passing of two feed-water pumps with five blades are coincident with the local acoustic modes of boiler reheater water-supply piping system. There are the phenomena amplified at the peaks of 5X, 10X, 15X and 20X in spectrums of piping vibration, sound pressure, and the feed-water's pressure pulsation waves. The shut-off device is installed in the piping system for the interception of pressure pulsation waves transmitted from two feed-water pumps and the modified design change of the piping layout is applied for the acoustic resonance avoidance. The acoustic natural frequencies are separated from the harmonics of pressure pulsation waves induced by the pump impellers passing through the design change of the span length. The acoustic vibration is gone by resonance avoidance measures. As a result, more than 20 dBA reduction is achieved from 100 dBA to 80 dBA.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.3
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• pp.293-298
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• 2008

Non-contact modal testing for longitudinal modes of a pipe is discussed in this work. The suggested method can generate and measure longitudinal vibrations without mechanical contact by using the coupling phenomenon between deformation and magnetic field, known as the magnetostrictive effect. This effect has been used to generate and measure ultrasonic waves, but seldom used to deal with audible vibrations. In this investigation, the validity of the developed method in a typical vibration frequency range is checked with an Inconel pipe being used in nuclear power plants.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1343-1347
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• 2006

Non-contact modal testing for longitudinal modes of a pipe is discussed in this work. The suggested method can generate and measure longitudinal vibrations without mechanical contact by using the coupling phenomenon between deformation and magnetic field, known as the magnetostrictive effect. This effect has been used to generate and measure ultrasonic waves, but seldom used to deal with audible vibrations. In this investigation, the validity of the developed method in a typical vibration frequency range is checked with an inconel pipe being used in nuclear power plants.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.11
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• pp.1049-1056
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• 2012

The forced vibration response characteristics of a cracked pipe conveying fluid with a concentrated mass are investigated in this paper. Based on the Euler-Bernoulli beam theory, the equation of motion is derived by using Hamilton's principle. The effects of concentrated mass and fluid velocity on the forced vibration characteristics of a cracked pipe conveying fluid are studied. The deflection response is the mid-span deflection of a cracked pipe conveying fluid. As fluid velocity and crack depth are increased, the resonance frequency of the system is decreased. This study will contribute to the decision of optimum fluid velocity and crack detection for the valve-pipe systems.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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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.