• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.975-978
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• 2004

There was transient vibration on the piping system from #4 heater to the deaerator in a power plant. We found it was resulted from resonance between the natural vibration of the piping system and vibration induced by flow of feedwater. We verified it would reduce vibration by increasing stiffness of the piping system. Therefore we concluded that it would be generally better to increase stiffness of the piping system to reduce vibration amplitude of 10Hz low for big sized piping systems.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1848-1853
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• 2000

Cause and the elimination method for the chattering phenomena were investigated the check valve attached exit of the auxiliary cooling water pump at a korean nuclear powerplant. From the site experiment and numerical calculation the incident angle of the disk was so small that it was not able to produce the lifting force to overcome the component of disk weight. Moreover, it turned out that the installed position was not symmetric for the secondary vortical flow generated inside the elbow, so that the flow structure had strongly unstable flow characteristics. From this technical support, the tapping noise and the chattering phenomena were eliminated exactly by changing the incidence angle of the valve disk and installed position of the check valve.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.05a
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• pp.578-579
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• 2010

최근 내연 기관에서 엔진상태 및 잠재적인 결함의 발견을 위해 연료분사, 실린더 내 연소과정, 실린더 내부와 피스톤 마모상태, 흡 배기 밸브 및 과급기 (turbocharger) 등의 상태 모니터링을 통해서 결함에 대한 진단 및 경향관리에 대한 연구들이 진행되고 있다. 본 연구에서는 기 개발된 선박용 대형디젤엔진에 대한 상시 모니터링 시스템을 이용하여 엔진상태 및 잠재적인 결함을 진단하고자 하였으며, 일차적으로 가속도 신호를 이용하여 실린더 내 연소과정에서 정상적인 상태와 착화실패에 따른 진동 양상을 비교 분석하였다. 신호 분석 기법으로 시간-주파수 분산 기법들은 충격파 신호인 엔진 폭발신호를 분석하는데 적합하였으며, 그 기법들 중 Short Time Fourier Transform 기법과 Wavelet Transform 기법을 이용하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.475-479
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• 2011

Leak problem with large pressure drop occurrs non-periodic shock pulsation due to the deterioration of a isolation valve in feed-water recirculation piping system. This paper discusses on the shock vibration and noise occurred due to the effect of acoustical shock pulsations by degradation of the isolation valve in a power site.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.2
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• pp.69-74
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• 2004

In general the surge pressure generated in hydraulic systems causes noise, vibration and odd effect to the system. To reduce the surge pressure, high frequency PWM control of 20KHz was attempted. To estimate the braking noise caused by surge, a vehicle equipped with on-board ABS hydraulic modulator has been experimented with respect to the various breaking condition. Thorough this experiments, it was found that breaking noise has been reduced using high frequency PWM control method compare with low frequency method. To evaluate high frequency control m practice, including verification of general functionality, EMI tests was experimented. Its was found that it is necessary to have the solution to electromagnetic interference(EMI) generated by switching elements.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.569-576
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• 2002

A case history is presented pertaining to piping fatigue by vibrations and sustain stresses in the hydraulic oil supply system for control valves in a 200MW thermal power plant that ultimately resulted in pipe rupture. The Piping was designed to supply the hydraulic oil for turbine control valves. Testing and analyses were performed on the system to develop solution to repair work on failures.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.737-740
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• 2002

Pressure fluctuation in the cylinder is one of the major sources on noise emission in oil hydraulic piston pumps. This paper reports an experimental study of pressure fluctuation characteristics in the cylinder of oil hydraulic piston pumps. We measured pressure fluctuation at BDC with delivery pressure, rotational speed. Because the pre-compression and the V-grooves in the valve plate is known of noise reduction, we investigated also the effect of pre-compression and V-grooves at the ends of the kidney ports with four types valve plates. We found that the pre-compression and the V-grooves in valve plate could reduce the noise of oil hydraulic piston pumps.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1218-1222
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• 2006

The bolts fixing the valve cover to the engine were often reported to be failed in a wheel loader model. Recently this failures were continually repeated in the specified equipment. In order to identify the fatigue fractures of the bolts, various vibration tests were carried out. From these tests, it was found out that the failure was due to the resonance between the excitation force of engine and the transverse mode of engine valve cover. So, the several modifications for the bolts were considered to avoid the resonance. Finally, the bolt failure problem was clearly resolved.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.470-475
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• 2012

The downstream piping system of the water supply system in a supercritical power plant is affected by the fluctuation pressure waves induced by accessing to the acoustic modes of the piping systems with the rotation and impeller passing pulsations of the feed water pump. There are the phenomena amplified at the same time in the range of 415 ~ 455Hz, 830 ~ 910Hz, 1245 ~ 1365Hz and 1660 ~ 1820Hz on the spectrums of the vibration, the sound pressure, and the pressure fluctuation waves.

• Journal of KSNVE
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• v.4 no.2
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• pp.221-230
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• 1994

This paper deals with the dynamic stability and the nonlinear behavior of a check valve system. The nonlinear equations of motion of fluid-valve interation model are derived, which are composed of the unsteady Bernoulli's equation included the jet flow mechanism and equation of motion of a check valve formulated by one degree of freedom. Also, the derived equations of motion are nondimensionalized. According to the change of the nondimensional parameters, the stabilities of the system are analyzed, and the nonlinear interaction responses of the check valve and the passing flow rate are obtained. As the results, the stability charts are constructed for the variation of nondimensional parameters. It is shown that self-excited vibrations exist in a check valve system. And also the Hopf bifurcation and the periodic doubling are found. The presented theoretical model of a check valve system can be utilized to the design and operation of a piping system with the check valve.