• 소음진동
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• 제9권5호
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• pp.922-927
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• 1999

The objective of this paper is to obtain the contribution of each source to the spectrum of pressure, when there are multiple incoherent sources in near-field acoustic holography. For this objective, we have to obtain signals very coherent to the input signals of the sources. To obtain the very coherent signals, many people have measured pressure signals in the vincinity of the sources. However, it is sometimes difficult to locate microphones near to the sources so that the signals are very coherent to the input signals. This paper proposed a method to obtain the very coherent signals by near-field acoustic holography. Therefore, the proposed method does not require the measurement of pressure near to each source. Simulation results for two incoherent monopole sources showed the possibility of the proposed method.

• Nuclear Engineering and Technology
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• 제26권4호
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• pp.562-569
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• 1994

이 연구에서는 피동형원자로의 과도현상을 분석하기 위한 KOTRAC 코드의 모델을 수정한 것이다. 이 코드에서 열수력학 모델로 도입하고 있는 mixture drift flux model은 피동형원자로와 같이 비상냉각수가 중력으로 주입되는 경우를 잘 모사할 수 있으나, 만일 가압기 밀림관 또는 수평관에서 상의 완전분리가 일어나게 될 때에는 증기상에서의 거의 영에 가까운 밀도로 인해 상당한 어려움이 존재하는 것이 밝혀졌다. 이 연구에서는 이러한 어려움을 극복하기 위해 일부 모델을 개선하였는데 가장 두드러진 것은 KOTRAC에서 사용하고 있는 flow distribution parameter를 Ishii 상관식으로 대체하여 코드를 수정하고 해석하였다. 이렇게 수정된 코드를 사용한 결과는 과도상태 해석코드인 RELAP5 /MOD3 계산결과와 비교적 잘 일치함을 볼 수 있었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.1020-1025
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• 2002

This paper exploits how vortex noise is generated around a cylinder. This is done by utilizing an acoustic holography. In this experiment. compressed air was Infected to tile cylinder through a hose. Therefore, major noise sources were at a hose end as well as around the cylinder： vortex shedding noise. The holography results show a resultant noise picture there it is not easy to clearly sort out the shedding noise and what is generated at the end of the tube. We attempted to separate those noise by the method we developed : contribution analysis scheme. The method, in fact, was found to be efficient and practical to separate the noise field into independent noise sources. The highlights of the results are. we believe, that lift and drag noise picture are now available. This procedure does not limit its application. therefore we may use this to visualize any noise field that we want to understand.