• 융합신호처리학회논문지
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• 제10권4호
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• pp.220-224
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• 2009

본 연구에서는 유체역학 분야의 Yabe 박사 팀에 의해 제안된 CIP법을 이용한 3차원 시간영역 음장해석법의 정밀도에 대해서 자세한 검토를 하였다. 즉, 3차원 CIP 음장해석의 위상오차의 특성과 전파방향에 따른 오차를 명확히 하고, 본 수치 해석법의 유효성을 나타내었다. 다차원 CIP법으로는 M형, C형, A형이 있지만, 본 논문에서는 M형 CIP법을 이용한 음장해석의 정밀도에 대해 검토하였다. 또, 종래의 수치해석법으로 staggered-grid 모델을 이용한 FDTD법에 따른 계산결과와의 비교 검토를 하였다. 본 논문의 검토에 의해 같은 이산화조건에서는 CIP법이 FDTD법보다 해석법이 가진 분산성이 적고, CIP법으로 계산된 음압 파형이 FDTD법으로 계산된 음압 파형보다 변형이 적은 것을 알 수 있었다.

• 센서학회지
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• 제19권6호
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• pp.490-496
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• 2010

In this study, in order to overcome the weakness of acoustic field analysis which is generally used for ultrasonic probe performance evaluation, automatic acoustic field measurement system and evaluation parameters were proposed. The comparisons between acoustic field simulation and measured acoustic distribution data of normal and abnormal channels were conducted to evaluate the availability of proposed system and evaluation parameters. First, the impulse response characteristic of sample probe was investigated to classify the normal elements and abnormal elements. And then, normal channels and abnormal channels with abnormal element were chosen. The suggested 12 evaluation parameters were calculated using the acoustic fields of these channels. The availability of proposed automatic acoustic field measurement system and evaluation parameters was confirmed. And the performance evaluation of ultrasonic probe using acoustic field analysis could be easier and faster.

• 한국전자통신학회논문지
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• 제5권2호
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• pp.125-132
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• 2010

본 연구는 C형 CIP법을 이용한 3차원 시간영역 음장해석법의 정밀도에 대해서 세밀한 검토를 하였다. 3차원 C형 CIP 음장해석의 위상오차 특성과 전파방향에 따른 오차를 명확히 하고, 본 수치 해석법의 유효성을 나타내었다. 또 종래의 수치해석법으로 staggered-grid 모델을 이용한 FDTD법에 따른 계산결과와 M형 CIP법에 의한 계산결과와 비교를 하였다. 본 논문의 검토에 의해 같은 이산화조건에서는 C형 CIP법은 M형 CIP법 및 FDTD법보다 해석법이 가진 분산성이 적고, C형 CIP법으로 계산된 음압 파형은 변형이 적은 결과가 되는 것을 알 수 있었다. 그리고 C-1형 CIP법, C-2형 CIP법, M형 CIP법 및 FDTD법의 메모리와 계산시간을 비교하였다. 그 결과 C형 CIP해석은 FDTD해석에 비하여 수치분산성이 적지만 많은 사용 메모리와 계산시간이 필요하였다. C-1형 과 C-2형 CIP법은 입방체의 격자 대각 방향에서는 축 방향에 비하여 정밀도가 약간 저하하는 것을 알 수 있었다. 그리고 C-2형 CIP법은 C-1형 CIP법보다 사용 메모리와 계산시간이 적고, 계산정밀도도 고려해서 보면 유효한 해석법이라는 것이 명확하였다.

• 한국생산제조학회지
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• 제8권3호
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• pp.66-75
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• 1999

This paper is concerned with a analysis of noise by inverse problem available for analyzing the two and three-dimensional acoustic field problems. The noise of analysis considered in this study can be reduced to an optimum problem to find the optimal set of parameters defining the vibrating state of noise source surfaces. The optimal set of parameters are searched by the standard optimization procedure minimizing the square sum of the residuals between the measured and computed quantities of sound pressure at some points in the acoustic field. Computation is carried out for typical examples in which the noise sources are located on the infinite plane. It is demonstrated that the noise of analysis can be effectively made by using the sensitive reference data.

• 한국자동차공학회논문집
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• 제9권5호
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• pp.148-156
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• 2001

Computational Fluid Dynamics (CFD) analysis was carried out to investigate exhaust gas flow and acoustic characteristics in the exhaust system of a passenger car. Transient 3-dimensional flow field in the front and rear mufflers was simulated by CFD and far-field sound pressure was modeled by a simple monopole source method. Engine performance simulation was also performed to obtain the boundary condition of instantaneous fluid flow variation at the inlet of the exhaust system. Detailed exhaust gas flow characteristics such as velocity and pressure distribution inside the mufflers were presented and the pulsating pressure amplitude was compared at several positions in the exhaust system to deduce sound pressure level. The present method of the acoustic analysis coupled with CFD techniques would be very effective for the prediction of sound noise from vehicle exhaust systems although the effects of the inlet boundary condition and heat transfer on the accuracy of the prediction have to be validated through further studies.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.297-301
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• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's $\kappa$-$\omega$ turbulence model. The flow field is observed to oscillate in the shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.297-301
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• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's ${\kappa}-{\varepsilon}$ turbulence model. The flow field is observed to oscillate in the "shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• 한국음향학회지
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• 제15권2호
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• pp.72-78
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• 1996

본 논문에서는 2차원 양방향 포물선 방정식 법과 푸리에 변환을 이용하여 3차원 굴절현상 및 3차원 후방 산란파를 포함하는 $2\frac12$차원 문제를 푸는 방법에 대해 다루었다. 여기서 $2\frac12$ 차원 문제란 2차원적 해양환경 하에 3차원적 음원이 존재할 경우를 의미한다. 2차원 양방향 포물선 방정식법은 수치기법으로 깊이 방향과 수평거리 방향에 대해 각각 Galerkin법과 Crank-Nicolson법을 사용하며 수직 불연속 경계면에 의한 후방 산란파를 포함한 수평거리 의존 문제에 대해 유용한 해를 제공한다. 2차원 해양환경에서는 파수 k가 종 또는 횡 수평거리 방향과 깊이 방향에 대한 함수이므로 3차원 Helmholtz방정식 법을 이용해 스펙트럴 해를 구하여 다시 푸리에 역변환하면 최종 해를 구할 수 있다. 본 연구방법의 정확성을 시험하기 위해서 계단형 해저면을 갖는 간단한 해양환경에서 계산을 수행해 보았으며 대한해협의 특정지역에서의 3차원적 음파전달 특성을 살펴보았다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.197-202
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• 2006

The low-altitude earth observation satellite is generally equipped with high performance camera as a main payload which is vulnerable to vibration environment. During the launch process of a satellite, the combustion and jet noise of launch vehicle produce severe acoustic environment and the acoustic loads induced may damage the critical equipments of the satellite including the camera. Therefore to predict and simulate the effect of the acoustic environment which the satellite has to sustain at the lift-off event is very important process to support the load-resistive design and test-qualification of components. Statistical Energy Analysis(SEA) has been widely used to estimate the vibro-acoustic responses of the structures and gives statistical but reliable results in the higher frequency region with less modeling efforts and calculation time than the standard FEA. In this study, SEA technique has been applied to a 3-Dimensional model of a low-altitude earth observation satellite to predict the acceleration responses on the structural components induced by the high level acoustic field in the launch vehicle fairing. In addition, the expected response on each critical component panel was calculated by the classical method in consideration of the mass loading and imposed sound pressure level, and then compared with SEA results.

• 플랜트 저널
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• 제4권3호
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• pp.54-59
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• 2008

The resonance of boiler is caused by exciting force in the gas path and it generates the vibration by the harmony of boiler's dimensional factor. According to trending toward the boiler of increasing capacity and a bigger size, it has a problem of the vibration at back-pass heating surfaces. We can predict such vibrations as comparison between vortex frequency and gas column's natural frequency. We can't rely on the method for the past decades because of changing parameters, such as an allowable error, gas temperature, gas velocity, Strouhal number. We can reduce the vibration to use the seasoning effect and change the operating condition in coal fired boiler but it's not essential solution. When the vibration occurred in the model boiler, we must measures the acoustic pressure and frequency of places for considering the means. So far, we confirmed the problem from field measures and theoretical analysis about the acoustic vibration of boiler. We installed anti-acoustic baffle in a existing boiler to change the acoustic natural frequency at the cavity, which results in reducing the acoustic vibration. The first, we prove that the acoustic resonance is caused by harmonizing vortex shedding frequency of tube heat surface with acoustic natural frequency of cavity in the range of 650~750 MW loads. The second, the acoustic resonance at the back-pass heating surface has the third order of acoustic natural frequency at the second economizer. We install five anti-acoustic baffles at the second economizer to reducing the resonance. We confirm considerably reducing the acoustic vibration of boiler during the commercial boiler.