• Journal of Mechanical Science and Technology
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• 제18권9호
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• pp.1630-1639
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• 2004

The present paper investigated the correlation between the acoustic pressure variations and the augmentation of heat transfer in the ultrasonic induced acoustic fields. The augmentation ratios of heat transfer coefficient were experimentally measured and were compared with the profile of the pressure distribution in the acoustic fields predicted by numerical analysis. For numerical analysis, a coupled finite element-boundary element method (coupled FE-BEM) was applied. The results of the present study reveal that the acoustic pressure is higher near two ultrasonic transducers than other points where no ultrasonic transducer was installed. The augmentation trend of heat transfer is similar with the profile of the acoustic pressure distribution. In other words, as the acoustic pressure increases, the higher augmentation ratio of heat transfer is obtained. Numerical and experimental studies clearly show that the acoustic pressure variations are closely related to the augmentation of heat transfer in the acoustic fields.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1603-1608
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• 2003

The Present Study reported on the experimental and numerical results of heat transfer in the acoustic fields induced by ultrasonic waves. The strong upwards flow called as acoustic streaming was visualized by a particle image velocimetry (P.I.V). in addition, the augmentation of heat transfer was experimentally investigated in the presence of acoustic streaming and was compared with the profiles of acoustic pressure calculated by the numerical analysis. Experimental and numerical studies clearly show that acoustic pressure variations are closely related to the augmentation of heat transfer.

• 소음진동
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• 제3권2호
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• pp.169-178
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• 1993

Internal & External duct acoustic fields are calculated by using a finite element method. The geometry is assumed as an axisymmetric duct. External acoustic field; outside the duct, and combined internal & external acoustic fields are solved. For both cases a far field's nonreflecting boundary condition is enforced by using a wave envelope element, which is a kind of finite element. First, a pulsating sphere and an oscillating sphere problem are calculated to verify the external problems, and the results are compared with exact solutions. When the wave envelope element is applied at the far boundary, the calculated finite element solutions show good agreements with the exact solutions. Secondly, the combined internal & external duct acoustic fields are calculated and visualized when monopole sources are distributed inside the duct. It is observed that the directivity of sound intensity outside the duct is beaming toward the axis for high frequency sources.

• 한국소음진동공학회논문집
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• 제17권1호
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• pp.41-47
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• 2007

Scattering fields of two dimensional acoustic waves by a circular cylinder are investigated. The present numerical approach for the acoustic scattering problem has difficulties of numerical robustness, long-time stability and suitability of far-field boundary treatments. The time-dependent periodic acoustic source is used to analyze Interference patterns between incident waves and waves reflected by the cylinder. Characteristic boundary algorithms coupled with 4th order Modified-Flux-Approach ENO(essentially non-oscillatory) schemes are employed in generalized coordinates to examine the effect of the wane frequency on the interference patterns. Non-reflecting boundary conditions, which is crustal for accurate computations of aeroacoustic problems, are used not to contaminate scattering fields by reflected waves at the outer boundary. Computed scattering fields show the circumferential acoustic modes generated by interacting between acoustic sources and scattered waves. At a lower frequency, the wave passes almost straight through the cylinder without Interacting with circular cylinder. Simulation results are presented and compared with the analytic solution. Computed RMS-pressure distribution on the cylinder wall is good agreement with exact solution.

• 한국음향학회지
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• 제16권3호
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• pp.45-50
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• 1997

쐐기각이 다른 4종류의 쐐기형 수중음파 흡수타일을 설계, 제작하고 각각의 흡음타일에 대한 반사음장의 크기를 측정하였다. 흡음타일의 정면에서 측정한 반사음장의 크기는 실험한 4개의 타일중 쐐기의 꼭지각이 30$^{\circ}$일 때 최소값을 갖고 120$^{\circ}$일 때 최대값을 가졌다. 쐐기형 흡음타일의 꼭지각이 클수록 그 반사계수가 증가되는 것을 확인하였다. 또한 본 실험에 사용된 10kHz~30kHz 주파수 범위에서 쐐기각이 같은 흡음판에 의한 반사음장의 크기는 주파수와 무관하였다. 그리고 쐐기형 흡음타일 후면에서 측정한 반사음장의 크기는 흡음판의 형태와 실험에 사용된 주파수들에 무관한 일정한 값을 가졌다. 쐐기형 흡음타일의 반사음장에 대한 측정값과 수치모델에 의한 계산값은 대체로 잘 일치하였다.

• 한국소음진동공학회논문집
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• 제20권11호
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• pp.1078-1088
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• 2010

In order to analyze the quantitative characteristics of acoustic streaming, experimental setup of 3-D stereoscopic PIV(particle imaging velocimetry) was designed and quantitative ultrasonic flow fields in the gap between the ultrasonic vibrator and heat source were measured. Utilizing acoustic streaming induced by ultrasonic vibration, surface temperature drop of cooling object was also measured. The study on smart cooling method by acoustic streaming induced by ultrasonic vibration was performed due to the empirical relations of flow pattern, average flow velocity, different gaps, and enhancement on cooling rates in the gap. Average velocity fields and maximum acoustic streaming velocity in the open gap between the stationary cylindrical heat source and ultrasonic vibrator were experimentally measured at no vibration, resonance, and non-resonance. It was clearly observed that the enhancement of cooling rates existed owing to the acoustic air flow in the gap at resonance and non-resonance induced by ultrasonic vibration. The ultrasonic wave propagating into air in the gap creates steady-state secondary eddy called acoustic streaming which enhances heat transfer from the heat source to encompassing air. The intensity of the acoustic streaming induced by ultrasonic vibration experimentally depended upon the gap between the heat source and ultrasonic vibrator. The ultrasonic vibration at resonance caused the increase of the acoustic streaming velocity and convective heat transfer augmentation when the flow fields by 3D stereoscopic PIV and temperature drop of the heat source were measured experimentally. The acoustic streaming velocity of air enhancement on cooling rates in the gap is maximal when the gap agrees with the multiples of half wavelength of the ultrasonic wave, which is specifically 12 mm.

• 에너지공학
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• 제13권2호
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• pp.152-160
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• 2004

The present study investigates on the experimental and numerical results of heat transfer in the acoustic fields induced by ultrasonic waves. The strong upwards flow which moves from the bottom surface in a cavity to the free surface called as "acoustic streaming" was visualized by a particle image velocimetry (PIV). In addition, the augmentation ratio of heat transfer was experimentally investigated in the presence of acoustic streaming and was compared with the profiles of acoustic pressure calculated by the numerical analysis. A coupled finite element-boundary element method (FE-BEM) was applied for a numerical analysis. The results of experimental and numerical studies clearly show that acoustic pressure variations caused by ultrasonic waves in a medium are closely related to the augmentation of heat transfer.

• Journal of Mechanical Science and Technology
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• 제15권5호
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• pp.555-561
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• 2001

A new approach to analyze the multi-domain acoustic system divided and enclosed by flexible structures is presented in this paper. The boundary element formulation of the Helmholtz integral equation is used for the internal fields and the finite element formulation for the structures surrounding the fields. We developed a numerical analysis program for the structural-acoustic coupling problems of the multi-domain system, in which boundary conditions such as the continuity of normal particle velocity and sound pressure in the structural interfaces between Field 1 and Field 2 are not needed. The validity of the numerical analysis program is verified by comparing the numerical results with the experimental ones. Example problems are included to investigate the characteristics of the coupled multi-domain system.

• 한국자동차공학회논문집
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• 제6권1호
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• pp.182-195
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• 1998

The relation between the vibration induced from machinery and the radiated sound is complicated. Acoustic intensity method is widely used to obtain the accuracy of noise identification. In this study, as groundwork, the complex acoustic intensity method is performed to identify noise source and transmission path on different free space point source fields. From the numerical analysis for these simple fields, it is possible to predict the sound field characteristics which noise sources are related with each other, and certificate the validity of complex acoustic intensity. As an industrial application, the complex acoustic intensity method is applied a diesel engine to identify sound radiation characteristics in the near field.

• KIEAE Journal
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• 제9권6호
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• pp.81-87
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• 2009

The purpose of the present study is to establish structural noise analyzing method for apartments building floor with structural-acoustic coupling analysis modeling. Noise through floor in the room is recognized as a significant problem with the consequence that noise isolation technique has been studied in the various fields of industry. From among noise factors, resonance sound is the main reason for solid noise of the floor, which is occurred by mechanical vibrations of the acoustic boundary line and the change of velocity. To analyse this phenomenon, numerical computation methods are provided in many fields, In this study, evaluation method for slab is established using finite element method, and a case study for analyzing acoustic phenomenon was suggested. The results show that numerical method, especially F.E.M, has a good approximation to predict noise at floors.