A Study on Correlation Between Pressure Variations and Augmentation of Heat Transfer in Acoustic Fields

Oh, Yool-Kwon,Yang, Ho-Dong The Korean Society of Mechanical Engineers 2004 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.18 No.9

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.

채널별 음장분포 분석을 통한 진단용 초음파 어레이 프로브의 평가방법에 관한 연구

유병철,최흥호,노시철,민해기,권장우,Yoo, B.C.,Choi, H.H.,Noh, S.C.,Min, H.K.,Kwon, J.W. 대한의용생체공학회 2006 의공학회지 Vol.27 No.5

The acoustic field analysis method is the superior calibration method for rectifying the ultrasonic probe sensitivity. This method also can be applied to evaluate the probe performance in clinical fields without numerical analysis and precise measurements. In this paper, we propose the method of acoustic field pattern analysis with probe channel division for the evaluation of diagnostic ultrasound probe characterization. In order to verify our purpose, we performed a set of experiments. We measured the acoustic-field pattern of the three inferiority probes by channel division to evaluate an acoustic field distribution and impulse response characteristics. By comparing the results of acoustic field measurement method with that of conventional method such as impulse response and live image test for linear array probes, it is demonstrated that the ultrasound field measurement method is more effective then conventional method in detection of defective elements.

Electric field effects on the dielectric and acoustic anomalies of Pb[(Mg_1/3Nb_2/3)_0.83Ti_0.17]O₃ single crystals studied by dielectric and Brillouin spectroscopies

Kim, T.H.,Kojima, S.,Ko, J.H. Elsevier 2014 CURRENT APPLIED PHYSICS Vol.14 No.12

The effect of the electric field on the dielectric and acoustic properties of Pb[(Mg<SUB>1/3</SUB>Nb<SUB>2/3</SUB>)<SUB>0.83</SUB>Ti<SUB>0.17</SUB>]O<SUB>3</SUB> single crystals was investigated as functions of temperature and the electric field strength. The dielectric constant and the acoustic mode behaviors exhibited typical relaxor behaviors when there was no bias field. The longitudinal acoustic mode showed splitting under a moderate electric field of 1 kV/cm applied along the [001] direction, indicating coexistence of macroscopic/mesoscopic ferroelectric states and relaxor states. Further increase in the electric field up to 2 kV/cm induced a clear ferroelectric phase transition, which became smeared out due to the proximity of the electric field to the critical point. The electric field-temperature phase diagram of Pb[(Mg<SUB>1/3</SUB>Nb<SUB>2/3</SUB>)<SUB>0.83</SUB>Ti<SUB>0.17</SUB>]O<SUB>3</SUB> was suggested based on the observed field-induced changes in the dielectric and the acoustic properties.

Electric field effects on the dielectric and acoustic anomalies of Pb [(Mg1/3Nb2/3)0.83Ti0.17]O3 single crystals studied by dielectric and Brillouin spectroscopies

김태현,Seiji Kojima,고재현 한국물리학회 2014 Current Applied Physics Vol.14 No.12

The effect of the electric field on the dielectric and acoustic properties of Pb[(Mg1/3Nb2/3)0.83Ti0.17]O3 single crystals was investigated as functions of temperature and the electric field strength. The dielectric constant and the acoustic mode behaviors exhibited typical relaxor behaviors when there was no bias field. The longitudinal acoustic mode showed splitting under a moderate electric field of 1 kV/cm applied along the [001] direction, indicating coexistence of macroscopic/mesoscopic ferroelectric states and relaxor states. Further increase in the electric field up to 2 kV/cm induced a clear ferroelectric phase transition, which became smeared out due to the proximity of the electric field to the critical point. The electric field-temperature phase diagram of Pb[(Mg1/3Nb2/3)0.83Ti0.17]O3 was suggested based on the observed field-induced changes in the dielectric and the acoustic properties.

3차원 밀폐음장에서의 능동소음 제어에 관한 연구

이규태,이태연 조선대학교 생산기술연구소 1993 生産技術硏究 Vol.15 No.2

A computer simulation is performed on the effectiveness of the active minimization of harmonically excited enclosed sound fields for producing global reductions in the amplitude of the pressure fluctuations. In this study for the appreciable reductions in total time averaged acoustic potential energy, E_(pp), the transducer location strategies for three dimensional active noise control is presented based on a state space modal model which approximates the closed acoustic field. In this study, the above theoretical basis is used to investigate the application of active control to sound fields of low modal density. By the use of room-like 3-dirnensional rectangular enclosure it is demonstrated that the reductions in E_(pp) are critically dependent on the source locations. In particular it is shown that for a lightly damped sound field of low modal density substantial reductions in E_(pp) can be achieved by using a single secondary source, provided that the source is placed placed within the half a wavelength from the primary source and placed away from nodal line of the sound field. Concerning the reductions in E_(pp) by minimizing the pressure in sound fields by the use of 3-dimensional rectangular enclosure, the effects of the number of sensors and the locations of these sensors are investigated. When a few modes dominate the response it is found that if only a limited number of sensors are located away from nodal line and located at the pressure maxima of the sound field such as at each cornor of a rectangular enclosure.

Near Bed Turbulence Measurement with Acoustic Doppler Velocimeter (ADV)

M. S. Sulaiman,S. K. Sinnakaudan,M. R. Shukor 대한토목학회 2013 KSCE Journal of Civil Engineering Vol.17 No.6

Acoustic Doppler Velocimeter (ADV) has become prominent device in flow and turbulence measurement. The in situ turbulence measurement requires laboratory-quality data to be obtained in the field. Thus, ADV vector type provides a better choice for flow measurement at field scale. A field study was undertaken at sand-gravel bed rivers to observe the flow field and turbulence characteristics in the presence of protuberant clast. Profile measurements were executed at near bed region to characterize the flow and turbulence characteristics at the proximity of clast reference. Four major areas were identified as sampling location relative to clast reference namely stoss side, adjacent area, wake area and the downstream area. Besides, bed load measurement was carried out concurrently to elucidate the possible relation between flow variation and transport rates. Physical meaning of flow field is expressed in term of mean velocity, turbulent intensity, turbulent kinetic energy, Reynolds stresses and horizontal-vertical interaction, local bed shear stress and quadrant analysis. It is postulated that the presence of protuberant clast modifies flow field and affect transport rates. Possible occurrences of transport rates are subject to accurate estimation of acting forces on moving particles. Estimation of critical Shields stress from Reynolds extrapolation provides better comparison with actual transport rates. Besides, contribution rate to Reynolds stress analysis compliment the importance of sweeps and ejection events to occurrence of bed load transport.

Measurement of the normal acoustic impedance using beamforming method

선종천,신창우,주형준,백순권,강연준 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.8

A beamforming technique is introduced to measure the normal acoustic impedance at both normal and oblique incidence in a free field. In the proposed method, microphone array signals are decomposed into incident and reflected waves using an adaptive nulling algorithm, which is a type of beamforming algorithm. The acoustic impedance can then be calculated from the ratio of these two signals. To obtain better results, the pressure vector commonly used in array signal processing is replaced with the transfer function vector between each microphone, and the white Gaussian noise is suppressed by a wavelet shrinkage technique. For an accurate experimental setup, the incident and reflected angles are estimated by the multiple signal classification method with spatial smoothing. The experiments conducted in a semi-anechoic room show that the proposed method is efficient and accurate in measuring the normal acoustic impedance of sound-absorbing materials under a free field condition.

Design and Analysis of Experimental Anechoic Chamber for Localization

Kim, Keon-Wook The Acoustical Society of Korea 2012 韓國音響學會誌 Vol.31 No.4

The anechoic chamber is essential tool to measure the various acoustic parameters with high precision. The chamber provides the climate controlled indoor environments but requires the dedicated room at a great cost in order to isolate and absorb sound field. Provided the purpose of the chamber is specific to the experiments of sound localization, the performance requirements excluding free field can be alleviated for cost effective solution. This paper designs low cost and profile anechoic chamber based on acoustic pyramids and evaluates the performance specified by the Annex of ISO 3745. Data analysis is employed to measure the free and hemi-free field performance over five straight paths for working areas and four paths for non-working areas. The identical two measurement campaigns were conducted for free and hemi-free field chamber which is easily interchangeable by simple labor in this chamber design. In the working area with conventional speaker, the results of these analyses demonstrate that lab-designed anechoic chamber is in conformance with ISO 3745 for 250 Hz - 16 kHz one-third octave band at free field chamber and for 1 kHz - 16 kHz one-third octave band at hemi-free field chamber.

자유 음장 조건에서 빔형성 방법을 이용한 수직 및 경사입사 음향 임피던스의 측정

신창우(Chang Woo Shin),선종천(Jong Choen Sun),강연준(Yeon June Kang),백순권(Soon Kwon Paik) 한국자동차공학회 2007 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

The improved Beamforming method is proposed to measure the acoustic impedance and absorption coefficient in a free field. It is possible to estimate the acoustic impedance by separating incident and reflected signals with the Adaptive Nulling Method. The wavelet shrinkage method is applied to reduce the White Gaussian noise. Transfer function vector is used for obtaining better results instead of pressure vector. The proposed method was verified by the comparison of measurement and theoretical method. The results show that the proposed method is efficient to measure acoustic impedance for frequencies higher than 400 ㎐.

음향 부양장(acoustic levitation field)에서 초음파 주파수(ultrasonic frequency)에 따른 단일 액적의 미립화 특성

서현규 ( Hyun Kyu Sub ) 한국분무공학회 2013 한국액체미립화학회지 Vol.18 No.3

This paper describes the effect of ultrasonic frequency(f) on the atomization and deformation characteristics of single water droplet in an acoustic levitation field. To achieve this, the ultrasonic levitator that can control sound pressure and velocity amplitude by changing frequency was installed, and visualization of single water droplet was conducted with high resolution ICCD and CCD camera. At the same time, atomization and deformation characteristics of single water droplet was studied in terms of normalized droplet diameter(d/d0), droplet diameter(d) variation and droplet volume(V) variation under different ultrasonic frequency(f) conditions. It was revealed that increase of ultrasonic frequency reduces the droplet diameter that is able to levitate with low sound pressure level. It also induces the wide oscillation range, large diameter and volume variation of water droplet. In conclusion, the increase of ultrasonic frequency(f) can enhance the atomization performance of single water droplet.