• 한국해양공학회지
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• 제33권5호
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• pp.421-426
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• 2019

The directivity of an underwater sound source should be measured in an acoustically open field such as a calm sea or lake, or an anechoic water tank facility. However, technical difficulties arise when practically implementing this in open fields. Signal processing-based techniques such as a sound intensity method and near-field acoustic holography have been adopted to overcome the problem, but these are inefficient in terms of acquisition and maintenance costs. This study established a simple directivity estimation technique with data acquisition, filtering, and analysis tools. A numerical simulation based on an acoustic radiosity method showed that the technique is practicable for sound source directivity estimation in a diffused reverberant acoustic field like a reverberant water tank.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.738-741
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• 2006

Virtual Acoustic Field Simulation System (VFASS) has been developed through soundscape technique research for making comfortable acoustic environment in urban public places. This system could suggest Introducing sounds which are suitable for certain area, Also this system gives certain area vitalities and amenity through with the correspondence to time, temperature, humidity, wind velocity and sunshine of the area. In this paper, Application possibility of VFASS is examined how can be adapted to D University square as a case study.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.643-648
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• 2011

This paper deals with the ESM(equivalent source method) with the continuation of acoustic near-field for NAH(near-field acoustic holography) to overcome the finite measurement aperture effect and reconstruct the normal velocity on an arbitrarily shaped structure surface. The continuation method is an extension of the measured sound field into a region outside and is based on the Green's function relating acoustic quantities on the two conformal surfaces. This algorithm is not limited to planar surfaces and can be applied to arbitrarily shaped surfaces. The ESM is an alternative approach of BEM-based NAH for the reconstruction on a general structure. In ESM the acoustic field is represented by a set of point sources located over a surface that is close to the structure surface. The simulation results of this study shows that the reconstruction error of particle velocity on the source surface is 11% and 16% for planar and cylindrical sources separately.

• 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.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.249-253
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• 2005

The turbulence noise generated from blunt trailing-edge is numerically predicted by using the hydrodynamic/acoustic splitting method at the Reynolds number based on thickness of flat plate, $Re_h=1000$, and the freestream Mach number $M_o=0.2$. The turbulent flow field is simulated by incompressible large-eddy simulation and the acoustic field is predicted efficiently with the linearized perturbed compressible equations (LPCE) recently proposed by the authors. The turbulent flow characteristics are validated with the results of the previous experimental study and direct numerical simulation. The acoustic properties predicted from LPCE are compared with the solutions of analytical formulations.

• 한국자동차공학회논문집
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• 제5권3호
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• pp.171-171
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• 1997

Sound intensity distributions and energy flow in the near field of dipole source system and flat plate were investigated. First, the effectiveness of complex acoustic intensity was proved by using mathmatical and experimental methods in order to indentify noise sources and transmission paths of dipole field which is effected by the presence of neighbouring coherent sources. Next, analytical complex acoustic intensity method was discussed and the characteristics and energy flow of sound induced from the plate are clarified. The velocity of plate obtained from Finite Element Method was used for calculation of complex acoustic intensity in the near field. Finally experimental complex acoustic intensity method was applied to a passenger car. It can be seen that complex acoustic intensity method using both of active and reactive intensity is vital in devising a strategy for the identification and the reduction of vibration and noise.

• Journal of Mechanical Science and Technology
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• 제18권10호
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• pp.1738-1746
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• 2004

When there are low signal to noise relationships or low coherences between measured pressure and a reference sensor, a pressure field measured and estimated by NAH (Nearfield Acoustic Holography) becomes noisy on the hologram and source planes. This paper proposes a method to obtain the high coherent de-noised pressure signals from low coherent noisy ones by combining a wavelet algorithm with NAH. The proposed method obtains the de-noised field from acoustic fields on a noise source plane reconstructed through backward propagation of NAH. Thus this method does not need high coherent pressure signals on the hologram surface while the conventional nearfield acoustic holography requires high-coherent signals. The proposed method was verified by numerical simulation using noisy signals, composed of original signals and imposed noises distributed on the hologram surface.

• 한국음향학회지
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• 제25권1호
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• pp.1-6
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• 2006

천해에서의 수중음장 계산에서 음향 임피던스를 해저면 입력인자로서 도입하는 방안의 가능성을 고찰하였다. 먼저 탄성 해저면에서의 음파반사 특성을 고찰한 결과, 임계 접지각 이하에서 음향 임피던스는 접지각이 거의 $0^{\circ}$에 가까울 때의 임피던스 $Z_0$ 1개 값으로 근사가 가능함을 나타내었다. 이러한 특성과 'effective depth' 개념을 접목시켜 전달손실을 계산한 결과, 수중음장 계산에서 임피던스를 해저면 음향 특성을 나타내는 입력인자로 사용하는 것이 가능성이 있음을 확인하였다.

• 센서학회지
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• 제8권3호
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• pp.211-218
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• 1999

This paper describes the application of a coupled finite element-boundary element method (FE-BEM) to obtain the steady-state response of a piezoelectric transducer. The particular structure considered is a PZT4 disc-typed projector. The projector is three-dimensionally simulated to transduce applied electric charge on axial surfaces of the piezoelectric disc to acoustic pressure in air or in water. The directivity pattern of the acoustic field formed from the projected sound pressure is also simulated. And the displacement of the disc caused by the externally applied electric charge is shown in temporal motion. The coupled FE-BE method is described in detail.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.798-803
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• 2003

The objective of the present study is to investigate the changes in the acoustic source characteristics and far-field noise propagation in an incompressible round jet at Re=10000 for single-frequency excitations using large eddy simulation and Lighthill acoustic analogy. We apply excitations at a frequency corresponding to the jet-column mode ($St_{D}=0.85$) or maximum growth rate in the shear layer ( $St_{\theta}=0.017$ ). The acoustic source derived from the Lighthill acoustic analogy is the second spatial derivative of the Reynolds stresses. In the case of $St_{D}=0.85$, vortex ring and large scale structures are dominant sources, whereas in the case of $St_{\theta}=0.017$, the main sources are located at an upstream position along the shear layer than in the uncontrolled case. Also, the far-field noise propagates along the axial direction due to excitation.