• Title/Summary/Keyword: Acoustic field simulation

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Simple Estimation of Sound Source Directivity in Diffused Acoustic Field: Numerical Simulation (확산음향장에서의 음원 지향성 간이추정: 수치시뮬레이션)

  • Kim, Kookhyun
    • Journal of Ocean Engineering and Technology
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    • v.33 no.5
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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.

Practical Application of Virtual Acoustic Field Simulation System(VAFSS) (능동형 음장조성시스템의 적용 사례)

  • Park, Sa-Keun;Jang, Gil-Soo;Kook, Chan;Song, Min-Jeong;Jeon, Ji-Hyeon;Shin, Hoon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2006.05a
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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.

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Study of Acoustic Holography using Equivalent Source Method with Continuation of Acoustic Near-field (근접음장 연속법과 등가 음원법을 이용한 음향홀로그래피 연구)

  • Kim, Sung-Hoon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2011.10a
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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.

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Quantitative evaluating method for diagnostic ultrasound probe using 3-dimensional acoustic field analysis (3차원 음장 분석법을 이용한 진단용 초음파 프로브의 정량적 성능평가)

  • Noh, Si-Cheol;Kim, Ju-Young;Park, Jae-Hyun;Kim, Jin-Su;Kang, Jung-Hoon;Choi, Heung-Ho
    • Journal of Sensor Science and Technology
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    • v.19 no.6
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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.

PREDICTION OF TURBULENCE TRAILING-EDGE NOISE AT LOW MACH NUMBERS (저마하수 난류 끝단 소음 예측)

  • Chang K.W.;Koh S.R.;Seo J.H.;Moon Y.J.
    • 한국전산유체공학회:학술대회논문집
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    • 2005.10a
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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.

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Computer Simulation for Noise Source Identification and Application to Vehicle Using Complex Acoustic Intensity Method (복소음향 인텐시티법을 이용한 소음원검출의 시뮬레이션 및 실차응용)

  • O, Jae Ung;Kim, Sang Heon;An, Ji Hun
    • Transactions of the Korean Society of Automotive Engineers
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    • v.5 no.3
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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.

Enhancing Nearfield Acoustic Holography using Wavelet Transform

  • Ko, ByeongSik
    • Journal of Mechanical Science and Technology
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    • v.18 no.10
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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.

Computation of Underwater Acoustic Field Using Acoustic Impedance as an Input Parameter for the Ocean Bottom (음향 임피던스를 해저면 입력인자로 이용하는 수중음장 계산)

  • Lee Seongwook;Oh Taekhwan;Na Jungyul;Lee Phil-Ho;Yoon Jong Rak
    • The Journal of the Acoustical Society of Korea
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    • v.25 no.1
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    • pp.1-6
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    • 2006
  • The Possibility of using acoustic impedance as an input Parameter for computation of underwater acoustic field in shallow waters was investigated. Analysis of the acoustic reflection from the ocean bottom with shear wave effect showed that acoustic impedances below the critical grazing angle have nearly angle-independent property and could be approximated with a single value of near-grazing impedance $Z_0$. Computations of the Propagation loss based on the concept of 'effective depth' indicate that near-grazing bottom acoustic impedances could be used as an input parameter for simulation of the acoustic fields in shallow waters.

Acoustic field simulation of a PZT4 disc projector using a coupled FE-BE method

  • Jarng, S.S.
    • Journal of Sensor Science and Technology
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    • v.8 no.3
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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.

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Control of Flow-Induced Noise from a Round Jet using Active Excitation (능동 가진을 이용한 원형 제트에서의 유동 소음 제어)

  • Kim, Jung-Woo;Cha, Seong-Dae;Choi, Hae-Cheon
    • Proceedings of the KSME Conference
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    • 2003.11a
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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.

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