• 한국소음진동공학회논문집
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• 제15권4호
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• pp.412-420
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• 2005

This article proposes analytical solutions for sound radiation from radial vibration modes of a thick annular disk. Structural eigensolutions are calculated using the transfer matrix method. The far-field sound pressure distribution is obtained using two alternate methods. In the first method, pressure is calculated using the Rayleigh integral technique. The second method treats sound radiating radial surfaces as cylindrical radiators of finite length. The Sinc function approach is employed for calculations. Acoustic powers and radiation efficiencies of radial modes are also determined from the far-field sound pressure calculations. Analytical predictions match well with measured data as well as computational results from a finite element code in terms of structural eigensolutions and from a boundary element code in terms of sound pressure, directivity etc.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.680-690
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• 2020

In ocean environment, the sound speed gradient of seawater has an important influence on far field sound propagation. The FEM/BEM is used to decouple the vibroacoustic radiation of the spherical shell, and the Green function of the virtual source chain is adopted for decoupling. For far field radiated Sound Pressure Level (SPL), the Beam Displacement Ray normal Mode (BDRM) is employed. The vibration and near-/far-field radiated SPL of spherical shell is analyzed in shallow sea uniform layer, negative/positive gradient, negative thermocline environment, and deep-sea sound channel. Results show that the vibroacoustic radiation of spherical shell acted at 300Hz can be analogous to dipole. When the radiated field of the spherical shell is dominated by large-grazing-angle waves, it can be analogous to vertically distributed dipole, and the far field radiated SPL is lower; while similar to horizontally distributed dipole if dominated by small-grazing-angle waves, and the far field SPL is high.

• 비파괴검사학회지
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• 제35권2호
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• pp.134-140
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• 2015

전통적인 뜸 요법은 시술자의 주관적이고 정성적인 치료로 인해 환자의 피부에 강한 열 자극이 가해져 심한 통증을 주거나 화상을 입히는 문제점을 갖고 있다. 이러한 한계를 극복하기 위한 대안으로 객관성과 정량화가 가능한 초음파를 활용한 뜸 자극 치료기술이 주목받고 있다. 하지만, 초음파 에너지를 열에너지로 변환하기 위해서는 초음파 치료기기의 음향렌즈에 따른 초음파 집속 특성 분석이 필요하다. 따라서, 본 논문에서는 초음파 집속 특성에 영향을 주는 음향렌즈의 형태(오목렌즈, 계단형 렌즈)에 따른 집속 시뮬레이션을 통해 각 렌즈의 음압 분포, 음압의 크기, 초점의 위치를 계산하였으며, 설계한 렌즈를 제작하여 음압 측정 실험을 통해 음향렌즈의 집속 성능을 검증하였다.

• 대한의용생체공학회:의공학회지
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• 제43권6호
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• pp.369-374
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• 2022

Purpose: Focused ultrasound is an emerging technology for treating the brain locally in a noninvasive manner. In this study, we have investigated the influence of skull properties on simulating transcranial pressure field. Methods: A 3D computational model of transcranial focused ultrasound was constructed using female and male CT data to solve for intracranial pressure. For heterogeneous model, the acoustic properties were calculated from CT Hounsfield units based on a porosity. The homogeneous model assigned constant acoustic properties for the single-layered skull. Results: A computational model was validated against empirical data. The homogeneous models were then compared with the heterogeneous model, resulted in 10.87% and 7.19% differences in peak pressure for female and male models respectively. For the focal volume, homogeneous model demonstrated more than 94% overlap compared with the heterogeneous model. Conclusion: Homogeneous model can be constructed using MR images that are commonly used for the segmentation of the skull. We propose the possibility of the homogeneous model for the simulating transcranial pressure field owing to comparable focal volume between homogeneous model and heterogeneous model.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.1767-1771
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• 2000

We report the number of calibration and test for acoustic field which were conducted in KRISS between the year of 1990 and 1999. The items contain sound level meter and calibrator for calibration and sound absorption coefficient, transmission loss, sound pressure level of siren, sound pressure level and power of acoustic instrument and relative accessories for test. The data show that the number of them have been increased continuously.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1869-1874
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• 2004

Acoustic pressure field around the cross-flow fan is predicted by a hydrodynamic-acoustic splitting method. Unsteady flow field is obtained by solving the incompressible Navier-Stokes equations using an unstructured finite-volume method on the triangular meshes, while the acoustic waves generated inside the cross-flow fan are predicted by solving the perturbed compressible equations(PCE) with a 6th-order compact finite difference method. Computational results show that the acoustic waves of BPF tone are generated by interactions of the blades wakes with the stabilizer, which then are reflected from the rear-guider and mainly propagate towards the fan inlet. Also, a directivity of BPF noise predicted by the PCE is noticeably different from that of the FW-H equations, in which a fan casing effect cannot be included.

• 한국음향학회지
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• 제36권3호
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• pp.165-171
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• 2017

유체로 채워진 원통형 압전진동자 내부에서 중심축으로 집속되는 음파에 대해 진동자 내부에 삽입된 동심원의 고체튜브가 음장분포에 미치는 영향을 해석하였다. 원통형 압전진동자의 내부로부터 방사된 음파는 유체매질을 지나 고체튜브의 벽면에서 반사 및 투과를 하여 중심축에 집속된다. 이때 고체튜브의 음향임피던스 및 두께 등에 의해 중심에 집속되는 음장 분포가 변한다. 이를 이론적으로 해석하기 위하여 각 매질에 대한 전달행렬을 도출하였고 이를 적용하여 중심축에서의 음압수준을 이론적으로 해석하였다. 여러 가지 두께를 갖는 아크릴 튜브에 대해서 중심축 상에서 측정한 음압수준의 변화는 이론해석의 결과와 잘 일치하였으며 중심에 형성되는 음압은 고체튜브의 두께에 따라 매우 민감하게 변화함을 확인하였다.

• 소음진동
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• 제8권3호
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• pp.435-440
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• 1998

The main objective of this study is to estimate location and strength of sound sources distributed on the surface of an enclosure. Acoustic holography method has been used to identify the sources in an interior sound field. However, it can not completely distinguish between the direct sound field from sources and the reflections from surfaces. The method just reconstructs the entire sound field based on the sound pressure at the finite number of measurement points. In this stduy, a method which estimates only the active sources by using measurements of field pressure and surface admittance is proposed. An in-situ technique to estimate the general boundary condition is also proposed by using acoustic holography, assuming the surfaces are locally reacting.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.629-632
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• 2005

What does sound look like if we can see it? It might depend on the acoustic variables we want to see. In this article, we propose various ways to visualize or express sound field in much more intuitive manner. In particular, new visualization schemes that can effectively visualize sound intensity and 3D pressure field are proposed. This allows us to represent sound pressure, particle velocity and acoustic conductance at the same time, even in three-dimensional coordinate. Visualization examples corresponding to the proposed techniques show that we can successfully transfer the meaning of physical variable to visual space.

• 소음진동
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• 제7권6호
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• pp.919-929
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• 1997

Induction motors are used in many areas to transform electrical energy to mechanical energy. In the design of an induction motor, not only energy efficiency but also noise becomes an important factor. To effectively address the noise problem, it will be convenient if one can see where and how noise is generated and propagated. In this study sound radiation by an induction motor is visualized using cylindrical acoustic holography. To minimize the bias error by window effect Minimum Error Window(MEW) is used. Its performance is verified by numerical simulations. Based on these theoretical understanding, sound pressure measurement with an induction motor are performed. Not only sound radiation are visualized but sound pressure level and sound power level are also estimated. Results show that the main source is located at nearly bottom part of the motor and the total sound pressure level is 49dB, which satisfies the guideline value suggested by the KS C 4202.