• Title/Summary/Keyword: 고유음향임피던스

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축대칭 셸의 음향방사 해석에 관한 연구

  • 홍진선;이장무
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.4
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    • pp.797-802
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    • 1990
  • 본 연구에서는 축대칭 셸의 고유모우드에 의하여 발생하는 음향의 방사특성을 유한요소법으로 구하고 실험을 수행하여 그 타당성을 검토하였다.축대칭 셸에서 원 주방향으로의 압력분포를 가정하여 2차원 문제로 단순화시키고 거리가 무한대인 영역 은 음향 임피던스 (acoustic impedance)를 이용하여 대처함으로써 축대칭 셸의 고유모 우드에 의하여 발생하는 음향세기와 방사효율을 구하였다. 각각의 고유모우드에 의 하여 방사되는 에너지는 서로 독립적이므로 강제진동에 의한 음향의 방사효율은 고유 모우드에 의한 방사효율의 가중치에 의한 평균(weighted average)을 취함으로써 구할 수 있다.

Acoustic Properties of Ultrasonic Transducer Using Piezocomposites (압전복합재료를 이용한 초음파 트랜스듀서의 음향 특성)

  • Lee, Sang-Wook;Ryu, Jeong-Tag;Nam, Hyo-Duk;Kim, Yeon-Bo
    • The Journal of the Acoustical Society of Korea
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    • v.26 no.2
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    • pp.80-86
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    • 2007
  • We have investigated on the development of 2-2 type piezocomposites that have better piezoelectric activity and lower acoustic impedance than those of conventional piezoceramics. In this study, we have investigated the piezoelectric and acoustic properties of 2-2 type piezocomposites sensor which was fabricated using dice-and-fill technique for the different volume fraction of PZT. The specific acoustic impedance of 2-2 type piezocomposites decreased linearly when PZT volume fraction was decreased. The resonance characteristics measured by an impedance analyzer(HP4194A) were similar to the analysis of finite element method (FEM). The resonance characteristics and the electromechanical coupling factor were the best when the volume fraction PZT was 0.6. It also showed the highest result from the standpoint of sensitivity, bandwidth and ring-down property and so on at the same condition. The specific characteristics show that the 2-2 type piezocomposites turned out to be superior to the ultrasonic sensor composed by single phase PZT.

An Analysis of the Sound Transmission through a Plate Installed inside an Impedance Tube (임피던스 튜브 내에 설치된 평판의 음파투과해석)

  • Kim, Hyun-Sil;Kim, Bong-Ki;Kim, Sang-Ryul;Lee, Seong-Hyun
    • The Journal of the Acoustical Society of Korea
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    • v.34 no.3
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    • pp.219-226
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    • 2015
  • In this paper, derivation of the STL (Sound Transmission Loss) of a square plate installed in an impedance tube is discussed using an analytic method. Coupled motion of the plate vibration and acoustic field is considered. Vibration of the plate and pressure field inside the tube are expressed in terms of the infinite series of modal functions. Under the plane wave assumption, it is shown that consideration of the first few modes yields sufficiently accurate results. When the boundary of the plate is clamped, vibration mode is assumed as a multiplication of the beam modes corresponding to the crosswise directions. The natural frequencies of the clamped plate are calculated using the Rayleigh-Ritz method. It is found that the STL shows a dip at the lowest natural frequency of the plate, and increases as the frequency decreases below the natural frequency. Comparison of the result in this paper with the STL obtained by measurements and FE computations in the reference shows an excellent agreement.

Analysis of the Propagation Characteristics of Two Dimensional Ultrasonic Fields in Layered Media (층상매질에서의 이차원 초음파음장 전파특성해석)

  • 윤혁준
    • Proceedings of the Acoustical Society of Korea Conference
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    • 1998.06c
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    • pp.445-448
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    • 1998
  • 고유음향 임피던스가 다른 물질이 층상구조를 이루고 있는 매질내에서 임의의 한 층에 형성된 이차원 초음파 음장이 다른 매질로 전파될 때에의 특성을 각스펙트럼법에 의해 해석하였다. 음원으로서는 baffle된 원형 트랜스듀서를, 층상구조를 매질로서는 물과 생체조직(지방)의 경계를 각각 고려하였다. 해석에 있어서는 먼저 각스펙트럼 분해요소, 즉, 음원의 크기 및 거리에 의존하는 기준음장의 최적 크기와 샘플링 간격을 균질매질을 이용하여 결정한 다음, 그 요소를 층상매질에 적용하였다. 그 결과, 경계면에서의 입사각(공간주파수)의 의존하는 투과계수에 입사음장의 곱으로 나타내어지는 투과음장은 각스펙트럼법에 의해 짧은 시간내에 정도 높게 산출될 수 있음을 보인다.

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A study of the intake manifold design for 4-cylinder high speed gasoline engine (4기통 고속 가솔린 기관의 흡기관 설계에 관한 연구)

  • 정동수;강건용;엄종호;우세종
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.5
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    • pp.1674-1682
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    • 1991
  • 본 연구에서는 4기통 고속 가솔린 기관의 흡기관 내 유체유동이 체적효율에 미치는 동적효과를 고려하여, 흡기관에 임피던스를 이용한 음향학적 방법을 이용해서 흡기관 최적설계를 해석하고, 기관실험을 통해 그 신뢰성을 확인하고자 한다.

Effects of the Shape and the Absorption in Reverberation Rooms on the Space Variances of the Sound Pressure Level (잔향실의 형상(치수비)과 내부표면 흡음율이 음압의 공간편차에 미치는 영향)

  • 최석주;장영자
    • The Journal of the Acoustical Society of Korea
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    • v.18 no.4
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    • pp.65-70
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    • 1999
  • To examine the space variances of the sound pressure level for five different types (normal frequency spacing) of reverberation rooms, simulations were conducted using the Finite Element Method. In case of infinite surface impedance, nonrectangular reverberation rooms showed small Standard Deviations across the band of frequency, and in case of finite surface impedance, ideal rectangular reverberation rooms showed the similar results as those in irregular shaped reverberation rooms.

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A study on the sound transmission through double plates installed inside an impedance tube (임피던스 튜브 내에 설치된 이중 평판의 음파투과연구)

  • Kim, Hyun-Sil;Kim, Bong-Ki;Kim, Sang-Ryul;Seo, Yun-Ho;Ma, Pyung-Sik
    • The Journal of the Acoustical Society of Korea
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    • v.35 no.4
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    • pp.253-260
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    • 2016
  • In this paper, derivation of the STL (Sound Transmission Loss) of the double plates installed in an impedance tube is discussed using an analytic method, where an air cavity exists between the plates. Vibration of the plates and sound pressure field inside the tube are expressed in terms of infinite series of modal functions. Under the plane wave assumption, it is shown that consideration of the first few modes yields sufficiently accurate results, and locations of peaks and dips are investigated. It is determined that the peak frequencies of the double plates coincide with those of each single plate. When the two plates are identical, the STL of the double plates as well as that of the single plate become zero at the natural frequencies of the single plate. The location and amplitude of the dips are investigated using an approximation solution when the cavity depth is very small.

Development of Helmholtz Solver for Thermo-Acoustic Instability within Combustion Devices (연소시스템의 열음향 불안정 예측을 위한 Helmholtz Solver 개발)

  • Kim, Seong-Ku;Choi, Hwan-Seok;Cha, Dong-Jin
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.38 no.5
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    • pp.445-455
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    • 2010
  • In order to effectively predict thermo-acoustic instability within real combustors of rocket engines and gas turbines, in the present study, the Helmholtz equation in conjunction with the time lag hypothesis is discretized by the finite element method on three-dimensional hybrid unstructured mesh. Numerical nonlinearity caused by the combustion response term is linearized by an iterative method, and the large-scale eigenvalue problem is solved by the Arnoldi method available in the ARPACK. As a consequence, the final solution of complex valued eigenfrequency and acoustic pressure field can be interpreted as resonant frequency, growth rate, and modal shape for acoustic modes of interest. The predictive capabilities of the present method have been validated against two academic problems with complex impedance boundary and premixed flame, as well as an ambient acoustic test for liquid rocket combustion chamber with/without baffle.

Sound absorption of micro-perforated elastic plates in a cylindrical impedance tube (원통형 임피던스 튜브 내 미세천공 탄성 판의 흡음)

  • Kim, Hyun-Sil;Kim, Bong-Ki;Kim, Sang-Ryul;Lee, Seong-Hyun;Ma, Pyung-Sik
    • The Journal of the Acoustical Society of Korea
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    • v.37 no.4
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    • pp.181-187
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    • 2018
  • In this paper, sound absorption of micro-perforated elastic plates installed in an impedance tube of a circular cross-section is discussed using an analytic method. Vibration of the plates and sound pressure fields inside the duct are expressed in terms of an infinite series of modal functions, where modal functions in the radial direction is given in terms of the Bessel functions. Under the plane wave assumption, a low frequency approximation is derived by including the first few plate modes, and the sound absorption coefficient is given in terms of an equivalent impedance of a single surface. The sound absorption coefficient using the proposed formula is in excellent agreement with the result by the FEM (Finite Element Method), and shows dips and peaks at the natural frequencies of the plate. When the perforation ratio is very small, the sound absorption coefficient is dominated by the vibration effect. However, when the perforation ratio reaches a certain value, the sound absorption is mainly governed by the rigid MPP (Micro-Perforated Plate), while the vibration effect becomes very small.

Acoustical Properties of Polyester Sound Absorbing Materials (폴리에스테르 흡음재의 음향특성)

  • 주경민;용호택;이동훈
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.11b
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    • pp.1347-1352
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    • 2001
  • In this study, the acoustic properties of polyester sound absorbing materials with three different bulk densities were investigated by calculating and measuring the acoustic parameters in terms of characteristic impedance, propagation constant, and absorption coefficient. For the calculations, Delany and Bazley's empirical equation was used together with the experimentally obtained specific flow resistivities under steady flow conditions. For the experimental measurements, the well-known two-thickness method was accessed. The experimentally measured values of characteristic impedance and propagation constant were generally agreed well with the corresponding calculated values. Based on the comparisons between the calculations and measurements, it was found that the magnitude of the absorption coefficient was closely related to the characteristic impedance and the real part of the propagation constant. Especially, the maximum magnitude of the absorption coefficient was depended upon the imaginary part of the propagation constant indicating the phase change of the propagation constant.

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