• 제목/요약/키워드: Acoustic Waves

검색결과 495건 처리시간 0.021초

태양에너지 이용을 위한 열음향 레이저의 특성 비교 연구 (A Comparative Study on the Characteristics of Thermoacoustic Laser for Using Solar Energy)

  • 박성식;안응진;오승진;천원기;김남진
    • 한국태양에너지학회:학술대회논문집
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    • 한국태양에너지학회 2012년도 춘계학술발표대회 논문집
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    • pp.516-521
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    • 2012
  • The conversion of solar energy into acoustic waves is experimentally studied. Measurements were made on the Sound Pressure Level (SPL), frequency, onset time and the temperature gradient across the stack. A pyrex resonance tube is used with a honey-comb structure ceramic stack along with Ni-Cr and Cu wires. An AL1 acoustical analyzer was used to measure the SPL and frequency of acoustic waves whereas K-type thermocouples were hired to estimate temperature gradients. For a resonance tube of 100mm, no acoustic waves were generated with a power input of 25W. By increasing its length to 200mm, however, maximum SPLs of 96.4 dB, 106.3 dB and 112.8 dB were detected for the tubes of 10mm, 20mm and 30mm in IDs and their respective stack positions of 70mm, 60mm and 50mm from the closed end.

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음향장 내의 상변화 열전달 촉진에 관한 연구 (A Study on the Enhancement of Phase Change Heat Transfer in Acoustic Fields)

  • 양호동;나기대;오율권
    • 에너지공학
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    • 제13권2호
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    • pp.152-160
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    • 2004
  • The present study investigates on the experimental and numerical results of heat transfer in the acoustic fields induced by ultrasonic waves. The strong upwards flow which moves from the bottom surface in a cavity to the free surface called as "acoustic streaming" was visualized by a particle image velocimetry (PIV). In addition, the augmentation ratio of heat transfer was experimentally investigated in the presence of acoustic streaming and was compared with the profiles of acoustic pressure calculated by the numerical analysis. A coupled finite element-boundary element method (FE-BEM) was applied for a numerical analysis. The results of experimental and numerical studies clearly show that acoustic pressure variations caused by ultrasonic waves in a medium are closely related to the augmentation of heat transfer.

유동-음향 분리 기법에 의한 횡류홴의 공력 소음 예측 (Aeroacoustic Tonal Noise Prediction of Cross-Flow Fan by a Hydrodynamic-Acoustic Splitting Method)

  • 조용;문영준
    • 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.

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선배열 예인 음탐기의 음향 모듈을 따라 전파하는 축대칭 진동에 기인한 음향 센서 자체 소음 해석 (Self Noise Analysis of Towed Array Sonar Induced by Axisymmetric Vibrations Propagating Along Fluid-filled Elastic Hoses)

  • 유정수;신현경;안형택;권오조
    • 한국소음진동공학회논문집
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    • 제21권5호
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    • pp.437-446
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    • 2011
  • Performance of array sonars towed underwater is limited due to the self-noise induced mainly by the strumming vibration of the towing cable and also turbulent flow around the acoustic sensor module. The vibration of the towing cable generates axisymmetric waves that propagate along the acoustic module of the array sonar and produce self-noise. The present study aims to investigate the characteristics of the self-noise induced by the axisymmetric vibrations of the acoustic module. The waves of interest are the bulge and extensional waves propagating along the fluid-filled elastic hose. Dispersion relations of these waves are predicted by means of the numerical simulation to evaluate the wave speeds. The self-noise induced by the axisymmetric waves are formulated taking into account the damping of the elastic hose and the effect of the damping is investigated.

Interference of Acoustic Signals Due to Internal Waves in Shallow Water

  • Na, Young-Nam;Jurng, Mun-Sub;Taebo Shim
    • The Journal of the Acoustical Society of Korea
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    • 제18권3E호
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    • pp.9-20
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    • 1999
  • To investigate the characteristics of internal waves (IWs) and their effects on acoustic wave propagation, a series of sea experiment were performed in the east coast of Donghae city, Korea in 1997 and 1998 where the water depth varies between 130 and 140 m. Thermistor strings were deployed to measure water temperatures simultaneously at 9 depths. CW source signals with the frequencies of 250,670 and 1000 Hz were received by an array of 15 hydrophones. Through the Wavelet transform analysis, the IWs are characterized as having typical periods of 2-17 min and duration of 1-2 hours. The IWs exist in a group of periods rather than in one period. Underwater acoustic signals also show obvious energy peaks in the periods of less than 12 min. Consistency in the periods of the two physical processes implies that acoustic waves react to the IWs through some mechanisms like mode interference and travel time fluctuation. Based on the thermistor string data, mode arriving structures are analyzed. As thermocline depth varies with time, it may cause travel time difference as much as 4-10 ms between mode 1 and 2 over 10 km range. This travel time difference causes interference among modes and thus fluctuation from range-independent stratified ocean structure. In real situations, however, there exist additional spatial variation of IWs. Model simulations with all modes and simple IWs show clear responses of acoustic signals to the IWs, i.e., fluctuations of amplitude and phase.

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PVDF interdigitated transducer for generating and detecting Lamb waves in plates

  • Gu, Hua;Lloyd, George M.;Wang, Ming L.
    • Smart Structures and Systems
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    • 제4권3호
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    • pp.291-304
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    • 2008
  • Piezoelectric materials have been widely used in ultrasonic nondestructive testing (NDT). PZT ceramics can be used to receive and generate surface acoustic waves. It is a common application to attach PZT transducers to the surface of structures for detecting cracks in nondestructive testing. However, not until recently have piezoelectric polymers attracted more and more attention to be the material for interdigitated (IDT) surface and guided-wave transducers. In this paper, an interdigitated gold-on-polyvinylidene fluoride (PVDF) transducer for actuating and sensing Lamb waves has been introduced. A specific etching technology is employed for making the surface electrodes into a certain finger pattern, the spacings of which yield different single mode responses of Lamb waves. Experiments have been performed on steel and carbon fiber composite plates. Results from PVDF IDT sensors have been compared with those from PZT transducers for verification.

압력섭동과 연관된 연소응답모델에 기초한 고주파 연소불안정의 이론-수치적 고찰 (Hybridal Analysis of High-Frequency Combustion Instability with Pressure-Coupled Combustion Response Model)

  • 윤웅섭;이길용
    • 한국추진공학회:학술대회논문집
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    • 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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    • pp.253-257
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    • 2003
  • Theoretical-numerical analysis of wave instability is conducted with parametric response function model. Fluctuating instantaneous mass evaporation rate functionally coupled with pressure perturbations with phase lag is assumed to examine the validity of the method. With sufficiently large amplitude and less phase lag to perturbation, combustion response is resonant to pressure waves, unstable waves are amplified, and the system is driven to instability. Magnitude of response is a crucial instability parameter in the determination of a stability margins and makes a critical change of balancing conditions between the amplifying and damping acoustic energies. In the phase regime the unstable waves are amplified, whereas, the acoustic waves are attenuated in the out-of-phase regime. In the intermediate regime, no distinct tendency of unstable waves was determined.

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HEATING OF SUNSPOT CHROMOSPHERES BY SLOW-MODE ACOUSTIC SHOCK WAVES

  • Lee, Myung-Gyoon;Yun, Hong-Sik
    • 천문학회지
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    • 제18권1호
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    • pp.15-31
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    • 1985
  • Making use of the arbitrary shock theory developed by Ulmschneider (1967, 1971) and Ulmschneider and Kalkofen (1978), we have calculated the dissipation rates of upward-travelling slow-mode acoustic shock waves in umbral chromospheres for two umbral chromosphere models, a plateau model by Avrett (1981) and a gradient model by Yun and Beebe (1984). The computed shock dissipation rates are compared with the radiative cooling rate given by Avrett (1981). The results show that the slow-mode acoustic shock waves with a period of about 20 second can heat the low umbral chromospheres travelling with a mechanical energy flux of $2.6{\times}10^6\;erg/cm^2s$ at a height of $300{\sim}400km$ above the temperature minimum region.

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강성 또는 연성 물체로 인한 음향파와 탄성파 산란의 수치해석 및 특성 분석 (Numerical Analysis and Characteristics of Acoustic and Elastic Wave Scattering from Rigid or Soft Objects)

  • Huinam Rhee
    • 소음진동
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    • 제8권6호
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    • pp.1172-1180
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    • 1998
  • 음향학적으로 강성인 물체와 연성인 물체로부터의 탄성파의 산란과 음향파의 산란을 수치적으로 해석하고 그 특성들을 비교하였다. 부분파들과. 또한 부분파들의 합인 전체 산란파의 위상 및 크기의 거동을 수치적으로 분석하고 토의하였다. 탄성파의 산란시 발생하는 종파와 횡파 사이의 모드변환 현상이 산란파의 크기와 위상에 주는 영향을 밝혔다.

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급수 배관계의 음향진동 현상 고찰 및 대책 (Mechanism Investigation and Measures on Acoustic Vibration Phenomena of Water Supply Piping)

  • 김연환;배용채;이두영
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2012년도 추계학술대회 논문집
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    • pp.470-475
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    • 2012
  • The downstream piping system of the water supply system in a supercritical power plant is affected by the fluctuation pressure waves induced by accessing to the acoustic modes of the piping systems with the rotation and impeller passing pulsations of the feed water pump. There are the phenomena amplified at the same time in the range of 415 ~ 455Hz, 830 ~ 910Hz, 1245 ~ 1365Hz and 1660 ~ 1820Hz on the spectrums of the vibration, the sound pressure, and the pressure fluctuation waves.

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