• 동력기계공학회지
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• 제10권1호
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• pp.65-70
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• 2006

A study of the possible axisymmetric modes that propagate at low frequencies in buried, water-filled iron pipes is presented. It is well known that for a vacuum-pipe-vacuum system the sole non-torsional axisymmetric mode that exists at low frequencies is the fundamental L(0,1) mode. When a pipe is filled with water and still surrounded by a vacuum it is also known that another mode then appears which at low frequencies is characterized by predominantly axial water-borne displacements. In addition to these modes, this paper explores two other, less well known axisymmetric modes whose existence depends on the acoustic properties of the outer medium that surrounds a pipe. In this paper the predicted characteristics of these modes are presented.

• Journal of Theoretical and Applied Mechanics
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• 제3권1호
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• pp.34-44
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• 2002

Theoretical analysis Is carried out to identify the modal coupling effect between some particular acoustic modes of a vehicle compartment cavity and vibration modes of body panels like side doors, roof or floor. A simplified panel-cavity coupled model is investigated on the coupled resonance frequencies, modes and frequency response characteristics. Through parametric study, It Is possible to explain how the acoustic response of a coupled system will be determined by the vibration and acoustic property of the individual panel and cavity system. Full coupled system shows some interesting features different from those of the semi-coupled system In frequency, mode and acoustic response.

• 음성과학
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• 제15권1호
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• pp.63-72
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• 2008

Various acoustic features were extracted and analyzed to estimate the inter- and intra-speaker variability of emotional speech. Tokens of vowel /a/ from sentences spoken with different modes of emotion (sadness, neutral, happiness, fear and anger) were analyzed. All of the acoustic features (fundamental frequency, spectral slope, HNR, H1-A1 and formant frequency) indicated greater contribution to inter- than intra-speaker variability across all emotions. Each acoustic feature of speech signal showed a different degree of contribution to speaker discrimination in different emotional modes. Sadness and neutral indicated greater speaker discrimination than other emotional modes (happiness, fear, anger in descending order of F-ratio). In other words, the speaker specificity was better represented in sadness and neutral than in happiness, fear and anger with any of the acoustic features.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.83-88
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• 2004

Acoustic modes of internal region of 4-hp scroll compressor are identified by measuring transfer functions between a reference and 84 measuring points. The corresponding acoustic mode-shapes and natural frequencies were calculated by analysis software SYSNOISE. There exist two clearly distinguishable dipole modes of vertical and horizontal direction and a single quadrupole mode in the frequency region of interest. It shows that the natural frequencies of the identified modes are linearly sensitive to suction pressure (Ps) but relatively in sensitive to discharge pressure (Pd) in operating condition.

• Journal of Mechanical Science and Technology
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• 제18권1호
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• pp.145-152
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• 2004

Effects of various baffle designs on acoustic characteristics in combustion chamber are numerically investigated by adopting linear acoustic analysis. A hub-blade configuration with five blades is selected as a candidate baffle and five variants of baffles with various specifications are designed depending on baffle height and hub position. As damping parameters, natural-frequency shift and damping factor are considered and the damping capacity of various baffle designs is evaluated. Increase in baffle height results in more damping capacity and the hub position affects appreciably the damping of the first radial resonant mode. Depending on baffle height, two close resonant modes could be overlapped and thereby the damping factor for one resonant mode is increased exceedingly. The present procedure based on acoustic analysis is expected to be a useful tool to predict acoustic field in combustion chamber and to design the passive control devices such as baffle and acoustic resonator.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.249-252
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• 2003

음향불안정을 억제하는 수동제어기구중 하나인 음향공의 음향학적 효과를 파악하기 위해, 음향공이 장착된 로켓엔진 연소실의 음향장 특성을 수치해석적으로 조사하였다. 음향공 모델로서 Helmholtz 형태의 공명기가 채택되었고, 조화해석을 통해 주로 음향공에 의해 야기되는 음향학적 효과를 관찰하였다. 음향공의 동조주파수를 변화시켜가면서 연소실의 음향진동 응답을 구하고, 제1접선방향 음향모드의 감쇠인자를 구하였다. 동조주파수가 공진주파수에 접근함에 따라 모드분할 현상이 나타났고, 이로 인해 음향공을 본래의 제1접선방향 음향모드에 동조시키더라도 음향감쇠효과가 저하됨을 알았다. 효과적인 감쇠를 위해서는, 억제하고자 하는 음향모드로부터 모드분할 현상이 나타나지 않으면서 그 음향모드의 감쇠효과를 극대화하도록 음향공을 동조시키는 것이 바람직함을 알 수 있었다.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1999년도 학술발표대회 논문집 제18권 1호
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• pp.189-197
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• 1999

To investigate internal waves (IW) effect on acoustic wave propagation, m analysis is conducted on mode travel time and model simulation. Based on the thermistor string data, it can be shown that the thermocline depth variation may cause travel time difference as much as 4-10 ms between mode 1 and 2 over range 10 km. This travel time difference causes interference among modes and thus fluctuation from range-independent stratified ocean structure. In real situations, however, there exist additionally spatial variation of IW. Model simulation with all modes and simple IW shows clear responses of acoustic signals to IW, amplitude and phase fluctuation.

• 대한기계학회논문집A
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• 제24권5호
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• pp.1314-1322
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• 2000

The acoustic property of reactive type single expansion chamber can be analyzed by traditional plane wave theory. This theory can be applied in low frequency range and has good performance. But this theory can't include higher order modes, therefore another method is essential to analyze acoustic filter in high frequency range. Many researcher suggested the method that can concern higher order modes, and their methods are using mode matching technique. But there is no method that can be applied to the analysis of single expansion chamber with arbitrary inlet/outlet duct position and numbers of higher order modes of inlet/outlet duct and middle chamber. In this paper, the method which can analyze single expansion chamber with arbitrary inlet/outlet duct position and numbers of higher order modes of inlet/outlet duct and middle chamber using fundamental mode matching technique, was suggested and the predictions by this method was compared with those by the finite element method, and the influence of inlet/outlet location to acoustic performance of single expansion chamber is investigated and explained by higher order mode effects.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.167-171
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• 2003

Acoustic characteristics of baffled combustion chamber to elucidate suppressing effect of baffle on combustion instability are numerically investigated by linear acoustic analysis. A hub-blade baffle of 5 blades is selected as a candidate one and five variants of baffles with various configuration are designed. Resonant-frequency shift and damping factor are analyzed quantitatively as damping parameters. When the hub is located radially at the pressure node, the decrease of resonant frequency and increase of damping factor in 1R mode are dominant. But sub-1T mode is formed within hub, therefore, there would be a possibility of initiating 1T mode in unbaffled region, which would occur another problem. For smaller hub size, four kinds of axial baffle length is selected. As the axial baffle length increases, resonant frequency shift and increase of damping factor of transverse acoustic modes is obtained. Especially, two close acoustic modes such as 1L and 1T could be overlapped for a certain axial length, resulting in extreme increase of damping factor. The present study based on linear acoustic analysis is expected to be a useful confirming tool to predict acoustic field and design a passive control devices such as baffle and acoustic cavity.

• 대한조선학회논문집
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• 제55권4호
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• pp.281-288
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• 2018

Acoustic radiation efficiency is a crucial factor to estimate Underwater Radiated Noise (URN) of ships accurately. This paper describes a numerical method to analyse acoustic radiation efficiency of one side-wetted rectangular Mindlin plate with simply supported boundaries excited by a harmonic point force. Transverse displacements of plate and acoustic radiation pressures are evaluated by the mode superposition method. The acoustic radiation efficiencies analyzed by both Mindlin and thin plate theories show little differences at monopole and corner modes of low frequency regions but relatively large differences at edge and critical modes of high frequency regions. Especially, the critical frequency with the highest acoustic radiation efficiency evaluated by the Mindlin plate theory is higher than that of thin plate theory. In addition, the acoustic loading effect of fluid also increases bending wave-number of plate and its critical frequency. Finally, the acoustic radiation characteristics of plates with different aspect ratios and thicknesses through numerical analyses are investigated and discussed.