• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2009년도 추계학술대회 논문집
• /
• pp.573-574
• /
• 2009

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2011년도 춘계학술대회 논문집
• /
• pp.291-292
• /
• 2011

• 기계저널
• /
• 제27권5호
• /
• pp.421-427
• /
• 1987

공력소음은 공기역학적 힘에 의해서나 또는 유동 내에서의 난류와 같은 유체운동에 의해서만 발 생되는 소리와 관계되며, 진동하는 바이올린 줄이나 확성기의 진동에 의해서 발생되는 즉, 고체 표면의 진동에 의해서 발생되는 고전적인 음향학과는 무관하다. 그리고 여기서는 주로 공력 소음문제를 다루되 자세하고 엄밀한 수학적 전개보다는, 간단한 실제적인 예를 들어서, 물리적 메카니즘을 가능한 한 자세히 기술하여 공력 소음의 이해를 돕고자 하였다. 또한 오래된 고전적 방법을 가능한 한 피하고 최근의 방법으로 설명하도록 하였다.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
• /
• pp.337-340
• /
• 2006

본 논문은 초음속 제트에서 발생하는 천음속 공명현상에 대한 실험적 연구를 기술한다. 초음속 노즐이 매우 낮은 압력비에서 작동될 때, 노즐내의 확대부에서 충격파가 발생한다. 천음속 공명현상은 이러한 충격파의 불안정한 진동에 의한 강한 음파의 발생에 기인한다. 제트 유동장은 쉴리렌 광학장치를 이용하여 가시화 하였다. 제트유동의 천음속 공명현상을 조사하기 위하여, 음향측정을 수행하였다. 천음속 공명 현상의 음향특성은 스크리치 톤과 비교하였다. 본 연구에서 얻어진 결과에 의하면, 스크리치 톤의 주파수와는 달리, 천음속 톤의 주파수는 노즐 압력비가 증가할수록 증가한다.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2008년도 춘계학술대회논문집
• /
• pp.21-24
• /
• 2008

The present study numerically investigates the glottal airflow characteristics as well as acoustic features of phonation fully coupled with dynamic behavior of vocal folds. The vocal folds are described by a low-dimensional body-covered model characterized by bio-mechanical parameters such as glottal width, vocal folds stiffness, and subglottal pressure. The flow in the vocal tract is modeled as an incompressible, axisymmetric form of the Navier-Stokes equations (INS), while the acoustic field is predicted by the linearized perturbed compressible equations (LPCE). The computed result shows that a two-mass model of vocal folds is sufficient to reproduce temporal variations in oral airflow and glottis motion produced by female speakers. It is also found that i) the glottal width has a significant effect on the amplitude of glottal flow, and thus on the amplitude of acoustic wave in the vocal tract, ii) the vocal fold tension is the main control parameter for the fundamental frequency of phonation, iii) the subglottal pressure plays an appreciable role on reproduction of the self-sustained oscillation of vocal folds, and iv) the strength of pulsating airflow and vortical structures are primarily affected by glottal width and subglottal pressure, and are closely related to pitch, loudness, and voice quality. Finally, more comprehensive explanation about the difference between one- and two-mass models is presented with discussion of effectiveness of vocal folds oscillation and voice quality.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2002년도 춘계학술대회논문집
• /
• pp.1020-1025
• /
• 2002

This paper exploits how vortex noise is generated around a cylinder. This is done by utilizing an acoustic holography. In this experiment. compressed air was Infected to tile cylinder through a hose. Therefore, major noise sources were at a hose end as well as around the cylinder： vortex shedding noise. The holography results show a resultant noise picture there it is not easy to clearly sort out the shedding noise and what is generated at the end of the tube. We attempted to separate those noise by the method we developed : contribution analysis scheme. The method, in fact, was found to be efficient and practical to separate the noise field into independent noise sources. The highlights of the results are. we believe, that lift and drag noise picture are now available. This procedure does not limit its application. therefore we may use this to visualize any noise field that we want to understand.

• 한국소음진동공학회논문집
• /
• 제25권8호
• /
• pp.532-538
• /
• 2015

In a reciprocating compressor, highly impulsive pressure fluctuations induced by a reciprocating piston give rise to serious noise and vibration problems. A muffler is frequently used to reduce this impulsive noise, but also has adverse effects on compressor performance due to additional pressure drop and heat transfer of refrigerants through it. Therefore, the flow and acoustic performances of mufflers used in a compressor should be considered simultaneously. In this study, both of flow and acoustic performances of mufflers are investigated using computational fluid dynamic techniques by solving full three-dimensional compressible Reynolds-Averaged Navier-Stokes equations. For validation purpose, the numerical method is initially applied to predict the transmission loss of a simple expansion muffler, and its predicted results show good agreements with theoretical and experimental results. Then, the flow and acoustic performances of an existing muffler is numerically investigated. On the basis of the analysis results, a new muffler is purposed and its performances are compared with the existing one. Improved performances of the new muffler are confirmed.

• 한국소음진동공학회논문집
• /
• 제14권6호
• /
• pp.528-535
• /
• 2004

Ultrasonic Vibrator is designed to achieve the maximum vibration amplitude at 30 kHz by in-cluding a horn (diameter, 40 mm), mechanical vibration amplifier at the top of the ultrasonic vibrator in the system and making the complete system resonate. In addition, it is experimentally visualized by particle imaging velocimetry (PIV) that the acoustic streaming velocity in the gap is at maximum when the gap between the ultrasonic vibrator and stationary plate agrees with the multiples of half-wavelength of the ultrasonic wave. This fact results from the resonance of the sound wave and the theoretical analysis of that is also accomplished and verified by experiment. It is observed that the magnitude of the acoustic streaming dependent upon the gap between the ultrasonic vibrator and stationary plate possibly changes due to the measurement of the average velocity fields of the acoustic streaming induced by the ultrasonic vibration at resonance and non-resonance. There exists extremely small average velocity at non-resonant gaps while the relatively large average velocity exists at resonant gaps compared with non-resonant gaps. It also reveals that there should be larger axial turbulent intensity at the hub region of the vibrator and at the edge of it in the resonant gap where the air streaming velocity is maximized and the flow phenomena is conspicuous than that at the other region. Because the variation of the acoustic streaming velocity at resonant gap is more distinctive than that at non-resonant gap, shear stress increases more in the resonant gap and is also maximized at the center region of the vibrator except the local position of center (r〓0). At the non-resonant gap there should be low values of vorticity distribution, but in contrast to the non-resonant gap, high and negative values of it exist at the center region of the vibrator with respect to the radial direction and in the vicinity of the middle region with respect to the axial direction. Acoustic streaming is noise-free due to the ultrasonic vibration and maintenance-free because of the absence of moving parts. Moreover, the proposed method by acoustic streaming can be utilized to the nano and micro-electro mechanical systems as a driving mechanism in addition to the augmentation of the streaming velocity.

• 한국유체기계학회 논문집
• /
• 제3권2호
• /
• pp.15-23
• /
• 2000

The present work describes the prediction method for the unsteady flow field and the acoustic pressure field of a ducted axial fan. The prediction method is comprised of time-marching free-wake method, acoustic analogy, and the Kirchhoff-Helmholtz BEM. The predicted sound signal of a rotor is similar to the experiment one. We assume that the rotor rotates with a constant angular velocity and the flow field around the rotor is incompressible and inviscid. Then, a time-marching free-wake method is used to model the fan and to calculate the flow field. The force of each element on the blade is calculated by the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. The newly developed Helmholtz-Kirchhoff BEM lot thin body is used to calculate tile sound field of the ducted fan. The ducted fan with 6 blades is analysed and the sound field around the duct is calculated.

• 대한기계학회논문집
• /
• 제16권4호
• /
• pp.775-786
• /
• 1992

본 연구에서는 DVM의 이론적 배경과 수치계산에 대해 자세히 다루었다. 음향 교란이 가졌을 때의 재부착에 대한 수치해석결과는 Kiya등의 실험결과와 비교하 였으며 만족할만한 일치를 보여주었다. 결과 및 고찰에서는 주로 음향교란이 있는 경우의 재부착길이를 최소화하는 주파수와 교란이 없는 유동의 난류구조해석을 평균속 도 및 압력과 그의 섭동치, 그리고 파워 스펙트럼과 상관계수등을 통해 자세히 비교검 토하였다.