• Journal of the Korean Society of Propulsion Engineers
• /
• v.9 no.3
• /
• pp.1-9
• /
• 2005

An acoustic analysis of a fuel-rich gas generator for the drive of a turbopump in a liquid rocket engine has been performed and the length of a duct has been determined by comparing the resonant frequency of unstable acoustic modes to simulate an flight model gas generator, A practical short-length simulating duct has been determined by considering 1 or 2 wavelength of the unstable modes. Length adjustment of duct to turbopump can be a method to suppress a combustion instability problem by decoupling of acoustic mode and combustion characteristics. This method has been set up and validated with acoustic analysis and hot firing tests.

• The Journal of the Acoustical Society of Korea
• /
• v.28 no.4
• /
• pp.363-369
• /
• 2009

In this paper, an estimation method is presented to determine the equivalent circuit model of an underwater acoustic piezoelectric transducer with multiple resonant modes. A fitness function that includes the coupled resonant effects is proposed to minimize an error between the measured impedance of the transducer and the calculated impedance of the equivalent model. Unknown parameters of the equivalent circuit are estimated by using PSO algorithm. The proposed method is applied to an example transducer of the sandwich type with 3 resonances in the frequency band of interest. The analytical impedance of the estimated equivalent circuit model is compared with the measured impedance of the transducer and the validity of proposed method is verified.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2012.04a
• /
• pp.150-154
• /
• 2012

A flow induced mechanical vibration and acoustic resonance should be considered at design stage because they are mainly occurred in the tube bank of boiler. Acoustic resonance is occurred when the vortex shedding frequency of tube bank coincides with the acoustic natural frequency of the cavity. Effective solution to avoid acoustic resonance is installing acoustic baffles in the tube banks parallelly inside of the flow cavity. Thus, location and number of acoustic baffles should be exactly calculated to eliminate the acoustic resonance. This paper presents case study of acoustic resonance due to inappropriate number and location of acoustic baffles. Measured frequency and mode in the study is verified by FEM acoustic modal analysis. The number and location of acoustic baffles to avoid acoustic resonance are calculated by using FEM acoustic modal analysis.

• Proceedings of the Acoustical Society of Korea Conference
• /
• 1998.06e
• /
• pp.251-254
• /
• 1998

초음파 수신 신호의 공진주파수 변화를 이용한 온도 측정법에서 협대역 변환기를 사용한 초음파 온도측정이 가능함을 보여준다. 그리고 이를 위하여 공진주파수 변화와 온도변화간의 비례상수를 변화시켰다. 기존의 측정법은 온도변화와 기본주파수 변화와의 관계를 비례상수로 정의하였기 때문에, 최소한 3개 이상의 하모닉을 포함하는 광대역 변환기가 필요하였다. 하지만 협대역 변환기를 이용한 온도측정법에서는 비례상수를 주파수 변화비와 온도변화간의 관계로 나타내기 때문에 한 성분의 하모닉만을 측정하여도 온도측정이 가능하게 된다.

• The Journal of the Acoustical Society of Korea
• /
• v.5 no.3
• /
• pp.21-27
• /
• 1986

LSP 방식은 음성의 주파수 특성을 포함하는 공진 주파수를 낮은 부분과 SHB은 부분의 주파수 로 표시되는 선스펙트럼쌍 계수를 구하는 방법이다. 본 논문은 LSP 방식을 사용하여 한국어의 기본 모 음 7개를 대상으로 하여 분석하고 LSP 계수를 구하는 Algorithm을 개발하였으며 PARCOR 방식과 비 교하였다. 실험 결과 LSP 방식의 연산량이 PARCO 방식의 연산량보다 약 1/2정도로 적음을 알 수 있었 고 Hardware 구성 시에 있어서도 경제적임을 알 수 있었다. 그리고 LSP는 계수 모음의 종류에 따라 각 기 다른 공진 주파수, 대역폭을 나타내기 때문에 음성 합성이나 음성 인식 분야에 있어 기초 자료로 이 용할 수 있을 것으로 사료된다.

• Proceedings of the Acoustical Society of Korea Conference
• /
• 1984.12a
• /
• pp.15-19
• /
• 1984

본 연구는 piezo-electric transducer 등가회로의 모델링에 관한 연구로서 진동시에 발생하는 공진주파수와 harmonics까지 고려한 등가모델을 제시하였다. 실험결과 공진주파수만을 고려한 모델의 경우 harmonics를 제외한 부분에서 평균 6.5%의 오차가 발생하였으며 harmonics까지 고려한 모델에서는 평균오차가 5.3%로서 그 차이점을 줄일 수 있어 실제등가회로에 접근함을 알 수 있었다. 본 연구의 결과는 음향변환기의 전기적 특성을 파악함으로써 전기-음향 상사관계의 제반응용에 이용될 것이 기대된다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.04a
• /
• pp.212-217
• /
• 2008

Acoustic noises generated during motor operation in mechanical system are from electromagnetic, mechanical, aerodynamic, and electrical sources. For identification of mechanical noise origins, misalignment, unbalance, fan shape, resonance, and vibration modes have been extensively considered to describe noise behavior. An experiment-based approach as well as a mathematical approach needs to be adopted for a realistic study into noise and vibration of the motor, because motor noise characteristics differ from type to type due to various noise sources. In this paper, a brushless DC motor for air-conditioner fan is analyzed by finite element method to identify noise source, and the analysis results are verified by experiments, and sensitivity analysis is performed by design of experiments.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.19 no.9
• /
• pp.863-869
• /
• 2009

Acoustic noises generated during motor operation in mechanical system are from electromagnetic, mechanical, aerodynamic and electrical sources. For identification of mechanical noise origins, misalignment, unbalance, fan shape, resonance, and vibration modes have been extensively considered to describe noise behavior. An experiment-based approach as well as a mathematical approach needs to be adopted for a realistic study into noise and vibration of the motor, because motor noise characteristics differ from type to type due to various noise sources. This paper analyzes noise characteristics of a brushless DC motor for air-conditioner fan, and proves that the test motor noise originates from acoustic modes of airspace in the motor. The motor noise sensitivity analysis by design of experiments reveals that the noise characteristics are closely related to switching frequency and frame thickness.

• The Journal of the Acoustical Society of Korea
• /
• v.31 no.7
• /
• pp.480-486
• /
• 2012

In the design of electro acoustic transducer, power factor improvement circuit is more required rather than impedance matching if the driving power amplifier has little inner resistance. Many research results have been focused on the power matching circuit designing for transferring maximum power in the wideband. There are few results in the designing study on the power factor improvement for the wide band electro acoustic transducer. In this paper, we propose a new design method on the power factor improvement for the wide band electro acoustic transducer. The proposed method consists of two steps, the chebyschev matching method and the constrained optimization, respectively.

• The Journal of the Acoustical Society of Korea
• /
• v.14 no.4
• /
• pp.12-20
• /
• 1995

This paper describes principles and experimental results in conjunction with examining the possibility of the detection of effects from a cylindrical objects. Cylindrical objects have its own resonance frequency. The frequency varies according to the diameter, length etc. And acoustic sound, whose frequency and the harmonic components corresponding to resonance frequency, is radiated from the object. When an object have defect in itself, the radiated acoustic sound is different from normal one. So we can detect its defect by analysing frequency components of acoustic sound. We proved that detection of defective objects by acoustic signal analysis is possible automatically. Also the result can be applied to other kinds of objects.