• Journal of Advanced Marine Engineering and Technology
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• 제24권2호
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• pp.97-103
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• 2000

Gas pulsation discharged from the cylinder causes noise in the rotary compressor. Mufflers are usually used to reduce the noise generated by the gas pulsation. The muffler has been designed to maximize the acoustic transmission loss of the muffler. The gas which went through muffler is discharged to the cavity in compressor. Thus, the acoustic characteristics of cavity should be taken into account in muffler design. In this paper, the program for the acoustic substructure synthesis method is developed. This program can be interfaced with SYSNOISE which is commercial acoustic package. Several types of mufflers designed to have the better acoustic performance are suggested in this work and compared with the existing commerical muffler in the compressor. The acoustic performance of mufflers taking into consideration of the cavity in the compressor is also carried out by the developed program.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.690-692
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• 2014

To identify characterization of a simple extension chamber that have the two internal partition, produce the curve to estimate the transmission loss without the computer analysis. For helpful for internal optimum design, identify the characteristic of internal partition on transmission loss. Made estimated transmission loss curve by function of relationship of internal partition and transmission. Check the similarity of predicted transmission loss and analysis transmission loss. Usage of the predicted transmission loss made by relationship of internal partition and transmission loss is good information to place the internal partition so as to maximize the transmission loss on target frequency at optimal design on muffler.

• 소음진동
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• 제3권3호
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• pp.271-278
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• 1993

Acoustic characteristics of silencer system are affected by various geometric parameters such as cross sectional geometry, size of chamber, and location of inlet-outlet port. It is impossible to obtain exact solutions of the equations of acoustic wave propagation except few simple cases. So, we resort to numerical techniques to analyze performance of acoustic system. In this work, finite element formulation has been obtained to predict transmission loss of an arbitrary 3-dimensional muffler in the presence of mean flow of low mach number. The effect of the degree of the ellipticity of expansion chambers on the transmission loss has been studied using the resulting finite element equation.

• 한국소음진동공학회논문집
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• 제14권10호
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• pp.975-982
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• 2004

Helmholtz resonator is used to reduce noise of the narrow frequency band. It has high transmission loss at its resonance frequency. The silencer that combines many resonators could control broadband noise at low frequency. To convey this rather simple idea, serial and parallel arrangement of resonators have been tested to obtain high transmission loss characteristics in the band of which are selects. Theoretical and experimental results explain these characteristics in the absence of mean flow. The change of acoustic characteristics by the resonance frequencies and resonators arrangement are explained by using the equivalent Impedance analysis that is defined in this paper. It shows that the transmission loss has a maximum value when the separation distance between each resonator is λ/4 of its wavelength.

• 소음진동
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• 제9권4호
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• pp.738-746
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• 1999

The performance of muffler can be improved for a frequency range of interest by moving inlet and outlet locations. And optimal location of inlet and outlet can be determined to improve the acoustic performance. The optimum design using FEM, however, may take a very long time and be very hard to take inlet and outlet locations as design variables. In this paper, the acoustic performance of reactive type single expansion chamber muffler is predicted using higher order mode theory. The sensitivity analysis of transmission loss with respect to the location of inlet and outlet is suggested. And the acoustic power transmission coefficient for a frequency of interest is used as cost function. Optimum location of inlet and outlet is determined to minimize cost function by using SUMT algorithm.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 춘계학술대회 논문집
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• pp.603-608
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• 2014

Underwater acoustic materials are installed in order to reduce reflection, transmission and radiation of an underwater structure. The acoustic performance of the materials should be evaluated in accurately-controlled environment in terms of temperature and static pressure. In this paper, three pulse tubes, which is equipped with temperature and pressure controllers, are designed and developed to evaluate echo reduction and transmission loss for evaluating the performance below 10 kHz and 30kHz, respectively. The new procedures of the evaluation are suggested to improve the accuracy and the validation for the developed pulse tubes is carried out by comparing theoretical values to experimental ones.

• 한국자동차공학회논문집
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• 제14권5호
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• pp.93-99
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• 2006

Flexible couplers are widely used for exhaust transmitted vibration reduction in vehicles. This paper describes an investigation into the acoustical characteristics of exhaust flexible coupler by the simulation and testing. Computational acoustic simulation is carrying out to investigate resonance frequency and transmission loss of decoupler using the boundary element method and transfer matrix approach. To confirm the acoustical simulation results of exhaust decoupler, we compare with measured experimental results by the test of transmission loss measurement system. In the comparison with simulation results and tests results, there is correctly fit the resonance frequency and the trend of transmission loss. Also, we show that the acoustical structure of decoupler is analogous to the expended tube or side branch resonator. The characteristics of exhaust decoupler have a marked increase in the acoustic attenuation at the specified frequency bend. Therefore the decoupler is applied to develop the exhaust system not only for the vibration isolator but also for the noise attenuator.

• 한국군사과학기술학회지
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• 제18권2호
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• pp.201-211
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• 2015

Acoustic propagation in shallow water with changing environments is a major concern of navy. Temporal and spatial variability of acoustic propagation in the northern East China Sea (ECS) is studied, using the 11 years hydrographic data and the Bellhop acoustic model. Acoustic propagation in the northern ECS is highly variable due to extensive interaction of various ocean currents and boundaries. Seasonal variations of transmission loss (TL) with various source depths are highly affected by sharp gradient of sound speed and bottoms interaction. Especially, various bottom sediment types lead to severely degrading a waterborne propagation with bottom loss. In particular, the highly increased TL near the ocean front depends on the source position, and the direction of sound propagation.

• 한국음향학회지
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• 제37권1호
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• pp.1-11
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• 2018

천해 환경에서 음파 전달은 경계면에 의해 구형 분산에서 원통형 분산으로 음파 전달 조건이 전환되는데, 이 지점을 음파 전달 조건의 변환점 (transition point)이라고 정의한다. 이론적으로 거리에 따른 전달손실을 이용하여 음파 전달 조건의 변환점을 계산할 수가 있으며, 본 논문에서는 포물선 방정식 기반 음향모델을 이용하여 Pekeris 도파관에서 송 수신기가 수층의 중심에 위치한 경우 전달손실을 모의한 후 변환점을 도출하였다. 계산된 변환점은 수층과 퇴적층의 음속비로 계산된 임계각으로 추정한 임계거리와 비교, 분석되었으며, 동일한 환경에서 수층에 음향채널이 존재하는 경우와 음원 수심 변화에 따른 변환점 변동성을 확인하였다. 최종적으로 2015년 5월, 제주도 서남쪽으로 약 65 km 떨어진 SAVEX15(Shallow Water Acoustic Variability EXperiment 2015) 실험에서 획득한 천해 환경에서의 거리에 따른 저 중주파수 음파 전달 실험의 전달손실 자료를 이용하여 실험 해역에서의 음파 전달 조건 변환점을 도출하였으며, 이를 실험해역의 해양환경과 비교를 통하여 음전달 특성을 파악하였다.

• 센서학회지
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• 제13권6호
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• pp.479-487
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• 2004

The prevention of noise induced hearing loss is very important, because there is no treatment for it. There are some kinds of devices for hearing protection, and those are effective in preventing a noise induced hearing loss. However, people often resist the use of hearing protection devices because it is difficult to have a conversation. Therefore, a hearing protection device is must effective not only in hearing protection but also in preserving communication ability. In this paper, we proposed a small acoustic filter for ITE type noise protector to solving the problem about the difficulties of conversation. That is applied a principle of acoustic filters that have been used for a muffler of automobiles, guns, and etc. To find out the sound transmission characteristic at the eardrum, we regarded an acoustic filter and external ear canal as a coupled system. So, we simulated the coupled system with OrCad, and experimented with a designed acoustic filter and a 2 cc coupler which has the same transmission characteristic as the external ear canal has. We confirmed that it is possible to adjustment acoustic transmission characteristics through simulation of electrical model for acoustic filter and external ear and experiments using designed small acoustic filters.