• 대한기계학회논문집A
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• 제32권3호
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• pp.267-273
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• 2008

The circular cylinder pipes are used in the many industrial areas. In this paper, the acoustic wave propagation in the pipe containing a gas is researched. First of all, the theory for the coupled acoustic wave propagation in a pipe is investigated. Acoustic wave propagation in pipe can not be occurred independently between the wave of the fluid and the shell. It requires complicated analysis. However, as a special case, the coupled wave in a high density pipe containing a light density medium is corresponded closely to the uncoupled in-vacuo shell waves and to the rigid-walled duct fluid waves. The coincidence frequencies of acoustic and shell modes contribute to the predominant energy transmission. The coincidence frequency means the frequency corresponding to the coincidence of the wavenumber in both acoustic and shell. In this paper, it is assumed that the internal medium is much lighter than the pipe shell. After the uncoupled acoustic wave in the internal medium and uncoupled shell wave are considered, the coincidence frequencies are found. The analysis is successfully confirmed by the verification of the experiment using the real long steel pipe. This work verifies that the coupled wave characteristic of the shell and the fluid is occurred as predominant energy transmission at the coincidence frequencies.

• 한국국방경영분석학회지
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• 제5권1호
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• pp.101-122
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• 1979

• 한국음향학회지
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• 제32권4호
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• pp.301-307
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• 2013

수중무기체계에 있어 소나 탐지 성능은 생존성 향상을 위한 중요한 인자이다. 소나의 음향수신 성능을 파악하기 위해서 탄성이론을 이용하여 소나 다층구조의 음향 성능을 해석하였다. 단순구조물에 대하여 탄성이론을 적용하여 얻은 본 해석 결과를 상용해석프로그램인 ANSYS와 비교하였고, 만족할만한 결과를 얻었다. 검증된 탄성이론을 이용하여 소나 다층구조의 층별 두께 변화에 따른 음압 및 반향음 감소 해석을 수행하였다. 무반향(anechoic)층의 두께가 증가할수록 주파수에 따른 음압이 고르게 분포하고 반향음 감소량이 약간 증가하는 것을 확인하였다. 비결합(decoupling)층과 스틸(steel)층의 경우 두께에 따른 음압의 변화는 거의 없으나 두꺼워질수록 반향음이 약간 감소하는 결과를 나타내었다. 탄소강화플라스틱(Carbon Reinforced Platic, CRP)층의 두께 변화는 음압과 반향음 감소량에 영향이 없는 것을 확인하였다. 따라서 소나 다층구조의 음향성능을 높이기 위해서는 무반향층을 두껍게 하고, 비결합층, 스틸층과 탄소강화플라스틱층은 최소화하는 것이 바람직할 것으로 예상된다.

• 한국정밀공학회지
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• 제24권3호
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• pp.55-60
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• 2007

The electro-acoustic guitar pickup converts the vibration of strings to the electric signals, and delivers them to an amplifier. The vibration of the strings is transferred to the piezoelectric material through the saddle. This paper aims to improve sound quality for electro-acoustic guitars through the finite element analysis of the saddle. Firstly, the conventional pickup is modeled and analyzed with a commercial program called ANSYS. It is obvious that there exists interference phenomenon of stress. A structural modification of the pickup is performed, based on the beam theory. The modified structure is modeled and analyzed. Finally, the fabricated structures are subjected to the measurements and compared with the conventional pickup. It can be concluded that the interference with the modified structure is much less than that with the conventional structure, and that the sound quality is improved with the modified structures.

• 한국유체기계학회 논문집
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• 제16권2호
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• pp.15-20
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• 2013

An aero-acoustic performance analysis method of regenerative blower is developed as one of the FANDAS codes. The aerodynamic performance of regenerative blower is predicted by using momentum exchange theory coupled with pressure loss and leakage flow models. Based on the performance prediction results, the noise level and spectrum of regenerative blower are predicted by discrete frequency and broadband noise models. The combination of the performance and the noise prediction methods gives aero-acoustic performance map and noise spectrum analysis results, which are well-agreed with the actual measurement results within a few percent relative error.

• 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.

• 소음진동
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• 제6권5호
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• pp.635-644
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• 1996

In this paper, Allard's modelling method which employs the method of acoustic transfer matrix(ATM) is applied to yield more precise results in the analysis of porous sound absorbing material. The method of ATM, based on Biot's theory, is known to play an important role in the estimation of the sound absorption when a sound projects onto the material. In the case of a single layered porous sound absorbing material, the surface impedance and the absorption coefficient by using the method of ATM are estimated. With the variation of the material properties, sound absorption characteristics and analyzed. Transmission Loss in a combination of the porous sound absorbing material with a thin plate is predicted.

• Geomechanics and Engineering
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• 제12권4호
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• pp.627-637
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• 2017

The high positive correlation between plastic strain of loaded coal-rock and AE (acoustic emission) characteristic parameter was studied and proved through AE experiment during coal-rock uniaxial compression process. The results show that plastic strain in the whole process of uniaxial compression can be gained through the experiment. Moreover, coal-rock loaded process can be divided into four phases through analyzing the change of the plastic strain curve : pressure consolidation phase, apparent linear elastic phase, accelerated deformation phase, rupture and development phase, which corresponds to conventional elastic-plastic change law of loaded coal-rock. The theoretical curve of damage constitutive model is in high agreement with the experimental curve. So the damage evolution law of coal rock damage can be indicated by both acoustic emission and plastic strain. The results have great academic and realistic significance for further study of both AE signal characteristics during loaded coal-rock damaged process and the forecasting of coal-rock dynamic disasters.

• Journal of Advanced Marine Engineering and Technology
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• 제23권6호
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• pp.748-754
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• 1999

The acoustic performance of reactive type single expansion chamber can be calculated theoretically by plane wave theory. But higher order modes should be considered to widen the frequency range. Munjal has suggested the method for analyzing the acoustic properties of simple expansion chamber with taking into consideration of higher order mode of inlet/outlet. But his method cannot predict the acoustic properties exactly when the dimensions of inlet/outlet and expansion chamber have not integer multiples. In this paper the new method was suggested to overcome the shortcomings of Munjal's method The predictions by this method were also compared with those by the finite element method.

• Journal of the Optical Society of Korea
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• 제13권2호
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• pp.261-266
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• 2009

The angular dispersion-type non-scanning Fabry-Perot was applied to an ethanol-water mixture in order to investigate its acoustic properties such as the sound velocity and the absorption coefficient. The scattered light from the mixture was analyzed by using the charge-coupled-device area detector, which made the measurement time much shorter than that obtained by using the conventional scanning tandem multi-pass Fabry-Perot interferometer. The sound velocity showed a deviation from ultrasonic sound velocities at low temperatures accompanied by the increase in the absorption coefficient, indicating acoustic dispersion due to the coupling between the acoustic waves and some relaxation process. Based on a simplified viscoelastic theory, the temperature dependence of the relaxation time was obtained. The addition of water molecules to ethanol reduced the relaxation time, consistent with dielectric measurements. The present study showed that the angular dispersion-type Fabry-Perot interferometer combined with an area detector could be a very powerful tool in the real-time monitoring of the acoustic properties of condensed matter.