• Journal of Advanced Marine Engineering and Technology
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• 제26권1호
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• pp.116-124
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• 2002

The bubble model by Keller and Prosperetti is adapted to solve the nonlinear oscillation of a gas bubble. This formulation leads to accurate results since it introduces the energy equation instead of the polytropic assumption for the bubble interior. The numerical method used in this study is stable enough to handle large amplitude of bubble oscillation. The numerical results show some interesting nonlinear phenomena fur the bubble oscillator. The excitation changes the natural frequency of the bubble and makes some harmonic resonances at $f/f_0=1/2, 1/3$ and so on. The natural frequency of a bubble oscillator decreases compared with the linear case result, which means that the nonlinear bubble oscillation system is a "softening"system. In addition, the frequency response curve jumps up or down at a certain frequency. It is also found that there exist multi-valued regions in the frequency response curve depending on the initial conditions of bubble. The dependency of the bubble motion on the initial condition can generate extremely large pressure and temperature which might be the cause of the acoustic cavitation and the sonoluminescence.inescence.

• 한국소음진동공학회논문집
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• 제18권2호
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• pp.231-237
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• 2008

With the advent of sound field simulator, many sound fields have been reproduced by obtaining the impulse responses of specific acoustic spaces like famous concert hall, opera house. This sound field reproduction has been done by the linear convolution operation between the sound input signal and the impulse response of certain acoustic space. However, the conventional finite impulse response based linear convolution operation always makes real-time implementation of sound field generator impossible due to the large amount of computational burden. This paper introduces the fast convolution method using perceptual redundancy in the processed signals, input audio signal and room impulse response. Temporal and spectral real-time masking blocks are implemented in the proposed convolution structure. It reduces the computational burden of convolution methods for real-time implementation of a sound field generator. The conventional convolutions are compared with the proposed one in views of computational burden and sound quality. In the proposed method, a considerable reduction in the computational burden was realized with acceptable changes in sound quality.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1994년도 FIFTH WESTERN PACIFIC REGIONAL ACOUSTICS CONFERENCE SEOUL KOREA
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• pp.692-697
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• 1994

In the actual sound environmental systems, it seems to be essentially difficult to exactly evaluate a whole probability distribution form of its response fluctuation, owing to various types of natural, social and human factors. Up to now, we very often reported two kinds of unified probability density expressions in the standard expansion from of Hermite and Laguerre type orthonormal series to generally evaluate non-Gaussian, non-linear correlation and/or non-stationary properties of the fluctuation phenomenon. However, in the real sound environment, there still remain many actual problems on the necessity of improving the above two standard type probability expressions for practical use. In this paper, first, a central point is focused on how to find a new probabilistic theory of practically evaluating the variety and complexity of the actual random fluctuations, especially through introducing some equivalence transformation toward two standard probability density expressions mentioned above in the expansion from of Hermite and Laguerre type orthonormal series. Then, the effectiveness of the proposed theory has been confirmed experimentally too by applying it to the actual problems on the response probability evaluation of various sound insulation systems in an acoustic room.

• 한국항해항만학회지
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• 제28권6호
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• pp.491-496
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• 2004

이 논문은 기적음에 대한 선박 음향전달특성 측정기술에 관한 것이다. 실습선 ‘새누리호’를 대상으로 선교 내부에 전달되는 기적음을 선교문 개폐상태에 따라서 B＆K 2260D으로 측정한 후, B＆K 7830 소프트웨어를 이용하여 주파수특성을 추출하였다. 측정한 주파수 특성을 이용하여 주파수 샘플링에 의한 FIR 필터 설계법으로 128차 FIR 필터를 구축하였다. 그리고, 지적원음과 FIR 필터의 콘볼류션 연산으로 실험음을 생성한 후, 6단계 평가지표를 이용하여 측정한 음향전달특성을 평가하였다. 평가결과, 실험음이 실제 선교에서 듣는 음과 ‘유사함’을 나타내는 $A_S$=3.3∼4.7로 나타나서 본 연구에서 개발한 기법이 선교의 음향전달특성 측정기술로서 유효함을 확인하였다.

• 수산해양기술연구
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• 제32권4호
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• pp.331-339
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• 1996

본 연구에서는 해양목장에서 음향을 사용한 어군행동제어에 관한 기초적인 자료를 얻기 위하여, 감지하기 쉬운 주파수의 순음과 먹이의 조합으로 어류를 학습시켜서, 음향 순치의 가능성을 검토했다. 미차체장이 385~459mm인 수컷 8마리와 암컷 5마리를 실험 수조에 수용하여, 수조내에 설치한 수중 스피커로부터 감지하기 쉬운 200Hz의 순음을 방성하면서 원격급이 장치로부터 급이하여 조건학습을 실시했다. 학습과정을 수록한 비디오 영상으로부터 물고기의 행동을 해석하여 색이장에 출현하는 빈도를 방성 전.방성 중.방성 후로 나눠서 해석했다. 학습 개시 일로부터 8일째에 학습 음에 첫 반응을 보였으며, 4일간 학습을 중지한 후에 학습 음을 방성 하여도 반응을 보였다. 방성 후에 음원부근에 위집 하는 율이 방성 전보다 높아져서, 1분간의 평균 출현빈도는 51%였다.

• Journal of Biosystems Engineering
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• 제33권5호
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• pp.348-354
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• 2008

Egg grading is determined by exterior and interior quality. Among the evaluation methods for the egg quality, a candling method is common to identify eggs with cracked shells and interior defects. But this method is time-consuming and laborious. In addition, practically, it is challenging to detect hairline and micro cracks. In this study, an on-line inspection system based on acoustic resonance frequency analysis was developed to detect hairline cracks on eggshells. A roller conveyor was used to transfer eggs along one lane to the impact position where each of eggs rotated by the roller was excited with an impact device at four different locations on the eggshell equator. The impact device was consisted of a plastic hammer and a rotary solenoid. The acoustic response of the egg to the impact was measured with a small condenser microphone at the same position as the impact device was installed. Two acoustic parameters, correlation coefficient for normalized power spectra and standard deviation of peak resonant frequencies, were used to detect cracked eggs. Intact eggs showed relatively high correlations among the four normalized power spectra and low standard deviations of the four peak resonant frequencies. On the other hand, cracked eggs showed low correlations and high standard deviations as compared to the intact. This method allowed a crack detection rate of 97.6%.

• 한국소음진동공학회논문집
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• 제15권9호
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• pp.1084-1091
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• 2005

The indoor noise limit for road traffic noises is needed to secure comfortable acoustical quality in apartment houses. To achieve this goal, psycho-acoustic experiments were carried out with road traffic noise sources modulated by the transmission loss characteristics of the external windows. Finally, a correlation analysis between noise rating index and subjective responses, and an analysis of satisfactory percentage of the dose-response curves varied with respondents was conducted. As a result of this study, followings are suggested. (1) On correlation between dose level and psycho-acoustical response, the initial level of negative feeling is located on $40.1\~40.6\;L_{eq}$ dB(A), (2) On the degree of satisfaction to road traffic noise. near $35\;\%$ point being same dissatisfaction degree is to be assumed $40\~41$ dB(A) of indoor noise level presented into three vocabulary. It is suggested to be reasonable level of 40 dB(A) on the indoor noise limits for intruding road traffic noise. and it is appropriate to be the 5 dB level difference between grades. The results of this study may be used to evaluate the acoustic threshold level for road traffic noise or as a basis for specifying the desired acoustic environment of dwellings.

• 한국소음진동공학회논문집
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• 제25권8호
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• pp.575-582
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• 2015

This paper deals with the dispersion relation of the waves sustained in a cylindrical shell submerged in the fluid. The waveguide finite method and the boundary element method are used to predict the dispersion characteristic of the cylindrical shell. The dispersion diagram of the cylinder is estimated from the eigenvalue problem and the forced vibration response. It follows that the water-loading leads to the decrease of the cut-on frequencies and the phase speeds of the bending waves. On the contrary, the longitudinal waves and the torsional waves are hardly affected by the fluid, and therefore the order of the cut-on frequencies of the waves is changed. The acoustic dispersion diagram is also estimated from the forced acoustic response to identify the characteristics of the wave radiated to the fluid. It follows that the acoustic waves on and near the surface of the cylinder are the same as those in the structure. But at the far field the acoustic waves caused by subsonic waves e.g., the bending waves disappear as the increase of the distance. Conclusively, the characteristics of waves in cylindrical shells are significantly affected by water-loading in terms of the cut-on frequency, the wave speed, the order of the cut-on and radiation.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2004년도 춘계학술대회 논문집
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• pp.55-60
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• 2004

이 논문은 기적음이 선박 선교에 전달되는 음향전달특성의 측정기술에 관한 것이다. 실습선 ‘새누리호’를 대상으로 선교 내부에 전달되는 기적음을 선교문 개폐상태에 따라서 B＆K 2260D으로 측정한 후, B＆K 7830소프트웨어를 이용하여 주파수특성을 축출하였다. 측정한 주파수 특성을 이용하여 주파수 샘플링에 의한 FIR 필터 설계법으로 128차 FIR 필터를 구축하였다. 그리고, 기적원음과 FIR 필터의 콘볼류션 연산으로 실험음을 생성한 후, 6단계 평가지표를 이용하여 측정한 음향전달특성을 평가하였다. 평가결과, 실험음이 실제 선교에서 듣는 음과 '유사함'을 나타내는 A／sub s／=3.3∼4.7로 나타나서 본 연구에서 개발한 기법이 선교의 음향전달특성 측정기술로서 유효함을 확인하였다.

• 한국음향학회지
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• 제36권1호
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• pp.57-63
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• 2017

본 논문에서는 FxLMS(Filtered-x Least Mean Square) 알고리즘을 이용한 단일 센서 기반의 능동 반향음 제어 알고리즘을 제안한다. 제안 알고리즘은 먼저 단일 센서 입력 신호로부터 입사음과 반향음을 분리하고, 분리된 신호들을 사용하여 반향음과 반대 위상을 갖는 제어 신호를 생성한다. 제어 신호는 센서 위치에서 반향음과 중첩되어 반향음의 음압을 감소시킨다. 적절한 신호 분리를 위해 반향 음향 경로와 제어 음향 경로가 필요하며 이는 swept sine 신호를 이용해 측정한 음향 응답으로부터 사전에 구할 수 있다. 효용성을 검증하기 위해 DSP(Digital Signal Processing) 보드를 사용하여 제안된 알고리즘을 실시간으로 구현하였으며, 공기 중 음향 덕트 환경에서 1 kHz 버스트 신호에 대해 반향음이 11.6 dB 감소함을 확인 하였다.