• Proceedings of KOSOMES biannual meeting
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• 2007.05a
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• pp.109-113
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• 2007

Yacht have an high powered main engine relatively light hull, so the noise generated from the engine have a bad influence upon the crew and passenger. Recently, cruise yacht is made an attempt by domestic production skill, however the insulation skill of the noise made by the main engine is not satisfy the real purchasing power of the buyer. Like this, yacht cabin's noise level is becoming the barometer to decide the purchase. the method to insufficient. However, if we use the skill of the monitoring equipment and the genetic algorithm system, the circumference of the main engine can be enclosed by an high quality absorbtion wall and the noise levels of the cabins are improved. In this study, the sound absorbtion barrier is experimentally researched by change the volume and the length of the neck for the Helmholtz resonator as the resonator can absorb the noise effectively.

• The Journal of the Acoustical Society of Korea
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• v.30 no.1
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• pp.9-16
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• 2011

When a hydrofoil ship plies at high speed, there exist possibilities of collision with ocean mammals dwelling near the surface. An active sonar located within the immersed hydrofoil structure that provides the lift for the vessel, can be used for early warning of their presence. The proper functioning of the active sonar system depends on its ability to reject noise and pick up the target signal. In this article, we measured the noise on a hydrofoil of an operating ship with two flush-mounted hydrophones. The measurements were conducted for the purpose of (1) identifying the effect of operating state of machinery likes engine, cooler and generator (2) observing the change of noise depending on the measuring position (3) observing the change of noise with increasing ship speed. To verify our experiment, experiments were performed three times and the measured results are compared with other investigations and they show similarity to each other. The results are analyzed with frequency domain in order to apply to operating active sonar detecting system and focus on high frequency band within sonar's operating frequency region. Through these experiments and analysis, it is expected that we can identify the generated noise around hydrofoil where active sonar is installed and these results lead us to design active sonar that could distinguish target signal from noise more effectively.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.235-241
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• 2022

Several studies using Convolutional Neural Network (CNN) have been conducted to detect and classify the sounds of marine mammals in underwater acoustic data collected through passive acoustic monitoring. In this study, the possibility of automatic classification of bearded seal sounds was confirmed using a CNN model based on the underwater acoustic spectrogram images collected from August 2017 to August 2018 in East Siberian Sea. When only the clear seal sound was used as training dataset, overfitting due to memorization was occurred. By evaluating the entire training data by replacing some training data with data containing noise, it was confirmed that overfitting was prevented as the model was generalized more than before with accuracy (0.9743), precision (0.9783), recall (0.9520). As a result, the performance of the classification model for bearded seals signal has improved when the noise was included in the training data.

• Journal of Ocean Engineering and Technology
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• v.26 no.2
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• pp.14-19
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• 2012

There are insufficient data to consider the effect zone for the marine life of coastal fisheries, because no standard has been defined for the sound level of marine life. In this study, equations for distance attenuation were used to determine the effect zone for oceanic noises. A reference noise level was divided into 4 parts to consider the characteristics of the fishes, and the effect zone of each reference noise level was determined. To increase the reliability of the effect scope, approximately 100 repetitions of blasting work split into several parts by the boring depth, the sound level of the source caused by an increase in weight, and the effect zone were calculated using the prediction equation. According to the prediction, the maximum distance of the effect zone was 4.92 km.

• The Journal of the Acoustical Society of Korea
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• v.10 no.1
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• pp.47-51
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• 1991

it is well observed in the ocean that the surface disturbances due to rain, wind and breaking waves generate bubble clouds several meters deep from the water surfaces. Thses kinds of bubble clouds can work as a physical mechanism to produce underwater ambient noise. In the laboratory experiment observing the noise generated from a bubble cloud we showed a role of individual bubbles in collective oscillations of a bubble cloud. The experimental data agree very well with the theoretical predictions. These results confirm that the collective oscillations of a bubble cloud is one of the more likely mechanisms for an ocean ambient noise source around several hundred hertz.

• The Journal of the Acoustical Society of Korea
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• v.42 no.3
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• pp.233-242
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• 2023

In this paper, the effect of mass injection on the control of tip vortex cavitation was studied experimentally. A mass injection system for a 3D hydrofoil was designed to control the location of injection as well as the injection rate. A series of cavitation tests were carried out in a cavitation tunnel for different injection locations and rates. The cavitation behaviour was observed using a high-speed camera and the corresponding noise was measured using a hydrophone installed in the observation window. The results showed that the tip vortex cavitation was suppressed under certain conditions and the noise was reduced in some frequency bands. It was also found that there is a location where the effect of mass injection could be maximized and hence the noise reduction.

• The Journal of the Acoustical Society of Korea
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• v.34 no.3
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• pp.200-209
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• 2015

An underwater sound surveillance system detects and tracks enemy ships in real-time using hydrophone arrays, in which seabed-mounted sensor arrays play a pivotal role. In this paper the conceptual design of seabed-mounted, cylindrical hydrophone arrays for use in shallow coastal waters is performed via finite element calculations. To stabilize the receiving characteristics under the ocean ambient noise, a technique for whitening the ambient noise spectrum using a metal baffle is proposed. Optimization of the array configuration is performed to achieve the directivity in the vertical and azimuthal directions. And the effects of the sonar dome shape and material on the structural vibration and sound scattering properties are studied. It is demonstrated that a robust hydrophone array, having a sensitivity deviation less than 4 dB over the frequency range of interest, can be obtained through the whitening of the ambient noise, the optimization of the array configuration, and the design of acoustically transparent sonar domes.

• The Journal of the Acoustical Society of Korea
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• v.41 no.4
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• pp.375-388
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• 2022

This paper deals with the process of obtaining sound transmission loss of a cylindrical silencer lined with multi-layered poroelastic sound absorbing materials. The Biot model and the Johnson-Champoux-Allard-Lafarge (JCAL) model were used to deal with waves propagating in multi-layered poroelastic materials. The boundary conditions required for analysis of the silencer were obtained and the numerical process of finding modes was explained. A numerical experiment was conducted on the 2-layered silencer using the modes and the transmission loss converged with the first 12 modes. Finally, the mode matching method proposed in this research was validated by being compared with the results calculated from Finite Element Method (FEM) about different kinds of sound absorbing materials.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.393-396
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• 2004

본 논문에서는 선박의 소음을 이용한 선박의 위치추적 및 지음향학적 인자의 역산 기법을 제안하였다. 예인 수평선배열에 의해 계측된 선박의 소음을 시간역전시켜(time reversed) 역전파(back propagation)시킨 음파는 해당 해양환경과 동일한 경우 원래의 음원 즉 선박의 위치에 가장 큰 에너지가 집중된다. 이러한 역전파된 신호의 집중 정도를 이용하여 음원의 위치 및 해양환경(특히 지음향학적 환경) 정보를 추정하였다. 본 역산에서 사용된 목적함수는 정합임펄스응답필터를 사용하여 음원의 위치에 집중된 정규화된 파워로 정의되었다. 최적화 알고리즘으로 유전알고리즘과 Powell 방법이 함께 사용되었다. 제안된 기법을 Elba섬 근해에서 실시된 MAPEX 2000 실험 데이터에 적용한 후 그 결과를 본 논문에서 제시하였으며 그 효용성을 확인하였다.

• The Journal of the Acoustical Society of Korea
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• v.34 no.6
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• pp.432-443
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• 2015

Coherence describing the similarity between physical quantities of two signals is a very useful tool to investigate the temporal and spatial characteristics of signals propagating in underwater acoustic waveguide. Ambient noise measurements were made by the vertical received array consisting of three hydrophones as part of the KIOST-HYU joint acoustics experiment, and the coherence for the underwater ambient noise was analyzed. In this paper, the coherence results in cases that the generator in the research vessel was off and turned on are presented. The coherence estimated in the case of the generator operation mode are compared to the predictions obtained using the theoretical model with the directional density function dominated by vertical components propagating downward from the ship. In the case of the generator switch-off, the results are compared to the model predictions with directional density function including the effects of sea surface noise and long-distance shipping noise.