• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.11
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• pp.747-752
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• 2015

Underwater radiated noise is an important characteristic in the naval weapon systems. It is difficult to measure the radiation efficiency of underwater vehicle, such as UUV(unmanned underwater vehicle) and underwater weapons in real operation environment. In this study, acoustic radiation efficiency of a circular cylindrical structure is measured in the laboratory-water tank. The radiation efficiency is compared with the numerical results and it is found that they are in a good agreement. Therefore, the measurement method can be applied effectively for predicting the underwater radiation noise and effectiveness of radiation reduction means.

• The Journal of the Acoustical Society of Korea
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• v.38 no.4
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• pp.378-386
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• 2019

Unlike ship noise that radiates from moving ships, wind noise is caused by breaking waves as a result of the interaction between the wind and the sea surface. In this paper, WNL (Wind Noise Level) was modeled by considering the noise source of the wind as the bubble cloud generated by the breaking waves. In the modeling, SL( Source Level) of the wind noise was calculated using the wind-speed data measured from the weather buoy operated in the coastal area of the East Sea. At the same time as observing the wind speed, NL (Noise Level) was continuously measured using a self-recording hydrophone deployed near the weather buoy. The modeled WNL according to the wind speed and the measured NL removing the shipping noise from the acoustic raw data were compared in the low-frequency band. The overall trends between the modeled WNL and the measured NL were similar to each other. Therefore, it was confirmed that it is possible to model the WNL in the shallow water considering the SL and distribution depth of bubble cloud caused by the wind.

• The Journal of the Acoustical Society of Korea
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• v.25 no.7
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• pp.333-338
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• 2006

This paper proposes an improved do-noising method using multi-thresholding function based on translation-invariant (W) wavelet proposed by Donoho et al. for underwater radiated noise measurement. The traditional wavelet thresholding de-noising method causes Pseudo-Gibbs phenomena near singularities due to discrete wavelet transform. In order to suppress Pseudo-Gibbs Phenomena, a do-noising method combining multi-thresholding function with the translation-invariant wavelet transform is proposed in this paper. The multi-thresholding function is a modified soft-thresholding to each node according to the discriminated threshold so as to reject かon external noise and white gaussian noise. It is verified by numerical simulation. And the experimental results are confirmed through sea-trial using multi-single sensors.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.397-400
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• 2004

소음원 또는 방사음장을 가시화하기 위하여 소음원을 둘러싸는 한 면에서의 음압측정을 통해 임의의 3차원 공간상의 음향 물리량을 예측하는 음향 홀로그래피 방법이 사용되고 있으며 이때 반사파가 존재하지 않는 기본 가정을 만족해야 한다. 반사파가 존재하는 경우에는 반사파를 보정하거나 또는 반사파의 음장이 미치는 영향이 무시할 만큼 작다고 가정하여 음장 예측이 가능하게 된다. 최근 해양연구원에서는 음향 홀로그래피 방법을 이용하여 수중음장을 가시화하는 시스템을 개발하였으며 시스템 검증을 위해 무향수조 내 단순음원을 이용하여 음장예측을 수행하였다. 무향수조 표면에는 흡음처리가 되지 않아 표면 반사파가 존재하나 해석 결과 반사파의 영향이 작은 경우에는 반사파를 무시하고 음장해석의 수행이 가능함을 확인하였다.

• The Journal of the Acoustical Society of Korea
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• v.38 no.2
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• pp.154-159
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• 2019

When measuring the radiating noise of an underwater moving source, the range information between the acoustic source and the receiver is an important evaluation factor, and the measurement standards such as a receiver position, a moving source depth and a speed are set. Although there is a method of using the cross correlation as a method of finding the range of the underwater moving source, this method requires a time synchronization process. In this paper, we proposed the method to estimate the range by comparing the Doppler frequency difference of the theoretically calculated multipath signal with the Doppler frequency difference of the multipath signal estimated from the received signal. The proposed method does not require a separate time synchronization process. Simulations were performed to verify the performance, and the ranging error of the proposed method reduced by about 95 % than that of the conventional method.

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.78-88
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• 2024

Ship-radiated noise received by passive sonar that can measure underwater noise can be identified and classified ship using Detection of Envelope Modulation on Noise (DEMON) analysis. However, in a low Signal-to-Noise Ratio (SNR) environment, it is difficult to analyze and identify the target frequency line containing ship information in the DEMONgram. In this paper, we conducted a study to extract target frequency lines using semantic segmentation among deep learning techniques for more accurate target identification in a low SNR environment. The semantic segmentation models U-Net, UNet++, and DeepLabv3+ were trained and evaluated using simulated DEMONgram data generated by changing SNR and fundamental frequency, and the DEMONgram prediction performance of DeepShip, a dataset of ship-radiated noise recordings on the strait of Georgia in Canada, was compared using the trained models. As a result of evaluating the trained model with the simulated DEMONgram, it was confirmed that U-Net had the highest performance and that it was possible to extract the target frequency line of the DEMONgram made by DeepShip to some extent.

• The Journal of the Acoustical Society of Korea
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• v.36 no.6
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• pp.413-418
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• 2017

When measuring the radiated noise of an underwater vehicle, range information between acoustic source and receiver is an important evaluating factor, but it cannot use GPS. There is a method of using the cross correlation for finding the range of the acoustic source instead of the GPS. However, this method has heavy computational loads. This paper proposes a fast Fourier transform based method with a relatively small amount of computation to estimate the range of a source. The proposed method estimates Doppler frequencies of CW signals received at multiple receivers by fast Fourier transform and estimates the source range by comparing theoretical Doppler frequencies map previously calculated by a receiver position and source depth information. Simulation and lake trial were performed to verify the performance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.5
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• pp.199-206
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• 2021

This paper describes the feasibility and reliability verification of installing a protective structure to protect attack periscopes. The attack periscope is the critical equipment of a submarine to enable the user to monitor surface and air activity, collect navigational data, and detect and identify targets. The attack periscope provides target information acquired through TV, IR camera, and laser range finder to the combat system. In the product improvement program, the upper part of the masts was exposed to the outside of the sail because the existing attack periscope was replaced with a new one. On the other hand, the head sensor can be damaged by floating objects, such as fishing nets, during sea navigation. Therefore, the installation of a protective structure for an attack periscope improved the equipment operation performance. The feasibility and reliability of the installation of the protective structure were verified by examining the influence of URN.

• The Journal of the Acoustical Society of Korea
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• v.26 no.4
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• pp.173-181
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• 2007

In this paper, we propose a moving target localization algorithm using acoustic spectrograms. A time-versus-frequency spectrogram provide a information of trajectory of the moving target in underwater. For a source at sufficiently long range from a receiver, broadband striation patterns seen in spectrogram represents the mutual interference between modes which reflected by surface and bottom. The slope of the maximum intensity striation is influenced by waveguide invariant parameter ${\beta}$ and distance between target and sensor. When more than two sensors are applied to measure the moving ship-radited noise, the slope and frequency of the maximum intensity striation are depend on distance between target and receiver. We assumed two sensors to fixed point then form a circle of apollonios which set of all points whose distances from two fixed points are in a constant ratio. In case of three sensors are applied, two circle form an intersection point so coordinates of this point can be estimated as a position of target. To evaluates a performance of the proposed localization algorithm, simulation is performed using acoustic propagation program.