• Title/Summary/Keyword: Underwater Radiated Noise

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Range estimation of underwater acoustic moving source using Doppler frequency map (도플러 주파수 맵을 이용한 수중 이동 음원의 거리 추정)

  • Park, Woong-Jin;Kim, Ki-Man;Han, Min su;Choi, Jae-Yong
    • 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.

Multiple vertical depression-based HMS active target detection using GSFM pulse (GSFM 펄스를 이용한 다중 수직지향각 기반 선체고정소나 능동 표적 탐지)

  • Hong, Jungpyo;Cho, Chomgun;Kim, Geunhwan;Lee, Kyunkyung;Yoon, Kyungsik
    • The Journal of the Acoustical Society of Korea
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    • v.39 no.4
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    • pp.237-245
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    • 2020
  • In decades, active sonar, which transmits signals and detects incident signals reflected by underwater targets, has been significantly studied since passive sonar in Anti-Submarine Warfare (ASW) detection performance becomes lowered, as underwater threats become their radiated noise reduced. In general, active sonar using Hull-Mounted Sonar (HMS) adjusts vertical tilt (depression) and sequentially transmits multiple Linear Frequency Modulation (LFM) subpulses which have non-overlapped bands, i. e. 1 kHz ~ 2 kHz, 2 kHz ~ 3 kHz, in order to reduce shadow zones. Recently, however, Generalized SFM (GSFM), which is generalized form of SFM, is proposed, and it is confirmed that subpulses of GSFM have orthogonality among each other depending on setting of GSFM parameters. Hence, in this paper, we applied GSFM to active target detection using HMS to improve the performance by the signal processing gain obtained from enlarged bandwidths of GSFM subpulses compared to those of LFM subpulses. Through simulation, we verified that when the number of subpulses is three, the matched filter gain of GSFM is approximately 5 dB higher than that of LFM.

Detection of low frequency tonal signal of underwater radiated noise via compressive sensing (압축센싱 기법을 적용한 선박 수중 방사 소음 신호의 저주파 토널 탐지)

  • Kim, Jinhong;Shim, Byonghyo;Ahn, Jae-Kyun;Kim, Seongil;Hong, Wooyoung
    • The Journal of the Acoustical Society of Korea
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    • v.37 no.1
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    • pp.39-45
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    • 2018
  • Compressive sensing allows recovering an original signal which has a small dimension of the signal compared to the dimension of the entire signal in a short period of time through a small number of observations. In this paper, we proposed a method for detecting tonal signal which caused by the machinery component of a vessel such as an engine, gearbox, and support elements. The tonal signal can be modeled as the sparse signal in the frequency domain when it compares to whole spectrum range. Thus, the target tonal signal can be estimated by S-OMP (Simultaneous-Orthogonal Matching Pursuit) which is one of the sparse signal recovery algorithms. In simulation section, we showed that S-OMP algorithm estimated more precise frequencies than the conventional FFT (Fast Fourier Transform) thresholding algorithm in low SNR (Signal to Noise Ratio) region.

Lofargram analysis and identification of ship noise based on Hough transform and convolutional neural network model (허프 변환과 convolutional neural network 모델 기반 선박 소음의 로파그램 분석 및 식별)

  • Junbeom Cho;Yonghoon Ha
    • The Journal of the Acoustical Society of Korea
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    • v.43 no.1
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    • pp.19-28
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    • 2024
  • This paper proposes a method to improve the performance of ship identification through lofargram analysis of ship noise by applying the Hough Transform to a Convolutional Neural Network (CNN) model. When processing the signals received by a passive sonar, the time-frequency domain representation known as lofargram is generated. The machinery noise radiated by ships appears as tonal signals on the lofargram, and the class of the ship can be specified by analyzing it. However, analyzing lofargram is a specialized and time-consuming task performed by well-trained analysts. Additionally, the analysis for target identification is very challenging because the lofargram also displays various background noises due to the characteristics of the underwater environment. To address this issue, the Hough Transform is applied to the lofargram to add lines, thereby emphasizing the tonal signals. As a result of identification using CNN models on both the original lofargrams and the lofargrams with Hough transform, it is shown that the application of the Hough transform improves lofargram identification performance, as indicated by increased accuracy and macro F1 scores for three different CNN models.

A Numerical Analysis on Acoustic Radiation Efficiency of One Side-Wetted Rectangular Mindlin Plate with Simply Supported Boundaries (Mindlin 판 이론을 적용한 단순지지 단면 접수평판의 음향방사효율 수치해석)

  • Lee, Jong-Ho;Cho, Dae-Seung
    • Journal of the Society of Naval Architects of Korea
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    • v.55 no.4
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    • pp.281-288
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    • 2018
  • Acoustic radiation efficiency is a crucial factor to estimate Underwater Radiated Noise (URN) of ships accurately. This paper describes a numerical method to analyse acoustic radiation efficiency of one side-wetted rectangular Mindlin plate with simply supported boundaries excited by a harmonic point force. Transverse displacements of plate and acoustic radiation pressures are evaluated by the mode superposition method. The acoustic radiation efficiencies analyzed by both Mindlin and thin plate theories show little differences at monopole and corner modes of low frequency regions but relatively large differences at edge and critical modes of high frequency regions. Especially, the critical frequency with the highest acoustic radiation efficiency evaluated by the Mindlin plate theory is higher than that of thin plate theory. In addition, the acoustic loading effect of fluid also increases bending wave-number of plate and its critical frequency. Finally, the acoustic radiation characteristics of plates with different aspect ratios and thicknesses through numerical analyses are investigated and discussed.

Flow-Induced Noise Prediction for Submarines (잠수함 형상의 유동소음 해석기법 연구)

  • Yeo, Sang-Jae;Hong, Suk-Yoon;Song, Jee-Hun;Kwon, Hyun-Wung;Seol, Hanshin
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.24 no.7
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    • pp.930-938
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    • 2018
  • Underwater noise radiated from submarines is directly related to the probability of being detected by the sonar of an enemy vessel. Therefore, minimizing the noise of a submarine is essential for improving survival outcomes. For modern submarines, as the speed and size of a submarine increase and noise reduction technology is developed, interest in flow noise around the hull has been increasing. In this study, a noise analysis technique was developed to predict flow noise generated around a submarine shape considering the free surface effect. When a submarine is operated near a free surface, turbulence-induced noise due to the turbulence of the flow and bubble noise from breaking waves arise. First, to analyze the flow around a submarine, VOF-based incompressible two-phase flow analysis was performed to derive flow field data and the shape of the free surface around the submarine. Turbulence-induced noise was analyzed by applying permeable FW-H, which is an acoustic analogy technique. Bubble noise was derived through a noise model for breaking waves based on the turbulent kinetic energy distribution results obtained from the CFD results. The analysis method developed was verified by comparison with experimental results for a submarine model measured in a Large Cavitation Tunnel (LCT).

Analysis of Hull-Induced Flow Noise Characteristics for Wave-Piercing Hull forms (파랑관통형 선형의 선체유기 유동소음특성에 관한 연구)

  • Choi, Woen-Sug;Hong, Suk-Yoon;Song, Jee-Hun;Kwon, Hyun-Wung;Seo, Jeong-Hwa;Rhee, Shin-Hyung
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.24 no.5
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    • pp.619-627
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    • 2018
  • As ships become faster, larger and are required to meet higher standards, the importance of flow noise is highlighted. However, unlike in the aeroacoustics field for airplanes and trains (where flow noise is considered in design), acoustics are not considered in the marine field. In this study, analysis procedures for hull-induced flow noise are established to investigate the flow noise characteristics of a wave-piercing hull form that can negate the effect of wave-breaking. The principal mechanisms behind hull-induced flow noise are fluid-structure interactions between complex flows underneath the turbulent boundary layer and the hull. Noise induced by the turbulent boundary layer was calculated using wall pressure fluctuation and energy flow analysis methods. The results obtained show that noise characteristics can be distinguished by frequency range and hull region. Also, the low-frequency range is affected by hull forms such that it is correlated with ship speed.

Measurement System for Performance Evaluation of Acoustic Materials in a Small Water Tank (소형수조에서 음향재료의 반향음감소와 투과손실 측정시스템 구성)

  • Shin, Mi-Ru;Cho, Jung-Hong;Lee, Kyung-Teak;Kim, Jea-Soo;Jeon, Jae-Jin;Ham, Il-Bea;Kang, Chang-Gi
    • The Journal of the Acoustical Society of Korea
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    • v.30 no.2
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    • pp.63-72
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    • 2011
  • Since the detection probability is critically dependent on the target strength (TS) in active sonar and on the radiated noise level (RNL) in passive sonar, the acoustic materials for echo reduction (ER) and transmission loss (TL) are widely used for the stealth of underwater targets. In this paper, a measurement system based on the small water tank, for the frequency range of greater than 30 kHz, is developed and verified using reference targets. In order to design the water tank and the geometry of test samples, a program is developed to calculate the arrival time of interfering signals due to the reflection from water tank walls and also due to the diffraction from the edge of the test samples. Considering all the interfering signals, an optimal experimental configuration for water tank and test samples is designed and used throughout the experiment. Next, the signal processing algorithms to estimate ER and TL are developed based on the measured propagation loss reflecting the geometric spreading characteristics of the transducer. Finally, a set of reference targets such as aluminium plate and perfectly reflecting plate are used in a small water tank to verify the developed measurement system.

Detection of tonal frequency of underwater radiated noise via atomic norm minimization (Atomic norm minimization을 통한 수중 방사 소음 신호의 토널 주파수 탐지)

  • Kim, Junhan;Kim, Jinhong;Shim, Byonghyo;Hong, Jungpyo;Kim, Seongil;Hong, Wooyoung
    • The Journal of the Acoustical Society of Korea
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    • v.38 no.5
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    • pp.543-548
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    • 2019
  • The tonal signal caused by the machinery component of a vessel such as an engine, gearbox, and support elements, can be modeled as a sparse signal in the frequency domain. Recently, compressive sensing based techniques that recover an original signal using a small number of measurements in a short period of time, have been applied for the tonal frequency detection. These techniques, however, cannot avoid a basis mismatch error caused by the discretization of the frequency domain. In this paper, we propose a method to detect the tonal frequency with a small number of measurements in the continuous domain by using the atomic norm minimization technique. From the simulation results, we demonstrate that the proposed technique outperforms conventional methods in terms of the exact recovery ratio and mean square error.

A Study on Improvement of Submarine Attack Periscope Operation Performance using Installing Protector on Sail (잠수함 공격잠망경 함교 보호구조물 설치를 통한 장비 운용성능 향상에 관한 연구)

  • Choi, Woo-Seok;Chang, Ho-Seong;Lee, Young-Suk;Kim, Sang-Il
    • 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.