• Title/Summary/Keyword: URN : Underwater Radiated Noise

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Analysis of Underwater Radiated Noise in Accordance with the ISO Standard and Class Notations Using the Hybrid Sound Propagation Model (하이브리드 음전달 모델을 이용한 ISO 및 선급별 수중방사소음 전달 특성 분석 )

  • Byungjun, Koh;Chul Won, Lee;Ji Eun, Lee;Keunhwa, Lee
    • Journal of the Society of Naval Architects of Korea
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    • v.59 no.6
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    • pp.362-371
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    • 2022
  • As considerable interests in noise emission from the ships have been increased, International Maritime Organization (IMO) standardized the Underwater Radiated Noise (URN) measurement process of commercial ships in deep seas by enacting the related ISO standard ISO 17208-1 and classification societies responded with the enactment or revision of corresponding notations. According to this trend, a new hybrid underwater sound propagation model based on underwater sound propagation theories was developed and its accuracy on analysis was verified through the result comparison with the results of other generally used models. Using the verified model, each URN propagation characteristics adjusted by the correction methods proposed in the ISO standard and class notations were analyzed and compared in two assumed URN measurement cases. The results showed that the effects of transmission loss corrections in the circumstances with less bottom reflections generally similar but they had rather large differences in the model analysis results with bottom-reflection-dominant conditions. It was concluded that the deep consideration of effective bottom-reflection-correction method should be made in future revisions of ISO standard and class notations.

A study on the Lloyd's mirror effect on the underwater radiated noise for the underwater vehicle (수중운동체 방사소음의 로이드 미러 효과 연구)

  • Kang, Seung-Hee
    • The Journal of the Acoustical Society of Korea
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    • v.40 no.4
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    • pp.314-319
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    • 2021
  • The measurement of the Underwater Radiated Noise (URN) for the underwater vehicle should consider both the acoustic interference due to the surface reflection and the calculation of the Closet Point of Approach (CPA). In this paper, I tried to analyze the underwater vehicle's URN using the Lloyd's mirror effect. First, the theoretical Lloyd's mirror pattern was compared with the sea trial result, and the sea trial results corresponded well with the theoretical predicted pattern. And then the CPA distance could be estimated by the Lloyd's mirror pattern. As a results, acoustic source level shows the spectral fluctuation due to the acoustic interference of the Lloyd's mirror effect.

Reduction of Fire Main Pipe System's Vibration Using Back Flow Prevent Globe Valve (역류방지 글로브 밸브를 이용한 소화 주관계의 진동개선)

  • Park, Mi-You;Han, Hyung-Suk;Lee, Seuk-Soo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2009.04a
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    • pp.518-523
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    • 2009
  • Main source of URN(Underwater Radiated Noise) which is related to the ship's survivability is divided into two groups. Cavitation is main source of URN when the speed of ship is upper than CIS(Cavitation Inception Speed). But when the speed of ship is lower than CIS, main source of URN is structure-borne noise on the hull which is originated from propulsion system, pump system or transmitted vibration of pipe system. In this paper, to reduce the vibration of discharge pipe and valve system, back flow prevent globe valve and new rubber mount are applied to the ship. As the result of applying new valve and mount, the vibration is reduced drastically.

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Reduction of Fire Main Pipe System's Vibration Using Back Flow Prevent Globe Valve (역류방지 글로브 밸브를 이용한 소화 주관계의 진동개선)

  • Park, Mi-You;Han, Hyung-Suk;Lee, Seuk-Soo
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.19 no.6
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    • pp.599-606
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    • 2009
  • Main source of URN(underwater radiated noise) which is related to the ship's survivability is divided into two groups. Cavitation is the main source of URN when the speed of ship is upper than CIS(cavitation inception speed). But when the speed of ship is lower than CIS, the main source of URN is the structure-borne noise on the hull which is originated from propulsion system, pump system and trnasmitted vibration of the pipe system. In this paper, to reduce the vibration of discharge pipe and valve system, back flow prevent globe valve and new rubber mount are applied to the ship. As the result of applying new valve and mount, the vibration is reduced drastically.

Analysis of Acoustic Radiation Efficiency and Underwater Radiated Noise of Double Bottom-shaped Structure (이중저 형상 구조물의 음향방사효율과 수중방사소음 해석)

  • Choi, Sung-Won;Kim, Kook-Hyun;Cho, Dae-Seung;Suh, Kyu-Youl
    • Journal of the Society of Naval Architects of Korea
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    • v.49 no.2
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    • pp.158-163
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    • 2012
  • Recently, reducing underwater radiated noise (URN) of ships has become an environmental issue to protect marine wildlife. URN of ships can be predicted by various methods considering its generating mechanism and frequency ranges. For URN prediction due to ship structural vibration in low frequency range, the fluid-structure interaction analysis technique based on finite element and boundary element methods (FE/BEM) is regarded as an useful technique. In this paper, URN due to a double bottom-shaped structure vibration has been numerically investigated based on a coupled method of FE/BEM to enhance the prediction accuracy of URN due to the vibration of real ship engine room structure. Acoustic radiation efficiency and URN transfer function in case of vertical harmonic excitation on the top plate of double bottom structure have been evaluated. Using the results, the validity of an existing empirical formula for acoustic radiation efficiency estimation and a simple URN transfer function, which are usually adopted for URN assessment in initial design stage, is discussed.

Experimental Validation on Underwater Sound Speed Measurement Method Using Cross-Correlation of Time-Domain Acoustic Signals in a Reverberant Water Tank (잔향 수조에서의 시간 이력 수음 신호 간 교차상관을 이용한 수중 음속 계측 방법에 관한 실험적 검증)

  • Joo-Yeob Lee;Kookhyun Kim;Sung-Ju Park;Dae-Seung Cho
    • Journal of the Society of Naval Architects of Korea
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    • v.61 no.1
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    • pp.1-7
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    • 2024
  • Underwater sound speed is an important analysis parameter on an estimation of the underwater radiated noise (URN) emitted from vessels. This paper aims to present an underwater sound speed measurement procedure using a cross-correlation of time-domain acoustic signals and validate the procedure through an experiment in a reverberant water tank. For the purpose, time-domain acoustic signals transmitted by a Gaussian pulse excitation from an acoustic projector have been measured at 20 hydrophone positions in the reverberant water tank. Then, the sound speed in water has been calculated by a linear regression using 190 cross-correlation cases of distances and time lags between the received signals and the result has been compared with those estimated by the existing empirical formulae. From the result, it is regarded that the presented experimental procedure to measure an underwater sound speed is reliably applicable if the time resolution is sufficiently high in the measurement.

Analysis for Reducing Vibration Transmitted from the Sea-Water Conveying Pipe to the Hull (선체로 전달되는 해수 이송 배관의 진동 저감 분석)

  • Han, Hyung-Suk;Park, Mi-Yoo;Jeong, Weui-Bong
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2008.11a
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    • pp.145-151
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    • 2008
  • URN(Underwater Radiated Noise) is one of the important performances of the battle ship related to the stealth. The main source of the URN is the structure-borne noise on the hull. And the pipe vibration transmitted to the hull is the main source of the structure-borne noise when the speed of the ship is lower than CIS(Cavitation Inception Speed). In this paper, the vibration isolator(rubber mount) for the pipe system is described in order to reduce the structure-borne noise transmitted to the hull. The vibrations on the sea-water conveying pipes and their supports are measured in order to know how much vibration occurs on those positions. Based on these test results, the improved design of the rubber mount is suggested by the parametric study and is verified numerically with the pipe and hull model.

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Analysis for Reducing Vibration Transmitted from the Sea-water Conveying Pipe to the Hull (선체로 전달되는 해수 이송 배관의 진동 저감 분석)

  • Han, Hyung-Suk;Jeong, Weui-Bong;Park, Kyung-Hoon;Hong, Chin-Suk
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.18 no.11
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    • pp.1177-1184
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    • 2008
  • URN(underwater radiated noise) is one of the important performances of the battle ship related to the stealth. The main source of the URN is the structure-borne noise on the hull. And the pipe vibration transmitted to the hull is the main source of the structure-borne noise when the speed of the ship is lower than CIS(cavitation inception speed). In this paper, the vibration isolator(rubber mount) for the pipe system is described in order to reduce the structure-borne noise transmitted to the hull. The vibrations on the sea-water conveying pipes and their supports are measured in order to know how much vibration occurs on those positions. Based on these test results, the improved design of the rubber mount is suggested by the parametric study and is verified numerically with the pipe and hull model.

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.

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.