• 한국군사과학기술학회지
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• 제24권2호
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• pp.228-236
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• 2021

In order to understand the underwater noise source factor of the linear pump type forced ejection system, a reduced-model compressed water experiment device was developed. The reduced-model compressed water experiment device consists of a reverberation tank, a linear pump type forced ejection device, and an underwater vehicle. The underwater noise source was selected from the hydraulic ram moving speed, the hydraulic ram/piston pipe spacing, the ejection pipe inlet/water ram area ratio, and the number of water ram inlets. The underwater vehicle was ejected into the reverberation tank by the device. The source level was derived from the measured sound pressure. The source level tends to increase as the hydraulic ram/piston tube spacing and the hydraulic ram moving speed increase. The source level tended to increase as the area ratio was increased, but the level was weak. The number of water ram inlet did not affect the source level.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.344-347
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• 2006

Noise reduction and control is an important problem in the performance of underwater acoustic system and on the habitability of the passenger ship for crew and passenger. Furthermore, sound generated by a propeller is critical in underwater detection and is often related to the survivability of the vessel especially for military purpose. Generally propeller noise is often the dominant noise source of marine vehicle. The flow field is analyzed with potential-based panel method, and then the time dependent pressure and sheet cavity volume data are used as the input for Ffowcs Williams-Hawkings formulation to predict the far-field acoustics. Through this study, the dominant noise source of underwater propeller is analyzed, which will provide a basis for proper noise control strategies.

• 한국해양공학회지
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• 제22권1호
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• pp.30-36
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• 2008

Underwater ambient noise originating from geophysical, biological, and man-made acoustic sources contains information on the source and the ocean environment. Such noise affectsthe performance of sonar equipment. In this paper, three steps are used to identify the ambient noise source, detection, feature extraction, and similarity measurement. First, we use the zero-crossing rate to detect the ambient noisesource from background noise. Then, a set of feature vectors is proposed forthe ambient noise source using the Hilbert-Huang transform and the Karhunen-Loeve transform. Finally, the Euclidean distance is used to measure the similarity between the standard feature vector and the feature vector of the unknown ambient noise source. The developed algorithm is applied to the observed ocean data, and the results are presented and discussed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.138-142
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• 2001

A comparison between theoretical and measured transfer function, which relates structure-borne noise source level to underwater radiated noise, of a naval ship is presented in this study. Transfer functions are obtained by dividing far field underwater noise by the value of structure borne noise source levels below machinery mounts. In prediction, statistical energy analysis of the whole ship structure is used to get vibration levels of wetted hull plates below water line. Then, far field radiated noise is calculated by summing up contributions from each plates using vibration levels and radiation efficiencies. And 1/3-octave band underwater sound pressure at the distance of 1 m away from the hull were measured to get experimental transfer functions. The two transfer functions are compared to show resonable agreements in spite of the subtle physical differences between each other.

• 한국음향학회지
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• 제41권3호
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• pp.268-277
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• 2022

본 논문에서는 KVLCC2 선체 축소모형에 설치된 추진시스템의 세부 구성품별 유동 소음원을 분석하였으며, 각각의 소음원이 수중방사소음에 미치는 영향에 대해 정량적으로 분석하였다. 수치 해석 영역은 실험 결과와의 비교를 위하여 선박해양플랜트연구소 대형 캐비테이션 터널의 시험부와 동일하게 설정하였다. 먼저 유동장내 소음원을 정확하게 모사하기 위하여 고정밀 해석기법인 비압축성 다상 Delayed Detached Eddy Simulation 방법을 적용하였고, 유동해석 결과를 기반으로 Ffowcs Williams and Hawkings 적분방정식을 사용하여 수중방사소음을 예측하였으며, 터널 실험결과와의 비교를 통해 해석절차의 유효성을 확인하였다. 추진시스템의 유동 소음원별 영향을 정량적으로 비교하기 위하여 추진기 날개 끝-와류 공동, 날개 표면 그리고 방향타 표면을 소음원 영역으로 선정하였으며, 음압과 파워 스펙트럼 밀도, 음향 파워를 비교하였다. 공동에 의한 홀극 소음원의 기여도가 추진기 날개 및 방향타에 의한 쌍극 소음원에 비해 수중방사소음에 크게 기여하였으며, 추진기 후류의 영향으로 방향타에 의한 기여도가 추진기 보다 더 크게 발생함을 확인하였다.

• 수산해양기술연구
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• 제16권2호
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• pp.69-76
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• 1980

This paper describes the measurement of the underwater noises produced by the engine vibration around the engine room of stern trawler MIS Sae-Ba-Da(2275GT, 3,600 PS) and pole kner M/S Kwan-Ak-San (243 GT, 1000 PS) while the ship is stopping. The underwater noise pressure level was measured with the underwater level meter of which measuring range is 100 to 200 dB(re bLPa). A and B denotes the maximum pressure level measured at right beneath the bottom of the engine room, while the main engine of the Sae-Ba-Da revoluted at 750 and 500 rpm, respectively. C denotes that of the main engine of the Kwan-Ak-San revoluted at 350 rpm, and D that of the generator of the Sae-Ba-Da revoluted at 720 rpm. Thus A, B, C and D were set for the standard sound source for the experiment. The results obtained are as follows: 1. The noise Pressure level at A, B, C and D were 170.5,165,153 and 158dB, respectively. 2. When the check points distanted vertically 1, 10, 20, 30, 40, 50m from the sound source, the underwater noise presure levels were 170.5, 155, 148, 144 and 138 dB and the directional angle was 116\ulcorner in case of A. 3. The sound level attenuated at the rate of 20dB per 10" meters of the horizontal distance from the sound sources. 4. The frequency distribution of the noise was 100Hz to 10KHz and predominant frequency was 700 to 800Hzminant frequency was 700 to 800Hz

• 대한조선학회논문집
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• 제48권6호
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• pp.569-574
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• 2011

In research vessels or naval ships, airborne noise from machineries such as diesel engine is the major source of underwater noise at low speed. In this paper, effect of engine noise on underwater noise is studied by considering two paths; sound radiation from hull plate and direct airborne noise transmission through hull plate. SEA (Statistical energy analysis) is used to predict hull plate vibration induced by engine noise, where SEA model consists of only two subsystems; engine room air space and hull plate. The pressure level in water is calculated from sound radiation by plate. Engine noise transmission through hull plate is obtained by assuming plane wave propagation in air-limp plate-water system. Two effects are combined and compared to the measurement, where speaker is used as a source in engine room and sound pressure levels in engine room and water are measured. The hydrophone is located 1 m away from the hull plate. It is found below 1000 Hz, prediction overestimates underwater sound pressure level by 5 to 12 dB.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 춘계학술대회 논문집
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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.

• 한국소음진동공학회논문집
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• 제19권6호
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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.

• 한국군사과학기술학회지
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• 제6권2호
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• pp.20-34
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• 2003

The good sea-keeping capability of the SWATH(Small Waterplane Area Twin Hull) ship has been attractive for research or surveillance vessels. Especially, for the naval ships accomplishing the underwater acoustic missions, it is necessary to access and minimize the underwater radiated noise level generated by the ships. Therefore, acoustic signature management and control are very important topics for these vessels. Underwater radiation pattern in the low frequency range is dominated by the tonals from the vibration of onboard machinery. In this work, the radiated noise level generated by the propulsion machine in the submerged hull is predicted using the transfer function technique and the hull transfer function for the submerged hull is determined by analyzing the longitudinal/circumferential stiffened infinitely long cylindrical shell and considering the empirical database of the previous vessels. It is confirmed that the transfer function technique can give useful information for identifying the noise source and estimating its contribution to the total radiatied noise level.