• Journal of the Society of Naval Architects of Korea
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• v.31 no.1
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• pp.84-93
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• 1994

The purpose of present study is to investigate the surface roughness on tip-vortex cavitation and its induced noise, emanating from an elliptic wing of NACA 0012 section. Roughness elements of $200{\mu}m$ are applied to the 10% portion of wing tip, and then, the wing tip as well as the leading edge. It is shown from cavitation observation that the cavitation inception is first visible at about half chord downstream of wing tip for most experimental conditions, and developed into the tip-vortex cavitation and finally the fully developed cavitation as cavitation number is decreased. Acoustic noise generated by a tip-vortex cavitation has its frequency range of 3 kHz to 50 kHz, while the fully-developed cavitation at lower cavitation number induces a broad band spectrum. It is also shown that, when the roughness elements are applied to the wing tip and the leading edge, the cavitation characteristics and its induced noise are improved. Moreover, it is appeared that the condition at which the rough surface is at pressure side gives a better result. although its lift-drag ratio is reduced.

• The Journal of the Acoustical Society of Korea
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• v.19 no.8
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• pp.47-53
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• 2000

In order to classify the underwater vehicles due to propeller propulsion, maximum likelihood classifier was developed. Propeller produces the cavitation and noise during its work. Cavitation-bubble makes the nonlinear medium in the water. The nonlinearity of cavitation leads to the generation of a complete spectrum of combination harmonics of the tonals of noise, and modulation of cavitation noise with propeller shaft-rates and blade-rates. The optimal estimator was derived mathematically and its capabilities were proven by simulation and real test.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.9
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• pp.1170-1174
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• 2014

If cavitation occurs in propeller, it generates vibration and noise accordingly which results in low efficiency of propeller. It's important to increase cavitation inception speed(CIS) since the noise of cavitation increases significantly from the beginning of cavitation. This paper describes the result of actual observation and measurement onboard ship with controllable pitch propeller(CPP), so as to verify the first occurrence phenomenon of cavitation. The research suggests new type of controllable pitch propeller with improved CIS at the bolt as it started with bolt cavitation as result of observation. It's not found bolt cavitation on the CPP proposed in this paper, furthermore its CIS is increased approximately by 4.5 knots than the existing CPP. The result of the research can be used for development of low-noise CPP and improving performance of CIS.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.3
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• pp.167-174
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• 2021

In this study, the amount and frequency characteristics of cloud cavitation formed on a navy ship rudder were investigated through cavitation image processing technique and cavitation noise analysis. A high-speed camera with high time resolution was used to observe the cavitation on a full-spade rudder. The deflection angle range of the full-spade rudder was set to 8 to 15 degrees so that cloud cavitation was generated on the rudder surface. For images taken at 10⁴ fps (frame per second), reference values for detecting cavitation were defined and detected in Red, Green, Blue and Hue, Saturation, Lightness color spaces to quantitatively analyze the amount of cavitation. Intrinsic frequency characteristics of cloud cavitation were detected from the time series data of the amount of cavitation. The frequency characteristics of cloud cavitation obtained by using the image processing technique were found to be the same through the analysis of the noise signal measured by the hydrophone installed on the hull above the rudder, and its peak value was in the frequency band of 30~60Hz.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.562-567
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• 2012

Noises from the large scale marine propeller are calculated numerically on non-cavitation condition. The hydrodynamic analysis are carried out by potential based panel method with time marching free wake approach. The distribution of hyrodynamic loads on the propeller surface and noise signals are obtained using the unsteady Bernoulli's equation and the Farasssat formula respectively. It turns out that the noise signal shows strong peak at the blade passage frequency. Noise signals and directivity patterns for both the thickness and the loading noise are compared with each other. The directivity pattern for the loading noise shows minor lobe at the backward side of the rotating disc plane.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.749-754
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• 2003

In this paper, we introduce the measurement of the underwater noise with 32channel hydrophone array of Samsung CAvitation Tunnel (SCAT) and the detection technique of noise sources by using the beam-forming method. Measurement and way signal Processing under fluid flow are essential works for the underwater acoustics, especially for the detection of noise sources. As the acoustic impedance of the water is relatively high and the tunnel is an enclosed system, we have to consider the interaction between tunnel and water together with the reflection of noise in the beam-forming technique. Also, for a hydrophone array system that is fixed on one side of tunnel wall as done in SCAT is liable to suffer from some limitations in the detection of the noise sources with the array, we discuss these limitations particularly on the frequency range and spacing of noise sources.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.81-89
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• 1999

The major source of noise in the process of transporting liquids is related to the cavitation phenomenon. The control valve noise is mostly dominated by bubble dynamics under cavitating conditions. In this investigation, an orifice configuration is set-up to correlate its flow-field and acoustic signatures with those from a control valve device. The performance and noise characteristics form the orifice configuration in anechoic surroundings were measured to reveal the noise sources depending on pressure differences across the orifice configuration. The sound powers from the orifice configuration are effectively normalized using proposed scaling parameters. Flow-excited dynamic systems for which there is no strong coupling between the flow and the system response can be described using a linear source-filter model. On this assumption, the normalized sound powers can be decomposed of noise source function and a response function. To find noise sources, pressure spectra measured over a range of pressure differences are transformed into the product of two non-dimensional frequency function : $P_{ss}(He,f_{ca},x/D) = F(f_{ca})\;G(He,x/D)$. This scheme of finding noise sources is shown to be applicable to the cavitation noise from the control valve effectively Two kinds of cavitating modes based on our experimental data are found and discussed.

• Journal of Ship and Ocean Technology
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• v.7 no.3
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• pp.13-33
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• 2003

This paper presents a numerical study on tip vortex cavitation inception predictions based on non-spherical bubble dynamics including splitting and jet noise emission. A brief summary of the numerical method and its validation against a laboratory experiment are presented. The behavior of bubble nuclei is studied in a tip vortex flow field at two Reynolds numbers, provided by a viscous flow solver. The bubble behavior is simulated by an axisymmetric potential flow solver with the effect of surrounding viscous flow taken into account using one way coupling. The effects of bubble nucleus size and Reynolds number are studied. An effort to model the bubble splitting at lower cavitation numbers is also described.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.1
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• pp.111-117
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• 2000

In the KRISO cavitation tunnel, the acoustic characteristics for the measurement of underwater noise are investigated, The background noise is measured and analyzed up to 100kHz at various test conditions. The noise level of the KRISO cavitation tunnel is compared with those of the other cavitation tunnels which have been designed for the noise study[HYKAT(Germany), GTH(France), etc.]. In order to investigate the background noise source. the coherence between structural vibration and noise level is analyzed using the B&K 3550 FFT analyzer. The experimental results show the possibility of the noise study and suggest the improvement plan.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.1
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• pp.1-7
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• 2011

Cavitation is the formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure. Various types of cavitations are generated on the propeller blades. As cavity bubbles passing the blade are forced to oscillate in size or shape and come to collapse, they cause very strong local acoustic waves in the fluid and radiate noise. Comparing the Sound Pressure Level(SPL) before and after cavitation, SPL increases 2dB per 1 knot increase in ship speed above the cavitation inception speed(CIS). Consequently, the CIS is an important criteria to design silent propellers. In this work, experimental measurements of radiated noise according to various types of cavitations from the model propeller are carried out in a large cavitation tunnel and their acoustical characteristics are extensively investigated.