• Journal of the Society of Naval Architects of Korea
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• v.40 no.6
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• pp.1-11
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• 2003

For an accurate shock response analysis of a floating structure such as a naval surface ship subjected to an UNDEX(UNDerwater Explosion), the cavitation effects due to reflected wave at free surface and wetted structural surface should be considered. In this study, for the consideration of cavitation effects an effective method using LS-DYNA/USA and its theoretical background were presented. Through the application of the analysis of bulk cavitation phenomena in the free field, it could be confirmed that almost the same results were obtained between LS-DYNA/USA code and the analytical method. for the investigation of cavitation effects from the structural shock response characteristics, three dimensional UNDEX shock response analysis of an idealized ship model was also carried out It could be found that the cavitation Phenomena gave significant effects on the structural shock response characteristics, and especially that the shock loadings calculated at the installed location of shipboard equipment were underestimated in the case of no consideration of the cavitation effects, which might cause the severe mistake in its shock-resistance design.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.6
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• pp.494-502
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• 2016

The accurate assessment of hull-appendage interaction in the early design stage is important to control the inflow to the propeller plane, which can cause undesirable hydrodynamic effects in terms of cavitation phenomenon. This paper describes a numerical analysis for the flow around a fully appended surface ship model for which KRISO has carried out a model test in the Large Cavitation Tunnel(LCT). This numerical study was performed with the LCT model test in a complementary manner for a good reproduction of the wake distribution of surface ships. A second order accurate finite volume method provided by a commercial computational fluid dynamics(CFD) program was used to solve the governing Reynolds Averaged Navier-Stokes(RANS) equations, where the SST $k-{\omega}$ model was used for turbulence closure. The numerical results were compared to available LCT experimental data for validation. The calculations gave good predictions for the boundary layer profiles on the walls of the empty cavitation tunnel and the wake at the propeller plane of the fully appended hull model in the LCT.

• Journal of Ship and Ocean Technology
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• v.7 no.2
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• pp.40-47
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• 2003

LDV measurements in large cavitation tunnel around a propeller in operation are carried out to provide valuable information for more accurate wake-adapted propeller design and to study hull-propeller interactions. Effective velocities are computed by both the simplified vortex ring method and by RANS solver with the body force representing the propeller load. The former method uses the nominal velocities measured at the propeller plane as an input data of the numerical method and shows a better agreement with experimental data. The latter shows the qualitative agreement and may be used as an alternative design tools in the preliminary design stage.

• 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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• 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.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.6
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• pp.620-630
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• 2008

The characteristics of complicated propeller wake influenced by hull wake are investigated by using a two-frame PIV (Particle Image Velocimetry) technique. As the propeller is significantly affected by the hull wake in a real marine vessel, the measurements of propeller wake under the hull wake would be certainly necessary for more reliable validation and the prediction of numerical simulation with wake modeling. Velocity field measurements have been conducted in a medium-size cavitation tunnel with a hull wake. Generally, the hull wake generated by the boundary layer of ship's hull produces the different loading distribution on the propeller blade in both upper and lower propeller planes. The difference of the propeller wake behaviors caused by the hull wake is discussed in terms of axial velocity, vorticity and turbulence kinetic energy distribution in the present study.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.2
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• pp.1-10
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• 2002

Hull-propeller-rudder interactions are studied by the iterative computational procedures. Hull effects on the propeller are reflected through the effective velocities computed by the vortex ring method which used the measured nominal wake as input data. A potential based panel method has been developed to solve the propeller-rudder interactions using the obtained effective velocities. Steady flow characteristics around the rudder surface can be obtained by computing the induced velocities on the rudder by the propeller and vice versa are computed by the iterative manner until the converged solutions are obtained. Flow characteristics around the propeller and the rudder are measured by Laser Doppler Velocimetry(L.D.V.) in large cavitation tunnel at Samsung Heavy industries. The gap flow model is adopted to solve the characteristics of the horn rudder. Numerical results are compared with the experimental values and the computed velocity fields and pressure distributions with rudder angle on the horn rudder surface show good agreement with measured ones in large cavitation tunnel.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.2
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• pp.163-177
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• 2010

This article examines hydrodynamic characteristics and speed performances of a ship attached with a full spade and a twisted rudder based on a computational method. For this study, a 13,100 TEU container carrier is selected. The turbulent flows around a ship are analyzed by solving the Reynolds-averaged Navier-Stokes equation together with the application of Reynolds stress turbulence model. The computations are carried out at the conditions of rudder, bare hull, hull-rudder and hull-propeller-rudder. An asymmetric body-force propeller is applied. The speed performance is predicted by the model-ship performance analysis method of the revised ITTC'78 method. The hydrodynamic forces are compared in both rudder-open-water and self-propulsion conditions. The flow characteristics, the speed performance including propulsion factors and the rudder-cavitation performance are also compared. The model tests are conducted at a deep-water towing tank to validate the computational predictions. The computational predictions show that the twisted rudder is superior to the full spade rudder in the respect of the speed and the cavitation performances.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.575-576
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• 2014

The Hull Mounted Sonar Dome housing the sonar sensor array is a ship's structure protruded from ship bottom, which is under turbulent flow. The flow of sonar surface is highly disturbed and turbulent. In this case the wall pressure fluctuations within the turbulent boundary layer are one of the most important flow induced self noise sources of the SONAR system. We investigate the characteristics of the wall pressure fluctuations of the hull mounted sonar dome through the model test in the cavitation tunnel. This paper contains the wall pressure fluctuation spectra at various free stream velocities.

• Journal of the Korean institute of surface engineering
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• v.45 no.6
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• pp.272-277
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• 2012

The hull of a fast sailing aluminium ship are generally prone to erosion owing to the impact of seawater. At this time, synergistic effects of the erosion and the corrosion by aggressive ions such as chlorides tend to aggravate the damage. There have been various attempts, including selection of erosion-resistant materials, cathodic protection and addition of corrosion inhibitors, to overcome damage by erosion or corrosion under marine environments. These approaches, however, have limits on identifying the damage mechanism clearly, because they depend on analogical interpretation by correlating two damage behaviors after the individual studies are assessed. In this research, it was devised a hybrid testing apparatus that integrates electrochemical corrosion test and cavitation test, and thus the erosion-corrosion behavior by cavitation was investigated more reliably. As a result, the slightest damage was observed at the potentials between -1.6 V and -1.5 V. This is considered to be due to a reflection or counterbalancing effect caused by collision of the cavitation cavities and the hydrogen gas formed by activation polarization.