• 대한조선학회논문집
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• 제40권4호
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• pp.30-36
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• 2003

Lately, the cavitation and erosion phenomena in the rudder have been increased for high-speed container ships. However, cavitation is not prone to occur in model experiments because of low Reynolds number. In order to predict the cavitation phenomena, the - analysis of the viscous flow in the rudder gap is positively necessary In this study, numerical calculation was applied to the two-dimensional flow around the rudder gap using FLUENT code. The velocity and pressure field were numerically acquired and cavitation phenomena could be predicted. And the case that the round bar was installed in the rudder gap was analyzed. For reducing the acceleration force when fluid flow through the gap, modified rudder shape is proposed, It is shown that modified rudder shape restrain the pressure drop at the entrance of the gap highly both in the computational results and in the model experiment, and reduce the cavitation bubbles.

• 대한조선학회논문집
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• 제47권4호
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• pp.553-564
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• 2010

This paper studies on the rudder shapes for the suppression of the cavitation around a horn-type rudder. To improve the problems due to cavitation, there have been several studies. However, these some studies are recognized as incomplete ways to suppress the rudder cavitation. In this study, the section shapes to suppress the cavitation phenomena are determined by moving the location of maximum thickness for reducing the curvature variation and changing the radius of leading edge. Also, in the pintle part, the curvature radius of the inlet outlet edge of rudder plate is changed. During the design of rudder shape, two-dimensional numerical simulations are firstly performed because those offer some advantages with that cavitation phenomena becomes predictable for a short time, and then the three-dimensional numerical simulations are performed to confirm the determination. The time mean distribution of the propeller slipstream is imposed on the inlet boundary condition. As some results, this paper shows the effects reducing the range of the occurrence of cavitation, and suggests the references on the design of a horn-type rudder for the suppression of cavitation phenomena.

• Journal of Ship and Ocean Technology
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• 제8권1호
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• pp.42-50
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• 2004

In these ten years, the cavitation and erosion phenomena in the rudder have been increased for high-speed container ships. The cavitation in the rudder blades which is injurious to rudder efficiency is mainly caused by the main flow with a large angle of attack induced by propellers, and the erosion which occurs as a result of repeated blows by shock wave that cavitation collapse may produce was observed in the gap legion of the rudder. However, gap cavitation is not prone to occur in model experiments because of low Reynolds number. So, the viscous effect should be considered for solving the flow of the narrow gap. In order to predict the cavitation phenomena and to improve the performance of the rudder, the analysis of the viscous flow in the rudder gap is positively necessary. In this study, numerical calculation for the solution of the RANS equation is applied to the two-dimensional flow around the rudder gap including horn part and pintle part. The velocity and pressure field are numerically acquired according to Reynolds number and the case that the round bar is installed in the gap is analyzed. For reduced the acceleration that pressure drop can be highly restrained numerically and in model experiment, the cavitation bubbles can be reduced.

• 한국유체기계학회 논문집
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• 제20권2호
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• pp.75-81
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• 2017

This paper presents a numerical investigation on the local hydraulic cavitation phenomena of water resulting from the rotor with high rotational speed in the hydraulic cavitation heat generator. The numerical simulation utilizes the standard k-epsilon turbulence model, the mixture multiphase model and the Schnerr-Sauer cavitation model to simulate the complex cavitation phenomena in the generator. For exploring the efficient shape of the dimples on the rotor to causing cavitation phenomena artificially, the pressure distributions and the volume fractions of the vapor on the rotor are investigated respectively about different shapes of the rotor in the generator. The optimum shape of the dimple to causing cavitation phenomena in the selected shapes is obtained by the means of the numerical simulation.

• 한국유체기계학회 논문집
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• 제18권6호
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• pp.76-80
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• 2015

The purpose of this study is to understand the cavitation phenomena in centrifugal pumps through computational fluid dynamics method. NPSH characteristic curve is measured from different flow operating conditions. Steady state, liquid-vapor homogeneous method with two equations transport turbulence model is employed to estimate the NPSH curve in centrifugal pumps. The Rayleigh-Plesset cavitation model is adapted as source term for inter-phase mass transfer in order to understand cavitation phenomena in centrifugal pumps. The cavitation incipient curve is clearly estimated at different flows operating conditions. A relationship is made between cavitation incipient and NPSH curve. Also the effects on water vapor volume fraction and pressure load distributions on the impeller blade are also described.

• International Journal of Fluid Machinery and Systems
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• 제5권1호
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• pp.18-29
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• 2012

This paper deals with the CFD analysis of cavitating flow in the mixed-flow pump with the specific speed of 1.64 which suffers from a high level of noise and vibrations close to the optimal flow coefficient. The ANSYS CFX package has been used to solve URANS equations together with the Rayleigh-Plesset model and the SST-SAS turbulence model has been employed to capture highly unsteady phenomena inside the pump. The CFD analysis has provided a good picture of the cavitation structures inside the pump and their dynamics for a wide range of flow coefficients and NPSH values. Cavitation instabilities were detected at 70% of the optimal flow coefficient close to the NPSH3 value (NPSH3 is the net positive suction head required for the 3% drop of the total head of the pump).

• 대한조선학회논문집
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• 제40권6호
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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 Advanced Marine Engineering and Technology
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• 제35권4호
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• pp.460-467
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• 2011

중속 디젤 엔진에 적용된 연료 펌프의 스필 포트 및 플런저 벽면에서 발생하는 캐비테이션 손상 원인을 규명하기 위해, 연료 펌프의 스필 포트 내부에서 일어나는 캐비테이션 유동 현상에 대한 가시화를 수행 하였다. 이를 위해 기존 연료 펌프를 개조하여 사파이어 가시창을 제작, 설치하고, 고속 카메라와 Nd-YAG 레이져 및 산업용 내시경을 이용한 다양한 가시화 방법을 모색하였다. 취득한 영상의 분석 결과 연료의 분사 과정 동안 네 가지 형태의 특징적인 캐비테이션 현상이 목격되며, 특히 연료 압송 과정의 종료 직전과 직후 에서 발생하는 분수 형태와 제트 형태의 캐비테이션이 손상의 지배적인 원인으로 판명되었다.

• 대한조선학회논문집
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• 제41권4호
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• pp.9-16
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• 2004

In the cavitation tunnel, the first corner playes role for the flow direction to execute 90-degree turn. So, energy loss is serious, and the cavitation phenomena well occur in the guide vane surface. In this paper, the flow in the first corner was numerically calculated. From the calculation result, cavitation phenomena mainly occurred in the suction side of the last guide vane and vicinity that vane and tunnel wall adjoin each other. And bubbles occurred from all guide vanes if the flow velocity in the test section reaches the any critical value. We could analogize with our experience in the water tunnel that bubbles that occurred in time not vanish, and become miniature in the flow although the pressure recover. So, they circulate with flow in the tunnel, and come into view in the test section. Therefore, first corner must be designed for bubbles not to appear in the test section according to the flow condition like velocity and pressure demanded by the experiment. We analyzed flow in case that the first elbow configuration was redesigned and some of the existing guides vanes were eliminated. And we presented that first elbow can be easely designed for the improvement of tunnel performance through the computational analysis.

• 한국유체기계학회 논문집
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• 제7권1호
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• pp.45-50
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• 2004

Two phenomena often encountered in liquid flow, which were completely absent in gas or vapor flow, were cavitation and flashing. These phenomena were of significant interest in any comprehensive discussion of control valves or contracted devices since their occurrence would affect the device sizing procedures, might introduce noise and vibration, and also may limit the life expectancy of device components and the immediate downstream piping. Thus, this study aimed to find the reduction method of occurred cavitation in system by the computer simulation. A derivative six model with different dimensions of cavity were adopted. From the results, it was found that the length of the cavity was mote important factor to reduce the pressure drop over the control valves or contracted devices than the depth of the cavity. And the pressures along the centerline of the contracted devices were dropped two times in the case of haying the large length (Lc=1.5D) of cavity.