• The KSFM Journal of Fluid Machinery
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• v.11 no.1
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• pp.18-25
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• 2008

Recent trends of a centrifugal pump are high speed in rotation and high pressure in head with high efficiency to meet the demands of industries. However, the newly developed pumps make trouble of pressure pulsation in the pumping system by performance instability of the pump. Moreover, cavitation, which is a main obstacle of high rotational speed in the pump, occurring in an impeller gives serious damages to the impeller and casing wall. The purpose of present study is not only to develop a simple method to improve pump performance but also to suppress the occurrence of cavitation in the centrifugal pump by use of J-Groove. J-Groove is a shallow groove installed on the casing wall in the meridional direction. The application of J-Groove to a centrifugal pump with a new type impeller of "semi-closed impeller" has proved its effectiveness as a useful countermeasure of the unstable pump performance and cavitation. The results show that the combination of semi-closed impeller and J-Groove can be applied successfully and improves both the pump performance and suction performance.

• Tribology and Lubricants
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• v.22 no.4
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• pp.218-224
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• 2006

The sludge oils were produced necessarily in the ships operation, so that it will be the best way to manage the sludge oils inside ship itself from a viewpoint of the prevention of marine oil pollution. The ultra-sonic breaking system which recycle the sludge oil from ship into usable oil to be brunt is recognized as a most possible recycling device. In this regards, the purpose of this study is to examine erosion damage,on the SS400 specimen by cavitation and the effect of impact pressure generated from the demolition of the cavity of ultrasonic vibration in the marine sludge oil environment.. The erosion damage of specimen was investigated mainly on weight loss, weight loss rate and maximum erosion rate with variation of the oil temperature as well as the change of space between transducer hem and specimen. The experimental results showed that as the space between ultrasonic vibrator horn and specimen disk increased, the weight loss and weight loss rate decreased and the values were larger in SFO than in SLO. The experimental results can be useful to the development of sludge oil disposing systems and to consider a countermeasure for the prevention of erosion damages by cavitation.

• Journal of Fisheries and Marine Sciences Education
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• v.12 no.2
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• pp.164-175
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• 2000

Port facilities and marine structures used in marine environment were encountered to corrosion damages because of the influence of Cl-. Generally, to protect these accidents, anti-corrosion paint and epoxy coating have been used. But they were still remained erosion-corrosion damage like impingement erosion, cavitation erosion and deposit attack. It is necessary to develope the new composite lining material in order to protective those corrosion damages. In this paper, polyester glass flake, vinylester glass flake lining and epoxy coating for SS400 were investigated by the electrochemical polarization test and the impingement-cavitation erosion test for corrosion behaviour under the sea water. The main results obtained are as follows ; 1) Epoxy coating appear potentiodynamic polarization behaviour, but polyester glass flake and vinylester glass flake lining do not appear potentiodynamic polarization behaviour. 2) Open circuit potential of polyester glass flake lining is more noble than that of epoxy coating and corrosion current density of polyester glass flake lining is less drained than that of epoxy coating in sea water. 3) Open circuit potential of vinylester glass flake lining is more noble than that of polyester glass flake lining and corrosion current density of vinylester glass flake lining is less drained than that of polyester glass flake lining in the sea water.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.2
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• pp.113-121
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• 2010

Recently, as container ships become larger and faster, rudder cavitations are more frequently observed near the gap between the horn and rudder plates of the ships to cause serious damages to the rudder surface of the ship. The authors already have suggested through a series of model experiments and numerical computations that employment of an appropriate blocking device for gap flow may retard the gap cavitation. For examples, a cam device installed near the outer edges of the vertical gap or a water-injection device combined with a pair of half-round bars installed inside the gap can considerably reduce the gap cavitation. However, it is also found that effective blocking of the flow through the vertical gap results in growth of the cavitation near the horizontal gap instead. In the present study, effectiveness of the simultaneous blocking of the flow through the horizontal and vertical gaps of a horn type rudder in minimizing the damage by gap cavitation is studied. Additional blocking disks are inserted inside the horizontal gaps on the top and bottom of the pintle block and numerical computations are carried out to confirm the combined effect of the blocking devices.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.1
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• pp.31-37
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• 2023

In the present study, a method of performing cavitation erosion test directly on the anodized surface of the rudder model is proposed, not applying ink or paint on its surface. An image processing technique is newly developed to quantitatively evaluate the erosion damages on the rudder model surface after erosion test. The preprocessing saturation image, image smoothing, adaptive hysteresis thresholding and eroded area detection algorithms are in the image processing program. The rudder cavitation erosion tests are conducted in the rudder deflection angle range of 0° to -4°, which is used to maintain a straight course at the highest speed of the targeted navy ship. In the case of the conventional flat-type full-spade rudder currently being used in the target ship, surface erosion can occur on the model rudder surface in the above rudder deflection angle range. The bubble type of cavitation occurs on rudder surface, which is estimated to be the main reason of erosion damage on the rudder surface.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.3
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• pp.225-232
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• 2017

Several maintenance issues related to cavitation erosion and fatigue cracks in the water turbine subcomponents of pumped-storage plants, such as a runner and a draft tube, have been reported in the past. Generally, the pumped-storage plants provide ancillary services, such as black-start and system stabilization. The ancillary services are responsible for cyclic low opening operation of the guide vanes. It has been empirically established that this low opening operation further damages the water turbine subcomponents. In this study, the acceleration effect of the low opening operation on the cavitation erosion and fatigue of the water turbine is quantitatively assessed through finite element flow analysis, finite element stress analysis, and fatigue analysis. As a result of the assessment, it is identified that the cavitation potential increases and the turbine efficiency decreases with a decrease in the opening of the guide vane. Also, the low opening operation has an insignificant effect on the fatigue even though it increases the maximum stress values at the runner blade roots.

• Solar Energy
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• v.16 no.2
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• pp.79-86
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• 1996

In order to reduce damages due to cavitation effects and to improve performance of fluid machinery, supercavitation around the cascade and the hydraulic characteristics of supercavitating cascade must be analyzed accurately. And the study on the effects of cavitation on fluid machinery and analysis on the performances of supercavitating hydrofoil through various elements governing flow field are critically important. In this study comparison of experiment results with the computed results of linear theory using singularity method was obtainable. Specially singularity points like sources and vortexes on hydrofoil and freestreamline were distributed to analyze two dimensional flow field of supercavitating cascade, and governing equations of flow field were derived and hydraulic characteristics of cascade were calculated by numerical analysis of the governing equations.

• Corrosion Science and Technology
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• v.9 no.6
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• pp.317-324
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• 2010

Marine transportation by ships is characterized by remote, large-volume and lower rates than the others carry system. Ships account for over 80% of all international trading, and marine transportation is an internationally competitive, strategic, and great national important industry. The construction of larger and faster ships has brought about many problems such as cavitations and erosion corrosion. Cavitations and erosion corrosion make damages on materials and leads to break down members due to continuous physical contacts with shock waves and fluids from the generation and extinction of air bubbles in sea water vortex. The steel used for ship constructions was spray-coated with Al wire, and additionally sealed with fluorine silicone sealing material. Results of experiment, corrosion resistance of sealed thermal spray coating was improved, however in cavitation resistance, the large effect was not appeared. Accordingly, this study applied for thermal spray coating to provide better electrochemical characteristics and corrosion resistance in marine environment.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.64-64
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• 2021

댐의 중요 구성요소 중 하나인 여수로 구조물은 관행적으로 단위길이당 100m³/s 정도의 유량이 흐를 수 있도록 설계를 하고, 이를 초과할 때는 여수로 구조물에 피해가 가지 않도록 공기혼입 장치를 설치하거나 콘크리트의 설계강도를 증가시키는 대책을 사용하는 것이 일반적이다(댐설계 기준·해설, 2011) 그러나 건설된 지 오래된 댐의 경우 여수로 콘크리트 구조물의 설계강도가 낮고(최저 16.7MPa) 수문방류 횟수가 많아 최근에 건설된 댐 여수로 보다 상대적으로 많은 손상이 발생되어 있어 잦은 보수보강이 요구되고, 점차 유지관리 비용이 증대되고 있어 노후된 여수로 구조물일수록 기능을 유지하면서도 유지관리 비용을 절감할 수 있는 방안의 수립이 요구되고 있다. 이에 본 연구에서는 𐩒𐩒𐩒댐 여수로를 대상으로 2020년 홍수기 전·후의 여수로 바닥슬래브의 손상상태를 3D드론 매핑, 육안조사 및 내구성 조사결과 등을 이용한 정밀분석을 통해 수문방류시 여수로 바닥슬래브에 가장 큰 손상을 일으키는 손상메커니즘으로 유수에 의한 부상(uplift)에 의한 파손 메커니즘(Flow-driven uplift failure mechanism)을 제시하였으며, 여수로 바닥슬래브의 가장 일반적 손상원인으로 간주되고 있는 공동현상(cavitation)이 공동지수(cavitation index)가 0.3이상인 경우에도 발생할 수 있음을 확인하였다. 이와 같은 관찰 및 분석결과는 보다 많은 사례를 통하여 보완될 경우 향후 여수로 구조물의 설계 뿐만 아니라 보수보강 방법이나 유지관리, 더나아가서는 종합적 댐시설물 자산관리 계획을 수립하는데 매우 유용한 자산이 될 수 있다.

• Proceedings of KOSOMES biannual meeting
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• 2003.11a
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• pp.157-162
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• 2003

The sludge oils were produced necessarily in the ships operation, so that it will be the best way to manage the sludge oils inside ship itself from a viewpoint of the prevention of marine oil pollution from ship. The ultrasonic breaking systems which recycle the sludge oil from ship into usable oil to be brunt is recognized as a most possible recycling device. In this regards, the purpose of this study is to examine erosion damage on the SS400 specimen by cavitation and the effect of impact pressure generated from the demolition of the cavity of ultrasonic vibration in the marine sludge oil environment .. The erosion damage of specimen was investigated mainly on weight loss, weight loss rate and maximum erosion rate with variation of the oil temperature as well as the change of space between transducer horn and specimen. The experimental results showed that as the space between ultrasonic vibrator horn and specimen disk increased, the weight loss and weight loss rate decreased and the values were larger in SFO than in SLO. The experimental results can be useful to the development of sludge oil disposing systems and to consider a countermeasure for the prevention of erosion damages by cavitation.