• Title/Summary/Keyword: 캐비테이션 손상

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The vibration impact assessment for long-term damage mechanism of a pump (펌프 장기손상 메커니즘 규명을 위한 진동영향 평가)

  • Kim, T.H.;Kim, H.S.;Kim, D.K.;Kim, W.T.;Han, B.S.
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2009.10a
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    • pp.441-445
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    • 2009
  • The most of the goals of pump designers and users are efficient operation and productivity. But the safety-grade pumps in nuclear power plants are needed to operate continuously for an essential condition of system operation. Also, most of the rules and regulatory standards that have been prepared for nuclear pumps are dedicated to achieve public safety. The study examined pump vibration in a pump outlet flow and distinguished the regions of pump vibration frequency cause by cavitation and recirculation. The study made a counterproposal in determination of pump outlet flow so that the discharge flow will be able to minimize the long-term damage of the pump.

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Uncoupled Solution Approach for treating Fluid-Structure Interaction due to the Near-field Underwater Explosion (근거리 수중폭발에 따른 유체-구조 상호작용 취급을 위한 비연성 해석방법)

  • Park, Jin-Won
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.20 no.10
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    • pp.125-132
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    • 2019
  • Because the water exposed to shock waves caused by an underwater explosion cannot withstand the appreciable tension induced by the change in both pressure and velocity, the surrounding water is cavitated. This cavitating water changes the transferring circumstance of the shock loading. Three phenomena contribute to hull-plate damage; initial shock loading and its interaction with the hull plate, local cavitation, and local cavitation closure then shock reloading. Because the main concern of this paper is local cavitation due to a near-field underwater explosion, the water surface and the waves reflected from the sea bottom were not considered. A set of governing equations for the structure and the fluid were derived. A simple one-dimensional infinite plate problem was considered to verify this uncoupled solution approach compared with the analytic solution, which is well known in this area of interest. The uncoupled solution approach herein would be useful for obtaining a relatively high level of accuracy despite its simplicity and high computational efficiency compared to the conventional coupled method. This paper will help improve the understanding of fluid-structure interaction phenomena and provide a schematic explanation of the practical problem.

Effect of Stabilizer on Corrosion and Cavitation Damage in the Sea Water of Electroless Nickel Plating Layer (무전해 니켈도금 층의 해수 내 부식과 캐비테이션 손상에 대한 안정제 효과)

  • Park, Il-Cho;Kim, Seong-Jong
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • 2018.06a
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    • pp.107-107
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    • 2018
  • 무전해 니켈도금 용액의 성분은 Ni(II)염, 환원제, 적합한 금속 배위 리간드, 안정제 및 특정 특성 요구에 대한 첨가제를 포함한다. 일반적으로 도금 욕에는 미량의 안정제가 함유되어 있다. 만약 적절한 안정화 시스템이 없는 도금 욕에서 도금 공정 시 도금 시작 직후에 많은 양의 니켈 플레이크(Ni flake)가 생성되어 빠르게 도금 용액이 분해되어 더 이상 도금이 어렵게 된다. 그러나 무전해 도금 욕에서 안정제의 역할 및 도금 층에 미치는 영향에 대한 연구는 여전히 부족한 실정이다. 따라서 본 연구에서는 $Pb^{2+}$ 안정제 농도가 도금 층에 미치는 영향과 캐비테이션 침식 실험을 통해 그 내구성을 평가하고자 하였다. 무전해 니켈코팅을 위한 모재는 회주철(FC250)을 $19.5mm{\times}19.5mm{\times}5mm$의 크기로 가공하였다. 회주철의 인장강도는 $330N/mm^2$이며, 그 성분 조성(wt.%)은 3.23 C, 1.64 Si, 0.84 Mn, 0.016 P, 0.013 S 그리고 나머지는 Fe이다. 시험편은 SiC 페이퍼 #1200까지 연마하여 시험편의 표면 거칠기는 $1.6-2.1{\mu}m$ 범위 내로 제작하였다. 무전해 도금 전 시험편은 탈지를 위해 상온의 아세톤 용액에서 3분간 초음파 세척하고, $90^{\circ}C$의 알카리 수용액으로 5분간 세척하였다. 그리고 표면 활성화를 위한 산세척은 5% 황산용액에서 30초 동안 실시하였다. 도금조로 500mL 비커를 사용하였으며, 모든 시험편은 2시간 동안 무전해 니켈도금을 실시하였다. 그리고 니켈도금 층의 내식성과 내구성을 평가하기 위해 전기화학적 분극 실험을 통한 타펠분석과 ASTM G32 규정에 의거한 캐비테이션 침식 실험을 실시하였다. 그 결과 안정제 농도가 도금 속도와 도금 층의 성분 변화에 크게 영향을 미쳤으며, 그에 따라 도금 층의 내식성과 내구성이 크게 변화되었다.

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Comparative Study of the Navier-Stokes Equation & the Reynolds Equation in Spool Valve Analysis Considering Cavitation (캐비테이션을 고려한 스풀밸브 해석에서 Navier-Stokes 방정식과 Reynolds 방정식에 의한 비교 연구)

  • Hong, Sung-Ho;Son, Sang-Ik;Kim, Kyung-Woong
    • Tribology and Lubricants
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    • v.29 no.5
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    • pp.275-285
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    • 2013
  • The Reynolds equation is commonly used to investigate the lubrication characteristics of a spool valve. However, the applicability of the Reynolds equation is questionable for analyzing a spool valve because cavitation often occurs in the grooves of the valve and the depth of a groove is much higher than the clearance in most cases. In this study, the validity of the Reynolds equation in the spool valve analysis is investigated by comparing the results obtained from the Reynolds equation and those obtained from the Navier-Stokes equation. The results are compared in terms of the lateral forces, friction forces, and volume flow rates (leakages). A significant difference of more than 20% is found in the lateral forces in cases where cavitation occurs and there are many grooves. Therefore, the Navier-Stokes equation should be used to investigate the lubrication characteristics of a spool valve when cavitation occurs and when the spool valve contains many grooves.

Investigation on Cavitation-Erosion Damage with the Cavitation Amplitude of Al Alloy Materials in Seawater (해수 내 다양한 알루미늄 선박용 재료의 캐비테이션 진폭에 따른 캐비테이션-침식 손상 연구)

  • Yang, Ye-Jin;Kim, Seong-Jong
    • Corrosion Science and Technology
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    • v.19 no.5
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    • pp.250-258
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    • 2020
  • Recently, 5000 series and 6000 series Al alloys have been used as hull materials for small and medium-sized ships because of their excellent weldability, corrosion resistance, and durability in marine environments. Al ships can navigate at high speed due to their light weight. However, cavitation-erosion problems cause reducing durability of Al ship at high speed. In this investigation, 5052-O, 5083-H321, and 6061-T6 Al alloy materials were used to evaluate the damage characteristics with amplitude (cavitation strength). As a result of the electrochemical experiments, the corrosion current density and corrosion potential of 6061-T6 in seawater were 8.52 × 10-7 A/㎠ and -0.771 V, respectively, presenting the best corrosion resistance. The cavitation-erosion experiment showed that 5052-O had the lowest hardness value and cavitation-erosion resistance. 5052-O also had a very short incubation period. As the experiment progressed for 5052-O, pitting formed and grew in a short time, and was observed as severe cavitation-erosion damage that eliminated in large quantities. Among the three specimens, 5083-H321 presented the highest hardness value and the damage rate was the smallest after the initiation of pitting.

Study on the Charactistics of Cavitation Erosion-Corrosion for Mild Steel(3) - Behavior of Erosion-Corrosion Damage Suppression Under Vibration Cavitation- (연강의 캐비테이션 침식-부식 특성에 관한 연구 (3) - 진동 캐비테이션 손상 억제 거동 -)

  • Hwang, Jae-Ho;Lim, Uh-Joh;Jeong, Ki-Cheol
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.33 no.3
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    • pp.202-208
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    • 1997
  • The component materials threatened by cavitation include ship propellers as well as turbine runners, pump impellers, pipe lines and radiators. Today it is known that cavitation damage takes place on many other components including on the coding water side of the cylinder liners of diesel engines. Cavitation erosion - corrosion implies damage to materials due to the shock pressure or shock wave that results when bubbles form and collapse at a metal surface within a liquid. To suppress cavitation erosion as well as cavitation erosion - corrosion to hydraulic equipment, innovations such as the improvement in the geometric design of the equipment or the selection of suitably resistant construction materials are necessary. In this study, we investigated that the cavitation erosion - corrosion damage under vibratory cavitation can be reduced by adding of side now velocity to the cavitation bubble group in order to eliminate bubbles formed in sea water environment.

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A Study on Development of Standard Propellers for Coastal Fishing Vessels (연근해 어선용 표준형 추진기 개발)

  • Lee, Chang-Sub;Kang, Dae-Sun;Lee, Kun-Hwa;Kim, Moon-Chan;Moon, Il-Sung
    • Journal of Korea Ship Safrty Technology Authority
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    • s.31
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    • pp.14-24
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    • 2011
  • 최근 국제유가 상승과 탄소배출량 규제에 따른 친환경 선박의 개발 요구가 증대되고 있으며 이는 일반선 뿐만 아니라 어선에서도 마찬가지이다. 본 논문에서는 유류비 증가 및 어선의 노후화 등으로 인한 국내 어업 경쟁력의 약화 및 채산성 악화를 극복하기 위한 방안으로 연근해 어선용 추진기 개발을 위한 연구를 수행하였다. 현재 국내 어선현황에 기초하여 대표 선종인 130톤급 예망어선을 대상선으로 선정하고 추진기의 추진성능을 이론 및 실험적으로 평가 분석하였으며, 모형 시험 및 수치 해석 결과를 종합해 볼 때, 대상선의 프로펠러는 과도한 캐비테이션이 발생되는 상태에서 매운 높은 수준의 소음과 진동이 발생하는 것으로 추측된다. 이는 어선의 추진력 감소에 따른 연료비의 증대, 캐비테이션에 의한 추진기 손상, 과도하게 발생되는 소음에 따른 어획량 감소의 주된 원인이 된다. 본 연구를 통해 일반 상선의 추진성능 평가에 적용되는 최신 기술을 어선 추진기에 적용하여 모형시험 및 이론 성능 평가 과정을 정립하였으며, 이를 통해 앞으로 어선 추진기의 성능을 상당 부분 개선할 수 있음을 확인하였다.

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Evaluation of Liquid Droplet Impingement Erosion through Prediction Model and Experiment (예측모델 및 실험을 통한 액적충돌침식 손상 평가)

  • Yun, Hun;Hwang, Kyeong-Mo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.10
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    • pp.1105-1110
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    • 2011
  • Flow-accelerated corrosion (FAC) is a well-known phenomenon that may occur in piping and components. Most nuclear power plants have carbon-steel-pipe wall-thinning management programs in place to control FAC. However, various other erosion mechanisms may also occur in carbon-steel piping. The most common forms of erosion encountered (cavitation, flashing, Liquid Droplet Impingement Erosion (LDIE), and Solid Particle Erosion (SPE)), have caused wall thinning, leaks, and ruptures, and have resulted in unplanned shutdowns in utilities. In particular, the damage caused by LDIE is difficult to predict, and there has been no effort to protect piping from erosive damage. This paper presents an evaluation method for LDIE. It also includes the calculation results from prediction models, a review of the experimental results, and a comparison between the UT data in the damaged components and the results of the calculations and experiments.

Experimental Study for the Prevention of Cavitation Damage in the Diesel Fuel Injection Pumps (디젤엔진 연료분사펌프 캐비테이션 손상 방지를 위한 실험적 연구)

  • Kim, Dong-Hun;Park, Tae-Hyung;Heo, Jeong-Yun;Ryu, Seung-Hyup;Kang, Sang-Lip
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • 2011.10a
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    • pp.61-61
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    • 2011
  • Cavitation phenomena during the injection process of the conventional fuel injection pump for a medium-speed diesel engine can cause surface damage with material removal or round-off on the plunger and barrel port and may shorten their expected life time. An experiment of flow visualization was carried out to investigate the main cause of these cavitation damages and find the prevention method. Experimental results of flow visualization show that these damages are mainly affected by fountain-like cavitation and jet-type cavitation generated before and after the end of fuel delivery process and therefore the prevention method was designed to control these cavitation flows. From the visualization and endurance test, it was proved that this method can effectively prevent cavitation damages by controlling cavitation flows.

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Cavitation Damage Behavior of Inconel 625 Coating Layer by Arc Thermal Spraying Method in Sea Water (아크 용사법을 이용한 Inconel 625 코팅 층의 해수 내 캐비테이션 손상 거동)

  • Park, Il-Cho;Kim, Seong-Jong
    • Journal of the Korean institute of surface engineering
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    • v.48 no.6
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    • pp.349-353
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    • 2015
  • In this paper, arc thermal spray coating was conducted onto the SS400 steel using Inconel 625 wires in order to improve the durability of marine steel structures, and then investigated cavitation damage behavior of Inconel 625 coating layer in sea water. For the Inconel 625 coating layer, surface hardness appeared similar to that of existing high velocity oxy-fuel coating technology with 380~480 HV, but the porosity of about 6 % was larger relatively. During the cavitation experiment, pit damages were originated and grown at the rough surface and pore defect area of Inconel 625 coating layer. And, after the 72 hours of experimental time, weight loss of Inconel 625 coating layer exhibited gradually increasing tendency due to surface damage effect of the undercut.