• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.333-339
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• 2003

Steady and unsteady cavitation characteristics of turbopump inducer were investigated in this paper. To see the effect of blade angle on the inducer performance, three inducers with inlet tip blade angle of $7.8^{\circ},\;7.0^{\circ},\;6.1^{\circ}$, respectively, were tested. For $7.8^{\circ},\;7.0^{\circ}$ inducers in the non-cavitating condition, head decreased linearly with flow rate, but head-flow rate curve had a dip at the flow coefficient ${\Phi}=0.065\;for\;6.1^{\circ}$ inducer. Rotating cavitation and cavitation surge were found in the $7.8^{\circ},\;7.0^{\circ}$ inducers in the cavitation tests. During the rotating cavitation one cell rotated at the same rotational speed as that of the inducer. The cavitation surge did not rotate and the oscillating frequency was $7{\sim}20\;Hz$. From the curve of the critical cavitation number versus flow rate, it was found that the steady cavitation performance of $6.1^{\circ}$ inducer was much lower than that of $7.8^{\circ},\;7.0^{\circ}$ inducers.

• 수산해양기술연구
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• 제32권3호
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• pp.302-309
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• 1996

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. If the liquids corrosive to the material, a condition typically encountered in industry, the component materials may suffer serious damage by a combination of mechanical and electrochemical attack. To suppress cavitation erosion as well as cavitation erosion-corrosion to hydraulic equipments, innovations such as the improvement in the geometric design of the equipment or the selection of suitably resistant construction materials are necessary. This study was tested by using the piezoelectric vibrator with 20kHz, 24${\mu}$m for cavitation generation. And also, the vibratory cavitation erosion-corrosion tests on commercial mild steel SS41were carried out. We carefully observed the erosion pattern and surface photography. The geometrical mechanism of pit growth, which is to be likely these processing; shallow typelongrightarrowundercut typelongrightarrowwide shallow type.

• 한국지반공학회논문집
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• 제21권1호
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• pp.43-50
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• 2005

고압분사주입공법은 지반개량, 차수벽, 흙막이벽, 기초 보강말뚝 등에 사용되고 있다. 고압분사주입공법은 사질토지반에 대해서는 지수목적으로, 연약한 점성토 지반에서는 지반강화를 위하여 사용되고 있다. 그러나 현재 국내에 적용되고 있는 경우의 대부분은 지반조건에 따른 강도증가 효과를 경험적으로 파악하여 설계에 적용하고 있는 실정이고 이에 대한 많은 연구가 진행되고 있다. 본 연구에서는 고압분사주입공법의 지반교란에의 효율성을 증대시킬 목적으로 공동현상(cavitation) 이론을 응용하고자 하였다. 그리고 이를 정량적으로 분석하기 위하여 공동현상(cavitation)을 적용한 경우와 적용하지 않은 경우에 대해 지반조건, 주입압력 및 주입시간 등을 변화시켜가며 점성토 및 사질토 모형지반에 대하여 그라우팅을 실시하였다. 시험결과 공동현상(cavitation)을 적용한 경우 점성토 및 사질토 지반 모두 좋은 결과를 보여, 실제 공법에 적용가능성이 높은 것으로 나타났다.

• 한국표면공학회지
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• 제51권2호
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• pp.87-94
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• 2018

Various sealing techniques were applied to the anodized 5083 aluminum alloy for marine environment to reduce corrosion and cavitation erosion damage. Electrochemical experiments and cavitation erosion tests were conducted to evaluate the corrosion resistance and cavitation resistance of the anodic oxide film treated with sealing in natural seawater solution. Then, damaged surface morphology was analyzed by scanning electron microscope(SEM) and 3D microscope. As the results of the electrochemical experiments, it was observed that the surface damage of all the experimental conditions in the anodic polarization experiment was locally grown by the combination of crack and corrosion damage. In the Tafel analysis, the corrosion resistance of all sealing treatment conditions was improved compared to the anodizing. On the other hand, cavitation erosion tests showed that the anodizing and all the sealing treatment conditions generated local pit damage by cavitation erosion attack and grew to crater damage in the observation of damaged surface by SEM. Also, the weight loss and the surface damage depth measured with the experiment time presented that most of the sealing treatment conditions showed better cavitation erosion resistance than the anodizing, and they had an incubation period at the beginning of the experiment.

• 한국표면공학회지
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• 제45권1호
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• pp.25-30
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• 2012

The galvanostatic tests for corrosion protection are conducted at various applied current densities during 93,600 sec, and evaluated in terms of the variations in current density with time and in the potential at the applied current density. In addition, the corrosion damage depth is analyzed with 3D analysis optical microscope after galvanostatic tests. In this study, it was investigated to decide condition of the corrosion protection gavalnostatic method for Cu-Al alloy that has an excellent corrosion resistance. In the galvanostatic test under the cavitation environment, the energy was reflected or cancelled out by the collision with the oxygen gas generated by the oxygen reduction action. The surface observation showed neither the cavitation damage nor the electrochemical damage in the current density over 0.01 $A/cm^2$ in the dynamic state under the cavitation environment.

• 대한조선학회논문집
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• 제52권1호
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• pp.34-42
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• 2015

The development of an azimuth thruster which has the function of dynamic positioning and propulsion has been greatly required as the demand of vehicles with it increases. To develop or design a reliable azimuth thruster, it is appropriate that the performance and cavitation observation tests should be conducted in the regime of high Reynolds number. In the present study, to satisfy high Reynolds number condition new dynamometer for a large azimuth thruster is manufactured and arranged in the test section of the Large Cavitation Tunnel (LCT). The test method composed of the open water and the cavitation observation tests is established successfully in LCT, considering the thruster design.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.1099-1102
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• 2017

액체로켓엔진용 연료펌프의 캐비테이션 시험 중 입출구 배관과 펌프 케이싱에서 계측된 고주파 신호를 분석하였다. 각각의 데이터의 RMS 값을 캐비테이션 수에 따라 표현하였다. 측정 결과는 산화제펌프의 결과와 비교하였으며, 캐비테이션 불안정성의 영향도 검토하였다. 산화제펌프와 연료펌프 고주파 신호 사이에 유사성이 확인되었다. 또한, 캐비테이션 불안정성은 연료펌프 출구 배관 압력섭동에 영향을 주었다.

• 해양환경안전학회지
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• 제20권3호
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• pp.296-303
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• 2014

The Axiom propeller is a unique 3 bladed propeller and it enables to generate the same amount of thrust going ahead as it does going astern because of its 's' type skew-symmetric blade section. A earlier variant of the design (Axiom I propeller) performed a low propeller efficiency, maximum 35 % efficiency, and further blade outline design was carried out to achieve a higher efficiency. The optimized new blade outline (Axiom II propeller) has more conventional Kaplan geometry shape than Axiom I propeller. Model tests of open water performance and propeller cavitation for both propellers were conducted at Emerson Cavitation Tunnel in order to compare their performances. Experiment results revealed that Axiom II propeller provides a maximum 53 % efficiency and provides better efficiency and cavitation performance over the Axiom I propeller under similar conditions.

• 대한조선학회논문집
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• 제58권2호
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• pp.105-111
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• 2021

The main source of underwater radiated noise of ships is cavitation generated by propeller blades. After the Cavitation Inception Speed (CIS), noise level at all frequencies increases severely. In determining the CIS, it is based on the results observed with the naked eye during the model test, however accuracy and consistency of CIS values are becoming practical issues. This study was carried out with the aim of developing a technology that can automatically recognize cavitation images using deep learning technique based on a Convolutional Neural Network (CNN). Model tests on a three-dimensional hydrofoil were conducted at a cavitation tunnel, and tip vortex cavitation was strictly observed using a high-speed camera to obtain analysis data. The results show that this technique can be used to quantitatively evaluate not only the CIS, but also the amount and rate of cavitation from recorded images.

• 대한조선학회논문집
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• 제56권3호
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• pp.281-289
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• 2019

In order to investigate the influence of thru holes near leading edge of model propeller on cavitation behavior, a model propeller with thru holes was manufactured and tested at Large Cavitation Tunnel (LCT). The pressure distribution around the thru hole on propeller blade was numerically calculated to help understand the local flow characteristics related to cavitation behavior. The model propeller is a five bladed propeller which has 2 blades with thru holes and 3 blades with smooth surface. The cavitation observation tests were conducted at angles of $0^{\circ}$ & $6^{\circ}$ using an inclined-shaft dynamometer in LCT. There are big difference on the suction side cavitation behavior each other due to the existence of thru hole. While the blades with thou holes start generation of the sheet cavitation from the leading edge on the suction side, the blades with smooth surface generate the cloud cavitation from the mid-chord. Cavitation on the blades with thru holes shows more similar behavior to those of the full-scale propeller of which the pipe line for air injection is closed. The numerical analysis result shows that the sharp pressure drop occurs around thru holes on the blade. Consequently, the thru hole around leading edge stimulates the cavitation occurrence and stabilizes the cavitation behavior. Based on these results, the effect of thru holes on propeller cavitation behavior behind a model ship should be studied in the future.