• Title/Summary/Keyword: Surface Erosion Pit

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The Effect of Compliance Structures Near the Mechanical Heart Valve on Valve Surface Erosion (기계식 인공 판막 주위의 유연성 구조가 표면 괴식에 미치는 영향)

  • Lee, Hwan-Sung;Hwang, Sung-Won;Sun, Kyung
    • Journal of Biomedical Engineering Research
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    • v.23 no.4
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    • pp.309-315
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    • 2002
  • Since the discovery, in the 1980s, of erosion-pit-induced fractures in implanted mechanical heart valves. cavitation on the surface of mechanical heart valves has been widely studied as a possible cause of pitting. Several factors, including peak dp/dt of the ventricular pressure. maximum closing velocity of the leaflet, and squeeze flow. have been studied as indices of the cavitation threshold. In the present study. cavitation erosion on the surface of a mechanical valve was examined by focusing on squeeze flow and the water hammer phenomenon during the closing period of the valve. In this study, we measures pressure wave forms near a valve and closing velocities of a disk, which were placed in a holder with and without compliance. In case of all holders, pressure drop of below vapor pressure expect at near the surface disk. It was also found that the closing velocity of the disk increased and that cavitation erosion was enhanced too. These results suggest that disk closing velocity during the closing phase has signifiant effects on pitting erosion.

Study on the Characteristics of Cavitation Erosion-Corrosion for Mild Steel ( 2 ) - Damage Behaviour of Vibration Cavitation Erosion-Corrosion - (연강의 캐비테이션 침식-부식 특성에 관한 연구 ( 2 ) - 진동 캐비테이션 침식-부식 손상 거동 -)

  • Hwang, Jae-Ho;Lim, Uh-Joh
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.32 no.3
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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.

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Characteristics of Cavitation-Erosion Damage with Amplitude in Seawater of 5052-O Al Alloy for Ship (선박용 5052-O 알루미늄 합금의 해수 내 진폭 변수에 따른 캐비테이션-침식 손상 특성)

  • Yang, Ye-Jin;Kim, Seong-Jong
    • Corrosion Science and Technology
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    • v.19 no.5
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    • pp.239-249
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    • 2020
  • The characteristics of cavitation-erosion damage with changes in the amplitude of 5052-O aluminum alloy for ships were investigated in a seawater environment. In the cavitation-erosion experiment, the cavitation environment was created using a vibration-generating device with a piezo-electric effect. The amplitudes of 5 ㎛, 10 ㎛, and 30 ㎛ were created by changing the geometric shape of the cavitation horn. The resistance characteristics of cavitation-erosion damage were evaluated by weight loss and pitting area. The damaged surface was analyzed using scanning electron microscopy (SEM) and 3D optical microscopy. As the amplitude increased, the amount of damage and the area of the damaged surface increased, and the damage was concentrated at the center and edge of the specimen. The pit was created after the initial incubation period with increasing experimental time, and then the pits were merged to grow and propagate into craters, and eventually, the surface was detached and damaged. The cavitation-erosion damage after 30 minutes with amplitude of 10 ㎛ and 30 ㎛ was 1.48 and 2.21 times compared to 5 ㎛, respectively.

Examination of Cavitation-Induced Surface Erosion Pitting of a Mechanical Heart Valve Using a Solenoid-Actuated Apparatus

  • Lee, Hwan-Sung;Hwang, Sung-Won;Katsuyuki Yamamoto
    • Journal of Mechanical Science and Technology
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    • v.17 no.9
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    • pp.1339-1348
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    • 2003
  • Several factors, including peak dp/dt of the ventricular pressure and maximum closing velocity of leaflet have been studied as indices of the cavitation threshold. In the present study, just before closing velocity of the leaflet has been studied as indices of the cavitation threshold, and cavitation erosion on the surface of a mechanical valve was examined by focusing on squeeze flow and the water hammer phenomenon during the closing period of the valve. A simple solenoid-actuated test device that can directly control the valve closing velocity was developed, and opening-closing tests of 3,000 and 40,000 cycles were performed at various closing velocities. There was a closing velocity threshold to occur erosion pitting of valve surface, and its value was about 0.4 m/s in this study. Cavitation-induced erosion pits were observed only in regions where squeeze flow occurred immediately before valve closure On the other hand, the number of the pits was found to be closely related to an area of water hammer-induced pressure wave below the critical pressure defined by water vapor pressure. Therefore, it was concluded that cavitation is initiated and augmented by the two pressure drops due to squeeze flow and water hammer phenomenon, respectively.

Development of New Cavitation Erosion Test Method for Analyzing the Durability of Erosion Resistance Paint (내침식페인트 성능 판별에 적합한 새로운 캐비테이션 침식시험기법 개발)

  • Paik, Bu-Geun;Kim, Kyung-Youl;Kim, Ki-Sup;Kim, Tae-Gyu;Kim, Kyung-Rae;Jang, Young-Hun;Lee, Sang-Uk
    • Journal of the Society of Naval Architects of Korea
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    • v.47 no.2
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    • pp.132-140
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    • 2010
  • The very erosive cavitation is simulated by an inclined propeller dynamometer in the medium-size cavitation tunnel of MOERI. The inclined shaft for propeller makes strong cavitaion, which occurs around the root of a propeller blade. The cavitation begins at the leading edge of the propeller and contracted toward the trailing edge through the reentrant jet action. The cavity focused on the region near the trailing edge collapsed over the blade surface. As the impact pressure by the cavitation collapsing is too strong, it can damage the blade surface in the form of pit. This cavitation impacts created by the collapsing process are similar to the full-scale ones and are different from those by other erosion test methods. The newly developed cavitation erosion test method can be applied to evaluate the materials such as metals, ceramics and coatings in terms of cavitation resistance.

Evaluation of Corrosion and Cavitation Erosion Resistance of Sealed Aluminum Alloy after Anodizing Treatment in Seawater (양극산화 후 실링처리된 알루미늄 합금의 해수 내 내식성과 캐비테이션 침식 저항성 평가)

  • Park, Il-Cho;Lee, Jung-Hyung;Han, Min-Su;Kim, Seong-Jong
    • Journal of the Korean institute of surface engineering
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    • v.51 no.2
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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.

Drainage Control and Prediction of Slope Stability by GIS-based Hydrological Modeling at the Large Scale Open Pit Mine (GIS에 의한 대규모 노천광에서의 배수처리 및 사면안정 예측)

  • SunWoo, Choon;Choi, Yo-Soon;Park, Hyeong-Dong;Jung, Yong-Bok
    • Tunnel and Underground Space
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    • v.17 no.5
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    • pp.360-371
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    • 2007
  • This paper presents an application of drainage control and slope stability by GIS-based hydrological modeling to control the surface water from an operational point of view. This study was carried out on a region of Pasir open-pit coal mine, Indonesia. A detailed topographical survey was performed at the study area to generate a reliable DEM (Digital Elevation Model). Hydrology tools implemented in ArcGIS 9.1 were used to extract the characteristics of drainage system such as flow direction, flow accumulation and catchment area from DEM. The results of hydrological modeling and spatial analysis showed that current arrangement of pumping facility is not suitable and some vulnerable places to erosion exist on the bench face due to concentrated surface runoff. Finally, some practical measures were suggested to optimize the design of drainage system and to monitor the slope stability by the surface water management at the study region during heavy rainfall.

A Study on the Surface Erosion by the Development of Cropland on the Hillslope in the West Coast Area of North Korea Using Quick Bird Satellite Images (Quick Bird 영상을 이용한 북한 서해안 구릉지 개간에 따른 지표 침식 분석)

  • Lee, Min-Boo;Kim, Nam-Shin;Lee, Gwang-Ryul;Han, Uk
    • Journal of the Korean association of regional geographers
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    • v.11 no.4
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    • pp.453-462
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    • 2005
  • The study deals with surface erosion patterns due to the development of cropland toward hillslope and hilltop in the Oncheon-gun, pyeongbuk province and Nampo city of west coast area in the North Korea, using Quick Bird satellite images with 60cm resolution. In North Korea, for national economic difficult after 1980 year, newly developed croplands have been along the gentle hillslope, in which it is possible for individual man power different from the tideland which needs large scaled man-power and equipment. The new croplands are named Darakbat(terraced farm with embankment) and Bitalbat(titled farm developed on the original hill slope), neighboring with orchard and grouped settlement in lower valley. For supplying agricultural water, irrigation ditches and temporal crop storages have been constructed, connecting Darakbat, Bitalbat and orchard. These cropland developments have caused surface erosion composed of 3 types such as pit, linear and headward erosion, together with rill and gully. Owing to poor management of cropland and irrigation system, topsoil erosion and, collapse and sedimentation of ditch and pool, caused the decrease of agricultural productivity. These analysis using Quick Bird images can suggest original raw data about geographical facts on North Korea agriculture and help to recover their agricultural system and plan future national unified land.

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A Study on Erosion Control Effect of Soil and Water Storable Pits (저사저수구(貯砂貯水溝)의 유토저지효과(流土沮止効果)에 관(關)한 연구(硏究))

  • Lee, Soo Wook;Lee, Tae Soo
    • Journal of Korean Society of Forest Science
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    • v.31 no.1
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    • pp.43-47
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    • 1976
  • This study was carried out to find out the effect of soil and water storable pits on reducing the surface runoff. 10 pits were digged in each plot of $50m^2$ along contour line. One kind of pits has a size of 30 cm width, 100cm length and 30cm depth, and the other has 30cm width, 100cm length and 20cm depth. 1. The soil and water storable pits have a significant effect on reducing surface runoff. Control plot had surface runoff 2.3-2.6 times more than the plots with pits. 2. There is no significant difference in surface runoff between 30cm depth pit and 20cm depth pit. 3. The soil and water storable pits did not have any effect on coverage, survival and growth of three species. 4. Steep slope had worse results than the other slopes in coverage, growth and fresh weight of experiment species.

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The Properties of Waveform and Plug Formed by Poor Contact of Power Cord Sets (전원코드의 접촉 불량에 의해 형성된 파형 및 플러그의 특성)

  • Choi Chung-Seog;Kim Hyang-Kon;Kim Dong-Ook;Kim Young-Seok
    • Journal of the Korean Society of Safety
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    • v.20 no.1 s.69
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    • pp.87-93
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    • 2005
  • In this paper, we analyzed ignition characteristics of combustible material and the waveform of power dissipation, voltage and current by poor contact. And the surface structure of plug by poor contact was analyzed. In the results of experiment, the heat generated by poor contact and ignited the combustible material on power cord sets. The insulation material was molten and carbonized by the heat conduction though plug pit and voids were formed inside of insulation material. The waveform of voltage and power dissipation distorted because of a growth of oxidation by poor contact. In particular, in case that load was big load, the waveform of voltage and power dissipation severely distorted as with the passage of time. The surface of plug pin was changed from erosion mark to welding mark according to big load. The results will be applied to the cause analysis of electrical disaster.