• Corrosion Science and Technology
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• 제12권5호
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• pp.227-232
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• 2013

A number of components installed in the secondary system of nuclear power plants are exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), Cavitation, Flashing, and LDIE (Liquid Droplet Impingement Erosion). Those aging mechanisms can lead to thinning of the components. In April 2013, one (1) inch small bore piping branched from the main steam line experienced leakage resulting from wall thinning in a 1,000 MWe Korean PWR nuclear power plant. During the normal operation, extracted steam from the main steam line goes to condenser through the small bore piping. The leak occurred in the downstream of an orifice. A control valve with vertical flow path was placed on in front of the orifice. This paper deals with UT (Ultrasonic Test) thickness data, SEM images, and numerical simulation results in order to analyze the extent of damage and the cause of leakage in the small bore piping. As a result, it is concluded that the main cause of the small bore pipe wall thinning is liquid droplet impingement erosion. Moreover, it is observed that the leak occurred at the reattachment point of the vortex flow in the downstream side of the orifice.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.32-37
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• 2002

High speed machining is one of most effective technologies to improve productivity. It can give great advantage for manufacture of die and Moulds. However, when the high speed machining of materials, especially in machining of micro groove, a severely thermal demage was generated on workpiece and tool. Generally, the cutting fluid is used to improve penetration, lubrication, and cooling effect. In order to rise the performance of lubrication, it contains extreme pressure agents (Cl, S, P). But the environment of work room go bad by those additive Therefore, the compressed chilly air with Oil mist system was developed to replace the conventional cutting fluid system. This paper carried out the tests to evaluate the machinability by the cutting environment in high speed micro groove machining of NAK80 (HRC40). Compressed chilly air with oil mist was ejected on the contact area between cutting edge and workpiece. The effectiveness of this developed compressed chilly air with oil mist system was evaluated in terms of tool life. The results showed that the tool life of carbide tool coated TiAIN with compressed chilly air mist cooling was much longer than with dry and flood coolant when cutting the material.

• 한국생산제조학회지
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• 제22권4호
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• pp.658-664
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• 2013

In this paper, we present a case study of vibration suppression based on the application of active damping to the small boring process of a boring bar with diameter below ${\Phi}12$. The proposed active damping system consists of an acceleration sensor for real-time monitoring of the vibration signal, a driver for phase control in a computer program, and piezoelectric actuators for damping. In this system, the vibration signals are detected by the acceleration sensor and sent to the computer as an input. The phase shift parameter of the natural frequency of the input signal is sent to the data acquisition board in the computer and calculated by the phase control program. This study confirmed the effectiveness of this damping system, and it opens up the possibility of the development of active damping systems for small boring processes.

• 대한의용생체공학회:의공학회지
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• 제16권1호
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• pp.1-8
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• 1995

A variety of experiments of endothelial cell seeding onto artificial vessels have been performed. To improve endothelialization, one or two components of the extracellular matrix (ECM) have been used as an underlying matrix. In this study, the whole ECM excreted from fibroblasts was used as an underlying matrix. Fetal human fibroblasts were cultured on a polyurethane (PU) sheet. After a conflu; ence was attained, the cytoskeleton and the nuclei of the fibroblast were destroyed using Triton-X. Mitomycin, or irradiation. Omental microvascular endothelial cells from adult human were seeded onto various substrates. After 12 days in culture, the cells were counted. It was observed that the ECM treated by irradiation had the highest cell number. In addition, the cells on this substrate exhibited the most typical endothelial cell morphology. For preliminary animal experiments the PU vessels (inner diameter, 1.5mm) coated with ECM were implanted in the infrarena] abdominal aorta of rat. After the vessels had been implanted for 5 weeks, it was found that the surface of the PU vessels was completely covered with endothelia] cells. In conclusion, we can state that the fibroblast-derived whole ECM makes a better underlying substrate for the endothelialization of small diameter artificial vessels.

• 토지주택연구
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• 제11권2호
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• pp.75-86
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• 2020

As the urban regeneration project and the old housing maintenance project are actively progressing in Korea, small-scale building construction is being carried out in downtown areas. Small buildings in the downtown area are constructed on about 4 to 10 floors, and since they are carried out in small units in residential areas, it is difficult to enter large equipment to construct existing piles, and it is more vulnerable to complaints about noise and vibration. in this study, helical piles suitable for urban areas or small sites where it is difficult to enter large equipment, such as noise and vibration. Reliability analysis was performed on the results of the static load tests and dynamic load tests conducted at the LH site and the bearing capacity calculated by the hydrostatic method and the empirical formula (N value). As a result of comparing and analyzing the design formula and the results of static load test and dynamic load tests, the correlation between the design formula of the bored pile (Road bridge design standard) formula using N value and the design formula by the modified Davisson method frequently used by method commonly European helical file practitioners.

• 지질공학
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• 제17권3호
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• pp.329-337
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• 2007

밀도, P파속도, S파속도, 공경 등 주요 시추공 환경 요소의 변화가 분산에 어떠한 영향을 미치는지를 파악하기 위하여 먼저 우리나라에 분포하는 주요 암석의 물성을 대표하는 7 가지의 모델에 대한 분산곡선을 구했다. 단극음원과 쌍극음원을 고려했으며 76 mm 시추공과 150 mm의 시추공 조건이 고려되었다. 음원과 시추공경 그리고 물성을 달리하는 여러 환경에서 유도된 분산곡선을 비교 분석함으로써 시추공 음파의 분산특성, 특히 소구경 시추공에서의 분산특성을 규명할 수 있었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.1585-1592
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• 2008

산업사회의 발전에 따라 사회 기반시설분야도 복잡다양해지고 특히 도시기능이 활발해지면서 지금의 도심지에는 지하철, 상수도, 하수도, 전력구, 통신구, 지하보차도, 지하상가, 지하주차장 등 여러 가지 용도의 지하공간이 요구되고 있으며, 이러한 지하 구조물을 축조하는데 있어 도로상에 차량 증가로 인한 교통 혼잡이나, 지하매설물의 장애로 인하여 기존의 개착식 공법으로 시행하지 못하고 지하터널공사로 시행하는 경우가 빈번하다. 기존 국내 외 터널공법 관련문헌과 현재 사용되는 터널공법의 실제 시공에 관한 정보를 수집하여 장 단점, 시공시 주의사항, 적용조건등의 조사내용을 바탕으로 RPS 공법을 고안하였다. 소규모 지하구조물을 구축하기 위한 RPS 공법은 출발갱내에서 상부에 파이프 루프를 시공한 후 광폭 유압 패널이 장착된 철제 선도관을 추진시켜 선도관을 원압잭에 의하여 압입한 후 P.C. 콘크리트 구조물을 거치하고 원압으로 압입 추진토록 하였다. 또한, 대규모 지하구조물 축조시에는 구조물 예정상단부에 지반조건에 따라 파이프 루프공법 또는 소구경 Semi-Shield 공법을 이용하여 루프를 시공함으로써 상부의 침하를 방지하고, 측벽은 광폭유압 패널을 이용하여 여굴의 최소화 및 곡선부 시공을 용이하게 하였다.

• 지질공학
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• 제18권2호
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• pp.137-144
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• 2008

강원대학교 구내에 설치된 4개의 보정시험공에서 플라스틱재질의 원통 및 반원통 케이싱을 이용한 이격오차 실험을 수행하였다. 이격실험 자료에 spine and ribs 기법을 적용한 결과 케이싱 두께 및 유형에 관계없이 하나의 밀도모델에서는 하나의 이격선이 얻어졌으며 그 기울기는 모델지층의 밀도에 비례하는 것으로 나타났다. 이러한 이격특성을 이용하여 플라스틱 케이싱이 설치된 NX시추공에서의 효과적인 밀도보정 방안이 제시되었다.

• 설비공학논문집
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• 제18권4호
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• pp.297-303
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• 2006

Friction and heat transfer coefficients were measured inside the corrugated tube using water as the working fluid. The test is performed for 16 tubes which outer diameter of tubes are 12.7 mm. These specifications are 4 indentation depths and 4 indentation pitches, respectively. The range of the water velocity inside the tube is from 0.5 to 3.0 m/s (8,500

• 한국토양비료학회지
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• 제16권3호
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• pp.260-265
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• 1983

인삼(人蔘)(3년근(年根))의 생육(生育)과 무기양분의 부위별(部位別) 분포(分布)를 네 농도의 질소형태 (황안, 뇨소, 질산칼슘)별로 사경(砂耕)조건에서 조사하였다. 형태에 관계없이 50ppm에서 지상부 및 근부생육이 최대였다. 질산태는 최대의 근중을 뇨소태는 최대의 지상부중을 보였다. 무질소구에서 엽폭이 켰다. 경장(莖長)과 경직경(莖直徑)의 비(比)는 질산태보다 암모니아태에서 적고 근동체부(根胴體部)의 장(長), 직경비(直徑比)는 이와 반대여서 지토부(地土部)와 근부(根部)의 장(長), 직경비(直徑比)는 부상관(負相關)을 보였다. 질소시용은 엽(葉)과 경(莖)에서 인산의 농도를 높인 반면 칼슘의 농도는 저하시켰다. 50ppm구에서는 모든 질소형태에서 무질소구에 비하여 잎으로의 P의 분배(分配)는 감소하였으며 Mg, Ca 및 N는 증가하였다.