• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.271-275
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• 2009

본 연구에서는 상수관로의 잔존수명을 통계적 기법 중 하나인 비례위험모형(PHM)에 적용하여 평가하였다. 비례위험모형을 구축하기 위한 개별관로의 생존시간은 관로의 파손율이 한계파손율에 도달하는 시간으로 정의하였다. 즉, Park and Loganathan(2002)에서 제시한 GPBM을 적용하여 시간에 따른 개별관로의 파손율을 추정하고 추정된 파손율과 한계파손율의 상등관계를 통해 생존시간을 산정하였다. 또한, 본 연구대상관로에 대한 GPBM을 구축함에 있어, 매설시점에서 누적파손횟수를 0으로 한 파손기록을 입력자료에 추가하는 방법과 가중계수(WF)의 범위를 수정함으로써 기존의 GPBM을 보완하였다. 이로써 파손사건이 최소 1회 이상 기록된 강관 및 주철관에 대한 비례위험모형을 구축하였다. 이와 같이 수정된 방법론은 관로 파손사건 등의 자료의 축적이 미비한 국내 여건에서 비례위험모형 및 GPBM과 같은 통계적 모형을 구축할 때 유용할 것으로 사료된다. 본 연구대상관로의 비례위험모형에 포함된 유의한 공변수는 관종과 관경 그리고 길이이며 관종은 비례성 가정을 위배하여 시간종속형 변수로 모형화되었다. 최종 채택된 PHM모형을 통해 생존함수를 추정하였으며 추정된 생존함수를 이용하여 개별관로의 잔존수명 및 경제적 수명 그리고 각 수명에 대한 95% 신뢰구간을 산정하였다. 또한 개별관로의 경제적 수명에 영향을 미치는 공변수의 위험비율도 분석하였다. 분석결과 강관의 평균 경제적 수명은 약 25.1년이고 주철관은 약 21년으로 산정되었다. 또한 관종에 따른 경제적 수명에 도달할 상대적인 위험률은 전반적으로 주철관이 높으나 20년 이상 매설된 관로에서는 강관의 위험률이 높을 것으로 분석되었다. 관경과 길이는 크기에 비례하여 상대적 위험률도 증가하였다.

• Nuclear Engineering and Technology
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• v.27 no.5
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• pp.775-783
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• 1995

This study is to assess the effects of increasing wall thickness on the safety margin of pressure tube in operating and of lowering initial hydrogen concentration on the DHC growth in respect to the improvement of the reliability of pressure tube in CANDU reactors. The pressure tube with thicker wall of 5.2 mm shows much higher safety margin for flaw tolerance by 25％ than the current 4.2mmm tube. The thicker pressure tubes have a great benefit in LBB assessment including the initial crack depth at which DHC occurs, the crack length at onset of leaking and the available time for action. The resistance for the pressure tube ballooning at LOCA accident is also increased with the thicker tube. The calculations for Heq concentration after 20 years of operation as a function of wall thickness and initial hydrogen concentration show that the 5.2 mm nil thickness tube with 5 ppm initial hydrogen concentration is the most resistant to DHC. with the lower initial hydrogen concentration, TSS temperature for the precipitation or hydride decreases and the crack growth during cooldown reduces.

• Journal of the KSME
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• v.35 no.1
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• pp.36-45
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• 1995

주노즐내의 공기제트의 효율을 높이기 위해, 주노즐 제트 속도는 높을수록 높은 마찰력을 초래 하여 위사의 속도를 증가시킨다. 가속관의 길이가 증가하면 노즐출구에서의 공기의 속도와 난 류가 감소하며; 가속관의 직경이 증가할 때에는 공기속도가 감소하며 난류는 증가한다. 탱크압력, 가속관의 길이 등 유동조건에 따라 유동은 니들 끝과 가속관 출구에서 이중 초크(M=1)가 발 생할 수 있다. 에어가이드 직경과 노즐직경의 그 비율이 클수록 제트에 의한 유동의 비말동 반(entrainment)이 크게 된다. 실제 노즐직기내의 유동은 위사를 동반한 유동이므로 위와 같은 정성적인 설명에 위사의 물성치에 따른 고려를 반드시 하여야만 한다. 현장에서의 노즐설계는 노즐형상 자체의 영향은 물론 각종 위사의 물성치에 맞는 압축공기 압력 최적조건이 무엇인가를 찾는 일도 매우 중요하다.

• Fire Science and Engineering
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• v.24 no.3
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• pp.93-98
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• 2010

Even though the sprinkler system is a essential fire suppression system, the design engineers do not fully understand the concept of design area which sprinklers operate. They frequently made a mistake to form design area and calculate it. The shape of design area is a square or a rectangle which branch side line is a little longer than the cross main side. NFPA demands to lengthen the branch side to 1.2 times than the cross main side and FM demands 1.4 times. The longer the branch side at the same design area is, the bigger the water quantity and pressure is. At the results of hydraulic calculation of design areas, when the branch side is longer 1.2 times, the water quantity became 4.6% bigger than exact square and the pressure came to 4.67% bigger. When it is longer 1.4 times, the water quantity and the pressure are bigger 7.52%, 14.51%. Therefore, the sprinkler design engineers should follow the general rule of design area, exact square or rectangle which length along the branch line is a little longer than length along the cross main, to design more stable system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.9
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• pp.2195-2201
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• 2009

This paper considers the influence of suction-line heat exchangers on the efficiency of a refrigeration cycle using hydrocarbon refrigerants such as R290, R600a and R1270. These suction-line heat exchangers can, in some cases, yield improved system performance while in other cases they degrade system performance. A steady state mathematical model is used to analyze the performance characteristics of refrigeration cycle with suction-line heat exchanger. The influence of operating conditions, such as the mass flowrate of hydrocarbon refrigerants, inner diameter tube and length of suction-line heat exchanger, to the performance of the cycle is also analyzed in the paper. Results showed that the mass flowrate of hydrocarbon refrigerants, inner diameter tube and length of suction-line heat exchanger, and effectiveness have an effect on the cooling capacity, compressor work and RCI(Relative Capacity Index) of this system. With a thorough grasp of these effect, it is necessary to design the compression refrigeration cycle of hydrocarbon refrigerants using suction-line heat exchanger.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.72-77
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• 2018

In this study, cutting robot system which could cut lateral protrusion into main pipes at the connection of sewer pipes was developed. In addition, the cutting test of the robot for the lateral protrusions were performed. The test parameters included materials used in the main pipes and diameters of the pipes, and materials used in the protruded pipes. The materials type of the main pipes were concrete and PE, and the diameters of the pipes were 300 and 500 mm. The materials type used in the protruded pipes were PE and PVC, and the diameter of the pipes was 100 mm. Remaining length of each lateral protruded pipe was less than 5 mm which was an target value of cutting performance. It showd that test results were within the target value. Therefore, in the repair of sewer pipes, the lateral protruded pipes can be cut by using the robot system developed in this paper.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.8
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• pp.823-829
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• 2014

In the present study, simple models were proposed to predict the capillary-driven flow length in a surfactant-added poly(dimethylsiloxane) (PDMS) rectangular microchannel. Owing to the hydrophobic nature of PDMS, it is difficult to transport water in a conventional PDMS microchannel by means of the capillary force alone. To overcome this problem, microchannels with a hydrophilic surface were fabricated using surfactant-added PDMS. By measuring the contact angle change on the surfactant-added PDMS surface, the behavior was investigated to establish a simple model. In order to predict the filling length induced by the capillary force, the Washburn equation was modified in the present study. From the investigation, it was found that the initial rate-of-change of the contact angle affected the filling length. Simple models were developed for three representative cases, and these can be useful tools in designing microfluidic manufacturing techniques including MIcroMolding In Capillaries (MIMIC).

• Applied Chemistry for Engineering
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• v.20 no.1
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• pp.104-108
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• 2009

In this study, for the flow of carbon dioxide/hydrogen mixture through a tubular type Pd-Ag membrane, hydrogen partial pressure, velocity profile, and concentration profile were simulated as a function of inlet flow rate using computational fluid dynamics (CFD) technique. The simulation results indicated that the mole fraction of carbon dioxide increased slowly in the longitudinal direction as the flow rate increased. In addition, the effects of inlet flow rate and the length of membrane on hydrogen recovery were investigated. At lower flow rate and for longer membrane, the hydrogen recovery was larger.

• Journal of Bio-Environment Control
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• v.25 no.3
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• pp.184-192
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• 2016

This study was carried out to investigate the effect of temperature ($15{\sim}40^{\circ}C$) and the spraying plant growth regulators ($GA_{4+7}+BA$ and prohexadione-calcium) during full blooming on pollen germination and pollen tube growth of the commercial apple cultivars ('Fuji' and 'Tsugaru') and apple cultivars bred in Korea ('Chukwang', 'Gamhong', 'Hongan', 'Honggeum', 'Hongro', 'Hwahong', 'Hongso', 'Summer dream' and 'Sunhong'). Pollen germination and pollen tube growth were increased with increasing temperature from 15 to $25^{\circ}C$, but high temperature over $30^{\circ}C$ inhibit those. The apple cultivar bred in Korea that shows the highest value on pollen germination and pollen tube growth at over $30^{\circ}C$ was 'Sunhong'. The spraying $GA_{4+7}+BA$ increased pollen germination and pollen tube growth than control, but that effect was not show at $40^{\circ}C$. The spraying prohexadione-calcium was not affect to pollen germination and pollen tube growth. In conclusion, if the air temperature during full bloom of apple tree rises about $30{\sim}35^{\circ}C$, the spraying $GA_{4+7}+BA$ after artificial pollination will be good to increasing fruit set.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.2
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• pp.77-84
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• 2007

The elastic buckling strength of a corrugated pipe made of orthotropic material was evaluated. The height and length of a corrugated wave and the thickness of the pipe were considered as factors affecting the buckling strength of the pipe. And also, the ratio of the longitudinal stiffness and transverse stiffness were considered as parameters affecting on the buckling strength of a pipe made of orthotropic material. Buckling strengths of various corrugated pipes with different shapes and stiffness ratio were evaluated by FE analyses. And a formula to estimate the elastic buckling strength was suggested by regression of FE analysis results. Analysis results show that a corrugated pipe has superior buckling strength to a general flat pipe and the suggested formula estimates accurate buckling strength of the corrugated pipe made of orthotropic material.