• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.6
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• pp.1310-1320
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• 1989

본 논문에서는 비교적 많은 계산이 수행되어온 수평원관 주위의 상변화 열전달 문제를 예로 들어, 상변화 물질이 유한한 열전도율을 갖는 일정 두께의 원관 주위에 존재할 때의 상변화 문제에 대하여 초기 액상의 영역을 임의로 가정하는 불합리점을 제거하고 문제를 풀 수 있는 수치해석 방법을 제시하고자 한다.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.438-444
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• 2019

In this study, the effect of polypropylene fiber on the freeze-thaw damage of mortar was evaluated experimentally. The effects of the reinforcing of polypropylene fiber on the compressive and bending performance of mortar after 300 cycles of freeze-thaw test were evaluated by comparing the normal mortar and the mortar with polyvinyl alcohol fiber. In addition, the mass loss, relative dynamic elastic modulus, and cumulated pore volume of mortar were measured by each cycle of freeze-thaw test. As a result, it was confirmed that the fiber reinforced mortar, regardless of the fiber type, was effective not only in maintaining the performance of the compressive strength and the bending strength but also suppressing the mass loss after the freeze-thaw test of 300 cycles. Meanwhile, it was confirmed that not only polyvinyl alcohol fibers but also polypropylene fibers can effectively act to suppress the damage of the mortar by freeze-thaw. However, in order to improve the freeze-thaw resistance of mortar mixed with polypropylene fiber, it is necessary to increase the bonding performance with the cement matrix which can be expected from polyvinyl alcohol fiber.

• Journal of the Korean earth science society
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• v.41 no.1
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• pp.1-18
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• 2020

This study presented the effects of the assumed mass-size relationship for snow on the simulated surface precipitation by using cloud microphysics parameterizations in Weather Research and Forecasting (WRF) model. The selected cloud microphysics parameterizations are WRF Double-Moment 6-class (WDM6) and WRF Single-Moment 6-class (WSM6) in the WRF model. We replaced the mass-size relationship for snow in WDM6 and WSM6 with Thompson's mass-size relationship retrieved from measurement data. The sensitivity of the modified WDM6 and WSM6 was tested for the idealized 2-dimensional squall line and winter precipitation system over the Korean peninsula, respectively. The modified WDM6 and WSM6 resulted in the increase of graupel/rain mixing ratios and the decrease of snow mixing ratio in the low atmosphere. The changes of hydrometeor mixing ratio and surface precipitation could be due to the collision-coalescence process between raindrops and snow and the graupel melting process.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.10
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• pp.887-894
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• 2016

The thermal control device using solid-liquid phase change material (PCM) is designed, manufactured, and experimented in thermal environment chamber. The n-Hexadecane is selected as a PCM and its melting point is placed within the component working temperature range. The PCM container is made of Al6061 and has the thermal spreading fins inside. To simulate the working condition for on-orbit satellite the heat pipes are used to connect the heater and radiator and the PCM thermal control device (PCMTD) is installed at the middle portion of heat pipes. The thermal buffer mass (TBM), which is same configuration and volume with PCMTD, is also manufactured to compare the thermal control performance. As a result, the PCMTD is not only more efficient than TBM in their temperature control features but both mass and power of compensation heater are reduced.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.2
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• pp.165-182
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• 2006

In this study, field test was performed to investigate the strength-improvement effect of shotcrete mixed Micro-silica fume and shotcrete quality was estimated by EFNARC standard. Deterioration test combined the Freezing-thawing and Carbonation was also performed in order to investigate a long-term durability of high-strength shotcrete. As a result of test, the compressive strength of shotcrete using Micro-silica fume was 45.2~55.8MPa and flexible strength was 5.01~6.66MPa, so a promotion ratio of strength was 37~79%, 17~61% respectively. And the strength-improvement effect of strength by silica fume addition ratio of 7.5~10% for cement mass was more superior to the others. Due to relative dynamic modulus, mass decrease rate and carbonation progress of shotcrete mixed Micro-silica fume, it was especially realized that Micro-silica fume reduced deterioration caused by steel fiber and improved a long-term durability of shotcrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.386-394
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• 2022

In this study, the mechanical properties and frost resistance of concrete with steel and nylon fibers were experimentally investigated. Both of OPC concrete with 100 % ordinary portland cement and SGC concrete replaced with 50 % GGBFS were manufactured to evaluate effects of fibers to the performance of concrete. Compressive and split tensile strength, ultrasonic pulse velocity and surface electric resistivity measurements of concrete were carried out at a predetermined interval. In addition, the freezing & thawing resistance of concrete in accordance with ASTM C666 standard was also examined. As a result, it is seemed that the effect of fibers was remarkable to improve the mechanical properties and frost resistance of concrete, especially for the concrete incorporating steel fiber.