• Clinical and Experimental Reproductive Medicine
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• v.28 no.1
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• pp.25-31
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• 2001

연구목적: $Isolate^{(R)}$ gradient와 swim-up 방법이 정자의 형상 및 정밀정자형태 (strict morphology)에 미치는 영창을 비교분석하고, 이러한 정자처리방법이 정자의 동결-융해과정에 미치는 영향을 비교하고자 하였다. 연구재료 및 방법: 20명의 정상 정자를 대상으로 하였으며 각각의 정자는 두 가지 정자처리방법으로 나누어 정자의 형상과 정밀정자형태를 컴퓨터를 이용한 정자자동분석기를 통하여 측정하였고, 동결보호제의는 TYB 용액을 사용하였으며, 동결 및 융해는 cryo Magic사의 기계를 사용하였다. 통계는 SPSS PC+(version7.0)를 이용하였으며 통계학적인 유의성은 p<0.05로 하였다. 결과: 정자의 농도는 $Isolate^{(R)}$ gradient 처리군이 swim-up 처리군보다 유의성 있게 높았으나 ($51.2{\pm}40.1,\;156.6{\pm}64.3$), 운동성 VCL, VSL, VAP, Linearity, 및 ALH는 swim-up 처리군에서 유의성 있게 높았다. 정밀 정자형태는 swim-up 처리군과 $Isolate^{(R)}$ gradient 처리군에서 차이가 없었다 ($53.7{\pm}6.8$ vs $50.3{\pm}9.1%$). 동결-융해과정 중 두 가지 정자 처리군에서 정자의 형상들은 swim-up 처리군에서 전반적으로 높은 양상을 보였으나, 정밀정자형태는 $Isolate^{(R)}$ gradient 처리군이 swim-up 처리군 보다 감소율이 컸지만 두 군간에 유의한 차이는 없었다 ($12.8{\pm}8.5$ vs $8.6{\pm}6.6$). 결론: 정상 정자에서 swim-up 방법이 $Isolate^{(R)}$ gradient 방법보다 정자 회수율은 우수하였으나, 동결-융해과정 중 정밀정자형태에는 차이가 없어 두 방법을 상호보완적으로 사용할 수 있을 것으로 사료된다.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.5
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• pp.137-144
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• 2016

This paper aims to ensure describe the a spring-back prevention technique for improving shape fixability by using an ultra-high strength steel sheet with 980 MPa to develop a lightweight seat rail parts. Ultra-high strength steel gives a potential for considerable weight reduction and a cost-effective way to produce energy efficient vehicles. The influence of a spring-back of seat rail parts on the shape fixability in forming processes was investigated to be solved by an adjustment of the appropriate tool design and process parameters. The computed results for improving shape fixability were in good agreement with the experimental results.

• Journal of Advanced Marine Engineering and Technology
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• v.16 no.3
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• pp.42-50
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• 1992

다공성 물질이 충전된 밀폐용기 내에서 수용성 이원혼합용액($H_2O{+}NaCl$)이 수평한 상부전열면으로 부터 동결될 때 혼합용액의 초기농도, 액체의 과열 및 다공성물질의 입자직경 크기가 온도와 농도분포에 미치는 영향을 실험하였으며, 동결이 진행됨에 따라 이동하는 고액상 혼합영역의 계명위치를 측정하였다. 다공성물질은 평균직경이 2.85mm, 6mm인 구형의 유리구슬을 이용하였다. 수용성 혼합용액의 초기농도는 공융농도도 이하로 하였으며 상부 전열면은 공융온도 이하로, 하부전열면은 액상선온도 이상으로 유지하여 동결 실험한 결과 상부 전열면으로 부터 고체 영역, 고액상혼합영역, 액체영역으로 구분되었다. 액체의 초기농도가 5%인 경우 과냉현상이 관찰되었으나 10%, 15%인 경우 액체온도는 액상선 온도보다 더 높았다. 용액의 초기농도를 감소시킬수록 고체와 고액상혼합영역의 범위는 증대되었으며 고액상혼합영역과 고체영역의 계면은 더욱 강해진 자연대류에 의하여 2차원성이 증가된 형상을 보였다. 용액의 자연대류는 다공성물질의 직경이 클수록 증가되었으며 계면에서의 제융해현상은 관찰되지 않았다.

• Transactions of Materials Processing
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• v.14 no.4 s.76
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• pp.303-309
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• 2005

Reverse Engineering 기술을 이용하여 금형 형상을 측정하고 이를 이용하여 자동차 주요 대형 성형 부품에 대하여 유한 요소 성형 해석을 수행하여 성형 인자들의 영향에 대하여 분석한 결과 다음과 같은 결론을 얻었다. (1) Reverse Engineering 기술의 사용은 대형 자동차 성형 부품에 대하여 성형 해석을 위한 금형 CAD 데이터를 확보하는데 유용함을 알 수 있었다. 그러나 보다 적극적으로 사용되기 위해서는 곡면 생성의 시간 단축과 제품 면에 발생한 주름에 의한 형상 차이 등의 문제를 해결하여야 할 과제가 남아 있다. (2) 성형 해석을 위하여 자동차 외판 부품 Trunk lid outer에 대하여 성형 해석을 수행 결과 부픔의 성형성에 영향을 주지 않는 한도 내에서 r값과 n 값이 낮은 소재를 사용하는 것이 부품의 형상 동결성을 확보하는데 유리한 것을 알 수 있었다. (3) 판재 성형 부품에 대한 적절한 소재의 재질 선정 방법으로서 유한 요소 해석이 매우 유용한 것을 알 수 있었다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.06a
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• pp.17-24
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• 1998

This paper deals with the springback characteristics of cold rolled sheet steel through the use of the V-bending process and U-bending one. The influence of material properties on the springback of forming processes was investigated. In the V-bending process there was an optimum bend radius for each combination of parameters which produced minimal springback. In the U-bending process the blank holder force can control the degree of springback. A high blank holding force resulted in a uniform strain distribution and reduced the level of springback.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.17-25
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• 2020

The artificial ground freezing method is a ground amelioration technology that does not have a permanent effect on the ground. One of the key factors that determine the efficiency and design criteria of the artificial ground freezing is the groundwater flow. Therefore, in order to accurately evaluate the behavior of the artificial ground freezing, studies on the effect of water flow on the formation of ice walls must be preceded. In this paper, experimental and numerical analyses were conducted using only pure water to maximize the effect of water flow on the formation of ice walls. A hydro-thermal coupled model for freezing behavior was proposed and the accuracy of the model was verified. Through the numerical and experimental studies, the flow rate dominates not only the formation time but also the shape of the ice wall. In addition, this study proposes a method to indirectly predict the ice wall formation time, which is expected to be highly useful for a practical application where it is difficult to visually identify ice walls.

• Journal of the Korean Geotechnical Society
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• v.25 no.9
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• pp.19-27
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• 2009

In order to investigate anti-freeze process of precast concrete L-type retaining walls in cold regions, test walls were installed in the campus of Kitami Institute of Technology (KIT, Hokkaido, Japan). The wall consists of following three sections, i) back filled with frost susceptible clay soil, ii) using thermal insulation material, and back filled with frost susceptible soil, iii) back filled with frost-unsusceptible soil. The freezing front distribution and ground temperature within the backfill were observed and deflections of the walls were measured over three freeze-thaw seasons. Some understanding of the mechanisms of the build-up of frost heave pressure was gained, and the effectiveness of replacement method was observed. A simulation was performed to predict the shape of the freezing front in the backfill behind L-type walls with various cross sections. These findings were employed to propose a method for determining the appropriate zone to be replaced with frost unsusceptible backfill material in cold regions.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.6
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• pp.1059-1075
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• 2017

The objective of this study was to evaluate the freezing and thawing resistance of the existing drainage system for leakage treatment of underground concrete structures operating in cold regions. The freezing and thawing test was conducted on 4 types of drainage system specimens to evaluate the freezing and thawing resistance of the drainage system. The freezing and thawing resistance was evaluated on 4 types of Hotty-gel, as a waterproofing material, connection methods and on two methods to fix the drainage board with Hotty-gel on the surface of cement concrete specimen. One cycle of the freeze-thaw testing was 48 hours (24 hours of freezing and 24 hours of thawing), and the temperatures of freezing and thawing were at $-18^{\circ}C$ and $10^{\circ}C$, respectively. Among the 4 types of Hotty-gel connection methods, leakage occurred after 28 cycles (8 weeks) of freeze-thawing only in the Hotty-gel connection method with the 'V' groove applied to the corner of the drainage board. No leakage occurred in the 3 types of Hotty-gel connection methods. In two fixing methods, leakage occurred in the method of fixing the drainage board on the cement concrete specimen using the washer, screw and plastic wall plug. Leakage occurred at one point after 10 cycles (3 weeks) of freezing and thawing. After 28 cycles (8 weeks) of freezing and thawing, leakage point increased to 5 points. As time passed, the leak point was not increased, but the amount of leakage was increased at each leak point. The Hotty-gel connection method with cross-sectional diagonal shape was evaluated to be the highest in the production efficiency considering the production time and manufacturing method of the Hotty-gel connection shape. In the construction efficiency considering the construction time and construction method, the fixing method of air nailer, fixed nail and washer was superior to that of the washer, screw and plastic wall plug.

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.789-795
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• 1999

In this study, carbon fiber reinforced cement composites(CFRCs) reinforced with short noncircular type carbon fibers were fabricated and properties(drying shrinkage, resistance to freezing and thawing, and fracture toughness) were compared with those of the CFRCs reinforced with circular type carbon fibers. It was found that these properties greatly depended on the shape and length of carbon fibers. The drying shrinkage of CFRCs reinforced with C-type carbon fiber was superior to other CFRCs. This effect was increased with a high aspect ratio of fiber. The resistance to freezing and thawing was increased with the fiber length and fiber volume percent, but there was on remarkable effect to fiber shape. Fracture toughness and resistance to crack propagation of CFRCs reinforced with C-CFs were improved compared with other CFRCs. It was believed that the more absorption of fracture energy into the larger interface caused an increase in fracture toughness and resistance to crack propagation.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.2
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• pp.160-167
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• 2018

The purpose of this study is to develop a process for forming a MPa ultra-high strength steel sheet to reduce weight and improve product strength. To do this, we performed the initial process design based on empirical formulas in a handbook and experience of skilled engineers, and researched the effects of major process variables on spring back by analyzing the forming analysis and experimental results. This paper suggests an optimal process design of the seat rail lower parts, using a MPa ultra-high strength steel sheet. This satisfies the dimensional accuracy and strength requirements for the product.