• Nuclear Engineering and Technology
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• 제54권1호
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• pp.244-254
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• 2022

For tensile tests, Vickers hardness tests and microstructure tests, plate-type and box-type specimens of austenitic 316L stainless steels were produced by a conventional machining (CM) process as well as two additive manufacturing processes such as direct metal laser sintering (DMLS) and direct metal tooling (DMT). The specimens were irradiated up to a fast neutron fluence of 3.3 × 10⁹ n/cm² at a neutron irradiation facility. Mechanical performance of the unirradiated and irradiated specimens were investigated at room temperature and 300 ℃, respectively. The tensile strengths of the DMLS, DMT and CM 316L specimens are in descending order but the elongations are in reverse order, regardless of irradiation and temperature. The ratio of Vickers hardness to ultimate tensile strength was derived to be between 3.21 and 4.01. The additive manufacturing processes exhibit suitable mechanical performance, comparing the tensile strengths and elongations of the conventional machining process.

• 환경정책연구
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• 제10권1호
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• pp.27-47
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• 2011

단독주택지의 도시환경보전 및 개선을 위해 서울시 강남구 수서동 일원의 단독주택지 밀집지역을 대상으로 생태 면적률 개념을 적용한 비오톱 유형화와 도시열환경 예측 시뮬레이션을 실시하였다. 생태면적률 개념을 적용하여 비오톱 유형 분류 결과 총 7개 유형으로 구분되었고 옥상녹화 미적용 건폐지비오톱(48.16%) > 불투수비건폐포장비오톱(39.75%) > 전면투수녹지비오톱(6.23%) > 틈새투수비건폐포장비오톱(3.26%) > 전면투수비건폐포장지비오톱(2.51%) > 부분투수비건폐포장지비오톱(0.04%) 순이었다. 단독주택지 외부 열환경 특성 및 변화 예측을 실시한 결과, 비오톱 유형별 지표면 온도값은 불투수비건폐포장지비오톱 > 옥상녹화미적용건폐지비오톱 > 전면투수녹지비오톱 > 투수포장지비오톱이 순이었다. 옥상녹화 100% 적용을 가정한 case 2의 경우 최대 $33.58^{\circ}C$, 최소 $23.85^{\circ}C$였고, 평균 $27.74^{\circ}C$로서 옥상녹화 전에 비해 약 $5.19^{\circ}C$ 감소한 것으로 예측되었다. 평균 외기온도는 case 2가 case 1보다 약 $0.18^{\circ}C$ 낮게 분석되었다.

• Computers and Concrete
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• 제8권3호
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• pp.293-309
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• 2011

A long-term structural health monitoring (SHM) system comprising over 700 sensors of sixteen types has been implemented on the Guangzhou Television and Sightseeing Tower (GTST) of 610 m high for real-time monitoring of the structure at both construction and service stages. As part of this sophisticated SHM system, 48 temperature sensors have been deployed at 12 cross-sections of the reinforced concrete inner structure of the GTST to provide on-line monitoring via a wireless data transmission system. In this paper, the differential temperature profiles in the reinforced concrete inner structure of the GTST, which are mainly caused by solar radiation, are recognized from the monitoring data with the purpose of understanding the temperature-induced structural internal forces and deformations. After a careful examination of the pre-classified temperature measurement data obtained under sunny days and non-sunny days, common characteristic of the daily temperature variation is observed from the data acquired in sunny days. Making use of 60-day temperature measurement data obtained in sunny days, statistical patterns of the daily rising temperature and daily descending temperature are synthesized, and temperature distribution models of the reinforced concrete inner structure of the GTST are formulated using linear regression analysis. The developed monitoring-based temperature distribution models will serve as a reliable input for numerical prediction of the temperature-induced deformations and provide a robust basis to facilitate the design and construction of similar structures in consideration of thermal effects.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.316-322
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• 2002

This paper presents the temperature-dependent hysteresis identification of an electro-rheological (ER) fluid under various operating temperatures using the Preisach model. As a first step, polymethylaniline (PMA) particles are prepared and mixed with silicone oil to make an ER fluid. A couette type electroviscometer is then employed to obtain the field-dependent shear stress. In order to show the suitability of the Preisach model to predict a physical hysteresis phenomenon of the ER fluid, two significant properties; the minor loop property and the wiping-out property are experimentally examined under three dominant temperature conditions. Subsequently, the Preisach model fur the PMA-based ER fluid is identified using experimental first order descending (FOD) curves. The effectiveness of the identified hysteresis model is verified in the time domain by comparing the predicted field-dependent shear stress with the measured one under the both specified and unspecified temperatures. In addition, the hysteresis model proposed in this work is compared to Bingham model.

• 한국소음진동공학회논문집
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• 제12권8호
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• pp.648-656
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• 2002

This paper presents the identification of temperature-dependent hysteresis of an electro-rheological (ER) fluid under various operating temperatures using the Preisach model. As a first step, polymethylaniline (PMA) particles are prepared and mixed with silicone oil to make an ER fluid. A couette type electroviscometer is then employed to obtain the field-dependent shear stress. In order to show the suitability of the Preisach model to predict a physical hysteresis phenomenon of the ER fluid, two significant properties; the minor loop property and the wiping-out property are experimentally examined under three dominant temperature conditions. Subsequently, the Preisach model for the PMA-based ER fluid is identified using experimental multiple first order descending (FOD) curves. The effectiveness of the identified hysteresis model is verified in the time domain by comparing the predicted field-dependent shear stress with the measured one under the both specified and unspecified temperatures. In addition, the hysteresis model proposed in this work is compared to Bingham model.

• 한국해양학회지
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• 제18권1호
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• pp.55-63
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• 1983

韓國 沿岸의 定期觀測所 41個所中 各海域別로 內灣側과 外海側 各各 1個所 씩 6個所를 選定 (東海 ; 浦港, 鬱陵島, 南海 ; 濾水, 馬羅島, 西海 ; 馬山, 小靑島) 하여 表面水溫과 氣溫의 旬別累年平均(16-51개년 ; 1923-1979)을 使用하여 Schuster法의 週期分析과 同時에 1個月前의 氣溫과 現在의 水溫과의 相關分析을 最小自乘法에 의한 2次相關式으로 考察한 缺課를 要約하면 다음과 같다. 1) 週期分析 가)年較差는 表面水溫이 外海側 12.77-17.99$^{\circ}C$(計算値 ; 11.67-16.64$^{\circ}C$), 內灣側 15.72-26.33$^{\circ}C$(計算値 ; 15.13-25.29$^{\circ}C$)였고, 氣溫은 外海側과 內灣側 區別 없이 21.71-28.6$0^{\circ}C$(計算値 ; 20.50-27.22$^{\circ}C$)였다. 나)年平均은 表面水溫이 11.25-18.78$^{\circ}C$로 外海側이 內灣側보다 高溫이었고, 氣溫은 11.39-16.16$^{\circ}C$로 緯度가 增加할수록 低溫을 보이고 있다. 다)年週期成分의 振幅은 水溫이 5.72-12.54$^{\circ}C$ 氣溫이 10.04-13.49$^{\circ}C$로서 각각 馬山이 最大, 馬羅島가 最小였다. 라)半年週期成分의 振幅은 水溫이 0.83-1.3$0^{\circ}C$, 氣溫이 0.72-1.26$^{\circ}C$로 外海側은 水溫이, 內灣側은 氣溫이 각각 컸다. 마)年週期成分의 位相은 水溫의 內灣側이 215-228 (極大 ; 8月 上-中旬), 外海側 이 238-244 (極大 ; 8月 下旬)였으며, 氣溫은 212-220 (極大 ; 7月 下旬-8月 上旬)였다. 바)半年週期成分의 位相은 水溫의 外海側이 87-110 로 極大期가 빨라지고, 內灣側은 167-212 로 水溫의 156-189 와 같이 極大期가 늦어진다. 2) 相關分析 가)水溫上昇期의 2次常數는 外海側이 0.010-0.026으로 증형이나, 內灣側은 -0.020-0.001로 漸減형 또는 比例型이었다. 나)水溫下落期의 2次常數는 0.012-0.021로 모두 漸增형이었다. 다)決定係數는 水溫上昇期가 r/sop 2/=0.964-0.992, 水溫下落期가 r$^{2}$=0.982-0.999로서 韓國 沿岸의 表面水溫은 1個月前의 氣溫으로 豫測이 可能하다고 推定된다.

• 동력기계공학회지
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• 제4권1호
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• pp.81-87
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• 2000

In this study, CT specimens were prepared from ASTM SA516 Gr. 70 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C,\;-60^{\circ}C,\;-80^{\circ}C\;and\;-100^{\circ}C$ and in the range of stress ratio of 0.05 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range ${\Delta}K_{th}$ in the early stage of fatigue crack growth (Region I) and stress intensity factor range ${\Delta}K$ in the stable of fatigue crack growth (Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm $d{\alpha}/dN\;-{\Delta}K$ in Region II, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It assumed that the fatigue crack growth rate $d{\alpha}/dN$ is rapid in proportion to descend temperature in Region II and the cryogenic-brittleness greatly affect a material with decreasing temperature.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2001년도 춘계학술발표대회 개요집
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• pp.224-227
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• 2001

In this study, CT specimens were prepared hem ASTM SA516 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C$, -3$0^{\circ}C$, -6$0^{\circ}C$, -8$0^{\circ}C$, -l$0^{\circ}C$ and -l2$0^{\circ}C$ and in the range of stress ratio of 0.1, 0.3 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range $\Delta K_{th}$ in the early stage of fatigue crack growth ( Region I ) and stress intensity factor range $\Delta$K in the stable of fatigue crack growth ( Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da/dN - $\Delta$K in Region II, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It assumed that the fatigue crack growth rate da/dN is rapid in proportion to descend temperature in Region H and the cryogenic-brittleness greatly affect a material with decreasing temperature.

• 대한기계학회논문집B
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• 제22권12호
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• pp.1726-1734
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• 1998

This paper focuses on the unsteady close-contact melting phenomenon occurring between a phase change material kept at its melting temperature and a flat surface on which constant heat flux is imposed. Based on the same simplifications and framework of analysis as the case of constant surface temperature, an approximate analytical solution which depends only on the liquid-to-solid density ratio is successfully derived. In order to keep consistency with the known solution procedure, both the dimensionless wall heat flux and the Stefan number are properly redefined. The obtained solution proves to agree quite well with the published numerical data and to be capable of resolving the fundamental features of unsteady close-contact melting, especially in the presence of the solid-liquid density difference. The density ratio directly affects the film growth rate and the initial value of solid descending velocity, thereby controlling the duration of unsteady process. The effects of other parameters can be evaluated readily from the steady solution which is implied in the normalized result. Since the dimensionless surface temperature for the present boundary condition increases from zero to unity along the evolution path of the liquid film thickness, the unsteady process lasts longer than that for the case of isothermal heating.

• 한국의류학회지
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• 제28권7호
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• pp.873-881
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• 2004

This research was aimed to investigate the effect of enzyme and the addition of chelators on rotting of the Kenaf bast. Enzyme rotting was effective only when the chelators were added with the enzyme. EDTA was a more effective chelator than oxalic acid under 1% concentration. There was no difference in the rotting effect under different enzyme concentration levels, and under different treatment time and temperature. Therefore, it was found that enzyme rotting can be carried out with low enzyme concentration(0.125%) at room temperature. Retting time can be shortened when higher enzyme concentration and higher temperature are applied. Cellulose I structure of kenaf fiber did not change after enzyme rotting, and different enzyme concentration did not affect the crytallinity structure. Non-cellulosic matters such as hemicellulose, lignin, and pectin were present in the descending order in the enzyme rotted kenaf fiber, and there were no differences in their amounts due to enzyme concentration levels. There was no difference in the dyeabilities of kenaf fiber rotted with different enzyme concentration levels. Enzyme rotted kenaf fiber showed better cyeability when pectin, lignin, and hemicellulose were removed.