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성장현,박준형,전종준,서승범 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.9
Although many studies have sought to characterize future meteorological droughts, a few efforts have been done for quantifying the uncertainty, inter-model variability, arises from global circulation models (GCM) ensemble. A clear understanding of the uncertainty in multiple GCMs should be preceded before future meteorological droughts are projected. Therefore, this study evaluates the uncertainty in future meteorological drought characteristics that are induced by GCM ensemble using the custom measure “the degree of GCM spreading”. Future meteorological drought indices, the standardized precipitation index (SPI) and standardized precipitation evapotranspiration index (SPEI), were computed to five different time scales: 3, 6, 9, 12 and 24 months using statistically downscaled 28 GCMs under Representative Concentration Pathway (RCP) 4.5 and 8.5 at 60 weather stations in South Korea. The frequency, duration, and severity of drought events were estimated for three different future periods; F1 (2010 2039), F2 (2040 2069), and F3 (2070 2099). It was found that the uncertainty increases as the time scale lengthens regardless of a choice of drought indices or RCP scenarios. It also turned out that the SPI exhibits larger uncertainty rather than the SPEI, because temperature data exhibit a relatively much smaller variability comparing to precipitation data. Moreover, there was a shift of regions having larger values of the increasing rate between F1 and F2, which is shift from the north-western to southern region of South Korea.
성장현,정은성 한국수자원학회 2014 한국수자원학회논문집 Vol.47 No.5
To estimate the severity of streamflow drought, this study introduced the concept of streamflow drought index based on threshold level method and Seomjingang Dam inflow was applied. Threshold levels used in this study are fixed, monthly and daily threshold, The 1st~3rd analysis results of annual drought, the severe hydrological droughts were occurred in 1984, 1988 and 1995 and the drought lasted for a long time. Annual compared to extreme values of total water deficit and duration, the drought occurred in 1984, 1988, 1995 and 2001 was serious level. In the results of study, because a fixed threshold level is not reflect seasonal variability, at least the threshold under seasonal level was required. Threshold levels determined by the monthly and daily were appropriate. The proposed methodology in this study can be used to forecast low-flow and determine reservoirs capacity. 하천수 가뭄을 평가하기 위하여 임계수준 방법을 이용한 하천수 가뭄지수 (streamflow drought index)를 소개하고 섬진강댐의 유입량을 대상으로 적용하였다. 사용한 임계수준은 고정, 월별 및 일별로써 연도별 가뭄의 1~3순위 분석결과, 1984년, 1988년과 1995년이 수문학적 가뭄의 크기도 컸고 오랫동안 지속되었다. 총 물 부족량과 지속기간의 극한값을 연도별로 비교해 본 바, 1984년, 1988년, 1995년과 2001년에 발생하였던 사상이 심각한 수준이었다. 또한 고정 임계수준은 계절 변동성을 반영하지 못하는 단점이 있어서 최소한 계절 이하의 임계수준 사용이 요구되었지만 월별과 일별로 정해진 임계수준은 적정한 것으로 판단되었다. 본 연구에서 제안한 방법론은 갈수예보 및 저수지 용량결정에 활용될 수 있겠다.
304L 스테인레스강의 변태유기 소성에 미치는 변형온도의 영향
성장현,강창룡 동아대학교 공과대학 부설 한국자원개발연구소 1992 硏究報告 Vol.16 No.1
The effect of deformation temperature on transformation induce plasticity in 304L stainless steel with metastable austenitic phase investigaged. The result obtained from this study are summarized as follows. Tensile properties of the metastable austenitic 304L stainless steel remarkably influenced by deformation temperature and mainly controlled by transformation induced martensite. Tensile strength increased with decreasing deformation temperature and the elongation showed maximum value near 40℃ With lowering the deformation temperature, the volume fration of transformation induced martensite increased at the same strain. ε-martensite was formed at the begining stage of deformation in the low temperature region of low stability of austenite. The volume fration of ε-martensite increased with increasing strain and decreased after showing the maximum value. The maxium quantity of ε-martensite was obtained at low strain with decreasing deformation temperature.
성장현,류영,정은성 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.4
This study explored return periods of the streamflow deficit characteristics by threshold levels with different time resolutions (daily, weekly, and monthly) using univariate and Copula functions, reflecting hydrological regimes like rapid recoveries from drought and anthropogenic dam operation by monthly basis in South Korea. As a result, the daily-based threshold had a large variability in severities and durations. This is because threshold levels include a large variability of daily streamflow with a small time interval. Joint return periods of duration under extreme droughts were similar to those from univariate frequency analysis. The severities in these extreme droughts were also around the average level, but the duration was relatively long, leading to an increase in the joint return period. This result helps to effectively manage water resource preparing for the assessment on the drought risk with a long duration.
5083 Al 합금 용접재의 조직 및 저온 인장성질에 미치는 시효처리의 영향
성장현,이해우,주동원,이준희,이태청 한국열처리공학회 2000 熱處理工學會誌 Vol.13 No.1
The microstructural characteristics and low temperature tensile properties between 25℃ and -196℃ for as-welded and age hardened specimen by using Al 5083-H321 for base metal, 5083-5356 and 5083-4043 weldments have been investigated. The hardness of 5083-5356 weldment decreases with aging treatment, whereas the weld region of 5083-4043 weldment shows remarkable increase in hardness after aging due to the precipitation of fine Si particle at the grain boundaries and interiors. Low temperature tensile properties of 5083 Al base metal, 5083-5356 and 5083-4043 weldments appear to be the increment of tensile strengths and elongations at the room temperature and -196℃, while the decrement of tensile properties around -50℃ is shown. Through the observation of fine serration to fracture in the stress-strain curve and tensile fractography, the increment of localized deformation leading to promote the neck initiation and the increment of the dimple size cause to decrease in tensile strengths and elongations around -50℃. For the tensile specimen of the 5083 base metal, 5083-5356 and 5083-4043 weldments, the reason to increase in elongation after solution and aging treatment is the diminishment of fine pit, the resolution of Mg into the matrix and the spheridization of the eutectic Si.
Al 함유 13%Cr 스테인리스강의 표면 질소침투 열처리에 미치는 첨가원소 탄소의 영향 : 13%Cr 스테인리스강의 고질소 표면침투 열처리
성장현,주동원,김기돈,유대경,박진욱 한국열처리공학회 2000 熱處理工學會誌 Vol.13 No.3
This study aims to investigate the effect of carbon content on the surface nitrogen permeation of 13%Cr-1.8%Al alloyed stainless steels. The surface nitrogen permeation was performed at 1050℃-1200℃ in the 1㎏/㎠ nitrogen gas atmosphere. The nitrogen permeated surface layer of the specimen containing 0.03%C consists of AlN, martensite and retained austenite phases, while the surface layer of the specimen containing 0.14%C appears the AlFe₃C_x phase including former three phases. The specimen containing 0.14%C shows lower total case depth than that containing 0.03%C at the nitrogen permeation temperatures of 1050℃ and 1100℃, while the total case depth of the specimen containing 0.14%C is remarkably increased at the temperature of 1150℃ and 1200℃ due to the increase in the retained austenite content. Martensitic phase, AlN and AlFe₃C_x precipitate of the nitrogen permeated surface layer cause to increase the surface hardness of 550∼600Hv.