• 대기
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• 제31권4호
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• pp.445-459
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• 2021

This study uses a cloud-resolving storm simulator (CReSS) to understand the individual effect of determinant meteorological factors on snowfall characteristics in the Yeongdong region based on the rawinsonde soundings for two snowfall cases that occurred on 23 February (Episode 1) and 13 December (Episode 2) 2016; one has a single-layered cloud and the other has two-layered cloud structure. The observed cloud and precipitation (snow crystal) features were well represented by a CReSS model. The first ideal experiment with a decrease in low-level temperature for Episode 1 indicates that total precipitation amount was decreased by 19% (26~27% in graupel and 53~67% in snow) compared with the control experiment. In the ideal experiment that the upper-level wind direction was changed from westerly to easterly, although total precipitation was decreased for Episode 1, precipitation was intensified over the southwestern side (specifically in terrain experiment) of the sounding point (128.855°E, 37.805°N). In contrast, the precipitation for Episode 2 was increased by 2.3 times greater than the control experiment under terrain condition. The experimental results imply that the low-level temperature and upper-level dynamics could change the location and characteristics of precipitation in the Yeongdong region. However, the difference in precipitation between the single-layered experiment and control (two-layered) experiment for Episode 2 was negligible to attribute it to the effect of upper-level cloud. The current results could be used for the development of guidance of snowfall forecast in this region.

• 열처리공학회지
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• 제12권3호
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• pp.206-214
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• 1999

The effect of cooling rate on carbide precipitation during quenching of austenitic manganese steel was investigated by optical microscopy, image analyzer and numerical analysis. A computer program based on the finite difference method for analyzing heat treatment processes was developed in order to evaluate cooling rates and the possibility of carbide precipitation during quenching. The area ratio of carbide precipitated in the austenite matrix was measured by the image analyzer, and used to determine the critical point of carbide precipitation. Temperature-dependent critical cooling rates at the critical points were calculated using the present simulation program, The calculated results showed a good agreement with the experimental ones.

• 소성∙가공
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• 제26권1호
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• pp.48-54
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• 2017

The dissolution and precipitation of Nb, which has been known as strong carbide-forming element, play a key role in controlling phase transformation kinetics of microalloyed steels. In this study, we analyzed both numerically and experimentally the precipitation behavior of Nb-microalloyed steel and its effect on the austenite decomposition during cooling. Nb precipitation in austenite matrix could be predicted by the thermo-kinetic software MatCalc, in which interfacial energy between precipitate and matrix is calculated. The simulated precipitation kinetics fairly well agrees with the experimental observations by TEM. Austenite decomposition, which is strongly affected by Nb precipitation during cooling, was measured by dilatometry and was modeled on the basis of a Johnson-Mehl-Avrami-Kolmorgorov(JMAK) equation. It was confirmed that the dissolved Nb delays the austenite decomposition, whereas, the precipitated Nb accelerates phase transformation during the austenite decomposition.

• 한국습지학회지
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• 제13권3호
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• pp.377-384
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• 2011

강수량변화가 도시 및 해안지역의 지하수함양량에 미치는 영향을 파악하기 위하여 부산광역시 수영구를 포함하는 광역 지하수유역에 강수량자료를 변화시켜 지하수함양량을 산정하고 강수량증감에 따른 지하수함양량의 변화특성을 분석하였다. 그 결과, 강수량 증감에 따라 지하수함양량의 증감량은 차이가 있으나 강수량과 지하수함양량의 변화 양상은 동일한 경향을 나타내었다. 강수량의 변화에 대한 지하수함양률의 변화폭이 최근으로 올수록 적어지는 경향을 나타내었다. 또한 연도가 증가함에 따라 지하수함양률이 감소하는 추세를 나타내었다. 강수량 변화 시의 지하수함양량의 전체 평균 변화율은 강수량이 10 % 증가 시에는 2.23 %, 10 % 감소 시에는 2.20 %, 20 % 증가 시에는 4.39 %, 20 % 감소 시에는 4.36 %로 강수의 변화율에 비하여 지하수함양량은 적은 변화율을 보였다. 이들 결과로부터 강수량의 변화율에 비하여 지하수함양률의 변화가 크지 않음을 알 수 있었다. 따라서 도시지역에서 강수량이 변화할 시에는 지하수함양량의 변화율이 이에 미치지 못함으로 직접유출에 미치는 영향이 그 양만큼 커지게 되어 도시홍수의 발생가능성이 지속적으로 증가하게 됨을 알 수 있었다.

• 한국환경과학회지
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• 제19권9호
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• pp.1109-1118
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• 2010

Characteristics of precipitation and temperature in Ulleung-do and Dok-do were analyzed with hourly accumulated precipitation and mean temperature data obtained from Automatic Weather System(AWS) for latest four years(2005~2008). In Ulleung-do, total annual mean precipitation for this period is 1,574.4 mm, which shows larger amount than 1434.2 mm of whole Korean peninsula for latest 10 years(1999~2008) and 1,236.2 mm at Ulleung-do on common years(1971~2000), shows that the trend of precipitation gradually increases during the recent years. This amount is also 1.4 times larger than the total annual mean precipitation of 660.1 mm in Dok-do. Mean precipitation intensity(mm $h^{-1}$) at each time of a day in each month at Ulleung-do represents that the maximum values larger than $3.0\;mm\;h^{-1}$ were shown in May and on 0200 LST, whereas these were found in August and 0700 LST with $3.1\;mm\;h^{-1}$ in Dok-do. The difference of the precipitation amount and its intensity between Uleung-do and Dok-do is explained by the topological effect came from each covering area, and this fact is also identified from similar comparison of the precipitation characteristics for the islands in West Sea. The annual mean temperature of $14.0^{\circ}C$ in Dok-do is $1.2^{\circ}C$ higher than that of $12.8^{\circ}C$ in Ulleung-do. Trends of monthly mean temperature in both islands are shown to increase for the observed period.

• 한국환경과학회지
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• 제29권1호
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• pp.1-13
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• 2020

Recently, a heavy rainfall with high spatial variation occurred frequently in the Korean Peninsula. The meteorological event that occurred in Busan on 3 May 2016 is characterized by heavy rain in a limited area. In order to clarify the reason of large spatial variation associated with mountain height and location of low level jet, several numerical experiments were carried out using the dynamic meteorological Weather Research and Forecasting (WRF) model. In this case study, the raised topography of Mount Geumjeong increased a barrier effect and air uplifting due to topographic forcing on the windward side. As a result, wind speed reduced and precipitation increased. In contrast, on the downwind side, the wind speed was slightly faster and since the total amount of water vapor is limited, the precipitation on the downwind side reduced. Numerical experiments on shifting the location of the lower jet demonstrated that if the lower jet is close to the mountain, its core becomes higher due to the effect of friction. Additionally, the water vapor convergence around the mountain increased and eventually the precipitation also increased in the area near the mountain. Hence, the location information of the lower jet is an important factor for accurately predicting precipitation.

• 동력기계공학회지
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• 제19권6호
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• pp.75-81
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• 2015

A deposited metal specimen of ER2594 which is a super duplex steel welding wire used to investigate the effect of sigma(${\sigma}$) phase on electrochemical corrosion characteristics was prepared by gas tungsten arc welding. Aging treatment was conducted for the specimen at the temperature range of $700^{\circ}C$ to $900^{\circ}C$ for 5 to 300 minutes after annealing at $1050^{\circ}C$. Corrosion current density has decreased a little with an increase of aging time over 60 minutes at $700^{\circ}C$ to $900^{\circ}C$ and the uniform corrosion of deposited metal had more influence on the precipitation of ferrite than the precipitation of sigma phase. Therefore, the precipitation of sigma phase did not have much effect on the uniform corrosion. Pitting potential representing pitting corrosion has shown decreasing tendency as the precipitation of sigma phase increased. The degree of sensitization representing intergranular corrosion has shown increasing tendency as the precipitation of sigma phase increased at $700^{\circ}C$ to $800^{\circ}C$, while it has decreased at $900^{\circ}C$ for 60 to 300 minutes.

• 자원리싸이클링
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• 제29권5호
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• pp.28-37
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• 2020

본 연구에서는 알칼리 영역의 소듐바나데이트(NaVO₃) 수용액을 출발물질로 사용하여 침전온도, 염화암모늄 첨가량 및 첨가방법, 수용액의 바나듐 및 수산화나트륨 함량 등이 암모늄메타바나데이트 침전거동에 미치는 영향을 알아보았다. 수용액 pH가 감소할수록, 염화암모늄 첨가량 그리고 수용액의 바나듐 함량이 증가할수록 암모늄메타바나데이트 침전률이 증가하였다. 본 연구조건에서 90% 이상의 암모늄메타바나데이트 침전률을 얻기 위한 기본 조건은 수용액 바나듐 함량 10,000mg/L, 고체 염화암모늄 첨가량 2당량, 침전온도 상온, 침전시간 2시간 이었다. 암모늄메타바나데이트는 침전속도 증가에 따라 침전물 크기가 감소하였으며, 특히 염화암모늄을 액체로 투입할 때, 침전속도는 가장 느리며 침전물 크기는 가장 크게 나타났다. 염화암모늄을 고체로 첨가하여 1차 침전반응 후, 새로운 반응물을 첨가하여 2차 침전반응을 시킬 때, 고체 염화암모늄을 첨가한 침전반응은 수용액에 존재하는 침전물에 영향을 받지 않았다. 그러나 염화암모늄 수용액을 첨가하였을 때는 수용액에 존재하는 침전물 표면에 침적되어 그 크기를 증가시켰다. 수용액 온도에 따른 암모늄메타바나데이트 용해도 차이에 의하여, 바나듐 함량 10,000mg/L 수용액에서는 침전온도가 암모늄메타바나데이트 침전에 영향을 미치며, 바나듐 함량 30,000mg/L 이상의 고농도 수용액에서는 침전온도가 침전반응에 영향을 미치지는 못하였다.

• Membrane and Water Treatment
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• 제9권3호
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• pp.163-172
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• 2018

This study investigated the effect of organic matter on the precipitation of struvite and calcium phosphate for phosphorus recovery from synthetic dairy wastewater. Batch precipitation experiments were performed to precipitate phosphorus from solutions containing $PO_4{^{3-}}$ and $NH_4{^+}$ by the addition of $Mg^{2+}$ and $Ca^{2+}$, separately, at varying pH, Mg/P and Ca/P molar ratios, and organic matter concentrations. Soluble total organic solids exhibited more inhibition to precipitation due to potential interaction with other dissolved ionic species involved in phosphorus precipitation. Xylan with low total acidity only exhibited significant inhibition at very high concentrations in synthetic wastewater (at up to 100 g/L). No significant inhibition was observed for Mg and Ca precipitation at relatively lower concentrations (at up to 1.2 g/L). MINTEQ simulations show that dissolved organic matter (DOM) as humic substances (HS) can cause significant inhibition even at relatively low concentrations of 0.165 g/L fulvic acid. However, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis suggested that xylan altered the crystal structure of both precipitates and had caused the formation of smaller sized struvite crystals with slightly rougher surfaces This could be due to xylan molecules adhering on the surface of the crystal potentially blocking active sites and limit further crystal growth. Smaller particle sizes will have negative practical impact because of poorer settleability.

• 한국세라믹학회지
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• 제25권5호
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• pp.465-472
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• 1988

Alpha alumina powder with fine particle size and narrow particle size distribution was prepared by precipitation method using Al2(SO4)3.18H2O as a starting material. The alpha alumina powder was prepared by calcining aluminum hydroxide which was formed under various pH values. The sinterabilityof alpha alumina powder and the effect of MgO on the sinterability of alpha alumina powder were investigated. The sinterability of alpha alumina powder was the order of pH=10≒pH11>pH=7≒pH9, and alpha alumina obtained from boehmite which was prepared by precipitation method reached to 97.5% of theoretcal density by the pressureless sintering. The effect of MgO on volume shrinkage of alumina was very slight in the initial sintering stage but remarkable in the final sintering stage. It was also found that MgO controlled effectively the grain growth of alumina.