Browsing by Author "Choi, J"

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    On the prediction of creep behaviour of alloy 617 using Kachanov-Rabotnov model coupled with multi-objective genetic algorithm optimisation
    (Elsevier, 2022-10) Choi, J; Bortolan Neto, L; Wright, RN; Kruzic, JJ; Muránsky, O
    The accurate prediction of elevated-temperature creep behaviour of alloys is important for preventing catastrophic failure of systems operating under prolonged elevated temperature-stress conditions. Here, we couple the Kachanov-Rabotnov (K-R) creep model with a multi-objective genetic algorithm (MOGA) to predict the creep behaviour of Alloy 617 at 800°C, 900°C, and 1000°C, under various stress conditions. It is shown that the MOGA-optimised K-R creep model can capture the overall elevated-temperature behaviour of the alloy at 800°C under a wide range of stress conditions. However, at 900°C and 1000°C, oxidation leads to the atypical accumulation of creep plasticity, which the K-R model cannot account for. Nevertheless, it is shown that the proposed methodology of optimising the K-R model with a MOGA can consistently provide accurate results within the limits of the K-R model. Crown Copyright © 2022 Published by Elsevier Ltd.
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    Seasonality of Radon-222 near the surface at King Sejong Station (62°S), Antarctic Peninsula, and the role of atmospheric circulation based on observations and CAM-Chem model
    (Elsevier, 2022-11) Jun, SY; Choi, J; Chambers, SD; Oh, M; Park, SJ; Choi, T; Kim, SJ; Williams, AG; Hong, SB
    We examined the seasonal cycle of radon concentration observed at King Sejong Station (KSG, 62°S), Antarctic Peninsula, during the period 2013–2016. The distribution of monthly radon concentration was found to be highly positively skewed from March through October (austral autumn to spring) due to large numbers of short-lived periods of high radon concentration. The global atmospheric chemistry model (CAM-Chem), which includes all global terrestrial sources of radon except for those in Antarctica, well reproduces the observed seasonal cycle of monthly-mean radon concentration at KSG. Further offline experiments suggest that uncertainties in radon emissions over South America and the Southern Ocean should be improved for the simulations of radon in Antarctica. The results demonstrate that seasonally varying transport of radon in the boundary layer from South America substantially affects the seasonality of monthly mean radon concentration at KSG. The composite analyses further reveal that high radon events at KSG are the result of a distinct east-west dipole-like structure associated with surface cyclonic circulation over the Bellingshausen Sea and anticyclonic circulation in the Weddell Sea. This atmospheric pattern provides favorable conditions for radon transport into KSG from the northwest. The relationship between radon concentration at KSG and climate variability is also discussed in this study. © 2022 Elsevier Inc.