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EFFICIENT AND ACCURATE COMPUTATIONS OF ALL-SPEED CRYOGENIC TWO-PHASE FLOWS AROUND TURBOPUMP INDUCER
Hyeongjun Kim,Daeho Min,Donghwan Kim,Chongam Kim 한국산업응용수학회 2013 한국산업응용수학회 학술대회 논문집 Vol.8 No.1
The present paper deals with a numerical method for all-speed cryogenic cavitating flows in turbopump inducer. Recently, we have developed an accurate and efficient baseline numerical scheme for the computations of all-speed two-phase flows. By extending such progress, we conduct some modification of preconditioning technique and propose an accurate and efficient numerical method to deal with the computations of cryogenic two-phase flows. To verify pressure and temperature depression effect in cryogenic cavitation, we carry out numerical simulations of cryogenic cavitation flows around hydrofoil. Compared with Hord’s experimental data, computed results are turned out to be quite satisfactory. Finally, numerical simulations of KARI turbopump inducer are carried out under various flow conditions with water and cryogenic fluids, and we examine the differences in inducer flow physics depending on the working fluids.
COMPUTATIONS OF ALL-SPEED CRYOGENIC CAVITATING FLOWS IN TURBOPUMP INDUCER
Hyeongjun Kim,Daeho Min,Donghwan Kim,Chongam Kim 한국산업응용수학회 2012 한국산업응용수학회 학술대회 논문집 Vol.7 No.2
The present paper deals with a numerical method for all-speed cryogenic cavitating flows in turbopump inducer. Recently, we have developed an accurate and efficient baseline numerical scheme for the computations of all-speed two-phase flows. By extending such progress, we conduct some modification of preconditioning technique and propose an accurate and efficient numerical method to deal with the computations of cryogenic two-phase flows. To verify pressure and temperature depression effect in cryogenic cavitation, we carry out numerical simulations of cryogenic cavitation flows around hydrofoil. Compared with Hord’s experimental data, computed results are turned out to be quite satisfactory. Finally, numerical simulations of KARI turbopump inducer are carried out under various flow conditions with water and cryogenic fluids, and we examine the differences in inducer flow physics depending on the working fluids.
머신러닝을 이용한 의사결정트리 기반의 식품교환표 구성 모델
김지윤 ( Jiyun Kim ),이상민 ( Sangmin Lee ),전형준 ( Hyeongjun Jeon ),김가은 ( Gaeun Kim ),김지현 ( Ji-hyun Kim ),박나은 ( Naeun Park ),진창균 ( Changgyun Jin ),권진영 ( Jin Young Kwon ),김종완 ( Jongwan Kim ) 한국정보처리학회 2020 한국정보처리학회 학술대회논문집 Vol.27 No.2
최근 국내에서는 식품에 대한 관심도가 높아짐에 따라 먹거리에 건강 환경 미래지향적 가치가 부여되고 있으며 식품 산업에서도 신규 식품 개발이 증가하는 추세이다. 식단을 구성할 때 기준이 되는 식품교환표는 개정과정에서 많은 인력과 시간이 소요되기 때문에 식품 섭취 변화를 신속하게 반영하기 어렵다. 본 논문에서는 식품교환표의 활용도를 높이기 위한 식품교환표 갱신 기법을 제안한다. 제안 기법은 의사결정트리 모델을 학습하여 새롭게 추가된 식품의 정보를 바탕으로 식품군을 분류하여 식품교환표를 갱신한다. 이는 영양 관리가 필요한 당뇨병 환자 등에게 실용적이며 기호성·다양성이 높은 식단을 구성하는 데 도움을 준다.
Kim, HyeongJun,Han, A-Reum,Cho, Chul-Hee,Kang, Hyunbum,Cho, Han-Hee,Lee, Moo Yeol,Fré,chet, Jean M. J.,Oh, Joon Hak,Kim, Bumjoon J. American ChemicalSociety 2012 Chemistry of materials Vol.24 No.1
<P>Conjugated polymers, in general, are unstable when exposedto air,solvent, or thermal treatment, and these challenges limit their practicalapplications. Therefore, it is of great importance to develop newmaterials or methodologies that can enable organic electronics withair stability, solvent resistance, and thermal stability. Herein,we have developed a simple but powerful approach to achieve solvent-resistantand thermally stable organic electronic devices with a remarkablyimproved air stability, by introducing an azide cross-linkable groupinto a conjugated polymer. To demonstrate this concept, we have synthesizedpolythiophene with azide groups attached to end of the alkyl chain(P3HT-azide). Photo-cross-linking of P3HT-azide copolymers dramaticallyimproves the solvent resistance of the active layer without disruptingthe molecular ordering and charge transport. This is the first demonstrationof solvent-resistant organic transistors. Furthermore, the bulk-heterojunctionorganic photovoltaics (BHJ OPVs) containing P3HT-azide copolymersshow an average efficiency higher than 3.3% after 40 h annealing atan elevated temperature of 150 °C, which represents one of themost thermally stable OPV devices reported to date. This enhancedstability is due to an in situ compatibilizer that forms at the P3HT/PCBMinterface and suppresses macrophase separation. Our approach pavesa way toward organic electronics with robust and stable operations.</P><P>We have demonstrated a simple and powerful approach to introducean azide cross-linkable group into conjugated polymers (P3HT-azide)for solvent-resistant and thermally stable organic electronics withremarkably improved air stability. This on-demand cross-linking mechanismenables production of a solvent-resistant hole-transporting materialfor OTFTs, as well as an in-situ compatibilizer for thermally stableOPVs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2012/cmatex.2012.24.issue-1/cm203058p/production/images/medium/cm-2011-03058p_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm203058p'>ACS Electronic Supporting Info</A></P>
An Empirical Study on Credit Card Loan Delinquency in Korea
( Hyeongjun Kim ),( Hoon Cho ) 한국금융공학회 2015 한국금융공학회 학술발표회 Vol.2015 No.1
This study investigates credit card loan delinquency in Korea. We define three states-no delinquency, delinquency, and serious delinquency-and test the transition probabilities between them using quarterly observed account-level data. Our findings have several economic implications. First, factors that affect delinquency risk can differ from those that affect the transition to serious delinquency. Second, the recent increase in the number of seriously delinquent accounts can be attributed to changes in the distribution of borrower ages. Third, macroeconomic conditions-especially differences in growth between the gross domestic product and consumption-have led to the recent increase in delinquent accounts.
Electro-Mechanically Responsive Ionoelastomer Heterojunctions
HyeongJun Kim(김형준) 한국고분자학회 2021 한국고분자학회 학술대회 연구논문 초록집 Vol.46 No.1
Soft solids capable of conducting ions offer promise for the design of entirely new classes of highly deformable and bio-inspired devices. Here, we introduce ‘ionoelastomers’—soft polymer networks capable of selectively conducting either anions or cations—to demonstrate liquid-free, elastic, and stretchable ionic diodes and transistors that operate entirely via non-Faradaic processes. We show that the junction of two oppositely charged ionoelastomers yields an ‘ionic double layer’, analogous to the depletion layer in a semiconducting p-n junction. Furthermore, soft and stretchable ionoelastomer junctions provide fundamentally new functionalities including: 1) low voltage reversible electro-adhesion and 2) electro-mechanical transduction, i.e., the conversion of mechanical deformation into electrical signals.