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김동훈,구자현,김대종,유영성,장창희,Kim, Donghoon,Koo, Jahyun,Kim, Daejong,Yoo, Young-Sung,Jang, Changheui 한국압력기기공학회 2011 한국압력기기공학회 논문집 Vol.7 No.2
To evaluate steam oxidation behaviours of Alloy 617 and Haynes 230, oxidation test were performed at $900^{\circ}C$ in steam and $steam+20\;vol.-%\;H_2$ environments. Oxidation rate in steam condition was similar to that in air for Alloy 617, while it was slightly lower for Haynes 230. When hydrogen was added to steam, oxidation rate was enhanced. Isolated $MnTiO_3$ particle were formed on $Cr_2O_3$ oxide layer and sub layer $Cr_2O_3$ were formed in steam and $steam+20\;vol.-%\;H_2$ for Alloy 617. On the other hands, $MnCr_2O_3$ layer were formed on top of $Cr_2O_3$ oxide layer for Haynes 230. The extensive sub layer $Cr_2O_3$ formation was resulted from the oxygen inward diffusion in such environments. When hydrogen was added, the oxide morphology was changed from polygonal to platelet because of the accelerated diffusion of cations under the oxide layer. In addition, decarburized zone was extended as hydrogen participated into the reactions causing carbide dissolution.
잠수함 구조해치구역 검사인증체계 및 유한요소해석에 관한 연구
김동훈(Donghoon Kim),이상주(Sangju Lee),김효철(Hyocheol Kim),이광호(Kwangho Lee) 한국해군과학기술학회 2020 Journal of the KNST Vol.3 No.1
The ROK Navy inspection and certification system for the submarine rescue hatch area was introduced. In addition, the finite element analysis results show that it can be safely mated with DSRV and PRM even in the certain submarine depth. Additional finite element analysis, which took the thinning of the hatch area over time into account, was performed. These analyses showed that, when the joint area was reduced to 15 ㎜ from the design standard 16 ㎜, the DSRV and submarine can still mate each other safely.
장비 진동데이터 분석을 통한 **** **함 예지정비 적용가능성 및 발전방향에 관한 연구
김동훈(Donghoon Kim),홍순국(Sunguk Hong),최경억(Gyeongeok Choi),신성균(Seonggyun Shin),김효철(Hyocheol Kim),김종환(Jonghwan Kim) 한국해군과학기술학회 2019 Journal of the KNST Vol.2 No.2
The strategy of maintenance was improved from the Break-down maintenance strategy, which is only for broken-down equipment, to the Preventive maintenance strategy. The Proactive maintenance strategy involves doing maintenance when data and sensors indicate it is needed, rather than after the equipment has broken down. The ROK Navy may want to adopt the Reliability centered maintenance strategy, which combines the Preventive and Proactive maintenance strategies. By this study, I suggested the applicability of the Proactive maintenance and its future with the vibration data analysis of the ***class **ship. Then, the remaining useful life of the ship was calculated with empirical equations for concatenate curve fitting. In the future, more reliable proactive maintenance will be possible using the improved automatic vibration data recording system.
잠수함 주요장비 진동에 대한 고속 푸리에 변환 분석 및 예지정비 적용
김동훈(Donghoon Kim),강상우(Sang Woo Kang),이지훈(Ji Hoon Lee),남경모(Kyung Mo Nam),성성훈(Seong Hun Seong),이효진(Hyo Jin Lee) 한국해군과학기술학회 2021 Journal of the KNST Vol.4 No.1
The maintenance strategy was improved from the Break-down maintenance strategy, which is only for broken-down equipment, to the Preventive maintenance strategy. The Proactive maintenance strategy involves doing maintenance when data and sensors indicate it is needed, rather than after the equipment has broken down. The ROK Navy may want to adopt Predictive maintenance, which includes both Preventive and Condition-based maintenance strategies, in the future. By this study, I predict the remaining useful life of the ships equipment and obtain real-time descriptive data by fast Fourier transform. At-risk technologies identified by Predictive maintenance should be added to the naval ship upgrade plan. We should plan to train new experts in Predictive maintenance, especially vibration analysis, as soon as possible.
김동훈(Donghoon Kim),배성호(Sung-Ho Bae) 한국방송·미디어공학회 2024 한국방송미디어공학회 학술발표대회 논문집 Vol.2024 No.6
데이터셋 증류는 원본 데이터셋과 비슷한 학습 성능을 보이는 매우 작고 유용한 데이터셋을 합성하는 것을 목표로 한다. 설명가능한 AI 분야에서 학습된 모델의 표현들 중 예측에 중심적으로 사용되는 의존도가 높은 특징들을 샤플리 값을 이용해 식별할 수 있음을 밝혔다. 본 논문은 이러한 발견으로 바탕으로 샤플리 값을 이용하여 각 클래스의 의존 특징을 효과적으로 고려한 데이터셋 증류 방법을 제안한다. 즉, 각 합성 데이터가 일부 특징만 학습하지 않도록 모델 뉴런의 샤플리 값을 계산하여 의존도가 높은 뉴런들을 식별하고, 이들 중 상위 n%의 뉴런을 조절하여 데이터셋 증류를 수행한다. CIFAR10 데이터셋, 10 IPC(Image per class)의 조건에서 제안 방법을 실험하였고 기존 데이터셋 증류 방법 대비 최대 1.3%p의 성능 향상을 보인다. 이는 제안하는 데이터셋 증류 방법이 효과적으로 각 클래스의 차별적인 특징을 포착할 수 있음을 시사한다.
김동훈(Donghoon Kim),김기현(Kihyun Kim),배충식(Choongsik Bae) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11
CFD (Computational Fluid Dynamics) method has been widely used to analyze internal combustion engines during the last few years. In CFD methods, there are many models to describe physical phenomena; combustion, spray breakup, and spray-wall impingement. Especially in a diesel engine, fuel spray characteristics are calculated with many models such as breakup, collision, evaporation, etc. Fuel spray characteristics, such as spray tip penetration length and spray angle, are major factors that affect heat release rate and fuel efficiency in internal combustion engine, so understanding of fuel spray characteristics is very important. In this paper, we used OpenFOAM (Open Field Operation and Manipulation) as a CFD tool and calculated diesel spray characteristics with three breakup models; RD (Reitz and Diwakar), KH/RT (Kelvin-Helmholtz / Rayleight-Taylor), and ETAB (Enhanced Taylor Analogy Breakup) models. OpenFOAM is a free open source CFD package released in 2004. Calculated results were validated with experimental data and KH/RT model had great accuracy.