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LSTM 오토인코더를 이용한 이상 탐지의 임계치 결정 방법
전승현(Seunghyeon Jeon),박채린(Chaelyn Park),이규원(Gyuwon Lee),김성종(Seongjong Kim),구본근(Bongen Gu) 한국정보기술학회 2023 한국정보기술학회논문지 Vol.21 No.4
The threshold is an important factor that affects the performance of anomaly detection using LSTM autoencoder for the purpose of reducing direct and indirect losses due to equipment failure. The LSTM autoencoder trained on normal data set has the characteristics that the reconstruction error of abnormal data is greater than that of normal data. In this paper, we propose a method of determining the threshold by using the ratio between the maximum reconstruction error of normal data and the minimum reconstruction error of abnormal data. To show the validity of the proposed threshold determination method, we implement an LSTM autoencoder model for detecting anomalies in pump data that is publicly available through Kaggle and determine the threshold using the threshold determination data set. The experimental results using the determined threshold on the test data set showed an improvement of 5% in accuracy and 25% in recall compared to the existing precision-recall curve method.
자율운항선박 성능검증을 위한 시뮬레이션 기반 테스트베드의 기능 분석
임승현(Seunghyeon Lim),안해성(Hae-Seong Ahn),전송만(Songman Jeon),한동원(Dongwon Han),임근태(Geun-Tae Yim) 한국항해항만학회 2022 한국항해항만학회 학술대회논문집 Vol.2022 No.2
전 세계적으로 자율운항선박 기술개발을 추진 중이며, 자율운항선박 핵심 기술뿐 아니라, 상용화의 기틀을 마련하는 평가·검증 관련한 연구도 활발히 수행되고 있다. 이에 따라 자율운항선박의 핵심 기술과 주요 장비의 성능검증을 위한 테스트베드의 개발이 필수적이다. 본연구에서는 국내외 자율운항선박 기술개발 현황과 자율운항선박의 시뮬레이션 기반 테스트베드가 갖춰야 할 요구사항을 분석하였으며, 자율운항선박의 특수성이 반영된 동역학 모델 기반의 조종 시뮬레이션 테스트베드에서의 성능검증을 위한 기능 분석 및 세분화를 통해 플랫폼 운영에 효과적인 기술들을 제안한다.
Effect of liquid droplet surface tension on impact dynamics over hierarchical nanostructure surfaces
Baek, Seunghyeon,Moon, Hyun Sik,Kim, Wuseok,Jeon, Sangmin,Yong, Kijung The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.37
<P>Analyzing impact dynamics is important for practical applications of superhydrophobic surfaces, because these nonwetting surfaces frequently encounter impacting liquid droplets in real environments. Thus, various studies have been conducted to investigate impact dynamics by examining the correlation between the behaviors of impacting liquid droplets and several determining parameters, such as impacting velocity, surface structure and surface energy. The impacting behaviors of pure water droplets were the main focus in most previous studies; the effect of surface tension, another critical parameter, on impact dynamics has rarely been investigated. In the current work, we have newly studied the effects of liquid surface tension on impact dynamics using an ethanol-water solution as a model liquid system. We systematically varied the liquid's surface tension between 72 and 32 mN m<SUP>−1</SUP> by changing the ethanol concentration from 0 to 20 wt%. This range of composition drastically changed the surface tension while it did not significantly affect other physical properties, such as density and viscosity. For an impact dynamics study, two surfaces, namely ZnO nanowires (NWs) and ZnO/Si hierarchical (HIE) structures, were prepared. As the surface tension decreased, the static water contact angle (CA) decreased on both surfaces. Under dynamic conditions, our analysis using a high-speed camera and a quartz crystal microbalance (QCM) showed that lowering the surface tension causes the transition from the anti-wetting to wetting state. The transition <I>We</I> numbers were obtained on both surfaces for various surface tensions of liquids. Under the same dropping conditions of liquids, the ZnO/Si HIE surface shows higher transition <I>We</I> numbers than the ZnO NW surface, which is due to the higher fraction of air pockets in the hierarchical structure, originating from dual dimensional structures. To understand the mechanism of dynamic transition, we developed a model for ZnO/Si HIE structures based on three determining pressures: anti-wetting, wetting, and effective water hammer pressures. The modeling results explain the experimental observations. The results of our model system are highly useful for understanding the impact dynamic behaviors of various liquids on non-wetting surfaces.</P>
Baek, Seunghyeon,Kim, Wuseok,Jeon, Sangmin,Yong, Kijung Elsevier 2018 Sensors and actuators. B Chemical Vol.262 No.-
<P><B>Abstract</B></P> <P>Quantitative analysis of water droplet behavior under dynamic conditions is one of the critical challenges for applications of wettability-controlled surfaces. Currently, various optical analysis techniques have been employed to analyze impact dynamics. Despite the convenience of direct observation of water droplets, most of these techniques have limited applicability to microscopic and quantitative investigations. In an effort to overcome these limitations, here, we suggest a complementary analysis platform using a quartz crystal microbalance (QCM) to study impact dynamics. A high-speed camera and QCM were applied together to study the behavior of water droplets that impact wettability-controlled surfaces with various <I>We</I> numbers (Weber number). For these experiments, ZnO nanowire surfaces were prepared and chemically modified by alkyl-thiol molecules with various carbon chain lengths (C0–C12) to control the surface energy. For nanowire surfaces with high surface energies (C0–C6) and for the lowest surface energy sample (C18), both methods exhibited highly consistent impact dynamics, showing stable wetting and dewetting properties, respectively. In addition to these apparent behaviors, QCM was further able to provide detailed microscopic information regarding the penetration and deformation of water droplets in a quantitative way based on acoustic sensing. More interestingly, QCM was able to determine the metastable water repellency of a C12-modified surface with a high <I>We</I> number, which could not be detected by the high-speed camera. These results suggest the significant potential of QCM as a new platform to analyze the impact dynamics of water droplets <I>via</I> quantitative, microscopic investigations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Non-optical technique was employed as a complementary analysis for impact dynamics. </LI> <LI> QCM can investigate in-situ changes of a surface state as the resonance frequency. </LI> <LI> Nanostructured surface with various surface energies were prepared for this study. </LI> <LI> QCM provided detailed microscopic information in a quantitative way. </LI> <LI> QCM compared water-repellency stability of the superhydrophobic surfaces. </LI> </UL> </P>
전송만(Songman Jeon),임승현(Seunghyeon Lim),한동원(Dongwon Han),안해성(Hae-Seong Ahn),임근태(Geun-Tae Yim) 한국항해항만학회 2022 한국항해항만학회 학술대회논문집 Vol.2022 No.2
자율운항선박기술의 상용화를 위하여 개발되는 요소 및 통합기술의 성능시험과 실증은 필수적이며, 이를 위한 테스트베드 개발이병행되어야 한다. 현재 국내에서는 자율운항선박 기술개발사업을 통해서 개발되는 기술의 성능검증을 위하여 울산시 고늘지구 인근에 성능실증센터가 구축되고 있으며, 성능실증센터는 시뮬레이션 기반 테스트베드를 비롯한 육상테스트베드와 시험해역과 시험선을 포함한 해상테스트베드로 구성된다. 해상테스트베드 시험선은 설계 단계에서부터 자율운항기술의 해상 실증 및 성능시험을 고려하여 건조되었으며, 본 논문을 통해 해상테스트베드 시험선의 기능과 구성요소에 대해 소개하고자 한다.
사물인터넷 환경에서 CoAP을 이용한 디바이스 해킹시나리오 및 대응방안
최승현 ( Choi Seunghyeon ),서초롱 ( Seo Chorong ),이근호 ( Keun-ho Lee ),전유부 ( You-boo Jeon ) 한국정보처리학회 2016 한국정보처리학회 학술대회논문집 Vol.23 No.1
최근 정보통신기술의 눈부신 발전으로 사람-사람, 사람-사물, 사물-사물 각각을 연결하여 최대한의 시너지를 발휘하려는 움직임이 활발해지고 있다. 즉 일상생활에서 사용되는 자동차, 가전제품, 드론 등의 제품도 연결되어 통신하는 사물인터넷 시대가 도래 하고 있다. 머지않아 모든 기기가 연결되는 시대가 오면 물리적 보안 보다 논리적 보안이 중요해 질 것이다. 또한 사물인터넷 해킹은 정보보호라는 단위를 넘어 사람의 생명과 직결되는 해킹 피해가 발생할 위험이 있다.