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황동현(Donghyeon Hwang),김지용(Jiyong Kim),이준헌(Junheon Lee),김관주(Kwanju Kim),조성산(Sungsan Cho),김재철(Jaechul Kim) 한국철도학회 2014 한국철도학회 학술발표대회논문집 Vol.2014 No.10
스킬 소음은 차량의 곡선 주행시 차륜과 레일 사이의 횡방향 점착-미끄럼 운동에 의해서 발생하는 소음이다. 대표적 과도 특성을 나타내는 스킬 소음의 정확한 예측을 위해서는 발생원인 차륜과 레일간의 횡방향 접촉력의 정확한 파악이 요구된다. 이를 설명하기 위한 다양한 이론이 존재한다. 하지만 해당 이론들은 다양한 가정에 의하여 사용이 제한된다. 본 논문에서는 유한요소 해석법을 이용하여 가능한 가정에 의한 제약없이 스킬소음이 발생하는 조건을 판단할 수 있는 해석적 방법 개발을 목적으로 한다. 이를 위하여 스킬 소음이 발생하는 조건에서의 유한요소 모델을 작성하고, 접촉영역에서 발생하는 횡방향 접촉력을 예측하여 점착계수와 크리피지의 관계를 도출한다. 작성된 마찰특성 곡선을 이용하여 크리피지가 약 0.005 이상일 경우 스킬 소음 발생을 예상했다. Squeal noise occurs due to lateral stick-slip mechanism while negotiating curve track. It is necessary to estimate lateral creep force that represent unstable response for prediction of squeal noise. There are many theories to estimate contact force for 3D rolling contact problem. But most of them are limited by various assumptions. This paper aims to predict occurrence of squeal noise without limitation that concerning 3D rolling contact theories using finite element analysis. The relationship between adhesion coefficient and creepage was presented by calculating lateral creep force in the contact area. Occurrence of squeal noise was assessed by friction characteristic curve. Squeal noise was expected when creepage is over 0.005.
황동현 ( Dong Hyun Hwang ),윤영현 ( Young Hyun Yoon ),한창엽 ( Chang Yeop Han ),이승은 ( Seung Eun Lee ) 한국인터넷정보학회 2020 인터넷정보학회논문지 Vol.21 No.5
최근 인공지능에 대한 관심이 높아짐에 따라 인공지능 프로세서를 하드웨어로 구현하는 연구가 활발히 진행되고 있다. 하지만 인공지능 프로세서는 기존에 기능 검증을 위한 프로세서 시뮬레이션 외에 애플리케이션 단계에서 인공지능 프로세서가 해당 애플리케이션에 적합한지에 대한 성능 검증이 추가로 필요하다. 본 논문에서는 인공지능 프로세서를 활용한 애플리케이션 성능 검증과 프로세서의 한계점을 탐색할 수 있는 내장형 인공지능 프로세서를 위한 성능 분석기를 제안한다. 본 논문은 내장형 인공지능 프로세서를 위한 성능 분석기를 구현하기 위하여 기존에 구현된 인공지능 프로세서의 구조를 분석하고 이를 기반으로 인공지능 프로세서를 모사하는 내장형 인공지능 프로세서를 위한 성능 분석기를 구현한다. 내장형 인공지능 프로세서를 위한 성능 분석기를 활용해 이미지 인식, 음성 인식 애플리케이션에서 인공지능 프로세서의 성능 분석 및 한계점을 탐색하고, 제한된 메모리 크기 안에서 인공지능프로세서의 구조를 최적화한다. Recently, as interest in artificial intelligence has increased, many studies have been conducted to implement AI processors. However, the AI processor requires functional verification as well as performance verification on whether the AI processor is suitable for the application. In this paper, We propose an AI processor performance analyzer that can verify the application performance and explore the limitations of the processor. By Using the performance analyzer, we explore the limitations of the AI processor and optimize the AI model to fit an AI processor in image recognition and speech recognition applications.
황동현(Donghyun Hwang),박수진(Sujin Bak),안규복(Kyubok Ahn) 한국연소학회 2019 KOSCOSYMPOSIUM논문집 Vol.2019 No.11
An experimental study was conducted to investigate the effects of swirler geometry and flow condition on self-excited thermo-acoustic instability and bifurcation of flame structure. The combustion chamber length was manufactured in two types to simulate acoustically coupled/uncoupled conditions. Dynamic pressure, heat release, inlet velocity fluctuation, and CH* chemiluminescence image were measured to analyze the mechanism for combustion instability. Bifurcation of the flame structure was not necessarily coincide with the onset of thermo-acoustic instability, but occurred at nearly same condition regardless of the combustor length. The results showed that the combustion instability occurred based on the principle of the limit cycle in the case of coupled long combustor. In the uncoupled short combustor, however, only stable combustion was observed under the same flow conditions.
다양한 탄화수소 연료를 이용한 난류 예혼합 화염에서 화염길이 스케일링
황동현(Donghyun Hwang),왕가흠(Kexin Wang),안규복(Kyubok Ahn) 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5
덤프연소기에서 다양한 탄화수소 계열의 연료를 이용한 화염길이 및 화염중심위치 스케일링이 실험적으로 수행되었다. 덤프연소기는 가스터빈엔진과 램제트엔진에 주로 사용된다. 하지만 높은 에너지 밀도로 인해 연소불안정에 취약하며 연소불안정 발생 시 압력섭동 및 유동섭동으로 인해 화염의 길이 및 중심위치가 변한다. 이번 연구는 에틸렌, 에탄, 프로판 그리고 공기를 사용하였다. 또한 불안정한 유동조건을 모사하기 위해 스피커를 사용하였고, 화염이미지는 CH* chemiluminescence 기법을 적용한 ICCD 카메라를 이용해 촬영하였다. 본 연구의 목적은 입구속도, 당량비, 음향가진에 따른 화염길이 및 화염중심위치의 변화를 조사하고 Reynolds, Strouhal, Damkohler 수와 같은 무차원수들과의 상관관계를 조사하였다. Flame length and flame center length scaling using different hydrocarbon fuels in a dump combustors were conducted experimentally. Generally, dump combustor is used gas turbine engines and ramjet engines. However, it has weakness for combustion instabilities because of high density energy and the flame length and flame center length are changed due to pressure and velocity fluctuation under combustion instabilities. In this work, experiments using ethylene, ethane, propane and air were performed. Also, an acoustic driver was used to simulate unstable flow condition and flame images were taken using ICCD camera with a CH* chemiluminescence technique. The objectives were to investigate about the effects of inlet velocity, equivalence ratio, acoustic forcing frequency on flame lengths and flame center lengths and to examine correlation between normalized flame lengths/flame center lengths and the non-dimensional parameters such as Reynolds, Strouhal, Damkohler number.
황동현 ( Donghyun Hwang ),박재민 ( Jaemin Park ) 한국생산성학회 2018 生産性論集 Vol.32 No.1
This paper describes industrial sector efficiency comparison by technology level through input oriented DEA methodology and shows a differentiated cause-effect relationship by independent variables in each technology level (OECD industrial classification of R&D intensity: low, medium-low, medium-high, and high). In Korea manufacturing industry, sectoral DEA approach of technical efficiency by technology level was un-precedent and could guide productivity improvement idea in a different technology level sector. In the efficiency comparison, medium-high technology sector is more efficient than medium-low and low technology sectors, but high technology sector’s is lower than medium-high sector due to more diverse employee and researcher structure. In a low technology sector, firms could improve efficiency through R&D investment. The other insight is that R&D investment, employee & researchers does not always improve efficiency especially in inefficient firms, which indicated that firms have to optimize their input factors effectively, sometimes reducing or transferring resources such as R&D investment according to its technology level. R&D investment would improve technical efficiency only in low-technology firms. In a cause and effect of efficiency, high tech. firms would have to choose a production scale to improve their scale efficiency. So far, “technology regime” topic of Marlerba & Osenigo(1996, 1997) has been researched with STEPI’s business innovation survey outcome by many researchers and indicated that R&D investment could induce a different outcome based on innovation condition and knowledge basement. In the meantime, Efficiency related research has focused on only firm-level studies without level-up to technology level. Thus, a combination of the both would be a new approach, which would be able to give a benchmarking idea to inefficient firms by technology level. For a future study, it would be meaningful to study an innovation and knowledge basement condition role with sub-industries categorized by sectoral innovation system. But, I also have to acknowledge that R&D investment and revenue at a same year could be a statistical issue of multi-collinearity though it comes from a survey data sample’s restriction.