Coefficient of friction of a starved lubricated spur gear pair

Hua iju Liu,Caichao Zhu,Zhangdong Sun,Yuanyuan Zhang,Chaosheng Song 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.5

The frictional power loss issue of gear pairs becomes an important concern in both industry and academia due to the requirement of the energy saving and the improvement of power density of gear drives. A thermal starved elastohydrodynamic lubrication model is developed to study the tribological performance of a spur gear pair under starved lubrication conditions. The contact pressure, the film thickness, the temperature rise, the frictional power loss, as well as the coefficient of friction are evaluated by considering the variation of the curvature radius, the sliding/rolling motion, and the load distribution of gear tooth within the meshing period. Effects of lubrication starvation condition, load and speed on the coefficient of friction are studied.

소셜네트워크 분석과 위계적 선형모형을 활용한 보험사의 비대면채널 성장성 인지 모형

전희주 ( Heu Iju Chun ),안철경 ( Chul Kyung Ahn ) 한국보험학회 2016 保險學會誌 Vol.105 No.-

본 연구에서는 국내 생명보험사와 손해보험사의 보험전문인들의 비대면채널 성장성 인지 모형을 위계적 선형모형을 기반으로 하여 제시한다. 설명변수로는 연결중심성, 근접중심성, 매개중심성, 위세중심성 등의 소셜네트워크 특성 변수들 및 환경요인, 경영요인, 소비자특성 요인, 정책/규제 요인 등을 사용한다. 분석결과, 비대면채널 성장성 인지에 영향을 주는 요인은 연결중심성, 아이겐벡터중심성, 환경요인, 경영요인, 소비자특성요인, 정책/규제요인 등인 것으로 나타났다. 경영요인과 환경요인은 높을수록, 소셜네트워크 연결중심성이 낮을수록, 위세중심성은 높을수록 비대면채널에 대한 성장성 인지는 높게 나타난다. This research intends to suggest hierarchical linear model considering degree centrality, closeness centrality, betweenness centrality, prestige centrality which represent social network’s characteristics, environmental factor, managemental factor, customer characteristic factor, political strategic factor and insurance company factors in order to find the factors to affect the recognition of non-face-to-face channel growth with insurance experts working at insurance companies. The hierarchical linear model shows that the factors influencing the recognition of non-face-to-face channel growth are degree centrality, eigenvector centrality which are social network’s characteristics, environmental factor, managemental factor, customer characteristic factor and political strategic factor. Higher factors are associated with higher recognition of non-face-to-face channel growth. Also if degree centrality or/and eigenvector centrality is higher then the recognition of non-face-to-face channel growth becomes high.

깊이 영상을 사용한 실내 인공암벽에서의 등반자 영역 검출

정다니엘 ( Daniel Chung ),고일주 ( Iju Ko ) 한국정보처리학회 2016 한국정보처리학회 학술대회논문집 Vol.23 No.1

최근 스포츠와 ICT 기술의 융합으로 스크린 스포츠라는 분야가 등장하였고, 스포츠 클라이밍도 스크린 스포츠로 구현하려는 시도가 이루어지고 있다. 이를 위해서는 실내 인공암벽에서 등반자의 모습을 추적해야 하는데, 이에 앞서 사람의 영역을 검출할 필요가 있다. 사람의 영역을 검출하는 데에는 키넥트를 이용하는데, 스켈레톤 정보와 영상 정보를 이용할 수 있다. 본 논문에서는 깊이 영상을 사용하여 등반자의 영역을 검출하는 방법을 제시한다. 실내 인공암벽 환경에서는 등반자의 영역을 검출하는 방법을 제시한다. 실내 인공암벽 환경에서는 등반자 이외에 주변환경의 변화가 없으므로 등반자의 영역

Shakedown analysis of a wind turbine gear considering strain-hardening and the initial residual stress

Haifeng He,Hua iju Liu,Caichao Zhu,Longhua Yuan 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.11

Under some heavy-duty conditions, the shakedown state may occur on gears such as those used in a megawatt wind turbine gearbox. The plastic deformation and the residual stress formed within the shakedown process further influence the contact behavior and the service life of the gear. The initial residual stress caused by the heat treatment of the case-hardening gear, together with the strain-hardening constitutive behavior of the material, have a combined effect on the shakedown state. A two-dimensional elastic-plastic contact numerical model was developed for a case-hardened wind turbine gear to study effects of the initial residual stress and the strain-hardening properties. Plastic strain and residual stress are calculated at each loading cycle without the consideration of the tooth friction. The initial yield limit and the hardening modulus of the material were obtained through a tension test on a universal tensile test machine. The initial residual stress distribution was measured with the X ray diffraction method and then embedded in the finite element model. The results show that strain-hardening behavior can significantly improve the shakedown performance, and the larger the hardening modulus is, the less the maximum plastic strain is at the final shakedown state. Initial residual compressive stress is helpful to improve the shakedown performance, while initial residual tensile stress has negative influence on the shakedown performance. As the normal load increases, the influence of the initial residual stress on the shakedown state becomes weakened.

Oil film stiffness and damping in an elastohydrodynamic lubrication line contact-vibration

Yuanyuan Zhang,Hua iju Liu,Caichao Zhu,Mingyong Liu,Chaosheng Song 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.7

An elastohydrodynamic lubrication line contact-vibration model is proposed to study the stiffness and damping of the oil film existed in the EHL contact region. An initial mutual approach between interacting surfaces, which deviates from the steady-state balanced position, is assumed under the free contact-vibration to predict the response of the mutual approach. An inertia term, which represents the acceleration of the gap motion, is added to the classical force balance equation to form the equation of motion of the mutual approach. Response of the mutual approach is solved based upon the solving of the contact-dynamic model. The oil stiffness is calculated according to the natural frequency of the response under damped and non-damped conditions, the latter of which represents dry contact conditions. The oil film damping is calculated in terms of the principle of the energy conservation which utilizes the whole history of response compared with the log decrement method. Effect of the normal load, the rolling speed and the amplitude of the regular sinusoidal surface waviness on the oil film stiffness, the contact stiffness and the oil film damping are studied. The study provides an insight on the oil film dynamic characteristics of lubricated contact-vibration problems which appear in gears, bearings, etc. The results show that the oil film damping factor decreases with the increasing normal load as well as the increasing rolling speed. The oil film stiffness increases with the normal load and decreases with the rolling speed. Also, compared to the contact stiffness, the oil film stiffness makes less contribution to the total stiffness. The surface waviness amplitude has little effect on the oil film stiffness and the oil film damping.

대학 캠퍼스 기반의 국내 마이크로그리드 활성화 추진 방안

이수연(Suyeon Lee),강이주(Iju Kang),손예지(Yeji Son) 한국신재생에너지학회 2021 한국신재생에너지학회 학술대회논문집 Vol.2021 No.7

현재 전 세계의 메가트렌드는 에너지전환(Energy Transition)이라고 할 수 있으며, 한국 역시 이 트렌드에 맞춰 한국판 그린 뉴딜 정책을 시행하고 있다. 이 정책의 핵심은 현재의 중앙 집중형 발전 방식을 분산 에너지 환경으로 전환하여 지역 맞춤형 인프라를 구축하는 것이다. 이러한 전환점에 있어 주목받고 있는 것이 바로 ‘마이크로그리드(Microgrid)’이다. 미국과 일본은 이미 캠퍼스 마이크로그리드를 통해 지역 기반 분산형 에너지 실증 단계에 있지만, 한국은 여전히 독립적인 섬 형태 위주로 구축되어 있다. 따라서 본 연구를 통해 도심형 분산 에너지로 확대 가능한 한국형 캠퍼스 마이크로그리드 모델을 도출하고자 하였다. 우선 미국의 선진사례를 중심으로 분석하여 한국 경우와 비교해 보았다. 미국 대학은 ACUPCC 위원회를 결성하여 에너지 수요가 많은 캠퍼스의 탄소 배출량을 마이크로그리드를 통해 줄이고자 하였다. 이들은 미국 내 천연가스 가격이 저렴하고 캠퍼스 부지가 넓다는 장점을 활용하여 열 병합 및 태양광 위주로 완전한 자가발전을 이루고자 한다. 이와 더불어 대학과 기업이 협력하여 교내 및 지역 환경문제를 해결하고, 학생도 프로젝트와 연구에 참여하여 많은 성과를 내고 있다. 하지만 미국과 한국의 상황이 다르기 때문에 그린 캠퍼스 달성을 위해서는 산학연 연계를 통한 시스템 구축과 맞춤형 법안 도입이 필수적이다. 캠퍼스 마이크로그리드의 구축은 LINC 사업단을 중심으로 한 산학연 연계를 통해 이루어질 수 있도록 한다. 정부는 사업에 참여할 대학을 선발하여 투자금을 지원하고, 대학은 이를 바탕으로 협력할 기업을 선정한다. 기업은 재학생에게 현장실습 참여 기회를 제공하여 학부생의 관련 프로젝트에 대한 적극적인 참여를 돕는다. 이렇게 형성된 협력 체계는 인재를 육성하고 교내 연구를 활성화시켜 기술 발전을 도모할 수 있다. 나아가 정부는 대학에서 수행한 데이터를 확장하여 도심형 분산 에너지 시스템을 구축도 가능할 것이다. 이외에도 정부는 ‘직접 PPA’ 법안 활성화를 통해 지역 사회 내 전력 거래가 가능하도록 해야 한다. 이렇게 된다면 대학은 남은 전력을 판매하여 수익을 얻을 수 있고, 또 하나의 ‘에너지 프로슈머(Energy prosumer)’로서의 역할을 기대할 수 있다. 이렇듯 본 발표에서 제시한 한국형 캠퍼스 마이크로그리드는 캠퍼스를 넘어 재생에너지 기반의 분산형 에너지 체계로의 발판이 될 것이다.

Dynamic analysis of a megawatt wind turbine drive train

Caichao Zhu,Shuang Chen,Chaosheng Song,Hua iju Liu,Houyi Bai,Fei Ma 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.5

The dynamic performance of a wind turbine drive train significantly influences the operation of an entire machine. In this work, amegawatt wind turbine drive train is subject to theoretical and experimental dynamic analysis. The method of rigid-flexible couplingmultibody dynamics was applied to develop a dynamic model of the entire drive train. This model was then used to study the naturalcharacteristics of the system. The blades, hub, main shaft, and speed-up gearbox in the dynamic model were modeled as flexible bodies. The potential resonances of the system were detected through Campbell and modal energy distribution analyses. Theoretical results showthat the first-order natural frequency of the system is approximately 1.72 Hz. This frequency represents a torsional vibration mode,Moreover, resonances are not observed within the normal operating speed range of the drive train. An experimental remote real-timesystem was developed to monitor the torsional vibration of the drive train. This vibration was used to measure the torsional vibration ofthe system overall. The experimental results are consistent with the theoretical results.

Dynamic modeling and analysis for transmission system of high-power wind turbine gearbox

Hongfei Zhai,Caichao Zhu,Chaosheng Song,Hua iju Liu,Guangfu Li,Fei Ma 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.10

As a key component to adjust the speed and torque, double-fed speed up gearbox plays a vital role in reliability and stability for thewind turbine system. Considering the base helix angle, normal pressure angle, position angle, rotation of carrier and the mesh of the ringgear and planet gear, a coupled dynamic model for high-power wind turbine gearbox transmission system, which consists of two helicalplanetary stages and one helical gear stage was established using the lumped parameter method in this paper. Numerical integration applyingthe explicit 4/5th order Runge-Kutta algorithm was used to solve the proposed model and the dynamic responses of transmissionsystem were investigated. Results show that the modal frequencies for the system are not coincided with the gear mesh frequencies of thestages. Then, the dynamic mesh forces of the 1st stage in different models are compared and analyzed in frequency domain.

다중 가중치 및 단기 기억 기능을 갖는 시냅스 소자 응용을 위한 수직 이종접합 쇼클리 다이오드 어레이 제작 및 동작

유병은(Byeong Eun Yoo),이이주(Iju Lee),백승조(Seungjo Baek),조성재(Seongjae Cho) 대한전자공학회 2021 대한전자공학회 학술대회 Vol.2021 No.6

Datura metel stramonium exacerbates behavioral deficits, medial prefrontal cortex, and hippocampal neurotoxicity in mice via redox imbalance

Vincent Onoriode Igben,Wilson Josiah Iju,Omogbiya Adrian Itivere,John Chukwuma Oyem,Peter Sunday Akpulu,Efe Endurance Ahama 한국실험동물학회 2023 Laboratory Animal Research Vol.39 No.2

Background: Datura metel (DM) stramonium is a medicinal plant often abused by Nigerians due to its psychostimulatory properties. Hallucinations, confusion, agitation, aggressiveness, anxiety, and restlessness are reported amongst DM users. Earlier studies suggest that DM induces neurotoxicity and affect brain physiology. However, the exact neurological effects of DM extract in the medial prefrontal cortex (mPFC) and hippocampal morphology have not been elucidated. In this study, we evaluated the hypothesis that oral exposure to DM extract exerts a neurotoxic effect by increasing oxidative stress in the mPFC and the hippocampus and induces behavioral deficits in mice. Results: DM methanolic extract exposure significantly increased MDA and NO levels and reduced SOD, GSH, GPx and CAT activities in mice brains. In addition, our results showed that DM exposure produced cognitive deficits, anxiety, and depressive-like behaviour in mice following oral exposure for 28 days. Moreover, the mPFC and hippocampus showed neurodegenerative features, loss of dendritic and axonal arborization, a dose-dependent decrease in neuronal cell bodies’ length, width, area, and perimeter, and a dose-dependent increase in the distance between neuronal cell bodies. Conclusions: Oral exposure to DM in mice induces behavioural deficits, mPFC and hippocampal neuronal degenerations via redox imbalance in the brain of mice. These observations confirm the neurotoxicity of DM extracts and raises concerns on the safety and potential adverse effects of DM in humans.