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A numerical study on the unsteady flow behavior and the performance of an automotive sirocco fan
정요한,백제현 대한기계학회 2008 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.22 No.10
An automotive sirocco fan has been widely used in air-conditioning devices. It is essential to understand the flow characteristics of an automotive sirocco fan to satisfy the trends for more efficient and less noise. In this study, numerical calculations were conducted to explain the three-dimensional unsteady, incompressible flow characteristics and performance of the sirocco fan using FLUENT. Reynolds-averaged Navier-Stokes equations with the standard rd k −ε turbulence model were used for the numerical analysis. The sliding mesh was used to simulate the relative transient motion of impeller against scroll. It was found that the inactive zone and the secondary flow reduce efficiency because they cause internal losses. A parametric study was performed to improve efficiency of the sirocco fan, using two geometric variables. Reducing the width of impeller could decrease the relative size of inactive zone and secondary flow. Changing the position of cut-off had little influence on the efficiency. Thus an improvement of efficiency could be achieved by reducing the width of impeller.
Risk Factors of Advanced Adenoma in Small and Diminutive Colorectal Polyp
정요한,김경옥,박찬서,이시형,장병익 대한의학회 2016 Journal of Korean medical science Vol.31 No.9
The aims of this study were to review the clinicopathological characteristics of diminutive (≤ 5 mm) and small polyps (> 5 mm but < 10 mm) and to evaluate the risk factors of advanced adenoma for polyps of diameter < 10 mm in the colon. The medical records of 4,711 patients who underwent first colonoscopy at outpatient clinics or health promotion center were reviewed retrospectively. We analyzed the presence and risk factors of advanced adenoma, which was defined as a villous or tubulovillous polyp, high-grade dysplasia or intramucosal carcinoma histologically. Total 5,058 polyps were detected in the 4,711 patients, and 93.0% (4,704/5,058) polyps were < 10 mm in size. Among them, advanced adenoma was noted in 0.6% (28/4,704) with a villous component in 19, highgrade dysplasia in 3, and adenocarcinoma in 6. Advanced and non-advanced adenomas differed significantly in age group, gender, and polyp size. Multivariate analysis showed that an advanced age (> 65 years), a male gender, and a polyp size of > 5 mm were risk factors of advanced adenoma. The incidence of advanced adenoma in polyps of < 10 mm was 0.6%. Polyp size, male gender, and age of > 65 years are independent risk factors of advanced adenoma.
예측모델 (Gaussian Process Regression) 을 통한 에너지저장시스템 운영전략
정요한,박진규 한국경영과학회 2017 한국경영과학회 학술대회논문집 Vol.2017 No.4
에너지 저장시스템은 에너지 생산과 소비의 불균형을 해소하여, 에너지의 탄력적 공급을 가능하게 하는 장점을 가진다. 이번 연구에서는, 에너지 소비량을 예측하기 위해 머신러닝 기법인 Gaussian Process Regression (GPR)을 도입할 것이다. 이 방법은 베이지안 모델로써, 결과값을 확률분포로 표현한다. 그래서, 불확실성이 연관된 의사결정 문제에 장점을 가진다. 이번 연구에서는, 에너지 소비 예측의 불확실성 정도를 다르게 고려함으로써, 비용, 부하(PEAK) 관점에서, 에너지 저장시스템의 운영전략을 도출할 것이다.
carbon fiber/Fe3O4/GO composite for high performance lithium ion battery
정요한,손희상 한국공업화학회 2020 한국공업화학회 연구논문 초록집 Vol.2020 No.-
With increasing interest in environmental regulations and environmentally friendly energy, demand for energy storage systems and electric vehicles is increasing, and the need for high performance lithium ion batteries as electrochemical energy storage devices is growing. The conventional lithium-ion battery anode material, graphite, has a theoretical capacity of 372 mAh/g, making it difficult to apply high-performance batteries. In this study, we synthesized anodic Iron oxide-carbon composite anode materials for high-performance lithium ion battery anode materials. Iron oxide (Fe3O4) exhibits low cycle stability and electrical conductivity compared to the high theoretical capacity (924 mAh/g). To solve this problem, the structure of Fe3O4 particles was embedded in porous carbon tubes with high conductivity.
예측모델 (Gaussian Process Regression) 을 통한 에너지저장시스템 운영전략
정요한,박진규 한국시뮬레이션학회 2017 한국시뮬레이션학회 학술대회집 Vol.2017 No.-
에너지 저장시스템은 에너지 생산과 소비의 불균형을 해소하여;에너지의 탄력적 공급을 가능하게 하는 장점을 가진다. 이번 연구 에서는;에너지 소비량을 예측하기 위해 머신 러닝 기법인 Gaussian Process Regression (GPR) 을 도입할 것이다. 이 방법은 베이지안 모델 로써;결과값을 확률분포로 표현한다. 그래서;불확실성이 연관된 의사결정 문제에 장점을 가진다. 이번 연구에서는;에너지 소비 예측의 불확실성 정도를 다르게 고려함으로써;비용;부하(PEAK) 관점에서;에너지 저장시스템의 운영전략을 도출할 것이다.