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난류열전달 향상을 위한 엇갈린 리브가 부착된 열전달면의 형상최적설계
김홍민,김광용,Kim, Hong-Min,Kim, Kwang-Yong 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.9
This study presents a numerical procedure to optimize shape of streamwise periodic ribs mounted on both of the principal walls to enhance turbulent heat transfer in a rectangular channel flow. The response surface method is used as an optimization technique. The optimization is based on Navier-Stokes analysis of flow and heat transfer with $k-{\varepsilon}$ turbulence model. The width-to-height ratio of a rib, rib height-to-channel height ratio and rib pitch to rib height ratio are chosen as design variables. The object function is defined as a function of heat transfer coefficient and friction drag coefficient with weighting factor. Optimum shapes of the rib have been obtained for the range of 0.02 to 0.1 of weighting factor.
Effect of coronavirus disease 2019 pandemic on children’s visits to the emergency department
김홍민,하상욱,양원석,박영선,김진혁 대한소아응급의학회 2022 대한소아응급의학회지 Vol.9 No.1
Purpose: In the coronavirus disease 2019 pandemic, it is essential to supplement the changes in visiting patterns of individual emergency departments (EDs) to determine how to allocate emergency medicine resources. We compared the clinical features of children visiting the ED before and during the pandemic. Methods: Children younger than 18 years who visited the ED from February 2019 through December 2020, except January 2020, were enrolled, and divided into those who visited before and after January 2020 (the pre-pandemic and pandemic groups, respectively). We compared the 2 groups in terms of the baseline characteristics (age, sex, mode and route of arrival, cause of visit, and time of visit), chief complaint, ED diagnosis, initial acuity and its accuracy, and ED outcomes (length of stay and disposition). Results: The 31,036 children were categorized into the pre-pandemic (21,027 [67.8%]) and pandemic (10,009 [32.2%]) groups with a 52.4% decrease in the number of visits to the ED in the latter group. This decrease was more prominent in age 2-5 years (from 37.3% to 33.2%; P < 0.001), fever as a chief complaint (from 27.8% to 16.5%), diagnoses related to infection or the respiratory system (from 36.8% to 14.3%) or transfer to the ED (from 8.1% to 6.4%; P < 0.001). In contrast, increases were noted in age 12-17 years (from 14.9% to 17.4%; P < 0.001), injury (from 36.5% to 52.5%; P < 0.001), visits in the evening (from 54.9% to 57.4%; P < 0.001), length of stay longer than 6 hours (from 3.5% to 6.3%; P = 0.033), and low acuity (from 97.8% to 98.2%; P = 0.031). Conclusion: The pandemic has brought about changes in visiting patterns of the ED. This study may help prepare strategies for the appropriate allocation and deployment of emergency medicine resources in the pandemic era.
김홍민,이동희,안진우 대한전기학회 2012 대한전기학회 학술대회 논문집 Vol.2012 No.4
This paper presents a design and analysis of drive characteristics of a two-phase SRM(Switched Reluctance Motor) for blower application. To increase the performance and torque production while decreasing the core losses due short flux path, In order to reduce torque ripple and torque dead-band, variable rotor air-gap structure is adopted and the air-gap is optimized according to torque production. The optimized torque output is verified by the FEM, Simulink and the experiments.