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중력모형을 이용한 우리나라의 원당 및 정제당 수입량 결정요인 분석
강두현(Kang, Doohyun),박지원(Park, Jiwon),박성진(Park, Seongjin) 한국농식품정책학회 2021 농업경영정책연구 Vol.48 No.2
Sugar is a very important agricultural product that is finally consumed or used as an intermediate product in the Korea food industry. However, raw sugar used to make sugar cannot be produced on its own, so it is mainly imported from Australia and Thailand, and the amount imported in the last three years is 1.78 million tons. Furthermore raw sugar is sensitive to weather conditions and oil prices, making it more price variability than other grains. For these reasons, it is important for Korea to bring in sugar stably to stabilize food prices and secure raw materials. Nevertheless, there is still lack of studies on the import of sugar in Korea. Thus, the purpose of this study is analyzing the determinants of raw sugar and refined sugar import volumes in Korea using gravity model. For this purpose, we constructed the panel data set over the 2000~2019 periods and carried out a gravity model by adopting random effect panel Tobit estimation. Also, we compared the estimates with Tobit model, OLS and PPML each other. From the empirical results, all estimates ware derived theoretically appropriate. First, Korean sugar imports was increased as growing GDP. Second, the decline in sugar imports was affected by the price of sugar and Action plan for sugars reduction. Third, decreased distance and FTA were proved to be a boost in sugar imports.
정방형 실린더의 모서리 원형화에 따른 유동 불안정성의 변화
박두현(Doohyun Park),양경수(Kyung-Soo Yang),이경준(Kyongjun Lee),강창우(Changwoo Kang) 한국전산유체공학회 2014 한국전산유체공학회지 Vol.19 No.1
This study performed numerical analysis for the characteristics of flow-induced forces and the flow instability depending on the cross-sectional shape of the cylinder in laminar flow. To implement the cylinder cross-section, we adopted an Immersed Boundary Method with marker particles. We analyzed flow characteristics based on the radius of corner curvature. Main parameters are corner radius and Reynolds number (Re). With Re= 40, 50, 150 we calculated the flow field, drag coefficient, RMS of lift coefficient, pressure coefficient and Strouhal number in conjunction with the corner radius variation. Also, we calculated critical Reynolds number (Re<SUB>c</SUB>) depending on the corner radius variation.
Rib이 설치된 파이프에서의 유동 및 열전달에 관한 수치모사
강창우(Changwoo Kang),양경수(Kyung-Soo Yang),김재희(Jaehee Kim),박두현(Doohyun Park) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
In the present study, Large Eddy Simulation (LES) of turbulent heat transfer in circular ribbed-pipe flow was performed in order to study the effects of periodically-mounted square ribs on flow and heat transfer enhancement. The ribs are implemented within a cylindrical coordinate system by using an immersed boundary method, and dynamic subgrid-scale models are used to model Reynolds stresses and turbulent heat flux terms. A constant heat flux is imposed on the pipe wall. The Reynolds number (Re) based on the bulk velocity and pipe diameter is 24,000, and Prandtl number (Pr) is 0.71. The blockage ratio is fixed with 0.125, while the pitch ratio based on the rib interval and rib height is varied with 2, 4, 6, 8, 10, and 18. Since the pitch ratio is the key parameter that can change flow topology and turbulence characteristics, we focus on its effect on the flow and temperature fields. Local heat transfer distributions between the ribs were obtained. Friction factor and mean heat transfer enhancement factor were calculated from the mean flow and temperature fields and compared to the previous correlations. Furthermore, simple correlations for the friction factor and the mean heat transfer coefficient were developed for the present blockage ratio. Our LES results shed light on a complete understanding of the heat-transfer mechanisms in turbulent ribbed-pipe flow which has numerous applications in engineering.