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최도형,신승용 대한기계학회 1987 대한기계학회논문집 Vol.11 No.6
A new improved inviscid separation model to calculate the mean flow past circular cylinders is proposed. The wake region is modeled by a pair of vortex sheets which emerge from the separation points and are allowed to move freely with the local stream. The vortex strength assumes a constant value for some initial distance which is related to the pressure drag and gradually decreases to zero as the sheet moves farther away from the body. This vorticity distribution automatically takes care of the length parameter which has been one of the deficiencies in the existing models. The procedure is tested against various experimental data and the agreement is quite good for both sub and super-critical regimes. The comparison with an existing model is also given. 본 연구에서는 이러한 경험적인면이 최소화되고 물리적 의미가 부여된 후류모 델을 제시하여 일반적인 형상에 대한 계산에 앞서 Celik등의 경우와 같이 원통 주위유 동장을 먼저 다루어 보고자 한다. 다른 방법들과는 달리 후류면의 길이를 조절하지 않고 후류면에서의 와도분포를 점차 감소시켜 후류영향이 자연적으로 감소되게 하였는 데, 이는 물체에서 떨어져 나간 와류(vortex)가 확산에 의해 점차 소멸해가는 점을 모 델링한 것이다. 본 계산은 경계층배제두께의 영향을 무시하고 후류모델에 필요한 박 리점은 실험치를 사용하여 수행하였다. 박리점의 예측은 기존의 경계층해법을 도입 하면 쉽게 해결할 수 있어 큰 문제가 아니라고 생각하며 다만 배제두께 영향은 Reyno- lds수에 따라 계산 결과에 다소 영향을 미칠 수 있게 되는데 이는 뒤에 다시 다루기로 한다.
최도형,이성우,이경재 한국부동산원 2023 부동산분석 Vol.9 No.1
This study aims to analyze how individual households’ tenure choice and housing demand have changed in housing sub-markets from 2014 to 2020. This study comprises two parts to satisfy the aims. First, this study delivers an accurate understanding of the housing consumption by analyzing the tenure choice with the application of the multinomial probit model. Second, applying the Heckman selection model, this study constructs the housing demand model by investigating the housing and household characteristics. Housing services obtained by consuming owner-occupied house include the intangible benefits as well as the tangible benefits of the house. Thus, this study analyzes the determinants of housing demand based on the asset value of housing that can explain exhaustive bundles of housing services. In the tenure choice model, we found that the influence of income was greater in the apartment market than the non-apartment market since non-apartment is regarded as inferior goods compared to apartment. In particular, incentive to obtain housing stability and asset accumulation from apartments in low-income families was greater than theother income cohorts. In the housing demand analysis, households with actual residential needs in both the apartment and non-apartment markets are hard to live in an owner-occupied houses, and in particular, the households in the non-apartment market are temporarily holding back their ownership to enter the apartment market later. Meanwhile, it was observed that the income elasticity of housing demand was generally higher in the non-apartment market than that in the apartment market. This study concludes with contributions, limitations and future study needs in parallel with policy implications for the well-behaved housing market.
채널 내 주기적으로 배열된 요철 형상이 난류 유동장/온도장에 미치는 영향 연구
최도형(D.H. Choi),유동렬(D.N. Ryu),한유신(Y.S. Han) 한국전산유체공학회 2002 한국전산유체공학회 학술대회논문집 Vol.2002 No.-
The heat transfer characteristics of a turbulent flow in a ribbed two-dimensional channel have been investigated numerically. The fully elliptic governing equations, coupled with a four-equation turbulence model, k-ω-t²-ε_t , are solved by a finite volume method of SIMPLE type. Calculations have been carried out for three rib cross-sections: square, triangular, and semicircular, with various rib pitches and Reynolds numbers. The procedure appears to be satisfactory as the results for the square rib compare favorably with available experimental data and earlier calculation. The optimal rib pitch that yields the maximum heat transfer has been identified. It is also found that the square rib is most effective in enhancing the heat transfer. The semicircular rib, on the other hand, incurs the least amount of pressure drop but the improvement in heat transfer is substantially lower.
최도형 ( Choi Do Hyeong ),최은지 ( Choi Eunji ),이성우 ( Lee Seong Woo ) 한국농촌계획학회 2021 농촌계획 Vol.27 No.4
The purpose of this study is to analyze the effect of crop diversification on farm households’ agricultural income. Abundant literature have explored the determinants and efficient strategies for crop diversification. Yet, there is a paucity of research studies that empirically test the effectiveness of crop diversification as a profitable farm management strategy. Utilizing the 2015 Agricultural Census, this study adopts a quasi-experimental research design to compare the outcomes between farm households that opted for crop diversification and farm households that did not engage in such a strategy. In doing so, this study applies the Heckman Selection Model and the decomposition technique to address the problem of selection bias and to identify the causal effect. Our empirical results show that farms that implement diversification are more likely to earn higher agricultural income than non-diversified farms, although the difference would not be much substantial. This study concludes with several policy proposals to stabilize agricultural income in conjunction with crop diversification.
[論文] 자동차 냉각장치를 통하는 유동에 의한 항력 변환 예측
최도형(D.H Choi),이응호(E.H.Lee) 한국자동차공학회 1992 오토저널 Vol.14 No.5
Using a commercial flow-analysis code VSAERO, a method to predict the drag of an automobile induced by the intake air of the cooling system has been devised. Given the pressure loss coefficient across the radiator, which varies with the radiator shape and the local Re, a simplified model of the internal flow is coupled with VSAERO to find the mass-flow rate through the car. The flow rate is obtained iteratively and that, in turn, gives the drag associated with this flow, which essentially is the momentum carried by the drained air. The results of a few sample cases are presented for two front-end shapes in combination with varying radiator frontal area.
[論文] 점성-비점성 유동 반복계산 방법을 이용한 2차원 자동차모형의 공력 특성 예측
최도형(D.H.Choi),최철진(C.J.Choi) 한국자동차공학회 1986 오토저널 Vol.8 No.1
An iterative viscous-potential flow procedure has been developed and used to predict aerodynamic characteristics of automobiles in ground proximity. The method is capable of predicting the effects of separated flows. The viscous-potential flow iteration procedure provides the connection between potential flow, boundary layer and wake modules. The separated wake is modeled in the potential flow analysis by thin sheets across which exists a<br/> jump in velocity potential. The ground effect is properly accounted for by placing a body image in the potential flow calculation. The agreement between theory and experiment is good and, thus, demonstrates that the method can be used in the preliminary design stage.