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임광옥,이관수,Lim, Kwang-Ok,Lee, Kwan-Soo 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.12
The transition from steady laminar to chaotic convection in a glass melting furnace specified by upper surface temperature distribution has been studied by the direct numerical analysis of the two and three-dimensional time dependent Navier-Stokes equations. The thermal instability of convection roll may take place when modified Rayleigh number($Ra_m$) is larger than $9.71{\times}10^4$. It is shown that the basic flows in a glass melting furnace are steady laminar, unsteady periodic, quasi-periodic or chaotic flow. The dimensionless time scale of unsteady period is about the viscous diffusion time, ${\tau}_d=H^2/{\nu}_0$. Through primary and secondary instability analyses the fundamental unsteady feature in a glass melting furnace is well defined as the unsteady periodic or weak chaotic flow.
임광옥,이관수,Im, Gwang-Ok,Lee, Gwan-Su 대한기계학회 1997 大韓機械學會論文集B Vol.21 No.7
The main purpose of this study is to determine bifurcation as the primary instability of a glass melting furnace. Steady-state and unsteady characteristics of natural convection in the partially open cavity as appeared in a glass melting furnace is investigated by using numerical analysis. Three types of convection, such as steady laminar, unsteady periodic or unsteady quasi-periodic convection may occur according to the temperature difference between upper two isothermal surfaces along the depth of cavity in a glass melting furnace. In the temperature difference of 150-900 K between batch and free surface, the larger the temperature difference, the weaker the convection strength and unsteadiness. Since the glass viscosity is increasing exponentially in the lower temperature, the batch freezes the thermofluidic field especially below the surface of it. If the depth of cavity is 0.5 m, the bifurcation to time-dependent natural convection may occur in the range of 60-650 K. If that is 1.0 m, it may occur in the whole range of temperature difference.
유리용융로에서 자유표면 열유속과 좌우벽면 온도차에 의한 자연대류
임광옥,이관수,Im, Gwang-Ok,Lee, Gwan-Su 대한기계학회 1996 大韓機械學會論文集B Vol.20 No.11
A numerical study on natural convection induced by free surface heat flux and cold left and hot right walls in glass melting furnaces has been performed. A function of heat flux derived from the combustion environments of actual glass melting furnace is applied to thermal boundary condition at free surface. Fundamentally there exist two flow cells in cavity (left counterclockwise one and right clockwise one). The effects of heat flux and Rayleigh number are investigated through two-dimensional steady-state assumption. The convection strength of two flow cell located in left region continuously increases. In the mean time the strength of flow cell in right region increases and then decreases. Critical Rayleigh number in which two flow cells take place above and below show linear dependence on the free surface heat flux. To maintain the traditional flow pattern (left and right flow cells) in glass melting furnace, Rayleigh number is recommended to be below 10$^{5}$ .
일반화된 Hoek-Brown 암반의 등가 Mohr-Coulomb 강도정수 산정법 고찰
임광옥,이연규 한국자원공학회 2017 한국자원공학회지 Vol.54 No.1
Many practical engineers are often accustomed to understanding the strength of the rock mass in terms of friction angle and cohesion. Therefore, it is necessary to provide a resonable tool implementing the Generalized Hoek-Brown (GHB) failure condition in the framework of the Mohr-Coulomb (M-C) criterion. In this study, the features of Lee (2015) and Hoek et al. (2002) methods for calculating the equivalent friction angle and cohesion of GHB rock masses were briefly reviewed. Subsequently, in order to compare the accuracy of the two methods, the ultimate bearing capacity of strip footing resting on the M-C rock mass was assessed by performing the 2D FE analysis incorporating the equivalent M-C strength constants from both approaches. The results show that Lee (2015)’s method, which exploits the upper bound solution of ultimate bearing capacity, is superior to that of Hoek et al. (2002)’s approach. 현장 암반공학 기술자는 암반의 강도를 마찰각과 점착력으로 표시하는 것에 익숙한 경우가 많다. 이에 따라일반화된 Hoek-Brown (GHB) 파괴조건식을 Mohr-Coulomb (M-C) 파괴조건식 틀 안에서 활용할 수 있는 합리적인방법의 개발 필요성이 제기되었다. 이 연구에서는 GHB 암반의 등가마찰각과 등가점착력을 계산하는 Lee (2015)의방법과 Hoek et al. (2002) 방법의 특징을 간략히 소개하였다. 두 방법의 정확성을 비교 검토하기 위해 Lee (2015)와Hoek et al. (2002)의 방법으로 산정한 등가 강도정수를 이용하여 M-C 암반의 줄기초 극한 지지력을 2차원 유한요소해석을 통해 계산하였다. 해석결과 줄기초 극한지지력의 상계해를 활용하는 Lee (2015)의 방법이 Hoek et al. (2002) 의 방법에 비해 상대적으로 우수한 것으로 나타났다.