• Tunnel and Underground Space
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• v.12 no.3
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• pp.220-228
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• 2002

Thermal flow through jointed rock mass was analyzed by numerical methods. The effect of a single set of joints on the heat conduction was analyzed by one-dimensional model and compared with the analytical solution. When a joint is completely dry, the joint behaves as a thermal break inducing jumps in temperature distribution even at steady state. Therefore when joints are completely dry, individual joint has to be taken into consideration to get a good result. When joints are partially or fully saturated, the thermal conductivity of the joints increases drastically and the jumps in temperature distribution become less severe. Therefore the effect of joint in heat conduction can be well absorbed by continuum anisotropic model whose thermal properties represent overall thermal properties of the intact part and the discontinuities. Since the effect of joints becomes less important as the degree of the saturation increases, the overall thermal response of the rock mass also becomes close to isotropic. Therefore it can be concluded that a great effort has to be made to obtain a precise in-situ thermal properties in order to get a good prediction of the thermal response of a jointed rock mass.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.194-198
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• 2006

In this study, numerical modeling was performed to analyze air flow including radiation heat transfer inside a small chamber. Characteristics of heat transfer between source plate and target through glass are investigated for various surface temperature of heat source plate with buoyancy effect due to gravity force. Conduction heat transfer through the glass is considered and heat source plate is assumed to be a black body. Target surface temperature is largely affected by the radiation heat transfer. It can also be seen that as the source temperature increases target surface is dominated by radiation rather than convective heat transfer by air.

• Solar Energy
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• v.11 no.2
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• pp.63-69
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• 1991

A Steady laminar natural convection heat transfer from two isothermal square beams attached to a vertical adiabatic plate has been studied numerically. The results have been obtained for dimensionless beam spacings, $0.5{\le}D/L{\le}3.0$, and for Gr=5000-10000 at ${\phi}_2/{\phi}_1=1.0$. 1. The local Nusselt number from the beam surface is increased with the dimension-less beam spacing D/L. but that of the downward surface of the lower beam is almost same as the D/L increases. And, the local Nusselt number from the upward surface of a lower beam is greatly increased with D/L. 2. The beam spacings of the maximum mean Nusselt number for the downward surface of an upper beam and the upward surface of a lower beam occur at. D/L =2.6 and 2.0 respectively. 3. The beam spacing for the maximum total mean Nusselt number occurs at D/L = 2.6.

• Journal of the Korean Solar Energy Society
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• v.30 no.4
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• pp.36-42
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• 2010

본 논문은 태양열이용 냉난방시스템 중에서 실제로 액체흡수제를 재생하는 재생탑 내의 충진층에 있어서의 열 및 물질전달의 실험치와 이론적 해석에 의한 결과치와의 비교를 나타내고 있다.특히 물질전달의 극대화를 위하여 충진층 내에서 공기와 흡수제의 접촉면적을 크게 할 필요가 있는데,이를 위해서 본 실험에서는 직경이 3cm인 플라스틱제 충진재를 사용하였으며, 흡수제로는 저농도의 염화리튬 수용액이 사용 되었다. 충진층 내에서의 최적 높이를 예측하기 위하여 해석의 모델인 실험장치를 직접 제작하여 실험을 수행하였고, 이론 해석에 있어서 체적 열전달을 고려한 정상상태를 모델화하여 해석하였다. 이 결과, 충진층 내에서 실험치와 이론적인 계산치가 잘 일치함을 알 수 있었으며, 충진층의 높이가 2m 이상인 경우에는 높이에 따른 재생량의 차이가 없어서 없음을 알 수 있었다.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2009.04a
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• pp.441-448
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• 2009

화재에 대한 안전성 확보는 ECC 등과 같은 신소재를 실제 구조물에 적용 또는 실용화하기 위해 필요한 중요한 요소 중 하나이다. 본 논문은 터널구조물에 대한 내화대책의 일환으로써 ECC의 적용가능성을 평가하고자 하는 것을 목적으로 한다. 이를 위하여 터널구조물의 화재 온도조건인 RABT 화재온도이력곡선을 적용하여 내화성능을 실험적으로 평가하였다. 또한 비정상 온도분포해석 기법을 이용하여 이를 해석적으로 묘사 검증하였으며, 실험결과를 통해 검증된 해석기법을 이용하여 터널라이닝에 대한 열전달 해석을 수행하여 ECC의 적용가능성을 고찰하였다. 실험결과 ECC는 폭렬 및 화재상태에서의 모체콘크리트에 열화가 발생하지 않았으며, 기존 콘크리트 및 내화소재와의 상대 비교에 있어서도 가장 우수한 내화성능을 나타냈다. 이를 통하여 터널구조물의 내화대책에 있어 ECC 소재가 적용가능성이 있는 것으로 판단되었다.

• Journal of the Korea Concrete Institute
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• v.25 no.5
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• pp.497-508
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• 2013

This paper introduces a numerical model which can evaluate the fire-resistant capacity of reinforced concrete members. On the basis of the transient heat transfer considering the heat conduction, convection and radiation, time-dependent temperature distribution across a section is determined. A layered fiber section method is adopted to consider non-linear material properties depending on the temperature and varying with the position of a fiber. Furthermore, effects of non-mechanical strains of each fiber like thermal expansion, transient strain and creep strain are reflected on the non-linear structural analysis to take into account the extreme temperature variation induced by the fire. Analysis results by the numerical model are compared with experimental data from the standard fire tests to validate an exactness of the introduced numerical model. Also, time-dependent changes in the resisting capacities of reinforced concrete members exposed to fire are investigated through the analyses and, the resisting capacities evaluated are compared with those determined by the design code.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.8
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• pp.739-747
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• 2010

Numerical calculations are carried out for evaluating the natural convection induced by the temperature difference between a hot inner circular cylinder and a cold outer square enclosure. A two-dimensional solution for unsteady natural convection is obtained by using the finite volume method to model an inner circular cylinder that was designed by using the immersed boundary method (IBM) for a Rayleigh number of $10^7$. In this study, we investigate the effect of the location ($\delta$) of the inner cylinder, which is located along the vertical central axis of the outer enclosure, on the heat transfer and fluid flow. The natural convection changes from unsteady to steady state depending on the $\delta$. The two critical lower bound and upper bound positions are ${\delta}_{C,L}$ = 0.05 and ${\delta}_{C,U}$ = 0.18, respectively. Within these defined bounds, the thermal and flow fields are in steady state.

• Tunnel and Underground Space
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• v.26 no.4
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• pp.266-273
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• 2016

We have numerically modeled thermal evolution of Ulleung Island after an emplacement of magma chamber. The disk-shape magma chamber is assumed to locate at 2.9 km beneath the island and has a diameter and a thickness of 10 km and 300 (or 600) m, respectively. The geothermal gradients evaluated from the numerical modeling coincide well with the range of the geotherms (${\sim}95^{\circ}C/km$) observed from the well logging. Although there are limitations in the application of the numerical results directly to the interpretation of the observed geotherms, we believe that an existence of a hot magma chamber in molten or in solidified state is the most plausible explanation for the observed geotherms.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.3
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• pp.239-245
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• 2008

A level set based topological shape optimization using extended B-spline basis functions is developed for steady-state heat conduction problems. The only inside of complicated domain identified by the level set functions is taken into account in computation, so we can remove the effects of domain outside parts in heat conduction problem. The solution of Hamilton-Jacobi equation leads to an optimal shape according to the normal velocity field determined from the sensitivity analysis, minimizing a thermal compliance while satisfying a volume constraint. To obtain exact shape sensitivity, the precise normal and curvature of geometry need to be determined using the level set and B-spline basis functions. Using topological derivative concept, the nucleation of holes for topological changes can be made whenever and wherever necessary during the optimization.

• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.23.2-23.2
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• 2011

과학기술위성3호의 주탑재체 Multi-purpose Infra-Red Imaging System(MIRIS)는 한국천문연구원이 개발하고 있는 소형 적외선 우주망원경이다. MIRIS는 적외선 센서의 열잡음을 최소화시키기 위하여 망원경의 온도가 허용범위를 넘지 않도록 설계되었다. 특히 3K의 심우주를 향해 MIRIS의 복사열을 자연 방출하는 Passive cooling은 임무 성공에 영향을 미치는 매우 중요한 과정이다. 이를 검증하고자 NX 7.0(Space Systems Thermal, TMG 탑재)을 사용하여 열 해석을 수행하였다. 각 부품별로 물성과 열광학 특성을 적용하여 전도 및 복사를 통한 열전달 과정을 계산하였고, MIRIS의 궤도 특성을 고려하여 정상상태에서의 망원경 온도를 얻었다. 그 결과 Passive cooling을 통해 MIRIS 망원경이 허용범위 아래로 냉각되는 것을 확인하였다.