• Nuclear Engineering and Technology
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• v.52 no.10
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• pp.2162-2172
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• 2020

Due to its computational efficiency and geometrical flexibility, the Method of Characteristics (MOC) has been widely used for light water reactor lattice physics analysis. Usually acceleration methods are necessary for MOC to achieve acceptable convergence on practical reactor physics problems. Among them, Coarse Mesh Finite Difference (CMFD) is very popular and can drastically reduce the number of transport iterations. In OpenMOC, CMFD acceleration was implemented but had the limitation of supporting only a uniform CMFD mesh, which would often lead to splitting MOC source regions, thus creating an unnecessary increase in computation and memory use. In this study, CMFD acceleration with a non-uniform Cartesian mesh is implemented into OpenMOC. We also propose a quadratic fit based CMFD prolongation method in the axial direction to further improve the acceleration when multiple MOC source regions are contained in one CMFD coarse mesh. Numerical results are presented to demonstrate the improvement of the CMFD acceleration capability in OpenMOC in terms of both efficiency and stability.

• Journal of the Korean Institute of Gas
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• v.23 no.6
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• pp.17-24
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• 2019

The combustion properties of the flammable substance used in industrial fields include lower/upper flash point, lower/upper explosion limit, autoignition temperature(AIT), fire point, and minimum oxygen concentration(MOC) etc.. The accurate assessment of these characteristics should be made for process and worker safety. In this study, tert-amylalcohol(TAA), which is widely used as a solvent for epoxy resins, oxidizers of olefins, fuel oils and biomass, was selected. The reason is that there are few researches on the reliability of combustion characteristics compared to other flammable materials. The flash point of the TAA was measured by Setaflash, Pensky-Martens, Tag, and Cleveland testers. And the AIT of the TAA was measured by ASTM 659E. The lower/upper explosion limits of the TAA was estimated using the measured lower/upper flash points by Setaflash tester. The flash point of the TAA by using Setaflash and Pensky-Martens closed-cup testers were experimented at 19 ℃ and 21 ℃, respectively. The flash points of the TAA by Tag and Cleveland open cup testers were experimented at 28 ℃ and 34 ℃, respectively. The AIT of the TAA was experimented at 437 ℃. The LEL and UEL calculated by using lower and upper flash point of Setaflash were calculated at 1.10 vol% and 11.95 vol%, respectively.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.3
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• pp.319-332
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• 2015

The pressure wave formed by the piston effects of the train proceeds within the tunnel when a train enters the tunnel with a high speed. Depending on the condition of tunnel exit, the compression waves reflect at a open end, change to the expansion waves, transfer to tunnel entrance back. Due to interference in the pressure waves and running train, passengers experience severe pressure fluctuations. And these pressure waves result in energy loss, noise, vibration, as well as in the passengers' ears. In this study, we performed comparison between numerical analysis and field experiments about the characteristics of the pressure waves transport in tunnel that appears when the train enter a tunnel and the variation of pressure penetrating into the train staterooms according to blockage ratio of train. In addition, a comparative study was carried out with the ThermoTun program to examine the applicability of the compressible 1-D model(based on the Method of Characteristics). Furthermore examination for the adequacy of the governing equations analysis based on compressible 1-D numerical model by Baron was examined.