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강창우(Changwoo Kang),양경수(Kyung-Soo Yang) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
Large eddy simulation(LES) of fully developed turbulent pipe flow has been performed to investigate the effect of Reynolds number on flow field at Re<SUB>τ</SUB>=180, 395, 590 based on friction velocity and pipe radius. A dynamic subgrid-scale model for the turbulent subgrid-scale stresses was employed to close the governing equations. The mean flow properties, mean velocity profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. The Reynolds number effects were observed in the mean velocity profile, root-mean-square of velocity and vorticity fluctuations, Reynolds shear stress and higher-order statistics(Skewness and Flatness factor). Furthermore, the budgets of the Reynolds stresses and turbulent kinetic energy were computed and analyzed to elucidate the effect of Reynolds number on the turbulent structures.
파이프 유동에서의 난류물질전달에 대한 Schmidt 수의 영향
강창우(Changwoo Kang),양경수(Kyung-Soo Yang) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
Large Eddy Simulation (LES) of turbulent mass transfer in circular-pipe flow has been performed to investigate the effects of Schmidt number on turbulent mass transfer. We consider a fully developed turbulent pipe flow with a constant wall concentration. The Reynolds number under consideration is Re<SUB>τ</SUB>=500 based on the friction velocity and the pipe radius, and the Schmidt numbers are 0.71, 5, 10, 20 and 100. Dynamic subgrid-scale(SGS) models for turbulent SGS stresses and mass fluxes are employed to close the governing equations. In this investigation, we examine the reliability of the LES technique for predicting turbulent mass transfer at high-Schmidt numbers and analyze the behavior of turbulent mass diffusion from the wall at different Schmidt numbers. To show the effects of Schmidt number on turbulent mass transfer, the statistical quantities such as mean concentration profiles, concentration variance, turbulent mass fluxes, turbulent Schmidt number, and mass transfer coefficients are presented for the selected Schmidt numbers. Turbulence budgets for concentration variance and turbulent mass fluxes are computed and the effect of Schmidt number is identified. In addition, to clarify the correlation between near-wall turbulence structures and concentration fluctuation, we report an Octant analysis in the vicinity of the pipe wall.
강창우(Changwoo Kang),김봉수(Bongsu Kim),손광록(Kwangrok Son),배우석(Wooseok Bae) 한국지반환경공학회 2016 한국지반환경공학회논문집 Vol.17 No.5
지표에 노출되는 암석은 기상작용 등의 영향으로 풍화가 가속되며, 풍화작용은 광물의 성질을 변화시켜 암석의 안정성을 저하시키게 되므로 암석의 풍화에 대한 저항은 광물의 조성을 파악하는 것이 중요하며 이는 풍화 민감도 분석을 통해 이루어진다. 따라서 본 연구에서는 시추된 시료에 대한 현미경 박편 시험을 실시하고 모드분석을 통해 풍화 취약광물의 구성비를 측정하였으며, 이를 통해 대상사면의 암석학적・광물학적 풍화요인을 평가하였다. 또한, X-Ray 회절분석을 이용하여 암석을 구성하는 실제적인 광물조성을 정량적으로 측정하고 주사현미경관찰을 통해 이차광물을 동정하여 풍화의 진행 정도를 파악하였다. 이러한 풍화 민감도기법을 통하여 풍화 저항도를 판단할 수 있는 적절한 지시자를 결정할 수 있으며 화학적 풍화속도를 이용한 풍화등급의 예측이 가능할 것으로 분석되었다. The rocks exposed on the surface undergo expedite weathering process due to the effects of climatic process, etc. and the weathering process changes the properties of minerals, thereby lowering the stability of rocks. Therefore, it is important to examine the composition of minerals in order to investigate the resistance of rocks against weathering, which is performed by weathering sensitivity analysis. And microscopic flaking test was performed for the bored samples in this study and the composition of minerals that are vulnerable to weathering was measured through mode analysis. The lithological and mineralogical weathering factors were evaluated through this process. Furthermore, the degree of progress of weathering was identified by quantitatively measuring the actual mineral composition of rocks through X-Ray diffraction analysis and identifying the secondary minerals through observation with a scanning electron microscope. This analyzing the weathering sensitivity was analyzed to be capable of determining appropriate indicators that can determine weather resistance and predicting the weathering grade using chemical weathering speed.