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이슬기(S.G. Lee),이승수(S. Lee),이주용(J.Y. Lee),엄정아(J.A. Um),이원호(W.H. Yi) 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.4
This paper presents the computational analysis of debris flow using multi-phase modeling and resulting impact force on the structure. The mixture of soil and water was modeled as slurry phase for various water content controlled by volume concentration of each material. Unsteady flow was solved for incompressible fluid in 3D domain and volume of fluid (VOF) method was introduced to trace the boundary between the slurry and the ambient air. Due to the shear thinning characteristics of slurry, nonlinear viscosity model was implemented. In order to verify the present method, the numerical computations were carried out for the experimental setup with the sloped channel employed in a previous study. As expected and shown in the previous experimental study, the greater impact force on the measuring plate was obtained for the larger angle of slope. In addition, the maximum impact force occurred much faster for the slurry with the higher water content. The comparison between the experimental results and the present computation shows a good agreement. It was also found that the critical water content at which the debris starts to flow was 35% at an inclination of 50° and 40% to 40°. As the result, it is expected that present method can be used to calculate the impact force of the debris flows on the structures, and can further be used for damage prediction and reduction.
스트로크 역행을 고려한 SF<SUB>6</SUB> 스위칭 아크 해석 및 열적 차단성능 평가
이종철(J. C. Lee),이원호(W. H. Lee),김홍규(H. K. Kim) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5
In SF<SUB>6</SUB> self-blast interrupters, which are being developed as the next-generation switching mechanism, the arc burns within insulating nozzles with an ablation of the nozzle material and leads to an incoming gas flow for the pressure chamber with a pressure-rise during the high-current phase. Close to current zero, the arc can be cooled down and quenched completely by the reverse gas flow from the chamber to the arcing zone according to the pressure gradient between them. Therefore, the interruption of fault currents is dependent on the thermal decay of arcs during the current-zero phase by the blowing-off force, which is generated by the pressure-rise of the chamber during the high-current phase. In this study, we calculated SF<SUB>6</SUB> switching arcs caused by fault current interruption inside a SF<SUB>6</SUB> self-blast interrupter with the reversed stroke of electrode and investigated the thermal breakdown with thermal decay near current zero
Blood Pulsation의 효과가 뇌 활성화에 미치는 영향을 알아보는 방법
이원호,구정훈,이형래,한기완,박진식,김재진,윤강준,김인영,김선일,Lee, W.H.,Ku, J.H.,Lee, H.R.,Han, K.W.,Park, J.S.,Kim, J.J.,Yoon, K.J.,Kim, I.Y.,Kim, S.I. 대한의용생체공학회 2007 의공학회지 Vol.28 No.3
BOLD T2*-weighted MR images reflects cortical blood flow and oxygenation alterations. fMRI study relies on the detection of localized changes in BOLD signal intensity. Since fMRI measures the very small modulations in BOLD signal intensity that occur during changes in brain activity, it is also very sensitive to small signal intensity variations caused by physiologic noise during the scan. Due to the complexity of movement of various organs associated with heart beat, it is important to reduce cardiac related noise rather than other physiological noise which could be required with relatively simple method. Therefore, a number of methods have been developed for the estimation and reduction of cardiac noise in fMRI study. But, each method has limitation. In this study, we proposed a new estimation method for brain activities influenced by blood pulsation effect using regression analysis with blood pulsation signal and the correspond slice of fMRI. We could find out that the right anterior cingulate cortex and right olfactory cortex and left olfactory cortex were largely influenced by blood pulsation effect for new method. These observed areas are mostly on the structure of anterior cerebral artery in the brain. That is convinced with that our method would be valid and our new method is easier to apply in practice and reduce computational burden than the retrospective method.