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유체-고체 상호작용(FSI) 기법을 이용한 이엽기계식 인공심장판막을 지나는 혈액유동과 판첨거동에 관한 수치해석적 연구
최청렬,김창녕 한국유체기계학회 2004 한국유체기계학회 논문집 Vol.7 No.3
Bileaflet mechanical valves have the complications such as hemolysis and thromboembolism, leaflet damage, and leaflet break. These complications are related with the fluid velocity and shear stress characteristics of mechanical heart valves. The first aim of the current study is to introduce fluid-structure interaction method for calculation of unsteady and three-dimensional blood flow through bileaflet valve and leaflet behavior interacted with its flow, and to overcome the shortness of the previous studies, where the leaflet motion has been ignored or simplified, by using FSI method. A finite volume computational fluid dynamics code and a finite element structure dynamics code have been used concurrently to solve the flow and structure equations, respectively, to investigate the interaction between the blood flow and leaflet. As a result, it is observed that the leaflet is closing very slowly at the first stage of processing but it goes too fast at the last stage. And the results noted that the low pressure is formed behind leaflet to make the cavitation because of closing velocity three times faster than opening velocity. Also it is observed some fluttering phenomenon when the leaflet is completely opened. And the rebounce phenomenon due to the sudden pressure change of before and after the leaflet just before closing completely. The some of time-delay is presented between the inversion point of ventricle and aorta pressure and closing point of leaflet. The shear stress is bigger and the time of exposure is longer when the flow rate is maximum. So it is concluded that the distribution of shear stress at complete opening stage has big effect on the blood damage, and that the low-pressure region appeared behind leaflet at complete closing stage has also effect on the blood damage.
Fluid-particle interaction simulations of the interception of red blood cells in shear flow
최청렬,김창녕 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.7
Numerical simulations of the motion of red blood cells (RBCs) freely suspended in shear flow have been successfully performed to investigate the nature of pairwise interception of RBCs using a fluid-particle interaction method based on the arbitrary Lagrangian-Eulerian (ALE) method and a dynamic mesh method. The applicability of the interaction method that we used was validated by comparing the simulation results with an analytical solution for an elliptical particle in shear flow. We found that positive and negative transverse shifts of the RBCs take place during the interceptions, yielding a non-zero RBC self-diffusivity, and that a phase shift occurs during the rotating behavior and lasts even after the separation. The behaviors of the approaching RBCs are adjusted by interactions with the surrounding flow fields during interception. The pressure between a pair of RBCs causes either an attractive or repulsive force. The nature of the pairwise interception is influenced not only by the flow fields but also by kinematic characteristics (i.e., instantaneous translational and rotational behavior) of the two RBCs.
최청렬,김창녕,Choi, Choeng Ryul,Kim, Chang Nyung 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.10
Characteristics of two-phase flow and heat transfer were numerically investigated in a submerged gas Injection system. Effects of both the gas flow rate and bubble size were investigated. In addition, heat transfer characteristic and effects of heat transfer were investigated when temperature of the injected gas was different from that of the liquid. The Eulerian approach was used for the formulation of both the continuous and the dispersed phases. The turbulence in the liquid phase was modeled by the use of the standard $k-{\varepsilon}$ turbulence model. The interphase friction and heat transfer coefficient were calculated by means of correlations available in the literature. The turbulent dispersion of the phases was modeled by introducing a "dispersion Prandtl number". The plume region and the axial velocities are increased with increases in the gas flow rate and with decreases in the bubble diameter. The turbulent flow field grows stronger with the increases in the gas flow rate and with the decreases in the bubble diameter. In case that the heat transfer between the liquid and the gas is considered, the axial and the radial velocities are decreased in comparison with the case that there is no temperature difference between the liquid and the gas when the temperature of the injected gas is higher than the mean liquid temperature. The results in the present research are of interest in the design and the operation of a wide variety of material and chemical processes.
Gas Bubble Driven Circulation Systems에서의 이상유동 특성의 시뮬레이션
최청렬 한국시뮬레이션학회 1998 한국시뮬레이션학회 논문지 Vol.7 No.2
The flow fields in Gas Bubble Driven Circulation Systems were numerically analyzed. In various gas flow rate and bubble size, the flow characteristics were predicted. Eulerian-Eulerian approach was used for the formulation of both the continuous and dispersed phases. The modification of the general purpose computer program PHOENICS code was employed to predict the mean flow fields, turbulent characteristics, gas dispersion, volume fraction. The predicted shows very satisfactory agreement with experimental results for all regions of ladle. The results are of interest in the design and operation of wide variety of material processing.
최청렬,김창녕 대한설비공학회 1999 설비공학 논문집 Vol.11 No.6
Characteristics of two-phase flow and heat transfer were numerically investigated in a submerged gas injection system when temperature of the injected gas was different from that of the liquid. The Eulerian approach was used for both the continuous and dispersed phases. The turbulence in the liquid phase was modeled using the standard $k-\varepsilon$$\varepsilon$ turbulence model. The interphase friction and heat transfer coefficient were calculated from the correlations available in the literature. The turbulent dispersion of the phases was modeled by a "dispersion Prandtl number". In the case with heat transfer where the temperature of the injected gas is higher than the mean liquid temperature, the axial and the radial velocities are lower in comparison with the case of homogeneous temperatures. The results in the present research are of interest in the design and operation of a wide variety of material and chemical processes.
최청렬,김창녕 慶熙大學校 大學院 院友會 1999 高凰論集 Vol.24 No.-
Characteristics of two-phase flow and heat transfer were numerically investigated in gas injected reactors. Heat transfer characteristic and effects of heat transfer were investigated when temperature of the injected gas is different from that of the liquid. The Eulerian approach was used for the formulation of both the continuous and dispersed phases. The turbulence in the liquid phase was modeled by the use of the standard κ-ε turbulence model. The interphase friction and heat transfer coefficient were calculated by means of correlations available in the literature. The turbulent dispersion of the phases was modeled in introducing a "dispersion Prandtl number". The results in the present research are of interest in the design and operation of a wide variety of material and chemical processes.