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안철오,류호선,Ahn, Cheol-O,Rew, Ho-Seon 한국유체기계학회 1998 한국유체기계학회 논문집 Vol.1 No.1
This study was carried out to investigate the effect of design parameters on the volume flow-rate and the noise level and to finally find the optimal design variables. Eighteen cross-flow fans were designed by the method of orthogonal array, and the flow-rate and the noise level were measured. These data were analyzed by the neural network system. The effects of eight design variables(scroll exit angle, scroll arc length et al.) on the fan performance and the noise level were valuated and discussed. This experiment shows that the design solutions suggested by neural network system may increase its volume flow-rate and reduce noise simultaneously.
안철오(Cheol-O Ahn),서인수(In Soo Seo),이상환(Sang Hwan Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
Astrophysics, fluid dynamics, molecular dynamics or many other physical problems can be considered as a system composed of many particles, so called N-body system. Because these simulations are prohibitively expensive for large N, the fast algorithms and the parallel schemes must be employed. In this study, the performance effects of three domain decomposition schemes(Orthogonal Recursive Bisection, Morton order, Peano-Hilbert Order) and the locally essential tree are examined. We simulated a spherical vortex sheet problem and a flow past a sphere at Re=100 using the vortex element method with the 128-node linux cluster. The performance difference was found according to different particle distributions. In the case of computational domain with large aspect ratio, the orthogonal recursive bisection shows more efficient than others. However, using the locally essential tree, the performance differences between domain decomposition schemes are decreased.
안철오(Cheol O Ahn),서인수(In Soo Seo),이상환(Sang Hwan Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
In this study, we compared two different fast algorithms for molecular dynamics simulations. One algorithm partitions simulation domain into several cells and assigns molecules to these cells by their positions. Using this cell-molecule relationship, this method is efficient to find the nearby molecules. We propose another algorithm which uses a hierarchical tree data structure. The tree structure is adaptive to the distribution of molecules. And both algorithms can be applied to make 'neighbor list' to reduce the number of unnecessary inter-atomic distance calculations in molecular simulations. However, the effectiveness of the neighbor list algorithm, it is useless when the number of molecules and simulation domain are increased with time. Results show that proposed algorithm is effective due to the adaptiveness to the distribution of molecules.
이상환,안철오 한국유체기계학회 2004 한국유체기계학회 논문집 Vol.7 No.2
In an attempt to solve multiobjective optimization problems, weighted sum method is most widely used for the advantage that a designer can consider the relative significance of each object functions by weight values but it can be highly sensitive to weight vector and occasionally yield a deviated optimum from the relative weighting values designer designated because the multiobjective function has the form of simple sum of the product of the weighting values and the object functions in traditional approach. To search the design solution agree well to the designer's weighting values, we proposed new multiobjective function which was the functional of each normalized objective functions and considered to find the design solution comparing the distance between the characteristic line and the ideal optimum. In this study, proposed multiobjective function was applied to design high efficiency and low noise axial flow fan and the result shows this approach is effective for the case that the quality of the design can be highly affected by the designer's subjectiveness represented as weighting values in multiobjective design optimization process.
Using a Lagrangian-Lagrangian approach for studying flow behavior inside a bubble column
손영우,안철오,이상환 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.12
Bubble columns are widely encountered in several industries, especially in the field of nuclear safety. The Eulerian-Eulerian and the Eulerian-Lagrangian methods are commonly used to investigate bubble columns. Eulerian approaches require additional tasks such as strict volume conservation at the interface and a predefined well-structured grid. In contrast, the Lagrangian approach can be easily implemented. Hence, we introduce a fully Lagrangian approach for the simulation of bubble columns using the discrete bubble model (DBM) and moving particle semi-implicit (MPS) methods. Additionally, we propose a rigorous method to estimate the volume fraction accurately, and verified it through experimental data and analytical results. The MPS method was compared with the experimental data of Dambreak. The DBM was verified by analyzing the terminal velocity of a single bubble for each bubble size. It agreed with the analytical results for each of the four drag correlations. Additionally, the improved method for calculating the volume fraction showed agreement with the Ergun equation for the pressure drop in a packed bed. The implemented MPS-DBM was used to simulate the bubble column, and the results were compared with the experimental results. We demonstrated that the MPS-DBM was in quantitative agreement with the experimental data.
Numerical analysis for prediction of flow rate of the motor cooling fan
강태인,안철오,서인수,이상환 대한기계학회 2008 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.22 No.10
In this study, we analyzed the three dimensional unsteady flow around a motor cooling fan using the vortex panel method. For a popular type of motor cooling fan that has thin blades, we predicted the flow rate through numerical analysis without experimental data, such as the free stream velocity, which is a boundary condition of the flow field. We also calculated the flow rate for various cooling fan geometries and rotating speeds. For these fans, the numerical results showed flow rates within 3% of the experimental results.