• Proceedings of the Korea Water Resources Association Conference
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• 2005.09b
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• pp.1271-1273
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• 2005

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.1204-1207
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• 2002

The fixed points of two known gradient flows defined on adjoint orbits of orthogonal groups are analyzed through the critical point analysis of the potential functions. The results show that some known properties of these gradient flows are shared with the gradient flows of the same potential functions with respect to other metrics.

• Journal of the Korean Mathematical Society
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• v.59 no.1
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• pp.151-170
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• 2022

In this paper we introduce a new notion of expansive flows, which is the combination of expansivity in the sense of Katok and Hasselblatt and kinematic expansivity, named KH-kinematic expansivity. We present new properties of several variations of expansivity. A new hierarchy of expansive flows is given.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.4 s.247
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• pp.364-372
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• 2006

The objective of this study is to evaluate the efficiency and the prediction accuracy of developed large eddy simulation (LES) program for complex turbulent flows, such as recirculating and swirling flows. To save the computational cost, a Beowulf cluster system consisting 16 processors was constructed. The flows in backward-facing step and dump combustor were examined as representative recirculating and swirling flows. Firstly, a direct numerical simulation (DNS) for laminar backward-facing step flows was previously conducted to validate the overall performance of program. Then LES was carried out for turbulent backward-facing step flows. The results of laminar flow showed a qualitative and quantitative agreement between simulations and experiments. The simulations of the turbulent flow also showed reasonable results. Secondly, LES results for non-swirling and swirling flows in a dump combustor were compared with the results of Reynolds-averaged Navier-Stokes (RANS) using standard $k-{\varepsilon}$ model. The results show that LES has a better performance in predicting the mean axial and azimuthal velocities, comer recirculation zone (CRZ) and center toroidal recirculation zone (CTRZ) than those of RANS. Finally, it was examined the capability of LES for the description of unsteady phenomena.

• Nuclear Engineering and Technology
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• v.46 no.2
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• pp.195-206
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• 2014

Heat transfer characteristics in a narrow rectangular channel are experimentally investigated for upward and downward flows. The experimental data obtained are compared with existing data and predictions by many correlations. Based on the observations, there are differences from others: (1) there are no different heat transfer characteristics between upward and downward flows, (2) most of the existing correlations under-estimate heat transfer characteristics, and (3) existing correlations do not predict the high heat transfer in the entrance region for a wide range of Re. In addition, there are a few heat transfer correlations applicable to narrow rectangular channels. Therefore, a new set of correlations is proposed with and without consideration of the entrance region. Without consideration of the entrance region, heat transfer characteristics are expressed as a function of Re and Pr for turbulent flows, and as a function of Gz for laminar flows. The correlation proposed for turbulent and laminar flows has errors of ${\pm}18.25$ and ${\pm}13.62%$, respectively. With consideration of the entrance region, the heat transfer characteristics are expressed as a function of Re, Pr, and $z^*$ for both laminar and turbulent flows. The correlation for turbulent and laminar flows has errors of ${\pm}19.5$ and ${\pm}22.0%$, respectively.

• Bulletin of the Society of Naval Architects of Korea
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• v.21 no.2
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• pp.9-17
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• 1984

Laminar and turbulent boundary layers on a rotating sector and a helical blade are calculated by differential method. The estimation of three dimensional viscous flows provide quite useful informations for the design of propellers and turbo-machinery. A general method of calculation is presented in this paper. Calculated laminar boundary layer on a sector shows smooth development of flows from Blasius' solution at the leading edge to von Karman's solution of a rotating disk at the down-stream. Eddy viscosity model is adopted for the calculation of turbulent flows. Turbulent flows on a rotating blade show similar characters as laminar flows. But cross-flow angle of turbulent flows are reduced in comparison with laminar boundary layers. Effects of rotation make flow structures significantly different from two-dimensional flows. In the range of Reynolds number of model scale propellers, large portion of the blade are still in the transition region from laminar to turbulent flows. Therefore viscous flow pattern might be quite different on the blade of model propeller. The present method of calculation is to be useful for the research of scale effects, cavitation, and roughness effects of propeller blades.

• Water for future
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• v.18 no.4
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• pp.335-345
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• 1985

The purpose of stochastic models for synthetic generation of river flows based on the short-term observed data is to provide abundant input data to the water resources systems of which the system performance and operation policy are to be determined beforehand. Among many of such models the Monte Carlo Method of synthetic generation, which is usually known to be appropriate for annual data generation, is employed to check if it can be applied for the generation of monthly flows. For the purpose of comparisons the statistical parameters of the generated monthly flows by Monte Carlo model based on the appropriate probability distribution for each month were compared with those of the generated flows by Thoms-Fiering multiseason model and with those of the observed monthly flows. On the other hand, the statistical parameters of the annual river flows obtained by adding the generated monthly flows year by year based on the Monte Carlo and Thomas-Fiering models were compared with those of the annual flows generated directly by annual Monte Carlo model with reference to those for the observed annual river flows. Based on the above comparative studies, the discussions are made and conclusions derived.

• Journal of the Economic Geographical Society of Korea
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• v.3 no.1
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• pp.35-51
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• 2000

International trade flows have been determined by social, cultural and political environment around the world as well as economic elements. The environment of international trade has changed rapidly as the world has globalized. Significant changes have been generated in the international trade flows. This study investigates the influences of economic globalization on the international trade flows. The changes in international trade flows examined comprehensively by integrating trade with industrial locations, investment, and the various trade related environments. The focus laid on the integration of world economies, such as widening and intensifying international linkages in economic, political and social relation. Special concerns are laid on the impacts of Foreign Direct Investments (FDI) by Trans National Corporations (TNCs), which affect the supply-demand distributions of commodities by industrial relocations, and the expansion of intra-firm trade flows on the international trade flow patterns. The geographical characteristics of tile origins and destinations of FDI flows analyzed, since the spatial patterns of the intra-firm trade flows are determined by them. The FDI and intra-firm trade flow patterns have changed significantly over time.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2B
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• pp.139-144
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• 2006

Using DNS data for turbulent flows in an open-channel with sidewalls, the mechanisms by which secondary flows are generated and by which Reynolds shear stresses are created, are demonstrated. Near the sidewall, secondary flows invading towards the sidewall are observed in the regions of both lower and upper corners, while secondary flows ejecting from the sidewall towards the center of the channel are created elsewhere. The distributions of Reynolds shear stresses near the sidewall are analyzed, connecting their productions with coherent structures. A quadrant analysis shows that sweeps are dominant in two corner regions where secondary flows invading towards the sidewall are generated, but that ejections are dominant in the region where secondary flows ejecting towards the center of the channel are created. Also, conditional quadrant analyses reveal that the productions of Reynolds shear stresses and the patterns of secondary flows are determined by the directional tendencies of coherent structures.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.129-132
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• 2002

To support UDP-based real-time multimedia applications over the Internet, it is necessary to provide a certain amount of bandwidth within the network so that the performance of the applications will not be seriously affected during periods of congestion. Since the flow rates of some of these applications do not back of during periods of congestion, it is also necessary to protect flow-controlled TCP flows from unresponsive or aggressive UDP flows. To achieve these goals, we propose a simple queue policy to support multimedia applications, called threshold-based queue management (TBQM). TBQM isolates UDP flows efficiently from TCP flows to protect TCP flows while supporting bandwidth requirements of UDP applications that require QoS. In addition, TBQM supports drop fairness between TCP flows without maintaining per-flow state. We also present some experimental results to show that the proposed queue policy can work well.