• Journal of Korea Water Resources Association
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• v.48 no.4
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• pp.291-298
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• 2015

The aim of this study is that a theoretical formula for estimating the one-dimensional longitudinal dispersion coefficient is derived based on a transverse distribution equation for the depth averaged stream-wise velocity in open channel. In "Part I. Theoretical equation for stream-wise velocity" which is the former volume of this article, the velocity distribution equation is derived analytically based on the Shiono-Knight Model (SKM). And then incorporating the velocity distribution equation into a triple integral formula which was proposed by Fischer (1968), the one-dimensional longitudinal dispersion coefficient can be derived theoretically in "Part II. Longitudinal dispersion coefficient" which is the latter volume of this article. SKM has presented an analytical solution to the Navier-Stokes equation to describe the transverse variations, and originally been applied to straight and nearly straight compound channel. In order to use SKM in modeling non-prismatic and meandering channels, the shape of cross-section is regarded as a triangle in this study. The analytical solution for the velocity distribution is verified using Manning's equation and applied to velocity data measured at natural streams. Although the velocity equation developed in this study do not agree well with measured data case by case, the equation has a merit that the velocity distribution can be calculated only using geometric data including Manning's roughness coefficient without any measured velocity data.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.7
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• pp.914-920
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• 2011

For a hydro turbine electricity generation system in river or bay, a venturi system could be applied to accelerate flow speed at the inlet of the turbine system in a flow field. In this study, a steady flow simulation was conducted to understand the effect of venturi system on the acceleration of current speed at the inlet of a hydro turbine system. According to the continuity equation, the flow speed is inversely proportional to the cross-section area in a conduit flow; however, it would be different in an open region because the venturi system would be an obstruction in the flow region. As the throat area is 1/5 of the inlet area of the venturi, the flow velocity is accelerated up to 2.1 times of the inlet velocity. It is understood that the venturi system placed in an open flow region gives resistance to the upcoming flow and disperses the flow energy around the venturi system. The result of the study should be very important information for an optimum design of a hydro turbine electricity generation system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.8
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• pp.978-986
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• 1999

In this study, the general thermal and flow characteristics of flat tube with micro-channels has been studied and the correlation of Nusselt number and friction factor is proposed. The optimal flat tube geometry is determined by optimal design process. It is assumed to be a three dimensional laminar flow in the analysis of thermal and flow characteristics. The periodic boundary condition is applied since the geometry of flat tube with micro-channels shows uniform cross-section in primary flow direction. Local Nusselt number is examined for thermal characteristics of each membrane, and module average Nusselt number and friction factor are calculated to determine the characteristics of the heat transfer and pressure drop in overall flat tube with microchannels. The correlations between Nusselt number and friction factor are given by Reynolds number, aspect ratio of membranes, and the width of flat tube. ALM (Augmented Lagrangian Multiplier) method is applied to the correlations to determine an optimal shape of flat tube. It is shown that the optimal aspect ratio of flat tube is approximately 1.0, irrespective of the width of flat tube and Reynolds number.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.2
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• pp.786-799
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• 2018

Recently, NFV has attracted attention as a next-generation network virtualization technology for hardware -independent and efficient utilization of resources. NFV is a technology that not only virtualize computing, server, storage, network resources based on cloud computing but also connect Multi-Tenant of VNFs, a software network function. Therefore, it is possible to reduce the cost for constructing a physical network and to construct a logical network quickly by using NFV. However, in NFV, when a new VNF is added to a running Tenant, authentication between VNFs is not performed. Because of this problem, it is impossible to identify the presence of Fake-VNF in the tenant. Such a problem can cause an access from malicious attacker to one of VNFs in tenant as well as other VNFs in the tenant, disabling the NFV environment. In this paper, we propose Auto-configurable Security Mechanism in NFV including authentication between tenant-internal VNFs, and enforcement mechanism of security policy for traffic control between VNFs. This proposal not only authenticate identification of VNF when the VNF is registered, but also apply the security policy automatically to prevent malicious behavior in the tenant. Therefore, we can establish an independent communication channel for VNFs and guarantee a secure NFV environment.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.1138-1142
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• 2005

The tidal river is a river affected by tide, which causes the water level to rise and fall two times everyday periodically. The local velocity across the river could be very fast because of the cross-sectional characteristics of the river even though it's not a rainy season. Therefore extreme local scour could take place around hydraulic structures such as piers and caissons due to backward flow velocity. For the construction of pier foundation of Ilsan-bridge In the Han River, the field observations were performed to get the velocity and water level. The numerical analysis was performed by HEC-RAS(UNET). The relationship between measured maximum velocity and calculated mean velocity is achieved, which is used to estimate the velocity and water level as the construction is proceeding. Countermeasures for scour were designed with the results of the hydraulic analysis to avoid potential damage during construction work. According to the results of monitoring, the velocity increase after temporary road embankment was negligible, from which it is considered that the degradation of main channel compensated for the constriction of cross-section by embankment.

• Proceedings of the Korea Water Resources Association Conference
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• 1992.07a
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• pp.55-66
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• 1992

The energy and momentum coefficients ${\alpha}$ and ${\beta}$ are measures of homogenerity of velocity distribution in a chanel section. They indicate the effect of energy and momentum transport. However, in most practical applications, they are assumed to be unity due to the difficulty in estimating them. Efforts have been made in this study to estimate these coefficients and to develop equations for practical applications. The Prandtl-von Karman logarithmic equation as being used today has limitations and far-reaching assumptions. Therefore, this paper uses Chiu's velocity distribution equation which seems to be capable of serving as such an alternative, to estimate the velocity distribution and the energy and momentum coefficients, ${\alpha}$ and ${\beta}$ results are compared with those computed by other existing equations. For practical applications, this paper also uses Chiu's equation along with the Mannig's equation to calculate ${\alpha}$, ${\beta}$ without velocity data

• Proceedings of the KIEE Conference
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• 2003.04a
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• pp.429-431
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• 2003

CCTV network has been implemented to transmit the image information of platform, ticket gate and transfer section to local headquarters in the KNR(Korean National Railroad). But, communication system for transferring image information around accident field or wayside has not been established ret. thus, at Present implementation of communication equipment is necessary for dynamic image of unspecified accident to be transmitted to headquarters. Copper cable communication network is run by KNR, but it is processing installation of optical cable in connection with the implemental plan for high-speed network from now on. And, the capacity of communication channel will be guaranteed much more than now between station and station. station and central headquarters when optical cable is completed. This study analyzes the image equipment of field for transmission and estimated matters to transmit image information of accident field to headquarters with using communication infrastructure. And, the study considers implemental method of communication network for long-distance image transmission from dozens to hundreds kilometers.

• Journal of computational fluids engineering
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• v.17 no.2
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• pp.53-57
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• 2012

Design of the cooling channels of a plastic injection mold affects the quality and the productivity of the injection processes. In the injection process, the melted resin with high temperature enters the mold cavity, and just after the cavity is filled the heat should be dissipated through the cooling channels simultaneously. The purpose of this study is to analyse the heat transfer phenomenon and to estimate the temperature distribution in the mold to evaluate the cooling effect of the channels. The injection mold is assumed to have cooling channels of circular cross section and each channel has the same coolant flow rate. and The cavity has a rectangular shape. The results show that as the cooling channels get closer to the cavity surface, the cooling efficiency increases as might easily be guessed. However, due to the final hot resin flow from the gate an intensive cooling is required in that region.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.6
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• pp.767-776
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• 1985

Unsteady thermally stratified flow caused by two-dimensional surface discharge of warm water into a oblong channel was investigated. Experimental study was focused on the rapidly developing thermal diffusion at small Richardson number. The basic objective were to study the interfacial mixing between a flowing layer of warm water and an underlying body of cold water and to accumulate experimental data to test computational turbulence models. Mean velocity field measurements were carried out by using NMR-CT (Nuclear Magnetic Resonance-Computerized Tomography). It detects quantitative flow image of any desired section in any direction of flow in short time. Results show that at small Richardson number warm layer rapidly penetrates into the cold layer because of strong turbulent mixing and instability between the two layers. It is found that the transfer ofheat across the interface is more vigorous than that of momentum. It is also proved that the NMR-CT technique is a very valuable tool to measure unsteady three dimensional flow field.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.22 no.2
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• pp.7-15
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• 1986

In order to investigate the performance for the mackerel purse seine of one boat purse seiner using in the sea area of Cheju Island, a model net is made of the scale of 1/400 of its full scale, and model test on the shape of net and the tension of purse line is carried out in the stagnant water channel of the circulating water tank. Designing and testing for the model net are based on the Tauti's law. The obtained results are as follows; 1. The sinking rate of net is maximized the value of 6.40 m/min from 5 to 10 minutes after shooting net, and the mean value is 6.13 m/min. 2. The enclosed area formed with the float line after pursing operation is 76-84% of the area which is formed immediately after the shooting operation. At that time, purse seine is pulled inward the circle of surrounding net about 26.5% of the diameter. 3. In operating, when longitudinal section area of the central part of the net is maximized, the split area of both the wing-ends is 31-32% of the former. 4. When the time for the completing of pursing is 20 minutes, the maximum tension of the purse line is about 10.2 tons.