• Journal of the Society of Naval Architects of Korea
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• v.41 no.4
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• pp.59-67
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• 2004

Direct numerical simulations of turbulent flows over riblet-mounted surfaces are performed to educe the mechanism of drag reduction by riblets. Numerical simulations are performed for flow fields with R $e_$\tau$/=180. For riblet ridge angle $\alpha$=60$^{\circ}$, two different riblet spacings of $s^+/=20 and 40 are used in this study. The computed drag on the riblet surfaces is in good agreement with existing computational and experimental data. The mean velocity profiles show upward and downward shifts in the log-law for drag-decreasing and drag-increasing cases, respectively Turbulence statistics above the riblets are computed and compared with those above a flat plate. The purpose of this study is in two categories: first, to understand the drag reduction mechanism on riblet surface, second, to verify our own code by comparison of the present results with those from previous studies.udies.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.12
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• pp.18-29
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• 2014

This paper proposes the integration of photovoltaic (PV) and energy storage systems for sustained power generation. In this proposed system, whenever the PV system cannot completely meet load demands, the super capacitor provides power to meet the remaining load. A power management strategy is designed for the proposed system to manage power flows between PV array systems and supercapacitors (SC). The main task of this study was to design PV systems with storage strategies including MPPT with direct control and an advanced DC-link controller and to analyze dynamic model proposed for a PV-SC hybrid power generation system. In this paper, the simulation models for the hybrid energy system are developed using Matlab/Simulink, SimPowerSystems and Matlab/Stateflow tool. This is the key innovative contribution of the research paper. The system performances are verified by carrying out simulation studies using practical load demand profile and real weather data.

• Journal of the Korea Society for Simulation
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• v.6 no.1
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• pp.25-40
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• 1997

This study deals with an autonomous generation of simulation codes for the design of processes of c CIM system based on the concept of model transformation. We assume we have a functional model of an organization which is developed using the well-known IDEF0 methodology. Then, a modeling methodology, called PROWD(PRocess flOW Description), is suggested to develop the flow processes of the organization. To Derive simulation specifications for the transformed PROWD model, we define a module of a "unit system" for each activity of PROWD model. Then specifications for system entities and resources are derived from input/control/mechanism/output and entity flows of PROWD model. Entitiy queues are defined from the sates and events of unit systems. Finally, SIMAN model frame is generated from those specifications through a suggested algorithm. The implementability and validity of the proposed approach is tested by developing a prototype of a computer-assisted design system on the operation processes of FMS installed at SNU-ASRI (Seoul National University-Automation and Systems Research Institute).nstitute).

• Journal of Korea Society of Industrial Information Systems
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• v.18 no.1
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• pp.19-24
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• 2013

As CMOS technology is scaled down more aggressively, the reliability mechanism (or aging effect) caused by the diffusion of metal atoms along the conductor in the direction of the electron flow, also called electromigration (EM), has become a major reliability concern. With the present of EM, it is difficult to control the current flows of the MOSFET device and interconnect. In addition, nanoscale CMOS circuits suffer from increased gate leakage current and power consumption. In this paper, the EM effects on current of the nanoscale CMOS circuits are analyzed. Finally, this paper introduces an on-chip current measurement method providing lifetime electromigration management which are designed using 45-nm CMOS predictive technology model.

• The KSFM Journal of Fluid Machinery
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• v.14 no.3
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• pp.5-9
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• 2011

Butterfly valves are widely used in current industry to control the fluid flow. They are used for both on-off and throttling applications involving large flows at relatively low pressure-drop especially in large size pipelines. In this study, we carried out the structure analysis of the butterfly valve components according to pressure testing of the industrial standard. the numerical simulation was performed by using ANSYS Workbench. The reliability of valve is evaluated under the investigation of the strain rate, the leak test and the durability of the valve.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.687-690
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• 2008

Currently, Stream flow analysis has been accomplished by one or two dimensional equations and was applied by simple momentum equations and fixed energy conservations which contain many reach uppermost limit. In this study, FLOW-3D using CFD(Computational Fluid Dynamics) was applied to stream flow analysis which can solve three dimensional RANS(Reynolds Averaged Navier-Stokes Equation) control equation to find out physical behavior and the effect of hydraulic structures. Numerical simulation accomplished those results was compared by using turbulence models such as $k-\varepsilon$, RNG(Renomalized Group Theory) $k-\varepsilon$ and LES(Large Eddy Simulation). Numerical analysis results have been illustrated by the turbulence energy effects, velocity of flow, water level pressure and eddy flows around the side overflow type structures at Jangwall bridge in urban stream.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.5
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• pp.1062-1068
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• 2007

We are using COS to block the excess current and to protect the transformer. But the fuse of COS is melt due to the overload resulting from the excess current flows and it destroys an air severing relations to clear as strong arc happens. Such phenomenon induces an impact ambient noise and it gives the circumstance area resident or pedestrian the fear. Thus, it is necessary that we urgently need to control the ambient noise from the actual circumstances. In this study, we investigate the characteristic of an impact ambient noise associate with the melting state of the COS fuse and suggest the method to reduce the noise.

• Journal of the Korean institute of surface engineering
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• v.39 no.4
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• pp.153-159
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• 2006

Nanodiamond films were deposited on Si substrate by introducing a time dependent on/off modulation of $CH_4\;and\;O_2$ flows in a vertical-type microwave plasma enhanced chemical vapor deposition system. Surface morphology and diamond quality of the film were investigated as a function of the on/off modulation time interval. The diamond nucleation density on the substrate was enhanced under low temperature and low pressure condition. In addition, the diamond nucleation density was enhanced by increasing the on/off modulation time interval. Enhanced diamond quality was noticeable under the condition of a longer on/off modulation time interval. It was suggested that the nanodiamond nuclei formed the cluster formation.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1668-1669
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• 2007

In this paper, we propose nonlinear congestion controller for active queue management of differentiated-services networks. Two important issues in differentiated-services architecture are bandwidth guarantee and fair sharing of unsubscribed bandwidth among TCP flows with and without bandwidth reservation. The nonlinear congestion controller was composed fuzzy logic controller and state feedback controller. The nonlinear congestion controller methodology has been applied to a TCP network. We use NS-2 simulation to demonstrate that the proposed control methodology achieves the desired behavior of the network, and possesses important attributes.

• Proceedings of the KIEE Conference
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• 2004.11b
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• pp.158-161
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• 2004

This paper presents practical applications of reactive power and voltage planning to obtain voltage stability and operational voltage level for 2005 year summer peak Korea power system. It also describes the new electric facilities, operation criteria, voltage levels, MVAr flows, reactive power reserves in each control area. And reactive compensation devices are installed to maintain established voltage levels and stability margins. This simulation results show the improvement of voltage levels and the increase of reactive margins & interface flow margins. Finally, the paper reports the necessity of dynamic reactive reserves. It can be applied to analysis reactive compensation requirements and P-V & V-Q curves by PSS/E & VSAT.