• Korean Journal of Computational Design and Engineering
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• v.1 no.1
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• pp.56-64
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• 1996

A quadrilateral-triangular mixed grid method for the solution of incompressible viscous flow is presented. The solution domain near the body surface is meshed using elliptic grid geneator to acculately simulate the viscous flow. On the other hand, we used unstructured triangular grid system generated by advancing front technique of a simple automatic grid generation algorithm in the rest of the computational domain. The present method thus is capable of not only handling complex geometries but providing accurate solutions near body surface. The numerical technique adopted here is PISO type finite element method which was developed by the present author. Investigations have been made of two-dimensional unsteady flow of Re=550 past a circular cylinder. In the case of use of the unstructured grid only, there exists a considerable amount of difference with the existing results in drag coefficient and vorticity at the cylinder surface; this may be because of the lack of the grid clustering to the surface that is a inevitable requirement to resolve the viscous flow. However, numerical results on the mixed grid show good agreements with the earlier computations and experimental data.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.5
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• pp.36-42
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• 2003

A CFD simulation technique has been developed to handle the unsteady body motion with large amplitude by use of overlapping multi-block grid system. The three-dimensional, viscous and incompressible flow around body is investigated by solving the Navier-Stokes equations, and the motion of body is represented by moving effect of the grid system. Composite grid system is employed in order to deal with both the body motion with large amplitude and the condition of numerical wave maker in convenience at the same time. The governing equations, Navier-Stokes (N-S) and continuity equations, are discretized by a finite volume method, in the framework of an O-H type boundary-fitted grid system (inner grid system including test model) and a rectangular grid system (outer grid system including simulation equipments for generation of wave environments). If this study, several flow configurations, such as an oscillating cylinder with large KC number, are studied in order to predict and evaluate the hydrodynamic forces. Furthermore, the motion simulation of a Series 60 model advancing in a uniform flow under the condition of enforced roll motion of angle 20$^{\circ}$ is performed in the developed numerical wave tank.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.210-210
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• 2006

IT technologies(Chips, Grid and e-Science) are rapidly changed from 1965. In 1965, Intel co-founder Gordon Mooresaq the future. His prediction popularly known as Moore's law, state that the computer chips double in power every 18 months Grid computing offers a model for solving massive computational problems by making use of the unused resources of large numbers of disparate, often desktop, computers treated as a virtual cluster embedded in a distributed telecommunications infrastructure. In this paper, I will discuss current status of supercomputing technology and haw we can use these on CFD. Functionally, one can classify Grids into several types:

• Journal of KIISE:Computer Systems and Theory
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• v.31 no.3_4
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• pp.152-159
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• 2004

The Grid system is an emerging computing infrastructure that will substitute for existing distributed systems. However end users have a difficulty in using the Grid because of its complicated usage, which is an inherent characteristic from the heterogeneous mechanism of the Grid. In this paper, we present the JCML(Job Control Markup Language) and its GUI-based editor, which not only provide users with ease of use, improved working environment, but assist users to execute their jobs efficiently The JCML is a job control language that improves the RSL of Globus, which defines global services in Grid. The JCML is designed to support flexibility among various Grid services using standard XML. And it makes use of a graph representation method, GXL(Graph eXchange Language), to specify detailed job properties and dependencies among jobs using nodes and edges. The JCML editor provides users with GUI-based interface. With the JCML editor, a complicated job order can be easily completed using very simple manipulations with a mouse, such as a drag-and-drop.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.05a
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• pp.735-737
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• 2017

An Off grid or remote solar electric systems are an energy supply to our home or to our companies without the utility of Grid at all. Off grid solar systems are very important for those who live in remote locations especially for developing countries where getting the electric grid is extremely expensive, inconvenient or for those who doesn't need to pay a monthly bill with the electric bill in general. The main critical components of any solar power system or renewable energy harvesting systems are the energy storage systems and its charge controller system. Energy storage systems are the essential integral part of a solar energy harvesting system and in general for all renewable energy harvesting systems. To provide an optimal solution of both high power density and high energy density at the same time we have to use hybrid energy storage systems (HESS), that combine two or more energy storage technologies with complementary characteristics. In this present work, design and simulation we use two storage systems supercapacitor for high power density and lithium based battery for high energy density. Here the system incorporates fast-response supercapacitors to provide power to manage solar smoothing and uses a battery for load shifting. On this paper discuss that the total energy throughout of the battery is much reduced and the typical thermal stresses caused by high discharge rate responses are mitigated by integrating supercapacitors with the battery storage system. In addition of the above discussion the off grid solar electric energy harvesting presented in this research paper includes battery and supercapacitor management system, MPPT (maximum power point tracking) system and back/boost convertors. On this present work the entire model of off grid electric energy harvesting system and all other functional blocks of that system is implemented in MATLAB Simulink.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.6
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• pp.60-66
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• 2010

Mesh grounding electrodes in Korea and abroad are designed as lattice-shaped equidistance grounding grids. In case of a lattice-shaped grounding Grid, however, there is a problem of higher touch voltage at the corner of the grid relative to the center. To overcome this problem, we used oblique-shaped equidistance grounding grid to reduce the area of the corner where mesh voltage occurs. As a result the mesh voltage was reduced. Therefore, this paper suggests the use of oblique-shaped grounding grid instead of the existing lattice-shaped ones. It applied the same grounding design dimensions for both lattice-shaped and oblique-shaped grounding grids, compared and analyzed mesh voltage, GPR, ground resistance, total length of grounding conductor, verified that oblique-shaped grounding grid is superior to the lattice-shaped.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.5
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• pp.117-126
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• 2010

In order to obtain more clear x-ray images, an antiscatter grid, which can absorb the scattered rays, is employed. In the high-resolution direct digital radiography, however, the artifacts due to the grid are visible. In this paper, the grid artifacts are reduced by applying simple 1-dimensional low-pass filters in the spatial domain based on the rotated grid. Since the proposed algorithm does not use any detection scheme for the artifact frequencies and discrete Fourier transforms for 2-dimensional filters, it can simply and fast reduce the grid artifacts. The performance using the order 1 average filter is compatible to that of using 2-dimensional filters in the frequency domain.

• Journal of Electrical Engineering and Technology
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• v.8 no.1
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• pp.20-30
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• 2013

An intelligent grid computing architecture is proposed and developed for transient stability constrained total transfer capability evaluation of future smart grid. In the proposed intelligent grid computing architecture, a model of generalized compute nodes with 'able person should do more work' feature is presented and implemented to make full use of each node. A timeout handling strategy called conditional resource preemption is designed to improve the whole system computing performance further. The architecture can intelligently and effectively integrate heterogeneous distributed computing resources around Intranet/Internet and implement the dynamic load balancing. Furthermore, the robustness of the architecture is analyzed and developed as well. The case studies have been carried out on the IEEE New England 39-bus system and a real-sized Chinese power system, and results demonstrate the practicability and effectiveness of the intelligent grid computing architecture.

• Journal of Power Electronics
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• v.18 no.3
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• pp.757-765
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• 2018

This paper deals with the instability and resonant phenomena in distribution systems with multiple grid-connected inverters with an LCL output filter. The penetration of roof-top and other types of small photovoltaic (PV) grid-connected systems is rapidly increasing in distribution grids due to the attractive incentives set forth by different governments. When the number of such grid-connected inverters increases, their interaction with the distribution grid may cause undesirable effects such as instability and resonance. In this paper, a grid system with several grid-connected inverters is studied. Since proportional-resonant (PR) controllers are becoming more popular, it is assumed that most inverters use this type of controller. An LCL filter is also considered at the inverters output to make the case as realistic as possible. A complete modeling of this system is presented. Consequently, it is shown that such a system is prone to instability due to the interactions of the inverter controllers. A modification of PR controllers is presented where the output capacitor is virtually decreased. As a result, the instability is avoided. Simulation results are presented and show a good agreement with the theoretical studies. Experimental results obtained on a laboratory setup show the validity of the analysis.

• International Journal of CAD/CAM
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• v.9 no.1
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• pp.111-120
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• 2010

In this paper, we propose a volume rendering method using grid computing for large-scale volume data. Grid computing is attractive because medical institutions and research facilities often have a large number of idle computers. A large-scale volume data is divided into sub-volumes and the sub-volumes are rendered using grid computing. When using grid computing, different computers rarely have the same processor speeds. Thus the return order of results rarely matches the sending order. However order is vital when combining results to create a final image. Job-Scheduling is important in grid computing for volume rendering, so we use an obstacle-flag which changes priorities dynamically to manage sub-volume results. Obstacle-Flags manage visibility of each sub-volume when line of sight from the view point is obscured by other subvolumes. The proposed Dynamic Job-Scheduling based on visibility substantially increases efficiency. Our Dynamic Job-Scheduling method was implemented on our university's campus grid and we conducted comparative experiments, which showed that the proposed method provides significant improvements in efficiency for large-scale volume rendering.