• Journal of Ship and Ocean Technology
• /
• v.3 no.2
• /
• pp.1-16
• /
• 1999

The incompressible Reynolds-Averaged Navier-Stokes(RANS) equations are solved using the standard $\textsc{k}-\varepsilon$ turbulence model and a finite volume method(FVM)with an O-type grid system. The computed results for its performance test are in good agreement with the published experimental data. The present method is applied to the study on the leading edge radius of a hydrofoil section Calculated results suggest that the leading edge radius has some effects on cavitation performances of a 2-D foil. A natural leading edge radius for the NACA66 section is determined from this study.

• Journal of computational fluids engineering
• /
• v.12 no.1
• /
• pp.1-8
• /
• 2007

A code is developed using the hybrid Cartesian/immersed boundary method and it is applied to simulate flows around a three-dimensional deforming body. A new criterion is suggested to distribute the immersed boundary nodes based on edges crossing a body boundary. Velocities are reconstructed at the immersed boundary nodes using the interpolation along a local normal line to the boundary. Reconstruction of the pressure at the immersed boundary node is avoided using the hybrid staggered/non-staggered grid method. The developed code is validated through comparisons with other experimental and numerical results for the velocity profiles around a circular cylinder under the forced in-line oscillation and the pressure coefficient distribution on a sphere. The code is applied to simulate the flow fields around a plate whose tail is periodically flapping under a translation. The effects of the velocity and acceleration due to the deformation on the periodic shedding of pairs of tip vortices are investigated.

• Journal of the Microelectronics and Packaging Society
• /
• v.17 no.4
• /
• pp.67-72
• /
• 2010

In this paper, a design optimization of ball grid array packaging geometry is studied based on the Taguchi method, which allowed robust design by considering the variance of the input parameters during the optimization process. Molding compound and substrate were modeled as viscoelastic, and finite element analyses were performed to calculate the strain energy densities of the eutectic solder balls. Six quality factors of the dimensions of the packaging geometry were chosen as control factors. After performing noise experiments to determine the dominant factors, main experiments were conducted to find the optimum packaging geometry. Then the strain energy densities between the original and optimized geometries were compared. It was found that the effects of the packaging geometry on the solder ball reliability were significant, and more than 40% of the strain energy density was reduced by the geometry optimization.

• Proceedings of the KIPE Conference
• /
• 2016.07a
• /
• pp.327-328
• /
• 2016

This paper proposes the PLL algorithms with both the quadrature signal generator (QSG) and the positive-sequence calculator (PSC) in order to remove the effects of the three-phase grid voltage with dc offset voltages. The performances of the proposed method are verified with both the simulation result and the experimental result with 32-bit DSP.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.60 no.6
• /
• pp.1122-1127
• /
• 2011

The thesis here by shows that the extant suspension wire, which is stretched between electric poles to support a variety of communication wires, can be replaced by specially-redesigned cables called OPSW(Composite Suspension Wire with Optical Fiber) which have been devised for the first time in the world so that the functions of both communication and support can be united into one cable which is sure to be successfully installed on site, hence leading to outstanding effects that it can sharply reduce the load applied to electric poles as well as the cost of forthcoming constructions and that it can accordingly make a great contribution to the building of Smart Grid network.

• Proceedings of the KIEE Conference
• /
• 2008.11a
• /
• pp.92-94
• /
• 2008

This paper introduces the modeling of grid-connected photovoltaic(PV) generation using Matiab/Simulink. The model is based on the equivalent circuit of the PV solar cell including the effects of solar irradiation and temperature changes. The PV arrays are modeled to be built up with the series/parallel combination of PV solar cell and are connected to the distribution system via an inverter. The simulation results show that the typical characteristics and outputs of the PV arrays are accurate.

• Journal of the Korean Society of Safety
• /
• v.17 no.1
• /
• pp.99-104
• /
• 2002

DQM(differential quadrature method) is applied to computation of eigenvalues of the equations of motion governing the free in-plane vibration for circular curved beams including mid-surface extension and the effects of rotatory inertia. Fundamental frequencies are calculated for the members with various end conditions and opening angles. The results are compared with numerical solutions by other methods for cases in which they are available. The differential quadrature method gives good accuracy even when only a limited number of grid points is used.

• Proceedings of the KSME Conference
• /
• 2007.05a
• /
• pp.532-537
• /
• 2007

Nano imprint lithography(NIL) is a cost-efficient, high-throughput processing technique to transfer nano-scale patterns onto thin polymer films. Polymers used as the resist include UV cured resins as well as thermoplastics such as polymethyl-methacrylate(PMMA). In this study, an analytic investigation was performed for the NIL process of transferring nano scale patterns onto polymeric films. Process optimization calls for a thorough understanding of resist flow during the process. We carried out 2D and 3D numerical analyses of resist flow during NIL process. The simulation incorporated continuum-hypothesis and the effects of surface tension were taken into account. For a more effective prediction of free surface, fixed grid scheme with the volume of fluid (VOF) method were used. The simulation results were verified with experimental results qualitatively. And the parametric study was performed for various process conditions.

• Journal of Electrical Engineering and Technology
• /
• v.9 no.6
• /
• pp.1864-1872
• /
• 2014

Maloperation of protective relays is one of the major causes for cascading tripping in WANS. Another line trip followed by a previous line trip may occur due to overloading of the line, because of the load redistribution or unwanted trip of a backup relay due to change in the flow of fault current. Evaluation of each line is required by considering both of these effects. A new index named Line Security Index (LSI) is proposed in this paper which combines both Vulnerability Index (VI) and Protectability Index (PI) to completely evaluate the security of individual lines and their importance in the power grid. Computer simulations have been performed on the Korean power grid data to establish the feasibility of the proposed idea.

• Journal of Electrical Engineering and Technology
• /
• v.9 no.6
• /
• pp.1805-1811
• /
• 2014

After an occurrence of a fault in any distribution system, it is desired to limit the effects of the fault to smallest possible area and restore the un-faulty areas as soon as possible. Due the advancements in communication technologies, this task can be achieved in multiple efficient ways. In order to decrease the restoration time in the Smart Grid Distribution Management System (SDMS) a communication based algorithm is proposed in this paper, in which the restoration can be done during reclosing. This paper also analyzes various communication failures with power failures cases including the entire network of communication failures. Results of all these cases have been verified by doing simulations.