• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.262-265
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• 2002

Fused deposition modelling(FDM) is a rapid prototyping(RP) process that fabricates part layer by layer by deposition of molten thermoplastic material extrude from a nozzle. RP system has many benefit. One of the benefit would be the ability to experiment wiか physical objects of my complexity in a relatively short period of time. But it has a matter of surface roughness and geometric accuracy. We study on Influence of angle of tangent line and area error on sphere surface roughness at fused deposition.

• Journal of Electrical Engineering and information Science
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• v.2 no.4
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• pp.99-105
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• 1997

The new classified model for N-p heterojunction diode is derived and used extensively in analyzing the current-voltage(I-V) characteristics of the HBTs. A new classification method is presented in order to simplify I-V equations and easily applied to the modeling of HBTs. This classification method is characterized by the properties of devices such as high level injection, the thickness of one or both bulk regions, the surface recombination and the generation-recombination. The simulation results using the proposed model agree well with the experimentally observed I-V behaviors and show good efficiencies in its application to HBTs with respect to mathematical formulation.

• Korean Journal of Computational Design and Engineering
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• v.2 no.2
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• pp.85-92
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• 1997

An axial flow fan design system has been made by integrating the self-developed programs and I-DEAS. By using the system, an axial flow fan was designed, manufactured and verified through the wind tunnel experiments in coorperation with a refrigerator appliance division. It has been shown that the optimal design without the ambiguity of the design parameters can be possible by the three-dimensional flow simulations using a self-developed CID code, FANS-3D. (Flow Analysis code using Navier Stokes aguations in Three-Dimensional curvilinear coordinates). By virtue of the fluency of the data flow, an optimally designed fan which satisfies design conditions can be selected in a short time and less cost. The manufacturing processes of a Mock-up and an injection molding die have been automated through the self-made interface programs which connnect from the start to the end. It has been shown that the newly developed fan by this system has a superior performance characteristics to an existing fan.

• The KSFM Journal of Fluid Machinery
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• v.12 no.4
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• pp.44-53
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• 2009

Numerical design optimization of a fan-shaped hole for film-cooling has been carried out to improve film-cooling effectiveness by combining a three-dimensional Reynolds-averaged Navier-Stokes analysis with the radial basis neural network method, a well known surrogate modeling technique for optimization. The injection angle of hole, lateral expansion angle of hole and ratio of length-to-diameter of the hole are chosen as design variables and spatially averaged film-cooling effectiveness is considered as an objective function which is to be maximized. Twenty training points are obtained by Latin Hypercube sampling for three design variables. Sequential quadratic programming is used to search for the optimal point from the constructed surrogate. The film-cooling effectiveness has been successfully improved by the optimization with increased value of all design variables as compared to the reference geometry.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.5
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• pp.640-648
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• 1998

A numerical study has been conducted to investigate the effect of inflow supply air temperature and velocity on ventilation effectiveness in an underfloor air conditioning space. A low Reynolds number k-$\varepsilon$ model is implemented to calculate steady state turbulent velocity distributions. A step-down injection method is used to calculate local and room mean ages from transient concentrations based on the concept of the age of air. Results show that there is a significant effect of Archimedes number on ventilation effectiveness especially for cooling conditions. Reynolds number shows relatively minor effect on velocity distribution and ventilation effectiveness especially for isothermal and heating conditions. It can be concluded that underfloor air conditioning system provides good ventilation characteristics for cooling conditions because of temperature stratification in the space.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.4
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• pp.305-312
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• 2015

In this study, inter-turn short fault models of interior permanent magnet synchronous motors (IPMSM) are developed by adding saliency modeling to surface-mounted permanent magnet motor models. The saliency model is obtained using the deformed flux models based on both fault-winding flux information and inductance variations caused by cross-flux linkages that depend on the distribution of the same phase windings. By assuming the balanced three-phase current injection, we obtain the positive and negative sequence voltages and the fault current in the positive and the negative synchronous reference frames. The output torque model is developed by adding the magnet and the reluctance torque, which are derived from the developed models. To verify the proposed IPMSM model with an inter-turn short fault, finite element method-based simulation and experimental measurement results are presented.

• Transactions on Electrical and Electronic Materials
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• v.16 no.3
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• pp.107-111
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• 2015

Our work is based on the development of a numerical model to develop a methodology for predicting the aging and breakdown in insulation due to the dynamics of space charge packets. The model of bipolar charge transports is proposed to simulate space charge dynamic for high DC voltage in law-density polyethylene (LDPE), taking into account the trapping and detrapping of recombination phenomena, this model has been developed and experimentally validation. Theoretical formulation of the physical problem is based on the Poisson, the continuity and the transport equations as well as on the appropriate models for injection. Numerical results provide temporal and local distributions of the electric field, the space charge density for the different kinds of charges, conduction and displacement current densities, and the external current.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.7
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• pp.1010-1019
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• 2000

The main purpose of this article is to propose and assess a new spray impingement model considering film formation, which is capable of describing the droplet distribution and film flows in direct injection diesel engines. The spray-wall interaction model includes several mathematical formulae, newly made by the energy conservation law and some experimental results. The model consists of three representative regimes, rebound, deposition and splash. In addition, the film flow is described in the present model by solving the continuity and momentum equations for film flows using the integral method. To assess the new spray impingement model, the calculated results using the new model are compared with several experimental data for the normally impinging diesel sprays. The film model is also validated through comparing film radius and thickness against experimental data. The results show that the new model is generally in better agreement with experimental data and acceptable for prediction of the film radius and thickness.

• The Journal of Engineering Geology
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• v.6 no.3
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• pp.119-130
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• 1996

The theory and numerical technique using boundary elements method (BEM) are given to solve 2-dimensional resistivity problems. Potential distributions from homogeneous resistivity model and layered model are calculated by using BEM for a point source of current injection. The potential distributions of BEM are compared with those of finite difference method (FDM) and finite elements method (FEM). Among the three numerical methods to solve 2-dimensional resistivity problem, it is proved that BEM is more efficient tool than FDM and FEM in consideration of computing storage and time as weU as the accuracy of solutions.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.25-28
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• 2000

In this study, Transient Characteristics of the Punch-Through Insulated Gate Bipolar Transistor (PT-IGBT) has been studied. On the contraty to Non-Punch Through Insulated Gate Bipolar Transistor(NPT-IGBT), PT-IGBT has buffer layer It has a simple drive circuit controlled by the gate voltage of the MOSFET and the low on-state resistance of the bipolar junction transistor. In this paper, the transient characteristics with temperature of the PT-IGBT has been analyzed analytically. PT-IGBT is made to reduce switching power loss. Excess Minority carrier distribution inactive base region and base charge, the rate of voltage with time is expressed analytically to include buffer layer.