• The KSFM Journal of Fluid Machinery
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• v.10 no.5
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• pp.27-33
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• 2007

Rarefied gas flows through two-dimensional micro channels are studied numerically for the performance optimization of a nanomembrane-based Knudsen compressor. The effects of the wall temperature distributions on the thermal transpiration flow patterns are examined. The flow has a pumping effect, and the mass flow rates through the channel are calculated. The results show that a steady one-way flow is induced for a wide range of the Knudsen number. The DSMC(direct simulation Monte Carlo) method with VHS(variable hard sphere) model and NTC(no time counter) techniques has been applied in this work to obtain numerical solutions. A critical element that drives Knudsen compressor Is the thermal transpiration membrane. The membranes are based on aerosol or machined aerogel. The aerogel is modeled as a single micro flow channel.

• Macromolecular Research
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• v.10 no.1
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• pp.18-23
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• 2002

We theoretically consider blends of two monodisperse one-end-functionalized homopolymers (denoted by A and B) capable of forming clusters between functional groups (stickers) using weak segregation theory. In this model system resulting molecular architectures via clustering resemble star copolymers having many A- and B-arms. Minimizing the total free energy with respect the cluster distribution, the equilibrium distribution of clusters is obtained and used for RPA (Random Phase Approximation) equations as input. For the case that polymers are functionalized by only one kind of sticker, the phase diagrams show that the associations promote the macrophase separation. When there is strong affinity between stickers belonging to the different polymer species, on the other hand, the phase diagram show a suppression of the macrophase separation at the range of high temperature regime, as well as the phase coexistence between a disordered and a mesoscopic phase at the relatively lower temperatures.

• Journal of the Semiconductor & Display Technology
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• v.2 no.4
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• pp.9-12
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• 2003

This paper describes a newly developed simulation environment for analysis and design of a plasma processing chamber based on first principles including complicated physical and chemical interactions of plasma, fluid dynamics of neutrals, and transport phenomena of particles. Capabilities of our simulator, named VIP-SEPCAD (Virtual Integrated Prototyping Simulation Environment for Plasma Chamber Analysis and Design), are demonstrated through a two dimensional simulation of an oxygen plasma chamber. VIP-SEPCAD can provide plasma properties such as spatiotemporal profiles of plasma density and potential, electron temperature, ion flux and energy, etc. By coupling neutral and particle transport models with a three moment plasma model, VIP-SEPCAD can also predict spatiotemporal profiles of chemically reactive species and particles exist in plasma.

• Journal of Welding and Joining
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• v.12 no.2
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• pp.76-86
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• 1994

Spot welding behavior of galvanized steel has been studied using both numerical and experimental techniques. The model that used to calculate temperature distribution within weldment is two-dimensional axis-symmetric finite difference method, and nugget sizes of specimen welded in condition of welding current and time has been estimated by experiment Results have shown that nugget sizes are increased in proportion to welding current and time, but the growth rate of nugget is decreased. Shear-tensile strength tests have shown interface fracture when welding current is 7, 9KA, welding time is 8-14cycle and 11KA, 8-10cycle respectively, but above 7, 9KA fracture shows button type. In button fracture, shear-tensile strengths have been proportional to nugget sizes.

• Proceedings of the KWS Conference
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• 1996.10a
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• pp.148-152
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• 1996

A transient two-dimensional (2D) model was developed for investigating the heat and fluid flow in old pools and determining velocity profile and temperature distribution for the Gas Metal Arc (GMA) welding process. The mathematical formulation deals with the driving farces (electromagnetic, buoyancy, surface tension and plasma drag forces) as well as energy exchange between the molten filler metal droplet and weld pools. A general thermofluid-mechanics computer program, PHOENICS, was employed to numerically solve the governing equation with the associated source terms. The results of computation have shown that the electromagnetic and surface tension farces as will as the molten filler metal droplet have major influence in shaping the weld pool geometry.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.421-423
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• 2003

To prevent fault effect in supply of electric power distribution system and plan stable operation of electric power system, must control magnitude of fault current. Although there are various kinds of method to solvethis, approached from super conductivity Fault Current Limiter application viewpoint among them. High Temperature Superconductor-Fault Current Limiter (HTS-FCL) development is progressing according to HTS technology development, and system application is tried. For actual system application of such super conductivity FCL, so that can reflect special quality of actuality supply of electric power distribution system just as it is in this treatise supply of electric power system by two modelling do. Also, by simulation of HTS-FCL action and protection coordination with another equipment appliances, verified the effectiveness in supply of electric power system applying itself super conductivity FCL EMTDC dynamic characteristic model that is develope.

• Proceedings of the KIPE Conference
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• 2019.11a
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• pp.200-201
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• 2019

Due to uncontrollability and non-repeatability of natural irradiation and temperature, the solar array simulator (SAS) is required to conduct the MPPT power processing experiments precisely. However, the nonlinearity of PV curve characteristic is a crucial task for the control of SAS. In the literature, this issue is addressed by many authors and various methods are proposed. However, stability analysis of SAS is not enough to evaluate the control performance. In this paper, the limitations of conventional SAS are studied according to the small signal model. By using the proposed approach, the performance of two different control method for SAS system are analyzed and compared.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.4
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• pp.367-372
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• 2004

Two new extraction methods for the thermal Resistance of HBT(Heterojunction Bipolar Transistors) are proposed. First, the analytical expression, based on the thermal characteristics that the base to emitter junction voltage drops with the increase of junction temperature, is derived. Second, the thermal resistance equation that can predict the measured DC(Direct Current) data optimally is derived. These optimal thermal resistance expression is applied to the 2 finger 2${\times}$20${\mu}{\textrm}{m}$-AlGaAs/GaAs HBT and shows the good agreement with the measured data.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.714-716
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• 2000

In the System-integrated modular advanced reactor(SMART), the motor for Control element drive mechanism(CEDM) requires high density power and simple drive mechanism to reduce volume because of restriction by install-space and must satisfy the reactor operating circumstances with high pressure and temperature. In this paper, we perform the basic design of the two kinds (Variable reluctance type and Hibrid-reluctance type) of the transverse flux motor to develop the prototype motor for the control element drive mechanism of SMART. Analyzed these motors by the FEM in the 2-dimension, we show the characteristics for each of the analysis model.

• Composites Research
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• v.16 no.1
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• pp.34-41
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• 2003

A cure process control model was proposed to optimize the curing process of thick filament wound structure. There are two types of smart cure, one is that the boundary conditions of the hollow cylinder are same between inner surface and outer surface, and the other is that inner surface temperature is slightly higher than outer surface to initiate cure reaction from the inner side to the outer side to reduce residual stress.