• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.5
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• pp.242-248
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• 2002

It is important to develop new effective technologies to increase the interruption capacity and to reduce the size of a UB(Gas Circuit Breakers). Major design parameters such as nozzle geometries and interrupting chamber dimensions affect the cooling of the arc and the breaking performance. But it is not easy to test real GCB model in practice as in theory. Therefore, a simulation tool based on a computational fluid dynamics(CFD) algorithm has been developed to facilitate an optimization of the interrupter. Special attention has been paid to the supersonic flow phenomena between contacts and the observation of hat-gas flow for estimating the breaking performance. However, there are many difficult problems in calculating the flow characteristics in a GCB such as shock wave and complex geometries, which may be either static or in relative motion. Although a number of mesh generation techniques are now available, the generation of meshes around complicated, multi-component geometries like a GCB is still a tedious and difficult task for the computational fluid dynamics. This paper presents the CFD program using CFB-CAD integration technique based on Cartesian cut-cell method, which could reduce researcher's efforts to generate the mesh and achieve the accurate representation of the geometry designed by a CAD tools.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.2 s.314
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• pp.12-18
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• 2007

The three dimensional interpolation is widely used for many kinds of color signal transformation such as real-time color gamut mapping. Given input color signal, the output color signal is approximately calculated by the interpolation with the input point and extracted values from a lookup table which is constructed by storing the values of transformation at regularly packed sample points. Apparently, errors of the interpolated approximation heavily depend on the selection of the lookup table. In this paper, a least square method is applied to assigning values of the lookup table with fixed size in order to minimize error of three-dimensional interpolation. The experimental result shows that the proposed method has better interpolation performance.

• Journal of the Korean Ceramic Society
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• v.41 no.9
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• pp.670-676
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• 2004

The synthesis of highly concentrated silver nano sol assisted by polymeric dispersant (polyelectrolytes) for inkjet method was studied. The silver nano sol was prepared with AgNO$_3$, polyelectrolytes (HS5468cf ; polyacrylic ammonium salt), and reducing agent. The polyelectrolytes play an important role in formation of complex composed of Ag$\^$+/ion and carboxyl group (COO$\^$-/), result in preparation of highly dispersed silver nano particles. The optimization of added amount of polyelectrolytes, and concentration of silver nano sol was studied. The silver nanoparticles were evaluated by XRD, particle size/zeta potential analyzer and FE-TEM. The silver nanoparticles with the range of 10 nm in diameter were produced. The concentration of batch-synthesized silver nano sol was possible up to 40 wt%.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.3
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• pp.53-60
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• 2011

As Construction & Demolition(C&D) debris increase every year, a system has enforced for recycled aggregate made out of C&D debris, then recycled aggregate usage increased in construction field. But as environmental problem by alkalinity of recycled aggregate occurred, the study for lowering alkalinity of recycled aggregate is needed. In this study we made alkalinity reducing facility and installed in the C&D debris midterm-treat field. Then we certified effect of lowering alkalinity and quality of recycled aggregates before and after carbonation. As a result, the most effective carbonation condition is 30seconds in carbonation time, -50~100 kPa of reaction pressure with change of 3cycles. This condition made pH 9.33~9.8 of recycled aggregate possible. The quality of recycled aggregate after carbonation was better than before carbonation in terms of plasticity index, modified CBR, abrasion loss, sand equivalent, liquid limit, size distribution, density and water absorption.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.8
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• pp.806-812
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• 2009

In this paper, the omnidirectional circularly polarized(CP) antenna using arc-shaped mushroom structure with curved branch is proposed. To obtain a vertical polarization and an omnidirectional radiation pattern, the CP antenna uses zeroth-order resonance(ZOR) mode of composite right and left handed(CRLH) transmission line. The horizontal polarization is achieved by the curved branches. Also, the spacing between curved branch and arc-shaped mushroom structure gives the $90^{\circ}$ phase difference between vortical and horizontal polarization. The proposed antenna, therefore, has an omnidirectional CP radiation pattern In the azimuthal plane. The electrical size of the proposed antenna is reduced by 38%, compared with that of the previously presented omnidirectional CP antenna. In addition, the CP antenna is simply designed without $90^{\circ}$ phase shifter and dual feed line. The proposed antenna uses a Bazooka balun for good impedance matching and radiation pattern. To improve 3 dB axial ratio in XY plane, the designed antenna is optimized. After optimization, the measured 3 dB axial ratio in XY plane is observed in $86{\sim}282^{\circ}$.

• Fire Science and Engineering
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• v.16 no.1
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• pp.66-76
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• 2002

This paper includes new nozzle design, basic design factors of water mist system that minimize a thermal damage of cable causing business interruption and applying underground utility tunnel. A underground concrete structure (2.5 m(H)$\times$2.5 m(W)$\times$25 m(D)) is constructed in order to test a nozzle performance. Under the designing fire scenario, critical thermal damage of cable sheath ($400^{\circ}c$) reached within a 2 minutes with unsuppressed fire, but type 1 nozzle (SMD 470 $\mu{m}$) and type 2 nozzle (SMD 650 $\mu{m}$) control cable temperature below $400^{\circ}c$. A system performance and fundamental design factors; K factor, flow rate, spray angle, size distribution, nozzle pressure, spray density are analyzed and proposed for system optimization.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.607-610
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• 2005

A remeshing algorithm using tetrahedral elements has been developed, which is adapted to the mesh density map constructed by a posteriori error estimation. In the finite element analyses of metal forging processes, numerical error increases as deformation proceeds due to severe distortion of elements. In order to reduce the numerical error, the desired mesh sizes in each region of the workpiece are calculated by a posteriori error estimation and the density map is constructed. Piecewise density functions are then constructed with the radial basis function in order to interpolate the discrete data of the density map. The sample mesh is constructed based on the point insertion technique which is adapted to the density function and the mesh size is controlled by moving and deleting nodes to obtain optimal distribution according to the mesh density function and the quality optimization function as well. After finishing the redistribution process of nodes, a tetrahedral mesh is constructed with the redistributed nodes, which is adapted to the density map and resulting in good mesh quality. A goodness and adaptability of the constructed mesh is verified with a testing measure. The proposed remeshing technique is applied to the finite element analyses of forging processes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6B
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• pp.1183-1190
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• 1999

This paper presents an efficient hardware architecture to improve the frame memory interface occupying the largest hardware area together with motion estimator in implementing MPEG-2 video encoder as an ASIC chip. In this architecture, the memory size for internal data buffering and hardware area for frame memory interface control logic are reduced through the efficient memory map organization of the external SDRAM having dual bank and memory access timing optimization between the video encoder and external SDRAM. In this design, 0.5 m, CMOS, TLM (Triple Layer Metal) standard cells are used as design libraries and VHDL simulator and logic synthesis tools are used for hardware design add verification. The hardware emulator modeled by C-language is exploited for various test vector generation and functional verification. The architecture of the improved frame memory interface occupies about 58% less hardware area than the existing architecture[2-3], and it results in the total hardware area reduction up to 24.3%. Thus, the (act that the frame memory interface influences on the whole area of the video encoder severely is presented as a result.

• Journal of Ocean Engineering and Technology
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• v.26 no.4
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• pp.37-41
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• 2012

Due to global warming, the need to secure alternative resources has become more important nationally. Because of the very strong current on the west coast, with a tidal range of up to 10 m, there are many suitable sites for the application of TCP (tidal current power) in Korea. In the southwest region, a strong current is created in the narrow channels between the numerous islands. A rotor is an essential component that can convert tidal current energy into rotational energy to generate electricity. The design optimization of a rotor is very important to maximize the power production. The performance of a rotor can be determined using various parameters, including the number of blades, shape, sectional size, diameter, etc. There are many offshore jetties and piers with high current velocities. Thus, a VAT (vertical axis turbine) system, which can generate power regardless of flow direction changes, could be effectively applied to cylindrical structures. A VAT system could give an advantage to a caisson-type breakwater because it allows water to circulate well. This paper introduces a multi-layer vertical axis tidal current power system. A Savonius turbine was designed, and a performance analysis was carried out using CFD. A physical model was also demonstrated in CWC, and the results are compared with CFD.

• Transactions on Electrical and Electronic Materials
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• v.17 no.5
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• pp.261-269
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• 2016

A high-performance transmit/receive (T/R) switch is essential for every radio-frequency (RF) device. This paper proposes a T/R switch that is designed in the CEDEC 0.13 μm complementary metal-oxide-semiconductor (CMOS) technology for 2.4 GHz ISM-band RF applications. The switch exhibits a 1 dB insertion loss, a 28.6 dB isolation, and a 35.8 dBm power-handling capacity in the transmit mode; meanwhile, for the 1.8 V/0 V control voltages, a 1.1 dB insertion loss and a 19.4 dB isolation were exhibited with an extremely-low power dissipation of 377.14 μW in the receive mode. Besides, the variations of the insertion loss and the isolation of the switch for a temperature change from - 25℃ to 125℃ are 0.019 dB and 0.095 dB, respectively. To obtain a lucrative performance, an active inductor-based resonant circuit, body floating, a transistor W/L optimization, and an isolated CMOS structure were adopted for the switch design. Further, due to the avoidance of bulky inductors and capacitors, a very small chip size of 0.0207 mm² that is the lowest-ever reported chip area for this frequency band was achieved.