• 대한조선학회논문집
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• 제48권4호
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• pp.363-367
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• 2011

In this paper, friction coefficients between ices and model ship were studied in order to predict the resistance of ice. The friction coefficient is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together. The coefficient of friction depends on the materials, roughness on surface, lubrication, etc. We tested and analyzed the friction coefficient for the development of the test methodology. The friction coefficient for ice model test is very dominant to predict the ship performance, so every ice tank uses their own painting technique. In this study, the friction coefficient with changing the moving speed of ice was studies by using a flat plates which were made by the MOERI's paining technique and the basic research for the developing the paining methodology in the MOERI ice model basin was carried out.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권4호
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• pp.242-253
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• 2011

Skin frictional drag reduction efficiency of "stiff" compliant coating was investigated in a wind tunnel experiment. Flat plate compliant coating inserts were installed in a wind tunnel and the measurements of skin frictional drag and velocity field were carried out. The compliant coatings with varying viscoelastic properties had been prepared using different composition. In order to optimize the coating thickness, the most important design parameter, the dynamic viscoelastic properties had been determined experimentally. The aging of the materials (variation of their properties) during half a year was documented as well. A design procedure proposed by Kulik et al. (2008) was applied to get an optimal value for the coating thickness. Along with the drag measurement using the strain balance, velocity and pressure were measured for different coatings. The compliant coatings with the thickness h = 7mm achieved 4~5% drag reduction within a velocity range 30~40 m/s. The drag reduction mechanism of the attenuation of turbulence velocity fluctuations due to the compliant coating was demonstrated. It is envisioned that larger drag reduction effect is obtainable at higher flow velocities for high speed trains and subsonic aircrafts.

• JSTS:Journal of Semiconductor Technology and Science
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• 제14권6호
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• pp.818-823
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• 2014

A high-gain wideband low noise amplifier (LNA) using $0.25-{\mu}m$ Gallium-Nitride (GaN) MMIC technology is presented. The LNA shows 8 GHz to 15 GHz operation by a distributed amplifier architecture and high gain with an additional common source amplifier as a mid-stage. The measurement results show a flat gain of $25.1{\pm}0.8dB$ and input and output matching of -12 dB for all targeted frequencies. The measured minimum noise figure is 2.8 dB at 12.6 GHz and below 3.6 dB across all frequencies. It consumes 98 mA with a 10-V supply. By adjusting the gate voltage of the mid-stage common source amplifier, the overall gain is controlled stably from 13 dB to 24 dB with no significant variations of the input and output matching.

• 대한조선학회논문집
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• 제45권3호
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• pp.303-308
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• 2008

The induction heating is more efficient for a plate bending because of its easy operation and control of working parameters, compared with the heating by a gas torch. The existing axis symmetric analysis method could neither handle initial curved plates nor be used in the optimization of coil shapes because of its limit of an axis symmetric coil shape. But the proposed method using some discrete part models and analysis processes could overcome these difficulties and show more accurate results in temperatures and deflections of flat or curved plates with initial curvature than those in the existing axis symmetric analysis method. This method is composed of the multi-disciplinary analyses such as an electro magnetic analysis, a heat transfer analysis and a deformation analysis based on inherent strain approach per each step. Traditionally, the coil shape in the induction heating is circular shape and it needs the moving process along heating lines. To overcome this, the 'Long Type Coil' with some linear parallel coils was proposed. It did not need the moving process along heating lines and reduced the heating process time. The results of experiments were compared with those of the simulation.

• 대한조선학회논문집
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• 제45권6호
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• pp.695-702
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• 2008

In this paper, a new numerical method is proposed to analyze near-field sonar cross section of acoustically large-sized underwater targets such as submarines. A near-field problem is converted to a far-field problem using a spherical projection method with respect to the objective target. Then, sonar cross section is calculated with a physical optics well established in far-field acoustic wave scattering problems. The analysis results of a square flat plate compared with those obtained by other method show the accuracy of the proposed method. Moreover, it is noted that the sonar cross section is varied with respect to the targeting point as well as the range. Finally, numerical analysis results of real-like underwater target such as a submarine pressure hull are discussed.

• 대한조선학회논문집
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• 제45권2호
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• pp.157-167
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• 2008

Six smooth flat tensile specimens and eighteen punch specimens with three different thicknesses were machined from steel of JIS G3131 SPHC. In addition to punch tests, incremental tensile tests were conducted to obtain average true flow stress - logarithmic true strain curves. Through parametric FE simulations for the tensile specimens, material parameters related to GTN model were identified. Using indenters with three kinds of radius, punch tests were carried out to obtain fracture characteristics of punch specimens. Numerical analyses using both fracture models, GTN and $J_2$ plasticity model, gave that the former estimated well the fracture of punch specimen but the latter did not. A new concept for critical size of plate elements was introduced based on minimum relative sharpness between contact structures. Consequently, a new criterion for critical element size was proposed to be less than 20% of minimum relative radius of interacting structures.

• 한국태양에너지학회 논문집
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• 제37권5호
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• pp.39-47
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• 2017

In a hot water system using solar energy, solar heat is not simply collected by the heat collecting plate, but by heat exchange between the solar collector (flat or vacuum type) and the hot water storage tank. Therefore, the amount of collected solar energy depends on the hot water usage patterns that determine the temperature of the thermal storage tank. Also, if the temperature of the hot water stored in the storage tank exceeds the dangerous temperature during the summer, the heat must be released for safety. If the temperature of the hot water in the storage tank is low, it is necessary to heat by the auxiliary heat source. In this study, three buildings are defined as hotel, swimming pool, and school facilities. And we calculated the released heat energy, auxiliary heat source, and pure storage heat energy based on different hot water usage patterns and installation angle of the solar collectors.

• 한국정보처리학회논문지
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• 제6권9호
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• pp.2548-2557
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• 1999

평판 디스플레이 분야의 발달로 대형화와 고해상도화가 진행됨에 따라 이에 알맞은 새로운 개념의 평판 디스플레이를 위한 컨트롤러가 필요하게 되었다. 이에 본 논문에서는 평판 디스플레이 중에서 가장 많은 비중을 차지하는 TFT LCD를 위한 SXGA급 해상도를 지원하는 컨트롤러를 설계하였다. 병렬 버스 구조의 새로운 LCD 컨트롤러의 구조를 제시하였으며, 저해상도 화면을 SXGA급 해상도의 화면으로 확대할 수 있도록 설계하였다. 또한 Synopsys VHDL을 이용하여 제안한 컨트롤러의 기능 검증 및 회로 합성을 수행하였다.

• 한국산학기술학회논문지
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• 제15권2호
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• pp.603-608
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• 2014

항공기와 자동차 부품과 관련된 많은 제조업에서, 낮은 비중과 높은 강도에서 뛰어난 알루미늄 합금(Al2024)은 효과적으로 사용되었다. 가공소재의 표면거칠기 품위를 위한 정면밀링 가공기술은 이들 분야에서 적용되어 왔다. 챔퍼된 드로우 어웨이 타입의 인서트를 갖는 정면밀링 가공은 단지 이론적으로 완전한 평면을 생산할 수 있다. 그러나 그것은 절삭온도, 소성변형, 동적효과 등으로 인하여 불가능하다. 본 논문에서 실험적 연구는 검증된 고속가공이 가능한 정면밀링커터 바디를 사용하여 Al2024의 고속가공 후 표면거칠기를 개선하기 위하여 수행되었다.

• 대한조선학회논문집
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• 제46권6호
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• pp.675-687
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• 2009

In general, the forming process of the curved hull plates consists of sub tasks, such as roll bending, line heating, and triangle heating. In order to complement the automated curved hull forming system, it is necessary to develop an algorithm to classify the curved hull plates of a ship into standard shapes with respect to the techniques of forming task, such as the roll bending, the line heating, and the triangle heating. In this paper, the curved hull plates are classified by four standard shapes and the combination of them, or saddle, convex, flat, cylindrical shape, and the combination of them, that are related to the forming tasks necessary to form the shapes. In preprocessing, the Gaussian curvature and the mean curvature at the mid-point of a mesh of modeling surface by Coon's patch are calculated. Then the nearest neighbor method to classify the input plate type is applied. Tests to verify the developed algorithm with sample plates of a real ship data have been performed.