• Proceedings of the KSME Conference
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• 2000.04b
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• pp.586-592
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• 2000

터보머신 태부에 존재하는 정익 - 동익의 상호작용 유동현상을 수치모사 하는 코드를 병렬화 하였다 정익 - 동익의 상호작용을 해석하는 데에 편리하도륵 Multi-Block Grid System을 도입하여 계산영역을 형성하였고, 동익의 움직임으로 인해 발생하는 Sliding Interface부분은 Patched 알고리즘을 적용하여 해석하였다. 정익과 동익의 수를 1대 1로 단순화시켜 수치모사한 결과와 정익과 동익의 수를 실제 조건과 더 비슷하게 설정한 3대 4의 비율로 맞추어 수치모사한 결과를 비교하였다. 또한, 병렬컴퓨팅으로 인해 단축된 계산시간을 다른 연구에서의 계산시간들과 서로 비교하였다. 2차원 비정상 압축성 Navier-Stokes 방정식이 이용되었고, 난류모델링에는 K-w SST 모델링이 적응되었다. Roe의 FDS 기법을 사용하여 플럭스를 계산하였고, MUSCL 기법을 적용하여 3차의 공간정확도를 갖도록 하였다. 시간적분에는 이보성의 DP-SGS를 사용하였다. 해석결과의 분석에는 Time-averaged pressure distribution과 Pressure amplitude distribution 데이터를 사용했다.

• Journal of Power Electronics
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• v.18 no.3
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• pp.879-891
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• 2018

A bidirectional dc-dc converter is used in battery energy storage systems owing to the growing requirements of a charging and discharging mode of battery. The magnetic coupling of output or input inductors in parallel-connected multi modules of a bidirectional dc-dc converter is often utilized to reduce the peak-to-peak ripple size of the inductor current. This study proposes a novel design guideline to achieve minimal ripple size of the inductor current under bidirectional power flow. The newly proposed design guideline of optimized coupling factor is applicable to the buck and boost operation modes of a bidirectional dc-dc converter. Therefore, the coupling factor value of the coupled inductor does not have to be optimized separately for buck and boost operation modes. This new observation is explained using the theoretical model of coupled inductor and confirmed through simulation and experimental test.

• Journal of Powder Materials
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• v.9 no.1
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• pp.11-18
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• 2002

The 6061 Al alloy based composites reinforced with 10 vol% SiC whiskers were prepared by powder metallurgy with the powders having the different sizes, i.e. < $30{\mu}m$ and > $30{\mu}m$ The composites were subjected to equal channel angular pressing (ECAP) at various conditions and the microstructural changes during ECAP were examined In the composites SiC whiskers were clustered and randomly aligned. The clusters were relatively well distributed in the composite with the smaller initial powder size. After ECAP, the clusters were aligned parallel to flow direction and became smaller. In addition, the shape of clusters was changed from irregular to round. The microstructure of the ECAPed samples were compared with those of the conventionally hot-extruded composites. The uniform microstructure and enhanced microhardness could be obtained by using the powders having the smaller size, decreasing ECAP temperature and repeating ECAP.

• Transactions of Materials Processing
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• v.19 no.7
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• pp.416-422
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• 2010

The $\{10\bar{1}2\}$ twinning characteristics, such as active twin variants, volume fraction of twins with strain, twin morphology, twin texture and angle relationship between twins, were dependent on the activation mode (i.e., tension parallel to the caxis or compression perpendicular to the c-axis). The selection criterion of active twin variants was governed by the Schmid law. This activation of selected twin variants depending on the activation mode consequently caused a totally different plastic deformation behavior in two activation modes. The differences in the deformation characteristics, such as flow stress and work hardening rate, between both activation modes were explained in relation with activation stresses for slips and twinning, relative activities of twinning and slips during plastic deformation, grain refining effect by twin boundaries (Hall-Petch effect), and twinning-induced change in activities of slips.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.10
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• pp.975-982
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• 2004

Helmholtz resonator is used to reduce noise of the narrow frequency band. It has high transmission loss at its resonance frequency. The silencer that combines many resonators could control broadband noise at low frequency. To convey this rather simple idea, serial and parallel arrangement of resonators have been tested to obtain high transmission loss characteristics in the band of which are selects. Theoretical and experimental results explain these characteristics in the absence of mean flow. The change of acoustic characteristics by the resonance frequencies and resonators arrangement are explained by using the equivalent Impedance analysis that is defined in this paper. It shows that the transmission loss has a maximum value when the separation distance between each resonator is λ/4 of its wavelength.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.1
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• pp.101-106
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• 2020

Along with dust collection efficiency, pressure loss is a very important cyclone operation factor. A severe rise in pressure loss causes the problem of cost. To solve the problem, the method connecting axial-vane type cyclones in parallel is suggested recently. The axial vane type cyclone dust collector applied in this study is a small portable type. Multiple cyclones are installed in a round type. The basic performance test on the axial vane type cyclone dust collector was conducted. As a result, the cut size reduced along with a rise in the wind velocity of the cyclone dust collector inlet. According to the test on dust collection efficiency, the effect of dust collection began to appear in the range of 3㎛ and dust collection efficiency was greatly improved at 5 ㎛. The noise of the cyclone dust collector well met the fan sound power level of KSB 6361.

• International Journal of Aeronautical and Space Sciences
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• v.9 no.1
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• pp.1-30
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• 2008

When the stagnation temperature of a perfect gas increases, the specific heats and their ratio do not remain constant any more and start to vary with this temperature. The gas remains perfect; its state equation remains always valid, except, it is named in more by calorically imperfect gas. The aim of this work is to trace the profiles of the supersonic axisymmetric Minimum Length Nozzle to have a uniform and parallel flow at the exit section, when the stagnation temperature is taken into account, lower than the dissociation threshold of the molecules, and to have for each exit Mach number and stagnation temperature shape of nozzle. The method of characteristics is used with the algorithm of the second order finite differences method. The form of the nozzle has a point of deflection and an initial angle of expansion. The comparison is made with the calorically perfect gas. The application is for air.

• Smart Media Journal
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• v.2 no.3
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• pp.47-53
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• 2013

Recently convergence of IT in logistics system as a typical application RFID/NFC technology is being used, such as, according to the distribution of the flow is generated by a lot of big data. The Hadoop distributed system to collect data items produced by the parallel processing capabilities of logistics information and logistics information for the record management can create. Hadoop system to support the design and development of prototypes were approaching the possibility of its utilization.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.3
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• pp.130-140
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• 2001

This paper presents the performance of a parallel active power filter(PT) system in unbalanced load condition. The unbalanced load leads to negative sequence of current, and makes 120Hz ripple in the DC-link voltage forcing large capacitance and increases the rating of APF. thus, the separation of negative sequence is performed in synchronous reference frame and controlled to flow into supply network. The validity of the scheme is investigated through simulation and the experimental results for a prototype active power filter system rated at 10kVA.

• Magazine of the Korean Society of Agricultural Engineers
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• v.40 no.6
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• pp.79-88
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• 1998

This study was conducted to measure the moisture content of soil using RF impedance in the range of 1 to 30MHz. Considering the water potential flow in the soils, two types of sensor such as parallel cylinder and perpendicular plate type were fabricated and tested. The capacitance and resistance of sonsors for soil samples having moisture content range of 2 to 27% were measured by Q-meter (HP4342). The higher soil moisture content was and the larger soil bulk density was, the more the capacitance of sensors increased. To eliminate the effect of bulk density on measuring soil moisture content using RF impedance, two kinds of model having the density independent functions such as the ratio of capacitance change to conductance change and weight of water and dry soils respectively were developed and estimated by regression analysis.