• 한국연소학회지
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• 제7권2호
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• pp.49-61
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• 2002

Numerical simulation is performed for stagnating turbulent flows of impinging and countercurrent jets by the Reynolds stress model(RSM). Results are compared with those of the ${\kappa}-{\varepsilon}$ model and available data to assess the flow characteristics and turbulence modes. Three variants of the RSM tested are those of Gibson and Launder(GL), Craft and Launder(GL-CL) and Speziale, Sarkar and Gatski(SSG). As well known, the ${\kappa}-{\varepsilon}$ model overestimates turbulent kinetic energy near the wall significantly. Although the RSM is superior to the ${\kappa}-{\varepsilon}$ model, it shows considerable difference according to how the redistributive pressure-strain term is modeled. Results of the RSM for countercurrent jets are improved with the modified coefficients for the dissipation rate, $C_{{\varepsilon}1}\;and\;C_{{\varepsilon}2}$ suggested by Champion and Libby. The performance of the three variants of the RSM model for stagnating flows are assessed.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.512-512
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• 2000

In this article, a current mode peak detector circuit is presented. The simple circuit configuration comprises four MOS transistors and one external capacitor. The realization method is suitable fur fabrication using CMOS technology and all transistors are operated in their saturation region. The proposed circuit exhibits a very low drop rate and provides high accuracy, high-speed and wide dynamic range. The proposed circuit has very low power dissipation and operates using a single 2.5V supply. Simulation results confirmed the characteristic of the proposed circuit are also included.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2002년도 제25회 KOSCI SYMPOSIUM 논문집
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• pp.11-17
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• 2002

The first-order conditional moment closure (CMC) model is applied to $CH_4$/Air turbulent jet diffusion flames(Sandia Flame D, E and F). The flow and mixing fields are calculated by fast chemistry assumption and a beta function pdf for mixture fraction. Reacting scalar fields are calculated by elliptic CMC formulation. The results for Flame D show reasonable agreement with the measured conditional mean temperature and mass fractions of major species, although with discrepancy on the fuel rich side. The discrepancy tends to increase as the level of local extinction increases. Second-order CMC may be needed for better prediction of these near-extinction flames.

• 한국통신학회논문지
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• 제25권1B호
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• pp.201-208
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• 2000

시분할 멀티플렉서는 여러 병렬 스트림(stream)들을 높은 비트율을 갖는 하나의 직렬 스트림으로 결합하는 장치로, 광통신 시스템의 송신부에 사용된다. 본 논문에서는 에미터 크기가 2$\times$8um\sup 2\인 SiGe HBT를 사용하여 4:1 (4채널) 시분할 멀티플렉서를 설계하였다. 설계된 회로의 동작속도는 10Gbps, 입력전압 및 출력전압은 각각 400mVp-p와 800mVp-p, 20-80% 간의 상승시간 및 하강시간은 각각 34ps와 34ps이며, 전력소모는 1.50W이다.

• 대한기계학회논문집
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• 제18권2호
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• pp.492-501
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• 1994

This study is an analysis of the turbulent diffusion flame with swirl flow and the calculated results are compared with experimental data in case of various swirl numbers and air-fuel rations. The mathematical model is restricted to single-phase, diffusion controlled combustion with swirl flow. Values of local flow properties were obtained by solving appropriate differential equation for continuity, momentum, stagnation enthalpy, concentration, turbulence energy, dissipation rate of turbulence energy, and the mean square of concentration fluctuation. The method is proposed for calculating the local probability of chemical reaction based on the use of the probability density function for the mixture fraction.

• 한국농공학회지
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• 제45권4호
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• pp.137-143
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• 2003

The initial condition of $\Delta \sigma_3 \;=\; \Delta u$ is used for analyzing the time dependent behavior of ground. This is based on the concept that the coefficient of pore water B is the unity on the condition of saturation. but some measured consolidation data in the field showed that the pore water pressure was not dissipated as time elapsed but it was maintained constant value or it's dissipation rate was slower than that of the predicted. and so the measured data of pore water pressure was not consistent with that of settlement. In this study, the rheological model for the pore water pressure behavior on undrained condition was induced and compared with the experiment data of the literature. The result showed that the suggested model was consistent well with the result of experiment, but the suggested model could not explain the effect of the decrease of void ratio according to consolidation.

• 한국농공학회지
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• 제45권1호
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• pp.83-90
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• 2003

In order to offer some fundamental data for recycling the excavated rocks, the component and mechanical characteristics was investigated for the excavated rocks, by means of X-ray diffraction analysis, strength test, slacking test and abrasion test were performed. It appeared that the unconfined compressive strength and the elastic wave velocity were the highest in the sound rock. The dissipation rate by stability tests was found to be high in the case of the slacking index of 98% because of more bedding and more clay minerals. The apparent specific gravity of some crushed aggregate was decreased because they included easily weathered minerals while both the absorption and the abrasion were increased. The results in this study were expected to be useful for recycling the excavated rocks as a concrete aggregate.

• International Journal of Automotive Technology
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• 제7권2호
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• pp.129-137
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• 2006

The representative interactive flamelet(RIF) concept has been applied to numerically simulate the combustion processes and pollutant formation in the HSDI diesel engine. In order to account for the spatial inhomogeneity of the scalar dissipation rate, the eulerian particle flamelet model using the multiple flamelets has been employed. The vaporization effects on turbulence-chemistry interaction are included in the present RIF procedure. the results of numerical modeling using the rif concept are compared with experimental data and with numerical results of the widely-used ad-hoc combustion model. Numerical results indicate that the rif approach including the vaporization effect on turbulent spray combustion process successfully predicts the ignition delay characteristics as well as the pollutant formation in the HSDI diesel engines.

• 반도체디스플레이기술학회지
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• 제3권4호
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• pp.29-32
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• 2004

Fully depleted Silicon-on-Insulator (FD-SOI) devices lead to better electrical characteristics than bulk CMOS devices. However, the presence of a thin top silicon layer and a buried SiO2 layer causes self-heating due to the low thermal conductivity of the buried oxide. The electrical characteristics of FDSOI devices strongly depend on the path of heat dissipation. In this paper, we present a new three-dimensional (3-D) analysis technique for the self-heating effect of the finger-type and bar-type transistors. The 3-D analysis results show that the drain current of the finger-type transistor is 14.7% smaller than that of the bar-type transistor due to the 3-D self-heating effect. We have learned that the rate of current degradation increases significantly when the width of a transistor is smaller that a critical value in a finger-type layout. The current degradation fro the 3-D structures of the finger-type and bar-type transistors is investigated and the design issues are also discussed.

• 한국해양공학회지
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• 제2권1호
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• pp.163-169
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• 1988

A beach nourishment method can be used as one of the beach. The beach nourishment is affected br a natural condition and an artificial condition; a natural condtion include conditions of bottom slope, diameter of bottom materials and wave, and an artificial condition include deposit position, method, diameter and quantity of the nourishing sand. To obtain and the best diameter of the nourishing sand a two-dimensional hydraulic model test, which simulates the erosional beach, has been accmplished. In this study the protection of the beach erosion can be maximized when the nourishing sand of 0.84mm in diameter, which is about 2.5-3.5 times of the natural bottom materials in diameter.