• 대한전자공학회논문지
• /
• 제26권11호
• /
• pp.1644-1651
• /
• 1989

In this paper, a two-dimensional numerical analysis of HEMT's with gate length of 0.6um is performed. In this case, Control Volume Formulation method which has been used in the analysis of heat transfer and fluid flow is used as a numerical method. As a mobility model, empirical formula including the velocithy overshoot phenomena is used instead of two-piece mobility model. The results obtained from this numerical analysis(i.e., the region in which cahnnel is formed, the strength of electric field in the channel, the distribution of potential, and the distribution of electron concentration etc.)are in good agreement with the previous analytic results. And our results also show the parasitic MESFET's operation in the range of the high gate voltage.

• 대한기계학회논문집B
• /
• 제29권11호
• /
• pp.1173-1181
• /
• 2005

The cooling effect of a mobile phone using PCM(Phase Change Material) module has been numerically investigated. A transient three-dimensional numerical analysis of heat and fluid flow with natural convection is performed in this study. Governing conservation equations for mass, momentum and energy are solved by an implicit finite volume method. An enthalpy-porosity technique has been used for modeling of the melting process. Two different ways of placing the PCM module are considered. One is to place a PCM module between the substrate and battery pack, and the other is to place a PCM module between MCM(multichip module) and battery pack. Three different types of PCMs are used to predict the performance of PCM. The results show that passive cooling with PCM can reduce the temperature rise and the effect of natural convection in PCM module considered in this study is negligible.

• 대한기계학회논문집B
• /
• 제31권3호
• /
• pp.273-282
• /
• 2007

Numerical calculations are carried out for the natural convection induced by temperature difference between a cold outer square cylinder and a hot inner circular cylinder. A two-dimensional solution for unsteady natural convection is obtained, using the immersed boundary method (IBM) to model an inner circular cylinder based on finite volume method, for different Rayleigh numbers varying over the range of $10^4\;to\;10^6$. The study goes further to investigate the effect of an inner cylinder location on the heat transfer and fluid flow. The location of inner circular cylinder is changed vertically along the center-line of square enclosure. The number, size and formation of cell strongly depend on Rayleigh number and the position of inner circular cylinder. The changes in heat transfer quantities have been presented.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2000년도 춘계학술대회논문집
• /
• pp.1429-1436
• /
• 2000

Suction muffler is one of the important component of a compressor for low noise level and high efficiency. The suction muffler which has the complicated flow path gives the higher transmission loss of sound, but lower efficiency of compressor results from the superheating effect and flow loss in suction flow path. It is shown that the computational analysis of fluid dynamics are very popular methods for designing of high performance and low noise suction muffler. To reduce the thermodynamic and flow loss in suction process, the flow path of suction muffler was estimated by FVM(Finite Volume Method) and verified by experiments. And to enlarge the transmission loss of sound, the acoustic properties inside the suction muffler was analyzed by FEM(Finite Element Method) and experiments. The smart muffler which gives a good efficiency and low noise character was developed by using those methods, and the effect was evaluated in compressor by experiment.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2005년도 추계학술대회 논문집
• /
• pp.269-272
• /
• 2005

For the three decades, the mold-filling of injection molding process was modeled as Hele-Shaw model. However, this model can not consider the 3D effect. In this paper, numerical simulations of three dimensional mold-filling during the filling phase were performed. The governing equations were discretized by segregated finite element method, which used equal order interpolation for pressure and velocity fields. The iterative linear equation solver (JCG, SOR) was employed for the solution of the momentum and pressure equations. Volume of Fluid (VOF) was employed for the melt front advancement. To check the validity of the numerical results, the results were compared with the experimental ones. The agreements between the experiment and the numerical results were found to be satisfactory.

• 대한기계학회논문집
• /
• 제12권4호
• /
• pp.813-824
• /
• 1988

본 연구에서는 플라즈마 키홀 용접 시의 열 및 물질 유동을 규명함으로써 용 접부 조직변화 예측과 더불어 용접부 형상설계, 열응력 계산 등의 기본자료를 제시하 여 전체적인 용접부 품질성능을 향상시키는데 목적이 있다.

• 대한인간공학회지
• /
• 제11권1호
• /
• pp.67-79
• /
• 1992

Cardiac systolic time intervals (STLs) and Heather index (HI) were used to access changes in left ventricular function of six male subjects exposed to postural changes,$0^{\circ}C$, ${\pm}2^{\circ}C$, ${\pm}45^{\circ}C$, ${\pm}90^{\circ}C$, Significant prolongation of the pre-ejection period (PEP) and PEP/ LVET ratio, shortening of the left ventricular ejection time (LVET), STI, HI and $1/PEP^{2}$were observed during exposure to both $+45^{\circ}C $ and $+90^{\circ}C $But the values measured during $-45^{\circ}C $ and$-90^{\circ}C $ were reversed. Changes in fluid shift, filling volume, preload, after load and sympathetic activities may account for the observed findings. Early response of cardiac foctions was recorded using impedance cardiography. This method is very simple but accurate. Thus it will be useful in this aerospace and work physiology. In conclusion, STIs appear to provide reliable noninvasive method for examining changes of cardiac function during exposure to postural changes.

• 한국화재소방학회논문지
• /
• 제6권1호
• /
• pp.17-22
• /
• 1992

We have derived the general transfer equation for governing the continuity, energy transfer, mass and momentum transfer, and turbulent energy dissipation rate within the fire compartment which has the 800t fire source at the center of the floor. The governing transfer equations have been descretized using the finite volume approach and numerically experimented under the SIMPLE algorithm. In order for the SIMPLE algorithm approach to be physically reliable, the test results are compared with those of Morita's SOR Method using Conjugate Residual Method and found to be close to physical values though the computational convergence time still remains to be upgraded. The treatment of source terms in the system of finite difference equations has been critical in order to converge the governing equations within the appropriate time steps. The criteria of convergence allowance for the whole domain have been checked and the sudden change of the non-linear effects from the source term have been avoided. The criteria has been allowed to be for 5$\times$10$^{-5}$ .

• Journal of Advanced Research in Ocean Engineering
• /
• 제4권4호
• /
• pp.204-216
• /
• 2018

A ship repeatedly face free surface under rough sea conditions owing to relative motion with wave encounter. The impact pressure is transferred to the hull structure and causes structural damage. In this study, the bow flare slamming load of a container ship is estimated using computations fluid dynamics (CFD) and prescript formula according to various classifications. It is found that the bow flare slamming load calculated by the formulas of the common structural rule and ABS tends to be similar to the CFD results.

• Tribology and Lubricants
• /
• 제22권2호
• /
• pp.66-72
• /
• 2006

Leakage reduction through annular type labyrinth seals of steam turbine is necessary for enhancing their efficiency and the precise prediction method of seal leakage is needed. In this study, numerical analysis for leakage prediction of the combination-type-staggered-labyrinth seal has been carried out using FLUENT 6 which is commercial CFD (Computational Fluid Dynamics) code based on FVM (Finite Volume Method) and SIMPLE algorism. The present CFD results are verified with the theoretical analysis based on Bulk-flow concept which has been mainly used in predicting seal leakage. Comparing with the result of Bulk-flow model analysis, the leakage result of CFD analysis shows good agreement within 7.1% error.