• Journal of the Korean Mathematical Society
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• v.43 no.5
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• pp.1081-1098
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• 2006

Mathematical analysis is made on a mesh free method for the compressible Euler equations. In particular, the Moving Least Square Reproducing Kernel (MLSRK) method is employed for space approximation. With the backward-Euler method used for time discretization, existence of discrete solution and it's $L^2-error$ estimate are obtained under a regularity assumption of the continuous solution. The result of numerical experiment made on the biconvex airfoil is presented.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.513-518
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• 2006

An investigation of the transport properties of polysilicon TFTs, using sequential laterally solidified, SLS, material, is presented. This material has a location controlled distribution of grain boundaries, GBs, which makes it particularly useful for the analysis of their influence on the performance of polysilicon TFTs, and to address the issue of the role of spatially localised trapping states. The experimental results were analyzed by using numerical simulations, and the effective medium approximation was compared with a discrete grain model.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.5
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• pp.491-501
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• 2011

We performed numerical simulation using a DPM (discrete phase model) to identify the optimal operation ranges in two representative PM burners widely used in domestic 500-MW pulverized coal-fired power plants. Recently there has been an increased utilization of low-cost coals such as sub-bituminous coal. We investigate the effects of coal blends on the distribution ratio of coal to air by varying the mass flow rates of pulverized coal and primary air and the particle size. We present and discuss optimal conditions for the distribution ratio of coal to air in PM burners.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.7
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• pp.1191-1202
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• 1994

We numerically investigate a stable propagation regime of soliton pulse trains in fibers with periodically copensated loss by lumped optical amplifiers. When amplification solition pulses is 1.2~1.5 and the minimum soliton separation normalized by the soliton width becomes about 6. In cases of L=50[km], the allowable range of A is 1.5~1.7 under =6. The maximum allowable variation of the loss compensation in each lumped amplifier becomes +-2% of the fiber loss when L=50[km], A=1.6, and =6. Generally, the allowable rages of the soliton amplitude A and amplifier gain are inversely proportional to the amplification period L.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.9
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• pp.883-890
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• 2011

A numerical study was conducted to determine the optimal design for a vehicle vacuum pump. The degree of vacuum was examined for different design factors such as the angle of vanes, number of vanes, angle and position of the pump inlet-outlet pipe, and angular rotational speed of vanes. The results show that there is a little difference in the degree of vacuum when the angle of vanes are changed, but an angular change in the outlet pipe reduces the pump loss. As the rotational speed is increased, the mass flow rate increases, but a high rotational speed does not result in the maximum degree of vacuum. In addition, when the number of vanes is increased, the scattering range of mass flow rate decreases and pressure drop is abated.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.4
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• pp.99-106
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• 2009

This research was to estimate quantitative infiltration volume of permeable block which is one of runoff reduction infiltration facilities. In this research, the permeable block experiments estimating infiltration volume for 50, 100, 150, 200 mm/hr rainfall intensity were carried out and hydraulic experiments results were compared with numerical simulation output to produce feasibility of numerical simulation. Final infiltration capacity analysis of permeable block hydraulic experiments reveals that every estimated infiltration volume before runoff beginning was above approximately 300.0 l despite rapid reduction of infiltration ratio and runoff initiation time were occurred in every rainfall intensity. Statistical calculation for coefficient of determination based on cumulative infiltration volume of hydraulic experiment and numerical simulation resulted in a high correlationship as $0.958{\sim}0.996$.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.13-18
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• 2009

Flight vehicles such as wheel wells and bomb bays have many cavities. The flow around a cavity is characterized as an unsteady flow because of the formation and dissipation of vortices brought about by the interaction between the free stream shear layer and the internal flow of the cavity. The resonance phenomena can damage the structures around the cavity and negatively affect the aerodynamic performance and stability of the vehicle. In this study, a numerical analysis was performed for the cavity flows using the unsteady compressible three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation with Wilcox's turbulence model. The Message Passing Interface (MPI) parallelized code was used for the calculations by PC-cluster. The cavity has aspect ratios (L/D) of 2.5 ~ 7.5 with width ratios (W/D) of 2 ~ 4. The Mach and Reynolds numbers are 0.4 ~ 0.6 and $1.6{\times}106$, respectively. The occurrence of oscillation is observed in the "shear layer and transient mode" with a feedback mechanism. Based on the Sound Pressure Level (SPL) analysis of the pressure variation at the cavity trailing edge, the dominant frequencies are analyzed and compared with the results of Rossiter's formula. The dominant frequencies are very similar to the result of Rossiter's formula and other experimental data in the low aspect ratio cavity (L/D = ~ 4.5). In the large aspect ratio cavity, however, there are other low dominant frequencies due to the leading edge shear layer with the dominant frequencies of the feedback mechanism. The characteristics of the acoustic wave propagation are analyzed using the Correlation of Pressure Distribution (CPD).

• Korean Journal of Plant Taxonomy
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• v.31 no.4
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• pp.359-373
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• 2001

One of Korean Typha species has been used two scientific names, T. angustifolia L. and T. angustata Bory et Chaubard without taxonomic examinations. Typha angustifolia has a longer females flowers than bracteoles and equal length of bracteoles and hairs in female flowers whereas T. angustata has equal length of female flowers and bracteoles and longer bracteloes than hairs in female flowers. In this study, the pattern of morphological variation of T. angustifolia in Korea is examined using numerical analysis to determine their taxonomical identities. Univariate analysis using morphological characters such as female flower length/bracteole length and bracteole lengh/hair length reveals that Korean T. angustifolia is composed of one group. The result of principal components analysis shows that Korean T. angustifolia is closely related to T. angustifolia distributed in Japan, Russia, and USA. Therefore, T. angustifolia L. (in Korea) is suggested as a legitimate scientific name.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.549-556
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• 2010

In general, materials that can be used to form elastic pads, such as urethane and rubber, are often used in flexible forming processes by inserting the pads between a blank and flexible die for smoothing the forming surface that is formed by a reconfigurable die. In this study, the effects of the elastic pad on formability in the flexible forming process for sheet metals are investigated by performing numerical simulations. In the simulation, the hyperelastic material model is used, where the urethane elastic pads serve as elastic cushions. Case studies are carried out for elastic materials with different hardness values and thicknesses. The results are used to evaluate formability by comparing the configuration of the deformed blank and its major cross-sectional profiles. It is verified that the elastic pad used in the flexible forming process for sheet materials should be hard and that its thickness should be chosen appropriately.

• Advances in aircraft and spacecraft science
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• v.4 no.6
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• pp.679-699
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• 2017

The aim of this study is to perform a finite element analysis of the Von Mises stresses distribution in the adhesive layer and of the J-Integral for a damaged plate repaired by a composite patch. Firstly, we study the effect of the fiber orientation, especially the position of the layers that have orientation angle different of $0^{\circ}$ from the first layer which is in all cases of our study oriented at ($0^{\circ}$) on the J-Integral. Secondly, we evaluate the effects of the mechanical properties of the patch and the use of a hybrid patch on the reduction of stresses distribution and J-Integral. The results show clearly that the stacking sequence for the composite patch must be selected to absorb optimally the stresses from the damaged area and to position the various layers of the composite under the first layer whose fibers orientation will remain in all cases equal to $0^{\circ}$. The use of a hybrid composite reduces significantly the J-Integral and the stresses in both damaged plate and the adhesive layer.