• Advanced Composite Materials
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• v.18 no.2
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• pp.135-152
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• 2009

Liquid molding processes, such as resin transfer molding, involve resin flow through a porous medium inside a mold cavity. Numerical analysis of resin flow and mold filling is a very useful means for optimization of the manufacturing process. However, the numerical analysis is quite time consuming and requires a great deal of effort, since a separate numerical calculation is needed for every set of material properties, part size and injection conditions. The efforts can be appreciably reduced if similarity solutions are used instead of repeated numerical calculations. In this study, the similarity relations for pressure, resin velocity and flow front propagation are proposed to correlate another desired case from the already obtained numerical result. In other words, the model gives a correlation of flow induced variables between two different cases. The model was verified by comparing results obtained by the similarity relation and by independent numerical simulation.

• Journal of the Optical Society of Korea
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• v.9 no.4
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• pp.140-144
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• 2005

In this paper we have investigated the guiding properties of photonic crystal fibers (PCFs) with a square-lattice of air-holes in the cladding. We have shown numerical results of PCFs with various air hole sizes and hole-to-hole spacings over a wide wavelength range. The group velocity dispersion, effective area and effective refractive index of PCF have been calculated numerically. The waveguide dispersion has greatly affected the group velocity dispersion when hole-to-hole spacing is about $1{\mu}m$. The effective area is quite flat over the wide spectral range whether the hole-to-hole spacing is large or ratio of diameter to pitch is large. From the field distribution, we found that the field is tightly confined within the core region of PCF when the pitch is $3{\mu}m$ and the air-filling fraction is 0.9.

• Korean Journal of Agricultural Science
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• v.25 no.2
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• pp.260-270
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• 1998

The field tests were performed to suggest the rational method for stability evaluation of soft clay. The behavior of settlement-displacement obtained by field monitoring system was to compare and analyze the results of the observationed method, and to investigate the complex behavior of soft clay with filling height. The results of this study are summarized as follows. 1. The horizontal displacement was suddenly increased when physical properties of soft clay showed maximum values and the part of the turning point. The values of these properties were available to the fundamental data for stability evaluation. The shear deformation appeared that difference of the horizontal displacement was maximum values. 2. Although the stability of embankment by step filling showed the unstable part over the failure standard line, the embankment was confirmed stable. So the evaluation of the stability of embankment is reasonable to use the inclination of curve than failure standard line. 3. The horizontal displacement and relative settlement were increased as same ratio at improvement ground. Estimation of shear deformation using Terzaghi's modified bearing capacity should consider the relations of embankment load and undrained shear strength at nonimprovement ground, and minimum safety factor is recommended to use larger than 1.2. 4. Excess pore water pressure was increased with increasing of filling height and decreased with maintain the filling height. The embankment was unstable when filling height was exceed the evaluation standard line, and the behavior of excess pore water pressure and horizontal displacement could use as a standard of judgement of the filling velocity control because their behavior were agree with each other.

• Transactions of Materials Processing
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• v.3 no.1
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• pp.97-109
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• 1994

Closed-die forging of the spur gears with circular are fillet has been analyses by using the upper-bound method. A kinematically admissible velocity field has been developed, wherein, the tooth profile consists of the involute curve and the circular arc fillet. In the analysis, the deformation regions have been divided into eight zones. A constant frictional stress has been assumed on the contacting surfaces Utilizing the formulated velocity field, numerical calculations have been carried out to investigate the effects of various parameters, such as module, number of teeth, addendum modification coefficient and friction factor, on the relative forging pressure of spur gears. As the result of numerical calculations, the relative forging pressure does not change so much against the variation of module. On the other hand, the relative forging pressure increases at the final filling stage as the addendum modification coefficient increases.

• Fire Science and Engineering
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• v.11 no.4
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• pp.3-14
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• 1997

The smoke filling process for the atrium space containing a fire source is simulated using two types of deterministic fire model : Zone model and Field model. The zone model used is the CFAST(version 1.6) model developed at the Building and Fire Research Laboratories, NIST in the USA. The field model is a self-developed frie field model based on Computational Fluid Dynamic (CFD) theories. This article is focused on finding out the smoke movement and temperature distribution in atrium space which is cubic in shape. For solving the liked set of velocity and pressure equation, the PISO algorithm, which strengthened the velocity-pressure coupling, was used. Since PISO algorithm is a time-marching procedure, computing time si very fast. A computational procedure for predicting velocity and temperature distribution in fire-induced flow is based on the solution, in finite volume method and non-staggered grid system, of 3-dimensional equations for the conservation of mass, momentum, energy, species and so forth. The fire model i.e Zone model and Field model predicted similar results for clear heights and the smoke layer temperature.

• Journal of Biosystems Engineering
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• v.23 no.6
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• pp.583-590
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• 1998

This study was performed to determine the kinetic friction coefficient bulk density, dynamic and static angle of repose, and terminal velocity of the chopped rice straw in the moisture range of 8~23%, which could be used for better design and operation of the processing machinery and handling facilities. Friction coefficient was determined from the horizontal traction force measured by pulling the container holding the mass of rice straw on the various plate materials. Bulk density was measured with an apparatus consisting of a filling funnel and a receiving vessel. Dynamic angle of repose was calculated from the photos of bulk samples piled by gravity flow on a circular platform. Static angle of repose was determined by measuring the side angle of the bulk material which was left in the cylindrical container after natural discharge of the bulk sample through a circular hole in the bottom plate. Kinetic friction coefficients of rice straw on the PVC, mild steel, stainless steel, and galvanized steel were in the range of 0.303~0.434, 0.222~0.439, 0.204~0.448, and 0.206~0.407, respectively. and indicated linear increase with moisture content. The effects of moisture change on the friction coefficients were in the order of PVC, mild steel, galvanized steel, and stainless steel. Bulk density, dynamic and static angle of repose, and terminal velocity were in the range of 56.8~60.3 kg/m$^3$, 41.4~45.9$^{\circ}$, 94.4~100.8$^{\circ}$, and 1.07~4.48 m/s, respectively, and were increased linearly with the moisture content.

• 한국금형공학회:학술대회논문집
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• 2008.06a
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• pp.163-166
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• 2008

Injection molding operation consists of filling, packing, and cooling phase. The highest pressure is involved during the packing phase among the operation phases. Cavity pressure depends upon velocity to pressure switchover time and magnitude of packing pressure. The cavity pressure is directly related to stress concentration in the cavity of mold. Thus the observation and control of cavity pressure is very important to prevent mold cracking. In this study, cavity pressures were observed for operational conditions using the commercial CAE software,Moldflow. Operational conditions were velocity to pressure switchover time and packing pressure. Cavity pressures were also measured directly during injection molding. Simulation and experimental results showed good agreement.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.8
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• pp.63-72
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• 1995

Closed-die forging of spur gears with hollow cylindrical billet has been analysed by using the upper-bound method. A kinematically admissible velocity field has been developed, wherein, an involute curve has been introduced to represent the forging die profile. In the analysis, the deformation region has been divided into nine zones. A constant frictional stress has been assumed on the contacting surfaces. Utilizing the formulated velocity field, numerical calculations have been carried out to investigate the effects of various parameters, such as module, number of teeth and friction factor, on the forging of spur gears. Hardness and accuracy of forged gears are measured. The following results have been obtained: (1) It is verified that an axisymmetric deformation zone exists between root circle and center of gear through forged gears. (2) The average relative forging pressure is predominantly dependent on the number of teeth and increases near the final filling stage as the addendum modification coefficient increases. (3) Close agreement was found between the predicted values of forging load and those obtained from experimental results.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2005.09a
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• pp.67-88
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• 2005

Mold-Flow 3 Die Stack CSP of Mold array packaging with different Gate types. As high density package option such as 3 or 4 die stacking technologies are developed, the major concerning points of mold related qualities such as incomplete mold, exposed wires and wire sweeping issues are increased because of its narrow space between die top and mold surface and higher wiring density. Full 3D rheokinetic simulation of Mold flow for 3 die stacking structure case was done with the rheological parameters acquired from Slit-Die rheometer and DSC of commercial EMC. The center gate showed severe void but corner gate showed relatively better void performance. But in case of wire sweeping related, the center gate type showed less wire sweeping than corner gate types. From the simulation results, corner gate types showed increased velocity, shear stress and mold pressure near the gate and final filling zone. The experimental Case study and the Mold flow simulation showed good agreement on the mold void and wire sweeping related prediction. Full 3D simulation methodologies with proper rheokinetic material characterization by thermal and rheological instruments enable the prediction of micro-scale mold filling behavior in the multi die stacking and other complicated packaging structures for the future application.

• Composites Research
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• v.12 no.1
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• pp.11-18
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• 1999

The compression molding is widely used in the automotive industry to produce products that are large, thin, lightweight and stiff. The molded product is formed by squeezing a fiber-reinforced plastic composites. During a molding process of fiber reinforced thermoplastic composites, control of filling patterns in mold, orientation and distribution of fibers are needed to predict the effects of molding parameters on the flow characteristics. It is the objective of this paper to develop an isothermal compression molding simulation that can handle both thin and thick charges and motion of the flow front, and can predict pressure distributions and accurate velocity gradients. The composites are treated as an incompressible Newtonian fluid. The effects of slip parameter $\alpha$ and extensional/shear viscosity ratio $\zeta$ on the mold filling parameters are also discussed.