• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.20-24
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• 2011

In this paper, numerical simulation of cavitation flow for modified NACA66 hydrofoil was made by using the multi-phase RANS equation based on pseudo-compressibility. The Homogeneous mixture model comprised of the mixture continuity, mixture momentum and liquid volume fraction equations was utilized. A vertex-centered finite-volume method was used in conjunction 2nd-order Roe's FDS to discretize the inviscid fluxes. The viscous fluxes were computed based on central differencing The Spalart-Allmaras one equation model was employed for the closure of turbulence. Reasonable agreements were obtained between the calculation results and the experiment for pressure coefficients on the hydrofoil surface.

• Korean Journal of Mathematics
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• v.20 no.3
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• pp.361-369
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• 2012

We get a theorem which shows the existence of at least six solutions for the semilinear wave equation with nonlinearity crossing three eigenvalues. We obtain this result by the variational reduction method and the geometric mapping defined on the finite dimensional subspace. We use a contraction mapping principle to reduce the problem on the infinite dimensional space to that on the finite dimensional subspace. We construct a three-dimensional subspace with three axes spanned by three eigenvalues and a mapping from the finite dimensional subspace to the one-dimensional subspace.

• Journal of applied mathematics & informatics
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• v.24 no.1_2
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• pp.231-243
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• 2007

The existence of solutions of a class of two-point boundary value problems for higher order differential equations is studied. Sufficient conditions for the existence of at least one solution are established. It is of interest that the nonlinearity f in the equation depends on all lower derivatives, and the growth conditions imposed on f are allowed to be super-linear (the degrees of phases variables are allowed to be greater than 1 if it is a polynomial). The results are different from known ones since we don't apply the Green's functions of the corresponding problem and the method to obtain a priori bound of solutions are different enough from known ones. Examples that can not be solved by known results are given to illustrate our theorems.

• Journal of the Korean School Mathematics Society
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• v.3 no.2
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• pp.59-67
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• 2000

Two groups of students, who are the students in the natural science course of high school in Korea, learned the equation of figure in space (point, line, plane) to understand more effectively with two different textbooks. One group was taught with the textbook used now in most high schools and the other group was taught with the textbooks systematized by associating old concept with new concept. The results are as follows : 1) We need understand the basic concept of vector plainly and flexibly to apply it to the solution of problems. 2) It helps students understand new concepts how we should establish the concept about point, line and plane in space by applying the concept about those on XY plane, 3) It is very effective in understanding the new knowledge system more easily to analyze the existent concepts and to arrange them systematically for efficient understanding of new concepts. 4) The texts which consist of contents organized by basic concepts improve students' learning ability.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.04b
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• pp.445-450
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• 1995

This paper deals with conversion from STL file to Slice cross-sectional information for Stereolithography. The STL file consist of three vertices of triangle and normal vectors in order to represent three dimension shape, but It is very difficult to convert STL file intoSlice file directly, because of file size from one Mbyte to tens of Mbytes. So, The system is accomplished data flow such as neutral.dat, .SL1, .SL2, .SL3, and .SLC file. The data processing is as follows: 1. Create a neutral file including common information. 2. Modify STL file within effective scope of SLA. 3. Calculate a point of intersection between plane equation and line equation. 4. Sort z values by increasing order. 5. Search closed loop by method of singlylinked linear list. The system is developed by using Borland C++ 3.1 compiler in the environment of Pentium PC. We get a satisfactory prototype as a result of application about a lot of household electrical appliances.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.04a
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• pp.304-307
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• 2005

A numerical modelling method using a backward-in-time advection dispersion equation is introduced in assessing the vulnerability of groundwater to contaminants as an alternative to classical vulnerability mapping methods. The flux and resident concentration measurements are normalized by the total contaminants mass released to the system to provide the travel time probability density function and the location probability function. With the results one can predict the expected travel time of a contaminant from up stream location to a well and also the relative concentration of the contaminant at a well. More specific groundwater vulnerability can be mapped by these predicted measurements.

• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.25-28
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• 2008

Steam reforming reaction is a matured technology to get hydrogen from hydrocarbon fuels compared with other reforming reactions such as partial oxidation(POX), autothermal reforming(ATR). It is so endothermic that it needs heat source to activate the reaction. Due to the reaction characteristics, heat transfer limitation phenomena generally occur in the steam reformer. As one of new ideas, the effect of discontinuous gas feeding is investigated based on heat transfer characteristics. The new operating method is usually favorable at high GHSV region(i.e. over $10,000h^{-1}$). In order to numerically simulate the physical issues, numerical approach is adopted based on heterogeneous reaction model, two-equation model in energy equation, and other constitutive models in porous media.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1747-1755
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• 2008

Design of the reinforced roadbed thickness is concerned with safe operation of trains at specified levels of speed, axle load and tonnage. There are two methods for evaluating it. One is using an experimental equation and the other is using elastic theory with considering axle load, material properties of subsoils and allowable elastic settlement. Multi-layered theory is used to determine reinforced roadbed thickness by RTRI. Although their reinforced roadbed thickness is designed with an objective of achieving a minimum standard 2.5mm of settlement on the subgrade surface, it is hardly applied to real design. Li(1994) has suggested the experimental model which design approach is to limit plastic strain and deformations for the design period. It is worth due to adopting soil equivalent number of repeated load application. Moreover, it has been a more advanced method than existing design methods because including resilient modulus of subsoil beneath track, soil deviator stress caused by train axle loads and MGT. In this paper, it is analyzed under domestic track conditions to estimate the reinforced roadbed thickness with different soil types.

• Design & Manufacturing
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• v.14 no.3
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• pp.31-36
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• 2020

In injection molding processes, the property of molten resin should be characterized accurately. Among several properties, the PvT state is the most important one, since it affects the shrinkage, warpage, molded weight, and the part density. Thus, the PvT data is crucial to the simulation of the injection molding process. This work shows how such a measurement can be performed for a semi-crystalline and amorphous polymers. The PvT measurement has been conducted using a capillary rheometer using a suitable accessory that blocks the capillary. The results have shown that the PvT data can be obtained using such a rheometer and then the PvT coefficients of the Tait equation can be reached.

• Journal of Electrical Engineering and Technology
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• v.9 no.4
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• pp.1360-1364
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• 2014

In this paper, RCS characteristics on defect pattern of crossed dipole slot FSS having a finite size have been analyzed. To analyze RCS, we applied the electric field integral equation analysis which applies BiCGSTab algorithm with iterative method and uses RWG basis function. To verify the validity of this paper, RCS of PEC sphere has been compared to the theoretical results and FSSs with defect patterns are fabricated and measured. As defect patterns in FSS, missing one column, missing some elements, and discontinuity in surfaces are simulated and compared with the measurement results. Resonant frequency shifts in pass band and changes in bandwidth are observed. From the results, precisely predicting and designing frequency characteristics over defect patterns are essential when applying FSS structures such as FSS radomes.