• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.2 s.233
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• pp.205-213
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• 2005

The drop ejection process from a micro nozzle is investigated by numerically solving the conservation equations for mass and momentum. The liquid-gas interface is tracked by a level set method which is extended for two-fluid flows with irregular solid boundaries. Based on the numerical results, the liquid jet breaking and droplet formation behavior is found to depend strongly on the pulse type of forcing pressure and the contact angle at the gas-liquid-solid interline. The negative pressure forcing can be used to control the formation of satellite droplets. Also, various nozzle shapes are tested to investigate their effect on droplet formation.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.32 no.1
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• pp.85-93
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• 2009

In this paper, the geometric design for the body of a 3"-PFA-lined plug valve is concerned, and body model which has less deformed PFA-resin after infection molding process is proposed. A CAE software is used to simulate the deformation due to heat in cooling. To reduce the deformation, some small shapes are added to PFA-resin surfaces related on wall of the valve housing. And thermal stress simulation with FEM methodology is followed after that. Also, the 3D-CAD package is used during the design processes. In this study, I tried to present the possibility to use the FEM analysis in the solid modeling process. So, the design engineer will be able to use analysis package effectively on his job within the limited range.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.37-44
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• 2000

Numerical investigation is made to study the effects of natural convection on the formation of macrosegregation of a Pb-Sn alloy solidification process in a 2-D confined rectangle mold. The governing equations are calculated using previous continuum models with SIMPLE algorithm doring the solidification process. In addition. to track the solid-liquid interface with time variations. the moving boundary condition Is adopted and irregular interface shapes are treated with Boundary-Fitted Coordinate system. As the temperature reduce from the liquidus to the solidus, the liquid concentration of Sn. the lighter constituent, increases. Then the buoyancy-driven flow due to temperature and liquid composition gradients, called thermosolutal convection or double diffusion, occurs in the mushy region and forms the complicated macrosegregation maps. Related to this phnomena, effects on the macrosegregation formation depending on the cooling condition and gravity values are described.

• Proceedings of the KOSOMBE Conference
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• v.1998 no.11
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• pp.273-274
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• 1998

We construct a volume whose boundary is a tetrahedron with triangular faces intersecting the cutting planes along the given contours. This volume is obtained by calculating the Delaunay triangulation slice by slice, mapping 2D to 3D as tetrahedron. Also, eliminate extra-voronoi skeleton and non-solid tetrahedron. In this paper, we propose new method to eliminate non-solid tetrahedron based on the modified extra-voronoi skeleton path. This method enable us to do a compact tetrahedrisation and to reconstruct complex shapes.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.10
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• pp.2690-2698
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• 1995

Fuel atomization and mixture formation in an gasoline engine has influence on the engine performance and pollutant emission. The throttle valve installed in an intake system plays a greater role in control of mixture quantity in accordance with engine drive condition. In this study, the characteristics of secondary atomization developed at the downstream of the valves were observed using an image processing method. Two major kinds of valves, solid and perforated ones, are chosen in order to compare the valve performance with the experimental parameters of air flow rate, valve opening angle, and valve shapes. For the perforated valve, we can obtain the relatively small sized droplets, and nearly uniformed and dense distributed sprays with low loss coefficient than for the solid valve.

• Research in Mathematical Education
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• v.18 no.1
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• pp.41-54
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• 2014

This study investigated the visual-mental capability of pre-service and in-service mathematics teachers as well as academicians making a career change to mathematics teachers with regard to manipulations of two geometric shapes (from 2- to 3-dimensional). Moreover, it investigated whether there are differences between the visual-mental capability of these participant groups. Findings illustrate that most of the participants demonstrate an adequate visual capability relating to the task dealing with a cube. Conversely, very low percentage of participants manifested a visual-mental capability in a task requiring the identification of a solid resulting from rotation of a square page, whose diagonal serves as the rotation axis. The study indicates that learners' high visual view should be developed in order to enhance their visual-mental capability.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2000.04a
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• pp.229-235
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• 2000

A study on the improvement of anti-abrasion nature of curved ducts for high-velocity gas-solid flow which are typically equipped in a coal-burned steam power plant has been investigated numerically and experimentally. To reduced the abrasion of pipe by particle, we have tried to form the vortex flow field in the region where flow changes its direction , modelled with two different shapes. 22.5$^{\circ}$and 90$^{\circ}$ elbows. the governing equations for three -dimensional , turbulent flow fields are discretized by FVM and solved bySIMPLE algorithm . From the numerical analysis, the new designed elbows for reducing abrasion have been developed. Numerical results are compared with the experimental abrasion data which are obtained from one of the operating coal burned steam power plants in Korea. Comparison of these results show that the developed elbows have much more durability than the original one.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.333-338
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• 1997

A hollow crankshaft is considered as part of an effort to reduce the weight of the automobile powertrain. Since the resulting mass reduction alters both the inertia and stiffness properties of the crankshaft, the vibration characteristics of the hollow crankshaft needs to be investigated in comparison with the original solid crankshaft. The crankshafts are modeled by 38 lumped mass and stiffness elements, in which the dynamic parameters for each lumped element are obtained by the finite element calculation. The fluid-film bearings supporting the crankshaft give rise to linear spring and damping elements that can be derived from the hydrodynamic bearing model. The transfer matrix method is applied to yield the natural frequencies and mode shapes of the crankshaft vibration. The natural frequencies of the hollow crankshaft are founded to be greater than that of the solid crankshaft, and the incorporation of the bearing stiffness tends to accentuate the difference.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.249-252
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• 2011

고체로켓추진기관의 추력조절을 위해 핀틀 기술이 사용된다. 아직까지 핀틀 유동에 대해 근본적인 물리적 이해를 돕는 연구가 공개되지 않아, 이 연구에서 다양한 형상의 needle형 핀틀에 따른 유동구조에 대한 수치적 연구를 진행하였다. 2차원 축대칭, 압축성을 고려하여, 상용 열유체 해석 프로그램인 FLUENT 6.2를 사용하여 해석을 수행하였다. 난류 모델을 검증하기 위해 기 수행된 실험 결과와 비교하였다. 핀틀 각도(tip angle)가 작아질수록 노즐에서 유동 박리점이 하류로 이동하며, 핀틀에서 발생하는 끝단 충격파가 약해진다. 핀틀 반경(tip radius)이 작아질수록 핀틀에서 발생하는 끝단 충격파가 하류로 이동하며, 크기는 약해진다. 핀틀 형상(contour)은 유동 박리 지점에 직접적인 영향을 미친다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.232-235
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• 2011

A typical unsteady internal ballistic analysis model was developed to take account the erosive burning of a solid rocket motor. The variance of local velocity and pressure along grain surface were analyzed by using the continuity and momentum equation. The coefficients of erosive burning were drew from comparing experiment data with analysis. It was investigated that the grain shapes of propellant affect the erosive burning.