• Journal of KSNVE
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• v.3 no.2
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• pp.169-178
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• 1993

Internal & External duct acoustic fields are calculated by using a finite element method. The geometry is assumed as an axisymmetric duct. External acoustic field; outside the duct, and combined internal & external acoustic fields are solved. For both cases a far field's nonreflecting boundary condition is enforced by using a wave envelope element, which is a kind of finite element. First, a pulsating sphere and an oscillating sphere problem are calculated to verify the external problems, and the results are compared with exact solutions. When the wave envelope element is applied at the far boundary, the calculated finite element solutions show good agreements with the exact solutions. Secondly, the combined internal & external duct acoustic fields are calculated and visualized when monopole sources are distributed inside the duct. It is observed that the directivity of sound intensity outside the duct is beaming toward the axis for high frequency sources.

• 한국가시화정보학회:학술대회논문집
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• 2004.11a
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• pp.80-83
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• 2004

This experiment has been carried out to measure the process of droplet formation between water phase fluid$(PVA\;3\%)$ and organic phase fluid(oil), Internal and External flow fields measured by a Dynamic Micro-PIV method Water-in-oil(W/O) droplets successfully generated at a cross junction and Y junction. Internal and external flow fields were measured when the droplet grew up, stretched and separated.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.58.1-58.1
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• 2014

We model the polarized dust emission from aligned grains by radiative torques in molecular clouds. We consider various models of molecular clouds and calculate the polarization spectrum from aligned grains by both internal and external radiation fields. We show that some polarization spectrum exhibits the bump at wavelengths ${\lambda}$ < $100{\mu}m$, which can be explained due to the polarized emission from a population of small grains aligned by internal radiation fields. Our polarization spectra can explain the anomalous spectra observed by Hildebrand et al, with the rising polarization toward short wavelengths

• Journal of the Korean Society for Precision Engineering
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• v.15 no.2
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• pp.81-89
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• 1998

Numerical calculation tools for forging of gear-like components based on kinematically admissible velocity fields for upper bound method applicable to various deformation features of workpiece in forging processes were suggested. Each one of them deals with unidirectional flow of metal on dies, such as external involute spur gear. square spline, internal serrations. A complex calculation tool of gear-like component forging process was built up by combining these kinematically velocity fields. In this paper the workpiece with 110th external and internal teeth is divided into two parts. The deformation of each part is analyzed simultaneously using numerical calculation tool from combined kinematically admissible velocity field. The experimental set-up was installed in a 200 ton hydraulic press. As a result, each kinematically admissible velocity field could be combined with others and the calculated solution are useful to predict the capacity of forging equipment.

• Journal of Biosystems Engineering
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• v.32 no.4
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• pp.215-222
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• 2007

In the study, the cone index, the cohesion and the internal friction angle of soil were measured before and after tillage in order to suggest relative improvement in soil properties by comparing the two measured values before and after tillage. The tillage methods tested in the study were five combinations of plowing and rotovating; one plow tillage operation, one plow followed by one rotary, one plow followed by two rotary, one rotary without plow and two rotary without plow. The experiments were performed in a soil bin in Sunggyunkwan Univ. and in four selected test fields in Yeoju, Seodun-Dong, Suwon (especially, two different fields) and Chungju. In general, the internal friction angle and cohesion of soil increased with the increase of soil compaction. After applying the tillage operations, the internal friction angle reduced by 14 degree and the cohesion decreased up to about $2.2N/cm^2$ on the soil bin in comparison with those before tillage. The two values, however, reduced by 9 degree and up to about $1.0N/cm^2$ on the tested fields. The CIs for all the tillage operations on the soil bin and on 4 different test fields were decreased by 800 kPa in comparison with those before tillage. The best combination of tillage operations for decreasing the CIs of soil was one plow operation followed by one rotary. The CIs for one plow operation followed by two rotary were slightly higher than that for one plow operation followed by one rotary because one plow operation followed by two rotary crushed down the soil excessively, so that the porosity of soil decreased.

• Journal of KSNVE
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• v.8 no.1
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• pp.122-131
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• 1998

Internal and external acoustic fields of the engine inlet are calculated by using a finite element method. The far fields non reflecting boundary condition is enforced by using a wave envelope element, which is a kind of infinite element. The geometry is assumed an axisymetric duct. Sources of the fan are modeled by the Tyler and Sofrin's theory. Effects of uniformly moving medium are considered. A pulsating sphere and an oscillating piston problem are calculated to verify the external problems, and compared with exact solutions. When the wave envelope element is applied at the far boundary, the calculated finite element solutions show good agreements with the exact solutions. The engine inlet is solved with the combined internal and external grid. The cut-off phenomena on engine inlet duct are observed.

• Journal of The Korean Astronomical Society
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• v.56 no.2
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• pp.187-194
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• 2023

The remote sensing technique of measuring the magnetic field was applied first to sunspots by Hale (1908). Later Babcock (1961) showed that the solar surface magnetic field on a global scale is a dipole in first-order approximation and that this dipole field reverses once every solar cycle. The Wilcox Solar Observatory (WSO) supplies the spherical harmonics coefficients of the solar corona magnetic field of each Carrington Rotation, calculated based on the remotely-sensed photospheric magnetic field of the solar surface. To infer the internal current system producing the global solar coronal magnetic field structure and evolution of the Sun, we calculate the multipole components of the solar magnetic field using the WSO data from 1976 to 2019. The prominent cycle components over the last 4 solar activity cycles are axis-symmetric fields of the dipole and octupole. This implies that the current inversion driving the solar magnetic field reversal originates from the equatorial region and spreads to the whole globe. Thus, a more accurate solar dynamo model must include an explanation of the origin and evolution of such solar internal current dynamics.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.2
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• pp.90-98
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• 1998

Forging of internal involute gears with alloy steel has been analyzed by means of upper bound method. Kinematically admissible velocity fields for forging of internal gear were proposed. It was assumed that the shape of free flow surface during forging operation is a straight line perpendicular to the plane of symmetry. Using the suggested velocity fields, forging loads and relative pressures were calculated by numerical method. Consequently forging die should be successfully designed without fracture or failure during forging operation. Experiments were carried out with the designed die and SCM415 alloy steel as billet material. The calculated loads were compared with experimental one and they are in good agreement with experimental inspections. As a result, the calculated solutions would be useful to predict the loads and the designed die is suitable for forging of internal involute spur gear with alloy steel. The forged gear is measured to be KS 4 class and its class should be improved by subsequent working such as shaving after forging operation.

• Journal of the Korean Society of Visualization
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• v.15 no.2
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• pp.21-25
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• 2017

If a liquid droplet evaporates on a solid substrate, when it completely dries, it leaves a peculiar pattern, which depends on the composition of the liquid. Not only a single component liquid but also complex liquids are studied for a different purpose. In particular, a binary mixture droplet has been widely studied and used for an ink-jet printing technology. In this study, we focus on investigating to visualize the internal flow field of an ethanol-water mixture by varying a concentration ratio between two liquids. We measure the in-plane velocity vector fields and vorticities. We believe that this fundamental study about the internal flow field provides a basic idea to understand the dried pattern of the binary mixture droplet.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.633-637
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• 1995

Numerical calculation tool for forging of gear-like components based on kinematically admissible velocity fields for upper bound method applicable to various deformation features of workpiece in forging processes were suggested. Each one of them deals with unidirectional flow of metal on dies, such as external involute spur gear, sequare spline, internal serrations. A complex calcuation tool of gear-like component forging process was built up by combining these kinematically velocity fields. In this paper, the workpiece with both external and internal teeth is divided into two parts. The deformation of each part is analyzed simultaneously using numerical calculation tool form combined kinematically admissible velocity field. The experimental set-up was installed in a 200 ton hydraulic press. As a result, each kinematically admissible velocity field could be combined with other and the calculated solution are useful to predict the capacity of forging equipment.