• The KIPS Transactions:PartB
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• v.15B no.6
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• pp.501-506
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• 2008

The classical snake algorithm has a problem in detecting the boundary of an object with deep concavities. While the GVF method can successfully detect boundary concavities, it consumes a lot of time computing the energy map. In this paper, we propose an algorithm to reduce the computation time and improve performance in detecting the boundary of an object with high concavity. We define the degree of complexity of object boundary as the local curvature. If the value of the local curvature is greater than a threshold value, new snake points are added. Simulation results on several different test images show that our method performs well in detecting object boundary and requires less computation time.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.6
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• pp.107-114
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• 2012

Fracture of brittle material due to dynamic load such a particle impact has been reported by many researchers as the fracture behavior by variation of stress for a short minute. Especially, the brittle material, such a ceramic, applied to the structural component of machine, is considered as the important project. In order to evaluate the improvement of impact resistance, the particle impact test for the $Al_2O_3-TiO_2$ coated glass is practiced. And then, the damage variation according to the impact energy of steel ball was evaluated. There was a large improvement by the ceramic coating on the surface of a glass substrate. The damage volume was especially imported to evaluate damage behavior in quantity. These data were plotted on logarithmic coordinate and experimental equations were induced by data analysis based on test results. And the variation of critical energy for crack initiation was analyzed with critical impact energy when each crack occurs.

• Journal of the Korean Solar Energy Society
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• v.23 no.3
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• pp.29-35
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• 2003

Generator for wind power can be either synchronous or asynchronous (induction) types. Induction and synchronous generators behave in a different way when subjected to severe faults. Induction generators does not have an angle stability limit and short circuit in the neighborhood of an Induction generator causes the demagnetization of the machine when the fault is cleared, the voltage raises slowly, while the grid contributes with reactive power to the generator and the magnetic flux recovers. On the other hand in the synchronous generators the recovery of the voltage is immediate, since the excitation of the rotor angle comes from an independent circuit. This paper shows the result of the transient state analysis in the network connected to wind generation system Several case studies have been conducted to determine the effect of the clearing time of a fault on the network stability. It has been found that the critical clearing time can be as low as 61ms in the case of induction generator compared to 370ms in the case of synchronous generator.

• Journal of the Korean Solar Energy Society
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• v.35 no.2
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• pp.53-62
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• 2015

Boiling heat transfer characteristic is very important in the various industries such as solar thermal system, power generation, heat exchangers, cooling of high-power electronics components and cooling of nuclear reactors. Therefore, in this study, boiling heat transfer characteristics such as critical heat flux (CHF) and heat transfer coefficient under the pool boiling state were tested using graphene nanofluids. Graphene used in this study, which have the same thermal conductivity but with different sizes. The experimental results showed that the highest the CHF and boiling heat transfer coefficient increase ratio for graphene nanofluids was at the 0.01 vol.%. At the present juncture, the CHF and boiling heat transfer coefficient increase ratio of the small-sized graphene nanofluids was higher than the large-sized graphene nanofluids.

• Journal of Energy Engineering
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• v.8 no.4
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• pp.576-582
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• 1999

this paper presents the results of experiments on subsooling degree characteristics which was analyzed in accordance with various test conditions. The test water was cooled below freezing point temperature, was measured. The results showed that using city water as the test water in pyrex tube indicated small standard deviation (SD) compared to using distilled water, and minimum subcooling degree was 6.9$^{\circ}C$ and 6.2$^{\circ}C$, respectively. In addition, a critical subcooling degree in a pyrex tube was larger than that in a stainless steel tube about 0.7$^{\circ}C$ for the same test water. It was also observed that the standard deviation of data for the distilled water showed decreasing tendency aw the increasing with cooling velocity. Then metaldehyde showed a considerable effect on the subcooling degree of distilled water as the ice nucleating substance with increase of test number.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.623-626
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• 2004

The purpose of this paper is to determinate and to confirm p-n junction depth with nondestructive method by using electron beam. By measuring the critical short circuit current on the p-n junction which induced by electron beam and calculating generation range, the diffusion depth can be obtained. It ran be seen that values destructively measured by constant angle lapping and nondestructively by this study almost concur. As this result, it is purposed that diffusion depth of p-n junction can be easily measured by non-destruction. And this nondestructive method ran be recommended highly to the industrial analysis.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.10
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• pp.1009-1015
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• 2013

Ultra-short laser pulses are effective, when high requirements concerning accuracy, surface roughness and heat affected zone are demanded for surface structuring. In particular, picosecond laser systems that are suited to be operated in industrial environments are of great interest for many practical applications. This paper focused on inducing optimum process parameters for higher volume ablation rate by analyzing a relationship between crater diameter and optical spot size. In detail, the dependency of the volume ablation rate, penetration depth and threshold fluence on the pulse duration 8 ps and wavelength of 515 nm was discussed. The experimental results showed that wavelength of 515 nm resulted in less threshold fluence ($0.075J/cm^2$) on copper than IR wavelength ($0.3J/cm^2$). As a result, it was possible that optimum fluence for higher volume ablation rate was achieved with $0.28J/cm^2$.

• Korean Journal of Materials Research
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• v.8 no.4
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• pp.304-311
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• 1998

0.07%C-0.014%Ti-0.015Nb-0.005%B강 (강종 B)을 각각 TMCP처리하여 그 기계적 특성과 B의 거동을 조사하였다. Ta-B강이 Ti-Nb-B강보다 인장강도는 더 우수하였으나 충격 흡수에너지는 훨씬 더 낮았다. Ta-B강의 강도가 Ti-Nb-B강보다 더 우수한 이유는 Ta-B강에서의 Ta의 석출강화 효과가 Ti-Nb-B강에서의 Ti와 Nb의 석출강화 효과보다 더 크기 때문으로 생각된다. Ta-B강은 입내파괴, Ti-Nb-B강은 임계파괴의 파괴양상을 보여이며, Ti-Nb-B강이 Ta-B 강보다 더 큰 충격 흡수에너지를 나타내었다. TMCP에서는 항온변태시의 평형석출과는 달리 연속냉각방법을 사용하였기 때문에 B가 결정립계에 평형적 또는 비평형적으로 편석되어 준안정상으로 생각되는 연속적인 필름 형태의 붕화물을 형성한다. 또한, 냉각속도의 차이에 따라 석출물은 결정질이 되거자 비정질이 되었다. B의 함량이 많은 Ti-Nb-B강에서는 석출물이 비정질상이었다. 한편, B함량이 적은 Ta-B강에서는 B강에서는 결정립계에서 B가 관찰되지 않아는데, 이것은 결정립계에서의 B의 석출이 B의 함량에 매우 민감함을 의미하는 것이다.

• Solar Energy
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• v.14 no.2
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• pp.3-16
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• 1994

The major objectives of the study are to suggest the optimal basic design conditions for the horizontal storage tank system. For this purspose computer simulation has been carried out to find the characteristics of flow patterns in horizontal storage tank, and experiments have been carried out for the duration of one turnover, Experimental parameters are volume flow rate(1 LPM to 4 LPM), amount of heat generated from heat sources(0 W to 100 W), and inlet and outlet port types of the storage tank(DD type, DO type, ID type, IO type).

• Journal of the Korean Chemical Society
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• v.66 no.4
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• pp.278-283
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• 2022

Using the Kirkwood's method, the free energy of a binary lattice solution consisting of two identical interpenetrating sublattices, such as a simple cubic lattice or a body-centered cubic lattice, was calculated up to the tenth order of the reciprocal of absolute temperature. Using this, liquid-liquid coexistence curves and critical solution temperatures for the binary lattice solutions were calculated to quantitatively investigate the effect of non-random mixing of molecules. And it was shown that the coexistence curve of the simple cubic lattice solution was in good agreement with the Monte-Carlo computer simulation result.