• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.352-353
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• 2007

The spectrum for $0_{\circ}$, $90_{\circ}$-polarized light coincides with the spectrum for non-polarized light and also with the spectrum was observed in the LB film deposited using a fresh solution. And, the formation and dissociation of J-aggregates, anisotropic behavior was no longer observed in the heat treated merocyanine dyes LB films. But, in the optical absorption spectra of same LB films by UV irradiation at room temperature, their were observed only dissociation of J-aggregates, that is decrease of absorbance peak without change spectral shape. On the other hand, in the case of optical absorption spectra of the LB films by the heat treatment at $70^{\circ}C$ in the air, both of the shifted absorption bands decay and a monomer absorption peak of about 530 nm appears instead.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.364-370
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• 2008

Spinning detonations propagating in a circular tube were numerically investigated with a one-step irreversible reaction model governed by Arrhenius kinetics. The time evolution of the simulation results was utilized to reveal the propagation mechanism of single-headed spinning detonation. The track angle of soot record on the tube wall was numerically reproduced with various levels of activation energy, and the simulated unique angle was the same as that of the previous reports. The maximum pressure histories of the shock front on the tube wall showed stable and unstable pitch modes for the lower and higher activation energies, respectively. The shock front shapes and the pressure profiles on the tube wall clarified the mechanisms of two modes. The maximum pressure history in the stable pitch remained nearly constant, and the single Mach leg existing on the shock front rotated at a constant speed. The high and low frequency pressure oscillations appeared in the unstable pitch due to the generation and decay of complex Mach interaction on the shock front shape. The high frequency oscillation was self-induced because the intensity of the transverse wave was changed during propagation in one cycle. The high frequency behavior was not always the same for each cycle, and therefore the low frequency oscillation was also induced in the pressure history.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.429-434
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• 1996

K-REM［1］, which is under development as a realistic evaluation model of large break LOCA, is applied to the analysis of cold leg guillotine break of Ulchin 3&4. Fuel parameters on which statistical analysis of their effects on the peak cladding temperature (PCT) are made and system parameters on which the concept of limiting value approach (LVA) are applied, are determined from the single parameter sensitivity study. 3 parameters of fuel gap conductance, fuel thermal conductivity and power peaking factor are selected as fuel related ones and 4 parameters of axial power shape, reactor power, decay heat and the gas pressure of safety injection tank (SIT) are selected as plant system related ones. Response surface of PCT is generated from the plant calculation results and on which Monte Carlo sampling is made to get plant application uncertainty which is statistically combined with code uncertainty to produce the 95th percentile PCT. From the break spectrum analysis, blowdown PCT of 1350.23 K and reflood PCT of 1195.56 K are obtained for break discharge coefficients of 0.8 and 0.5, respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.4
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• pp.1395-1405
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• 1996

The purpose of this experimental research is to investigate the local heat transfer characteristics in the upward free water jet impinged on a downward flat plate of uniform heat flux. The inner shape of rectangular nozzle used was sine curve type and its contraction ratio of inlet to outlet area was five. Experimental parameters considered were Reynolds number, nozzle exit-flat plate distance, and level of supplementary water. Local Nusselt number was influenced by Reynolds number, Prandtl number, supplementary water level, and distance between the nozzle exit and flat plate. Within the impingement region, the Nusselt number has a maximum value on the nozzle center axis and decreases monotonically outward from center. Outside of the impingement region, on the other hand, the Nusselt number has a secondary peak near the position where the distance from nozzle center reaches four times the nozzle width. However if nozzle exit velocity exceeds 6.2 m/s, the secondary peak appears also in the impingement region. The empirical equation for the stagnation heat transfer is a function of Prandtl, Reynolds, and axial distance from the nozzle exit. The optimum level of supplementary water to augment the heat transfer rate at stagnation point was found to be twice the nozzle width.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.188-192
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• 2004

A Numerical analysis method is developed in order to compute the flaw and wave field for 2-dimensional floating body in the free roll motion with 3 degrees of freedom. Navier-Stokes and continuity equations are gaverning equations in tire present study. Finite Difference method is introduced to discretize the governing equation. The free surface is traced by the interface tracking method and the grid system is fitted to boundaries including free surface and body surface, which is moving in the flow field. The numerical scheme is based on Maker and Cell method. For the sake of validation of the numerical method, the computed roll decay factors according to tire midship section shapes are compared with measured results. The numerical results are discussed in order to understand the effect of midship section shape on roll motion.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.19 no.2
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• pp.163-170
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• 2023

Since spent nuclear fuel assemblies (SFA) are transported to interim storage or final disposal facility after cooling the decay heat, finite element analysis (FEA) with simplification is widely used to show their integrity against cladding failure to cause dispersal of radioactive material. However, there is a lack of research addressing the comprehensive impact of shape and element simplification on analysis results. In this study, for the optimization of a typical pressurized water reactor SFA, different types of finite element models were generated by changing number of fuel rods, fuel rod element type and assembly length. A series of FEA in use of these different models were conducted under a shock load data obtained from surrogate fuel assembly transportation test. Effects of number of fuel rods, element type and length of assembly were also analyzed, which shows that the element type of fuel rod mainly affected on cladding strain. Finally, an optimal finite element model was determined for other practical application in the future.

• Journal of Sensor Science and Technology
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• v.16 no.5
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• pp.337-341
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• 2007

$CsSrCl_{3}$ crystal was grown using Czochralski method from equimolar mixture of CsCl and $SrCl_{2}$. The spectrum range of the luminescence excited by 205 nm of wavelength was about $280{\sim}550$ nm, and its peak emission appeared at 343 nm. The luminescence decay curve of the $CsSrCl_{3}$ revealed two exponential components with time constants of 60 ns and 700 ns. The energy resolution for $^{137}Cs$ 662 keV ${\gamma}$-ray was 10.3 %. The pulse shape was linear at high energy, but some deviation existed in the low energy region.

• Nuclear Engineering and Technology
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• v.13 no.4
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• pp.207-220
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• 1981

The Np-237 fission cross-sections up to 20 MeV incident neutron energy are calculated by means of the computer code STAPRE- a statistical model code with consideration of preequilibrium decay. The higher chance fissions up to third compound nucleus are taken into account, and the main input parameters in the treatment of fission under consideration of a double-humped fission barrier are carefully adjusted, so that the current trend of experimental data can be fitted within an apparent deviation of about 10% throughout the entire energy range. Results are presented in the form of point-wise cross-section values, and also in the form of graph to demonstrate the shape agreement.

• Journal of the Korean Geophysical Society
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• v.6 no.1
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• pp.25-29
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• 2003

We suggest a method that vectorially composes 3-component earthquake records in the frequency domain, to reduce the uncertainties in the analysis of the Fourier amplitude spectrum. The use of the Fourier amplitude spectrum composed from 3 components has two advantages. First, it provides a more accurate estimate of seismic moment by eliminating the vector-partition term that appears in individual component. Second, it provides more accurate estimates of seismic moment, corner frequency, high-frequency decay constant($χ$) .etc., by enhancing the shape of the Fourier amplitude spectrum. The latter is especially useful in the analysis of small earthquakes with low signal-to-noise ratios.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.7
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• pp.1201-1208
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• 2022

In general, to maximize the supply and efficiency of floating offshore wind power generation energy, the motion caused by wave attenuation of the substructure must be reduced. According to previous studies, the motion response was reduced due to the vortex viscosity generated by the damping plate installed in the lower structure among the waves. In this study, a 5 MW semi-submersible OC5 platform and two platforms with attenuation plates were designed, and free decay experiments and numerical calculations were performed to confirm the effect of reducing motion due to vortex viscosity. As a result of the model test, when the heave free decay tests were conducted at drop heights of 30 mm, 40 mm, and 50 mm, compared with the OC5 platform, the platform with two types of damping plates attached had relatively improved motion damping performance. In the model test and numerical calculation results, the damping plate models, KSNU Plate 1 and KSNU Plate 2, were 1.1 times and 1.3 times lower than OC5, respectively, and the KSNU Plate 2 platform showed about two times better damping performance than OC5. This study shows that the area of the damping plate and the vortex viscosity are closely related to the damping rate of the heave motion.