• Nuclear Engineering and Technology
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• v.26 no.2
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• pp.247-256
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• 1994

The nuclide chain model used in SAV90 has been modified for the CASMO3/MEDIUM3 procedure. Since the default nuclide chain in SAV90, using 21 nuclides, is not sufficient to reproduce the CASMO3 results in the MEDIUM3 calculation, the extended nuclide chain models have been investigated and verified with various types of fuel assemblies. Among the extended nuclide chain models proposed, the 22 nuclide chain model, which contains only Pu238 additionally to the 21 nuclide chain, is recommended in terms of both accuracy and computing efficiency. Using this model core follow calculations for YGN-1 have been performed. The results showed good performance when compared to plant measurements.

• Nuclear Engineering and Technology
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• v.21 no.1
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• pp.56-61
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• 1989

A simple, approximate method for determining the two-group adjoint flux based on the Borresen's coarse-mesh 1.5 group diffusion theory scheme is proposed. With the principle of the 1.5 group diffusion theory scheme, the method describes the thermal leakage term of the adjoint flux approximately by the geomerical buckling determined from the fast adjoint flux. The accuracy of the adjoint flux is investigated tv the comparison of the adjoint flux constructed from this method with a fine-mesh finite-difference KIDD computations. It is shown that the proposed method can predict the adjoint flux as good as the KIDD results. Possible applications of the present method are then suggested in conjunction with the application of the perturbation theory.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.45-45
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• 2015

고전전인 천수방정식을 적용한 도시침수 해석모형에서 건물의 영향을 고려한 정확한 해석을 수행하기 위해서는 고해상도 격자가 요구되며 이는 계산시간의 증가가 야기된다. 고전 천수방정식을 적용한 도시침수해석 모형의 이러한 문제점을 극복하기 위해서 본 연구에서는 도시지역에 존재하는 건물 체적에 레이놀즈 이송이론을 적용한 수정 천수방정식을 제안하고, 제안 천수방정식을 이용한 효율적인 2차원 도시침수해석 모형을 개발하였다. 도시지역의 침수 모델링을 위해 고전 천수방정식은 건물을 고려하기 위해 고해상도 격자를 사용하는 것과 달리 수정 천수방정식은 건물의 영향을 매개변수화함으로서 저해상도 격자의 사용에도 고전 천수방정식과 유사한 정확도를 얻을수 있다. 건물의 영향을 매개변수화하기 위해서는 건물로 인한 저류와 흐름방향의 변화를 지배방정식이 고려할 수 있도록 수정하였다. 즉. 수정 천수 방정식은 고전 천수방정식을 기본으로 하여 건물의 저류영향을 고려하기 위해 각 계산격자에 적용되는 체적 매개변수와 건물의 흐름방향을 고려하기 위해 흐름방향과 직각방향에 위치한 선분(격자를 구성하고 있는 경계선)에 적용되는 면적 매개변수가 추가된다. 수정 천수방정식을 검증하기 위해 개발모형을 건물이 균일하게 위치한 실험하도와 비균일하게 위치한 실험하도에 적용하고 그 결과를 고전 천수방정식을 사용한 계산결과 및 계산시간과 비교함으로서 개발모형의 정확성과 효율성을 검증하였다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.38 no.6
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• pp.717-723
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• 2020

Determination of local tie vectors between the space geodetic techniques such as VLBI (Very Long Baseline Interferometer), SLR (Satellite Laser Ranging), DORIS (Doppler Orbit determination and Radiopositioning Integrated on Satellite), GNSS (Global Navigation Satellite System) is essential for combination of ITRF (International Terrestrial Reference Frame). Therefore, it is required to compute IVP (Invariant Point) position of each space geodetic technique with high accuracy. In this study, we have computed Sejong VLBI IVP position by using updated mathematical model for adjustment computation so that the improvement on efficiency and reliability in computation are obtained. The measurements used for this study are the coordinates of reflective targets on the VLBI antenna and their accuracies are set to 1.5 mm for each component. The results show that the position of VLBI IVP together with its standard deviation is successfully estimated when they are compared with those of the results from previous study. However, it is notable that additional terrestrial surveying should be performed so that realistic measurement errors are incorporated in the adjustment computation process.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.290-297
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• 2009

A two-phase (gas and liquid) flow analysis solver, named CUPID, has been developed for a realistic simulation of transient two-phase flows in light water nuclear reactor components. In the CUPID solver, a two-fluid three-field model is adopted and the governing equations are solved on unstructured grids for flow analyses in complicated geometries. For the numerical solution scheme, the semi-implicit method of the RELAP5 code, which has been proved to be very stable and accurate for most practical applications of nuclear thermal hydraulics, was used with some modifications for an application to unstructured non-staggered grids. This paper is concerned with the effects of interpolation schemes on the simulation of two-phase flows. In order to stabilize a numerical solution and assure a high numerical accuracy, the second-order upwind scheme is implemented into the CUPID code in the present paper. Some numerical tests have been performed with the implemented scheme and the comparison results between the second-order and first-order upwind schemes are introduced in the present paper. The comparison results among the two interpolation schemes and either the exact solutions or the mesh convergence studies showed the reduced numerical diffusion with the second order scheme.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.5 no.1
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• pp.49-58
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• 1987

The use of digital terrain model has been enlarged in calculating the earthwork due to the development of aerial photogrammetry. The calculation of earthwork plays a major role in plan or design of many civil engineering projects, and thus it has become very important to advance the accuracy of earthwork calculation. In this study, I have made an analysis of influences which DTM makes on the height accuracy of data ; on the basis of the analysis, we can develop the predictive model formula of profile shape coefficients by which the accuracy of earthwork can he preestimated in practical design according to data density of terrain, making thereby good contribution to the calculation of both earthwork amount and its expenses. This study shows that the accuracy of earthwork is more affected by the distances of cross-sections than by data density and that the effects by the standard errors of height decrease in proportion as the distances of cross-sections are great It also shows that when the prediction model formula of profile shape coefficients is applied to ordinary cases, the differences between the predicted earthwork errors and the errors by ordinary est imation are at 0.8374~3.1437$cm^3$/m, on flat terrain and 1.5628~6.967$cm^3$/m, on mountainous terrain-so little as to be ignored ; thus it can be safely ascertained that the accurate earthwork errors can be predicted applying the prediction model formula made in this study.

• Journal of Korean Society for Geospatial Information Science
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• v.23 no.4
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• pp.43-48
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• 2015

We studied on pseudo-range correction(PRC) modeling in order to improve differential GNSS(DGNSS) accuracy. The PRC is the range correction information that provides improved location accuracy using DGNSS technique. The digital correction signal is typically broadcast over ground-based transmitters. Sometimes the degradation of the positioning accuracy caused by the loss of PRC signals, radio interference, etc. To prevent the degradation, in this paper, we have designed a PRC model through polynomial curve fitting and evaluated this model. We compared two quantities, estimations of PRC using model parameters and observations from the reference station. In the case of GPS, the average is 0.1m and RMSE is 1.3m. Most of GPS satellites have a bias error of less than ${\pm}1.0m$ and a RMSE within 3.0m. In the case of GLONASS, the average and the RMSE are 0.2m and 2.6m, respectively. Most of satellites have less than ${\pm}2.0m$ for a bias error and less than 3.0m for RMSE. These results show that the estimated value calculated by the model can be used effectively to maintain the accuracy of the user's location. However;it is needed for further work relating to the big difference between the two values at low elevation.

• Geophysics and Geophysical Exploration
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• v.3 no.2
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• pp.39-47
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• 2000

A great deal of computing time and a large computer memory are needed to solve wave equation in a large complex subsurface layers using the finite difference method. The computing time and memory can be reduced by decreasing the number of grid points per minimum wave length. However, the decrease of grids may cause numerical dispersion and poor accuracy. In this study we performed the grid dispersion analysis for several rotated finite difference operators, which was commonly used to reduce grids per wavelength with accuracy in order to determine the solution for the acoustic wave equation in frequency domain. The rotated finite difference operators were to be extended to 81, 121 and 169 difference stars and studied whether the minimum grids could be reduced to 2 or not. To obtain accuracy (numerical errors less than $1\%$) the following was required: more than 13 grids for conventional 5 point difference stars, 9 grids for 9 difference stars, 3 grids for 25 difference stars, and 2.7 grids for 49 difference stars. After grid dispersion analysis for the new rotated finite difference operators, more than 2.5 grids for 81 difference stars, 2.3 grids for 121 difference stars and 2.1 grids for 169 difference stars were needed. However, in the 169 difference stars, there was no solution because of oscillation of the dispersion curves in the group velocity curves. This indicated that the grids couldn't be reduced to 2 in the frequency acoustic wave equation. According to grid dispersion analysis for the determination of grid points, the more rotated finite difference operators, the fewer grid points. However, the more rotated finite difference operators that are used, the more complex the difference equation terms.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.36 no.4
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• pp.263-270
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• 2018

Land surface temperature is known to be an important factor in understanding the interactions of the ground-atmosphere. However, because of the large spatio-temporal variability, regular observation is rarely made. The existing land surface temperature is observed using satellite images, but due to the nature of satellite, it has the limit of long revisit period and low accuracy. In this study, in order to confirm the possibility of replacing land surface temperature observation using satellite imagery, images acquired by TIR (Thermal Infrared) sensor mounted on UAV (Unmanned Aerial Vehicle) are used. The acquired images were transformed from JPEG (Joint Photographic Experts Group) to TIFF (Tagged Image File Format) format and orthophoto was then generated. The DN (Digital Number) value of orthophoto was used to calculate the actual land surface temperature. In order to evaluate the accuracy of the calculated land surface temperature, the land surface temperature was compared with the land surface temperature directly observed with an infrared thermometer at the same time. When comparing the observed land surface temperatures in two ways, the accuracy of all the land covers was below the measure accuracy of the TIR sensor. Therefore, the possibility of replacing the satellite image, which is a conventional land surface temperature observation method, is confirmed by using the TIR sensor mounted on UAV.

• Journal of Advanced Navigation Technology
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• v.21 no.4
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• pp.325-331
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• 2017

As a GPS stability problem arises, MLAT system is spotlighted as an alternative technology of ADS-B. MLAT system has a high position accuracy as much as ADS-B. Also, MLAT receives the mode A,C,S, and 1090ES(ADS-B) signals from the mounted aircraft transponder. MLAT receives signals from several receiver units and calculates aircraft positions. MLAT has ADS-B level positioning accurarcy using GPS and can calculate the position information with objects independently. According to global environment changes, Local area multiltilateration(LAM) surveillance system is under development for moving vehicles and aircraft detection in airport. These are still under testing in Tae-an Airfield. In the paper, we analyzed the performance by comparing the calculated position data from MLAT to RTK. In order to confirm the position accuracy of MLAT and the deviation of position data between fixed target and moving target on the ground during the field test in Tae-an Airfield.