• Journal of Astronomy and Space Sciences
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• v.22 no.3
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• pp.283-292
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• 2005

Ionosphere is deeply coupled to the space environment and introduces the perturbations to radio signal because of its electromagnetic characteristics. Therefore, the status of ionosphere can be estimated by analyzing the GPS signal errors which are penetrating the ionosphere and it can be the key to understand the global circulation and change in the upper atmosphere, and the characteristics of space weather. We used 9 GPS Continuously Operating Reference Stations (CORS), which have been operated by Korea Astronomy and Space Science Institute (KASI) , to determine the high precision of Total Electron Content (TEC) and the pseudorange data which is phase-leveled by a linear combination with carrier phase to reduce the inherent noise. We developed the method to model a regional ionosphere with grid form and its results over South Korea with $0.25^{\circ}\;by\;0.25^{\circ}$ spatial resolution. To improve the precision of ionosphere's TEC value, we applied IDW (Inverse Distance Weight) and Kalman Filtering method. The regional ionospheric model developed by this research was compared with GIMs (Global Ionosphere Maps) preduced by Ionosphere Working Group for 8 days and the results show $3\~4$ TECU difference in RMS values.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.7
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• pp.265-274
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• 2018

The increasing use of curved beams in buildings, vehicles, ships, and aircraft has prompted studies directed toward the development of an accurate method for analyzing the dynamic behavior of such structures. The stability behavior of elastic curved beams has been the subject of a large number of investigations. Solutions of the relevant differential equations have been obtained traditionally using standard finite difference or finite element methods. These techniques require a great deal of computer time as the number of discrete nodes becomes relatively large under the conditions of complex geometry and loading. One of the efficient procedures for the solution of partial differential equations is the method of differential quadrature. The differential quadrature method (DQM) has been applied to a large number of cases to overcome the difficulties of the complex algorithms of programming for the computer, as well as the excessive use of storage due to the conditions of complex geometry and loading. The in-plane buckling of curved beams considering the extensibility of the arch axis was analyzed under uniformly distributed radial loads using the DQM. The critical loads were calculated for the member with various parameter ratios, boundary conditions, and opening angles. The results were compared with the precise results by other methods for cases, in which they were available. The DQM, using only a limited number of grid points, provided results that agreed very well (less than 0.3%) with the exact ones. New results according to diverse variations were obtained, showing the important roles in the buckling behavior of curved beams, and can be used in comparisons with other numerical solutions or with experimental test data.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.6A
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• pp.609-616
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• 2011

The Delay/Disruption Tolerant Network (DTN) is a network designed to operate effectively using the mobility and storage of intermediate nodes under no end-to-end guaranteed network. This new network paradigm is well-suited for networks which have unstable path and long latencies (e.g. interplanetary network, vehicular network). In this paper, we first found that each taxi has its own regularly visiting area and define this property as spatial regularity. We analyze 4000 taxi trace data in Shanghai and show the existence of spatial regularity experimentally. Based on a spatial regularity in urban environment, we present a new DTN routing method. We introduce a Weighted Center (WC) which represents spatial regularity of each node. Through the association with evenly distributed access points (APs) in urban environment, most of vehicles get their grid locations and calculate their WCs. Since our routing method only uses neighbors' WCs for building routing paths, it can be regarded as distributed and practical protocols. Our experiments involving realistic network scenarios created by the traces of about 1500 Shanghai taxies show that our routing method achieves the higher performance compared to ECT, LET by 10%~110%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.5
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• pp.738-744
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• 2017

Recently, the installation of energy storage systems (ESSs) has increased in parallel with the extension of renewable energy resources. However, there has been no concrete analysis ofthe performance verification and economic evaluation of ESSs,which makes it difficult to perform aneffective installation and operation of an ESS. In particular, there are no international technical standards and guidelines on electric ESS for frequency regulation applications. Therefore, acomprehensive study on the power quality, impact on grid, extent of contribution, and cost benefit study of ESS are strongly being required. Under these backgrounds, this paper proposes a performance verification algorithm on ESS for frequency regulation application based on ananalysis of the AGC(Automatic Generation Control) performance verification method of PJM in USA. In addition,this paper proposes an economic evaluation algorithm on a 500 MW installation of ESS for frequency regulation applications using the account settlement of an expensive gas-fired generation plant and coal-fired power generation plant. From the simulation with real ESS operation data and 500 MW installation case, it wasconfirmed that the ESS showssuperior performance toany other conventional generators and provides anannual benefit of 500 MW ESS are between 345~429 billon won.

• Geophysics and Geophysical Exploration
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• v.17 no.3
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• pp.137-146
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• 2014

This study presents a procedure for discrimination of artificial events from earthquakes occurred in and around the Korean Peninsula using data set in the Wonju KSRS seismograph network, Korea. Two training sets representing natural and artificial earthquakes were constructed with 150 and 56 events, respectively, with high signal to noise ratio. A frequency band, Pg(4-6 Hz)/Lg(5-7 Hz), which is optimal for the discrimination of seismic sources was derived from the two-dimensional grid of Pg/Lg spectral amplitude ratio. The corrections for the effects of earthquake magnitude and hypocentral distance were carried out for improvement of discrimination capability. For correcting the effect of magnitude dependence due to the inverse proportionality of corner frequency to seismic moment, the Brune's source spectrum was subtracted from the observation spectrum. The spectrum was corrected using the optimal damping coefficient to remove damping effect with the hypocentral distance. The effect of locally varying spectrum ratio was cancelled correcting variation of wave propagation along the ray path. The performance in discrimination between training sets of natural and artificial events was compared using the Mahalanobis distance in each step of correction. The procedure of magnitude, distance, and path corrections show clear improvements of the discrimination results with increasing Mahalanobis distance, from 1.98 to 3.01, between two training sets.

• Journal of the Korean Association of Geographic Information Studies
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• v.19 no.1
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• pp.154-166
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• 2016

This study aims to contribute to better understanding the effects of the changes in the parameter values of GroundFilter algorithm(GF), which performs filtering process, and of GridsurfaceCreate algorithm(GC), which creates regular grid, provided in Fusion software on the accuracy of elevation of the final LiDAR-DEM products through comparative analysis. In order to test whether there are significant effects on the accuracy of the final LiDAR-DEM products due to the changes of GF(1, 3, 5, 7, 9) parameter levels and GC(1, 3, 5, 7, 9) parameter levels, two-way ANOVA is conducted based on residuals. The residuals are calculated using the differences between each sample plot's paired field-measured and DEM-derived elevation values given each individual GF and GC level. After that, Tukey HSD test is conducted as a post hoc test for grouping the levels. As a result of two-way ANOVA test, it is found that the change in the GF levels significantly affects the accuracy of LiDAR-DEM elevations(F-value : 27.340, p < 0.01), while the change in the GC levels does not significantly affect the accuracy of LiDAR-DEM elevations(F-value : 0.457). It is also found that the interaction effect between GF and GC levels is not likely to exist(F-value : 0.247). From the results of the Tukey HSD test in the GF levels, GF levels can be divided into two groups('7', '5', '9', '3' vs '1') by the differences of means of residuals. Given the current conditions, LiDAR-DEM can achieve the best accuracy when the level '7' and '3' are given as GF and GC level, respectively.

• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.1
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• pp.62-68
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• 2012

Steady-State Visually Evoked Potentials (SSVEP) are natural response signal associated with the visual stimuli with specific frequency. By using SSVEP, occipital lobe region is electrically activated as frequency form equivalent to stimuli frequency with bandwidth from 3.5Hz to 75Hz. In this paper, we propose an experimental paradigm for analyzing EEGs based on the properties of SSVEP. At first, an experiment is performed to extract frequency feature of EEGs that is measured from the image-based visual stimuli associated with specific objective with affordance and object-related affordance is measured by using mirror neuron system based on the frequency feature. And then, linear discriminant analysis (LDA) method is applied to perform the online classification of the objective pattern associated with the EEG-based affordance data. By using the SSVEP measurement experiment, we propose a Brain-Computer Interface (BCI) system for recognizing user's inherent intentions. The existing SSVEP application system, such as speller, is able to classify the EEG pattern based on grid image patterns and their variations. However, our proposed SSVEP-based BCI system performs object pattern classification based on the matters with a variety of shapes in input images and has higher generality than existing system.

• Journal of the Korean Geographical Society
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• v.47 no.2
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• pp.208-225
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• 2012

The spatial characteristics of changes in extreme temperature indices for 2070-2099 relative to 1971-2000 in the Republic of Korea were investigated using daily maximum (Tmax) and minimum (Tmin) temperature data from a regional climate model (HadGEM3-RA) based on the IPCC RCP4.5/8.5 at 12.5km grid spacing and observations. Six temperature-based indices were selected to consider the frequency and intensity of extreme temperature events. For validation during the reference period (1971-2000), the simulated Tmax and Tmin distributions reasonably reproduce annual and seasonal characteristics not only for the relative probability but also the variation range. In the future (2070-2099), the occurrence of summer days (SD) and tropical nights (TR) is projected to be more frequent in the entire region while the occurrence of ice days (ID) and frost days (FD) is likely to decrease. The increase of averaged Tmax above 95th percentile (TX95) and Tmin below 5th percentile (TN5) is also projected. These changes are more pronounced under RCP8.5 scenario than RCP4.5. The changes in extreme temperature indices except for FD show significant correlations with altitude, and the changes in ID, TR, and TN5 also show significant correlations with latitude. The mountainous regions are projected to be more influenced by an increase of low extreme temperature than low altitude while the southern coast is likely to be more influenced by an increase of tropical nights.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.217-225
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• 2017

This research represents comparison and validation of static aerodynamic results in different wind tunnel organizations and EFD-CFD results. KAFA conducted wind tunnel tests with Standard Dynamics Model(SDM) which is based on the NRC model, the same configuration of KARI; and then compared and analyzed similarities and differences of the data from KARI and NRC results for verifying the accuracy of wind tunnel tests. Also, We compared the result of CFD with that of wind tunnel tests and examined strakes effect in static characteristics which are attached on the forward fuselage of SDM for investigating the cause of some discrepancies. From this analysis, there are some discrepancies in Cm tendency between EFD-CFD and it did not show the big difference of aerodynamic characteristics by strake effects. Thus, we need to research additionally for analyzing the different cause of some discrepancies such as vortex structures by the rear strut or intake of SDM and regenerating grid resolution of CFD.

• Atmosphere
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• v.26 no.3
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• pp.413-421
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• 2016

Climate Analysis Seoul (CAS) which provides gridded data relevant for thermal assessment was applied to one of the urban green areas, the Seonjeongneung, in Seoul, Korea. The thermal environment in the Seonjeongneung was evaluated from the CAS simulation for the five heat-wave issued cases during the last five years (2011~2015). The CAS has been improved continuously since it was developed. An updated version with a higher resolution of the CAS simulation domain and an addition of the vegetation information was used in this study. The influence of vegetation in the Seonjeongneung is estimated through the amount of the cold air generation ($Q_{ca}$) and air temperature deviation at each grid points, which are calculated by incorporating Geographic Information System (GIS) analysis on the simulation domain and meteorological analysis with the METeorology and atmospheric PHOtochemistry mesoscale MODel (MetPhoMod) in the CAS. The average amount of the cold air generation ($Q_{ca}$) at the Seonjeongneung is about $25.5m^3m^{-2}h^{-1}$ for the whole cases, and this value is similar to the ones in a forest or a well-wooded region. The average value of the total air temperature deviation (TD) is $-2.54^{\circ}C$ at the Seonjeongneung for the five cases. However, this cooling effect of the urban green area disappeared when the region is replaced by high-rise buildings in the CAS simulation. The $Q_{ca}$ drastically decreases to about $1.1m^3m^{-2}h^{-1}$ and the average TD shows an increase of $1.14^{\circ}C$ for the same events. This result shows that the vegetation in the Seonjeongneung supposes to keep down temperature during the heat-wave issued day and the average cooling effect of the green region is $3.68^{\circ}C$ quantitatively from the TD difference of the two simulations. The cooling effect represented with the TD difference is larger than $0.3^{\circ}C$ within 200 m distance from the boundary of the Seonjeongneung. Further improvements of the thermodynamical and advection processes above the model surface are required to consider more accurate assessment of the cooling effect for the urban green area.