• Magazine of the Korean Society of Agricultural Engineers
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• v.27 no.2
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• pp.23-37
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• 1985

This studies were carried out to get characteristics of frequency distribution, probable flood flows according to the return periods, and the correlation between return periods and those length of records affect the Risk of failure in the annual maximum series of the main river systems in Korea. Especially, Risk analysis according to the levels were emphasized in relation to the design frequency factors for the different watersheds. Twelve watersheds along Han, Geum, Nak Dong, Yeong San and Seom Jin river basin were selected as studying basins. The results were analyzed and summarized as follows. 1. Type 1 extremal distribution was newly confirmed as a good fitted distribution at selected watersheds along Geum and Yeong San river basin. Three parameter lognormal Seom Jin river basin. Consequently, characteristics of frequency distribution for the extreme value series could be changed in connection with the watershed location even the same river system judging from the results so far obtained by author. 2. Evaluation of parameters for Type 1 extremal and three parameter lognormal distribution based on the method of moment by using an electronic computer. 3. Formulas for the probable flood flows were derived for the three parameter lognormal and Type 1 extremal distribution. 4. Equations for the risk to failure could be simplified as $\frac{n}{N+n}$ and $\frac{n}{T}$ under the condition of non-parametric method and the longer return period than the life of project, respectively. 5. Formulas for the return periods in relation to frequency factors were derived by the least square method for the three parameter lognormal and Type 1 extremal distribution. 6. The more the length of records, the lesser the risk of failure, and it was appeared that the risk of failure was increasing in propotion to the length of return periods even same length of records. 7. Empirical formulas for design frequency factors were derived from under the condition of the return periods identify with the life of Hydraulic structure in relation to the risk level. 8. Design frequency factor was appeared to be increased in propotion to the return periods while it is in inverse proportion to the levels of the risk of failure. 9. Derivation of design flood including the risk of failure could be accomplished by using of emprical formulas for the design frequency factor for each watershed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.118-124
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• 2017

In this study, a numerical simulation was performed using commercial code Fluent(v.17.1). The underground Combined Cycle Power Plant (CCPP) was simplified to analyze the methane gas leakage with the crack size and position. In addition, extensive numerical simulations were carried out for different crack sizes from 10 mm to 20 mm. The crack position is the gas leakage, which is assumed to be near the pipe elbow and the gas turbine. A total of 4 cases were compared and analyzed. To analyze the gas leakage, the concept of the Lower Flammable Limit (LFL) was applied. The leakage distance was defined in the longitudinal direction, and the transverse direction was estimated and quantitatively analyzed. As a result, the leakage distance in the longitudinal direction varies by 52.3 % depending on the crack size at the same crack position. Moreover, the maximum difference was 34.8 % according to the crack position when the crack sizes are identical. As jet flow impacts on the obstacle and changes its direction, the recirculation flows are formed. These results are expected to provide useful data to optimize the location and number of gas detections in confined spaces, such as underground CCPP.

• Journal of Korea Water Resources Association
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• v.52 no.11
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• pp.931-940
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• 2019

In hydrologic models, parameters are mainly used to reflect hydrologic elements or to supplement the simplified models. In this process, the proper selection of the parameters in the model can reduce the uncertainty. Accordingly, this study attempted to quantify the uncertainty of SWAT parameters using the General Likelihood Uncertainty Estimation (GLUE). Uncertainty analysis on SWAT parameters was conducted by using the formal and informal likelihood measures. The Lognormal function and Nash-Sutcliffe Efficiency (NSE) were used for formal and informal likelihood, respectively. Subjective factors are included in the selection of the likelihood function and the threshold, but the behavioral models were created by selecting top 30% lognormal for formal likelihood and NSE above 0.5 for informal likelihood. Despite the subjectivity in the selection of the likelihood and the threshold, there was a small difference between the formal and informal likelihoods. In addition, among the SWAT parameters, ALPHA_BF which reflects baseflow characteristics is the most sensitive. Based on this study, if the range of SWAT model parameters satisfying a certain threshold for each watershed is classified, it is expected that users will have more practical or academic access to the SWAT model.

• Ecology and Resilient Infrastructure
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• v.8 no.4
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• pp.165-178
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• 2021

We studied driftwood behaviors including generation and deposition in a tsunami using a numerical simulation. We used an integrated two-dimensional numerical model, which included a driftwood dynamics model. The study area was Sendai, Japan. Observation data collected by Inagaki et al. (2012) were used to verify the simulation results by comparing them with driftwood deposition patterns. A simplified model was developed to consider the threshold of driftwood generation by the drag force of water flows. To consider the volume of driftwood generated, we estimated the total wood number in the study area using Google Earth. Therefore, we simulated more than 13,000 pieces of driftwood that were generated and transported inland from approximately 300,000 trees that were growing in the forest. The final distribution of the driftwood was similar to the observation data. The reproducibility of the generation and deposition patterns of driftwood showed good agreement in terms of longitudinal deposition pattern. In the future, a sensitivity analysis on driftwood parameters, such as the size of the wood, boundary conditions, and grid size, will be implemented to predict the travel patterns of driftwood. Such modeling will be a useful methodology for disaster prediction based on water flow and driftwood.

• Korean Journal of Optics and Photonics
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• v.30 no.4
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• pp.142-145
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• 2019

Normally, a corner cube retroreflector (CCRR) sheet is used as a retroreflective mirror array (RRMA) in a volumetric display. Each CCRR unit reflects light in the retroreflective direction, which is parallel to the incident light, and it makes a blurred image, as it shifts the position of light within its dimensions. Adopting a "curved planar wall" and "parabolic focusing" (x-axis), a hybrid-t(transverse direction)-RRMA is proposed, to improve the image quality and brightness. The improvement of image contrast is achieved by tuning a "linear v-shaped groove" structure to a "parabolic v-shaped groove". Also, the system has been simplified and the brightness enhanced 4 times by removing the half mirror.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.167-178
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• 2021

Since 2014, the quality level survey of the defense industry has been carried out annually. The need for this was felt as the quality control policy was inadequately reflected in the survey results. In this study, to secure valid and reliable data, the quality level survey measurement indicators and questionnaires used previously were analyzed and developed as customized papers according to the size of the company. The questionnaire index was simplified through the elimination of unnecessary and redundant items to improve the response rate and reliability. In addition, a comprehensive score was computed based on the improvement index so that the result of the quantitative quality level survey could be calculated. Through this, it was possible to determine the quality level attained by the defense industry. Through the quality level survey, we intend to secure data that can analyze the quality management environment to maintain quality levels of the defense industry and identify ways to establish mid-to-long-term quality management strategies and improve systems to enhance the quality level of the defense industry in the future.

• The Journal of the Korea Contents Association
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• v.21 no.6
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• pp.62-70
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• 2021

2020 was a year in which the world spent in disorder due to the pandemic of Coronavirus infection-19(COVID-19). The pandemic was at the beginning of a turning point in history. For examples, the Black Death(Pest) that destroyed the feudal system of medieval Europe in the 14th century, smallpox that led to the destruction of the Inca Empire by Spain in the 17th century, and the Spanish flu that ended World War I early. The great transformation that will come after COVID-19 is presented from various fields and perspectives, but the understanding and direction of the transformation is ambiguous. This study attempts to derive and to analyze core terms based on a network of the future of globalization after COVID-19. Four Networks related to globalization, anti-globalization, and globalization and digitalization after COVID-19 were established respectively. A network integrating four networks was also constructed. The core terms were extracted from the hub nodes, the stress centrality, and the simplified network to which the K-core algorithm was applied. After COVID-19, the changes in globalization were analyzed from the extracted core terms. This study is thought to be meaningful to propose a method of deriving and analyzing core terms based on a network in understanding social changes after COVID-19.

• Therapeutic Science for Rehabilitation
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• v.10 no.4
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• pp.81-94
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• 2021

Objective : Response time plays a prominent part in research on cognitive ability and the aging effect. This study aimed to identify the impact of cognitive ability on information processing by conducting cognitive response time (CRT) using a computer program. Methods : This study was conducted in 30 normal elderly (NE) and 30 elderly with amnestic MCI (aMCI), aged 65-79 years old living in Daegu and Gyeongbuk. The results were analyzed using the statistical analysis program R 4.0.2 (University of Auckland, New Zealand). Results : In the three sub-areas of CRT, the total response time showed a significant difference depending on group or age, and the error rate showed a significant difference depending on age or group in some sub-areas. In the aMCI group, the performance of CRT significantly correlated with that of the overall cognition and memory test. Conclusion : Information processing depending on aging or cognitive ability and the differential performance of processing speed could be observed through CRT. The performance of this test was found to be significantly correlated with that of the overall cognition and memory test. Therefore, CRT could be used meaningfully as a simplified tool to predict the initial cognitive disorder of the elderly in the community.

• Computers and Concrete
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• v.31 no.4
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• pp.337-348
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• 2023

Shear wall is commonly used as a lateral force resisting system of concrete mid-rise and high-rise buildings, but it brings challenges in providing relatively large space throughout the building height. For this reason, the structure system where the upper structure with bearing, non-bearing and/or shear walls that sits on top of a transfer plate system supported by widely spaced columns at the lower stories is preferred in some regions, particularly in low to moderate seismic regions in Asia. A thick reinforced concrete (RC) plate has often been used as a transfer system, along with RC transfer girders; however, the RC plate becomes very thick for tall buildings. Applying the post-tensioning (PT) technique to RC plates can effectively reduce the thickness and reinforcement as an economical design method. Currently, a simplified model is used for numerical modeling of PT transfer plate, which does not consider the interaction of the plate and the upper structure. To observe the actual behavior of PT transfer plate under seismic loads, it is necessary to model whole parts of the structure and tendons to precisely include the interaction and the secondary effect of PT tendons in the results. This research evaluated the seismic behavior of shear wall-type residential buildings with PT transfer plates for the condition that PT tendons are included or excluded in the modeling. Three-dimensional finite element models were developed, which includes prestressing tendon elements, and response spectrum analyses were carried out to evaluate seismic forces. Two buildings with flat-shape and L-shape plans were considered, and design forces of shear walls and transfer columns for a system with and without PT tendons were compared. The results showed that, in some cases, excluding PT tendons from the model leads to an unrealistic estimation of the demands for shear walls sit on transfer plate and transfer columns due to excluding the secondary effect of PT tendons. Based on the results, generally, the secondary effect reduces shear force demand and axial-flexural demands of transfer columns but increases the shear force demand of shear walls. The results of this study suggested that, in addition to the effect of PT on the resistance of transfer plate, it is necessary to include PT tendons in the modeling to consider its effect on force demand.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.70-78
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• 2023

The ordinary concentrically braced frame has an advantage of having simple design procedure. For this reason, it has been widely used for the small-sized frame structures subject to moderate or lower magnitude earthquake, even though its seismic performance against the earthquake load is not much effective compared to that of other frame systems. To enhance seismic performance of the ordinary concentrically braced frame where the bracing has a weakness for compressive behavior under lateral earthquake, seismic retrofitting by viscous damper has been commonly introduced. However, the viscous damper, itself, generally does not have stiffness for restoring the structure to the original position. This may cause residual displacement to the structure. In this paper, a self-centering viscous damper system in which upper and lower beams having flexural rigidity play a role as a nonlinear-elastic spring, restoring the spring-damper system subject to external displacement history to its original location, is developed. The numerical analysis for a simplified frame structure shows how including the developed self-centering viscous damper system leads to an enhanced seismic performance of the frame structure through energy dissipation during earthquake excitation.