• Journal of the Korean Geotechnical Society
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• v.23 no.12
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• pp.61-73
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• 2007

As a part of Load and Resistance Factor Design(LRFD) code development in Korea, in this paper an intensive reliability analysis was performed to evaluate reliability levels of the two static bearing capacity methods for driven steel pipe piles adopted in Korean Standards for Structure Foundations by the representative reliability methods of First Order Reliability Method(FORM) and Monte Carlo Simulation(MCS). The resistance bias factors for the two static design methods were evaluated by comparing the representative measured bearing capacities with the design values. In determination of the representative bearing capacities of driven steel pipe piles, the 58 data sets of static load tests and soil property tests were collected and analyzed. The static bearing capacity formula and the Meyerhof method using N values were applied to the calculation of the expected design bearing capacity of the piles. The two representative reliability methods(FORM, MCS) based computer programs were developed to facilitate the reliability analysis in this study. Mean Value First Order Second Moment(MVFOSM) approach that provides a simple closed-form solution and two advanced methods of FORM and MCS were used to conduct the intensive reliability analysis using the resistance bias factor statistics obtained, and the results were then compared. In addition, a parametric study was conducted to identify the sensibility and the influence of the random variables on the reliability analysis under consideration.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.7 no.6
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• pp.709-718
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• 2017

The installation of the elevator ARD(Automatic Rescue Device) system has been forced into law in these days in order to safely rescue passengers during power failure. The configuration of the ARD system consists of energy storage device, power converter and control systems. The EDLC(Electric Double Layer Capacitor) are used as energy storage device for rapid charge/discharge purposes. The power conditioning system (PCS) consists of bi-directional converter, 3-phase converter and control system. The dead-beat control system is adopted for most systems however it requires complex mathematical calculations, the high performance microprocessors are mandatory and thus it can be a cause of high manufacturing cost. In this paper the new control method for average current mode control is presented for simple structure. The control algorithm is applied to the single phase system and then expands to three phase system to meet the sysem requirements. The mathematical modeling using average modeling method is presented and analysed by PSIM computer simulation to verifie the validity of the proposed control methods.

• KIPS Transactions on Computer and Communication Systems
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• v.12 no.10
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• pp.299-308
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• 2023

As the spectrum shortage problem has accelerated by the emergence of various services, New Radio-Unlicensed (NR-U) has appeared, allowing users who communicated in licensed bands to communicate in unlicensed bands. However, NR-U network users reduce the performance of Wi-Fi network users who communicate in the same unlicensed band. In this paper, we aim to simultaneously maximize the fairness and throughput of the unlicensed band, where the NR-U network users and the WiFi network users coexist. First, we propose an optimal power allocation scheme based on Monte Carlo Policy Gradient of reinforcement learning to maximize the sum of rates of NR-U networks utilizing rate-splitting multiple access in unlicensed bands. Then, we propose a channel occupancy time division algorithm based on sequential Raiffa bargaining solution of game theory that can simultaneously maximize system throughput and fairness for the coexistence of NR-U and WiFi networks in the same unlicensed band. Simulation results show that the rate splitting multiple access shows better performance than the conventional multiple access technology by comparing the sum-rate when the result value is finally converged under the same transmission power. In addition, we compare the data transfer amount and fairness of NR-U network users, WiFi network users, and total system, and prove that the channel occupancy time division algorithm based on sequential Raiffa bargaining solution of this paper satisfies throughput and fairness at the same time than other algorithms.

• Journal of Korea Water Resources Association
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• v.56 no.10
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• pp.641-653
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• 2023

As climate change and urbanization are causing unprecedented natural disasters in urban areas, it is crucial to have urban flood predictions with high fidelity and accuracy. However, conventional physically- and deep learning-based urban flood modeling methods have limitations that require a lot of computer resources or data for high-resolution flooding analysis. In this study, we propose and implement a method for improving the spatial resolution of urban flood analysis using a deep learning based super-resolution technique. The proposed approach converts low-resolution flood maps by physically based modeling into the high-resolution using a super-resolution deep learning model trained by high-resolution modeling data. When applied to two cases of retrospective flood analysis at part of City of Portland, Oregon, U.S., the results of the 4-m resolution physical simulation were successfully converted into 1-m resolution flood maps through super-resolution. High structural similarity between the super-solution image and the high-resolution original was found. The results show promising image quality loss within an acceptable limit of 22.80 dB (PSNR) and 0.73 (SSIM). The proposed super-resolution method can provide efficient model training with a limited number of flood scenarios, significantly reducing data acquisition efforts and computational costs.

• Explosives and Blasting
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• v.41 no.3
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• pp.38-61
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• 2023

An Excavation Damaged Zone(EDZ) caused by blasting impact changes rock properties, in situ stress distribution, etc., and its effects are noticeable at around a radioactive waste repository located at deep underground. In particular, the increase in permeability due to the formation of cracks may significantly increase the amount of groundwater inflow and the possibility of radioactive nuclide outflow. In this study, FLAC2D and FLAC3D were used to analyze the mechanical and thermal behaviors for three categories: a)No EDZ, b)Uniform EDZ, and c)Random EDZ. It was found that the tunnel displacement in the Random EDZ case was 423% higher than that in the No EDZ case and was 16% higher than that in the Uniform EDZ case. Tunnel inflow in the Random EDZ was also 17.3% and 10.8% higher than that in the No EDZ and the Uniform EDZ case, respectively. The permeability around the tunnel was increased by up to 10 times in the corner of the tunnel wall and roof due to the stress redistribution after excavation. From the computer simulation, it was found that the permeability around the tunnel wall was partially increased but the overall tunnel inflow was decreased with increase of stress ratio. Mechanical analysis using FLAC 3D showed similar results. Slight difference between 2D and 3D could be explained with the development of plastic zone during the advance of tunnel excavation in 3D.

• Journal of the Korean Association of Geographic Information Studies
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• v.27 no.2
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• pp.1-18
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• 2024

This study aimed to identify the optimal street tree planting method to improve the summer thermal environment in Seoul, Republic of Korea. The effects of road direction and street tree planting patterns on urban thermal environments using ENVI-met simulations were analyzed. The 68 scenarios were analyzed based on four road directions and 17 planting patterns. The results showed that tree planting had a reducing air temperature, mean radiant temperature, human thermal sensation (PET and UTCI). The most effective planting pattern among all scenarios was low tree height (6m), wide crown width (9m), high leaf area index (3.0), and narrow planting interval (8m). The largest improvement in the thermal environment was the northern sidewalk of the east-west road. Since this study used computer simulations, the difference from real urban spaces should be considered, and further research is needed through field measurement and consideration of more variables.

• Science of Emotion and Sensibility
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• v.26 no.4
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• pp.103-114
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• 2023

Augmented reality (AR) and virtual reality (VR) differ fundamentally, with AR overlaying computer-generated information onto the real world in a nonimmersive way. Despite extensive research on cybersickness in VR, its occurrence in AR has received less attention (Vovk et al., 2018). This study examines cybersickness and discomfort associated with AR usage, focusing on the impact of content intensity and exposure time. Participants viewed 30-minute racing simulation game clips through AR equipment, varying in racing speed to alter content intensity. Cybersickness was assessed subjectively using the Simulator sickness questionnaire (SSQ; Kennedy et al., 1993). Findings revealed a progressive increase in cybersickness with longer exposure, persisting even after removing the AR equipment. Contrarily, content intensity did not significantly influence cybersickness levels. Analysis of the SSQ subscales revealed higher oculomotor (O) scores compared to nausea (N) and disorientation (D), suggesting that discomfort primarily stemmed from oculomotor strain. The study highlights distinct differences in user experience between AR and VR, specifically in subjective responses.

• Journal of the Korea Organic Resources Recycling Association
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• v.32 no.2
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• pp.37-48
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• 2024

Wastewater treatment plants (WWTPs) are obligated to reduce carbon emissions as a part of public sector greenhouse gas (GHG) emission reduction targets. However, Sewage Statistics(2022) shows that CO₂ emissions per wastewater treatment volumes have decreased by only 3.03 % compared to 2020, which is far from enough to meet the Nationally Determined Contribution (NDC) targets. This study aimed to find operational conditions of biological reactors that minimize total carbon footprint (CFP). Total CFP considers both direct emissions from biological processes and indirect emissions from energy consumption. A study was conducted using a computer simulation program which is called as EQPS for a 4-stage BNR WWTP. The results showed that total CFP was reduced by 10.97% compared to the design condition when the mixed liquor recirculation (MLR) was set to 100 % of the influent flow. The N₂O emission factor (EF) of the target WWTP was calculated to be 0.138-0.199 %, which is significantly lower than the IPCC default value of 1.6 %. This study proposes a method to minimize total CFP in WWTPs by optimizing biological reactor operation and emphasizes the need for further research on N₂O emission reduction.

• Journal of the Korean Institute of Landscape Architecture
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• v.52 no.3
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• pp.18-32
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• 2024

This study aims to analyze the summer human thermal environment in Jeju City's outdoor parking lots by measuring microclimate data and comparing pavement and vegetation albedoes and elements through computer simulations. In measured cases, results due to albedo showed no significance, but there was a significant difference between sunny and shaded areas by trees. The sunny area had a PET (physiological equivalent temperature) in the 'very hot' level, while the shaded area exhibited a 2-step lower 'warm' level. UTCI (universal thermal climate index) also showed that the sunny area was in the 'very strong heat stress' level, whereas the shaded area was 1-step lower in the 'strong heat stress' level, confirming the role of trees in reducing incoming solar radiant energy. Simulation results, using the measured albedoes, closely resembled the measured results. Regarding vegetation, scenarios with a wide canopy, high leaf density, and narrow planting spacing were effective in mitigating the human thermal environment, and the differences due to tree height varied across scenarios. The scenario with the lowest PET value was H9W9L3D8 (tree height 9m, canopy width 9m, leaf area index 3.0, planting spacing 8m), indicating a 0.7-step decrease compared to the current landscaping scenario. Thus, it was confirmed that, among landscaping elements, trees have a significant impact on the summer human thermal environment compared to ground pavement.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.24 no.3
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• pp.55-61
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• 2024

In a hybrid architecture that combines the technological advantages of P2P(peer-to-peer) and cloud computing, it is possible to efficiently supply resources and allocate loads. In other words, by appropriately utilizing the processing power of the players constituting P2P as well as the server in the cloud computing environment, MMOG(Massively Multiplayer Online Game) can be configured that considers the scale of economic cost and service quality. In fact, the computing power and communication bandwidth of servers in the cloud are important demand-based resources. The more it is used when renting, the higher the cost, while the quality of service improves. On the other hand, if the player's processing power is utilized a lot, the quality of service deteriorates relatively while the economic cost decreases. In this paper, a bandwidth adjustment technique between servers and players for MMOG based on this hybrid structure is described. When the number of players running at the same time increases, the players' actions are appropriately distributed to servers and players to effectively utilize the server's computing power and communication volume. Simulation results show that in the MMOG based on cloud and P2P hybrid architecture, the bandwidth of the server is proportionally decreased as the bandwidth directly handled by players is increased.