• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1604-1615
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• 2023

In an open-pool type research reactor with a downward forced flow in the core, pipes can be under sub-atmospheric pressure because of the large pressure drop at the reactor core in the atmospheric pool. Sub-atmospheric pressure can result in air inflow into the pipe from the pressure difference between the atmosphere and the inside of the pipe, which in a postulated pipe break scenario can lead to the breakdown of the cooling pump. In this study, a plant-scale experiment was conducted to study air inflow in large piping systems by considering the actual operational conditions of an advanced research reactor. The air inflow rate was measured, and the entrained air was visualized to investigate the behavior of air inflow and flow regime depending on the pipe break size. In addition, the developed drift-flux model for a large vertical pipe with a diameter of 600 mm was compared with other correlations. The flow regime transition in a large vertical pipe under downward flow was also studied using the newly developed drift-flux model. Consequently, the characteristics of two-phase flow in a large vertical pipe were found to differ from those in small vertical pipes where liquid recirculation was not dominant.

• Nuclear Engineering and Technology
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• v.56 no.4
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• pp.1254-1266
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• 2024

This study investigates the application of supercritical carbon dioxide (S-CO₂) direct-cycle micro modular reactors (MMRs) in primary frequency control (PFC), which is a scenario characterized by significant load fluctuations that has received less attention compared to secondary load-following. Using a modified GAMMA + code and a deep neural network-based turbomachinery off-design model, the authors conducted an analysis to assess the behavior of the reactor core and fluid system under different PFC scenarios. The results indicate that the acceptable range for sudden relative electricity output (REO) fluctuations is approximately 20%p which aligns with the performance of combined-cycle gas turbines (CCGTs) and open-cycle gas turbines (OCGTs). In S-CO₂ direct-cycle MMRs, the control of the core operates passively within the operational range by managing coolant density through inventory control. However, when PFC exceeds 35%p, system control failure is observed, suggesting the need for improved control strategies. These findings affirm the potential of S-CO₂ direct-cycle MMRs in PFC operations, representing an advancement in the management of grid fluctuations while ensuring reliable and carbon-free power generation.

• Journal of Korean Society of Transportation
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• v.36 no.2
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• pp.67-85
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• 2018

Vehicle platooning through wireless communication and automated driving technology has become realized. Platooning is a technique in which several vehicles travel at regular intervals while maintaining a minimum safety distance. Truck platooning is of keen interest because it contributes to preventing truck crashes and reducing vehicle emissions, in addition to the increase in truck flow capacity. However, it should be noted that interactions between vehicle platoons and adjacent manually-driven vehicles (MV) significantly give an impact on the performance of traffic flow. In particular, when vehicles entering from on-ramp attempt to merge into the mainstream of freeway, proper interactions by adjusting platoon size and inter-platoon spacing are required to maximize traffic performance. This study developed a methodology for establishing operational strategies for truck platoonings on freeway on-ramp areas. Average speed and conflict rate were used as measure of effectiveness (MOE) to evaluate operational efficiency and safety. Microscopic traffic simulation experiments using VISSIM were conducted to evaluate the effectiveness of various platooning scenarios. A decision making process for selecting better platoon operations to satisfy operations and safety requirements was proposed. It was revealed that a platoon operating scenario with 50m inter-platoon spacing and the platoon consisting of 6 vehicles outperformed other scenarios. The proposed methodology would effectively support the realization of novel traffic management concepts in the era of automated driving environments.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.19 no.2
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• pp.135-148
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• 2020

The ongoing development of autonomous driving-related technology may cause different kinds of accidents while testing new changes. As a result, more information on ODD suitable for the domestic road environment will be necessary to prevent safety accidents. Besides, implementation of the Autonomous Vehicle Act will increase autonomous driving demonstrations on roads currently in use. This study describes an ODD for demonstrating an autonomous driving shuttle in downtown areas. It addresses a possible scenario of autonomous driving around a downtown road in Anyang. Geometric, operational, and environmental factors are considered while maintaining a domestic road environment and safety. Autonomous driving shuttles are demonstrated in 30 nodes, each identified by node type and signal-communication. Link criteria are an autonomous driving restriction in 42 morning peak (8-9am) hours, 39 non-peak (12-13pm) hours, and 40 afternoon peak (18-19pm) hours. In the future, conclusions may be considered for preliminary safety assessments of roads where autonomous driving tests are performed.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.5
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• pp.543-551
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• 2014

This study has searched to find a program in order to manage simply and practically use the expelled AtoN database from the AtoN Simulator and to support the idea decision for the AtoN placement. It examines a program that manages AtoN database through the hierarchy structure, history card and endowment with condition same as a scenario. And accomplishes this study's goal owing to realizing AtoN operational software that helps for visual, hearing sense, fixed amount verification upon AtoN placement project. The AtoN operational software contributes not only flexible control like a newly establishment, relocation etc, but also supports idea decision for AtoN placement plan through many functions such as condition search, virtual sailing and fixed amount appraisal result exhibition, etc. Through utilization of this, it is to help upon the presupposition of the impact to ship or sailor about many designs and in addition, upon the judgment of whether or not for the efficiency and appropriation of the design. It is expected to reduce possible failure costs and management costs due to AtoN design and placement plans, because to compare more various designs thru the easier verification method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.429-438
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• 2021

Owing to the development of science technology, particularly the smart concept and defense policy factors of the 4th industry, military weapon systems are advanced, and the scientific and operational force is reduced dramatically. The aspect of the future war is characterized by the operation of troops with reduced forces from advanced and scientific weapon systems in an operational area that has expanded more than four times compared to the present. Reflecting on these situational factors, it is necessary to improve combat methods based on the changes in the battlefield environment and advanced weapon systems. In this study, to find a more efficient future combat method in a changing war pattern, this study applied the battle experiment methodology using Vision21 war game model, which is an analytical model used by the army. Finally, this study aimed to verify the future combat method and unit structure. Therefore, the scenario composition and experiment method that reflect the change in the ground operational environment and weapon system was first composed. Subsequently, an analysis method based on the combat effectiveness was applied to verify the effective combat performance method and unit structure of future infantry units.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.3
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• pp.218-227
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• 2016

Korean government plans to launch a lunar orbiter and a lander to the Moon by 2020. Before launch these two proves, an experimental lunar orbiter will be launched by 2018 to obtain key space technologies for the lunar exploration. Several payloads equipped in experimental lunar orbiter will monitor the surface of the Moon and will gather science data. Lunar orbiter sends telemetry and receives tele-command from ground using S-band while science data is sent to ground stations using X-band when the visibility is available. Korean deep space network will be mainly used for S and X-band communication with lunar orbiter. Deep Space Network or Universal Space Network can also be used for the S-band during trans-lunar phase when korean deep space network is not available and will be used for the S-band in normal mission orbit as a backup. This paper analyzes a visibility condition based on the combination of various ground antennas and its mask angles according to mission scenario to predict the number of contacts per day and to build an operational scenario for the lunar orbiter.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.3
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• pp.137-149
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• 2021

Cable-stayed bridges are infrastructure facilities of a highly public nature; therefore, it is essential to ensure operational safety and prompt response in the event of a collapse or damage caused by natural and social disasters. Among social disasters, impact accidents can occur in bridges when a vehicle collides with a pier or when crashes occur due to aircraft defects. In the case of offshore bridges, ship collisions will occur at the bottom of the pylon. In this research, a procedure to evaluate the structural behavior of a cable-stayed bridge for aircraft impact is suggested based on a numerical analysis approach, and the feasibility of the procedure is demonstrated by performing an example assessment. The suggested procedure includes 1) setting up suitable aircraft impact hazard scenarios, 2) structural modeling considering the complex behavior mechanisms of cable-stayed bridges, and 3) structural behavior evaluation of cable-stayed bridges using numerical impact simulation. It was observed that the scenario set in this study did not significantly affect the target bridge. However, if impact analysis is performed through various scenarios in the future, the load position and critical load level to cause serious damage to the bridge could be identified. The scenario-based assessment process employed in this study is expected to facilitate the evaluation of bridge structures under aircraft impact in both existing bridges and future designs.

• Korean Chemical Engineering Research
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• v.62 no.2
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• pp.163-172
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• 2024

In this study, two different scenarios for ammonia liquefaction in the green ammonia manufacturing process were proposed, and the economic-feasibility and environmental impact of each scenario were analyzed. The two liquefaction processes involved gas-liquid separation before cooling at high pressure (high pressure cooling process) or after decompression without the gas-liquid separation (low pressure cooling process). The high-pressure cooling process requires higher capital costs due to the required installation of separation units and heat exchangers, but it offers relatively lower total utility costs of 91.03 $/hr and a reduced duty of 2.81 Gcal/hr. In contrast, although the low-pressure cooling process is simpler and cost-effective, it may encounter operational instability due to rapid pressure drops in the system. Environmental impact assessment revealed that the high-pressure cooling process is more environmentally friendly than the low-pressure cooling process, with an emission factor of 0.83 tCO₂eq less than the low-pressure cooling process, calculated based on power usage. Consequently, the outcomes of this study provide relevant scenario and a database for green ammonia synthesis process adaptable to various process conditions.

• Journal of Digital Convergence
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• v.12 no.2
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• pp.379-389
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• 2014

The purpose of this study is to optimize the patient(examinee) flow in a health examination center via a simulation model and to improve operational efficiency. Two experimentation scenarios were implemented into the simulation model to determine which proposed scenario provides better improvement in terms of the following performance measures: LOS(Length of Stay), staff utilization, and occupancy level. The simulation results demonstrated that there was no significant difference in response results of two scenarios. Although the original motivation of this study was suggest optimal policy for a patient(examinee) flow, the insight into applying simulation in efficiently managing hospital operations is of more value. Simulation approach is a powerful technique that supports efficient decision-making compared to traditional healthcare management approach based on past experience, feelings, and intuition. Therefore, the proposed experimentation model has wide applicability in healthcare systems.