• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2003.11a
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• pp.279-281
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• 2003

We analysed the operating properties of resistive type superconducting fault current limiters (SFCLs) based on YBCO thin films with a single line-to-ground fault. When a single line-to-ground fault occurred, the short circuit current of a fault phase increased up to about 6 times of transport currents immediately after the fault instant and was effectively limited to the designed current level within 2 ms by the resistance development of the SFCL. The fault currents of the sound phases almost did not change because of their direct grounding system. The unsymmetrical rates of a fault phase were distributed from 6.4 to 1.4. It was found that the unsymmetrical rates of currents were noticeably improved within one cycle after the fault instant. We calculated the zero phase currents for a single line-to-ground fault using the symmetrical component analysis. The positive sequence resistance was reduced remarkably right after the fault but eventually approached the balanced positive resistance component prior to the system fault. This means that the system reaches almost the three-phase symmetrical state in about 60 ㎳ after the fault. The ground currents were almost 3 times of the zero phase mts since most of the fault currents flowed through the grounding line.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.1
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• pp.305-321
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• 2012

Since Internet Protocol (IP) is the most important protocol in Next Generation Networks (NGNs), 3rd Generation Partnership Project (3GPP) utilizes Session Initial Protocol (SIP) based on IP as the base protocol for negotiating sessions in IP Multimedia Subsystem (IMS). Different from traditional circuit-switched network, in IMS, the media traffic and signaling are delivered through IP transport. The media traffic may affect the signaling efficiency in core network, due to traffic collisions and best effort packets delivery. This paper proposes a novel path-migration mechanism for enhancing the traffic efficiency in integrated NGN-IMS. The simulation results show that the interference and traffic collision can be reduce by applying proposed path-migration mechanism and the signaling efficiency in core network can be improved with higher system capability and voice quality.

• Nuclear Engineering and Technology
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• v.53 no.10
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• pp.3196-3206
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• 2021

For the Korean design of the PCCS (passive containment cooling system) in an innovative PWR, the overall thermal resistance around a condenser tube is dominated by the heat transfer coefficient of steam condensation on the exterior surface. It has been reported, however, that the calculated heat transfer coefficients by thermal-hydraulic system codes were much lower than measured data in separate effect tests. In this study, a new empirical model of steam condensation in the presence of a noncondensable gas was implemented into the MARS-KS 1.4 code to replace the conventional Colburn-Hougen model. The selected correlation had been developed from condensation test data obtained at the JERICHO (JNU Experimental Rig for Investigation of Condensation Heat transfer On tube) facility, and considered the effect of the Grashof number for naturally circulating gas mixture and the curvature of the condenser tube. The modified MARS-KS code was applied to simulate the transient response of the containment equipped with the PCCS to the large-break loss-of-coolant accident. The heat removal performances of the PCCS and corresponding evolution of the containment pressure were compared to those calculated via the original model. Various thermal-hydraulic parameters associated with the natural circulation operation through the heat transport circuit were also investigated.

• Metals and materials international
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• v.24 no.6
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• pp.1232-1240
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• 2018

Corrosion properties of dissimilar friction stir welded 6061 aluminum and HT590 steel were investigated to understand effects of galvanic corrosion. As cathode when coupled, HT590 was cathodically protected. However, the passivation of AA6061 made the aluminum alloy cathode temporarily, which leaded to corrosion of HT590. From the EIS analysis showing Warburg diffusion plot in Nyquist plots, it can be inferred that the stable passivation layer was formed on AA6061. However, the weld as well as HT590 did not show Warburg diffusion plot in Nyquist plots, suggesting that there was no barrier for corrosion or even if it exists, the barrier had no function for preventing and/or retarding charge transport through the passivation layer. The open circuit potential measurements showed that the potential of the weld was similar to that of HT590, which lied in the pitting region for AA6061, making the aluminum alloy part of the weld keep corrosion state. That resulted in the cracked oxide film on AA6061 of the weld, which could not play a role of corrosion barrier.

• Journal of Drive and Control
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• v.18 no.3
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• pp.8-15
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• 2021

A rear axle steering (RAS) system is attached to the rear of medium and large commercial vehicles that transport large cargo. The existing RAS systems are driven by electro-hydraulic actuator (EHA), and most commercialized EHAs consist of electric motors, hydraulic pumps, relief valves, prefill valves and cylinders. The prefill valve required for such EHAs is a type of check valve with extremely low cracking pressure that should not allow RAS to have noise or vibration, and the prefill valve prevents system negative pressure as well as unstable operation. Most papers on this topic rely on experiments to predict valve performance, and theoretically detailed modeling of valves or pipelines is performed, but it is very rare to evaluate hydraulic vibration characteristics by analysing everything from hydraulic pumps to valves comprehensively. In this study, we proposed an experimental circuit that can predict the performance of the prefill valve. The study also analysed the pressure-flow pulsation that is transmitted to the valve through the pipeline, and how the transmitted pressure-flow pulsation affects the valve vibration.

• Nuclear Engineering and Technology
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• v.54 no.9
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• pp.3567-3579
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• 2022

This paper provides an assessment of fluid transport and mixing processes inside the primary circuit of the test facility ROCOM through the numerical simulation of Test 2.1 with the system code ATHLET. The experiment represents an asymmetric injection of cold and non-borated water into the reactor coolant system (RCS) of a pressurized water reactor (PWR) to restore core cooling, an emergency procedure which may subsequently trigger a core re-criticality. The injection takes place at low velocity under single-phase subcooled conditions and presents a major challenge for the simulation in lumped parameter codes, due to multidimensional effects in horizontal piping and vessel arising from density gradients and gravity forces. Aiming at further validating ATHLET 3-D capabilities against horizontal geometries, the experiment conditions are applied to a ROCOM model, which includes a newly developed horizontal pipe object to enhance code prediction inside coolant loops. The obtained results show code strong simulation capabilities to represent multidimensional flows. Enhanced prediction is observed at the vessel inlet compared to traditional 1-D approach, whereas mixing overprediction from the descending denser plume is observed at the upper-half downcomer region, which leads to eventual deviations at the core inlet.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.993-994
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• 2008

Electrochromic (EC) devices are capable of reversibly changing their optical properties upon charge injection and extraction induced by the external voltage. The characteristics of the EC device, such as low power consumption, high coloration efficiency, and memory effects under open circuit status, make them suitable for use in a variety of applications including smart windows and electronic papers. Coloration due to reduction or oxidation of redox chromophores can be used for EC devices (e-paper), but the switching time is slow (second level). Recently, with increasing demand for the low cost, lightweight flat panel display with paper-like readability (electronic paper), an EC display technology based on dye-modified $TiO_2$ nanoparticle electrode was developed. A well known organic dye molecule, viologen, was adsorbed on the surface of a mesoporous $TiO_2$ nanoparticle film to form the EC electrode. On the other hand, ZnO is a wide bandgap II-VI semiconductor which has been applied in many fields such as UV lasers, field effect transistors and transparent conductors. The bandgap of the bulk ZnO is about 3.37 eV, which is close to that of the $TiO_2$ (3.4 eV). As a traditional transparent conductor, ZnO has excellent electron transport properties, even in ZnO nanoparticle films. In the past few years, one-dimension (1D) nanostructures of ZnO have attracted extensive research interest. In particular, 1D ZnO nanowires renders much better electron transportation capability by providing a direct conduction path for electron transport and greatly reducing the number of grain boundaries. These unique advantages make ZnO nanowires a promising matrix electrode for EC dye molecule loading. ZnO nanowires grow vertically from the substrate and form a dense array (Fig. 1). The ZnO nanowires show regular hexagonal cross section and the average diameter of the ZnO nanowires is about 100 nm. The cross-section image of the ZnO nanowires array (Fig. 1) indicates that the length of the ZnO nanowires is about $6\;{\mu}m$. From one on/off cycle of the ZnO EC cell (Fig. 2). We can see that, the switching time of a ZnO nanowire electrode EC cell with an active area of $1\;{\times}\;1\;cm^2$ is 170 ms and 142 ms for coloration and bleaching, respectively. The coloration and bleaching time is faster compared to the $TiO_2$ mesoporous EC devices with both coloration and bleaching time of about 250 ms for a device with an active area of $2.5\;cm^2$. With further optimization, it is possible that the response time can reach ten(s) of millisecond, i.e. capable of displaying video. Fig. 3 shows a prototype with two different transmittance states. It can be seen that good contrast was obtained. The retention was at least a few hours for these prototypes. Being an oxide, ZnO is oxidation resistant, i.e. it is more durable for field emission cathode. ZnO nanotetropods were also applied to realize the first prototype triode field emission device, making use of scattered surface-conduction electrons for field emission (Fig. 4). The device has a high efficiency (field emitted electron to total electron ratio) of about 60%. With this high efficiency, we were able to fabricate some prototype displays (Fig. 5 showing some alphanumerical symbols). ZnO tetrapods have four legs, which guarantees that there is one leg always pointing upward, even using screen printing method to fabricate the cathode.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.646-651
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• 2018

This paper reports that the electronic properties at a $P3HT/TiO_2$ interface associated with exciton dissociation and transport can be tailored by the insertion of a graphene quantum dot (GQD) layer. For donor/acceptor interface modification in an $ITO/TiO_2/P3HT/Al$ photovoltaic (PV) device, a continuous GQD film was prepared by a sonication treatment in solution that simplifies the conventional processes, including laser fragmentation and hydrothermal treatment, which limits a variety of component layers and involves low cost processing. The high conductivity and favorable energy alignment for exciton dissociation of the GQD layer increased the fill factor and short circuit current. The origin of the improved parameters is discussed in terms of the broad light absorption and enhanced interfacial carrier transport.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.19 no.2
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• pp.48-61
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• 2020

The objective of this study is to estimate traffic capacity based on the heavy-vehicle ratio in a two-lane freeway work zone where one lane is blocked by construction. For this, closed circuit television (CCTV) video data of the freeway work zone was collected, and the congestion at an upstream point was observed. The traffic volume at a downstream point was analyzed after a bottleneck was created by the blockage due to the upstream congestion. A distribution model was estimated using observed-time headway, and the road capacity was analyzed using a goodness-of-fit test. Through this process, the general capacity and an equation for capacity based on the heavy-vehicle ratio passing through the work zone were presented. Capacity was estimated to be 1,181~1,422 passenger cars per hour per lane (pcphpl) at Yeongdong, and 1,475~1,589pcphpl at Jungbu Naeryuk. As the ratio of heavy vehicles increased, capacity gradually decreased. These findings can contribute to the proper capacity estimation and efficient traffic operation and management for two-lane freeway work zones that block one lane due to a work zone.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.22 no.6
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• pp.114-123
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• 2023

With the development of computer vision technology, video sensors such as CCTV are detecting incident. However, most of the current incident have been detected based on existing fixed imaging equipment. Accordingly, there has been a limit to the detection of incident in shaded areas where the image range of fixed equipment is not reached. With the recent development of edge-computing technology, real-time analysis of mobile image information has become possible. The purpose of this study is to evaluate the possibility of detecting expressway emergencies by introducing computer vision technology to dash cam. To this end, annotation data was constructed based on 4,388 dash cam still frame data collected by the Korea Expressway Corporation and analyzed using the YOLO algorithm. As a result of the analysis, the prediction accuracy of all objects was over 70%, and the precision of traffic accidents was about 85%. In addition, in the case of mAP(mean Average Precision), it was 0.769, and when looking at AP(Average Precision) for each object, traffic accidents were the highest at 0.904, and debris were the lowest at 0.629.