• Journal of Korea Water Resources Association
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• v.53 no.7
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• pp.507-519
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• 2020

This study developed the radon measurement system that can be used for crustal movement monitoring and seismic occurrence and prediction, and compared and analyzed the results of test-operated radon measurement system and observed seismic occurrence cases. First, the developed radon measurement system consists of an NB-IoT radon measurement device, data center, data analysis, and data supply server. Because the measured radon data can be remotely trasmitted by using NB-IoT, this system is very suitable for installation and operation in unmaaned groundwater station. Second, the developed radon measurement device was test-operated at two groundwater stations in Gimpo from May to July 2019. The measured radon data was compared with the groundwater-level and electrical conductivity measurement data, and it was confirmed that the radon measurement device developed in this study has some potential for commercialization. Finally, from November 2019 to February 2020, three observed seismic cases and daily measured radon, groundwater-level, electrical conductivity data by the NB-IoT radon measurement device installed at three groundwater stations in Pohang, which is a test-bed, were compared and analyzed. As a result of the analysis, it was confirmed that the seismic occurrence correlated with radon, groundwater level, and electrical conductivity and all of these measured data will be able to provide basic data to help in seismic monitoring and prediction in the future.

• Journal of the Korean earth science society
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• v.28 no.7
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• pp.925-935
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• 2007

Water sources in volcanic Jeju Island are almost entirely dependent on groundwater because there are actually no perennial streams or rivers due to the permeable nature of surface soils derived from basaltic or trachytic rocks. Uncontrolled development of groundwater resulted in substantial water-level decline, groundwater pollution, and seawater intrusion in several places of the island. To maintain its sustainable groundwater, the provincial government has declared some parts of the island as the Special Groundwater Conservation/Management Area since 1994. Hence, all the activities for the groundwater development in the area should obtain official permit from relevant authorities. Furthermore, to acquire information on groundwater status, a network of groundwater monitoring was established to cover most of the low land and coastal areas with the installation of automatic monitoring systems since 2001. The analysis of the groundwater monitoring data indicated that the water levels had decreased at coastal area, especially in northern part of the island. Moreover, very high electrical conductivity (EC) levels and their increasing trends were observed in the eastern part, which was ascribable to seawater intrusion by intensive pumping in recent years. Water level decline and EC rise in the coastal area are expected to continue despite the present strict control on additional groundwater development.

• Horticultural Science & Technology
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• v.32 no.4
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• pp.473-483
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• 2014

In this work, the effects of shade combination, shade height and wind regime on greenhouse climate were quantified. A two-dimensional (2-D) computational fluid dynamics (CFD) model was developed based on an 11-span plastic greenhouse in eastern China for wind almost normal to the greenhouse orientation. The model was first validated with air temperature profiles measured in a compartmentalized greenhouse cultivated with mature lettuce (Lactuca sativa L., 'Yang Shan'). Next, the model was employed to investigate the effect of shade combinations on greenhouse microclimate patterns. Simulations showed similar airflow patterns in the greenhouse under different shade combinations. The temperature pattern was a consequence of convection and radiation transfer and was not significantly influenced by shade combination. The use of shade screens reduced air velocity by $0.02-0.20m{\cdot}s^{-1}$, lowered air temperature by $0.2-0.8^{\circ}C$ and raised the humidity level by 0.9-2.0% in the greenhouse. Moreover, it improved the interior climate homogeneity. The assessment of shade performance revealed that the external shade had good cooling and homogeneity performance and thus can be recommended. Furthermore, the effects of external shade height and wind regime on greenhouse climate parameters showed that external shade screens are suitable for installation within 1 m above roof level. They also demonstrated that, under external shade conditions, greenhouse temperature was reduced relative to unshaded conditions by $1.3^{\circ}C$ under a wind speed of $0.5m{\cdot}s^{-1}$, whereas it was reduced by merely $0.5^{\circ}C$ under a wind speed of $2.0m{\cdot}s^{-1}$. Therefore, external shading is more useful during periods of low wind speed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.116-122
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• 2017

The environmental lighting of a city advances its landscape standards and the city's touristic value because the lighting can help improve the city's safety and security as well as its esthetic value. The types of parks in cities vary in size and function and should be reflected carefully in lighting planning to gain the best effect. The importance of city lighting has been increased in recent years due to the expanded span of urban night life. Lighting systems around rivers and coastal waterfronts in cities play an important role not only in their functional aspects, such as safety and security, but also in boosting the city's identities. This paper performed comparison analysis among Tsim Sha Tsui Promenade in Hong Kong, Fukuoka Nakagawa Park in Japan, and the walking path in Hamdeok Beach in Jeju City, Korea. According to the evaluation, Hong Kong is excellent in 8 evaluation criteria for park lighting so that the city shows its superior installation and management. Fukuoka is also good by being analyzed as 'fair' in 5 criteria. Finally, Jeju is judged as inferior overall by showing 'poor' in several criteria. The paper shows how they differ in their environment lighting characteristics and aims to suggest stable lighting planning strategies for seaside parks in Jeju so the citizens and visitors of Jeju can enjoy the beautiful sceneries and nighttime activities.

• Journal of the Korean Society for Railway
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• v.15 no.4
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• pp.357-363
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• 2012

This paper presents a new operation method for the single phase PWM(Pulse Width Modulation) converter train. Recently, the trains adopting the PWM converter have become the majority in the electric locomotives since there are distinct advantages over the predecessors, which can be operated at near unity power factor. However, a slight modification of the control scheme makes this kind of vehicles run in the region of leading power factor. Although this feature seems to be of no significant use by itself, the leading phase operation can improve the voltage profile and the line loss of the feeding systems is decreased by compensating the reactive power loss along the line when it considered together with the feeding systems. This method is even more economical and efficient comparing with the installation of SVC that is mainly used for this purpose since the train can become a movable compensator. With the conditions and some essential formula for the leading phase operation, a new power factor control algorithm has been proposed to implement this scheme. The results of simulation through SIMULINK model show that the proposed method is suitable enough for practical use.

• Fire Science and Engineering
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• v.33 no.6
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• pp.181-185
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• 2019

In this study, Exit light installed in offices, malls, hospitals, and factories were analyzed to analyze the luminance performance of CCFL and LED light sources. In addition, fire protection products with electrical characteristics such as Exit light may change their performance due to ambient temperature, humidity, and dust. So it was extracted by installation place and analyzed its characteristics. As a result of the experiment, Exit light for CCFL type showed the value of 'ratio of luminance 2' for large, medium and small. Considering that the reference value was 'lower than 9', the value was very good and it can be seen that there is almost no change in ratio of luminance due to aging. The Exit light for LED type showed a value of 'ratio of luminance 5', which means that the light on the display surface is not uniform. In addition, there was almost no change in ratio of luminance due to ageing, but the ratio of luminance was larger than Exit light for LED type. This is an unsatisfactory result from a visual point of view. To improve this, it is necessary to disperse the light of LED light source and strengthen the regulation on ratio of luminance.

• Journal of Aerospace System Engineering
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• v.14 no.5
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• pp.42-48
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• 2020

This research illustrates how the hybrid engine system comprising of a two-cycle reciprocal engine with an integrated generator and a battery is prepared for the design process. The purpose of this research is to increase flight endurance taking advantage of the high energy density of hybrid propulsion systems as well as to cope with current environmental issues by reducing fossil fuel. The hybrid system is designed to offer 6 kW power, and the power can be adjusted by controlling the engine's RPM in accordance with load variations. In addition, the battery is adopted to offer extra electric power that this hybrid system cannot cover, and can function as the main power source in limited time in the case of an emergency situation. Besides that, the generator is directly mounted on an engine crank-shaft, and in turn, they can share the same RPM. Thus, it is hypothesized that this integration method can make a compact design possible by reducing space for the installation in the fuselage of UAVs.

• Geomechanics and Engineering
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• v.8 no.4
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• pp.615-630
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• 2015

The use of helical anchors has been extensively beyond their traditional use in the electrical power industry in recent years. They are commonly used in more traditional civil engineering infrastructure applications so that the advantages of rapid installation and immediate loading capability. The majority of the research has been directed toward the tensile uplift behaviour of single anchors (only one plate) by far. However, anchors commonly have more than one plate. Moreover, no thorough numerical and experimental analyses have been performed to determine the ultimate pullout loads of multi-plate anchors. The understanding of behavior of these anchors is unsatisfactory and the existing design methods have shown to be largely inappropriate and inadequate for a framework adopted by engineers. So, a better understanding of helical anchor behavior will lead to increased confidence in design, a wider acceptance as a foundation alternative, and more economic and safer designs. The main aim of this research is to use numerical modeling techniques to better understand multi-plate helical anchor foundation behavior in soft clay soils. Experimental and numerical investigations into the uplift capacity of helical anchor in soft clay have been conducted in this study. A total of 6 laboratory tests were carried out using helical anchor plate with a diameter of 0.05 m. The results of physical and computational studies investigating the uplift response of helical anchors in soft clay show that maximum resistances depend on anchor embedment ratio and anchor spacing ratio S/D. Agreement between uplift capacities from laboratory tests and finite element modelling using PLAXIS is excellent for anchors up to embedment ratios of 6.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.4
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• pp.296-301
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• 2016

Using high magnetic flux from a 60 Hz high-current cable, a 2 W wireless-powered energy harvesting receiver for sensor operation, internet of things (IoT) devices, and LED lights inside electrical cable tunnels is proposed. The proposed receiver comprises a copper coil with a high number of turns, a ring-shaped ferromagnetic core, a capacitor for compensating for the impedance of the coil in series, and a rectifier with various types of loads, such as sensors, IoT devices, and LEDs. To achieve safe and easy installation around the power cable, the proposed ring-shaped receiver is designed to easily open or close using a clothespin-shaped handle, which is made of highly-insulated plastic. Laminated silicon steel plates are assembled and used as the core because of their mechanical robustness and high saturation flux density characteristic, in which the thickness of each isolated plate is 0.3 mm. The series-connected resonant capacitor, which is appropriate for low-voltage applications, is used together with the proposed receiver coil. The concept of the figure of merit, which is the product weight and cost of both the silicon steel plate and the copper wire, is used for an optimized design; therefore, the weight of the fabricated receiver and the price of raw material is 750 gf and USD $2 each, respectively. The 2.2 W powering capability of the fabricated receiver was experimentally verified with a power cable current of $100A_{rms}$ at 60Hz.

• Journal of the Korea Computer Industry Society
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• v.6 no.2
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• pp.357-364
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• 2005

The prefabricated type used generally in Korea to join cable runs on new installations or to repair broken Cable runs on existing installations, because installation is very simple and save time. This type is a permanent, shielded and submersible cable joint for direct burial or vault application. It confirms to the requirements of IEEE std. 404-1993 by factory testing, but many problems of insulated cable systems are caused by internal defects of the joint part which have to be mounted ensile. Faults arise from impurities or voids. A suitable solution for a monitoring of cable joints during the after-laying test and service is partial discharge detection. Specimen obtained 1mm thickness from the insulation of real power cable and cable joint. <중략>The partial discharges are measured to determine their time dependence for 60 minutes and the influence of applied electrical stress under 30kV. $\Phi-q-n$ properties were measured using detection impedance, high pass filter and computerized data acquisition system. Statistic Value like maximum charge, repetition rate, average charge, etc. are calculated. It is possible to quantitative analysis of $\Phi-q-n$ properties from this statistic value and pattern analysis.