• 한국태양에너지학회 논문집
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• 제38권3호
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• pp.21-28
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• 2018

The objects of PV (Photovoltaic) monitoring system is to reduce the loss of system and operation and maintenance costs. In case of PV plants with configured of centralized inverter type, only 1 PV module might be caused a large loss in the PV plant. For this reason, the monitoring technology of PV module-level that find out the location of the fault module and reduce the system losses is interested. In this paper, a fault diagnosis algorithm are proposed using thermal and electrical characteristics of PV modules under failure. In addition, the monitoring system applied with proposed algorithm was constructed. The wireless sensor using LoRa chip was designed to be able to connect with IoT device in the future. The characteristics of PV module by shading is not failure but it is treated as a temporary failure. In the monitoring system, it is possible to diagnose whether or not failure of bypass diode inside the junction box. The fault diagnosis algorithm are developed on considering a situation such as communication error of wireless sensor and empirical performance evaluation are currently conducting.

• 인간식물환경학회지
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• 제21권6호
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• pp.445-460
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• 2018

Exposure to indoor air pollution is an emerging world-wide problem, with growing evidence that it is a major cause of morbidity worldwide. Whilst most indoor air pollutants are of outdoor origin, these combine with a range of indoor sourced pollutants that may lead to high pollutant levels indoors. The pollutants of greatest concern are volatile organic compounds (VOCs) and particulate matter (PM), both of which are associated with a range of serious health problems. Whilst current buildings usually use ventilation with outdoor air to remove these pollutants, botanical systems are gaining recognition as an effective alternative. Whilst many years research has shown that traditional potted plants and their substrates are capable of removing VOCs effectively, they are inefficient at removing PM, and are limited in their pollutant removal rates by the need for pollutants to diffuse to the active pollutant removal components of these systems. Active botanical biofiltration, using green wall systems combined with mechanical fans to increase pollutant exposure to the plants and substrate, show greatly increased rates of pollutant removal for both VOCs, PM and also carbon dioxide ($CO_2$). A developing body of research indicates that these systems can outperform existing technologies for indoor air pollutant removal, although further research is required before their use will become widespread. Whilst it is known that plant species selection and substrate characteristics can affect the performance of active botanical systems, optimal characteristics are yet to be identified. Once this research has been completed, it is proposed that active botanical biofiltration will provide a cheap and low energy use alternative to mechanical ventilations systems for the maintenance of indoor environmental quality.

• 품질경영학회지
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• 제49권4호
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• pp.581-594
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• 2021

Purpose: The purpose of this study is to compare machine learning models for anomaly detection of mechanical facility equipment and suggest an anomaly detection system for mechanical facility equipment in subway stations. It helps to predict failures and plan the maintenance of facility. Ultimately it aims to improve the quality of facility equipment. Methods: The data collected from Daejeon Metropolitan Rapid Transit Corporation was used in this experiment. The experiment was performed using Python, Scikit-learn, tensorflow 2.0 for preprocessing and machine learning. Also it was conducted in two failure states of the equipment. We compared and analyzed five unsupervised machine learning models focused on model Long Short-Term Memory Variational Autoencoder(LSTM-VAE). Results: In both experiments, change in vibration and current data was observed when there is a defect. When the rotating body failure was happened, the magnitude of vibration has increased but current has decreased. In situation of axis alignment failure, both of vibration and current have increased. In addition, model LSTM-VAE showed superior accuracy than the other four base-line models. Conclusion: According to the results, model LSTM-VAE showed outstanding performance with more than 97% of accuracy in the experiments. Thus, the quality of mechanical facility equipment will be improved if the proposed anomaly detection system is established with this model used.

• 전력전자학회논문지
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• 제26권5호
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• pp.325-333
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• 2021

A 3 kW grid-tied PV inverter with Gallium nitride high-electron mobility transistor (GaN HEMT) for domestic commercialization was developed using boost converter and full-bridge inverter with LCL filter topology. Recently, many GaN HEMTs are manufactured as surface mount packages because of their lower parasitic inductance characteristic than standard TO (transistor outline) packages. A surface mount packaged GaN HEMT releases heat through either top or bottom cooling method. IGOT60R070D1 is selected as a key power semiconductor because it has a top cooling method and fairly low thermal resistances from junction to ambient. Its characteristics allow the design of a 3 kW inverter without forced convection, thereby providing great advantages in terms of easy maintenance and high reliability. 1EDF5673K is selected as a gate driver because its driving current and negative voltage output characteristics are highly optimized for IGOT60R070D1. An LCL filter with passive damping resistor is applied to attenuate the switching frequency harmonics to the grid-tied operation. The designed LCL filter parameters are validated with PSIM simulation. A prototype of 3 kW PV inverter with GaN HEMT is constructed to verify the performance of the power conversion system. It achieved high power density of 614 W/L and peak power efficiency of 99% for the boost converter and inverter.

• 대한조선학회논문집
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• 제58권5호
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• pp.294-302
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• 2021

In this study, the 3D printing technique called design for additive manufacturing (DfAM) that is widely used in various industries was applied to marine leisure ships of equipment. The DfAM for the stanchion for crew safety was applied to the equipment used in an actual recreational craft. As design constraints, the design alternatives were not to exceed the safety and weight of the existing stainless steel material, which were reviewed, and the production of a low-cost FFF-type 3D printing method that can be used even in small shipyards was considered. Until now, additive manufacturing has been used for manufacturing only prototypes owing to its limitations of high manufacturing cost and low strength; however, in this study, it was applied to the mass production process to replace existing products. Thus, a design was developed with low manufacturing cost, adequate performance maintenance, and increased design freedom, and the optimal design was derived via structural analysis comparisons for each design alternative. In addition, a life-cycle assessment based on the ISO 1404X was conducted to develop sustainable products. Through this study, the effectiveness of additive manufacturing was examined for future applications in the shipbuilding industry.

• 한국지반공학회논문집
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• 제37권12호
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• pp.117-125
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• 2021

시민의 안전을 위협하는 지반재해 중 하나인 지반함몰이 최근 도심지에서 빈번하게 보고되고 있다. 다양한 지반함몰 발생 메커니즘 중, 하수관 손상부를 통한 토사 유실이 서울시에서 발생하는 지반함몰의 주요원인으로 나타났다. 본 연구에서는 서울시 하수관 정보와 지반함몰이 발생한 위치 정보를 기반으로 머신러닝 기법 중 하나인 랜덤 포레스트 알고리즘을 이용하여 하수관 정보로부터 손상 하수관으로 유발되는 지반함몰의 발생 여부를 예측하는 모델을 학습하였다. 모델 성능 평가 결과, 본 연구에서 도출한 모델이 지반함몰을 상당히 훌륭하게 예측할 수 있는 것으로 나타났다. 또한, 입력변수로 사용한 하수관 정보 중 하수관 길이, 해발고도, 경사, 매립 심도, 하수관 순서로 지반함몰 발생 위험에 영향을 미치는 것을 확인하였다. 본 연구의 결과는 지반함몰 위험도 지도 작성, 지하공동 탐사 계획 수립 및 하수관 정비 사업 계획 수립의 기초 자료로 활용될 수 있을 것으로 기대된다.

• 디지털산업정보학회논문지
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• 제17권4호
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• pp.177-195
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• 2021

The purpose of this study is to examine the trouble of recruitment and research and development of ICT SMEs. Recently, many ICT SMEs have emerged for selling products and services using the technology of the 4th industrial revolution. However, SMEs have relatively deficient resources compared to large companies, the difficulty of maintenance or growth of human resources and intangible resources. This research methodology organized the four stages of the analysis process. The first analysis is the association rules for human resource recruitment. The second analysis is the difficulty of hiring jobs and experienced workers by each stage of company growth. The third analysis is a regression analysis of the trouble of R&D activity. The last analysis is an analysis of association rules on the difficulties of management activities by company growth. As the research result, the first analysis has shown a difference in favored human resources by the ICT industry. The second analysis also showed factor differences in job recruitment difficulties for each stage of corporate growth. In the third analysis, the operation of research institutes in ICT SMEs is influenced by industry type, corporate certification, corporate growth stage, self-technology development, joint technology development, technology transfer, and commercialization. As the last analysis, ICT SMEs showed factor differences in difficulties in management activities by stage of corporate growth. This study contributed empirically emphasizing the troubling phenomenon of human resources and R&D necessary for the growth of ICT SMEs. As a theoretical implication, this research contributed to the research-area expansion of management information using big-data technologies. In particular, this research practically suggests the differentiated direction of recruitment and R&D by ICT SMEs based on industry and each stage of company growth through the association rules of big data.

• 대한건축학회연합논문집
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• 제20권6호
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• pp.121-129
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• 2018

The present study analyzed what policies are being executed for deteriorated apartments in Japan and what characteristics each policy had in order to examine policy direction and implications for the improvement of vitalization of remodeling business of deteriorated apartments in Korea. The study results are as follows. Japan recognized social problems of deteriorated apartments and pushed forward a national level remodeling actively by preparing financial support of central government and supporting plan by city and province. First, Japan maintained initial performance of buildings through phased maintenance for deterioration of buildings and aimed to reduce environmental load and maintain asset values of buildings through enlarging durability of buildings by responding to lifestyle according to social changes. To this end, they promoted the long life of buildings through the establishment of systematic long term repair plan from the stage of moving in the buildings. Second, in order to reduce the risk of remodeling projects, they prepared an environment where business could be carried out with an easy mind in various aspects by introducing remodeling business registration system and large scale repair construction defect insurance system. Third, they reduced economic burden of main agents of remodeling business with tax preferential treatment and financial support policies. Fourth, they have established remodeling support system based on overall social issues and connected it with social effect that could be obtained through this. The remodeling policies of Japan were carried out in the direction of solving social problems and considering economic aspect rather than just improving individuals' residence environment.

• 한국압력기기공학회 논문집
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• 제15권1호
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• pp.62-70
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• 2019

The APR1400 reactor may be operated for a long time under high temperature and pressure conditions, causing damage to the stud holes and causing stud bolts and holes to stick. The present practice is to manually remove the anti-sticking agent and foreign matter remaining in the APR1400 reactor stud hole and to visually check the surface condition of the thread to check the damage status of the threads. In the case of the APR1400 reactor stud holes, manually cleaning the threads increases the risk of radiation exposure and operator's fatigue. To avoid this, the autonomous mobile robot is used to automatically clean the reactor stud holes. The purpose of this study is to optimize the cleaning performance of the mobile robot by looking at the behavior of the surface roughness of the stud surface cleaned by the brush attached to the mobile robot due to changes in brush material, thickness of wire, and rotation speed. A microscopic approach to the surface roughness of the flank is needed to investigate the effects of the newly proposed brush of the autonomous mobile robot on the thread holes. According to this experiment, it is reasonable to use STS brush rather than Carbon one. Optimal operating conditions are derived and the safety of APR1400 reactor stud holes maintenance can be improved.

• 한국수소및신에너지학회논문집
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• 제30권3호
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• pp.282-288
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• 2019

When liquefied natural gas (LNG) is vaporized to form natural gas for industrial and household consumption, a tremendous amount of cold energy is transferred from LNG to seawater as a part of the phase-change process. This heat exchange loop is not only a waste of cold energy, but causes thermal pollution to coastal fishery areas by dumping the cold energy into the sea. This project describes an innovative new design for reclaiming cold energy for use by cold storage warehouses (operating in the 35 to $62^{\circ}C$ range). Conventionally, warehouse cooling is done by mechanical refrigeration systems that consume large amounts of electricity for the maintenance of low temperatures. Here, a closed loop LNG heat exchange system was designed (by simulator) to replace mechanical or vapor-compression refrigeration systems. The software PRO II with PROVISION V9.4 was used to simulate LNG cold energy, gas re-liquefaction, and the vaporized process under various conditions. The effects on sensible and latent heats from changes to the array type of heat exchangers have been investigated, as well as an examination of the optimum.