• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.1
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• pp.78-82
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• 2014

Power Transformers with more than one secondary winding are not uncommon in industrial applications. But new classes of applications where very large number of independent secondaries are used are becoming popular in controlled converters for medium and high voltage applications. Cascade H-bridge medium voltage drives and Pulse Step Modulation (PSM) based high voltage power supplies are such applications. Regulated high voltage power supplies (Fig. 1) with 35-100 kV, 5-10 MW output range with very fast dynamics (${\mu}S$ order) uses such transformers. Such power supplies are widely used in fusion research. Here series connection of isolated voltage sources with conventional switching semiconductor devices is achieved by large number of separate transformers or by single unit of multi-secondary transformer. Naturally, a transformer having numbers of secondary windings (~40) on single core is the preferred solution due to space and cost considerations. For design and simulation analysis of such a power supply, the model of a multi-secondary transformer poses special problem to any circuit analysis software as many simulation softwares provide transformer models with limited number (3-6) of secondary windings. Multi-Secondary transformer models with 3 different schemes are available. A comparison of test results from a practical Multi-secondary transformer with a simulation model using magnetic component is found to describe the behavior closer to observed test results. Earlier models assumed magnetising inductance in a linear loss less core model although in actual it is saturable core made-up of CRGO steel laminations. This article discusses a more detailed representation of flux coupled magnetic model with saturable core properties to simulate actual transformers very close to its observed parameters in test and actual usage.

• The Journal of Fisheries Business Administration
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• v.46 no.1
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• pp.1-13
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• 2015

This study is aimed comparative analysis for business performance of land-based ezo abalone (Haliotis discus hannai) seed farms by standardizing cost structures by region and farming size. The result of survey on average farming incomes by region showed that farming incomes in Haenam and Jindo regions were much higher than those in other regions. Followed by Wando region, incomes in other regions were analyzed to be relatively lower. It is shown that farming incomes became higher as farm size increased. Farming incomes per unit size which were modified from farming incomes by region were highest in Jindo region, followed by East sea region, Wando and Haenam regions. Incomes in Jeju and Yeosu regions were analyzed to be relatively lower. Results on farming incomes per unit size ($m^2$) showed that both farming incomes and profits became higher as size increased. It implies that a scale effectiveness might exist in case of land-based abalone culture system. Impacts of major factors on farming profits and returns on investment in abalone seed aquaculture are summarized as follow. First, only if the survival rate increased by 10% with improvement of component ratio, variable effects became largest. In variable effects of other factors, a variation in Jindo region was largest and on the other hand, a variation in Yeosu region was shown to be smallest.

• Journal of Welding and Joining
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• v.30 no.4
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• pp.31-37
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• 2012

In recent years, a demand for precision-welding is increasing in wide industrial fields for getting a high quality welded structures. Although laser welding is commonly used for precision-welding, gas tungsten arc (GTA) welding is also attempted as a precision-welding due to the cost benefit. However, welding heat causes an uneven temperature distribution leading to welding deformation. Since it causes geometric errors and degrades product quality, welding distortion recently rises as an important issue in the field of automobile parts. To control welding deformation, it is needed to design in shapes that can maximize stiffness against deformation during welding; control the welding sequence; minimize heat input; and weld allowing reverse deformation; etc. Thus it is necessary to find the one, among such approaches, that can minimize the deformation range by mathematical analysis and understand how effective it would be when it is actually used in industrial fields. This study performs analyses by numerical calculations and experiments for the De-Tent Lever, one of transmission part that requires precision the most among automobile parts, as the subject of experiment. Decrease in welding deformation is required for this part, since there is currently a trouble in guaranteeing precision due to angular deformation by welding between boss and plate. Finally the ways to minimize welding deformation has been suggested in this study through analyses on it.

• Journal of the Korean Society of Safety
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• v.34 no.4
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• pp.1-5
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• 2019

In the field of combined cycle power generation, thermal barrier coating(TBC) protects the super-heat-resistant alloy, which forms the core component of the gas turbine, from high temperature exposure. As the turbine inlet temperature(TIT) increases, TBC is more important and durability performance is also important when considering maintenance cost and safety. Therefore, studies have been made on the fabrication method of TBC and super-heat-resistant alloy in order to improve the performance of the TBC. In recent years, due to excellent properties such as high temperature creep resistance and high temperature strength, turbine blade material have been replaced by a single crystal superalloy, however there is a lack of research on TBC applied to single crystal superalloy. In this study, to understand the isothermal degradation performance of the TBC applied to the single crystal superalloy, isothermal exposure test was conducted at various temperature to derive the delamination life. The growth curve of thermally grown oxide(TGO) layer was predicted to evaluate the isothermal degradation performance. Also, microstructural analysis was performed by scanning electron microscope(SEM) and energy dispersive X-ray spectroscopy (EDS) to determine the effect of mixed oxide formation on the delamination life.

• Journal of the Korean GEO-environmental Society
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• v.12 no.11
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• pp.59-64
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• 2011

Clogging in drainage pipe is one of the important problems, so it needs a remedy urgently. Recently, scale in drainage pipe is removed by water jet cleaning and other treatment. But these treatments need much cost and regular management. The principal component of scale in drainage pipe is $CaCO_{3}$. It was observed the setting of $CaCO_{3}$ by some kind of analysis such as SEM, XRD, visual and weight measuring analysis to solve these problems and prevent setting formation in drainage pipe. As a result, in case of magnetic, particle shape of $CaCO_{3}$ is changed Aragonite from Calcite. Also in case of Quantum Stick, the amount of scale is reduced by expert inspector's result. As a whole, Magnetic treatment and Quantum Stick have the effect for protecting of scale precipitation.

• Earthquakes and Structures
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• v.24 no.3
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• pp.217-235
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• 2023

Orthogonal pairs of rollers on concave beds (OPRCB) are a low-cost, low-tech rolling-based isolating system, whose high efficiency has been shown in a previous study. However, seismic performance of OPRCB isolators has only been studied in the two-dimensional (2D) state so far. This is while their performance in the three-dimensional (3D) state differs from that of the 2D state, mainly since the vertical accelerations due to rollers' motion in their beds, simultaneously in two orthogonal horizontal directions, are added up and resulting in bigger vertical inertia forces and higher rolling resistance. In this study, first, Lagrange equations were used to derive the governing equations of motion of the OPRCB-isolated buildings in 3D. Then, some regular shear-type OPRCB-isolated buildings were considered subjected to three-component excitations of far- and near-source earthquakes, and their responses were compared to those of their fixed-base counterparts. Finally, the effects of more realistic modeling and analysis were examined by comparing the responses of isolated buildings in 2D and 3D states. Response histories were obtained by the fourth-order Runge-Kutta-Nystrom method, considering the geometrical nonlinearity of isolators. Results reveal that utilizing the OPRCB isolators effectively reduces the acceleration response, however, depending on the system specifications and earthquake characteristics, the maximum responses of isolated buildings in the 3D state can be up to 40% higher than those in the 2D state.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.162-162
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• 2022

Stormwater management is an essential component of land-use planning and development. Due to the additional challenges posed by climate change and urbanization, various stormwater management schemes have been developed to limit flood damages and ease water quality concerns. Nature-based solutions (NBS) are increasingly used as cost-effective measures to manage stormwater runoff from various land uses. Specifically, constructed wetlands were already considered as socially acceptable green stormwater infrastructures that are widely used in different countries. There is a large collection of published literature regarding the effectiveness or efficiency of constructed wetlands in treating stormwater runoff; however, metadata analyses using bibliographic information are very limited or seldomly explored. This study was conducted to determine the trends of publication regarding stormwater treatment wetlands using a bibliometric analysis approach. Moreover, the research productivity of various countries, authors, and institutions were also identified in the study. The Web of Science (WoS) database was utilized to retrieve bibliographic information. The keywords ("constructed wetland*" OR "treatment wetland*" OR "engineered wetland*" OR "artificial wetland*") AND ("stormwater*" or "storm water*") were used to retrieve pertinent information on stormwater treatment wetlands-related publication from 1990 up to 2021. The network map of keyword co-occurrence map was generated through the VOSviewer software and the contingency matrices were obtained using the Cortext platform (www.cortext.net). The results obtained from this inquiry revealed the areas of research that have been adequately explored by past studies. Furthermore, the extensive collection of published scientific literature enabled the identification of existing knowledge gaps in the field of stormwater treatment wetlands.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.6
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• pp.955-967
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• 2016

As transportation systems for connecting lands and islands, oversea long-span bridges, underwater tunnels, and immersed tunnels have been mainly used so far. Submerged floating tunnels (SFTs) moored under specific water depth are one of the newest oversea transportation system. Compared to other existing systems, the new system requires relatively less construction cost and time. But, there is still no construction example. For reasonable design of the tunnel and mooring lines the rational structural analysis should be firstly performed. Unlike common transportation structures, the submerged tunnels are mainly affected by the wave, vary irregular excitation component. So, the analysis scheme might be difficult because of the characteristics of the submerged structures. This study aims to suggest the rational global performance analysis methodology for the submerged tunnels. Using ABAQUS the dynamic response of the experimental models studied by KIOST (2013) was investigated considering regular waves. By comparing the simulation results with the experimental results, the feasibility of the numerical simulation was verified. Using the suggested method, the effects of initial inclination of the tethers and draft of the tunnel on the dynamic behavior were studied. In addition, dynamic response of a SFT under the irregular wave was examined.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.2567-2572
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• 2011

It is the key component that motor block system affect safety and performance of railway. It is very important to examine the performance of motor block for improvement of safety and reliability of rolling stock. As such, the motor block is an essential part of rolling stock. But provisioning quantities and spare quantities depend on the operator' experience. There are many problems that occur lots of spare or lack of spare. If there are lots of spare, it is difficult to keep the circumstance by cost issues. On the contrary, if there are lack of spare, it may have a adverse effect on the whole railway. Thus, this study offers method to estimate optimal spare of motor block using the analysis of data related with Failure rate, MTBF, standards and guidelines. And we expect this study to contribute to determine optimal spare parts.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.1
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• pp.63-69
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• 2018

Bearing is an essential component in many rotary machineries. To prevent its unpredicted failures and undesired downtime cost, many researches have been made in the field of Prognostics and Health Management(PHM), in which the key issue is to establish a proper feature reflecting its current health state properly at the early stage. However, conventional features have shown some limitations that make them less useful for early diagnostics and prognostics because it tends to increase abruptly at the end of life. This paper proposes a new feature extraction method using the envelope analysis and weighted sum with correlation coefficient. The developed method is demonstrated using the IMS bearing data given by NASA Ames Prognostics Data Repository. Results by the proposed feature are compared with those by conventional approach.