• Journal of Power Electronics
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• v.19 no.3
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• pp.645-654
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• 2019

In this paper, a new high step up DC/DC converter with a modified super-lift technique is presented. The coupled inductor technique is combined with the super-lift technique to provide a tenfold or more voltage gain with a proper duty cycle and a low turn ratio. Due to a high conversion ratio, the voltage stress on the semiconductor devices is reduced. As a result, low voltage ultra-fast recovery diodes and low on resistance MOSFET can be used, which improves the reverse recovery problems and conduction losses. This converter employs a passive clamp circuit to recycle the energy stored in the leakage inductance. The proposed convertor features a high conversion ratio with a low turn ratio, low voltage stress, low reverse recovery losses, omission of the inrush currents of the switch capacitor loops, high efficiency, small volume and reduced cost. This converter is suitable for renewable energy applications. The operational principle and a steady-state analysis of the proposed converter are presented in details. A 200W, 30V input, 380V output laboratory prototype circuit is implemented to confirm the theoretical analysis.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.247-250
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• 2008

Biomass gasification is a promising technology for producing a fuel gas which is useful for power generation systems. In biomass gasification processes, tar formation often causes some problems such as pipeline plugging. Thus, proper tar treatment is necessary. So far, nickel (Ni)-based catalysts have been intensively studied for the catalytic tar removal. However, the deactivation of Ni-based catalysts takes place because of coke deposition and sintering of Ni metal particles. To overcome these problems, we have been using ruthenium (Ru)-based catalyst for tar removal. It is reported by Okada et al., that a Ru/$Al_2O_3$ catalyst is very effective for preventing the carbon deposition during the steam reforming of hydrocarbons. Also, this catalyst is more active than the Ni-based catalyst at a low steam to carbon ratio (S/C). Benzene was used for the tar model compound because it is the main constituent of biomass tar and also because it represents a stable aromatic structure apparent in tar formed in biomass gasification processes. The steam reforming process transforms hydrocarbons into gaseous mixtures constituted of carbon dioxide ($CO_2$), carbon monoxide (CO), methane ($CH_4$) and hydrogen ($H_2$).

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.220.1-220.1
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• 2011

In recent years, the importance of Carbon Capture and Storage (hereafter CCS) is growing bigger and bigger. The development and commercialization of CCS technology are concerned for reducing carbon dioxide($CO_2$) emissions. For the most studies, the technology of $CO_2$ storage is known as the geological storage, ocean sequestration, mineral carbonation, industrial utilization, and so on. The geological storage is adjudged the most reasonable technology from economic and environmental aspects. Generally, the $CO_2$ geological storage is comprised of compression - transportation - drilling/injection - storage/management process. The critical problem is a leakage of $CO_2$ in all process. For resolving a leakage problem, it is necessary to predict and build a monitoring system. Those systems are proved safety of a leakage and received positive social perceptions of $CO_2$ geological storage. For those reasons, a risk assessment of $CO_2$ geological storage is required. A risk assessment is an estimated process of the possible effects when spilling $CO_2$. Although numerous studies of risk assessment have studied, it is incomplete to evaluate a risk and disaster quantitatively. The risk assessment will be developed for domestic application and safe $CO_2$ geological storage considering characteristics of Korea.

• Wind and Structures
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• v.21 no.6
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• pp.597-607
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• 2015

With an increasing demand of a renewable energy, new offshore wind turbine farms are being planned in some parts of the world. Foundation installation asks a significant cost of the total budget of offshore wind turbine (OWT) projects. Hence, a cost reduction from foundation parts is a key element when a cost-efficient designing of OWT budget. Mono-piles have been largely used, accounting about 78% of existing OWT foundations, because they are considered as a most economical alternative with a relatively shallow-water, less than 30 m of seawater depth. OWT design standards such as IEC, GL, DNV, API, and Eurocode are being developed in a form of reliability based limit state design method. In this paper, reliability analysis using the response surface method (RSM) and numerical simulation technique for an OWT mono-pile foundation were performed to investigate the sensitivities of mono-pile design parameters, and to find practical implications of RSM reliability analysis.

• The KSFM Journal of Fluid Machinery
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• v.19 no.5
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• pp.20-27
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• 2016

The Francis-99 is a workshop initiated by the Norwegian University of Science and Technology (NTNU), Norway, and Lulea University of Technology (LTU), Sweden, in order to further validate the capabilities of the CFD technologies. The goal of the first workshop is to determine the state of the art of numerical predictions for steady operating conditions. When performing the CFD analysis, some geometry details are often neglected. In case of Francis Turbine, labyrinth seals are usually not include in the simulation domain, this may lead to inaccurate prediction of turbine efficiency. In this study, the CFD analysis for Francis-99 Workshop model has been performed for full domain of machine including top and bottom labyrinth seals. The efficiency value and distribution of velocity and pressure have been investigated and compared to the experimental data obtained from NTNU. By comparing the results, it was found that: With the top and bottom labyrinth seals in the domain, the CFD result was significantly improved in prediction of efficiency at all the operating point, especially at part load.

• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.178-181
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• 2008

다양한 조성을 갖는 $CH_4+CO_2$ 혼합 기체 하이드레이트 샘플의 미세 구조 분석을 위하여 X-ray 회절 방법을 이용하였다. X-ray 회절 분석을 이용할 경우, 하이드레이트로의 전환율과 같은 정성적인 분석뿐 아니라 각 객체별 cage occupancy와 같은 정량적인 분석까지도 가능한 것으로 나타났다. 또한 이렇게 얻어진 X-ray 회절 분석 결과 및 refinement 결과를 $^{13}C$ 고체 NMR 방법과 교차 비교함으로써 측정 결과의 신뢰도를 높이려 하였다. 얻어진 분석 결과는 이후 가스 하이드레이트를 이용한 다양한 연구 분야에서 저장용량 평가 및 객체 점유율과 같은 미세 구조 정보를 얻는 데에 유용하게 사용될 것으로 전망된다.

• Journal of Hydrogen and New Energy
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• v.17 no.4
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• pp.389-394
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• 2006

Mg and Mg-based alloys are promising hydrogen storage alloys for renewable clean energy applications. It is a lightweight and low cost material with high hydrogen storage capacity. However, commercial applications of the Mg hydride are currently hindered by its high absorption/desorption temperature, and very slow reaction kinetics. In this work, we aim to study the absorption properties of the $Mg_2Ni$-5mass% Nb composite prepared by mechanical alloying under hydrogen. The absorption capacity of the sample is found to be about 3.0 wt.% at T=573 K and P=1.0 MPa. The absorption characteristics observed have been compared with those of the prepared $Mg_2Ni$.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.394-394
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• 2009

Water solubility of conjugated polymers may offer many applications. Potential applications of water-soluble conjugated polymers include the polymer light-emitting diode and new materials for nano and micro hollow-capsules, and bio- or chemo-sensors. We synthesized neutral polyfluorenes containing bromo-alkyl groups by the palladium catalyzed Suzuki coupling reaction. Bromo-alkyl side groups in neutral polyfluorenes were quaternized by tri-methyl amine solution. The electrochemical and optical properties of water-soluble conjugated polymers are discussed. This novel synthesized water-soluble conjugated polymers were used as a interfacial dipole layer between active layer and metal cathode in polymer solar cell for enhancement of open-circuit voltage (Voc), which is one of the most critical factors in determining device characteristics. We also investigated the device performance of polymer solar cell with different metal cathode such as Al, Ag, Au and Cu. In polymer solar cell, novel cationic water-soluble conjugated polymers were inserted between active layer and high-work function cathode (Al, Ag, Au and Cu).

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.168.2-168.2
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• 2010

The growing market for geothermal heat pump system requires great consideration of quality control and assurance in design and construction. The borehole heat exchanger of GHP system should be sustainable, economical and ecological. Thermal Response Test (TRT) is a useful method for site investigation to obtain reliable data for a optimal system design from the technical and economical aspect. Intensive researches combined with exchange of experiences on an international level within the IEA ECES Annex 21 improved the technology. Major subjects on the interpretation of TRT are development of improved evaluation models, evaluation of the TRT with respect to geological layers and investigation of the influence of ground water. Current status of TRT in South Korea, as well as a new version of the Korean TRT standard test procedure was presented. TRT is mostly used for governmental supported projects with corresponds to more than 100 GCHP systems per year. More than 200 tests are applied, mostly on single U-tube heat exchangers (about 95%). Bentonite is the most common grouting to be used. KIGAM (Korea Institute of Geoscience & Mineral Resources) is also keeping a GIS geological and geothermal database. In the institute also laboratory measurements of rock properties are carried out. About 90% of the laboratory measurements of the rock heat conductivity shows higher values than the in-situ TRT.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.188-191
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• 2007

This paper shows the Development of In-tank pressure regulator and Solenoid Valve used in FCV(Fuel Cell Vehicle). We have developed new type of Regulator and Solenoid through analysis of the structure and characteristics of component of FCS(Fuel Cell System) from the advanced technology. Now it is possible to localize the component by making use of the development of Regulator and Solenoid made by us. Regulator and Solenoid is a equipment to control hydrogen pressure supplied into a stack. Therefore, outlet pressure, a flow of fluid and temperature are important parameters according to a inlet pressure. And leak test, endurance test and burst test should be done to guarantee the performance and safety of Regulator and Solenoid used in the fuel of high pressure. Also, Hydrogen friendly materials are applied to inner parts of the Regulator, Solenoid and weight reduction is done to cost saving in part not related to performance. As a result, we have proven the good performance and reliability in endurance of Regulator, Solenoid and will make an development in performance as well as durability to ensure industrialization.