• 한국수소및신에너지학회논문집
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• 제30권2호
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• pp.147-154
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• 2019

In this study, effects of flow types and size of molten carbonate fuel cells (MCFCs) were investigated using CFD simulation. In the simulation, the current collector of MCFCs were assumed to be an porous media. With the area of $0.09m^2$, the effect of flow types such as Co-flow, Counter-flow, Cross-flow were studied. After that the effect of the size and flow direction was studied. Among three-flow types, MCFCs with co-flow type shows more uniform distribution and current density distribution.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.430-438
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• 2021

The spatial distribution of neutron flux or reaction rate was calculated by cell or mesh tally in traditional Monte Carlo simulation. However, either cell or mesh tally leads to the increase of memory consumption and simulation time. In this paper, the function expansion tally (FET) method was developed in Reactor Monte Carlo code RMC to solve this problem. The FET method was applied to the tallies of neutron flux distributions of uranium block and PWR fuel rod models. Legendre polynomials were used in the axial direction, while Zernike polynomials were used in the radial direction. The results of flux, calculation time and memory consumption of different expansion orders were investigated, and compared with the mesh tally. Results showed that the continuous distribution of flux can be obtained by FET method. The flux distributions were consistent with that of mesh tally, while the memory consumption and simulation time can be effectively reduced. Finally, the convergence analysis of coefficients of polynomials were performed, and the selection strategy of FET order was proposed based on the statistics uncertainty of the coefficients. The proposed method can help to determine the order of FET, which was meaningful for the efficiency and accuracy of FET method.

• Earthquakes and Structures
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• 제24권3호
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• pp.205-215
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• 2023

Currently, many studies are underway at home and abroad on the seismic performance evaluation and dry construction method of the masonry structure. In this study, a dry stack masonry wall system without mortar using concrete blocks is proposed, and investigate the seismic performance of dry filling wall frames through experimental studies. First, two types of standard blocks and key blocks were designed to assemble dry walls of concrete blocks. And then, three types of experiments were manufactured, including pure frame, 1/2 height filling wall frame, and full height filling wall frame, and cyclic load experiments in horizontal direction were performed to analyze crack patterns, load displacement history, rebar deformation yield, effective stiffness change, displacement ductility, and energy dissipation capacity. According to the experimental results, the full height filling wall frame had the largest horizontal resistance against the earthquake load and showed a high energy dissipation capacity. However, the 1/2 height filling wall frame requires attention because the filling wall constrains the effective span of the column, limiting the horizontal displacement of the frame. In addition, the concrete block was firmly assembled in the vertical direction of the wall as the horizontal movement between the concrete blocks was allowed within installation margin, and there was no dropping of the assembled concrete block.

• Nuclear Engineering and Technology
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• 제56권4호
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• pp.1480-1489
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• 2024

Displacement cascade behaviors of Ti-6Al-4V alloys are investigated using molecular dynamics (MD) simulation. The embedded atom method (EAM) potential including Ti, Al and V elements is modified by adding Ziegler-Biersack-Littmark (ZBL) potential to describe the short-range interaction among different atoms. The time evolution of displacement cascades at the atomic scale is quantitatively evaluated with the energy of primary knock-on atom (PKA) ranging from 0.5 keV to 15 keV, and that for pure Ti is also computed as a comparison. The effects of temperature and incident direction of PKA are studied in detail. The results show that the temperature reduces the number of surviving Frenkel pairs (FPs), and the incident direction of PKA shows little correlation with them. Furthermore, the increasing temperature promotes the point defects to form clusters but reduces the number of defects due to the accelerated recombination of vacancies and interstitial atoms at relatively high temperature. The cluster fractions of interstitials and vacancies both increase with the PKA energy, whereas the increase of interstitial cluster is slightly larger due to their higher mobility. Compared to pure Ti, the presence of Al and V is beneficial to the formation of interstitial clusters and indirectly hinders the production of vacancy clusters.

• 풍력에너지저널
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• 제14권4호
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• pp.87-97
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• 2023

Due to the limitations of onshore wind power, the wind power industry is currently transitioning to offshore wind power. There has been active research on the development of a floating LiDAR system (FLS) that is easy to install at a low cost. The Carbon Trust published a commercialization roadmap for FLS in 2013, and an updated version was released in 2018, taking into account industry experience. The roadmap divides the development maturity of FLS into three stages: Stage 1 (prototype), Stage 2 (pre-commercialization), and Stage 3 (commercialization), each of which requires availability and accuracy assessment. The results must meet the requirements of the Key Performance Index (KPI) for each stage. Therefore, when developing FLS, the motion compensation algorithm of the FLS is essential because the LiDAR can produce incorrect measurements of wind speed and direction due to the six degrees of freedom in motion. In this study, we implemented the FLS motion compensation algorithm developed by Nassif, F.B. et al. and validated it using data provided by Fraunhofer. In conclusion, the results showed that the determination coefficients of wind speed and wind direction were improved compared to those obtained from the met mast.

• 풍력에너지저널
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• 제14권3호
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• pp.69-82
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• 2023

Offshore wind farms (OWFs) should be promoted as part of global efforts to respond to climate change, and efforts to preserve biodiversity in terms of climate change adaptation should also be considered. However, the ecological status of marine birds related to OWFs on the Korean Peninsula, such as habitat and reproduction, are not well known. In this study, ecological reasons for the reproductive status of Black-tailed gulls in Korea and representation related to OWFs, the evaluation direction of marine birds related to OWFs was presented. In a review of the techniques for monitoring marine birds, it was confirmed that Korea also needs to provide basic status information on marine birds at the national level. In addition, this study analyzed the reproductive status and related research status of Black-tailed gulls, an important indicator and dominant species on the Korean Peninsula, in relation to marine development projects including OWFs. Furthermore, the direction of environmental impact assessment preparation and impact prediction for various development projects promoted in the ocean, such as OWFs, was considered.

• Ocean and Polar Research
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• 제42권3호
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• pp.211-223
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• 2020

With the increasing demand for improved marine environments and safety, greater ability to minimize damages to coastal areas from harmful organisms, ship accidents, oil spills, etc. is required. In this regard, an accurate assessment and understanding of current systems is a crucial step to improve forecasting ability. In this study, we examine spatial and temporal characteristics of current systems in the adjacent seas of Jeju Island using a high-resolution regional ocean circulation model. Our model successfully captures the features of tides and tidal currents observed around Jeju Island. The tide form number calculated from the model result ranges between 0.3 and 0.45 in the adjacent seas of Jeju Island, indicating that the dominant type of tides is a combination of diurnal and semidiurnal, but predominantly semidiurnal. The spatial pattern of tidal current ellipses show that the tidal currents oscillate in a northwest-southeast direction and the rotating direction is clockwise in the adjacent seas of Jeju Island and counterclockwise in the Jeju Strait. Compared to the mean kinetic energy, the contribution of tidal current energy prevails the most parts of the region, but largely decreases in the eastern seas of Jeju Island where the Tsushima Warm Current is dominant. In addition, a Lagrangian particle-tracking experiment conducted suggests that particle trajectories in tidal currents flowing along the coast may differ substantially from the mean current direction. Thus, improving our understanding of tidal currents is essential to forecast the transport of marine pollution and harmful organisms in the adjacent seas of Jeju Island.

• 한국수소및신에너지학회논문집
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• 제31권1호
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• pp.82-88
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• 2020

Recently, a fuel reforming plant for supplying high purity hydrogen has been studied to increase the operation time of underwater weapon systems. Since steam reforming is an endothermic reaction, it is necessary to continuously supply heat to the reactor. A fuel reforming plant needs a methanol-O₂ catalytic burner to obtain heat and supply heat to the reformer. In this study, two types of designs of a catalytic burner are presented and the results are analyzed through the experiments. The design of the catalytic burner is divided into that the O₂ supply direction is perpendicular to the methanol flow direction (Design 1) and the same as the methanol flow direction (Design 2). In case of Design 1, backfire and flame combustion occurred in the mixing space in front of the catalyst, and in the absence of the mixing space, combustion reaction occurred only in a part of the catalyst. For above reasons, Design 1 could not increase the exhaust gas temperature to 750℃. In Design 2, no flashback and flame combustion were observed, the exhaust gas could be maintained up to 750℃. However, the O₂ distributor was exposed to high temperatures, resulting in thermal damage.

• 한국태양에너지학회 논문집
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• 제32권3호
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• pp.146-152
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• 2012

To install a wind power generator, the survey on the wind environment resources must be conducted in advance. The survey on the wind environment resources is to collect and analyze data regarding the wind speed and direction on a data logger. The data logger consists of a sensor, signal processing circuit and storage device. According to the analysis of the stored data, the amount of power generation by the types of generators can be predicted and the most optimal generator including safety grade can be selected, and in case of installing a generator in the future, it can be utilized as basic data regarding supporting base and foundation construction method of survey points. Data logger was developed for a small wind power generator that is suitable for the international standard(IEC 61400) by using DSP-F28335 micro controller in this paper. It was developed to measure the wind speed of 1 [m/s]~17 [m/s], the wind direction of 0 [$^{\circ}$]~359 [$^{\circ}$], and temperature of -30 [$^{\circ}C$]~50 [$^{\circ}C$], and the comparative experiment with other companies' data loggers was conducted, and an error was measured to be less than ${\pm}0.1$ [m/s] for wind speed and less than +1 [$^{\circ}$] for wind direction.

• 한국광학회지
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• 제22권2호
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• pp.108-113
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• 2011

본 논문에서는 단일경계 표면플라즈몬 도파로의 모드특성을 잘 이해하기 위해 복소차분도표를 제안한다. 기존의 표면플라즈몬 모드는 군속도의 부호가 바뀌는 부분을 기준으로 분류되었는데, 여기에서 군속도는 표면플라즈몬 모드 진행방향의 전파상수와 광자 에너지에 대한 분산 관계식에서 접선의 기울기이다. 표면플라즈몬 모드는 진행방향에 대해 수직한 방향의 전파상수도 가지고 있기 때문에 이를 종합적으로 이용하여 모드를 분류하는 것이 필요하다. 복소차분도표는 전파상수의 실수 부와 허수 부의 차이를 변수로 하여 나타낸 도표로서 이를 이용하면 모드 분류가 가능하고 또한 광자 에너지에 따른 종합적인 전파상수의 변화 경향을 살펴보는 것이 용이하다.