• 전기학회논문지
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• 제67권12호
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• pp.1587-1594
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• 2018

In south korea, the government make a plan to generate the 20% of the total electrical power as renewable source like wind generation and solar generation. This plan will accelerate the increase of fault current with power industry's growth. As the increase of fault current, the superconducting fault current limiter (SFCL) has been studied. In case that the SFCL is applied in power system, it can cause the overcurrent relay (OCR)'s trip delay because of the reduced fault current. In this paper, the overcurrent relay with voltage component was suggested to improve the OCR's trip delay caused by the SFCL and compensational constant was introduced to have the trip time similar to the trip time of case without the SFCL. For conforming the effect of the suggested OCR with voltage component, the PSCAD/EMTDC simulation modeling and analysis were conducted. Through the simulation, it was conformed that the trip delay could be improved by using the suggested OCR and compensational constant.

• 한국해양공학회지
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• 제32권6호
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• pp.474-484
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• 2018

In this study, a new numerical modeling system was proposed to predict oil spills, which increasingly occur at sea as a result of abnormal weather conditions such as global warming. The hydrodynamic conditions such as the flow velocity needed to calculate oil dispersion were estimated using a three dimensional hydrodynamic model based on the Navier-Stokes equation, which considered all of the physical variations in the vertical direction. This improved the accuracy compared to those estimated by the conventional shallow water equation. The advection-diffusion model for the spilled oil was combined with the hydrodynamic model to predict the movement and fate of the oil. The effects of absorption, weathering, and wind were also considered in the calculation process. The combined model developed in this study was then applied to various test cases to identify the characteristics of oil dispersion over time. It is expected that the developed model will help to establish initial response and disaster prevention plans in the event of a nearshore oil spill.

• 전기전자학회논문지
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• 제23권1호
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• pp.151-158
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• 2019

본 논문에서는 태양광 및 풍력 발전소 등에 설치되어 있는 다수의 계통 연계형 인버터를 사용하여 Virtual D-STATCOM을 구성하고, 배전계통의 부하의 무효전력과 배전선로의 거리에 따른 케이블의 무효전력을 보상하여 기존의 단일 대용량 D-STATCOM을 설치하지 않고 변전소 인근의 PCC단의 무효전력을 보상하는 방법을 제시한다. 제안된 방식은 Matlab Simulink 시뮬레이션을 통해 동작원리와 무효전력 보상 성능을 검증하였다.

• 문화기술의 융합
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• 제5권2호
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• pp.355-360
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• 2019

본 연구에서는 고속열차 주행 중 발생하는 풍하중 안정성 검토조건을 준용하여, 열차속도 300km/h와 360km/h에 대한 고속선로용 고무보판 패널 구조의 열차 풍하중에 대한 구조적 안정성을 검토하였다. 이를 위해 고무보판 패널 시스템이 가장 복잡한 구성으로 설치될 수 있는 현장조건을 적용하여 3차원 해석모델링을 이용한 정밀 수치해석을 수행하였으며, 이를 통해 고속열차 풍하중에 대한 고무보판 패널 시스템의 구조적 안정성을 해석적으로 입증하였다.

• 시스템엔지니어링학술지
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• 제16권2호
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• pp.1-15
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• 2020

Nuclear power plants in South Korea are operated to cover the baseload demand. Hence they are operated at 100% rated power and do not deploy power tracking control except for startup, shutdown, or during transients. However, as the contribution of renewable energy in the energy mix increases, load follow operation may be needed to cover the imbalance between consumption and production due to the intermittent nature of electricity produced from the conversion of wind or solar energy. Load follow operation may be quite challenging since the operators need to control the axial power distribution and core reactivity while simultaneously conducting the power maneuvering. In this paper, a systems engineering approach for multi-physics load follow simulation of APR1400 is performed. RELAP5/SCDAPSIM/MOD3.4/3DKIN multi-physics package is selected to simulate the Korean Advanced Power Reactor, APR1400, under load follow operation to reflect the impact of feedback signals on the system safety parameters. Furthermore, the systems engineering approach is adopted to identify the requirements, functions, and physical architecture to provide a set of verification and validation activities that guide this project development by linking each requirement to a validation or verification test with predefined success criteria.

• Nuclear Engineering and Technology
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• 제54권8호
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• pp.2883-2897
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• 2022

According to the Renewable Energy 3020 Implementation Plan announced in 2017 by the South Korean government, the electricity share of renewable energy will be expanded to 20% of the total electricity generation by 2030. Given the intermittency of electricity generation from renewable energy, realization of such a plan presents challenges to managing South Korea's isolated national electric grid and implies potentially large excess electricity generation in certain situations. The purpose of this study is: 1) to develop a model to accurately simulate the effects of excess electricity generation from renewables which would arise during the transition, and 2) to propose strategies to manage excess electricity generation through effective utilization of domestic electricity generating capabilities. Our results show that in periods of greater PV and wind power, namely the spring and fall seasons, the frequency of excess electricity generation increases, while electricity demand decreases. This being the case, flexible operation of coal and nuclear power plants along with LNG and pumped-storage hydroelectricity can be used to counterbalance the excess electricity generation from renewables. In addition, nuclear energy plays an important role in reducing CO₂ emissions and electricity costs unlike the fossil fuel-based generation sources outlined in the 8th Basic Plan.

• 드라이브 ㆍ 컨트롤
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• 제19권1호
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• pp.62-68
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• 2022

Considering the characteristics of industrial machines that lack vehicle-induced wind, forced convection by a cooling fan is mostly required. Therefore, numerical analysis of an engine room is usually performed to examine the cooling performance in the room. However, most engine rooms consist of a number of parts and components at specific positions, leading to high costs for numerical modeling and simulation. In this paper, a new methodology for three-dimensional computer-assisted design simplification was proposed, especially for the pile of components and parts at the engine room outlet. A porous media model and regression analysis were used to derive a meta-model for imitating the flow rate reduction at the outlet by the pile. The results showed that the fitted model was reasonable considering the coefficient of determination. The final numerical model of the engine room was then used to simulate the velocity distribution by changing the mass flow rate at the outlet. The results showed that both velocity distributions were significantly changed in each case and the meta-model was valid in imitating the flow rate reduction by some piles of components and parts.

• 천문학회보
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• 제44권2호
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• pp.37.1-37.1
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• 2019

We perform Lyα radiative transfer calculations for reproducing Lyα properties of star-forming galaxies at high redshifts. We model a galaxy as a halo in which the density distributions of Lyα sources and HI plus dust medium are described with exponential functions. We also consider an outflow of the medium that represents a momentum-driven wind in a gravitational potential well. We demonstrate that this outflowing halo model with Lyα scattering can successfully reproduce both the spectrum and the surface brightness profile of eight star-forming galaxies at z=3-6 observed with MUSE. The best-fit model parameters (i.e., the outflowing velocity and optical depth) for these galaxies are in good agreement with other studies. We also demonstrate benefits of using spectrum and surface brightness profile simultaneously to the constraints on model parameters and thus spatial/kinematic distributions of medium. We examine the impacts of individual model parameters and intrinsic spectrum on emerging spectrum and surface brightness profile. Further investigations on the escape fraction, spatially resolved spectra, and the spatial extent of Lyα halos are presented as well.

• Geomechanics and Engineering
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• 제34권5호
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• pp.529-545
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• 2023

The coupled soil-pile-structure seismic response is recently in the spotlight of researchers because of its extensive applications in the different fields of engineering such as bridges, offshore platforms, wind turbines, and buildings. In this paper, a simple analytical model is developed to evaluate the dynamic performance of seismically isolated bridges considering triple interactions of soil, piles, and bridges simultaneously. Novel expressions are proposed to present the dynamic behavior of pile groups in inhomogeneous soils with various shear modulus along with depth. Both cohesive and cohesionless soil deposits can be simulated by this analytical model with a generalized function of varied shear modulus along the soil depth belonging to an inhomogeneous stratum. The methodology is discussed in detail and validated by rigorous dynamic solution of 3D continuum modeling, and time history analysis of centrifuge tests. The proposed analytical model accuracy is guaranteed by the acceptable agreement between the experimental/numerical and analytical results. A comparison of the proposed linear model results with nonlinear centrifuge tests showed that during moderate (frequent) earthquakes the relative differences in responses of the superstructure and the pile cap can be ignored. However, during strong excitations, the response calculated in the linear time history analysis is always lower than the real conditions with the nonlinear behavior of the soil-pile-bridge system. The current simple and efficient method provides the accuracy and the least computational costs in comparison to the full three-dimensional analyses.

• Wind and Structures
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• 제38권2호
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• pp.147-160
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• 2024

The aerodynamic force is a significant component that influences the stability and safety of structures. It has unstable properties and depends on computer precision, making its long-term prediction challenging. Accurately estimating the aerodynamic traits of structures is critical for structural design and vibration control. This paper establishes an unsteady aerodynamic time series prediction model using Long Short-Term Memory (LSTM) network. The unsteady aerodynamic force under varied Reynolds number and angles of attack is predicted by the LSTM model. The input of the model is the aerodynamic coefficients of the 1 to n sample points and output is the aerodynamic coefficients of the n+1 sample point. The model is predicted by interpolation and extrapolation utilizing Unsteady Reynolds-average Navier-Stokes (URANS) simulation data of flow around a circular cylinder, square cylinder and airfoil. The results illustrate that the trajectories of the LSTM prediction results and URANS outcomes are largely consistent with time. The mean relative error between the forecast results and the original results is less than 6%. Therefore, our technique has a prospective application in unsteady aerodynamic force prediction of structures and can give technical assistance for engineering applications.