• Journal of Electrical Engineering and Technology
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• 제13권3호
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• pp.1110-1122
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• 2018

This paper proposes an alternative method to evaluate the effect of wind power to the power system stability with small disturbance. Alternatively, available techniques for stability analysis of a power system based on deterministic methods are less accurate for high penetration of wind power. Numerical simulations of random behaviors are computationally expensive. A stochastic stability index (SSI) is proposed for the power system stability evaluation based on the theory of stochastic stability and energy function, specifically the stochastic derivative of the relative well-defined energy function and the critical energy. The SSI is implemented on the modified nine-bus system including wind turbines under different conditions. A doubly-fed induction generator (DFIG) wind turbine is characterized and modeled using measured wind data from several sites in Thailand. Each of the obtained wind power data is analyzed. The wind power effect is modeled considering the aggregated effect of wind turbines. With the proposed method, the system behavior is properly predicted and the stability is quantitatively evaluated with less computational effort compared with conventional numerical simulation methods.

• 신재생에너지
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• 제17권2호
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• pp.9-23
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• 2021

In Korea, various community investment renewable project models are being implemented to increase community acceptance of renewable energy. An important factor for enhancing local acceptance is that renewable energy projects have a positive effect on revitalizing the local economy such as income increase or job creation for residents and local companies. To maximize the local economic effect of large-scale community investment renewable energy projects, this study developed an evaluation index for local economy activation, whose indicators are the local return on investment, local companies' participation, local job creation, regional cooperation, transparency, and governance. Analysis of existing evaluation indicators and current renewable projects, financial analysis, and expert interviews were used in this research. The pilot evaluation determined that, the local economic effect was high in the following order: a fund investment wind project (Gangwon), benefit-sharing wind project (Jeju), and general wind project. In particular, residents' investment amount, the number of participating residents, and the amount and transparency of the regional cooperation fund were key factors to expand the effect of local economy activation. This evaluation index could be used in public bidding for renewable energy projects such as offshore wind zoning areas of local government.

• Journal of Periodontal and Implant Science
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• 제24권2호
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• pp.390-396
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• 1994

This study investigates the effect of wind instrument playing on the periodontal condition by comparing and analyzing wind instrument players and non-wind instrument players by various clinical paramenters, including periodontal index, bleeding index, simplified oral hygiene index, and non-functional tooth index. The subjects consist of 65 wind instrument players and 31 non-players. The players were divided into 4 groups ; Those who use cup-shaped mouthpieces as Group A, single reed mouthpieces as Group B, double reed mouthieces as Group C, and hole mouthpieces as Group D. Non-players are designated as Group E. The results are as follows ; 1. Periodontal Index Group A recorded $1.2{\pm}0.7$, Group B $1.1{\pm}0.7$, Group C $1.3{\pm}0.5$, Group D $2.1{\pm}0.5$, and Group E $0.9{\pm}0.6$, with no statistically significant differences among the groups. 2. Bleeding Index Group A shwed 0.23, Group B 0.25, Group C 3.0, Group D 0.38, and Group E 0.23, with no statistically significant differences among the groups. 3. Non-functional Tooth Index Group A recorded 2.0, Group B 1.0, Group C 3.0, Group D 0, Group E 0.7, with no statistically significant differences among the groups. 4. Simplified Oral Hygiene Index Buccal sides of maxillary 1st molars, lingual sides of mandibular 1st molars, labial sides of maxillary anterior teeth, and lingual sides of mandibular anterior teeth were investigated, and there was no statistically significant differences among the groups.

• Structural Monitoring and Maintenance
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• 제4권1호
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• pp.53-68
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• 2017

The response sensitivity method in time domain has been applied extensively for damage identification. In this paper, the relationship between the error of damage identification and the sensitivity matrix is investigated through perturbation analysis. An index is defined according to the perturbation amplify effect and an optimal sensor placement method is proposed based on the minimization of that index. A sequential sub-optimal algorithm is presented which results in consistently good location selection. Numerical simulations with a two-dimensional high truss structure are conducted to validate the proposed method. Results reveal that the damage identification using the optimal sensor placement determined by the proposed method can identify multiple damages of the structure more accurately.

• 풍력에너지저널
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• 제14권3호
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• pp.34-42
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• 2023

The reduction of operation and maintenance (O&M) costs is a critical factor in determining the competitiveness of wind energy. Predictive maintenance based on the estimation of remaining useful life (RUL) is a key technology to reduce logistic costs and increase the availability of wind turbines. Although a mechanical component usually has sudden changes during operation, most RUL estimation methods use the trend of a state index over the whole operation period. Therefore, overestimation of RUL causes confusion in O&M plans and reduces the effect of predictive maintenance. In this paper, two RUL estimation methods (load based and data driven) are proposed for the bearings of a wind turbine with the results of trend classification, which differentiates constant and increasing states of the state index. The proposed estimation method is applied to a bearing degradation test, which shows a conservative estimation of RUL.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
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• pp.226-227
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• 2006

Wind power is one of the fastest growing distributed generation types. As part of a worldwide trend, the concerns of large wind generation have been risen rather than small wind generation since it influences the whole power system Including the transient stability. The objective of this paper is to understand the effect of a large-scale wind generation on power system transient stability and to develop a systematic procedure to assess the effect according to the location and capacity of a wind farm. In the proposed procedure, an index is presented to evaluate the appropriateness of the location and capacity of a wind farm for transient stability contingencies.

• Structural Engineering and Mechanics
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• 제82권4호
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• pp.517-542
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• 2022

The effect of mean angle of wind attack on the flutter critical wind speed of two generic bridge deck cross-sections, viz, one closed box type streamlined section (deck-1) and closed box trapezoidal bluff type section with extended flanges/overhangs (deck-2) type of section have been studied using Computational Fluid Dynamics (CFD) based forced vibration simulation method. Owing to the importance of the effect of the amplitude of forcing oscillation on the flutter onset, its effect on the flutter derivatives and flutter onset have been studied, especially at non-zero mean angles of wind attack. The flutter derivatives obtained have been used to evaluate flutter critical wind speeds and flutter index of the deck sections at non-zero mean angles of wind attack studied and the same have been validated with those based on experimental results reported in literature. The value of amplitude of forcing oscillation in torsional degree of freedom for CFD based simulations is suggested to be in the range of 0.5° to 2°, especially for bluff bridge deck sections. Early onset of flutter from numerical simulations, thereby conservative estimate of occurrence of instability has been observed from numerical simulations in case of bluff bridge deck section. The study aids in gaining confidence and the extent of applicability of CFD during early stages of bridge design, especially towards carrying out studies on mean incident wind effects.

• 대한지리학회지
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• 제42권5호
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• pp.761-768
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• 2007

풍수지리의 기본 개념인 생기가 '연중 일정한 온도가 유지되며 상대 습도의 큰 변동 없이 통풍이 잘되고 일조량이 상당한 조건을 갖춘 곳의 쾌적성'이라고 한다면 이는 생리적으로 comfort한 기후조건을 갖춘 곳이 된다. Terjung은 신체적으로 comfort한 기후조건에 영향을 주는 요소로서 온도와 상대습도, 그리고 바람의 세기에 대하여 언급하고 comfort index, wind effect index를 개발하여 인간의 체감조건에 적용하였다. 따라서 풍수지리가 추구하는 '생기가 넘치는 곳'이 '보다 편안한 장소(more comfortable place)'가 되면 풍수지리는 과학적인 분야로 자리매김할 수 있게 된다. 미국 코넥티컷주에서도 풍수의 기본형에 부합되는 장소로서 Hampton 시의 North Cemetry가 발견되어 한국 뿐 아니라 세계의 다른 어떤 지역에도 풍수가 적용될 수 있다. 한국이건 미국이건 풍수지리적으로 선정된 이른바 쾌적한 곳의 온도, 상대습도, 바람의 세기와 방향 등의 기후 자료가 있다면 Terjung의 견해와 더불어 특정 장소의 편안함이 밝혀질 수 있다. 이것은 같은 기후 지역 내에서 두 장소에 대한 서로 비교하는 자료가 요청되며 풍수지리는 특정 기후 조건 아래에서 보다 comfort한 곳을 찾는 인간의 적응 전략으로 자리매김하기에 충분하다.

• Journal of Electrical Engineering and Technology
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• 제9권4호
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• pp.1248-1257
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• 2014

Overhead transmission lines are crucial components in power transmission systems. Well-designed maintenance strategy for overhead lines is required for power utilities to minimize operating costs, while improving the reliability of the power system. This paper presents a maintenance priority index (MPI) of overhead lines for a reliability centered approach. Proposed maintenance strategy is composed of a state index and importance indices, taking into account a transmission condition and importance in system reliability, respectively. The state index is used to determine the condition of overhead lines. On the other hand, the proposed importance indices indicate their criticality analysis in transmission system, by using a load effect index (LEI) and failure effect index (FEI). The proposed maintenance method using the MPI has been tested on an IEEE 9-bus system, and a numerical result demonstrates that our strategy is more cost effective than traditional maintenance strategies.

• Journal of international Conference on Electrical Machines and Systems
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• 제3권2호
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• pp.229-234
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• 2014

In this paper, a design problem of the flywheel energy storage system controller using genetic algorithm (GA) is investigated for a frequency control of the wind diesel hybrid power generation system in an isolated power system. In order to select parameters of the FESS controller, two performance indexes are used. We evaluated a frequency control effect for the wind diesel hybrid power system according to change of the weighted values of a performance index. To verify performance of the FESS controller according to the weighted value of the performance index, the frequency domain analysis using a singular value bode diagram and the dynamic simulations for various weighted values of performance index were performed. To verify control performance of the designed FESS controller, the eigenvalue analysis and the dynamic simulations were performed. The control characteristics with the two designed FESS controller were compared with that of the conventional pitch controller. The simulation results showed that the FESS controller provided better dynamic responses in comparison with the conventional controller.