• 응용통계연구
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• 제30권5호
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• pp.747-757
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• 2017

본 논문은 다변량 실현 변동성 계산에서 주기 선택 방안에 대해 연구하고 있다. 고빈도(high frequency) 시계열 자료에 기초한 일간 변동성인 실현변동성을 계산하고 차원 축소 방법인 주성분을 도입하였다. Cholesky 모형을 포함한 다양한 다변량 변동성모형을 주성분을 통해 비교하였으며 KOSPI/삼성전자/현대차 고빈도 수익률 자료를 이용하여 예시하였다.

• KIEE International Transactions on Power Engineering
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• 제2A권4호
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• pp.136-144
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• 2002

Load models are very important for improving the accuracy of stability analysis and load flow studies. Various loads are connected to a power bus and their characteristics of power consumption change with voltage and frequency. Thus, the effect of voltage/frequency changes must be considered in load modeling. In this work, artificial neural networks-ANNs- were used to construct the component load models for more accurate modeling. A typical residential load was selected and subjected to a test under variable voltage/frequency conditions. Acquired data were used to construct component models by ANNs. The aggregation process of separately determined load models is also presented in the paper. Furthermore, this paper proposes a method to transform a single load model constructed by the aggregation method into a mathematical load model that can be used in traditional power system analysis software.

• 한국해양공학회지
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• 제13권2호통권32호
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• pp.90-98
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• 1999

Boiler high-temperature pipelines such as main steam pipe, header and steam drum in fossil power plants are degraded by creep damage due to severe operationg conditions like high temperature and high pressure for an extended period time. Such material degradation lead to various component faliures causing serious accidents at the plant. Conventional measurement techniques such as replica method, electric resistance method, and hardness test method have such disadvantages as complex preparation and measurement procedures, too many control parameters, and therefore, low practicality and they were applied only to component surfaces with good accessibility. In this study, both artificial creep degradation test using life prediction formula and frequency analysis by ultrasonic tests for their preparing creep degraded specimens have been carried out for the purpose of nondestructive evaluation for creep damage which can occur in high-temperature pipelline of fossil power plant. As a result of ultrasonic tests for crept specimens, we confirmed that the high frequency side spectra decrease and central frequency components shift to low frequency bans, and bandwiths decrease as increasing creep damage in backwall echoes.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.367-372
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• 1999

In this paper, an inverter fed induction motor drive system is analyed in order to predict the conducted interference. High frequency model for inverter, motor and system parasitic components are proposed. High frequency component allows time and frequency domain analysis to be performed with standard PSpice tool. The overall high frequency component and model are verified by comparing simulation and experimental result.

• 응용통계연구
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• 제30권3호
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• pp.441-451
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• 2017

본 논문에서는 주파수공간에서의 주성분 분석을 사용하여 기상자료를 분석하고자 한다. 주파수공간에서의 주성분분석은 차원축소를 위해서도 사용되지만, 주요한 패턴을 뽑아내는 데 사용되는 통계적 방법 중 하나이다. 일반적으로 주파수공간에서의 주성분 분석은 두 가지의 방법이 있는데, Hilbert PCA와 frequency domain PCA가 그것이다. 본 논문에서는 기존의 시간공간 주성분 분석과 함께 두 가지 주파수공간 주성분 분석 방법을 비교하였다. 시뮬레이션 자료를 통하여 주파수공간 주성분 분석 방법의 유용성을 보였으며, 열대 태평양 지역의 해수표층 온도값에 주성분 분석 방법들을 적용하여 기상자료 분석에 대한 유용성을 확인하였다.

• Journal of Power Electronics
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• 제15권4호
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• pp.1085-1092
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• 2015

In this paper, the expressions of the estimated information of a single-phase enhanced phase-locked loop (EPLL), when input signal contains harmonics and a DC offset while the fundamental component takes step changes, are derived. The theoretical analysis results indicate that in the estimated information, the n^th-order harmonics cause n+1^th-order periodic ripples, and the DC offset causes a periodic ripple at the fundamental frequency. Step changes of the amplitude, phase angle and frequency of the fundamental component cause a transient periodic ripple at twice the frequency. These periodic ripples deteriorate the performance of the EPLL. A hybrid filter based EPLL (HF-EPLL) is proposed to eliminate these periodic ripples. A delay signal cancellation filter is set at the input of the EPLL to cancel the DC offset and even-order harmonics. A sliding Goertzel transform-based filter is introduced into the amplitude estimation loop and frequency estimation loop to eliminate the periodic ripples caused by the residual input odd-order harmonics and step change of the input fundamental component. The parameter design rules of the two filters are discussed in detail. Experimental waveforms of both the conventional EPLL and the proposed HF-EPLL are given and compared with each other to verify the theoretical analysis and advantages of the proposed HF-EPLL.

• 조명전기설비학회논문지
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• 제13권4호
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• pp.96-101
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• 1999

전력계통에서 부하모델은 안정도 해석과 조류계산의 정도를 높이기 위하여 매우 중요하다. 전력계통의 모선은 전압/주파수 변화에 따라 소비형태가 다른 다양한 부하들로 구성되어 있다. 따라서 전압/주파수 변화에 따른 부하모델을 고려하지 않으면 안된다. 본 연구는 정도 높은 부하모델링을 위해 신경회로망을 사용하였다. 대표적인 주거용 부하를 선정하여 전압과 주파수를 변화시키면서 부하특성을 측정하였다. 실험에서 얻은 실적자료로 신경회로망을 이용한 개별부하모델을 구축하고, 개별부하모델과 부하구성비에 의한 집단부하 모델을 제시하였다. 또, 전력계통해석 프로그램에 적용하기 위한 수학적 모델로의 변환기법을 제시하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.663-666
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• 2004

An analysis of the annual frequency of collapse(AF) is performed for each bridge pier exposed to ship collision. AF is computed for each bridge component and vessel classification. The summation of AFs computed over all of the vessel classification intervals for a specific component should equal the annual frequency of collapse of the component. The designer should use judgment in developing a distribution of the vessel frequency data based on discrete groupings or categories of vessel size by DWT. In the present study the effect of vessel classification on the annual frequency of collapse in the ship collision risk assessment is investigated by illustrative numerical examples based on the vessel frequency data of the domestic harbor. The DWT interval for larger vessels has more effect on the ship collision risk. Therefore the expert judgement in determining the larger DWT interval is required because the design impact lateral resistances of bridge components depend on the ship collision risk.

• 한국음향학회지
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• 제38권2호
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• pp.177-183
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• 2019

본 논문에서는 수동 선배열 소나의 저주파 영역에서 수신된 표적 신호로부터 간섭신호를 분리해 내기 위해 독립성분분석 알고리즘을 적용하는 방안을 제안하고 기존 알고리즘들의 성능을 비교해 보았다. 저주파 대역 신호의 경우 비교적 넓은 방위로부터 수신되기 때문에 인접 빔 신호를 관측신호로 활용하여 독립성분분석을 수행할 수 있다. 신호분리에 사용한 독립성분분석 알고리즘은 FastICA(Fast Independent Component Analysis), NNMF (Non-negative Matrix Factorization), JADE (Joint Approximation Diagonalization of Eigen-matrices)이다. 실측 선배열 수동소나신호를 이용하여 독립성분분석을 수행한 결과 제안한 방법으로 간섭신호분리가 가능함을 확인하였으며, JADE 알고리즘의 신호 분리 성능이 가장 우수한 것으로 나타났다.

• Smart Structures and Systems
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• 제31권2호
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• pp.171-181
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• 2023

Using the most up-to-date system identification methods in both time and frequency domains, the dynamic monitoring data from the reinforced concrete Egebaekvej Bridge near Holte, Denmark, is examined in this investigation. The bridge was erected in the 1960s and was still standing during test campaign before demolishing. The ARTeMIS Modal was adopted to derive the modal parameters from ambient vibration data. Several Operational Modal Analysis (OMA) approaches were applied, including Enhanced Frequency Domain Decomposition (EFDD), Curve-fit Frequency Domain Decomposition (CFDD), and Frequency Domain Decomposition (FDD). Afterward, Principal Component (SSI-PC), Unweighted Principal Component (SSI-UPC) Stochastic Subspace Identification methods were utilized. Danish engineering consulting company, COWI with the allowance of the bridge contractor BARSLUND, allow the researcher for this experimental test to demonstrate the impact of OMA applications.