• 한국해양공학회지
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• 제17권3호
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• pp.1-6
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• 2003

This study presents the results of series of studies, which are mainly devoted to the application of wavelet transforms to various problems in ocean engineering. Both continuous and discrete wavelet transforms were used. These studies attempted to solve detection of wave directionality, detection of wave profile, and decoupling of the rolling component from free roll decay tests. The results of these analysis, using wavelet transform, demonstrated that the wavelet transform can be a useful tool in analyzing many problems in the filed of ocean engineering.

• 한국시뮬레이션학회논문지
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• 제19권2호
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• pp.127-135
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• 2010

시뮬레이션에서 모델의 검증 문제는 그 모델의 신뢰성을 의미하며, 그에 따라 모형의 정당성을 입증하는 가장 중요한 열쇠 중 하나이다. 하지만 지금까지 연구된 다양한 방법들 중 시계열형태의 자료를 이용한 검증 방법론은 개념적인 측면에서는 정립되었으나 구체적인 기법에 대한 연구는 부족한 상태이다. 그리하여 본 연구에서는 Wavelet 변환과 Power Spectrum을 이용한 시계열 데이터의 시뮬레이션 검증 방법을 제시하고자 한다. 이를 위해 첫 번째로 비주기적인 신호분리가 가능한 Wavelet 변환을 이용하여 스펙트럼을 추출하고, 두 번째로 스펙트럼 분석을 이용하여 실제 시스템에서 출력 데이터의 패턴이 시뮬레이션을 통해 나온 패턴과 일치하는지의 여부를 Coherence를 이용해 검정하였다. 실제 사례를 통하여 다른 검증방법들과 비교한 결과, 시뮬레이션 모델링의 완성도에 따른 모델의 일치도 여부를 보다 명확하게 검증하였다. 본 연구에서 제시한 방법을 통해, 하나의 통계량을 통한 검증이 아닌 한 구간별 검증을 통해 지금까지의 획일적인 타당성 검증 방법에서는 할 수 없었던 다양한 상황에서의 시뮬레이션 모형의 타당성 검증이 가능하게 하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.2142_2143
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• 2009

Many waveform characteristics of arc signal support the detection of hazardous arc faults. The shoulder is one of main characteristics of arc signal. This paper provide a method for the detection of shoulder from series arc fault based on discrete wavelet transform. The simulation results show that the proposed method is reliable and simple.

• International Journal of Control, Automation, and Systems
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• 제6권5호
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• pp.639-650
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• 2008

Electricity price forecasting has become an integral part of power system operation and control. In this paper, a wavelet transform (WT) based neural network (NN) model to forecast price profile in a deregulated electricity market has been presented. The historical price data has been decomposed into wavelet domain constitutive sub series using WT and then combined with the other time domain variables to form the set of input variables for the proposed forecasting model. The behavior of the wavelet domain constitutive series has been studied based on statistical analysis. It has been observed that forecasting accuracy can be improved by the use of WT in a forecasting model. Multi-scale analysis from one to seven levels of decomposition has been performed and the empirical evidence suggests that accuracy improvement is highest at third level of decomposition. Forecasting performance of the proposed model has been compared with (i) a heuristic technique, (ii) a simulation model used by Ontario's Independent Electricity System Operator (IESO), (iii) a Multiple Linear Regression (MLR) model, (iv) NN model, (v) Auto Regressive Integrated Moving Average (ARIMA) model, (vi) Dynamic Regression (DR) model, and (vii) Transfer Function (TF) model. Forecasting results show that the performance of the proposed WT based NN model is satisfactory and it can be used by the participants to respond properly as it predicts price before closing of window for submission of initial bids.

• 한국수자원학회논문집
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• 제45권11호
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• pp.1187-1199
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• 2012

본 연구에서는 Wavelet Transform과 Support Vector Machine (SVM)을 결합한 Hybrid 상수도 수요량 예측 모형을 개발하였다. Wavelet Transform 방법을 활용하여 다양한 스케일이 존재하는 상수도 수요량 시계열을 분해하여 단순한 형태의 시계열로 변환하는데 이용하였으며, 비선형 예측모형인 SVM은 이들 단순화된 시계열을 예측하는데 활용하여 예측성능을 극대화시키는 방안을 수립하였다. 본 연구에서는 상수도 수요량 자료에서 내재되어 있는 주기의 특성과 비선형 예측모형의 장점을 서로 연계한 해석이 가능하였으며 시각적인 검토 및 모든 통계지표에서 개선된 예측결과를 확인할 수 있었다. 특히, 기존 ARIMA 모형 계열에서 나타나는 자기예측문제를 상당부분 개선한 결과를 보여줌으로서 실질적인 수요량 예측모형으로서 활용이 가능할 것으로 판단된다.

• 대한기계학회논문집A
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• 제28권1호
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• pp.70-78
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• 2004

This paper presents study of efficiency of wavelet transformation for on-line chatter detection during hard fuming process. From comparison with other time series and statistical methods such as fast fourier transformation (FFT), Kurtosis and standard deviation (STD), wavelet transform is better than others in on-line chatter detection. With using wavelet function with pseudo frequency corresponding to chatter frequency, chatter could be detected more sensitively. And for both force signal from dynamometer and displacement signal from capacitance type cylindrical sensor (CCS), wavelet transform with DB2 function on level 4 could be well used for chatter detection in hard turning process.

• Computers and Concrete
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• 제2권6호
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• pp.481-498
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• 2005

A wavelet based approach is proposed for structural damage detection in beams, plate and delamination of composite plates. Wavelet theory is applied here for crack identification of a beam element with a transverse on edge non-propagating open crack. Finite difference method was used for generating a general displacement equation for the cracked beam in the first example. In the second and third example, damage is detected from the deformed shape of a loaded simply supported plate applying the wavelet theory. Delamination in composite plate is identified using wavelet theory in the fourth example. The main concept used is the breaking down of the dynamic signal of a structural response into a series of local basis function called wavelets, so as to detect the special characteristics of the structure by scaling and transformation property of wavelets. In the light of the results obtained, limitations of the proposed method as well as suggestions for future work are presented. Results show great promise of wavelet approach for damage detection and structural health monitoring.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2006년도 학술발표회 논문집
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• pp.1450-1454
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• 2006

Empirical mode decomposition (EMD) is applied to analyze time series characterized with nonlinearity and nonstationarity. This decomposition could be utilized to construct finite and small number intrinsic mode functions (IMF) that describe complicated time series, while admitting the Hilbert transformation properties. EMD has the capability of being adaptive, capture local characteristics, and applicable to nonlinear and nonstationary processes. Unlike discrete wavelet transform (DWT), IMF eliminates spurious harmonics and retains meaningful instantaneous frequencies. Examples based on data representing natural phenomena are given to demonstrate highlight the power of this method in contrast and comparison of other ones. A presentation of the energy-frequency-time distribution of these signals found to be more informative and intuitive when based on Hilbert transformation.

• Journal of applied mathematics & informatics
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• 제17권1_2_3호
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• pp.719-736
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• 2005

An understanding of Fourier series and their generalization is important for physics and engineering students, as much for mathematical and physical insight as for applications. Students are usually confused by the so-called Gibbs' phenomenon, an overshoot between a discontinuous function and its approximation by a Fourier series as the number of terms in the series becomes indefinitely large. In this paper we give short story of Gibbs phenomenon in chronological order.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2004년도 가을 학술발표논문집 Vol.31 No.2 (2)
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• pp.85-87
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• 2004

유클리드 거리에 기반하여 유사한 시퀀스 검색을 하는 기법들은 각 시퀀스에서 특징을 추출하여 차원을 감소시킨 후, R-tree 같은 다차원 인덱싱 기법을 사용하여 검색을 수행한다. 본 논문에서는 시계열 데이터 베이스에서의 유사 검색 성능 향상을 위한 새로운 특징 추출 기법인 Polar Wavelet 기법을 제안한다. 이 기법은 유사 검색 시 후보 시퀀스의 개수를 줄임으로써 검색 성능을 향상시킬 수 있고, 특징 추출을 위해 시퀀스의 길이를 2$^n$으로 만들 필요가 없는 장점을 갖고 있다.