• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회(1)
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• pp.820-821
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• 2005

• Structural Engineering and Mechanics
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• 제14권4호
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• pp.417-434
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• 2002

This paper explores the possibility of using a combination of the empirical mode decomposition (EMD) and the Hilbert transform (HT), termed the Hilbert-Huang transform (HHT) method, to identify the modal damping ratios of the structure with closely spaced modal frequencies. The principle of the HHT method and the procedure of using the HHT method for modal damping ratio identification are briefly introduced first. The dynamic response of a two-degrees-of-freedom (2DOF) system under an impact load is then computed for a wide range of dynamic properties from well-separated modal frequencies to very closely spaced modal frequencies. The natural frequencies and modal damping ratios identified by the HHT method are compared with the theoretical values and those identified using the fast Fourier transform (FFT) method. The results show that the HHT method is superior to the FFT method in the identification of modal damping ratios of the structure with closely spaced modes of vibration. Finally, a 36-storey shear building with a 4-storey light appendage, having closely spaced modal frequencies and subjected to an ambient ground motion, is analyzed. The modal damping ratios identified by the HHT method in conjunction with the random decrement technique (RDT) are much better than those obtained by the FFT method. The HHT method performing in the frequency-time domain seems to be a promising tool for system identification of civil engineering structures.

• Nuclear Engineering and Technology
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• 제47권2호
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• pp.219-225
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• 2015

In this paper, a three-dimensional model for the dynamic analysis of a flywheel based on the finite element method is presented. The static structure analysis for the model provides stress and strain distribution cloud charts. The modal analysis provides the basis of dynamic analysis due to its ability to obtain the natural frequencies and the vibration-made vectors of the first 10 orders. The results show the main faults are attrition and cracks, while also indicating the locations and patterns of faults. The harmonic response simulation was performed to gain the vibration response of the flywheel under operation. In this paper, we present a Hilbert-Huang transform (HHT) algorithm for flywheel vibration analysis. The simulation indicated that the proposed flywheel vibration signal analysis method performs well, which means that the method can lay the foundation for the detection and diagnosis in a reactor main coolant pump.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.939-951
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• 2019

A novel empirical mode decomposition strategy based on Fourier transform and band-pass filter techniques, contributing to efficient instantaneous vibration analyses, is developed in this study. Two key improvements are proposed. The first is associated with the adoption of a band-pass filter technique for intrinsic mode function sifting. The primary characteristic of decomposed components is that their bandwidths do not overlap in the frequency domain. The second improvement concerns an attempt to design narrowband constraints as the essential requirements for intrinsic mode function to make it physically meaningful. Because all decomposed components are generated with respect to their intrinsic narrow bandwidth and strict sifting from high to low frequencies successively, they are orthogonal to each other and are thus suitable for an instantaneous frequency analysis. The direct Hilbert spectrum is employed to illustrate the instantaneous time-frequency-energy distribution. Commendable agreement between the illustrations of the proposed direct Hilbert spectrum and the traditional Fourier spectrum was observed. This method provides robust identifications of vibration modes embedded in vibration processes, deemed to be an efficient means to obtain valuable instantaneous information.

• 지구물리와물리탐사
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• 제14권1호
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• pp.1-6
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• 2011

상업적인 주파수영역 항공전자탐사 장비의 개별적인 하부시스템의 계기변화와 보정에 대한 점검방법으로 유인성 제약조건만을 사용하여 광대역 이상성분 자료로부터 통상성분을 예측하고자 한다. 이상성분 자료로부터 통상성분의 반응을 예측하는 방법은 다음을 포함한 몇 가지가 있다: (1) 기준면 변화, 보정, 위상의 점검에 대한 품질관리; (2) 이상생분 측정으로부터 통상성분의 잡음수준 예측 및 확인 그리고 향후에는 그 반대과정도 가능할 것이다; (3) 주파수영역과 시간영역의 더 나은 변환과 유인성을 충족시키기 위해 성기게 측정된 자료의 내삽 및 외삽 실제로 수치모형자료와 Resolve 헬리곱터에 탑재된 전자기 탐사 장비로 측정된 주파수 영역 자료에 대한 실험 결과, 통상성분 자료들은 비율을 맞춘 힐버트 변환에 의해서 40에서 80 ppm의 표준편차를 갖고 예측될 수 있다는 것을 알았다. 그러나, 비행간의 기준면들 사이의 상대적인 차이는 1 ppm보다 더 정확히 분석될 수 있으며 이는 계기변화 보정의 정밀도에 대해 독립적인 품질관리를 가능하게 한다.

• 전기전자학회논문지
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• 제18권2호
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• pp.240-247
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• 2014

안압의 측정은 각막에 air puff 후 각막의 변형 즉, 각막의 두께나 변위 등 생역학적 성질을 관찰함으로써 이루어진다. 본 논문에서는 녹내장이나 라식의 진단을 위하여 사용되는 안압계의 air puff에 의한 각막의 변형을 주파수 영역에서 분석하였다. Air puff 후 각막의 중심부 주변의 변위에 대한 진동 주파수를 측정함으로써 환자와 정상인을 구별한다. 동영상으로부터 이진 영상을 구하고, 상하 변위 데이터와 곡선 정합의 차를 구하여 시간에 따른 각막 상하 진동 프로파일 데이터를 추출하였다. Fourier 변환으로 비정상인의 진동 주파수는 479.2Hz를 얻었고 정상인의 경우 단단함으로 인하여 702.8Hz의 고주파 성분을 볼 수 있었다. 또한 Hilbert-Huang 변환의 EMD 방법을 이용, 고유 모드 함수로 분해하여 국소적, 비선형, 비정상성을 가지는 데이터를 얻고 주파수와 전력을 분석하였다. 마지막으로 특정 고유 모드 함수에 대한 환자와 정상인의 전력비가 6배 이상 차이가 나는 것을 확인하였다.

• 대한수학회보
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• 제60권6호
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• pp.1555-1566
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• 2023

A Hilbert space operator A ∈ B(H) is a generalised n-projection, denoted A ∈ (G-n-P), if A^*n = A. (G-n-P)-operators A are normal operators with finitely countable spectra σ(A), subsets of the set $\{0\}\,{\cup}\,\{\sqrt[n+1]{1}\}.$ The Aluthge transform à of A ∈ B(H) may be (G - n - P) without A being (G - n - P). For doubly commuting operators A, B ∈ B(H) such that σ(AB) = σ(A)σ(B) and ${\parallel}A{\parallel}\,{\parallel}B{\parallel}\;{\leq}\;{\parallel}{\tilde{AB}}{\parallel},$ ${\tilde{AB}}\;{\in}\;(G\,-\,n\,-\,P)$ if and only if $A\;=\;{\parallel}{\tilde{A}}{\parallel}\,(A_{00}\,{\oplus}\,(A_0\,{\oplus}\,A_u))$ and $B\;=\;{\parallel}{\tilde{B}}{\parallel}\,(B_0\,{\oplus}\,B_u),$ where A₀₀ and B₀, and A₀ ⊕ A_u and B_u, doubly commute, A₀₀B₀ and A₀ are 2 nilpotent, A_u and B_u are unitaries, A^*n_u = A_u and B^*n_u = B_u. Furthermore, a necessary and sufficient condition for the operators αA, βB, αà and ${\beta}{\tilde{B}},\;{\alpha}\,=\,\frac{1}{{\parallel}{\tilde{A}}{\parallel}}$ and ${\beta}\,=\,\frac{1}{{\parallel}{\tilde{B}}{\parallel}},$ to be (G - n - P) is that A and B are spectrally normaloid at 0.

• 천문학논총
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• 제30권2호
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• pp.605-607
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• 2015

The development of time-frequency analysis techniques allow astronomers to successfully deal with the non-stationary time series that originate from unstable physical mechanisms. We applied a recently developed time-frequency analysis method, the Hilbert-Huang transform (HHT), to two non-stationary phenomena: the superorbital modulation in the high-mass X-ray binary SMC X-1 and the quasi-periodic oscillation (QPO) of the AGN RE J1034+396. From the analysis of SMC X-1, we obtained a Hilbert spectrum that shows more detailed information in both the time and frequency domains. Then, a phase-resolved analysis of both the spectra and the orbital profiles was presented. From the spectral analysis, we noticed that the iron line production is dominated by different regions of this binary system in different superorbital phases. Furthermore, a pre-eclipse dip lying at orbital phase ~0:6-0:85 was discovered during the superorbital transition state. We further applied the HHT to analyze the QPO of RE J1034+396. From the Hilbert spectrum and the O-C analysis results, we suggest that it is better to divide the evolution of the QPO into three epochs according to their different periodicities. The correlations between the QPO periods and corresponding fluxes were also different in these three epochs. The change in periodicity and the relationships could be interpreted as the change in oscillation mode based on the diskoseismology model.

• Journal of Biosystems Engineering
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• 제34권2호
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• pp.127-132
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• 2009

In the working population, muscle fatigue and musculoskeletal discomfort are common, which, in the case of insufficient recovery may lead to musculoskeletal pain. Workers suffering from musculoskeletal pains need to be rehabilitated for recovery. Isokinetic testing has been used in physical strengthening, rehabilitation and post-operative orthopedic surgery. Frequency analysis of electromyography (EMG) signals using the mean frequency (MNF) has been widely used to characterize muscle fatigue. During isokinetic contractions, EMG signals present strong nonstationarities. Hilbert-Haung transform (HHT) and autoregressive (AR) model have been known more suitable than Fourier or wavelet transform for nonstationary signals. Moreover, several analyses have been performed within each active phase during isokinetic contractions. Thus, the aims of this study were i) to determine which one was better suitable for the analysis of MNF between HHT and AR model during repetitive maximum isokinetic extensions and ii) to investigate whether the analysis could be repeated for sequential fixed epoch lengths. Seven healthy volunteers (five males and two females) performed isokinetic knee extensions at $60^{\circ}/s$ and $240^{\circ}/s$ until 50% of the maximum peak torque was reached. Surface EMG signals were recorded from the rectus femoris of the right thigh. An algorithm detecting the onset and offset of EMG signals was applied to extract each active phase of the muscle. Following the results, slopes from the least-square error linear regression of MNF values showed that muscle fatigue of all subjects occurred. The AR model is better suited than HHT for estimating MNF from nonstationary EMG signals during isokinetic knee extensions. Moreover, the linear regression can be extracted from MNF values calculated by sequential fixed epoch lengths (p> 0.0I).

• 한국정보전자통신기술학회논문지
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• 제7권3호
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• pp.121-125
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• 2014

DSP 시스템에서 널리 사용되는 힐버트 변환에서 곱셈 연산은 반드시 필요한 요소이며 변환에 사용되는 계수의 차수가 높아질수록 하드웨어는 복잡하고 많은 양의 게이트를 필요로 한다. 본 연구에서는 힐버트 변환에 사용되는 곱셈연산에 MAG 알고리즘이 적용된 쉬프트와 덧셈을 사용한 곱셈블록을 구현하여 하드웨어의 복잡도를 줄일 수 있다.