• Journal of Communications and Networks
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• 제16권1호
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• pp.92-97
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• 2014

A novel method for extracting frequency slippage signal from radar full pulse sequence is presented. For the radar full pulse sequence received by radar interception receiver, radio frequency (RF) and time of arrival (TOA) of all pulses constitute a two-dimensional information sequence. In a complex and intensive electromagnetic environment, the TOA of pulses is distributed unevenly, randomly, and in a nonstationary manner, preventing existing methods from directly analyzing such time series and effectively extracting certain signal features. This work applies Gaussian noise insertion and structure function to the TOA-RF information sequence respectively such that the equalization of time intervals and correlation processing are accomplished. The components with different frequencies in structure function series are separated using empirical mode decomposition. Additionally, a chaos detection model based on the Duffing equation is introduced to determine the useful component and extract the changing features of RF. Experimental results indicate that the proposed methodology can successfully extract the slippage signal effectively in the case that multiple radar pulse sequences overlap.

• Structural Engineering and Mechanics
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• 제75권3호
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• pp.377-387
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• 2020

Modern long-span floor system typically possesses low damping and low natural frequency, presenting a potential vibration sensitivity problem induced by human activities. Field test and numerical analysis methods are available to study this kind of problems, but would be inconvenient for design engineers. This paper proposes a simplified method to determine the acceleration amplitudes of long-span floor system subjected to walking or running load, which can be carried out manually. To theoretically analyze the acceleration response, the floor system is simplified as an anisotropic rectangular plate and the mode decomposition method is used. To facilitate the calculation of acceleration amplitude a_P, a coefficient α_wmn or α_Rmn is introduced, with the former depending on the geometry and support condition of floor system and the latter on the contact duration t_R and natural frequency. The proposed simplified method is easy for practical use and gives safe structural designs.

• 한국공간구조학회논문집
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• 제20권2호
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• pp.77-85
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• 2020

This paper examined the dynamic instability of a shallow arch according to the response characteristics when nearing critical loads. The frequency changing feathers of the time-domain increasing the loads are analyzed using Fast Fourier Transformation (FFT), while the response signal around the critical loads are analyzed using Hilbert-Huang Transformation (HHT). This study reveals that the models with an arch shape of h = 3 or higher exhibit buckling, which is very sensitive to the asymmetric initial conditions. Also, the critical buckling load increases as the shape increases, with its feather varying depending on the asymmetric initial conditions. Decomposition results show the decrease in predominant frequency before the threshold as the load increases, and the predominant period doubles at the critical level. In the vicinity of the critical level, sections rapidly manifest the displacement increase, with the changes in Instantaneous Frequency (IF) and Instant Energy (IE) becoming apparent.

• 한국광학회:학술대회논문집
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• 한국광학회 2009년도 동계학술발표회 논문집
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• pp.449-450
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• 2009

위그너 분포 함수 측정을 통하여 진행하는 laser beam의 상관함수와 진행 특성들을 연구하였다. 위그너 분포 함수는 진행하는 laser beam의 total degree of coherence, beam quality parameter, 그리고 근접장 및 원거리장의 정보들을 보여준다. 위그너 분포 함수를 이용하여 공간상관 함수와 방향상관 함수를 구할 수 있으며, 이를 Schmidt mode decomposition을 이용하여 분석하면 laser beam의 보다 여러가지 특성들을 분석 할 수 있다. 이렇게 분석된 eigenmode들은 진행하는 laser beam의 보다 정확한 coherence 특성을 이해하게 해준다.

• 응용통계연구
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• 제24권6호
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• pp.995-1006
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• 2011

A time series can be decomposed into simple components with a multiscale method. Empirical mode decomposition(EMD) is a recently invented multiscale method in Huang et al. (1998). It is natural to apply a classical prediction method such a vector autoregressive(AR) model to the obtained simple components instead of the original time series; in addition, a prediction procedure combining a classical prediction model to EMD and Hilbert spectrum is proposed in Kim et al. (2008). In this paper, we suggest to adopt principal component analysis(PCA) to the prediction procedure that enables the efficient selection of input variables among obtained components by EMD. We discuss the utility of adopting PCA in the prediction procedure based on EMD and Hilbert spectrum and analyze the daily worm account data by the proposed PCA adopted prediction method.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2000년도 종합학술발표회 논문집 Vol.10 No.1
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• pp.29-33
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• 2000

Stripmap SAR 시스템에서 레이더는 Slant range-domain에서 고정된 Strip상에 Data acquisition period 동안 계속해서 같은 Broadside 방사 패턴을 유지하며, Range domain에서 고정돈 Strip내의 지형의 지도를 제공하는 SAR 영상 시스템이다. Stripmap SAR를 위한 고전적인 영상 복원을 Synthetic aperture (slow-time) domain에서 Deramping 또는 Chirp deconvolution을 이용하는 Fresnel approximaptio에 의존하였다. 또 다른 Stripmap SAR 영상화의 접근방법으로 SAR wavefront reconstruction이론과 레이더 방사형태에 대한 spherical wave Fourier decomposition을 통하여 slow-time domain에서의 SAR 신호의 분석에 기본을 두고 있다. 본 논문에서는 컴퓨터 모의 실험을 통해 생성된 Stripmap SAR 데이터를 이용하여 Fresnel approximation 기법과 Wavefront Reconstruction 기법을 비교 분석한다.

• ETRI Journal
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• 제34권5호
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• pp.684-689
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• 2012

A mode-singular-value-decomposition (SVD) maximum likelihood (ML) estimation procedure is proposed for the source localization problem under an additive measurement error model. In a practical situation, the noise variance is usually unknown. In this paper, we propose an algorithm that does not require the noise covariance matrix as a priori knowledge. In the proposed method, the weight is derived by the inverse of the noise magnitude square in the ML criterion. The performance of the proposed method outperforms that of the existing methods and approximates the Taylor-series ML and Cram$\acute{e}$r-Rao lower bound.

• Computers and Concrete
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• 제12권1호
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• pp.79-90
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• 2013

In this study, dynamic characteristics such as natural frequencies, mode shapes and damping ratios of RC frame is determined for different construction stages using Operational Modal Analyses method under ambient vibration. Full scaled, one bay and one story RC frames are selected as an application for different construction stages such as plane, brick in-filled and brick in-filled with plaster. The RC frame is vibrated by natural excitations with small impact effects and the response signals are measured using sensitive accelerometers during ambient vibration tests. Measurement time-frequency span and effective mode number are determined by considering similar studies in literature. Sensitive seismic accelerometers are used to collect signals obtained from the experimental tests. To obtain experimental dynamic characteristics, output-only system identification technique is employed namely; Enhanced Frequency Domain Decomposition technique in the frequency domain. It is demonstrated that the ambient vibration measurements are enough to identify the most significant modes of RC frames.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2008년도 추계학술발표논문집
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• pp.164-166
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• 2008

소음은 현대 사회에서 쉽게 접하게 되는 환경 오염원이다. 능동소음제어(Active Noise Control)는 발생된 소음을 제거하기 위해 구현이 간단한 LMS 알고리즘을 많이 사용하고 있다. 그러나 LMS 알고리즘은 수렴 속도와 소음신호의 변화속도에 따라 발산의 위험을 가지고 있다. 본 논문에서는 이러한 LMS의 문제점을 보완하기 위해 경험 모드 분석법을 이용한 feedback FXLMS(Filtered-X Least Mean Square) 알고리즘을 제안하였다. 소음제거 시스템의 출력단에서 검출된 잔차소음을 경험 모드 분석법(Empirical Mode Decomposition)을 이용하여 IMF 신호들로 분해하고, 분해된 각 신호를 FXLMS 알고리즘을 이용하여 수렴시킨 후, 결과들을 다시 결합하여 소음 제거에 이용하였다. 각각의 IMF 신호를 FXLMS 알고리즘으로 수렴시킬 때 수렴속도에 변화를 주어 소음제거의 효율성을 높였다. 제안한 알고리즘을 Matlab을 이용하여 시뮬레이션하였고 기존의 FXLMS알고리즘보다 향상된 수렴속도 및 안정성을 가짐을 입증하였다.

• Structural Engineering and Mechanics
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• 제54권3호
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• pp.419-432
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• 2015

The free vibration of rotating Euler-Bernoulli beams with the thickness and/or width of the cross-section vary linearly along the length is investigated by using the Adomian modified decomposition method (AMDM). Based on the AMDM, the governing differential equation for the rotating tapered beam becomes a recursive algebraic equation. By using the boundary condition equations, the dimensionless natural frequencies and the closed form series solution of the corresponding mode shapes can be easily obtained simultaneously. The computed results for different taper ratios as well as different offset length and rotational speeds are presented in several tables and figures. The accuracy is assured from the convergence and comparison with the previous published results. It is shown that the AMDM provides an accurate and straightforward method of free vibration analysis of rotating tapered beams.