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Correlation analysis between fault frequency and service time of underground fluid instruments
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作者 Xiao Tian Guoying Su 《Geodesy and Geodynamics》 EI CSCD 2023年第4期411-418,共8页
In this paper, we make a statistical analysis of the fault information of the underground fluid instruments of 12 models in China from January 2021 to May 2022 based on the Pearson correlation coefficient, and compare... In this paper, we make a statistical analysis of the fault information of the underground fluid instruments of 12 models in China from January 2021 to May 2022 based on the Pearson correlation coefficient, and compare the fault statistics of the meteorological three-element instruments of 3 models during the study period. The results show that:(1) The numbers of faults of the underground fluid instruments of 12models with different service times are basically positively correlated with the numbers of the corresponding instruments, with good consistency. Moreover, the automatic observation instruments(8models) with more than 30 units are significantly correlated at a 0.05 significance level(95% confidence level). Even at a 0.01 significance level(99% confidence level), there are 7 models(7/8) with significant correlation.(2) The positive and negative correlations between the monthly average number of faults and the corresponding service times of the underground fluid instruments of 12 models with different service times are random, and there are 9 models(75%) with no significant correlation at a 0.05 significance level(95% confidence level), while 12 models(100%) with no significant correlation at a 0.01significance level(99% confidence level).(3) The monthly average numbers of faults of the underground fluid instruments of 12 models are basically 0.02-0.05 times/(unit·month), and the overall fault frequency is low.(4) The fault statistics results of the meteorological three-element instruments of 3 models are consistent with the characteristics of the underground fluid instruments of 12 models. In general,there is no significant correlation between the fault frequency and the service time of underground fluid instruments.(5) The results of this paper demonstrate that the service time of underground fluid instruments cannot be taken as the main reason for whether to update the instruments. Similarly, the fault frequency of the instruments cannot be taken as the main reason for the service life of the instruments in the process of formulating the service life standards of underground fluid instruments. 展开更多
关键词 Underground fluid instruments Fault frequency Service time Correlation analysis
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Adaptive Fourier Decomposition Based Time-Frequency Analysis 被引量:3
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作者 Li-Ming Zhang 《Journal of Electronic Science and Technology》 2014年第2期201-205,共5页
The attempt to represent a signal simultaneously in time and frequency domains is full of challenges. The recently proposed adaptive Fourier decomposition (AFD) offers a practical approach to solve this problem. Thi... The attempt to represent a signal simultaneously in time and frequency domains is full of challenges. The recently proposed adaptive Fourier decomposition (AFD) offers a practical approach to solve this problem. This paper presents the principles of the AFD based time-frequency analysis in three aspects: instantaneous frequency analysis, frequency spectrum analysis, and the spectrogram analysis. An experiment is conducted and compared with the Fourier transform in convergence rate and short-time Fourier transform in time-frequency distribution. The proposed approach performs better than both the Fourier transform and short-time Fourier transform. 展开更多
关键词 Adaptive Fourier decomposition Fourier transform instantaneous frequency time frequency analysis
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Frequency Time Analysis (FTAN) and Moment Tensor Inversion Solutions from Short Period Surface Waves in Cameroon (Central Africa) 被引量:2
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作者 Eric N. Ndikum Charles T. Tabod Alain-Pierre K. Tokam 《Open Journal of Geology》 2014年第2期33-43,共11页
Short period surface waves generated by a local earthquake recorded by broadband seismometers at distances of about 186 to 778 km from the earthquake’s epicenter located in Cameroon (Central Africa) were processed fo... Short period surface waves generated by a local earthquake recorded by broadband seismometers at distances of about 186 to 778 km from the earthquake’s epicenter located in Cameroon (Central Africa) were processed for group velocity maps and dispersion waveforms using the frequency time analysis (FTAN) method. The resulting group velocity fundamental modes of the extracted Rayleigh and Love waves were used for a joint amplitude spectral and P polarity inversion using moment tensor inversion. The corresponding group velocity dispersion curves, the residual as a function of depth, the amplitude spectra and the moment tensor solutions of the regions from the epicenter to the different stations up to a depth of about 10 km were obtained. 展开更多
关键词 frequency time analysis (FTAN) Surface Waves Group Velocity Dispersion CURVES MOMENT TENSOR Inversion
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Novel Doppler Frequency Extraction Method Based on Time-Frequency Analysis and Morphological Operation 被引量:2
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作者 侯舒娟 吴嗣亮 《Journal of Beijing Institute of Technology》 EI CAS 2006年第4期443-447,共5页
A novel method of Doppler frequency extraction is proposed for Doppler radar scoring systems. The idea is that the time-frequency map can show how the Doppler frequency varies along the time-line, so the Doppler frequ... A novel method of Doppler frequency extraction is proposed for Doppler radar scoring systems. The idea is that the time-frequency map can show how the Doppler frequency varies along the time-line, so the Doppler frequency extraction becomes curve detection in the image-view. A set of morphological operations are used to implement curve detection. And a map fusion scheme is presented to eliminate the influence of strong direct current (DC) component of echo signal during curve detection. The radar real-life data are used to illustrate the performance of the new approach. Experimental results show that the proposed method can overcome the shortcomings of piecewise-processing-based FFT method and can improve the measuring precision of miss distance. 展开更多
关键词 Doppler frequency time-frequency analysis morphological operation miss distance
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Parameterized time-frequency analysis to separate multi-radar signals 被引量:1
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作者 Wenlong Lu Junwei Xie +1 位作者 Heming Wang Chuan Sheng 《Journal of Systems Engineering and Electronics》 SCIE EI CSCD 2017年第3期493-502,共10页
Multi-radar signal separation is a critical process in modern reconnaissance systems. However, the complicated battlefield is typically confronted with increasing electronic equipment and complex radar waveforms. The ... Multi-radar signal separation is a critical process in modern reconnaissance systems. However, the complicated battlefield is typically confronted with increasing electronic equipment and complex radar waveforms. The intercepted signal is difficult to separate with conventional parameters because of severe overlapping in both time and frequency domains. On the contrary, time-frequency analysis maps the 1D signal into a 2D time-frequency plane, which provides a better insight into the signal than traditional methods. Particularly, the parameterized time-frequency analysis (PTFA) shows great potential in processing such non stationary signals. Five procedures for the PTFA are proposed to separate the overlapped multi-radar signal, including initiation, instantaneous frequency estimation with PTFA, signal demodulation, signal separation with adaptive filter and signal recovery. The proposed method is verified with both simulated and real signals, which shows good performance in the application on multi-radar signal separation. 展开更多
关键词 intercepted multi-radar signal parameterized time-frequency analysis DEMODULATION adaptive filtering
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A Recursive Method of Time-Frequency Analysis for the Signal Processing of Flutter Test with Progression Variable Speed 被引量:1
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作者 宋叔飚 裴承鸣 《Chinese Journal of Aeronautics》 SCIE EI CAS CSCD 2005年第3期213-217,共5页
Focused on the non-statlonarity and real-time analysis of signal in flutter test with progression variable speed (FTPVS), a new method of recursive time-frequency analysis is presented. The time-varying system is tr... Focused on the non-statlonarity and real-time analysis of signal in flutter test with progression variable speed (FTPVS), a new method of recursive time-frequency analysis is presented. The time-varying system is tracked on-line by building a time-varying parameter model, and then the relevant parameter spectrum can be obtained. The feasibility and advantages of the method are examined by digital simulation. The results of FTPVS at low-speed wind-tunnel promise the engineering application perspective of the method. 展开更多
关键词 flutter test with progression variable speed (FTPVS) non-stationary signal processing recursive time-frequency analysis (Rtfa)
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NEW SAR IMAGE INTERPRETATION METHOD OF AIRCRAFT BASED ON JOINT TIME-FREQUENCY ANALYSIS 被引量:1
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作者 Zhu Jiwei Qiu Xiaolan Lei Bin 《Journal of Electronics(China)》 2014年第4期325-333,共9页
With the continuous improvement of Synthetic Aperture Radar(SAR) resolution, interpreting the small targets like aircraft in SAR images becomes possible and turn out to be a hot spot in SAR application research. Howev... With the continuous improvement of Synthetic Aperture Radar(SAR) resolution, interpreting the small targets like aircraft in SAR images becomes possible and turn out to be a hot spot in SAR application research. However, due to the complexity of SAR imaging mechanism, interpreting targets in SAR images is a tough problem. This paper presents a new aircraft interpretation method based on the joint time-frequency analysis and multi-dimensional contrasting of basic structures. Moreover, SAR data acquisition experiment is designed for interpreting the aircraft. Analyzing the experiment data with our method, the result shows that the proposed method largely makes use of the SAR data information. The reasonable results can provide some auxiliary support for the SAR images manual interpretation. 展开更多
关键词 Synthetic Aperture Radar (SAR) image interpretation Joint time-frequency analysis Scattering centers Basic structureCLC number:TN957
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Time-Frequency Analysis of Asymmetric Triaxial Galaxy Model Including Effect of Spherical Dark Halo Component
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作者 Beena R. Gupta Vinay Kumar 《International Journal of Astronomy and Astrophysics》 2015年第2期106-115,共10页
A method of time-frequency analysis (TFA) based on wavelets is applied to study the phase space structure of three-dimensional asymmetric triaxial galaxy enclosed by spherical dark halo component. The investigation is... A method of time-frequency analysis (TFA) based on wavelets is applied to study the phase space structure of three-dimensional asymmetric triaxial galaxy enclosed by spherical dark halo component. The investigation is carried out in the presence and absence of dark halo component. Time-frequency analysis is based on the extraction of instantaneous frequency from the phase of the continuous wavelet transform. This method is comparatively fast and reliable. This method can differentiate periodic from quasi-periodic, chaotic sticky from chaotic non-sticky, ordered from chaotic and also, it can accurately determine the time interval of the resonance trapping and transitions too. Apart from that, the phenomenon of transient chaos can be explained with the help of time-frequency analysis. Comparison with the method of total angular momentum (denoted as Ltot) proposed recently is also presented. 展开更多
关键词 time-frequency analysis TRIAXIAL GALACTIC Potential Instantaneous frequency Total Angular MOMENTUM
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Detection and Delineating of Hydrocarbon Contaminants by Using Time and Frequency Analysis of Ground Penetrating Radar
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作者 José Vicente Fuente 《Journal of Geoscience and Environment Protection》 2021年第12期35-56,共22页
This paper provides the results of using ground penetrating radar (GPR) method to detect hydrocarbon products (diesel and gasoline) in a controlled lab test. The work addresses the environmental problem generated by t... This paper provides the results of using ground penetrating radar (GPR) method to detect hydrocarbon products (diesel and gasoline) in a controlled lab test. The work addresses the environmental problem generated by the uncontrolled leakage of hydrocarbon product</span><span style="font-family:"">s</span><span style="font-family:""> and the subsequent contamination </span><span style="font-family:"">of </span><span style="font-family:"">plumes in the subsoil. Most of the research propose</span><span style="font-family:"">s</span><span style="font-family:""> the geophysical techniques to evaluate the plumes but some controversial were discussed on how i</span><span style="font-family:"">t</span><span style="font-family:""> affected the electrical and dielectric response depending on the excitation of the non-invasive method. The present work focuses </span><span style="font-family:"">on</span><span style="font-family:""> a comparative analysis of some signal attributes of the GPR traces to determine under what premises the detection is properly done. These signal attributes were from the time and frequency domain as attenuation coefficient, instantaneous amplitude and frequency have been considered to analyze three different soil samples. The laboratory tests consist of buried liquid (total hydrocarbon of petroleum</span><span style="font-family:"">, </span><span style="font-family:"">so called TPH) bags in the soil sample boxes reveal</span><span style="font-family:""> </span><span style="font-family:"">the range of target detection and consistency of data on </span><span style="font-family:"">the </span><span style="font-family:"">controlled test regarding the dielectric soil characterization and the delimiting position and depth. Instantaneous amplitude and time-frequency shift are revealed as promising signal attributes to accura</span><span style="font-family:"">te</span><span style="font-family:""> detection of the TPH presence. Numerical simulation data were also carried out to interpret the signal reflections on radargrams and to confirm experimental trends and the benefits of us</span><span style="font-family:"">ing</span><span style="font-family:""> the above signal attributes in time-frequency domain. 展开更多
关键词 time-frequency analysis Instantaneous Amplitude GPR Survey Hydrocar-bon Products
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Application of Wavelet Packet De-noising in Time-Frequency Analysis of the Local Wave Method
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作者 LI Hong kun, MA Xiao jiang, WANG Zhen, ZHU Hong Institute of Vibration Engineering, Dalian University of Technology, Dalian 116024, P.R.China 《International Journal of Plant Engineering and Management》 2003年第4期233-238,共6页
The local wave method is a very good time-frequency method for nonstationaryvibration signal analysis. But the interfering noise has a big influence on the accuracy oftime-frequency analysis. The wavelet packet de-noi... The local wave method is a very good time-frequency method for nonstationaryvibration signal analysis. But the interfering noise has a big influence on the accuracy oftime-frequency analysis. The wavelet packet de-noising method can eliminate the interference ofnoise and improve the signal-noise-ratio. This paper uses the local wave method to decompose thede-noising signal and perform a time-frequency analysis. We can get better characteristics. Finally,an example of wavelet packet de-noising and a local wave time-frequency spectrum application ofdiesel engine surface vibration signal is put forward. 展开更多
关键词 local wave time-frequency analysis wavelet packet DE-NOISING signal-noise-ratio
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DEVELOPMENT OF VIRTUAL INSTRUMENT IN CHARACTERISTIC ANALYSIS OF ROTATING MACHINERY BASED ON INSTANTANEOUS FREQUENCY ESTIMATION 被引量:4
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作者 YangJiongming QinShuren +1 位作者 JiZhong GuoYu 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2004年第4期490-493,共4页
Based on the recently quick-developing time-frequency analysis (TFA)technique and virtual instrument (VI) technique, a virtual instrument in characteristic analysis ofrotating machinery is researched and developed suc... Based on the recently quick-developing time-frequency analysis (TFA)technique and virtual instrument (VI) technique, a virtual instrument in characteristic analysis ofrotating machinery is researched and developed successfully. By utilizing instantaneous frequencyestimation (IFE) theoretics of TFA technique, and based on IFE of peak searching on thetime-frequency spectrum, order analysis (OA) functions is put forward and implemented, such as orderspectrum, order spectrum matrix, order tracking, order tracking filtering, and order componentextraction, etc. Unlike the home and abroad existing popular characteristic analyzers, which needkey phasing devices such as shaft encoder, phase-locked loop (PLL), phase-locked multiple frequency,tachometer, etc, to implement constant angle sampling directly or indirectly, whereas thisinstrument only uses the vibration signal of rotating machinery to carry out OA. This instrumentmakes up the shortage of these traditional instruments in analyzing the non-stationary signal ofrun-up and run-down process of rotating machinery. Therefore, it is a great breakthrough for theexisting order analyzers. 展开更多
关键词 Rotating machinery time-frequency analysis Instantaneous frequency Orderanalysis Virtual instrument
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Wigner Frequency Point Slice Analysis of Superposition Data for Phased-Array Ground Penetrating Radar 被引量:2
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作者 ZOULian CHENShu-zhen +2 位作者 YANGShen WEIDan XIAOBo-xun 《Wuhan University Journal of Natural Sciences》 EI CAS 2004年第6期904-908,共5页
According to the frequency property of Phasedarray ground penetrating radar (PGPR), this paper gives a frequency point slice method based on Wigner time-frequency analysis. This method solves the problem of analysis f... According to the frequency property of Phasedarray ground penetrating radar (PGPR), this paper gives a frequency point slice method based on Wigner time-frequency analysis. This method solves the problem of analysis for the PGPR's superposition data and makes detecting outcome simpler and detecting target more recognizable. At last, the analytical results of road test data of the Three Gorges prove the analytical method efficient. Key words phased-array ground penetrating radar - wigner time-frequency analysis - superposition data - object identification CLC number TN 715.7 Foundation item: Supported by the National Nature Science Foundation of China (50099620) and 863 Program Foundation of China (2001AA132050-03)Biography: ZOU Lian (1975-), male, Ph. D candidate, research direction: signal processing. 展开更多
关键词 phased-array ground penetrating radar wigner time-frequency analysis superposition data object identification
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Time-Frequency Characteristics of the Relationships Between Tropical Indo-Pacific SSTs 被引量:9
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作者 Song YANG 丁晓利 +1 位作者 郑大伟 Soo-Hyun YOO 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 2007年第3期343-359,共17页
In this study, several advanced analysis methods are applied to understand the relationships between the Nino-3.4 sea surface temperatures (SST) and the SSTs related to the tropical Indian Ocean Dipole (IOD). By a... In this study, several advanced analysis methods are applied to understand the relationships between the Nino-3.4 sea surface temperatures (SST) and the SSTs related to the tropical Indian Ocean Dipole (IOD). By analyzing a long data record, the authors focus on the time-frequency characteristics of these relationships, and of the structure of IOD. They also focus on the seasonal dependence of those characteristics in both time and frequency domains. Among the Nino-3.4 SST, IOD, and SSTs over the tropical western Indian Ocean (WIO) and eastern Indian Ocean (EIO), the WIO SST has the strongest annual and semiannual oscillations. While the Nino-3.4 SST has large inter-annual variability that is only second to its annual variability, the IOD is characterized by the largest semiannual oscillation, which is even stronger than its annual oscillation. The IOD is strongly and stably related to the EIO SST in a wide range of frequency bands and in all seasons. However, it is less significantly related to the WIO SST in the boreal winter and spring. There exists a generally weak and unstable relationship between the WIO and EIO SSTs, especially in the biennial and higher frequency bands. The relationship is especially weak in summer and fall, when IOD is apparent, but appears highly positive in winter and spring, when the IOD is unimportantly weak and even disappears. This feature reflects a caution in the definition and application of IOD. The Nino-3.4 SST has a strong positive relationship with the WIO SST in all seasons, mainly in the biennial and longer frequency bands. However, it shows no significant relationship with the EIO SST in summer and fall, and with IOD in winter and spring. 展开更多
关键词 Indian Ocean dipole ENSO time-frequency relationship coherence analysis
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Parametric adaptive time-frequency representation based on time-sheared Gabor atoms 被引量:2
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作者 Ma Shiwei Zhu Xiaojin Chen Guanghua Wang Jian Cao Jialin 《Journal of Systems Engineering and Electronics》 SCIE EI CSCD 2007年第1期1-7,共7页
A localized parametric time-sheared Gabor atom is derived by convolving a linear frequency modulated factor, modulating in frequency and translating in time to a dilated Gaussian function, which is the generalization ... A localized parametric time-sheared Gabor atom is derived by convolving a linear frequency modulated factor, modulating in frequency and translating in time to a dilated Gaussian function, which is the generalization of Gabor atom and is more delicate for matching most of the signals encountered in practice, especially for those having frequency dispersion characteristics. The time-frequency distribution of this atom concentrates in its time center and frequency center along energy curve, with the curve being oblique to a certain extent along the time axis. A novel parametric adaptive time-frequency distribution based on a set of the derived atoms is then proposed using a adaptive signal subspace decomposition method in frequency domain, which is non-negative time-frequency energy distribution and free of cross-term interference for multicomponent signals. The results of numerical simulation manifest the effectiveness of the approach in time-frequency representation and signal de-noising processing. 展开更多
关键词 time-frequency analysis Gabor atom time-shear Adaptive signal decomposition time-frequency distribution.
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APPLICATION OF WAVELET TIME-FR EQUENCY ANALYSIS TO IDENTIFICA-TION OF CRACKED ROTOR 被引量:2
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作者 Zou JianChen JinPu YapengGeng ZunminState Key Laboratory of Vibration,Shock & Noise,Shanghai Jiaotong University,Shanghai 200030, China 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2003年第1期50-53,共4页
Based on the simple hinge crack model and the local flexibility theorem, thecorresponding dynamic equation of the cracked rotor is modelled, the numerical simulation solutionsof the cracked rotor and the uncracked rot... Based on the simple hinge crack model and the local flexibility theorem, thecorresponding dynamic equation of the cracked rotor is modelled, the numerical simulation solutionsof the cracked rotor and the uncracked rotor are obtained. By the continuous wavelet time-frequencytransform, the wavelet time-frequency properties of the uncracked rotor and the cracked rotor arediscussed. A new detection algorithm that uses the wavelet time-frequency transform to identify thecrack is proposed. The influence of the sampling frequency on the wavelet time-frequency transformis analyzed by the numerical simulation research. The valid sampling frequency is suggested.Experiments demonstrate the validity and availability of the proposed algorithm in identification ofthe cracked rotor for engineering practices. 展开更多
关键词 WAVELET time-frequency analysis Cracked rotor IDENTIFICATION
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Residual Phase Noise and Time Jitters of Single-Chip Digital Frequency Dividers
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作者 Lu-Lu Yan Sen Meng +3 位作者 Wen-Yu Zhao Wen-Ge Guo Hai-Feng Jiang Shou-Gang Zhang 《Journal of Electronic Science and Technology》 CAS CSCD 2015年第3期264-268,共5页
In this paper, we demonstrate the residual phase noise of a few microwave frequency dividers which usually limit the performance of frequency synthesizers. In order to compare these dividers under different operation ... In this paper, we demonstrate the residual phase noise of a few microwave frequency dividers which usually limit the performance of frequency synthesizers. In order to compare these dividers under different operation frequencies, we calculate additional time jitters of these dividers by using the measured phase noise. The time jitters are various from -0.1 fs to 43 fs in a bandwidth from 1 Hz to 100 Hz in dependent of models and operation frequencies. The HMC series frequency dividers exhibit outstanding performance for high operation frequencies, and the time jitters can be sub-fs. The time jitters of SP8401, MC10EP139, and MC100LVEL34 are comparable or even below that of HMC series for low operation frequencies. 展开更多
关键词 frequency divider phase noise spectra analysis time jitter
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A NEW QUADRATIC TIME-FREQUENCY DISTRIBUTIONAND A COMPARATIVE STUDY OF SEVERAL POPULARQUADRATIC TIME-FREQUENCY DISTRIBUTIONS
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作者 Liu Guizhong Liu Zhimei(information Engineering Institute, Xi’an Jiaotong University, Xi’an 710049) 《Journal of Electronics(China)》 1997年第2期104-111,共8页
A new quadratic time-frequency distribution (TFD) with a compound kernel is proposed and a comparative study of several popular quadratic TFD is carried out. It is shown that the new TFD with compound kernel has stron... A new quadratic time-frequency distribution (TFD) with a compound kernel is proposed and a comparative study of several popular quadratic TFD is carried out. It is shown that the new TFD with compound kernel has stronger ability than the exponential distribution (ED) and the cone-shaped kernel distribution (CKD) in reducing cross terms, meanwhile almost not decreasing the time-frequency resolution of ED or CKD. 展开更多
关键词 SIGNAL processing time-frequency analysis time-frequency distribution of Cohen’s CLASS
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DOPPLERLET BASED TIME-FREQUENCY REPRESENTATION VIA MATCHING PURSUITS
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作者 Zou Hongxing Zhou Xiaobo Dai Qionghai Li Yanda(State Key Lab. of Intelligent Technology and Systems, Tsinghua University, Beijing 100084) 《Journal of Electronics(China)》 2001年第3期217-227,共11页
A new time-frequency representation called Dopplerlet transform, which uses the dilated, translated and modulated windowed Doppler signals as its basis functions, is proposed, and the Fourier transform, short-time Fou... A new time-frequency representation called Dopplerlet transform, which uses the dilated, translated and modulated windowed Doppler signals as its basis functions, is proposed, and the Fourier transform, short-time Fourier transform (including Gabor transform), wavelet transform, and chirplet transform are formulated in one framework of Dopplerlet transform accordingly.It is proved that the matching pursuits based on Dopplerlet basis functions are convergent, and that the energy of residual signals yielded in the decomposition process decays exponentially. Simulation results show that the matching pursuits with Dopplerlet basis functions can characterize compactly a nonstationary signal. 展开更多
关键词 time-frequency analysis Dopplerlet TRANSFORM PSEUDO time-frequency DISTRIBUTION MATCHING PURSUIT
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The Time-Frequency Characteristics of Pulse Propagation Through Plasma
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作者 Dong Xiaoting Liu Yaxun & Wang Wenbing(Electromagnetic and Communication Laboratory, School of Electronic and Information Engineering,Xi’an Jiaotong University 710049, P. R. China) 《Journal of Systems Engineering and Electronics》 SCIE EI CSCD 2000年第2期55-60,共6页
In this paper, propagated δ pulses through different distance of plasma are calculated,and their time-frequency characteristics are studied using CWD (Choi-William distribution). It is found that several horizontal s... In this paper, propagated δ pulses through different distance of plasma are calculated,and their time-frequency characteristics are studied using CWD (Choi-William distribution). It is found that several horizontal spectra appear at early arrival time like discrete spectrum, at last time a hyperbolic curve lies in the time-frequency spectrum which corresponds to the frequency-group delay curve of plasma. To understand the time-frequency the property of a signal is helpful for obtaining the plasma parameters. 展开更多
关键词 Electromagnetic scattering Scattering center time-frequency analysis
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Application of short-time Fourier transform to high-rise frame structural-health monitoring based on change of inherent frequency over time
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作者 郭少霞 PEI Qiang 《Journal of Chongqing University》 CAS 2017年第1期1-10,共10页
The high-rise frame structure has become more and more widespread, like its damage from the complication of the environment. The traditional method of damage detection, which is only suitable for the stationary signal... The high-rise frame structure has become more and more widespread, like its damage from the complication of the environment. The traditional method of damage detection, which is only suitable for the stationary signal, does not apply to a high-rise frame structure because its damage signal is non-stationary. Thus, this paper presents an application of the short-time Fourier transform(STFT) to damage detection of high-rise frame structures. Compared with the fast Fourier transform, STFT is found to be able to express the frequency spectrum property of the time interval using the signal within this interval. Application of STFT to analyzing a Matlab model and the shaking table test with a twelve-story frame-structure model reveals that there is a positive correlation between the slope of the frequency versus time and the damage level. If the slope is equal to or greater than zero, the structure is not damaged. If the slope is smaller than zero, the structure is damaged, and the less the slope is, the more serious the damage is. The damage results from calculation based on the Matlab model are consistent with those from the shaking table test, demonstrating that STFT can be a reliable tool for the damage detection of high-rise frame structures. 展开更多
关键词 short-time Fourier transform fast Fourier transform damage identification shaking table test time-frequency analysis
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