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Grinding Burn Detection Based on Cross Wavelet and Wavelet Coherence Analysis by Acoustic Emission Signal 预览
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作者 Zheyu Gao Jing Lin +1 位作者 Xiufeng Wang Yuhe Liao 《中国机械工程学报:英文版》 SCIE EI CAS CSCD 2019年第4期94-103,共10页
Grinding burn monitoring is of great importance to guarantee the surface integrity of the workpiece. Existing methods monitor overall signal variation. However, the signals produced by metal burn are always weak. Ther... Grinding burn monitoring is of great importance to guarantee the surface integrity of the workpiece. Existing methods monitor overall signal variation. However, the signals produced by metal burn are always weak. Therefore, the detection rate of grinding burn still needs to be improved. The paper presents a novel grinding burn detection method basing on acoustic emission(AE) signals. It is achieved by establishing the coherence relationship of pure metal burn and grinding burn signals. Firstly, laser and grinding experiments were carried out to produce pure metal burn signals and grinding burn signals. No-burn and burn surfaces were generated and AE signals were captured separately. Then, the cross wavelet transform(XWT) and wavelet coherence(WTC) were applied to reveal the coherence relationship of the pure metal burn signal and grinding burn signal. The methods can reduce unwanted AE sources and background noise. Novel parameters based on XWT and WTC are proposed to quantify the degree of coherence and monitor the grinding burn. The grinding burn signals were recognized successfully by the proposed indexes under same grinding condition. 展开更多
关键词 GRINDING BURN Cross WAVELET TRANSFORM WAVELET COHERENCE ACOUSTIC emission
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小波及小波包降噪在高密度电法中的效果对比
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作者 谭超先 朱国维 +2 位作者 周作黎 刘卫刚 胡永蓁 《煤炭技术》 CAS 2019年第3期56-58,共3页
在高密度电法资料降噪处理中,传统的处理方法有坏点剔除、滑动平均和滤波等方法,但效果往往不够理想,不能为后期的处理提供可靠数据。小波变换及小波包变换对于降噪是非常有用的2种方法,在许多领域得到了很好的应用,相比于小波降噪,小... 在高密度电法资料降噪处理中,传统的处理方法有坏点剔除、滑动平均和滤波等方法,但效果往往不够理想,不能为后期的处理提供可靠数据。小波变换及小波包变换对于降噪是非常有用的2种方法,在许多领域得到了很好的应用,相比于小波降噪,小波包降噪对高频信号做了更细的细分,能更好地分析信号,但在高密度电法数据处理中,小波包降噪效果不一定优于小波降噪。现对2种降噪方法通过模型试验与工程实例进行对比研究,分析2种方法在高密度电法数据处理中的效果。 展开更多
关键词 高密度电法 小波 小波包 降噪
Relationship between the Atmospheric CO<sub>2</sub>and Climate Indices by Wavelet-Based Multifractal Analysis 预览
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作者 Fumio Maruyama 《地球科学和环境保护期刊(英文)》 2019年第1期38-51,共14页
Atmospheric concentrations of greenhouse gases are rising, leading to a positive radiative forcing of climate and an expected warming of surface temperatures. In general, fractal properties may be observed in the time... Atmospheric concentrations of greenhouse gases are rising, leading to a positive radiative forcing of climate and an expected warming of surface temperatures. In general, fractal properties may be observed in the time series of the dynamics of complex systems. To study the relation between the atmospheric CO2 concentration and the climate indices, we investigated the change of fractal behavior of the CO2, the carbon isotope ratio (δ13C) of atmospheric CO2, the El Ni?o-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the North Atlantic Oscillation (NAO) indices using the multifractal analysis. When the atmospheric CO2 growth rate was large, the multifractality of CO2, δ13C in CO2, ENSO, and NAO was large and the changes were large from the change of fractality. The changes of CO2 and ENSO were closely related and the influence of the CO2 on the ENSO was strong from the change in fractality and wavelet coherence. When the El Ni?o occurred, the CO2 growth rate was large. The CO2 related to PDO, NAO, and global temperature from the change in fractality and wavelet coherence. Especially, the changes of CO2 and global temperature were closely related. When the global warming hiatus occurred, the multifractality of the global temperature was weaker than that of CO2 and the change of the global temperature was stable. These findings will contribute to the research of the relation between the atmospheric CO2 and climate change. 展开更多
关键词 Atmospheric CO2 δ13C ENSO PDO NAO WAVELET MULTIFRACTAL
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Relationship between the Sunspot Number and Solar Polar Field by Wavelet-Based Multifractal Analysis 预览
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作者 Fumio Maruyama 《应用数学与应用物理(英文)》 2019年第5期1043-1051,共9页
There is increasing interest in finding the relation between the sunspot number (SSN) and solar polar field. In general, fractal properties may be observed in the time series of the dynamics of complex systems, such a... There is increasing interest in finding the relation between the sunspot number (SSN) and solar polar field. In general, fractal properties may be observed in the time series of the dynamics of complex systems, such as solar activity and climate. This study investigated the relations between the SSN and solar polar field by performing a multifractal analysis. To investigate the change in multifractality, we applied a wavelet transform to time series. When the SSN was maximum and minimum, the SSN showed monofractality or weak multifractality. The solar polar field showed weak multifractality when that was maximum and minimum. When the SSN became maximum, the fractality of the SSN changed from multifractality to monofractality. The multifractality of SSN became large before two years of SSN maximum, then that of the solar polar field became large and changed largely. It was found that the change in SSN triggered the change in the solar polar field. Hence, the SSN and solar polar field were closely correlated from the view point of fractals. When the maximum solar polar field before the maximum SSN was larger, the maximum SSN of the next cycle was larger. The formation of the magnetic field of the sunspots was correlated with the solar polar field. 展开更多
关键词 SUNSPOT Number SOLAR POLAR FIELD WAVELET MULTIFRACTAL
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Rigid Bridges Health Dynamic Monitoring Using 100 Hz GPS Single-Frequency and Accelerometers 预览
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作者 Jo?o Olympio de Araújo Neto Jorge Luiz Alves Trabanco +2 位作者 Ana Paula C. Larocca Andre Luiz Cunha Marcelo Carvalho dos Santos 《导航(英文)》 2019年第2期17-33,共17页
This article presents the modal frequency recordings of a rigid bridge, monitored by the GPS receivers (Global Positioning System) with a data recording rate of 100 Hz and accelerometers. The GPS data processing was p... This article presents the modal frequency recordings of a rigid bridge, monitored by the GPS receivers (Global Positioning System) with a data recording rate of 100 Hz and accelerometers. The GPS data processing was performed through the double-difference phase, using the adjusted interferometry technique (i.e. phase residue method—PRM&reg). In the method, the double-difference phase of the carrier L1 is realized by using two satellites only, one was positioned at the zenith of the structure and the other satellite was positioned near the horizon. The results of the parametric adjustment of the PRM observations were finalized through software Interferometry, mathematical algorithm were applied and compared with the accelerometer. The comparison served to validate the use of GPS as a fast and reliable instrument for the preliminary monitoring of the dynamic behavior of the bridge, road artworks which are common in several countries, especially in the Brazilian road network. The data time series from the GPS and accelerometers were processed using the Wavelet. The detection of frequencies means that the combination of 100 Hz GPS receivers and the PRM allows detecting vibrations up to 5 mm. It presented significant results which were never obtained by the Fourier Transform. 展开更多
关键词 GPS RIGID Bridge MODAL Frequency Wavelet ACCELEROMETER HEALTH Monitoring
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Influence of the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation on Global Temperature by Wavelet-Based Multifractal Analysis 预览
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作者 Fumio Maruyama 《地球科学和环境保护期刊(英文)》 2019年第8期105-117,共13页
Oceanic–atmospheric patterns, Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO), and their respective influence on the global warming hiatus were the main interests of this study. In gener... Oceanic–atmospheric patterns, Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO), and their respective influence on the global warming hiatus were the main interests of this study. In general, a fractal property is observed in the time series of dynamics of complex systems;hence, we investigated the relations among the AMO, PDO, and El Ni?o-Southern Oscillation (ENSO) from the point of view of multifractality, in which changes in fractality were detected with multifractal analysis using wavelet transform. For the periods 1950-1976 and 1998-2012, global temperature increased little, with positive AMO and negative PDO indices;subsequently, the rate of temperature increase weakened. Global temperature increased again in 1976, with the reversal of the AMO and PDO indices from negative to positive. More specifically, AMO, PDO, and Ni?o3.4 (ENSO index) exhibited fractality change from multifractality to monofractality, providing them stability. Generally, the PDO was influenced largely by the ENSO. But, around 1960 and around 2000, whose periods corresponded to hiatus periods in global warming, the influence of the ENSO on the PDO was weak. In 1998, the AMO increased and PDO decreased and global temperature increased little and the multifractality of PDO, and Ni?o3.4 was weak, which corresponded to the change from multifractality to monofractality in 1976. Wavelet analysis showed the leads of PDO and Ni?o3.4 indices with respect to global temperature. Consequently, the PDO and ENSO showed large influence on global temperature and, further, on the global warming hiatus. 展开更多
关键词 AMO PDO ENSO GLOBAL Temperature WAVELET MULTIFRACTAL
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Wavelet Transform in Vibroacoustic Diagnostics of Combustion Engines 预览
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作者 Radoslaw Wrobel Andrzej Kazmierczak 《工程(英文)(1947-3931)》 2019年第7期395-406,共12页
This article discusses the use of wavelet decomposition in the diagnostics of vibrometric signals of an engine. Apart from presenting the possibility of using wavelets in diagnostics, the authors take up the subject o... This article discusses the use of wavelet decomposition in the diagnostics of vibrometric signals of an engine. Apart from presenting the possibility of using wavelets in diagnostics, the authors take up the subject of the applicability range of processing for stationary signals, which until now has been reserved for non-stationary signals. A unified definition of signal stationarity has been proposed, which is not based on statistics. The authors presented methods of wavelet decomposition of a vibrometric signal of combustion engine vibrations, measured with the use of LDV (Laser Doppler Vibrometry). Laser measurements allow for studying an object without “touching” its housing. Basing on the relative velocity of engine vibrations, the authors indicate how reliable vibrations are in diagnostics. Despite higher costs, this measurement method gives better results (for specific cases) than acoustic studies. Transform-wavelet decomposition is a solution hardly ever used in machine diagnostics;it is more often applied in medicine and image recognition. The authors presented the differences that can be obtained for different levels of decomposition, and also presented the impact on the engine condition assessment through the use of filtering (windowing) the signal before decomposition. 展开更多
关键词 DSP WAVELET LDV COMBUSTION ENGINE
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海上拖缆宽方位多源地震采集枪阵设计与应用 预览
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作者 张福祥 唐松华 +3 位作者 胡斌 刘文峰 李珂 王家伟 《海洋石油》 CAS 2019年第3期9-14,20共7页
针对海上拖缆宽方位多源地震资料采集对震源的要求,以及现有设备条件的限制,开展了枪阵设计关键技术的研究。在不同枪架和不同容量枪的条件下,通过对大量不同气枪阵列组合震源开展地震子波模拟分析,设计出了不同组合容量的枪阵震源激发... 针对海上拖缆宽方位多源地震资料采集对震源的要求,以及现有设备条件的限制,开展了枪阵设计关键技术的研究。在不同枪架和不同容量枪的条件下,通过对大量不同气枪阵列组合震源开展地震子波模拟分析,设计出了不同组合容量的枪阵震源激发得到地震子波特征相同、能量一致的气枪阵列震源组合。将针对不同枪架和配件的枪控设计出的震源阵列组合应用到宽方位多源地震采集项目中,所采集到的实际地震资料的能量和频谱达到预期设计目标,表明所设计的震源阵列符合海上拖缆宽方位多源地震资料采集的要求。 展开更多
关键词 宽方位多源地震采集 枪阵 子波 能量一致
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基于小波变换的分形图像编码压缩算法 预览
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作者 赵蓉 王辉 张爱华 《计算机应用与软件》 北大核心 2019年第11期262-266,305共6页
有效的压缩算法可以给数据的储存和传输带来极大的方便.针对现有压缩算法存在的不足,定义图像子块的九块和特征,并提出结合小波和分形编码优势的有损压缩算法.该算法将图像进行二级小波分解,得到7个子带;保留低频子带的小波系数,并对其... 有效的压缩算法可以给数据的储存和传输带来极大的方便.针对现有压缩算法存在的不足,定义图像子块的九块和特征,并提出结合小波和分形编码优势的有损压缩算法.该算法将图像进行二级小波分解,得到7个子带;保留低频子带的小波系数,并对其余子带采用基于图像块九块和特征的分形编码.新定义的九块和算法,把全搜索问题变为在九块和意义下的近邻搜索问题,缩短了搜索范围.实验结果表明,与同类算法相比,该算法不仅提高了重构图像的质量,还缩短了编解码时间. 展开更多
关键词 分形 图像压缩 九块和 小波
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基于Canny算子边缘检测的小波变换多聚焦图像融合方法
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作者 王园园 张娜 韩美林 《电子测量技术》 2019年第17期148-151,共4页
为了获得多聚焦图像的最佳融合效果,得到更多细节信息,分析了相关的图像融合算法,选择变换域内融合方法对图像进行融合。对两张待融合图像使用小波变换进行分层(小波基选择sym4,分解层数为3层),低频系数采用加权平均法融合。高频系数使... 为了获得多聚焦图像的最佳融合效果,得到更多细节信息,分析了相关的图像融合算法,选择变换域内融合方法对图像进行融合。对两张待融合图像使用小波变换进行分层(小波基选择sym4,分解层数为3层),低频系数采用加权平均法融合。高频系数使于Canny算子的边缘检测,对检测到的边缘图像采用最大系数法进行融合。对加权平均法、小波变换(低频平均、高频最大系数融合)、及改进后算法进行仿真分析,直观视觉及参数分析中均表明改进后算法图像融合效果更好,细节保留、轮廓清晰度显著提高。 展开更多
关键词 图像融合 小波 CANNY算子
New Calderón reproducing formulae with exponential decay on spaces of homogeneous type
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作者 Ziyi He Liguang Liu +1 位作者 Dachun Yang Wen Yuan 《中国科学:数学英文版》 SCIE CSCD 2019年第2期283-350,共68页
Assume that(X,d,μ) is a space of homogeneous type in the sense of Coifman and Weiss(1971,1977). In this article, motivated by the breakthrough work of Auscher and Hyt(o|¨)nen(2013) on orthonormal bases of regula... Assume that(X,d,μ) is a space of homogeneous type in the sense of Coifman and Weiss(1971,1977). In this article, motivated by the breakthrough work of Auscher and Hyt(o|¨)nen(2013) on orthonormal bases of regular wavelets on spaces of homogeneous type, we introduce a new kind of approximations of the identity with exponential decay(for short, exp-ATI). Via such an exp-ATI, motivated by another creative idea of Han et al.(2018) to merge the aforementioned orthonormal bases of regular wavelets into the frame of the existed distributional theory on spaces of homogeneous type, we establish the homogeneous continuous/discrete Calderón reproducing formulae on(X, d,μ), as well as their inhomogeneous counterparts. The novelty of this article exists in that d is only assumed to be a quasi-metric and the underlying measure μ a doubling measure,not necessary to satisfy the reverse doubling condition. It is well known that Calderón reproducing formulae are the cornerstone to develop analysis and, especially, harmonic analysis on spaces of homogeneous type. 展开更多
关键词 SPACE of HOMOGENEOUS type Calderón reproducing formula APPROXIMATION of the IDENTITY wavelet SPACE of test functions distribution
自适应多分类相关向量机的滚动轴承故障识别 预览
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作者 王波 王志乐 +2 位作者 张青 张健康 熊鑫州 《机械科学与技术》 CSCD 北大核心 2019年第10期1535-1541,共7页
提出了一种基于自适应相关向量机(Adaptive multiclass relevance vector machines,A-MRVM)的滚动轴承故障识别方法,该方法利用遗传算法对多分类相关向量机核函数参数进行优化,依据故障样本自身特性自适应地选取最优核参数,克服核参数... 提出了一种基于自适应相关向量机(Adaptive multiclass relevance vector machines,A-MRVM)的滚动轴承故障识别方法,该方法利用遗传算法对多分类相关向量机核函数参数进行优化,依据故障样本自身特性自适应地选取最优核参数,克服核参数人为选取的不确定性,从而构建基于自适应多分类相关向量机的故障识别模型。将该故障识别模型应用于滚动轴承故障识别中,分别提取滚动轴承振动信号小波包能量及EEMD(Ensemble empirical mode decomposition)能量作为故障特征进行故障识别,并与其它方法进行实验对比研究。实验结果表明,所提方法不仅能有效识别出故障类型,且具有较高的故障识别模型构建效率,验证了所提方法的可行性及优越性。同时,该方法也能对故障类型发生的可能性进行评估,为分析滚动轴承故障类型提供更多的参考信息。 展开更多
关键词 故障识别 滚动轴承 多分类相关向量机 自适应 遗传算法
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Two-channel model based adaptive schlieren detection algorithm for BOS system 预览
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作者 LIU Han ZHANG Yanmei +2 位作者 ZHAO Baojun GUO Haichao ZHAO Boya 《系统工程与电子技术:英文版》 SCIE EI CSCD 2019年第2期251-258,共8页
A schlieren detection algorithm is proposed for the ground-to-air background oriented schlieren(BOS) system to achieve high-speed airplane shock waves visualization. The proposed method consists of three steps. Firstl... A schlieren detection algorithm is proposed for the ground-to-air background oriented schlieren(BOS) system to achieve high-speed airplane shock waves visualization. The proposed method consists of three steps. Firstly, image registration is incorporated for reducing errors caused by the camera motion.Then, the background subtraction dual-model single Gaussian model(BS-DSGM) is proposed to build a precise background model. The BS-DSGM could prevent the background model from being contaminated by the shock waves. Finally, the twodimensional orthogonal discrete wavelet transformation is used to extract schlieren information and averaging schlieren data. Experimental results show our proposed algorithm is able to detect the aircraft in-flight and to extract the schlieren information. The precision of schlieren detection algorithm is 0.96. Three image quality evaluation indices are chosen for quantitative analysis of the shock waves visualization. The white Gaussian noise is added in the frames to validate the robustness of the proposed algorithm.Moreover, we adopt two times and four times down sampling to simulate different imaging distances for revealing how the imaging distance affects the schlieren information in the BOS system. 展开更多
关键词 BACKGROUND model BACKGROUND ORIENTED SCHLIEREN (BOS) SCHLIEREN detection WAVELET DECOMPOSITION
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Pigeon-inspired optimization and extreme learning machine via wavelet packet analysis for predicting bulk commodity futures prices
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作者 Feng JIANG Jiaqi HE Zhigang ZENG 《中国科学:信息科学(英文版)》 SCIE EI CSCD 2019年第7期45-63,共19页
In this paper, a hybrid approach consisting of pigeon-inspired optimization(PIO) and extreme learning machine(ELM) based on wavelet packet analysis(WPA) is presented for predicting bulk commodity futures prices. First... In this paper, a hybrid approach consisting of pigeon-inspired optimization(PIO) and extreme learning machine(ELM) based on wavelet packet analysis(WPA) is presented for predicting bulk commodity futures prices. Firstly, WPA is applied to decompose the original futures prices into a set of lower-frequency subseries. Secondly, the PIO algorithm is used to optimize the parameters of ELM and then the optimized ELM is utilized to forecast the subseries. Finally, we adopt the hybrid method to calculate the final forecasting outcomes of futures prices. In order to further test the predictive ability of the hybrid forecasting model on bulk commodity futures prices, we use the prices of West Texas Intermediate crude oil futures and Chicago Board of Trade soybean futures to make one-step, two-step and four-step ahead predictions. In comparison with complete ensemble empirical mode decomposition with adaptive noise, empirical mode decomposition and singular spectrum analysis, WPA is the most suitable for decomposing bulk commodity futures prices.The experimental outcomes show that the hybrid WPA-PIO-ELM model has better performance on horizontal precision, directional precision and robustness. 展开更多
关键词 wavelet packet analysis extreme learning machine pigeon-inspired OPTIMIZATION bulk COMMODITY FUTURES price prediction directional precision
基于PLS特征提取的WNN装备保障性评估 预览
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作者 魏燕明 甘旭升 +2 位作者 孙静娟 孟祥伟 王宁 《火力与指挥控制》 CSCD 北大核心 2019年第8期177-181,185共6页
为科学合理地评估装备的保障性水平,更好地发挥装备的作战使用效能,提出了一种基于偏最小二乘(PLS)的小波神经网络(WNN)装备保障性评估方法。该方法在系统分析基础上,构建了装备保障性评估指标体系;利用PLS提取诸多指标数据的主元特征;... 为科学合理地评估装备的保障性水平,更好地发挥装备的作战使用效能,提出了一种基于偏最小二乘(PLS)的小波神经网络(WNN)装备保障性评估方法。该方法在系统分析基础上,构建了装备保障性评估指标体系;利用PLS提取诸多指标数据的主元特征;并利用获取的主元特征构建WNN模型,进而完成装备保障性评估。仿真结果表明,所提出方法的平均相对误差可达到0.009 6,比单一WNN模型评估效果有了改善,从而验证了它的可行性和有效性。 展开更多
关键词 装备保障性 偏最小二乘 特征提取 小波 神经网络
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Detecting Deterioration Stages in Epoxy Resins Specimens under Partial Discharge Process 预览
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作者 Cristian R.Bonini Marcos U.Maillot Franco M.Pessana 《电气工程:英文版》 2019年第2期39-50,共12页
This paper presents a novel analysis tool based on partial discharge(PD)pulses waveform to determinate deterioration process as the fault evolves carbonizing the insulating medium in epoxy resin specimens.The PD pulse... This paper presents a novel analysis tool based on partial discharge(PD)pulses waveform to determinate deterioration process as the fault evolves carbonizing the insulating medium in epoxy resin specimens.The PD pulses were acquired in the laboratory under controlled conditions;specially designed specimens were tested with a tip-flat electrode configuration immersed in a thermostable polymer(epoxy resin).Then,in the processing step,all acquired PD pulses were characterized with the Shannon entropy,and its variations along the deterioration process were studied.It was observed that the dispersion of this quantity increases with the deterioration of the medium,which allowed identifying different deterioration stages.The evolution of the deterioration has a correlation with the appearance of a greater number of pulses,whose entropy values diverge from average value(close to 2).These new pulses were analyzed using signal processing tools.It was found that there are important differences in the spectral content of each family,in the time-scale characteristics and in the energy distribution of the same frequency bands corresponding to each pulses family.In this work,the deterioration of epoxy resin specimens was characterized throughout the modifications observed in the characteristics of PD pulses during the entire failure process.It could be verified that there is information about the deterioration of the medium contained in the characteristics of the analyzed pulses. 展开更多
关键词 PARTIAL discharge entropy EPOXY resin WAVELET transform
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中国IGS站点ZTD长时序特征及其与年降水量的关系研究 预览
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作者 王勇 娄泽生 +1 位作者 刘严萍 郝振航 《大地测量与地球动力学》 CSCD 北大核心 2019年第10期1037-1040,1085共5页
利用小波变换方法对中国IGS站点ZTD时间序列进行分解与重构,分析ZTD序列的低频趋势项、高频年变化周期项与年降水量的对应关系,并结合气候资料分析原因。研究发现,ZTD低频趋势项与年降水量的变化趋势相同,ZTD高频周期项与年降水量变化... 利用小波变换方法对中国IGS站点ZTD时间序列进行分解与重构,分析ZTD序列的低频趋势项、高频年变化周期项与年降水量的对应关系,并结合气候资料分析原因。研究发现,ZTD低频趋势项与年降水量的变化趋势相同,ZTD高频周期项与年降水量变化存在较好的对应关系,ZTD年周期项峰值的高低对应年降水量的多少。 展开更多
关键词 对流层延迟 水汽 小波 降水
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Monitoring localized corrosion of Inconel 82 weld overlay on 304L SS weld by electrochemical noise 预览
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作者 Girija Suresh Hemant Kumar 《材料工程研究(英文)》 2019年第2期45-55,共11页
The manuscript presents the results from the electrochemical noise (EN) monitoring of Inconel 82 weld overlay on Type 304L stainless steel (SS) weld in 0.01M FeCl3. The microstructure of the weld overlay obtained from... The manuscript presents the results from the electrochemical noise (EN) monitoring of Inconel 82 weld overlay on Type 304L stainless steel (SS) weld in 0.01M FeCl3. The microstructure of the weld overlay obtained from optical and scanning electron microscopy (SEM) showed an austenite structure, containing equiaxed dendrites and secondary phases at the interdendritic region. Energy dispersive spectroscopy (EDS) attached to SEM revealed the secondary phases to be Nb rich Laves phase. The electrochemical potential noise was monitored using a three identical electrode configuration. The acquired signals were detrended, and wavelet analysis was employed to encode useful information from the noise transients. Visual examination of the potential noise-time record contained distinct high amplitude transients typical of localized corrosion attack. The energy distribution plots (EDP) of the potential noise derived from wavelet analysis depicted maximum relative energy on D6-D8 crystals, which represent large time scale events such as those occurring from localized attacks. Also, repassivation events too could be divulged from the potential EDP. The micrographs of the post electrochemical noise experimented specimens revealed the occurrence of localized attacks along the interdendritic region and none inside the dendritic cores. The presence of secondary phases along the interdendritic regions was found to be detrimental in chloride medium, imparting inferior localized corrosion resistance to the weld overlay. 展开更多
关键词 INCONEL 82 WELD OVERLAY 304L SS WELD electrochemical noise LOCALIZED CORROSION wavelet analysis
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近65年桂林市降雨侵蚀力变化特征与周期演化 预览
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作者 王朋辉 张陶 于小磊 《贵州师范大学学报:自然科学版》 CAS 2019年第2期23-28,47共7页
采用Sen’s斜率估计法、Mann-Kendal趋势分析法、M-K突变检验法和Morlet小波变换对1951—2015年桂林市降雨侵蚀力进行特征分析、趋势估计、突变检验和周期分析。结果表明:近65年桂林市降雨侵蚀力呈不显著增大趋势,年际变差系数为0.19,... 采用Sen’s斜率估计法、Mann-Kendal趋势分析法、M-K突变检验法和Morlet小波变换对1951—2015年桂林市降雨侵蚀力进行特征分析、趋势估计、突变检验和周期分析。结果表明:近65年桂林市降雨侵蚀力呈不显著增大趋势,年际变差系数为0.19,为中等程度变异;20世纪90年代侵蚀力最强,80年代侵蚀力最小;年降雨侵蚀力自1968年以后呈增大趋势,分别在1968、2002和2015年发生了三次突变;雨季侵蚀力控制着年降雨侵蚀力的趋势;降雨侵蚀力存在34a、56a、12a和3a左右的周期。 展开更多
关键词 降雨侵蚀力 趋势 周期 突变 小波 桂林市
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Application of Fast Wavelet Analysis on Early Stall Warning in Axial Compressors
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作者 LIU Yang LI Jichao +2 位作者 DU Juan LI Fan ZHANG Hongwu 《热科学学报:英文版》 SCIE EI CAS CSCD 2019年第5期837-849,共13页
The timely detection of stall inception is of great significance for safe operation and stability control of axial compressor. In the current study, a fast wavelet tool was selected to predict stall precursor in axial... The timely detection of stall inception is of great significance for safe operation and stability control of axial compressor. In the current study, a fast wavelet tool was selected to predict stall precursor in axial compressors with spike-type and modal-wave stall inception. Dynamic pressure was measured in the casing wall by using a collection of time-resolved pressure transducers with circumferential and chord-wise spatial resolution. Fast wavelet analysis with low frequency reconstruction results demonstrate that the initial inception can be detected 110 rotor revolutions prior to stall for modal-wave stall inception in a 1.5 stage axial compressor. For spike-type stall inception, despite the failure of early stall warning via low frequency reconstruction, an increase amplitude frequency band of 0.2–0.8 blade passing frequency was identified using high frequency reconstruction in an isolated-rotor axial compressor. Fast wavelet method can predict two kinds of stall inceptions simultaneously in advance and realize the early stall warning in axial compressors through a reasonable selection of reconstructed frequency. 展开更多
关键词 AXIAL COMPRESSOR STALL INCEPTION pre-stall INCEPTION STALL WARNING FAST wavelet
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