期刊文献+
共找到6篇文章
< 1 >
每页显示 20 50 100
Feature Extraction of Acoustic/Seismic Signal of Target 被引量:1
1
作者 张中民 李科杰 +1 位作者 李贵涛 尚雅玲 《Journal of Beijing Institute of Technology》 EI CAS 2000年第3期312-317,共6页
A microphone and a seismic sensor always become a basic unit of UGS(unattended ground sensors) system. The mechanism of acoustic and seismic property of target and its propagation are described. The acoustic and seism... A microphone and a seismic sensor always become a basic unit of UGS(unattended ground sensors) system. The mechanism of acoustic and seismic property of target and its propagation are described. The acoustic and seismic signals of targets are analyzed with time frequency distribution according to its non stationary property. Narrow band energy function (NEF) and local power spectral density (LPSD) are proposed to extract features for target identification. Experiment results show that local power spectral density indicates corresponding target clearly. 展开更多
关键词 time frequency analysis narrow band energy function (NEF) local power spectral density(LPSD)
下载PDF
利用小波分析研究近地空间高能电子的周期变化特征 被引量:2
2
作者 廖偲含 王宏伟 +2 位作者 鲁同所 杨兴 匡攀 《天文学报》 CAS CSCD 北大核心 2021年第3期67-84,共18页
利用小波变换对GOES(Geostationary Operational Environmental Satellites)系列卫星(GOES 10/11)1999年3月至2010年12月和风云2号系列卫星(FY 2C/2D)2004年10月至2012年5月记录的2 MeV高能电子通量变化情况进行了相关研究,发现GOES卫... 利用小波变换对GOES(Geostationary Operational Environmental Satellites)系列卫星(GOES 10/11)1999年3月至2010年12月和风云2号系列卫星(FY 2C/2D)2004年10月至2012年5月记录的2 MeV高能电子通量变化情况进行了相关研究,发现GOES卫星观测到的高能电子通量存在明显的13.9 d、27.7 d、187.0 d和342.9 d周期,FY卫星观测到的高能电子通量存在明显的13.9 d、27.7 d、222.3 d和374.0 d周期,在某些年份GOES和FY卫星均存在9 d的周期,与地磁Dst(赤道环电流指数)、AE(极光电射流指数)指数周期高度相似.将高能电子通量和Dst、AE指数进行交叉小波分析,并利用该算法的多分辨率特点以及时域、频域局部化分析方法,将数据按不同频率进行分解,从低频系数重构图像和交叉小波谱图可以清楚看出高能电子通量和地磁指数的关系.基于FY和GOES卫星高能电子通量良好的相关性,对多卫星高能电子通量变化短周期相同、中长周期不同进一步研究,对比发现不同地磁扰动引起的GOES和FY卫星高能电子通量变化存在各向异性,小磁暴也可以对高能电子通量造成和强磁暴一样的效果,并且某些时候存在地方时一致的24 h周期.这一结果表明对地磁宁静期高能电子研究至关重要,同时对理解太阳活动,预报高能电子能谱和预警深层充电事件以及验证预测磁暴、亚暴等事件具有重要意义. 展开更多
关键词 卫星:FY GOES 空间粒子:高能电子 方法:数据分析:小波分析 基本数据:地磁扰动 参数:周期 函数:功率
下载PDF
Influence of surface treatments on fatigue life of a two-stroke free piston linear engine component using random loading
3
作者 RAHMAN M.M. ARIFFIN A.K. +1 位作者 JAMALUDIN N. HARON C.H.C. 《Journal of Zhejiang University-Science A(Applied Physics & Engineering)》 SCIE EI CAS CSCD 2006年第11期1819-1830,共12页
This paper describes the finite element (FE) analysis technique to predict fatigue life using the narrow band frequency response approach. The life prediction results are useful for improving the component design meth... This paper describes the finite element (FE) analysis technique to predict fatigue life using the narrow band frequency response approach. The life prediction results are useful for improving the component design methodology at the very early development stage. The approach is found to be suitable for a periodic loading but requires very large time records to accurately describe random loading processes. This paper is aimed at investigating the effects of surface treatments on the fatigue life of the free piston linear engine’s components. Finite element modelling and frequency response analysis were conducted using computer aided design and finite element analysis commercial codes, respectively. In addition, the fatigue life prediction was carried out using finite element based fatigue analysis commercial code. Narrow band approach was specially applied to predict the fatigue life of the free piston linear engine cylinder block. Significant variation was observed between the surface treatments and untreated cylinder block of free piston engine. The obtained results indicated that nitrided treatment yielded the longest life. This approach can determine premature products failure phenomena, and therefore can reduce time to market, improve product reliability and customer confidence. 展开更多
关键词 Vibration fatigue Finite element (FE) Power spectral density function Frequency response Surface treatment
下载PDF
Research on Real-time Monitoring of Abnormal Seismic Noise 被引量:1
4
作者 Lin Binhua Jin Xing +3 位作者 Liao Shirong Li Jun Huang Linzhu Chen Huifang 《Earthquake Research in China》 CSCD 2016年第2期224-232,共9页
The noise data in vertical component records of 85 seismic stations in Fujian Province during 2012 is used as the research object in this paper. The noise data is divided into fiveminute segments to calculate the powe... The noise data in vertical component records of 85 seismic stations in Fujian Province during 2012 is used as the research object in this paper. The noise data is divided into fiveminute segments to calculate the power spectra. The high reference line and low reference line of station are then identified by drawing a probability density function graph( PDF)using the power spectral probability density function. Moreover, according to the anomalies of PDF graphs in 85 seismic stations,the abnormal noise is divided into four categories: dropped packet, low noise, high noise, and median noise anomalies.Afterwards,four selection methods are found by the high or low noise reference line of the stations,and the system of real-time monitoring of seismic noise is formed by combining the four selection methods. Noise records of 85 seismic stations in Fujian Province in July2013 are selected for verification,and the results show that the anomalous noise-recognition system could reach a 90% success rate at most stations and the effect of selection are very good. Therefore,it could be applied to the seismic noise real-time monitoring in stations. 展开更多
关键词 Seismic noise Power spectral density Probability density function Powerspectrum Abnormity Data quality
下载PDF
Establishment of N_mF_2 empirical model in the northern hemisphere based on COSMIC occultation data 被引量:1
5
作者 NIU Jun FANG HanXian WENG LiBin 《Science China(Technological Sciences)》 SCIE EI CAS 2014年第2期339-344,共6页
Ionospheric peak value of F2 layer (NmF2) is an important parameter in the ionosphere, which has important applications in short-wave communication, ionospheric modeling and so on. In this paper, the empirical ortho... Ionospheric peak value of F2 layer (NmF2) is an important parameter in the ionosphere, which has important applications in short-wave communication, ionospheric modeling and so on. In this paper, the empirical orthogonal function (EOF) decompo- sition method is used to analyze the NmFz obtained from the occultation data. Daily spatial distribution of NmF2 at the same time is relatively even. Variance of first modal is much larger than the other modals. A local wavelet power spectrum (LWPS) method is applied to analysis the cycle of Flo.7 index and time coefficient of first modal. The result shows that they have simi- lar cycle distribution, indicating that Flo.7 index is the main factor affecting variation of NmF〉 A function is established be- tween the tine coefficient of first modal and F10.7 index, average F10.7 index value of early 81 days fp by least squares method. The results show that contribution coefficient offp is negative which indicates that fp has an inert effect existing in the iono- sphere. Contribution coefficient of F10.7 is positive, which is consistent with the fact that it has an anomaly in winter/spring seasons. In summary, it is feasible to establish a mid-latitude empirical NmF2 model in northern hemisphere based on occulta- tion data and EOF decomposition method. 展开更多
关键词 empirical NmF2 model empirical orthogonal function decomposition local wavelet power spectrum method least squ-ares method
原文传递
Use of probabilistic and deterministic measures to identify unfavorable earthquake records 被引量:2
6
作者 Abbas MOUSTAFA Izuru TAKEWAKI 《Journal of Zhejiang University-Science A(Applied Physics & Engineering)》 SCIE EI CAS CSCD 2009年第5期619-634,共16页
This study introduces measures to identify resonant (concentration of energy in a single or a few frequencies) or unfavorable earthquake ground motions. Probabilistic measures based on the entropy rate and the geometr... This study introduces measures to identify resonant (concentration of energy in a single or a few frequencies) or unfavorable earthquake ground motions. Probabilistic measures based on the entropy rate and the geometric properties of the power spectral density function (PSDF) of the ground acceleration are developed first. Subsequently, deterministic measures for the frequency content of the ground acceleration are also developed. These measures are then used for identifying resonance and criticality in stochastic earthquake models and 110 acceleration records measured at rock, stiff, medium and soft soil sites. The unfavorable earthquake record for a given structure is defined as the record having a narrow frequency content and dominant frequency close to the structure fundamental natural frequency. Accordingly, the measures developed in this study may provide a basis for selecting records that are capable of producing the highest structural response. Numerical verifications are provided on damage caused to structures by identified resonant records. 展开更多
关键词 Entropy rate Dispersion index Power spectral density function (PSDF) Frequency content Unfavorable groundmotion Resonant acceleration Critical accelerogram Energy Damage index
原文传递
上一页 1 下一页 到第
使用帮助 返回顶部