基于小波分析和神经网络的框架结构损伤诊断方法   总被引：24，自引：5，他引：24  

李宏男  孙鸿敏 《地震工程与工程振动》2003,23(5):141-148

本文提出了基于“能量—损伤”原理，综合利用小波包分析和神经网络的框架结构损伤诊断方法。在结构损伤诊断中，时域信号经小波分析后其缺损特征会更加明显，把分布在不同频带的结点能量作为神经网络的训练样本能够很好地反映结构缺损特征。以美国土木工程师学会提出的基准结构为例，阐述了结构损伤的发生、位置和程度诊断过程，取得了令人满意的结果。  相似文献   

RESEARCH OF THE INHOMOGENEITY TEST OF CLIMATOLOGICAL DATA SERIES IN CHINA^*          下载免费PDF全文

LIU Xiaoning  LI Qingxiang 《Acta Meteorologica Sinica》2003,17(4):492-502

Some achievements on the inhomogeneity test of climatological data series and some correlative conclusions were described,from which we concluded that it was very necessary to test the homogeneity of the Chinese climatological data series.Many techniques on this field developed by foreign experts are suitable for Chinese climatological series,and the main factors for the inhomogeneity of the Chinese climatological data are the relocation of stations and the change of instruments.  相似文献   

地壳磁化强度模型和居里等温面   总被引：3，自引：0，他引：3       下载免费PDF全文

徐元芳  D．R．Barraclough  D．J．Kerridge 《地球物理学报》1997,(4)

利用卫星观测的长波磁异常，用等效偶极源方法推导了中国地区的视磁化强度分布．因卫星的高度远大于磁性地壳的厚度，将视磁化强度转换成磁化强度的垂直积分，它代表地壳内磁性物质的区域变化，利用视磁化强度与地表热流相应关系，计算了中国的新疆和东部一些地区居里等温面的深度．新疆地区的居里面深度为35-50km，其分布形态与塔里木盆地和准噶尔盆地的地貌比较相似；中国东部一些地区居里面深度在20-40km之间，与一些作者用航磁等数据得到的居里深度十分接近．  相似文献   

地磁1年周期变化的响应函数     

陈伯舫 《地震地磁观测与研究》1997,18(2):40-44

用通日月均值减去夜均值计算的月均值资料和Ｓｏｍｐｉ谱分析法分析了１４个台站的北向分量１年周期变化的振幅向相位，时段为１９８４－１９８８年。分析结果显示用Ｐ＾０ｎ（ｄｎｄ＝１，…，６）复合模式的估算的Ｃ值较合理。各台的Ｃ值比较一致。  相似文献   

11 million years of Oligocene geomagnetic field behaviour   总被引：2，自引：0，他引：2  

Lisa Tauxe  Paul Hartl 《Geophysical Journal International》1997,128(1):217-229

An 11 million year long record of the Oligocene geomagnetic field has been obtained from pelagic sediments of DSDP Hole 522 An average sample spacing of 4 cm yielded approximately one specimen per 4 to 8 kyr. The rock magnetics are remarkabh consistent across the entire interval. Previous work demonstrated a magnetic mineralogy dominated by magnetically stable magnetite. The natural remanent magnetism (NRM) carries an Oligocene polarity timescale that is in excellent agreement with the Oligocene reversal record as determined from marine magnetic anomalies (MMAs), including many of the so-called 'crypto-chrons'. Normalized NRM intensities from the undisturbed portions of the record yield a time series of variations with features consistent with a number of other palaeointensity time series derived from both sedimentary and lava sequences. These features include consistent, major decreases in palaeointensity (DIPs) at reversal boundaries, and occasional DIPs between reversal boundaries that could correspond to lineated 'tiny wiggles' in the MMA records. The data set suggests that the overall field strength was 40 per cent higher in the first half of the Oligocene when the average reversal frequency was 1.6 Myr^-1 than in the second half when the reversal frequency was 4 Myr^-1. There is also a weak dependence of average field strength on length of polarity interval. Finally, in the three cores suited to spectral analysis (of coherent polarity and relative intensity independent of lithological contamination), there is a persistent ca. 30–50ka periodicity in the variations of the relative intensity, suggesting that the geomagnetic field 'pulses' at about this frequency, not only during the Brunhes (as demonstrated by Tauxe & Shackleton 1994), but in the Oligocene as well.  相似文献   

Preliminary palaeomagnetic results of an Archaean dolerite dyke of west Greenland: geomagnetic field intensity at 2.8 Ga     

Chiyo Morimoto  Yo-ichiro Otofuji  Masako Miki  Hidefumi Tanaka  Tetsumaru Itaya 《Geophysical Journal International》1997,128(3):585-593

The geomagnetic field intensity during Archaean times is evaluated from a palaeomagnetic and chronological study of a dolerite dyke intruded into the 3000 Ma Nuuk Gneisses at Nuuk (64.2°N, 51.7°W), west Greenland. Plagioclase from the dolerite dyke yields a mean K-Ar age of 2752 Ma. Palaeomagnetic directions after thermal demagnetization of the dyke and the gneiss reveal a positive baked-contact test, indicating that the high-temperature-component magnetization of the dyke is primary. Thellier experiments on 12 dyke specimens yield a palaeointensity value of 13.5±4.4 μT. The virtual dipole moment at ca. 2.8 Ga is 1.9±0.6 × 10²² Am², which is about one-quarter of the present value. The present study and other available data imply that the Earth's magnetic field at 2.7 ∼ 2.8 Ga was characterized by a weak dipole moment and that a fairly strong geomagnetic field similar to the present intensity followed the weak field after ca. 2.6 Ga.  相似文献   

A model for the Am (Km) planetary geomagnetic activity index and application to prediction     

Christian Francq  Michel Menvielle 《Geophysical Journal International》1996,125(3):729-746

We studied the existence of dynamical stochastic relations in the evolution of the am index. A first analysis of the autocorrelation functions showed evidence of several seasonalities. We first used linear (ARMA) models, and it was found that these do not account for the whole internal dynamics of the data series. We then used various non-linear models to provide a better fit to reality. The forecast performances of the non-linear models are not significantly different from those of the linear model. We give a tentative explanation for the failure of the non-linear predictions. Finally, ARCH models were used in order to take into account the fact that the confidence interval for the predicted value depends on past observations.  相似文献   

Invariants in toroidal and tangentially geostrophic frozen-flux velocity fields     

Andrew Jackson  Raymond Hide 《Geophysical Journal International》1996,125(3):925-927

We derive two new types of invariant that must be obeyed by the radial magnetic field at the core-mantle boundary if the hypothesis of frozen flux is valid and the fluid motion is either toroidal or tangentially geostrophic there. These general invariants incorporate specific invariants that are already known and can, in principle, be tested using magnetic data that cover an interval of time.  相似文献   

A simple approach to the transformation of spherical harmonic models under coordinate system rotation     

A. De Santis  J. M. Torta  C. Falcone 《Geophysical Journal International》1996,126(1):263-270

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Periodicity of magnetic intensities in magnetic anomaly profiles: the Cenozoic of the South Atlantic     

B. D'Argenio  M. Iorio  D. H. Tarling 《Geophysical Journal International》1996,127(1):141-155

Spectral analyses of several published magnetic anomaly profiles from Candé & Kent (1992a) were undertaken prior to analysing, in the same way, raw magnetic anomaly data from similar parts of the South Atlantic. It was found that similar and distinct medium and short wavelengths were present in both the published and raw data. When these are converted into the time domain using the average rate of spreading for each profile, these periodicities appear similar, possibly identical, to those expected from the long-term eccentricity orbital parameters (Fischer, DeBoer & Premoli Silva 1990). While such correlations are not necessarily causative, they suggest that magnetohydro-dynamical processes near the core-mantle boundary may be affected by gravitational changes due to planetary orbital perturbations.  相似文献