用小波变换方法提取地下流体观测异常信息     

耿杰  陈安方  潘双进 《地震研究》2009,32(1)

首先对小波分析方法作了简单介绍,然后运用该方法,对1992～2002年上海地区9口水氡观测井的资料进行了6阶小波变换,提取的地震异常信息与实际地震有较好的对应关系;对1983年山东荷泽5.9级地震和1998河南清丰4.0级地震前聊古1井的氡观测资料进行了小波分析,发现1～6阶小波系数均出现异常;对1999年山东苍山5.2级地震前枣庄十里泉井的水汞观测资料进行了小波分析,发现1～6阶小波系数也出现异常.因此,运用小波分析方法可以有效地提取地震前兆异常信息.  相似文献   

Wavelet regression model as an alternative to neural networks for monthly streamflow forecasting   总被引：3，自引：0，他引：3  

Özgür Kişi 《水文研究》2009,23(25):3583-3597

The accuracy of the wavelet regression (WR) model in monthly streamflow forecasting is investigated in the study. The WR model is improved combining the two methods—the discrete wavelet transform (DWT) model and the linear regression (LR) model—for 1‐month‐ahead streamflow forecasting. In the first part of the study, the results of the WR model are compared with those of the single LR model. Monthly flow data from two stations, Gerdelli Station on Canakdere River and Isakoy Station on Goksudere River, in Eastern Black Sea region of Turkey are used in the study. The comparison results reveal that the WR model could increase the forecast accuracy of the LR model. In the second part of the study, the accuracy of the WR model is compared with those of the artificial neural networks (ANN) and auto‐regressive (AR) models. On the basis of the results, the WR is found to be better than the ANN and AR models in monthly streamflow forecasting. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

曲率模态小波法用于网壳结构损伤的识别和定位   总被引：1，自引：0，他引：1  

殷志祥  徐文杰  毛丽强 《地震工程与工程振动》2009,29(4)

工程结构损伤的识别与定位研究以往主要针对梁、框架等结构形式,根据大跨度空间结构杆件和节点繁多等特点,提出用曲率模态和小波混合方法对空间结构的损伤进行识别和定位.以跨度100 m的Schwedler网壳结构损伤前、后的曲率模态作为标识量,分别通过离散和连续小波变换,判断网壳结构有无损伤和损伤位置,统计了小波系数差与结构损伤的图形关系,计算了各种损伤工况下该方法判断损伤的准确程度.结果发现基于曲率模态和小波方法的大跨度网壳结构损伤定位精度很高,充分证明该方法对此类结构损伤定位具有有效性和实用性.  相似文献   

近断层地震动的频谱周期参数和非平稳特征分析     

杨迪雄  王伟 《地震工程与工程振动》2009,29(5)

分析地震动的频谱周期参数和频率非平稳特征,是地震危险性分析和结构抗震设计的重要内容.本文对近断层地震动记录按照不同的运动特征分组,进行了Hilbert-Huang变换分析.结合相关的定义得到了表征地震动频谱特性的7个周期参数,包括:Fourier幅值谱平均周期Tm、Hilbert边际谱平均周期Tmh、特征周期Tc、卓越周期等,并计算了地震动的Hilbert谱瞬时频率时程变异系数.计算结果表明,从整体上把握地震动频谱特性的三个周期参数Tm 、Tmh 和Tc适合于表征近断层地震动的频谱成份.近断层地震动的频率非平稳特征显著,Hilbert谱瞬时频率变异系数良好地反映了地震动的频率非平稳性质和程度.而且,考察了近断层地震动运动特征对地震动频谱周期参数和频率非平稳性的影响.  相似文献   

基于小波变换和GALSSVM的边坡位移预测   总被引：1，自引：0，他引：1  

马文涛 《岩土力学》2009,30(Z2):394-398

边坡变形是一个受多种因素综合作用的复杂非线性动力学演化过程,用现有的物理模型来解决边坡变形的预测问题有很大难度。大量的研究工作表明,用实测的边坡位移时间序列来预测边坡未来变形更为准确,而将多种方法组合起来进行预测成为研究的主要趋势。在此基础上,建立了一种基于小波变换和进化最小二乘支持向量机(GALSSVM)的边坡位移预测模型。首先利用小波变换将边坡时间序列分解为低频分量和高频分量,然后利用互信息法和伪近邻法得到各分量的时间延迟和嵌入维数并进行相空间重构,再根据各个相空间的特点建立相应的GALSSVM预测模型,最后把各分量的预测结果进行小波重构,重构后的结果即为最终的边坡位移预测结果。对丹巴滑坡预测研究表明,这种新的预测模型具有较高的预测精度,可以应用于实际工程  相似文献   

基于Curvelet变换的地震资料信噪分离技术   总被引：1，自引：1，他引：0       下载免费PDF全文

周怀来  李枚  郑文锋  彭小明 《地球物理学进展》2009,24(2):620-625

在地震资料中,噪声干扰严重影响了有效信号的提取,为此必须进行信噪分离处理.本文提出一种基于Curvelet变换和KL变换相结合的软硬阈值折衷处理方法.首先对地震数据进行Curvelet变换,然后对各尺度系数选取适当阈值压制噪声干扰,再利用KL变换提取数据中的相干有效信号,最后重构得到去噪后的记录.经合成记录和实际地震资料处理实验证明,该方法与小波变换法相比较,更能有效进行信噪分离,提高地震剖面信噪比和分辨率.  相似文献   

Axisymmetric transient waves in transversely isotropic half-space     

Morteza Eskandari-Ghadi  Siamak Sattar 《Soil Dynamics and Earthquake Engineering》2009

A transversely isotropic material in the sense of Green is considered. Using a series of potential functions proposed in [Eskandari-Ghadi M. A complete solution of the wave equations for transversely isotropic media. J Elasticity 2005; 81:1–19], the solutions of the transient wave equations within a half-space under surface load are obtained in the Laplace–Hankel domain for axisymmetric problems. The solutions are investigated in detail in the special case of a surface point force pulse varying with time as Heaviside function. Using Cagniard–De Hoop method, the inverse Laplace transform and inverse Hankel transform of the solutions are then obtained in the form of integrals with finite limits. For validity of the analytical results, the final formulations for surface waves are degenerated for an isotropic material and compared with the existing formulation obtained by Pekeris [The seismic surface pulse. Proc Natl Acad Sci USA 1955;41:469–80], to show that they are exactly the same. The numerical evaluations of the integrals for some transversely isotropic materials as well as an isotropic one are obtained. The present approach is then numerically verified by comparing a particular case of displacements for the surface of an isotropic half-space subjected to a point load of Heaviside function with the solutions obtained by Pekeris [The seismic surface pulse. Proc Natl Acad Sci USA 1955;41:469–80]. In addition, the wave equations for the mentioned medium are obtained on the vertical line directly under the applied surface load. The final formulations are degenerated for an isotropic material and compared with the existing formulation given in Graff [Wave motion in elastic solids. New York: Dover Publications Inc; 1975 [New Ed edition, November 1991]], to show that they are also exactly the same. Then equations are presented in graphical forms using an appropriate numerical evaluation.  相似文献   

A new multiscale scheme for computing statistical moments in single phase flow in heterogeneous porous media     

Marcio R. Borges  Márcio A. Murad  Felipe Pereira  Frederico Furtado 《Advances in water resources》2009

In this work we develop a new multiscale procedure to compute numerically the statistical moments of the stochastic variables which govern single phase flow in heterogeneous porous media. The technique explores the properties of the log-normally distributed hydraulic conductivity, characterized by power-law or exponential covariances, which shows invariance in its statistical structure upon a simultaneous change of the scale of observation and strength of heterogeneity. We construct a family of equivalent stochastic hydrodynamic variables satisfying the same flow equations at different scales and strengths of heterogeneity or correlation lengths. Within the new procedure the governing equations are solved in a scaled geology and the numerical results are mapped onto the original medium at coarser scales by a straightforward rescaling. The new procedure is implemented numerically within the Monte Carlo algorithm and also in conjunction with the discretization of the low-order effective equations derived from perturbation analysis. Numerical results obtained by the finite element method show the accuracy of the new procedure to approximated the two first moments of the pressure and velocity along with its potential in reducing drastically the computational cost involved in the numerical modeling of both power-law and exponential covariance functions.  相似文献   

Efficient uncertainty quantification techniques in inverse problems for Richards’ equation using coarse-scale simulation models     

P. Dostert  Y. Efendiev  B. Mohanty 《Advances in water resources》2009

This paper concerns efficient uncertainty quantification techniques in inverse problems for Richards’ equation which use coarse-scale simulation models. We consider the problem of determining saturated hydraulic conductivity fields conditioned to some integrated response. We use a stochastic parameterization of the saturated hydraulic conductivity and sample using Markov chain Monte Carlo methods (MCMC). The main advantage of the method presented in this paper is the use of multiscale methods within an MCMC method based on Langevin diffusion. Additionally, we discuss techniques to combine multiscale methods with stochastic solution techniques, specifically sparse grid collocation methods. We show that the proposed algorithms dramatically reduce the computational cost associated with traditional Langevin MCMC methods while providing similar sampling performance.  相似文献   

强随机噪声条件下时窗类型局部线性化对TFPF技术的影响   总被引：6，自引：6，他引：0       下载免费PDF全文

李月  林红波  杨宝俊  吴宁  李诗宽  高峘 《地球物理学报》2009,52(7):1899-1906

为了更广泛地应用时频峰值滤波方法消减地震勘探记录中强随机噪声,本文比较详细地探讨了该方法在应用时需要处理的时窗选取、一个时窗内局部线性化等主要基础技术问题.经过时变时窗的仿真计算,运用多项指标比较,包括整体背景强弱、振幅谱、信噪比、均方误差、有效子波波峰波谷幅值、畸变程度,综合评价出（L₀+L_x）时窗滤波的效果较理想.对于三角波这类简单类型的周期波,其时频峰值滤波效果与边线段平均曲率变化、时窗长度等条件有关,即三角波边线段平均曲率越大,滤波结果的均方误差越大;另外,边线段平均曲率增大时,选取的时窗长度有变小的趋势.总之,在地震勘探中应用时频峰值滤波方法消减强随机噪声时,一方面要合理地选取时窗参数,另一方面时窗参数又不能变化过大,以避免对有效子波波形产生畸变影响.  相似文献