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1.
推导了模态参数对于损伤构件的一阶和二阶灵敏度矩阵,并对在推导一阶和二阶振型灵敏度的过程中产生的模态截尾误差进行了改进。根据泰勒级数展开的原理分别建立了一阶和二阶的灵敏度方程。考虑到一阶灵敏度方程求解速度快和二阶灵敏度方程求解精度高的特点,本文提出了一种用于结构损伤识别的混合迭代算法,该算法用二阶非线性的解析解作为算法的第一次迭代值,用一阶灵敏度方程的求解值对该算法的第一次迭代值进行关于泰勒级数截尾误差的修正。研究表明,本文提出的混合迭代算法由于采用了精确度较高的二阶非线性解析解作为迭代修正的初值,因此,迭代修正精度更高,收敛性更好。 相似文献
2.
以Turkey Flat标准试验场为基准场地,以Toro剪切波速模型为基础,进行Monte Carlo模拟,生成剪切波速、层厚和密度随机样本各200条,将各土层随机参数组成4个工况作为不确定分析的基础。采用常用的四分之一波长法和传递函数法计算场地放大因子,分析放大因子以及特征周期对4种工况的敏感度。结果表明:土层剪切波速、层厚和密度的随机性对2种方法计算得到场地放大因子有相同的影响;剪切波速的随机性对放大因子和特征频率的影响比其他参数大;四分之一波长法得到的放大因子和特征频率对土层各参数的敏感性弱于传递函数方法。 相似文献
3.
本文概述了一维土层地震反应分析等效线性化方法评价结果不确定性研究的进展,比较了中美两国核设施土层地震反应分析中参数不确定性的处理方法。基于实测数据,令参数随机变化,建立土层剖面模型,采用随机振动理论方法,分析了土层动力特性、剪切波速、基岩地震动输入界面对评价结果的影响。结果表明,土层剪切波速的不确定性对评价结果影响最大,主要表现为加速度反应谱平台段的延长。对比参数随机变化模型和最佳估计模型的计算结果可知,随机振动理论反映了土层对基岩地震动的影响,将随机模型分析结果的中值加减1倍标准差基本可以包络最佳估计模型的分析结果。 相似文献
4.
《应用地球物理》2016,(2)
分数阶S变换(FRST)具有较强的时频聚集性。利用FRST处理地震数据,通过合适的分数阶参数将频率轴旋转到适当位置,即可实现目标地质特征信息的最佳识别。由于不同的地震信号的最优分数阶参数可能不同,因而对整体的分数阶参数的最优估计不利于对多道地震数据的处理。本文首先利用FRST分离出共频率数据体,并利用共频率数据体进行了低频伴影分析,然后提出FRST和盲分离结合的方法,不需要对地震数据的最优分数阶参数进行估计,即可提取识别有效地质特征信息的独立频谱,提高对地震数据的解释效率。仿真实验表明在分数阶时频域内此方法能有效分离出独立的频率信息。将该方法用于实际的地震数据,并与已知井信息进行比对,验证了其有效性。 相似文献
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对比分析了随机结构动力可靠度计算的三种估计算法.渐进展开法是基于Laplace算法对概率积分进行渐进估计的,此法通过计算最大被积分式值对应点,并将其代入概率积分的渐进估计表达式求解失效概率.由于概率积分的主要贡献来自于最大被积分式值对应点的周围,因此本文的重要抽样法假定重要抽样函数的最大似然值等于最大被积分式值对应点值.极值分布-泰勒展开法首先通过结构随机参数的极值分布函数给出失效概率的表达式,随后利用泰勒展开法对失效概率进行估计,其中采用中心差分法对极值分布函数的梯度进行估算.最后应用三种算法和Monte Carlo法对受高斯白噪声激励作用的单自由度随机结构进行了计算,结果表明三种方法不但运算简便,而且对比Monte Carlo法计算效率有显著提高. 相似文献
6.
传统有限差分系数是通过泰勒级数展开求取的,这样导致所计算的频散曲线在大波数区域会产生较强的数值误差.针对二阶空间偏导数的显式有限差分离散,本文发展了一种新的优化差分系数方法：首先将泰勒级数展开与多点采样方法结合应用于空间频散关系,基于最大范数建立直观有效的优化目标函数,采用Remez算法求解该目标函数,从而获得最优化差分系数.利用优化有限差分方法求解三维垂直对称轴横向各向同性（VTI）介质中的声波和弹性波方程.另外,本文将二维混合吸收边界条件推广到三维VTI介质中,用于吸收人工截断边界反射;基于各向异性特征,合理调整了边界区域的速度值来提高吸收效果.考虑到三维情况下计算效率的问题,本文波场外推过程中采用图形处理器（GPU）取代传统的中央处理器（CPU）.数值精度分析表明,相比较于传统的泰勒级数展开方法,优化有限差分方法在大波数区域对频散误差的压制效果更明显.在三维均匀和修改的Hess VTI模型中的数值模拟实验证明了本文方法具有更高的精度与效率,混合吸收边界条件在三维VTI介质中具有良好的边界吸收效果. 相似文献
7.
本文以宝鸡市和西安市地震小区划工作中获得的大量实测资料为基础,建立了一维随机土层结构模型,应用随机振动的理论和摄动法,就随机场地条件对土层地震反应分析的影响进行了初步的研究和讨论。结果表明,土壤力学参量的随机性对于土层地震反应分析的影响是不可忽略的,一般情况下,可造成土层地震反应分析的方差发生20%左右的变化,也可使土层结构的自振频率发生15%—40%左右的变化。因此,人们应当对土壤力学参量的随机性给予足够的重视。 相似文献
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四阶非线性海浪波面高度的统计分布 总被引：5，自引：3，他引：5
基于非线性随机海浪模型,在四阶近似下,通过直接求矩的方法,导出了海浪波面高度统计分布为截断的Gram-Charlier级数.解释了Huang等发现的增致λ~g时符合更坏的现象.讨论了近似阶次对级数截断和系数确定的影响.对于m阶近似,分布级数的截断项为H_(3m-3),并且H_(3m-4)项不出现,H_(3m-3)与H_(3m-6)项的系数间存在简单的代数关系. 相似文献
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Expected spectral ordinates and their standard deviations are computed for ground motions produced by SH waves at the surface of a homogeneous soil formation resting on a half-space of rock. Wave transmission is idealized as linear and one-dimensional. Uncertainties about soil properties are taken into account using various approximations: a Taylor series expansion of the Fourier spectrum magnification factors with different numbers of terms and different intervals for numerical differentiation; discretization of the joint probability density function of the soil properties so as to match its moments up to those of third order including the crossed moments; a discretization that matches up to some fifth-order moments; and a fine numerical integration for the marginal density function of the modulus of rigidity, discretizing the rest of the density function. The latter approach gives sufficiently accurate results for practical purposes. Effects of even moderate uncertainty about soil properties on the statistics of spectral ordinates are found to be decisive. 相似文献
12.
The magnetic interface forward and inversion method is realized using the Taylor series expansion to linearize the Fourier transform of the exponential function. With a large expansion step and unbounded neighborhood, the Taylor series is not convergent, and therefore, this paper presents the magnetic interface forward and inversion method based on Padé approximation instead of the Taylor series expansion. Compared with the Taylor series, Padé’s expansion’s convergence is more stable and its approximation more accurate. Model tests show the validity of the magnetic forward modeling and inversion of Padé approximation proposed in the paper, and when this inversion method is applied to the measured data of the Matagami area in Canada, a stable and reasonable distribution of underground interface is obtained. 相似文献
13.
In this paper the temporal behaviour of soil moisture is modelled and statistically characterized by use of the zero‐dimensional model for soil moisture dynamics and the rectangular pulses Poisson process model for rainfall forcing. The mean, covariance and spectral density function of soil moisture (both instantaneous and locally averaged cases) are analytically derived to evaluate its sensitivity to the model parameters. Finally, the probability density function of soil moisture is derived to evaluate the effect of rainfall forcing. All the model parameters used have been tuned to the Monsoon '90 data. Results can be summarized as follows. (1) Only the soil moisture model parameters (η and nZr) are found to affect the autocorrelation function in a distinguishable manner. On the other hand, both the rainfall model parameter (θ) and the effective soil depth (nZr) are found to be of impact to the soil moisture spectrum. However, as the smoothing (or damping) effect of soil is so dominant, about ±20% variation of one parameter seems not to affect significantly the second‐order statistics of soil moisture. (2) More difference can be found by applying a longer averaging time, which is found to obviously decrease the variance but increase the correlation even though no overlapping between neighbouring soil moisture data was allowed. (3) Among rainfall model parameters, the arrival rate (λ) was found to be most important for the soil moisture evolution. When increasing the arrival rate of rainfall, the histogram of soil moisture shifts its peak to a certain value as well as becomes more concentrated around the peak. However, by decreasing the arrival rate of rainfall, a much smaller (almost to zero) mean value of soil moisture was estimated, even though the total volume of rainfall remained constant. This indicates that desertification may take place without decreasing the total volume of rainfall. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
14.
L. Jones 《Stochastic Environmental Research and Risk Assessment (SERRA)》1989,3(3):179-190
The expected head and standard deviation of the head from the first order Taylor series approximation is compared to Monte Carlo simulation, for steady flow in a confined aquifer with transmissivity as a random variable. Emphasis is on the effect of changes in the covariance structure of the transmissivity, and pumping rates, on the errors in the first order Taylor series approximation. The accuracy of the first order Taylor series approximation is found to be particularly sensitive to pumping rates. With significant pumping the approximation is found to under estimate both the expected drawdown and head variance, and the error increases as the pumping rate increases. This can lead to large errors in probability constraints based on moments from the first order Taylor series approximation. 相似文献
15.
We propose a new numerical solution to the first‐order linear acoustic/elastic wave equation. This numerical solution is based on the analytic solution of the linear acoustic/elastic wave equation and uses the Lie product formula, where the time evolution operator of the analytic solution is written as a product of exponential matrices where each exponential matrix term is then approximated by Taylor series expansion. Initially, we check the proposed approach numerically and then demonstrate that it is more accurate to apply a Taylor expansion for the exponential function identity rather than the exponential function itself. The numerical solution formulated employs a recursive procedure and also incorporates the split perfectly matched layer boundary condition. Thus, our scheme can be used to extrapolate wavefields in a stable manner with even larger time‐steps than traditional finite‐difference schemes. This new numerical solution is examined through the comparison of the solution of full acoustic wave equation using the Chebyshev expansion approach for the matrix exponential term. Moreover, to demonstrate the efficiency and applicability of our proposed solution, seismic modelling results of three geological models are presented and the processing time for each model is compared with the computing time taking by the Chebyshev expansion method. We also present the result of seismic modelling using the scheme based in Lie product formula and Taylor series expansion for the first‐order linear elastic wave equation in vertical transversely isotropic and tilted transversely isotropic media as well. Finally, a post‐stack migration results are also shown using the proposed method. 相似文献
16.
We hypothesize that the spatial and temporal variation in large-scale soil moisture patterns can be described by a small number of spatial structures that are related to soil texture, land use, and topography. To test this hypothesis, an empirical orthogonal function (EOF) analysis is conducted using data from the 1997 Southern Great Plains field campaign. When considering the spatial soil moisture anomalies, one spatial structure (EOF) is identified that explains 61% of the variance, and three such structures explain 87% of the variance. The primary EOF is most highly correlated with the percent sand in the soil among the regional characteristics considered, but the correlation with percent clay is largest if only dry days are analyzed. When considering the temporal anomalies, one EOF explains 50% of the variance. This EOF is still most closely related to the percent sand, but the percent clay is unimportant. Characteristics related to land use and topography are less correlated with the spatial and temporal variation of soil moisture in the range of scales considered. 相似文献
17.
An approximate method and a rigorous method are presented for the time-domain soil-structure interaction analysis, both of which use the stiffness of soil obtained numerically or experimentally in the limited frequency range. In the aseismic design of a large-scale structure, the approximate and rigorous methods are intended to be used in a preliminary analysis and a detailed study, respectively. Both methods are based on the approximation that the first few terms of the Fourier or Taylor expansions of a frequency-dependent function are used. The difference lies in the number of coefficients of each series, and also in the manner in which the coefficients can be determined. In order to demonstrate the validity of the proposed methods, a soil-structure system, whose soil has a complex profile under the foundation, is analysed. The dynamic stiffness of the soil is calculated by a 3-D hybrid approach that combines the finite element method and the boundary element method. As a result, the present methods are capable of evaluating the complexity of the soil more precisely and efficiently than conventional methods. 相似文献
18.
A criterion is developed for the simulation of realistic artificial ground motion histories at soft‐soil sites, corresponding to a detailed ground motion record at a reference firm‐ground site. A complex transfer function is defined as the Fourier transform of the ground acceleration time history at the soft‐soil site divided by the Fourier transform of the acceleration record at the firm‐ground site. Working with both the real and the imaginary components of the transfer function, and not only with its modulus, serves to keep the statistical information about the wave phases (and, therefore, about the time variation of amplitudes and frequencies) in the algorithm used to generate the artificial records. Samples of these transfer functions, associated with a given pair of soft‐soil and firm‐ground sites, are empirically determined from the corresponding pairs of simultaneous records. Each function included in a sample is represented as the superposition of the transfer functions of the responses of a number of oscillators. This formulation is intended to account for the contributions of trains of waves following different patterns in the vicinity of both sites. The properties of the oscillators play the role of parameters of the transfer functions. They vary from one seismic event to another. Part of the variation is systematic, and can be explained in terms of the influence of ground motion intensity on the effective values of stiffness and damping of the artificial oscillators. Another part has random nature; it reflects the random characteristics of the wave propagation patterns associated with the different events. The semi‐empirical model proposed recognizes both types of variation. The influence of intensity is estimated by means of a conventional one‐dimensional shear wave propagation model. This model is used to derive an intensity‐dependent modification of the values of the empirically determined model parameters in those cases when the firm‐ground earthquake intensity used to determine these parameters differs from that corresponding to the seismic event for which the simulated records are to be obtained. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
19.
Optimal implicit staggered‐grid finite‐difference schemes based on the sampling approximation method for seismic modelling 
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下载免费PDF全文 We propose new implicit staggered‐grid finite‐difference schemes with optimal coefficients based on the sampling approximation method to improve the numerical solution accuracy for seismic modelling. We first derive the optimized implicit staggered‐grid finite‐difference coefficients of arbitrary even‐order accuracy for the first‐order spatial derivatives using the plane‐wave theory and the direct sampling approximation method. Then, the implicit staggered‐grid finite‐difference coefficients based on sampling approximation, which can widen the range of wavenumber with great accuracy, are used to solve the first‐order spatial derivatives. By comparing the numerical dispersion of the implicit staggered‐grid finite‐difference schemes based on sampling approximation, Taylor series expansion, and least squares, we find that the optimal implicit staggered‐grid finite‐difference scheme based on sampling approximation achieves greater precision than that based on Taylor series expansion over a wider range of wavenumbers, although it has similar accuracy to that based on least squares. Finally, we apply the implicit staggered‐grid finite difference based on sampling approximation to numerical modelling. The modelling results demonstrate that the new optimal method can efficiently suppress numerical dispersion and lead to greater accuracy compared with the implicit staggered‐grid finite difference based on Taylor series expansion. In addition, the results also indicate the computational cost of the implicit staggered‐grid finite difference based on sampling approximation is almost the same as the implicit staggered‐grid finite difference based on Taylor series expansion. 相似文献
20.
A.Mébarki 《地震工程与工程振动(英文版)》2010,9(2):213-221
This paper deals with the effect of layer height randomness on the seismic response of a layered soil. These parameters are assumed to be lognormal random variables. The analysis is carried out via Monte Carlo simulations coupled with the stiffness matrix method. A parametric study is conducted to derive the stochastic behavior of the peak ground acceleration and its response spectrum,the transfer function and the amplification factors. The input soil characteristics correspond to a site in Mexico City and the input seismic accelerations correspond to the Loma Prieta earthquake. It is found that the layer height heterogeneity causes a widening of the frequency content and a slight increase in the fundamental frequency of the soil profile,indicating that the resonance phenomenon is a concern for a large number of structures. Variation of the layer height randomness acts as a variation of the incident angle,i.e.,a decrease of the amplitude and a shift of the resonant frequencies. 相似文献