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91.
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通过对多种连续小波基的平稳序列时频分析,提出经验模态的非平稳序列的时频分析方法,并在地震资料处理解释应用中作探索性试验.试验结果表明:对地震记录道长为5 s和2 ms采样资料,经验模态分解后可获得6-7个固有模态函数单分量,分解的第一个分量C1(t)具有较宽的频率成分,可作为地震属性的主分量. 相似文献
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Geotechnical experiments show that Lode angle‐dependent constitutive formulations are appropriate to describe the failure of geomaterials. In the present study, we have adopted one such class of failure criteria along with a versatile constitutive relationship to theoretically analyze the effects of Lode angle on localized shear deformation or shear band formation in loose sand for both drained and undrained conditions. We determine the variation in the possible stress states for shear localization due to the introduction of Lode angle by considering the localized deformation as a bifurcation problem. Further, similar bifurcation analysis is performed for the stress states along a specific loading path, namely, plane strain compression at the constitutive level. In addition, the plane strain compression tests have been simulated as a boundary value finite element problem to see how Lode angle affects the post‐localization response. Results show that the inclusion of a Lode angle parameter within the failure criterion has considerable effects on the onset, plastic strain, and propagation of shear localization in loose sand specimens. For drained condition, we notice early inception of shear localization and multiple band formation when the Lode angle‐dependent failure criterion is used. Undrained localization characteristics, however, found to be independent of Lode angle consideration. 相似文献
96.
The appearance of shear banding in granular materials has been investigated intensively during the last decades and is still of ongoing importance in terms of understanding the stress–strain behaviour of the material, the localization phenomena and the interaction between soil and structure. Only less attention has been paid to the occurrence of systems of shear bands although such systems can be identified in geotechnical structures as well as in geological formations. In this paper we present results of experiments on sand specimens under extensional load in natural gravity as well as in increased gravity in the centrifuge where the influence of the stress level on the geometry of a shear band pattern, specified by the spacing of the shear bands and the angle between failure surfaces and minor stress direction, has been investigated. X‐ray technique has been used to visualize the failure zones inside the specimen, an optical measurement system called Digital Image Correlation has been applied to identify and observe the appearing deformation mechanism on the sides of the specimens in natural gravity as well as during the flight in the centrifuge. It can be shown that the geometry of the shear band pattern is sparsely influenced by the change of the stress level. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
97.
本文研究了UHF-RFID(超高频-射频识别)环境下的移动目标定位问题,提出了一种结合自适应卡尔曼滤波和BVIRE(边界虚拟参考标签)的移动机器人定位方法,即B-AKF(Boundary-Adaptive Kalman Filter)定位方法.首先,利用UHF-RFID系统对移动机器人进行初始定位,其次,考虑模型和噪声统计特性不确定性,采用自适应卡尔曼滤波方法对机器人的运动状态进行预测和更新,并引入自适应因子补偿噪声方差不确定性问题.最后,搭建了基于UHF-RFID的定位实验平台,并通过实验研究表明,相比于传统的线性BVIRE和线性卡尔曼滤波方法,所提出的自适应卡尔曼滤波方法具有更高的定位精度和更强的鲁棒性能. 相似文献
98.
利用2010~2012年的IGS天顶对流层延迟(ZTD)序列、ERA5格网数据积分ZTD序列,在中国4个VLBI站点上对目前常用的经验模型进行优化,分别建立Local_ERA和Local_ZTD模型。基于2013~2014年IGS并址站点ZTD数据,将改进后的2种模型与全球GPT2w模型、SHAO-Gm模型进行对比。结果表明,改进后的Local_ERA、Local_ZTD模型精度相近,相对于GPT2w、SHAO-Gm模型平均精度在4个VLBI站点上都有提高,尤其在水汽季节性变化较强的北京站改进效果明显;其中Local_ERA平均精度略高于Local_ZTD,比GPT2w模型精度提高7.90%,比SHAO-Gm模型精度提高21.26%。 相似文献
99.
对称和非对称载荷下声发射特征的数值模拟研究 总被引:3,自引:0,他引:3
利用自行开发的岩石破裂过程分析RFPA^2D系统,研究了对称载荷和非对称载荷下岩样的破坏过程以及破坏过程中所呈现的声发射特征。数值模拟结果演示两种条件下由微破裂诱致宏观破坏的演化过程以及和微破裂相关的声发射事件源的空间分布特征和事件序列特征。数值模拟结果指出,和对称载荷压缩实验相比,两者的最大区别在于在非对称载荷压缩实验中局部的剪切破坏的发生以及一个更加局部化的声发射事件源分布。从物理意义上讲非对称载荷实验提供了在预定破裂路径下研究脆性破坏的方法,从声发射研究方面来说非对称实验比对称实验能更好地观察声发射事件源的局部化。 相似文献
100.
Evolution of nonperiodic forms in geological folds 总被引:1,自引:0,他引:1
An elastic layer resting on a viscoelastic (Maxwell) foundation is used to model the initiation and subsequent development
of a geological fold. This study focuses on the effect of nonlinear terms, of both geometric and material origin, in the formulation
of the governing differential equation. The result, during the initial elastic phase of deformation, is to admit the infinite
variety of shapes familiar to the field of localized buckling. Their continued effect during the evolutionary phase allows
the development of nonperiodic forms hitherto ignored by linear stability analyses. Numerical results are presented for two
viscoelastic models subjected to loading conditions of constant end displacement and constant rate of end displacement. 相似文献