噪声源瑞利面波波场的数值模拟研究

发布时间：2018-03-02 00:27

本文关键词： 噪声源瑞利面波频散曲线粘性边界数值模拟　出处：《西南交通大学》2015年硕士论文　论文类型：学位论文

【摘要】：随着大量工程应用深入地质条件复杂地区,工程施工越发依赖全面的地质信息资料。为了给工程施工提供信息化保障,地球物理科学及物探技术在工程领域快速发展。利用噪声源瑞利面波的波场特性进行探测的实际应用已在国内外地震、工程勘探等领域展开,而对噪声源瑞利面波波场的理论研究还相对较少。由于噪声源的随机维度多、模拟难度大,噪声源瑞利面波波场的研究主要集中在现场试验,数值模拟研究发展较慢。本文基于波动理论及瑞利面波的频散曲线特性,利用Ansys有限元软件,采用Plane182四角点平面单元建立了简化的噪声源数值模型空间,并使用Combine14弹簧单元完善了模型边界条件,形成粘性边界。最后,使用Geogia Seismic Pro数据处理软件,利用噪声源F-K与SPAC法提取频散曲线,展开了噪声源瑞利面波在均匀介质及非均匀介质条件下的波场数值模拟及分析,得到了以下结论：在均匀介质中,展开了同侧源、异侧源两种噪声源简化模拟模型,实验发现噪声源F-K法和SPAC法能有效提取同侧源和异侧源瑞利面波的频散曲线,达到了较好的探测效果。此外,利用均匀介质本文开展了近场干扰和假频干扰分析研究。研究发现在近场区瑞利面波的波速向体波波速偏移,当体波与面波的到时相差一个雷克子波时长,体波与面波完全分离,近场干扰现象消失。在提取频散曲线时出现空间域假频干扰,这种干扰在主动源和噪声源中均存在。主动源信号在奈奎斯特频率外出现同向假频信号,噪声源除含有同向假频信号外还具有逆向的假频分量,影响频散曲线的提取。通过提高空间采样率能在波数域增大真实信号与假频信号的区分度,压制假频信号的存在区间,能有效压制空间假频信号。在非均匀介质中,本文分别建立了矩形空洞、矩形高速层、圆形低速体三种异常体的非均匀介质,通过数值模拟研究噪声源瑞利面波频散特性对其的分辨及适用情况。研究发现,噪声源对矩形异常体的分辨能力较好,可以判断异常体的中心位置,但异常体边界呈现速度过渡段,无法准确判断异常体边界位置。在圆形低速异常体的研究中,噪声源瑞利面波频散所绘制速度剖面相较矩形异常体的误差较大,对圆形异常体无法准确定位,且无法判断圆形异常体的底部边界,但依然可以判断速度变化趋势,辅助少量取芯钻孔,依然可以取得较好的预报效果。
[Abstract]:With a large number of engineering applications going deep into complex geological areas, engineering construction relies more and more on comprehensive geological information materials. In order to provide information support for engineering construction, Geophysical science and geophysical exploration technology have developed rapidly in the engineering field. The practical application of Rayleigh wave characteristics of noise source to the detection has been carried out in the fields of earthquake and engineering exploration at home and abroad. But the theoretical study of Rayleigh surface wave field of noise source is relatively few. Because of the random dimension of noise source and the difficulty of simulation, the research of Rayleigh surface wave field of noise source is mainly focused on the field test. Based on the wave theory and the dispersion curve characteristics of Rayleigh surface waves, a simplified numerical model space of noise source is established by using Ansys finite element software and Plane182 quadrilateral plane element. Combine14 spring element is used to perfect the boundary condition of the model to form viscous boundary. Finally, using Geogia Seismic Pro data processing software, the dispersion curve is extracted by using F-K and SPAC method of noise source. The numerical simulation and analysis of Rayleigh surface waves of noise sources in homogeneous and non-uniform media are carried out. The following conclusions are obtained: in homogeneous media, two simplified simulation models of the same side source and different side source are developed. The experimental results show that the noise source F-K method and SPAC method can effectively extract the dispersion curves of Rayleigh surface waves from the same side source and the other side source, and achieve a good detection effect. In this paper, the near field interference and false frequency interference are studied in homogeneous medium. It is found that the velocities of Rayleigh surface waves in the near field are shifted to body wave velocities, and when the arrival time of bulk wave and surface wave is one different from that of surface wave, the length of Rayleigh wavelet is one. Body wave and surface wave are separated completely, and near-field interference disappears. There is spatial false frequency interference in the extraction of dispersion curve, which exists in active source and noise source. The active source signal appears codirectional false frequency signal outside Nyquist frequency. The noise source not only contains the codirectional false frequency signal, but also has the reverse false frequency component, which affects the extraction of the dispersion curve. By increasing the spatial sampling rate, the division between the real signal and the false frequency signal can be increased in the wavenumber domain, and the existence interval of the false frequency signal can be suppressed. In this paper, three kinds of non-uniform media, rectangular cavity, rectangular high-speed layer and circular low velocity body, are established in non-uniform medium. The resolution and application of Rayleigh surface wave dispersion characteristics of noise source are studied by numerical simulation. It is found that the noise source has better resolution ability to rectangular abnormal body and can judge the center position of abnormal body. However, the boundary of abnormal body presents a velocity transition section, which can not accurately judge the position of abnormal body boundary. In the study of circular and low velocity abnormal body, the velocity profile drawn by Rayleigh wave dispersion of noise source is larger than that of rectangular anomalous body. It is impossible to locate the circular anomaly accurately and to judge the bottom boundary of the circular anomaly, but it is still possible to judge the trend of velocity change and to assist a small number of coring holes to achieve good prediction results.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.4

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