The Numerical Simulation Research Of Rayleigh Wave Field Based On Ambient Noise

As a large number of projects are carried out in mountainous area, geophysical information becomes more inportant for the construction. To support the engineering construction with geological information system, geophysical science and technology are extensively applied. The applications of rayleigh dispersion based on noise signal are put into pratice at home and abord, however, theoretical study make slow progress. In addition, because it’s difficult to simulate the noise by mathematical method, the researches of rayleigh wave field aroused by ambient noise focus on site test more than numberical simulation.Firstly, the simplified numberical simulation, which is based on wave theory and the dispersion of rayleigh wave, is set up by Ansys finite element software. Secondly, Plane 182 element is used to estamate stratum model and the stickiness boundary is optimized by element Combine 14. Finally, taking advantage of geogia-seismic-pro software, according to F-K and SPAC method which are used for the determine of dispersion curve,the research of numberical simulation of rayleigh wave dispersion aroused by noise is carried out in homogeneous medium and inhomogeneous medium. Conclusions are as follows:In homogeneous medium:ipsilateral and bilateral ricker wavelets are used as simplified noise signal to simulate the ambent noise rayleigh wave field and found that dispersion curves can be obtained precisely in both F-K and SPAC method. Futher more, near-field interference research and spurious frequency analysis are achieved in homogeneous medium. In near-field region, the velocity of surface wave shift towards body wave until getting away from near feild. The research found that when arrivalling time of first detector increase to ricker wavelet length, rayleigh wave detach with body wave, and near-field interference will disapper completely. Spurious frequency signal is unavoidable by either active or passive source detecting. In active source method, the spurious signal is in the same direction with real signal. However, positive and negative direction spurious signals come out when using passive source detecting approuch. This affect the figuring of dispersion curve intensely. To avoid it, the rate of spatial sampling increases to separate the spurious one and the real one. And this method proved effective to suppress spurios frequency signal.In inhomogeneous medium:rectangle cavity, rectangle bedrock and circle abnormality models are established by ANSYS, and these modles are used to stduy wether the dispersion feature of rayleigh wave based on ambient noise is applicable for these situation or notThe simulation shows that this feature can precisely locate the center of rectangle abnormality,however, the rectangle’s boundary is fuzzy. In circle abnormality study, the accuracy of dispersion can not meet the detecting requirements that the center and the boundary of abnormality is hard to show. However, the dispersion reflect the trend of velocity transformation. And a more precise result we can get if we detect with bore hole.