Numerical Simulation Of Time-Domain IP With 2D FEM

IP method,which is a very effective way to prospect metal ores,has several unique advantages,especially when the conductivity of the abnormality is very close to surrounding rocks. In order to employ the IP parameters more efficiently in the inverse problem and abnormality evaluation,it's of great signification to study the forward numerical simulation of this method.In this thesis, based on the two-dimensional point source problem of geoelectricity field, finite element method (FEM) was chosen to carry out the numerical simulation for geoelectricity field; unstructured triangular mesh was used for calculation. For fixed point source sounding (FPS) device, a variety of models was designed for forward modeling, and mainly discussed the accuracy of arc intersection & relative intensity (AIRI) method in determining the center of single abnormal body. It further discussed the mechanism which was produced by false anomalies when using the AIRI method to deal with a number of anomaly bodies. The data processing of the AIRI method also be improved, and effectively eliminated the false anomaly of the inversion results. The numerical simulation of time-domain IP with 2D FEM was completed.Main works are as follows.(1) Based on the geophysical theory and field theory, basic equations of two-dimensional point source and the solution of FEM process were derived. According to the concept of equivalent resistivity, the calculation of polarizability was discussed.(2) According to the geoelectricity field characteristics of forward modeling, the mesh generation method of FEM calculation was improved, a two-dimensional triangulation method with constraint condition was put forward, and the automatic mesh generation program was designed. In this process, techniques of the fixed-point mesh refinement and gradient mesh have been used. The program was well suited to complex geoelectricity section and the actual results have shown good effect.(3) Coefficient matrix was stored in memory by using the fixed-bandwidth, the LDLT decomposition method was used to solve linear equations, the speed and accuracy was very high.(4) According to the requirements of two-dimensional Time-domain IP (TDIP) forward modeling, Two-dimensional FEM forward modeling program was designed, and the reliability and accuracy of the program has been tested; by using equivalent resistance method to calculate apparent polarizability parameters, forward modeling was realized.(5) The FPS device was chosen to carry out forward modeling for a number of models, discussed the accuracy of AIRI method in determining of the center of single abnormal body. The mechanism was studied which was produced by false anomalies when using the AIRI method was to deal with a number of anomaly bodies. Abnormal separation and image fusion technology was used to improve the data processing of AIRI method, and effectively eliminate the false anomaly of the inversion results.