Research Of Finite Element Modeling Of2.5D CR On Undulate Topography

While carrying out the measurement of the complex resitivity on the the undulate topography, the undulate topography can throw impact on the current distribution and in turn, it can cause the aberrance of the observed data, which consequently cannot truly reflects the distribution of the underground geological bodies.In order to process and interpret the observed data, this thesis mainly takes some abnormal characteristics of2.5-D complex resitivity method on undulate topography, and try to find out some regularity. On account of some advantages owned by finite element method in geophysical numerical modelings, this thesis carries out the forward modeling of the complex resitivity on undulate topography by adopting the finite element method.First of all, this thesis introduces the research background and significance with respect to the complex resitivity method on undulate topography; and offers a review of the current research sitution about the forward modeling problem of the complex resitivity method.Then, it discusses the variation resulting from the process in which the complex resistivity amplitude and phase of the mathematical model-Cole-Cole model of the rock and ore’s induced polarization change with the Cole-Cole parameters m、(?)and c. Without considering the case of electromagnetic coupling, it realizes to sovle the expressions by introducing the linear filtering method, designs the theoritical geoelectric sections, and also analyses the characteristics of the curves which illustrate that the complex resistivity’s amplitude and phase make changes along with the polar distance under condition of three different geoelectric sections,which is according to the expressions of the multi-layered polarization underground derived from the Laplace’s equation. Meanwhile, for the2.5-D complex resitivity forward modeling, its validity of calculation procedure is proved.Furthermore, it deduces the Laplace’s partial differential equations and its relative variational equations for2.5-D structrue with3-D alternating two-point sources; sovles the equations by employing the finite element method, carries out the grid partition in the computing area, also the complex potential and the complex conductivity of rocks within each triangular lattice are described by a linear interpolation to creat alinear equation system from the variational equation;then, the linear equations are solved to calculate the anomalous complex potential at each node, and different survey configurations are selected to calculate the apparent complex resitivity on the surface. In turn, the amplitude, the phase, and the real and imaginary components of the complex resitivity are calculated. After that, it establishes corresponding calculation procedure which has been proved reliable by comparing the one-dimensional forward result; finally, the models of three typical landforms including the ridge, valley and brae are designed to carry through the complex resivitity forward modeling algorithm of various typical geoelectric models by respectively employing Schlumberger array and dipole-dipole array. Thus, analysis have been given on the calculated results, and some abnormal characteristics of2.5-D complex resivitity method on undulate topography have been summarized.To conclude, those work above can play a reference role in carrying out the complex resistivity measurement in the field and in data interpretation.