A Study Of Parameters On Frequency-domain IP Method By Finite-element Method

Frequency-domain IP method establishes its position and function in exploration of mineral resources with its portable, rapid, and Efficient. The FEM ( finite element method ) is very simple to deal with complex boundary condition, and to simulate the frequency-domain IP. Studying the characters and laws of IP's parameters under different measuring devices and undulate topography will provide scientific references and basis and reduce the multiplicities of interpretation. It is will be an attempt and exploration.Because of the frequency of the exciting current is usually between 10^-2～10² Hz, the vector A can be seen is not change with the time and the EM effect can be ignored in the low frequency. So the resistivity of the model can be replaced with the Cole-Cole model's response under different frequency, and the model can be subdivide and interpolation, analysis, general synthesis. Solving the last received linear equations, we can get the complex voltages on each nodes. According to the definition of the IP's parameter, we can get the frequency-domain parameters without considering the EM effect. Using the triangular prism element can finished the simulation of IP's parameters under the undulate topography.The following is the main study results:1. On the base of other researcher, the paper from the basic equations of stable current field to derived the expressions of boundary problems under 3-D condition. without considering the EM effect and using the generalized variational structure principle, It can get the corresponding variational structure equation. For subdivide the 3-D model, interpolation, analysis, and general synthesis with the triangular prism element, we can carry out the simulation on frequency-domain IP's parameters under level and undulate topography.2. Derived the tri-linear interpolation-shape function of hexahedron-tetrahedron and tri-prism element, and carry out frequency-domain IP forward simulation under 3-D level and undulate topography.3. Using the MATLAB computer language, complete a set of program of forward simulation based on FEM. Finally, using the simulation experiment, the result show that the program is stable, reliability and correct.4. In this chapter, the author simulate the frequency-domain IP parameters with the middle-gradient and the dipole-dipole array under level condition, and discuss the corresponding parameter-phase frequency, and show that the phase frequency can be regard as important parameter to distinguish different polarization body's time constant, and it can be seen a choice to resolve the metal sulfides and the carbonaceous shale.5. In this chapter, the paper simulate the IP parameters with different depth-sounding equipment and polarization bodies under undulate topography, and plotted the model's sectional drawing, discussed the abnormality's character and the change law under the valley topography and ridge topography, and complex topography respectively. The results show that the terrain can not generate IP anomaly, but it can tensile, squeeze, and invert the anomaly greatly. It is even the basic changes.6. Finally, the paper simulate the parameters of the dual-frequency IP method and pseudo-random IP method, and discuss the character and law under different earth-electricity model, and show that the dual-frequency IP method has the frequency-domain IP's character. And it has it's special advantage. through simulate the pseudo-random IP method, the results show that this method can improve the efficiency and obtain multiple parameters at same time.In the last part of this paper, the author give some conclusions and proposals, which points out the deficiency in the paper and need to perfect place in the future.