High-precision Calculation Of Complex Gravity Field Based On Adaptive Finite Element Method With Tetrahedron

As a natural physical field generated by the density field source of the underground medium,the earth’s gravity field has a rich research history and important value in earth and planetary science,which is widely used in mineral resource exploration,engineering geology,groundwater research,and planetary internal structure research.With the development of air and satellite gravity measurement technology,the inversion of gravity field data has become a research hotspot,and the factors restricting inversion are the efficiency and accuracy of forward modeling.The core of forward modeling is model construction and algorithm.At present,the target body of gravity field research has become more complex and largerscale,so model construction technology is the bottlenecks of forward modeling.At the same time,the closed analytical method commonly used in 3D forward modeling of gravity field is ineffective when there are too many grid elements.Therefore,this paper is concentrated on two aspects:in order to construct the large-scale model,this paper propose three schemes include spherical triangular prism-tetrahedral mesh,spherical tetrahedral mesh and spherical hexahedral mesh.Meanwhile,we also analyzed their applicability,advantages and disadvantages,and proposed the construction of large-scale regional grids in different situations,which model the Qinghai-Tibet Plateau and Taiwan Island as examples.The results show that the grids constructed in this paper are portable.It has good performance and high adaptability,and provides new ideas for the construction of large-scale models.In order to improve the efficiency of forward modeling,this paper develops a goal-oriented h-type finite element three-dimensional forward modeling method based on tetrahedral meshes with different boundary conditions for comparative analysis.The finite element solution is obtained by the Galerkin weighted margin method.In order to solve the unreasonable grid distribution,the goaloriented h-type adaptive finite element method is introduced to refine the grid.The accuracy and efficiency of the algorithm proposed in this paper are verified by the forward modeling of the gravitational field response of the cube model,the real asteroid 101955 Bennu model and the geosphere model.The forward calculation has laid the foundation for the next largescale gravity field inversion.