Study On The Processing Method Of The Interface Problem Of IFE-PIC Numerical Model

IFE-PIC(Immersed finite element- particle in cell) is a numerical simulation algorithm which combines of immersed finite element and particle in cell method. The algorithm is simulated in the structured grids of Cartesian coordinate system, using PIC method to govern the movement of particles in the region, and solving the electric field by the method of IFE. Because of the superiority of the algorithm in the simulation of particle motion, at present, it is widely used in study on the electromagnetic field finite element simulation. However, due to the use of structured grids, some elements will intersect object to form the so-called interface element. The basis functions supported on these elements are no longer continuous, as a result, the charge distribution become less accurate. Finally, the error of the numerical simulation on those elements will be much larger.Based on the application of IFE-PIC algorithm in the plasma field, this paper focuses on the improvement of the IFE-PIC interface precision, and the application of the improved algorithm in engineering simulation. The specific research contents are as follows:First of all, this paper improves the solution algorithm of the IFE interface element, based on PPIFE(Partially Penalized IFE) theory to solve the interface unit. The PPIFE algorithm program and numerical examples are designed, and the accuracy of the algorithm is verified by analyzing the error. This paper mainly completes the overall design of the algorithm program, including the selection of the calculation area, structure of analytic solution, the solution of basis function and the synthesis of the right-hand-side vector and the stiffness matrix. Finally, numerical results are obtained and the error analysis is done, through the error comparison, it shows that the new algorithm has higher simulation accuracy.Then, the unreasonable phenomenon of the interface charge interpolation algorithm of standard PIC is introduced in this paper. Based on this phenomenon, a new improved scheme is proposed, the proposed method uses the same weight coefficients as the standard PIC charge interpolation. And the processing program of the new algorithm is compiled, finally, a numerical example is constructed to verify the rationality of the improved algorithm.At the end of this paper, PPIFE-PIC computing program is designed to complete, which combines PPIFE algorithm with the improved PIC charge interpolation method, and it has higher accuracy in interface elements than traditional IFE-PIC method. Then the new program is used to simulate the classical sheath environment of the lunar surface. This paper analyzes the forming processing of sheath and the effect of solar wind incident angle on the structure of the sheath. Finally, by analyzing the simulation results, it is concluded that the new algorithm can improve the accuracy of the interface in the electromagnetic field finite element simulation.