The SHASTA Code Modified by Self-adaptive Mesh and Numerical Experiment of Magnetic Reconnections

Abstract

SHASTA (Sharp and Smooth Transport Algorithm) is a code with single mesh to solve the 2-dimensional magnetohydrodynamic (MHD) equations. When SHASTA is used to the numerical simulation of magnetic reconnection problem, it is modified to be the code which adopts the method of the selfadaptive mesh. The modified code can carry out refined calculations in diffusion regions. In the process of the self-adaptive calculations with SHASTA, a “plugand-play” strategy is adopted and the original algorithm to solve 2-dimensional MHD partial differential equations is treated as an independent cell. In addition, the hierarchical data structure is used in this modification and parameters in each refined level are described by a 2-dimensional variable array. The regions where the distributions of magnetic field and pressure exhibit steep variations are marked as the refined regions. Then, the distributions of physical quantities and the boundary conditions in the grid points of refined levels are deduced via interpolation method. Finally, the refined calculated results of refined regions are assigned to the previous level of mesh and the existing results are updated. The numerical experiment of magnetic reconnections which adopts refined calculations indicates that compared with the code with single mesh, the resolution of details is improved and the corresponding increment of computing time is related to the selection of parameters in the simulation. The calculation accuracy and effect on instability, which are caused by a part of the self-adaptive code, depend on the boundary settings, push strategy over each single step as well as the interpolation algorithm.