Novel Adaptive Preconditioner for Contact Problem in Fuel Rod

The contact problem between the fuel core block and the cladding is a key point in the simulation of nuclear reactor fuel rods, and the inclusion of a contact model increases the difficulty of solving the set of algebraic equations. By analyzing the sparse structure of the Jacobi matrix before and after contact, a novel adaptive preprocessing method based on the contact pressure judgment criterion is constructed. The full Jacobi matrix is used as the preprocessing matrix for the Preconditioned Jacobian-free Newton-Krylov (PJFNK) method when the contact pressure is zero, and the block diagonal of the Jacobi matrix is used as the preprocessing matrix when the contact pressure is non-zero. Numerical experiments show that the adaptive preprocessing method in this paper can effectively improve the simulation efficiency, and the total solution time is reduced by 15.2%~33.1% compared with the existing methods in Multiphysics Object-Oriented Simulation Environment(MOOSE).