A Parallel S_N Transport Sweeping Algorithm For Non-uniform Discontinuous Grid

The discrete ordinates method(SN)is one of the common deterministic calculation methods for radiation shielding calculation,and the spatial mesh distribution is crucial to computational accuracy.The strong heterogeneity of complex shielding models requires targeted geometrical description accuracy in different areas.However,global subdivision used by uniform traditional Cartesian grids often introduces unbearable computational cost,which challenges computational efficiency and computer storage.For large-sized complex shielding problems,this dissertation investigates a parallel SN transport sweeping algorithm for non-uniform discontinuous grid.Besides,the parallel angular multigrid acceleration method is employed to further improve computational efficiency.A dual domain decomposition strategy is adopted to balance the multi-core load according to the tree-based hierarchical structure and discontinuous grid distribution.Due to the fact that different discrete angular sweeping tasks own identical solve order in the same quadrant,we aggregate the discrete angular sweeping tasks to reduce the communication overhead.After region decomposition,there are non-matching meshes at the boundary of neighboring blocks.The grid preprocessing process establishes a consistent one-to-one match between global and discontinuous grids.The boundary grid pieces are constructed in order to realize efficient communication.The parallel angular multigrid acceleration method is based on triple angular multigrid,which accelerates the convergence of source iteration method by iterating the coarse and fine angular mesh.The numerical results show that the dual domain decomposition strategy can effectively reduce the load imbalance of different processors,and the acceleration effect is optimal when each processor has a similar calculation amount.For those multi-region problems,the increase of angular aggregation factor can reduce computational time.Venus-3 benchmark problem verifies the accuracy of the parallel algorithm.Favorable weak expansibility is achieved in the numerical results of different quadrature sets.The parallel angular multigrid acceleration method improves the computational speed to more than 1.6 times the original in the self-designed shielding problem.The research in this paper can expand the ability of multilevel octree grid algorithm to deal with large scale complex problems,and improve computational efficiency,which has a well application value in engineering.