Development of coarse mesh finite difference acceleration in the three-dimensional discrete-ordinates discontinuous finite element transport code TARS

The coarse mesh finite difference method (CMFD) is implemented to expedite the computation of the 3D SN- DFEM code TARS, supporting both cuboid and hexagonal prism coarse cells. To enhance iteration stability, the optimally diffusive CMFD (odCMFD) technique is implemented. Moreover, in order to make the odCMFD method more straightforward to implement, we propose the technique of using only one uniform artificial diffusion coefficient, determined by volume-weighted averaging the recommended values of literatures, for the entire problem. In our numerical tests of the Takeda benchmark, this assumption achieves good performance. The acceleration module effectively speeds up the iterations without causing any alterations to the final results and the most significant speed-up ratios of the uniform artificial diffusion coefficients in three models are 21.45, 45.59, and 5.94, respectively.