Sweep3d

SWEEP3D: 3D Discrete Ordinates Neutron Transport. The benchmark code SWEEP3D represents the heart of a real ASCI application. It solves a 1-group time-independent discrete ordinates (Sn) 3D cartesian (XYZ) geometry neutron transport problem. The XYZ geometry is represented by an IJK logically rectangular grid of cells. The angular dependence is handled by discrete angles with a spherical harmonics treatment for the scattering source. The solution involves two steps: the streaming operator is solved by sweeps for each angle and the scattering operator is solved iteratively. The two step solution coded in SWEEP3D is known as an inner iteration. A realistic Sn code would solve a multi-group problem, which in simple terms is nothing more than a group-ordered iterative solution on top of what SWEEP3D does. Groups are solved sequentially since there is strong coupling between groups due to downscattering. The multi-group iterations are known as outer iterations. Finally, a realistic ASCI Sn code would include time-dependence with 1000’s of time steps on top of what a multi-group code does. Work and memory increases substantially for these real problems. The increased work is predominantly just more inner iterations. Multi-group problems add another dimension to the flux moments array while time-dependent problems are even worse since they require saving the angle-dependent phi array for all grid points, all angles, and all energy groups at both the old and new times. ...