HPC FAQ: Difference between revisions

No. TUFLOW Classic uses a 2nd order ADI (Alternating Direction Implicit) finite difference solution of the 2D SWE, while the HPC solver uses a 2nd order explicit finite volume TVD (Total Variation Diminishing) solution (a 1st order HPC solution is also available). As there is no exact solution of the equations (hence all the different solvers!), the two schemes produce different results. <br>

However, in 2nd order mode the two schemes are generally consistent with testing thus far indicating Classic and HPC 2nd order produce peak level differences usually within a few percentage points of the depth in the primary conveyance flow paths. Greater differences can occur in areas adjoining the main flow paths and around the edge of the inundation extent where floodwaters are still rising or are sensitive to a minor rise in main flow path levels, or where upstream controlled weir flow across thick or wide embankments occurs due to the different numerical approaches. <br>

For deep, fast flowing waterways, 1st order HPC tends to produce higher water levels and steeper gradients compared with the Classic and HPC 2nd order solutions. These differences can exceed 10% of the primary flow path depth. Typically, lower Manning’s n values are required for HPC 1st order (or the original TUFLOW GPU), to achieve a similar result to TUFLOW Classic or HPC 2nd order. <br>

Significant differences may occur at 2D HQ boundaries. Classic treats the 2D HQ boundary as one HQ boundary across the whole HQ line, setting a water level based on the total flow across the line. Due to model splitting to parallelise the 2D domain across CPU or GPU cores, HPC applies the HQ boundary slope to each individual cell along the boundary. As with all HQ boundaries, the effect of the boundary should be well away from the area of interest, and sensitivity testing carried out to demonstrate this.