HPC FAQ: Difference between revisions

=Will TUFLOW HPC and TUFLOW Classic results match?=

* Solution Scheme: 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, however 2nd order HPC is preferred for higher accuracy). As there is no exact solution of the equations (hence all the different solvers!), the two schemes produce different results. However, in 2nd order mode (default) 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>

* HQ boundary treatment: Significant differences may occur at 2D HQ boundaries for models using TUFLOW release 2020-01-AB and earlier. 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 of 2020-10-AA release HPC new default for HQ boundaries is similar to Classic and treating the 2D HQ boundary as one. Nevertheless, 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.<br>