Revision as of 10:30, 4 November 2021 view source Pavlina Monhartova (talk \| contribs) Bureaucrats, Administrators 5,342 edits →Why is my HPC model getting unstable? And why are my control numbers lower than they could be? ← Older edit		Revision as of 15:13, 23 April 2022 view source Pavlina Monhartova (talk \| contribs) Bureaucrats, Administrators 5,342 edits →Why is my model using post 2020 HPC slower than pre 2020 HPC? Newer edit →
Line 68: = Why is my model using post 2020 HPC slower than pre 2020 HPC? = From 2020 TUFLOW includes a number of new features (Quadtree, Sub-Grid Sampling, Wu turbulence model) which are making the solution scheme more computationally complex. As such 2020 and newer releases of TUFLOW are running on average about 20% slower than their predecessors even though the new features are not used. This applies for models with unchanged cell size. Using Quadtree and SGS can warrant changing to a bigger cell size at some parts of the model and decrease runtimes far beyond the 20%.<br> ~~The~~Further change in run time can be due to different timestepping applied with the new default mesh size insensitive turbulence model (Wu instead of Smagorinsky). To confirm this is the case, the model can be run with 2020 release and the following commands:<br> <font color="blue"><tt>Viscosity Formulation </tt></font> <font color="red"><tt>==</tt></font><tt> Smagorinsky</tt> <br> <font color="blue"><tt>Viscosity Coefficients</tt></font> <font color="red"><tt>==</tt></font><tt> 0.5, 0.05</tt> <br> Not all HPC models will show an increase in run time bigger than 20% when changing from the pre 2020 to post 2020 releases. Models that are controlled by the <u>[[HPC_Adaptive_Timestepping \| Wave Celerity or Courant Control Numbers ~~and not the Diffusion Control Number~~]]</u> are likely to be similar in runtime~~. Some models will be even faster with the last 2020 release due to other improvements~~. However, especially where the cell size is smaller than the depth, the Wu approach is vastly superior to the Smagorinsky, and the more sophisticated Wu solution may start causing the <u>[[HPC_Adaptive_Timestepping \| Diffusion Control Number]]</u> to control the timestepping causing longer run times.<br> Despite the possible increase in runtime for some models, the Wu turbulence scheme is warranted particularly as cell sizes are typically getting smaller.<br> <br>

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