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= Why is my model using 2020 HPC slower than 2018 HPC? =
The change in runtimerun 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, test run your model with 2020release2020 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 runtimerun time when changing from the 2018 to the 2020 release - models that are controlled by the wave celerity or velocity control numbers and not the diffusion control number 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 diffusion control number (the third one displayed) to control the timestepping causing longer run times.
= I have been given a model developed in an older release and the results are different in a newer release. Why? =
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