Quadtree and Sub-Grid Sampling FAQ: Difference between revisions
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=If I run one SGS model, double the cell size and run it again, would I get the same results?=
SGS isn't a silver bullet that resolves all. If the hydraulic controls aren't adequately defined by the chosen cell resolution the results will vary until the said features are defined by the mesh adequately. Check the gully lines and ridge lines questions above. For a situation where there is little variation in velocity across channel the results might be impressive. In the real world, where there are significant velocity gradients across the channel the modeller might need to use a finer resolution to converge to a solution.
=My HPC model runs with double precision, using SGS the model initialisation slows down significantly. Why?=
Due to an Intel compiler issue this grid inspection has to be done with un-optimised code and will be slow. HPC solution scheme doesn't generally require double precision engine. If XF files are enabled (default), subsequent initialisations will be much faster.<br>
The need for using double precision with HPC should be revisited. From experience the models that still require double precision when using HPC are models with carved 1D channels. Either the channel itself is causing the mass error or the boundary links between 1D and 2D domain do. Unfortunately, it is not possible to run the 1D engine in double precision and 2D engine in single precision for the same model. There are two ways how to go about this, we would recommend the second one:
* Try to improve stability of the 1D features and 1D/2D links so it would perform well in single precision. The _TSMB and _TSMB1d2d layers might help locating specific features that could be worked on. The drawback of this suggestion is that it might be very time consuming to achieve even a small improvement and sometimes it is just not possible to get the mass error low enough.
* Remove 1D channel completely and use Quadtree mesh to sufficiently refine resolution of the creek in 2D.
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