Max Mesh Size, Nested/unstructured Mesh and Connections

[Anonymous]

I have been trying to ‘push’ what Hec-Ras 5.0.3 can do and in looking at this forum (and other sources) there are a few questions that I haven’t found an answer too.

First is the maximum mesh size – With my setup (64-bit Win10, 16GB RAM) I get crashes/errors when the mesh exceeds approximately 1,000,000 cells. Is this the approximate cap or is it just me? Another poster had the same problem with 2,000,000 cells.

Secondly is the potential to use nested meshes. I have seen others (e.g. Dewberry) use unstructured meshes (though some sorcery that would be useful to unpack) – but I haven’t come across nested mesh options. The idea of a nested mesh is relevant for rainfall – where effective rainfall (i.e. runoff depth) needs to be uniformly distributed over a single mesh. To overcome this, you could model your effective rainfall for various areas and apply to semi-homogeneous zones – but then how does the software handle that? (I tried – but having a ‘hole’ in a mesh being filled by another mesh created problems with vertices).

Lastly – Were I to succeed in setting up a rainfall model (perhaps by not using any totally enclosed meshes) – would the next problem be the connectivity – since ‘2D Flow Area Hydraulic Connectors’ appear necessary – I’m a little worried about the possible errors when you have many kilometers worth of 2D flow connectors.

Some of these (potential) limits may be addressed in future versions – hopefully.

[cameron]

I have done models with over 2,000,000 elements, but I have 64gb of ram.

There is no way to nest models so you would have to use unstructured meshes or break up the model into multiple 2D meshes connected by 2D connectors.

[Anonymous]

When generating the mesh in ‘geometric data’ editor, I can get over 1,000,000 cells (around 2,000,000). Higher than this (3,500,000 as I would prefer) and the mesh builder stops – says its successful but then has no data to display (i.e. no cells indicated).

In RAS Mapper, however, when using the 2,000,000 result for instance – I get an error “Exception – System out of Memory” when computing hydraulic tables.

In both instances I have watched my system resources which haven’t approached the approximate 3.5GB 32-bit memory limit (assuming that applies).

So I’m unsure of the actual cause – which doesn’t appear linked to RAM?

So in my case – 1,000,000 appears to be the unexplained upper limit

[Author]

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