Posted Thu, 01 Mar 2018 23:42:09 GMT by RDRYSDA

I am currently making a 3D model that includes a basement of a building in the overall model area. I need to have the walls of the building finely discretized so they have 3 layers of elements within 0.5m, but only to a depth of 3m (the depth the building’s basement). However, the depth of my model needs to be at least 130m (I will be adding BHEs eventually), and having such high discretization all the way down to 130m generates far too many nodes and elements which is too much for my system to handle.

I am wondering if there is a way to selectively discretize only the layers or slices that make up the top 3m of the model, leaving the lower layers with fewer elements/nodes.  I do have a shapefile for the walls themselves (as well as the interior of the building, excluding the width of the walls), if that helps in any way. I did see previous posts that suggested using TetGen for re-meshing around points, however I’m not sure that would apply to my issue.

Thanks in advance,

Posted Fri, 16 Mar 2018 05:11:12 GMT by Jarrah Muller Civil Engineer
You can make the model have a 3D unstructured mesh, so that lower layers have different node layouts to upper layers. You need to use Tetgen to do that, as you mentioned.

There are some caveats:
- you lose the ability to look at results by slice afterwards
- you can't use the free movable surface option for modelling the water table, but need to use unsaturated flow equations which generally are much slower, need more data to define the soil, and make models not run. Unless you have a confined aquifer.

When I've had this sort of problem, I've not gone down the unstructured mesh route, but tried to make the slice model work by compromising on the number of nodes. Going down to 130 m is fine if your layers are thick, for example. Generally models with up to about 300,000 nodes run ok on modern PCs. Mostly the bad effects of too many nodes are limited to long run times.

Or maybe you can run a 2D slice model with the discretisation that you want. They tend to run very quickly.

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