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Posted Mon, 11 Jul 2011 01:55:09 GMT by garth
I'm currently modelling the heat interactions between a river and the aquifer in a 3d model. The aquifer thickness is 30m and the model is currently being run for 20 days.

I've noticed a large difference in calculated temperature at certain observational wells between the pump and the river depending on the number of slices used to represent the current nodes. For example when the number of slices is 21 there's a huge difference in temperature change from 41 slices when the observational well is placed 20m inbetween the river and the pumping bore.

Is there a "rule of thumb" or any sort of guidelines in determing the number of slices? Any references to literature would be great!

Thanks in advance!
Posted Mon, 11 Jul 2011 07:09:51 GMT by Denim Umeshkumar Anajwala
There's no direct guideline. In general, every model - strictly speaking - would have to be tested for 'mesh convergence', i.e., the mesh would have to be refined vertically and horizontally until no more changes in the result are observed. Practically, this is seldom done - maybe too seldom.
On the other hand, in specific configurations mesh convergence does not exist. For example, refining the mesh around a pumping well placed on a single node, the calculated head at the well node will decrease with mesh refinement, no matter how small the elements become. In this case, there is something like an equivalent well radius, i.e., one specific element size that fits to the real well radius.

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