Enable Mass Lumping in Heat Transport BHE
Add mass lumping as optional to the Heat-Transport-BHE process accordingly to the implementation in the Heat-Conduction process.
Why it is necessary? Without Mass Lumping the soil temperature at the BHE connected nodes shows unphysical lowered temperatures due to numerical oscillations. Interpret the BHE as a line source, we see the same behavior in the heat conduction (Neumann) benchmark.
To minimise the impact of Mass Lumping as much as possible, it is only applied to BHE connected soil elements:
In the following images the impact of Mass Lumping is shown for the Beier Sandbox Benchmark: The BHE is heated and the initial soil temperature was 295.175 K, so lower temperatures than this are not plausible.
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Edited by Max Jäschke