[aspect-devel] Negative pressure

[Wolfgang Bangerth]

On 03/09/2016 11:45 PM, Lev Karatun wrote:
>
> thank you for the quick reply. The pressure normalization was actually
> set to "no". I tried changing it to "surface", but it made made it so
> that the pressure across the entire model domain except for the very lop
> layer became negative =(

But the point remains true: the Stokes equations only determine the 
pressure up to a constant. If you want to add 100 GPa to the pressure 
everywhere, it will still solve the equations. In other words, whether 
the pressure is negative or positive matters from a physical 
perspective, but has no mathematical meaning in the context of the 
equations you are solving because you can make the pressure positive 
everywhere or negative everywhere by just adding a constant. 
Mathematically, what matters are only pressure *differences*, not the 
overall pressure.

Best
  W.

-- 
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Wolfgang Bangerth               email:            bangerth at math.tamu.edu
                                 www: http://www.math.tamu.edu/~bangerth/