[aspect-devel] Evenly spaced vectors, dynamic pressure

[Wolfgang Bangerth]

On 09/07/2018 11:42 AM, Adam Holt wrote:
> Thanks much for the explanation! I'm interested in the component of
> the pressure that drives flow, so yes it sounds like this
> "nonadiabatic pressure". (For my incompressible models, I'm assuming
> this is just total minus hydrostatic pressure.)

The problem is that there is no one "pressure that drives flow", or 
"dynamic pressure". You can define it in many ways -- basically, you can 
think of the dynamic pressure as the total pressure minus a "static" 
pressure p_s where p_s is chosen so that it does not result in any flow 
or mass movement. (Mathematically, p_s equals a gravity potential -- any 
gravity potential --, then it does not result in any flow.)

The problem is that you can choose p_s in many different ways. For 
example, if you choose p_s to be the static, 1d (depth dependent) 
pressure for *any* stable stratification where the density increases 
with depth, then that satisfies the conditions. For this density 
profile, you can choose the adiabatic profile, or the laterally averaged 
density at any given time.

The point is that since
   p_d = p_total - p_s
and because p_s can be chosen in different ways, there are different 
ways to define p_d all of which can be considered to have a component 
that "drives the flow". The postprocessor mentioned above defines one 
particular way of choosing it.

Best
  W.

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