[aspect-devel] Far different velocity magnitudes & timestep sizes of the same Ra

[Shangxin Liu]

Hi Wolfgang and Juliane,

Thanks for clarifying. I have one more question/concern to confirm with
you. If I use a material model in which the density has no constant
term and only contains perturbation term to make the full pressure equals
the dynamic pressure, what will the density term in the temperature
equation be? If Boussinesq approximation formulation is used, I can see
that it should be the input reference density of the material model, yes?
However, if the compressible formulation is used, what will it be since the
input density in the material model is actually only the density
perturbation?

Best,
Shangxin



> On 04/24/2017 12:10 PM, Juliane Dannberg wrote:
> > As far as I know we always use the full pressure (unless one chooses the
> > density in the material model to only be the density deviations from the
> > reference profile, in which case the computed pressure would be the
> dynamic
> > pressure), and looking at the manual, I agree that we could document
> this better.
>
> Yes, we use the full pressure. The full pressure, however, equals the
> dynamic
> pressure if you use a material model in which the density has no constant
> term
> and only contains the thermal expansion term, i.e.,
>    rho(T) = -\alpha T
> There is a hydrostatic component of the pressure if the density is given as
>    rho(T) = rho_0 - \alpha T
>
> Which of the two you use is up to you.
>
> Best
>   W.
>
>
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