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

[Timo Heister]

Shganxin,

if you use BA as the formulation, the density in the temperature comes
from the "adiabatic conditions" module. The density from the material
model is only used in the buoyancy term. See the section on
"formulation" in the manual.

On Wed, Apr 26, 2017 at 3:32 PM, Shangxin Liu <sxliu at vt.edu> wrote:
> 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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-- 
Timo Heister
http://www.math.clemson.edu/~heister/