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

[John Naliboff]

Hi Scott, Hi Shangxin,

Shangxin - Thank you for the clarification regarding the models. CFL=0.5 
is certainly more reasonable, but it still might be worth it to try a 
value like 0.1 just to make sure nothing odd is going on there.

Scott - Thanks for the explanation and definitely interested to see what 
solution(s) arise.

Cheers,
John

*************************************************
John Naliboff
Assistant Project Scientist, CIG
Earth & Planetary Sciences Dept., UC Davis

On 04/21/2017 04:23 AM, Scott King wrote:
>
> John;
>
> See the section of the Aspect manual for the 2D incompressible 
> Cartesian benchmarks.   This is a trick used to try to circumvent the 
> density term in the time derivative of the temperature equation, which 
> is not constant (as it would be for Bousinessq).   The small alpha 
> makes that term nearly constant while keeping the buoyancy term as Ra. 
>  In 2D the manual shows this works up to Ra=7000*1e10, alpha-1e-10.   
> Trying to use this for 3D spherical it breaks around 10^3/1e-3.   It 
> suggests either the 3D spherical matrix is more illconditioned to 
> begin with or something about the iterations and tolerance levels for 
> the solver is different between 2D and 3D.   Or it needs to be 
> different between the two and isn’t.
>
> Scott
>
>
>
>> On Apr 20, 2017, at 12:16 PM, John Naliboff <jbnaliboff at ucdavis.edu 
>> <mailto:jbnaliboff at ucdavis.edu>> wrote:
>>
>> On a side note, I personally have trouble interpreting results that 
>> vary the Ra number by orders of magnitude through terms other than 
>> the viscosity. While this is certainly an interesting numerical case 
>> study, is there a different motivation for varying the Ra number 
>> through terms other than the viscosity?
>

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