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

[Scott King]

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> 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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