[aspect-devel] Internal heating in aspect (Ludovic Jeanniot)

[Max Rudolph]

On Tue, Aug 28, 2018 at 8:01 PM Wolfgang Bangerth <bangerth at colostate.edu>
wrote:

> On 08/28/2018 05:33 PM, Max Rudolph wrote:
> >  From this, it is very obvious why the solution to the convection
> problem at
> > low resolution is very diffusive and also why the interior temperature
> is much
> > closer to the surface temperature than to the CMB temperature because
> the
> > artificial viscosity is on the order of 20 times larger than the thermal
> > conductivity near the surface.
>
> Would it be easy to verify whether the artificial viscosity ("artificial
> conductivity") decreases at the expected rate with mesh refinement?
>

What is the most helpful way for me to show this? Visualization of a couple
of slices from the 3D conduction model? I tried to get the depth average of
artificial viscosity but the postprocessor is not implemented.


> > For the conduction problem, the default values of the artificial
> viscosity are
> > also much larger than the thermal conductivity.
>
> I think that's the point worth investigating. Since in this case the
> velocity
> is zero, one would expect the artificial viscosity to also be at least
> quite
> small. Why is it not?
>

*Maybe the spherical and 2D annulus geometry models are returning an
unhelpful length scale, like planetary radius instead of layer depth?*

aspect/source/simulator/entropy_viscosity.cc (starting line 191):
// If the velocity is 0 we have to assume a sensible velocity to calculate
// an artificial diffusion. We choose similar to nondimensional
// formulations: v ~ thermal_diffusivity / length_scale, which cancels
    // the density and specific heat from the entropy formulation. It seems
    // surprising at first that only the conductivity remains, but remember
    // that this actually *is* an additional artificial diffusion.
    if (std::abs(global_u_infty) < 1e-50)
      return parameters.stabilization_beta *
             max_conductivity / geometry_model->length_scale() *
             cell_diameter;



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