[Mesa-users] shock_spread controls no supported on r23.05.1, and alternatives for resolving shocks with v_flag hydro?

[Ebraheem Farag]

Hello Jaime,

> Is there an alternative to shock_spread_linear and shock_spread_quadratic
in the later versions of MESA to help v_flag hydro when a shock is formed?
And if possible, does someone knows why that form of artificial viscosity
is no longer supported?

I can't speak to the removal of the Tscharnuter & Winkler form of artificial
viscosity from MESA star. However the simpler Neumann & Richtmyer quadratic
form is still available in MESA star and is what is currently used in MESA
RSP. See
https://docs.mesastar.org/en/release-r24.06.1-rc1/reference/controls.html#use-pvsc-art-visc

use_Pvsc_art_visc = .false.Pvsc_cq = 4.0d0Pvsc_zsh = 0.1d0


No promises here, but if the numerical viscosity doesn't help, you can also
try incorporating a drag term in the momentum equation, see
https://docs.mesastar.org/en/release-r24.06.1-rc1/reference/controls.html#min-q-for-drag.
However, this is only available in MESA r24.03.1 onward.

If neither helps and you're feeling cheeky, you can try reimplementing
the Tscharnuter
& Winkler form into MESA star, using the RSP implementation and a previous
MESA version as a reference. See "*subroutine* calc_Pvsc" in
$MESA_DIR/star/private/rsp_step.f90.

I hope this helps.

-EbF

On Mon, Jul 1, 2024 at 5:37 AM Jaime Roman Garza via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> Hi,
>
> I am using MESA r23.05.1 to model common envelope evolution. In a given
> time of the evolution the donor, due to the energy deposited in its
> envelope, starts to pulsate, similarly as in Clayton et al. 2017. This
> behaviour leads to pressure jumps of one order of magnitude between two
> consecutive cells; where the cells below this jump, in the radial
> coordinate, are expanding and the ones above are contracting. I am
> currently using the v_flag hydro to evolve the models where that issue is
> present. Switching to u_flag framework solves the issue on the
> discontinuity but the average timestep for the simulation drop three orders
> of magnitude making this option very expensive.
>
> From the documentation, as well from literature, I encounter the
> possibility to control the shock spread in MESA, something that might help
> on the issue I described above. Such controls are shock_spread_linear and
> shock_spread_quadratic, described in the MESA's 3rd  instrument paper.
>
> In MESA r23.05.1 such controls are no longer available, the only similar
> things I found are RSP_Qvisc_linear and RSP_Qvisc_quadratic, only used when
> RSP_flag is switched on. And as an extra comment, by searching for those
> controls in the source code, it seems they are not used (see
> Terminal_ouput.txt file).
>
> Is there an alternative to shock_spread_linear and shock_spread_quadratic
> in the later versions of MESA to help v_flag hydro when a shock is formed?
> And if possible, does someone knows why that form of artificial viscosity
> is no longer supported?
>
> Kind regards,
> Jaime.
>
>
>
> *Jaime ROMAN GARZA*
>
> Ph.D. candidate – Département d'Astronomie
>
>
> ______________________________________________________________________________________________________________________________________________________________________________________________________________________________________
>
>
>
> *GW sources | Stars, formation and evolution*
>
> Observatoire de Genève | 51 Chemin Pegasi - 1290 - Versoix - CH
>
> ( +41 22 379 24 17                 * : Jaime.RomanGarza at unige.ch
> _______________________________________________
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