[Mesa-users] Using other_momentum in Riemann solver

[Jeremy Sakstein]

Hi Jing-Ze,

I am not able to help you with your question, but I wanted to make you
aware of another potential issue you may run up against down the line.

After the pulses end, the star is relaxed to the new model. The initial
step for this is to load a  ZAMS model and begin the relaxation from there
(see https://arxiv.org/pdf/1710.08424.pdf sec 7 and appendix B). When I ran
with a different value of [image: G] (a less complicated example of what
you want to do) I found that the relaxation failed and the code terminated.
The reason for this is that the ZAMS models that are called are not in
hydrostatic equilibrium with extra forces present (or different values
of [image:
G]).

I was able to solve this in 12778 by generating new ZAMS models with
modified values of [image: G] and calling those instead. It is likely that
you will be able to overcome this issue using a similar method, but it may
be tricky in r-15104. The routine where these models are called has been
moved to the /star/public/star_lib.f90 (star_relax_to_star_cut) so you may
find it harder to load modified models.

An immediately obvious solution would be to go back to 12778 but I am not
sure if you need some features of 15140.

Cheers,

Jeremy



On Fri, Feb 19, 2021 at 12:13 AM Jing-Ze Ma via Mesa-users <
mesa-users at lists.mesastar.org> wrote:
>
> Hi everyone,
>
> I'm trying to add another kind of force into the momentum equation in the
ppisn test_suite, but the other_momentum and other_momentum_implicit hooks
are not implemented into the Riemann solver. I can always introduce a
vector change to cgrav (setting cgrav to different values in different
cells) so that an additional force is equivalently added to the momentum
equation, but I think the energy equation would be physically wrong
according to section 4 of MESA instrument paper IV published in 2018 (or
perhaps I'm getting it wrong?). Is there any other way to add another force
into Riemann solver using hooks?
>
> I'm using MESA r15140.
>
> Thanks a lot!
>
> Best regards,
> Jing-Ze
>
>
> --
> Jing-Ze Ma
> Undergraduate Student,
> Tsien Excellence in Engineering Program (TEEP) 2018,
> School of Aerospace Engineering,
> Tsinghua University
>
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
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