[Mesa-users] Question about using other_cgrav with the PPISN test_suite

[Jeremy Sakstein]

Thanks Adam,

As far as I am aware, I am not loading a pre made model but using
create_pre_main_sequence_model=.true. so I don't think this should be an
issue no?

The first 300 odd steps appear to be model relaxation.

Cheers,

Jeremy

On Thu, Jul 2, 2020 at 3:58 PM Adam Jermyn <adamjermyn at gmail.com> wrote:

> Hi Jeremy,
>
> I’m not familiar with the PPISN test case specifically, but changing cgrav
> and then loading a pre-existing model can be tricky. The pre-existing model
> likely had the standard_cgrav value. When you change that value even by a
> small amount you’re kicking the model way out of hydrostatic equilibrium,
> which will require significant adjustment to restore.
>
> For instance, if you take a solar model and change cgrav down by 1% with
> hydro on I’d expect the surface to expand at ~1%*(escape velocity), which
> can be large…
>
> Someone more familiar with PPISN might be able to say more though...
>
> -Adam
> On Jul 2, 2020, 3:48 PM -0400, Jeremy Sakstein <sakstein at hawaii.edu>,
> wrote:
>
> Hi everyone,
>
> I have a question about the PPISN test suite.
>
> I am trying to use other_cgrav with G rescaled by a constant (1 + a small
> number) and I have run into some issues. When I change G by a few % or more
> I am finding that the code terminates due to reaching the time step limit
> (I set this to 1d-99).
>
> My initial explorations of changing various controls led me to believe
> that the star was going away from hydrostatic equilibrium, my evidence for
> this being that I kept running into various stropping conditions telling me
> that the surface velocity was too high. These errors show up before hydro
> is turned on for the first time.
>
> My two leading hypotheses are:
>
>    1. Hydro is turning on too late i.e. after the star begins to expand or
>    2. other_cgrav is not implemented in every equation being solved in
>    this test_suite leading to cumulative errors.
>
>
> I tested (1) by turning hydro on from the start of the run. In this case I
> didn't get any termination codes but the runs take a very long time. I was
> able to get past the temperatures and densities where the code previously
> terminated however.
>
> I tested (2) by turning off other_cgrav and instead setting:
>
> standard_cgrav = 1.05*standard_cgrav
>
> in extras_controls in run_star_extras. I have used this procedure before
> for e.g. the RSP module.
>
> Is anyone able to give me any insight into what is happening here, and
> whether I am on the right track with (1) or (2).
>
> My own tests suggest that my procedure (2) is working as expected i.e. the
> value of G is indeed altered for every equation being solved by setting it
> in extras_controls but it would be great if someone were able to confirm
> this for me.
>
> I'd be very grateful for any help you can give.
>
> Cheers,
>
> Jeremy
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