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

[Rob Farmer]

Hi,

We need more information on what is happening to the star at the point it's
crashes.

Try making a kippenhan plot
What is limiting mesa's timestep?
What are the exact error messages mesa is returning?

Rob


On Thu, 2 Jul 2020, 22:32 Adam Jermyn via Mesa-users, <
mesa-users at lists.mesastar.org> wrote:

> Hi Jeremy,
>
> Ok in that case I’m not sure what’s going on...
>
> -Adam
> On Jul 2, 2020, 4:03 PM -0400, Jeremy Sakstein <sakstein at hawaii.edu>,
> wrote:
>
> 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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>>
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