[Mesa-users] Query regarding implementing hydrodynamics

Tue Mar 19 15:34:02 UTC 2024

Dear Jared and Ebraheem,

Thanks a lot for your reply. I had some misunderstanding about the v_flag
and u_flag parameters and this does seem to clarify it.

To answer Jared's question, I am trying to model a common envelope system,
in which the companion is a neutron star with a 12 solar mass red giant
primary, and it is modelled by injecting extra_heat(as accretion energy)
into the star at a radius corresponding to the orbital evolution of the
system. To model the envelope expansion due to the accretion energy, and
capturing potential shocks, I want to switch on hydrodynamics. It seems
like I don't need to use u_flag for this purpose, as it is not an explosive
system.

I had a few more questions regarding this:

   1. So, just to confirm, for my purposes all I need to do to keep
   hydrodynamics on throughout the evolution is to set change_v_flag =
   .true. and new_v_flag = .true., and not do anything to u_flag parameters
    ?
   2. Do I need to set the use_split_merge_amr = .true. because I will be
   injecting extra_heat at specific zones which might need more refinement?
   3. My evolution will not be on the scales of stellar evolution, it
   should be around the order of 10 years or so, and I just wanted to know if
   this timescale is consistent with the typical timescales in which MESA
   simulations run with v_flag = .true. for red giant systems.

I shall give more thought to the surface phenomena and boundary conditions
as Ebraheem has pointed out and come back to this if I have any questions.
Any help on the above listed questions will be very helpful!

Best,
Abha

On Tue, Mar 19, 2024 at 3:18 AM Jared Goldberg <
jgoldberg at flatironinstitute.org> wrote:

> Dear Abha,
>
> What science case are you trying to do? MESA has 2 hydro solvers
> implemented, including the HLLC (u_flag) and the non-HLLC (v_flag) solver.
> The latter may be more stable for your purposes, depending on your desired
> use case.
>
> You mention that you change both u_flag and v_flag to true.
>
> change_initial_u_flag = .true.
>> change_initial_v_flag = .true.
>>
>
> U_flag is for the newer (as of instrument paper IV) cell-centered,
> better-shock-capturing hydro scheme useful for core-collapse supernova
> explosions. V_flag turns on the older, more traditional face-centered hydro
> solver with artificial viscosity. It’s not a good idea to have both on at
> the same time (though only one will take priority anyway). See Paxton+18
> <https://ui.adsabs.harvard.edu/abs/2018ApJS..234...34P/abstract> for a
> detailed explanation of the different hydro solvers and various tests.
>
> In the various test_suite cases bringing 12 and 20Msun stars to
> core-collapse (e.g. 20M_pre_ms_to_core_collapse), the v_flag hydro is set
> on and u_flag is off. Maybe try using one of those test cases as a point of
> reference instead.
>
> Cheers,
> ~Jared
>
> On Mar 18, 2024, at 2:35 PM, Ebraheem Farag via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
>
> 
> Hello Abha,
>
> I don't have a whole lot to say here beyond "Here be dragons".
>
> In the current form we only use the HLLC rieman solver for explosion
> modeling, not normal evolution calculations.
> Perhaps investigate the $MESA_DIR/star/test_suite/PPISN test_suite to get
> an idea for what might be needed to get rieman hydro working during a
> normal evolution run with the core intact.
> Also note that this was only done for very short timescales and a large
> mesh with tight time steps might be necessary to get anywhere. Sometimes
> the numerical initialization of riemann hydro can even drive the surface
> crazy as well if done during an evolution calculation. I have some working
> fixes for this but they are quite involved and do not exist in the current
> release version. Just know that we're working on it and we'll likely
> implement a future test suite to showcase how it's done :).
>
> -EbF
>
> On Fri, Mar 8, 2024 at 5:15 AM Abha Vishwakarma via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
>
>> Dear MESA Users,
>>
>> I have been trying to switch on hydrodynamics in a 12 solar mass red
>> giant star. I first ran the hse_reimann test suite which implements
>> hydrodynamics in a 12 solar mass star with the core excised. But, I wish to
>> implement hydrodynamics with the core intact.
>>
>> I switched on hydrodynamics by adding the following lines to my inlist:
>>
>>         change_initial_u_flag = .true.
>>     change_initial_v_flag = .true.
>>     new_v_flag = .false.
>>     new_u_flag = .true.
>>
>> My program takes as input a 12 solar mass red giant. But, the program
>> crashes because it hits the timestep limit or because of crossing some
>> tolerances. But, if I instead take the 12 solar mass star with the core
>> removed, as is done in the hse_reimann module, the code works fine.
>>
>> I am not sure what I am missing here, but I feel it has something to do
>> with the core of the red giant, or some boundary conditions or physics that
>> I might have missed. I have attached my inlist to this email, and any help
>> in this regard would be greatly appreciated!
>>
>> Sincerely,
>> Abha Vishwakarma
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