[mesa-users] Convergence issues when simulating massive eruptions by modifying .mod file
Bill Paxton
paxton at kitp.ucsb.edu
Thu Apr 18 12:32:43 EDT 2013
Hi,
1) instantaneous mass loss
you can use very high mass loss rates (e.g. 10 to 100 Msun/year) with small timesteps (e.g., 1d-2 years) to remove a large amount of mass in a short time.
rather than playing with a wind recipe to remove the mass, you can directly set the "mass_change" parameter in the inlist.
mass_change = 0d0 ! rate of accretion (Msun/year). negative for mass loss.
! this only applies when the wind scheme = ''
you can set the max timestep too
max_years_for_timestep = 0 ! max_years_for_timestep <= 0 means no upper limit.
the code might not be happy making the jump to very high mdot in a single step,
so you may need to use these to turn the mass_change on.
relax_mass_change = .false.
relax_mass_change_min_steps = 10
relax_mass_change_max_yrs_dt = 10 ! years
relax_mass_change_init_mdot = 0 ! Msun/year
relax_mass_change_final_mdot = 0 ! Msun/year
you may also need to use them again after mass removal to turn the mass_change off.
2) energy conservation with mass loss
interesting question!
you can compute the energy loss rate for the mass_change rate yourself and remove that amount from
the envelope using the "other_energy" hook. once you have it working, let us know so we can add it as an option. ;-)
cheers,
Bill
On Apr 18, 2013, at 8:43 AM, Alexey Zinger wrote:
> Hi Josiah,
>
> Thanks for pointing me to the relaxation routines direction! I haven't yet looked into those. Hopefully, they might get me through some of the simulations.
>
> Before fiddling with the .mod files I've tried to simulate the eruptions using the built-in wind schemes with high wind coefficients. There are two issues with this: first, I'm trying to observe how the star adjusts to a (nearly) instantaneous mass removal, and all of the wind routines remove mass gradually. Second, as far as I know, the wind schemes in the code do not account for the conservation of energy, and this might be important when so much mass is removed so quickly.
>
> Alexey
>
>
> On Thu, Apr 18, 2013 at 9:56 AM, Josiah Schwab <jwschwab at berkeley.edu> wrote:
> > I do this by artificially modifying the saved model file and restarting the evolution with loading that file.
>
> I tried manipulating model files once and in my experience (and as you seem to be finding) that way lies madness :)
>
> Is there something about MESA's built-in routines for changing the mass of model that are insufficient/inappropriate for what you want to explore? What other (if any) approaches have you tried?
>
> My personal recommendation is to use an existing relaxation routine or to add something you write yourself to run_star_extras.f to do the relaxation. I think it will save you a lot of grief.
>
> Perhaps others will share their experiences.
>
> Josiah
>
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