[mesa-users] Convergence issues when simulating massive eruptions by modifying .mod file

[Alexey Zinger]

Thanks, Bill!

I've used the mass_change parameter too, and it worked (sorry, forgot to
mention it - this was the first thing I've tried). But I guess there still
might be a difference between an instantaneous, 'geyser-like' eruption, and
a very rapid but gradual eruption at a pre-defined rate.

Anyway, the main reason I ventured into modifying the saved files was for
the sake of the energy conservation. I've expected it to be easier to
implement than to modify the code. Guess I was wrong :). I'll try to see
what I can do about adding this to the code.

Alexey


On Thu, Apr 18, 2013 at 11:32 AM, Bill Paxton <paxton at kitp.ucsb.edu> wrote:

> 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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