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

Thu Apr 18 13:07:15 EDT 2013

Hi Alexey,
what Bill means is that you do NOT need to modify the code.
You just can use the run_star_extras.f in your local src folder
and the hook other_energy to be sure that your total energy is conserved.
You have an option for doing this using both an implicit or explicit scheme.

To start have a look at

star/other/other_energy.f

and

star/other/other_energy_implicit.f

-m

On Apr 18, 2013, at 6:57 PM, Alexey Zinger wrote:

> 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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Dr. Matteo Cantiello ------------------------
Kavli Institute for Theoretical Physics 
Room 1226 Kohn Hall CA 93106-4030
University of California, Santa Barbara
---------------- http://matteocantiello.com/

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