Re: mesa-users] Manual Change of Accretion Composition

[Bill P. <pa...@ki...>]

On Jul 2, 2010, at 10:06 AM, Max Katz wrote:

> The simulation works just fine without accretion, and mass change without manual composition change works fine - it just accretes C and O (I noticed that after a while something started happening where the timestep got really small, but I didn't wait around long enough to see what happened).
> 

The default is to accrete the same composition as the surface, so you must have a WD with no H/He on the surface, right?

If it is happy accreting C/O at that rate but fails with H/He, perhaps the surface conditions are such that the H/He immediately ignites.

Try running it for long enough to make sure the surface has cooled below the H ignition range and try again.  Any change?


> 
> I tried your suggestion, both at your suggested settings and even smaller ones, and the same result occurred. I set max_backups_in_a_row to 50, and I noticed that after a number of retries, it eventually gives up on mass change and continues without it (lg Mdot is -99 on the pgplot screen); I even stopped it, increased the mass_change rate and restarted, and it continued on with zero mass change, without any backups or retries.


At each backup, the code reduces the timestep.  Eventually it hits the limit for doing mass change.

         ! these params provide the option to turn off mass change when have small timesteps.
         ! mass change doesn't do much in such cases except make convergence harder.
         mass_change_full_on_dt = 1d4 ! (seconds)
         mass_change_full_off_dt = 1d3 ! (seconds)
         ! between these limits, mass change is gradually reduced

For dt < mass_change_full_off_dt, you'll get lgMdot of -99 meaning it has been shut off.

-B