Re: mesa-users] Manual Change of Accretion Composition

[Max K. <ka...@rp...>]

Bill,

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).

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.

- Max

On Fri, Jul 2, 2010 at 12:08 PM, Bill Paxton <pa...@ki...> wrote:

>
>
> Hi Max,
>
> The change in accretion composition should be fine.  Perhaps the problem is
> the abrupt start of accretion at the 5d-9 rate.
>
> Let's separate the 2.   What happens if you do the 5d-9 mass change without
> changing the accretion composition?
>
> Also, you should try manually turning up the accretion rate while keeping
> the timestep small.
>
> Try something like max_years_for_timestep = 1d-7 to start with, and
> mass_change = 1d-12 -- or whatever it
> takes to get things to converge.   (BTW: I'm assuming that everything works
> without accretion turned on, right?)
> Let things run for a while until it is happy (i.e., running at max allowed
> timestep).   Then start increasing the
> mass_change -- at each increment, let it run until it is happy, then
> increase again.  Once you reach the
> desired accretion rate, remove the limit on max_years_for_timestep.
>
> This is a crude manual version of what the various "relax" operations do.
>  And if you feel ambitious, you can
> write your own relax routine to do "relax_to_mass_change".
>
> Let me know how it goes.
>
> -Bill
>
>
>
>
>
> On Jul 2, 2010, at 6:46 AM, Max Katz wrote:
>
> > Hello,
> >
> > In an attempt to create my own nova, I used the model 1.000_Tc_3e7.mod in
> mesa/data/star_data/white_dwarf_models. This is a pure C/O white dwarf of 1
> solar mass. The goal is to get it to go nova, so I set an accretion rate of
> 5 x 10^-9 (units are solar masses per year). However, the default behavior
> for accretion is to use the same composition for the accreted matter as
> there is on the surface. Since adding C and O to the surface wouldn't yield
> the nova I was looking for, I set the following in the controls namelist:
> >
> > mass_change = 5d-9
> > accrete_same_as_surface = .false.
> > accretion_h1 = 0.75
> > accretion_h2 = 0.
> > accretion_he3 = 0.
> > accretion_he4 = 0.25
> >
> > However, when I try to run with these settings on, the run cites
> "adjust_mass_failed", and crashes after hitting the default max number of
> backups (15). I tried the same settings on a different case and got the same
> error. If anyone has experience with changing the accretion composition, I
> would appreciate it if you could give some insight as to what I might be
> doing wrong. Thanks.
> >
> > Max Katz
> > Rensselaer Polytechnic Institute
> > Physics, Class of 2011
> >
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