[Mesa-users] Fwd: other_momentum subroutine

sheyda najafi sh.najafi8590 at gmail.com
Mon Oct 23 03:32:07 EDT 2017


Dear Francis

I changed the resolution and it seems that it was numerical instability in
the code. Thank you very much for your suggestion it was really helpful.


Best Regards,



Sheyda Najafi

On Sat, Oct 21, 2017 at 10:48 PM, Francis Timmes <fxt44 at mac.com> wrote:

> hi sheyda,
>
> thanks for relevant files.
>
> i regret to say that i do not have the time to more fully engage your
> research project,
> but now armed with the relevant files, maybe another mesa user can help
> you more.
>
> fxt
>
>
>
>
> > On Oct 21, 2017, at 4:00 AM, sheyda najafi <sh.najafi8590 at gmail.com>
> wrote:
> >
> >
> > Dear Francis
> >
> > Thank you very much. I have attached the run_star_extras.f file. In the
> other_momentum subroutine i have defined new variable named xn(i) which is
> dependent on density in each zone therefore i assumed that it is defined at
> cell center and added the extra force  (- beta* (clight**2)* (rho)*
> (d(xn)/dm) ) as follows
> >
> > -((   xn(k+1)-    xn(k)) / s% dm_bar(k)) * beta* (clight**2)* ( s% rho).
> >
> > Also the inlist_project for pre MS and MS phases and inlist_load for the
> RGB phase of 1 solar mass star ( without rotation) are attached.
> >  I am not sure whether i chose suitable values for the parameters in the
> inlist_load or i must add some other information and change the values from
> their defaults(controls_defaults).
> >  I would be grateful if you could help me.
> >
> >
> > Best Regards,
> >
> >
> >
> > Sheyda Najafi
> >
> > On Fri, Oct 20, 2017 at 6:39 PM, Francis Timmes <fxt44 at mac.com> wrote:
> > one standard technique to investigate if an effect is numerical or
> perhaps physical
> > is to conduct a convergence study with respect to mass resolution and
> time resolution.
> > if the behavior changes significantly with improved mass and/or time
> resolution,
> > then its probably numerical.
> >
> > you don't include your run_star_extras, so no one knows how you are
> coding other_momentum,
> > but you should carefully study how mesa sets up its momentum equation,
> paying  attention
> > to what quantities are defined at cell faces and which are defined at
> cell center.
> >
> > another suggestion, since your changing the momentum equation, is to
> explore the
> > velocity and radial coordinate of your models to see if they make sense
> relative
> > to the other assumption of your model (e.g., mass loss, etc).
> >
> > good luck!
> >
> > fxt
> >
> >
> >
> >
> > > On Oct 20, 2017, at 4:07 AM, sheyda najafi via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
> > >
> > >
> > > ---------- Forwarded message ----------
> > > From: sheyda najafi <sh.najafi8590 at gmail.com>
> > > Date: Fri, Oct 20, 2017 at 1:57 PM
> > > Subject: other_momentum subroutine
> > > To: mesa-users at lists.sourceforge.net
> > >
> > >
> > > Hi MESA users
> > >
> > > I am trying to find the evolution of the RGB star in the presence of
> an extra force ((-Beta) * dx/dm), which is added to the other_momentum
> subroutine as follows
> > >
> > > dp/dm = - G m/4 pi r^4 - (Beta) * dx/dm
> > >
> > > where Beta is an arbitrary constant.
> > >
> > > I have run mesa for different Betas and as you can see in the attached
> plot (Tip of the RGB.png), the temperature of the Tip of the Red Giant
> Branch increases for (0<Beta<300) but for ( 300<Beta<400) there are some
> instabilities in the evolutionary track of the star and for (450<Beta<500)
> the instabilities increase in such a way that  the star leaves the standard
> track which is shown in the plot (HR.png) for Beta=450, and the code
> terminates therefore the evolution stops after RGB phase.
> > >  Also for (Beta>500) the code does not converge even in zams phase.
> > >
> > > My question is whether we can have physical interpretation for the
> instabilities in the evolutionary track of the star or it is just the
> instability in the numerical code?
> > >
> > > In other words, is it admissible that the extra force becomes so large
> for beta>300, and makes the star unstable so the star can not live any
> longer and these models are not physical, or it is just a large quantity
> that makes the numerical code unstable?
> > >
> > > Thank you in advance
> > >
> > >
> > >
> > > Sheyda Najafi
> > >
> > >
> > > <HR.png><Tip of the RGB.png>
> >
> >
> > <run_star_extras.f><inlist_load><inlist_project>
>
>
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