[mesa-users] questions about the "Eulerian" scheme for eps_grav

[Dean Townsley]

Hi Masanobu,

Nice to have you using this stuff!  Hopefully I can help you a bit with 
your questions.

First, if it's not too much trouble, you might want to use the most 
recent release (7184).  This release contains some changes to how the 
boundaries for the Eulerian vs. Lagrangian forms for eps_grav are 
determined, and some updates for consistency with how the mesh behaves 
(constant dq or constant dm) in these regions.  With this new version 
min_dxm_Eulerian_div_dxm_added should work.  Please let me know if it 
doesn't do what you expect and I can investigate.

I think the CpTMdot controls aren't being used anymore because either 
the "Eulerian" or Lagrangian form of eps_grav is valid in the whole star 
so that it doesn't make sense to limit on this quantity anymore.   I 
still need to clear this control out cleanly, sorry about that.  The 
control used to adjust for accuracy  (or validity) is now 
eps_grav_time_deriv_separation, but you shouldn't need to adjust it if 
you push the transition region far into the star anyway.  I reproduce 
the comment about it below, since it may be that you don't need to push 
the Eulerian region over the whole star and you can just let this 
control adjust to the mass added each time step for you.


          !### eps_grav_time_deriv_separation

          ! Separation (in grid cells) over which eps_grav can be 
time-differenced when Mstar changes
          ! The mesh has two major regions - an interior region where 
the cells are
          ! Lagrangian and an outer region where they are homologous 
(constant dq =dm/M).
          ! There is also a small transition region between these two.  
In the Lagrangian
          ! region Ds/dt is evaluated with a Lagrangian finite 
difference in time, while in the
          ! homologous region Ds/dt is evaluated with a finite 
difference in time at constant q
          ! plus an advection-like term accounting for the movement of 
the q boundaries in mass.
          ! In the transition region, these two derivatives are 
combined.  This means that at
          ! the edges of the transition region, finite differences may 
cross cell boundaries.
          ! This control determines how the mesh for the end of the 
current timestep is
          ! placed to ensure that finite differences cross no more than 
this many cell
          ! boundaries.

       eps_grav_time_deriv_separation = 1.5




On your second question:  The new material is added at the outside of 
the star - not throughout the star.  The size of the mesh zones change 
in the "Eulerian" or "constant q" part of the star (which may be the 
whole star if you push the boundary that deep), but the entropy and its 
derivatives are evaluated locally, not with respect to the surface.  So 
a parcel of material enters the star at the surface with the same 
entropy as the surface, but its entropy then evolves appropriately as it 
moves down through the star.


Hopefully that helps.  Like I said, let me know if the newer version 
doesn't do what you expect.

Dean


On 11/09/2014 07:06 PM, Masanobu Kunitomo wrote:
> Dear all,
>
>
> I would like to ask two questions about (1) changing the region of 
> \93Eulerian scheme\94 (s% k_below_Eulerian_eps_grav) and (2) the validity 
> of the Eulerian scheme. I am using ver. 6596 and working on a 
> protostar\92s evolution with intense accretion (the mass accretion rate 
> is 1e-5Msun/yr and CpTMdot/L is at most ~100).
>
>
> (1)
> I would like to try the case that eps_grav is calculated by the 
> \93Eulerian\94 scheme in the entire star, namely s% 
> k_below_Eulerian_eps_grav = s% nz (although this may not be good 
> because the Eulerian scheme can cause a numerical diffusion).
> I tried to set a large \93min_dxm_Eulerian_div_dxm_added\94 in the inlist 
> file, but this did not work. Next I tried to modify the subroutine 
> "set_Eulerian_Lagrangian_for_eps_grav\94 in 
> \93mesa/star/private/evolve.f\94. I tried some modifications such as 
> \93dxm_kA = s% xmstar\94, but it did not work. (In fact, even if I write 
> \93stop\94, it was not reflected...) Is it inappropriate to modify the 
> evolve.f file?
>
> (2)
> If my understanding is correct, in the Eulerian scheme, the newly 
> accreted mass is distributed in the entire star uniformly and 
> instantaneously, and its entropy is assumed to match the local value 
> of the stellar interior as shown in the Fig. 6 of Sugimoto et al. 1981 
> (I have attached this figure). If the star is radiative, the accreting 
> material\92s entropy can be much lower than that of the stellar surface. 
> Thus, I think this underestimates the accreting material\92s entropy. Is 
> this correct?
>
>
>
> I apologise if these are already discussed in this mailing list.
> I appreciate any comments. Thanks in advance!
>
> Best wishes,
> Masanobu
>
> --
> Masanobu Kunitomo
> Ph.D. student / JSPS Research Fellow
> Tokyo Institute of Technology
> Dept. of Earth and Planetary Sciences
> Email: kunitomo at geo.titech.ac.jp <mailto:kunitomo at geo.titech.ac.jp>
>
>
>
> ------------------------------------------------------------------------------
>
>
> _______________________________________________
> mesa-users mailing list
> mesa-users at lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/mesa-users

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20141109/a69304e3/attachment.html>