[Mesa-users] Dh_div_H_limit

[Bill Paxton]

The trick is to copy the string from the terminal output and search for it in star/defaults/controls.defaults

Turns out there are 2 different limits related to dH for absolute and relative changes.

            !          'dH'                   dH_limit
            !          'dH/H'                 dH_div_H_limit

You want to then look at the info about dH_div_H_limit

         ! Limit on magnitude of relative decrease in any cell hydrogen abundance.
         ! `dH_div_H` here is `abs(xa(h1,k) - xa_old(h1,k))/xa(h1,k)`
         ! considers all cells except where have convective mixing.
         ! `dH_decreases_only` applies to `dH_div_H` also.


         !### dH_div_H_limit_min_H

         ! `dH_div_H` limits only apply where xa(h1,k) >= this limit.

      dH_div_H_limit_min_H = 1d-3


         !### dH_div_H_limit

         ! If max `dH_div_H` is greater than this, reduce the next timestep by `dH_limit/max_dH`.

      dH_div_H_limit = 0.9d0


         !### dH_div_H_hard_limit

         ! If max `dH_div_H` is greater than this, retry with smaller timestep.

      dH_div_H_hard_limit = 1d99



> On Jun 16, 2020, at 9:06 AM, Hannah Brinkman via Mesa-users <mesa-users at lists.mesastar.org> wrote:
> 
> Dear All,
> 
> When checking some of my recent models, I see a lot of times that the timestep is limited by DH/H. After checking this in the controls, I noticed that when this limiter appears, the timestep is decreased by DH_limit/max_DH. However, DH_limit is 1d99 by default. Wouldn't this lead to an enormous decrease of the timestep each time this control limits the timestep? Or do I misinterpret this limiter? I cannot find what determines max_dH.
> 
> I hope someone can explain to me what is happening in the star when this limiter shows up.
> 
> With kind regards,
> Hannah
> 
> 
> 
> 
>  <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>	Virusvrij. www.avg.com <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> <x-msg://54/#m_7616241268521075874_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>_______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20200616/525cacad/attachment.htm>