[Mesa-users] Using other_momentum in Riemann solver

[Jing-Ze Ma]

Hi Josiah,


Thank you for your reply. I looked deeper into the code and you are absolutely right. It appears that extra_pressure only shows up in hydro_energy and hydro_momentum as an additional pressure. I wonder if the presence of extra_pressure in momentum equation and energy equation will cause some problem when fitting the interior solution to the atmosphere. I will also try to see if it would be too much trouble to add other_pressure routine into Riemann solver.


Thanks a lot!


Regards,
Jing-Ze


-----Original Messages-----
From:"Josiah Schwab" <jwschwab at ucsc.edu>
Sent Time:2021-02-27 07:32:04 (Saturday)
To: "Jing-Ze Ma" <mjz18 at mails.tsinghua.edu.cn>
Cc: "Jing-Ze Ma via Mesa-users" <mesa-users at lists.mesastar.org>
Subject: Re: [Mesa-users] Using other_momentum in Riemann solver


Hello Jing-Ze,


I was wondering how the other_pressure routine enters MESA r15140.
When I grep into star/private for extra_pressure I get this message:
grep -rin extra_pressure *.f90


alloc.f90:1027:            call do1(s% extra_pressure, c% extra_pressure)
alloc.f90:1028:            if (failed('extra_pressure')) exit
hydro_energy.f90:623:            if (s% use_other_pressure) PR_18%val = PR_18%val + s% extra_pressure(k-1)
hydro_energy.f90:647:         if (s% use_other_pressure) PL_18%val = PL_18%val + s% extra_pressure(k)
star_utils.f90:3370:         if (s% use_other_pressure) XP_18%val = XP_18%val + s% extra_pressure(k)


And I am not sure how to interpret these.
The main questions I want to ask are:


1. Is s% extra_pressure a P_extra so that P_total = P_rad + P_gas + P_extra ? When I refer to s% P(k), is it correct that I get P_total?


2. If so, can extra_pressure automatically enter the momentum equation and energy equation in Riemann solver?


3. Will this extra_pressure affects thermodynamic quantities?


Your search for a key string (followed by reading the surrounding code) is a good strategy for understanding what happens inside MESA.


As you showed, the way in which extra_pressure enters the equations is quite limited, and so the answers to your questions 1-3 are no.


Josiah
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