[mesa-users] Experimenting with adjust_mlt_gradT_fraction

Bill Paxton paxton at kitp.ucsb.edu
Mon Aug 11 11:18:06 EDT 2014

On Aug 11, 2014, at 5:50 AM, Ehsan Moravveji wrote:

> Dear all,
> Special greetings to those of us who already started their morning in the exciting Summer School. 
> I was thinking of a gedankenexperiment to modify the temperature gradient in the semi-convective layers of a 15Msun main sequence star. There is a wonderful variable already implemented to vary gradT between gradr and grad_ad, called "adjust_mlt_gradT_fraction" (hereafter called f in the plots and the following text). I have traced this variable in hydro_vars.f and mlt_info.f in /star/private. 
> I took three values of f = 0.00, 0.25 and 0.50. Then, I use the other_mlt hook in my run_star_extras to change the value of f "only" in the semi-convective zones. Indeed, it works. Please see the attached gradT.png plot. 
> However, the temperature and pressure profiles and all other hydro variables should be modified as well to be consistent with ad-hoc modifications in gradT.

Hi Ehsan,

The pressure and temperature profiles are set by the newton solver to approximate solutions to the structure equations.  The value of gradT appears in the temperature equation, so changing gradT will cause the solver to come up with a different solution for the temperature profile, and since everything depends on everything else that will cause a change in the pressure profile which is also a product of the solve.

In other words, gradT is one of the inputs while temperature and pressure are outputs of the solve.  Since gradT and the other right hand sides depend on the values of the variables such as T and P, i.e. we have an implicit system to solve, the values of the variables that will give a good enough solution must be found iteratively.   But it is the solver that determine profiles for T and P; you only indirectly influence the outcome by setting the values for gradT. 

hope that helps,

> In other words, direct differentiation of temperature and pressure profiles must consistently result in gradT for any arbitrary value of f == adjust_mlt_gradT_fraction.
> Currently, this is not the case. To convince myself, I did three other plots of T, P and Rho in the same semi-convective zone; see the attachments, please.
> I totally understand that gradT and hydro_vars are evaluated across different modules, and that can make life complicated. But, I desire having self-consistent outcome in my profile files.
> In case one likes to reproduce the results, I have attached my inlist and run_star_extras.f (compatible with v.6794).
> I would be grateful if you enlighten me with your comments/feedbacks. 
> Kind regards,
> Ehsan.
> <gradT.png>
> <Density.png><Pressure.png><Temperature.png>
> <inlist_general><run_star_extras.f>
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