[Mesa-users] numerical noise in Brunt-Vaisala -- eos issue

[Alina Istrate]

Hi Morgan,

really happy to hear that! Thanks for letting us know :)

Alina

On Wed, Jul 15, 2020 at 10:24 PM Morgan Taylor <taylormorgan32 at gmail.com>
wrote:

> Hi Alina and Josiah,
>
> Thank you for the post!  I've been having the same problem and Frank and I
> were also trying to understand the noise/spike.  Switching to PC removed
> the peak for me as well, so I'm grateful for the post.
>
> Thanks,
> Morgan
>
> On Wed, Jul 15, 2020 at 9:55 AM Alina Istrate via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
>
>> Hi Josiah,
>>
>> Thank you so much for the quick (and very kind) answer!
>>
>> By just using the PC eos, I am happy to report that it did remove the
>> noisy peak and now I have a beautiful Brunt -Vaisala plot.  I am sure that
>> the same fix would solve the problem for the more massive CO WD case.
>>
>>  Thanks again and looking forward to the new MESA release!
>>
>> Best regards,
>> Alina
>>
>>
>>
>> On Wed, Jul 15, 2020 at 4:21 PM Josiah Schwab <jwschwab at ucsc.edu> wrote:
>>
>>> Hi Alina,
>>>
>>> First, thank you for the excellent message. This is a great example of
>>> what a useful problem report looks like!
>>>
>>> Does anyone have a suggestion on how to get rid of this type of noise ?
>>>>
>>>
>>> As you suspected, I think you're hitting an eos discontinuity,
>>> specifically, the Z-switch between HELM and PC.  By default, that occurs at
>>> PC_min_Z = 0.999d0, which matches the location of the jump in your
>>> eos_sample.
>>>
>>> Evan was also displeased by these sudden switches between HELM and PC as
>>> a function of composition in WD interiors and led a successful campaign to
>>> eliminate PC_min_Z in future MESA versions.
>>>
>>> For now, I'd suggest putting that switch at Z = 0, so that MESA
>>> always uses PC.
>>>
>>> Please try
>>>
>>>     set_eos_PC_parameters = .true.
>>>     PC_min_Z = 0d0
>>>     mass_fraction_limit_for_PC = 0d0 ! default of 1d-3 can also cause
>>> small discontinuities
>>>
>>> in your star_job inlist and see if that helps.
>>>
>>> Let us know how it goes.
>>>
>>> Josiah
>>>
>>
>>
>> --
>> *--------------------------------------------------------------------*
>> Dr. Alina Istrate
>> Institute for Mathematics, Astrophysics & Particle Physics
>> Department of Astrophysics
>> Radboud University
>> P.O. Box 9010, MC 62
>> NL-6500 GL Nijmegen, The Netherlands
>> r: HG02.738
>> a.istrate at astro.ru.nl
>>
>>
>> _______________________________________________
>> mesa-users at lists.mesastar.org
>> https://lists.mesastar.org/mailman/listinfo/mesa-users
>>
>>

-- 
*--------------------------------------------------------------------*
Dr. Alina Istrate
Institute for Mathematics, Astrophysics & Particle Physics
Department of Astrophysics
Radboud University
P.O. Box 9010, MC 62
NL-6500 GL Nijmegen, The Netherlands
r: HG02.738
a.istrate at astro.ru.nl
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