[Mesa-users] sound speed and mesa eos

[Michael Zingale]

is the EOS with ionization convex?  A non-convex EOS can cause hydro
problems.

On Thu, May 31, 2018 at 6:46 PM, Philip Chang <chang65 at uwm.edu> wrote:

> For what it is worth, r10398 had the same error. Any recommendations for
> an EOS with ionization that is reasonably easy to use (ideally with the
> multithreaded interpolation function)?
>
> Cheers,
>
> Phil
>
>
>
>
> On 05/30/2018 04:21 PM, Francis Timmes wrote:
>
>> perhaps try the latest public version, r10398.
>>
>> i will say there is work going on (today even!)
>> that further improves the mesa eos in the indicated regime.
>>
>> fxt
>>
>>
>>
>>
>>
>> On May 30, 2018, at 2:15 PM, Philip Chang <chang65 at uwm.edu> wrote:
>>>
>>> Hi Frank,
>>>
>>> r9575.
>>>
>>> -Phil
>>>
>>> On 05/30/2018 04:13 PM, Francis Timmes wrote:
>>>
>>>> hi phil,
>>>>
>>>> what version of mesa are you trying this with?
>>>>
>>>> fxt
>>>>
>>>>
>>>>
>>>> On May 30, 2018, at 12:34 PM, Philip Chang <chang65 at uwm.edu> wrote:
>>>>>
>>>>> Dear Mesa users,
>>>>>
>>>>> I am using mesa for a rather specialized purpose.  I have integrated
>>>>> the mesa eos into a hydrodynamics code (moving-mesh voronoi tessellation)
>>>>> and am using it for dynamically stellar problems.  Right now I have been
>>>>> simulating a 15 solar mass ZAMS star both in SPH and moving mesh mode.  SPH
>>>>> works great.  But the moving-mesh stuff crashes.
>>>>>
>>>>> The reason is that I need the sound speed or some estimate for the
>>>>> Riemann solve. In doing so, I get P, rho and gamma_1 from the mesa eos.
>>>>> However, I have found that the return values of gamma_1 are sometimes < 1
>>>>> -- bad -- and sometimes < 0 -- really bad.  As the sound speed is
>>>>> \sqrt{\gamma_1 P/rho}, this gives NaN's everywhere.  Negative gamma_1's are
>>>>> occuring around that appears to be ionization zones for H or He and are
>>>>> fairly strongly negative like -2 or -3.
>>>>>
>>>>> I'm trying to see what the best way of dealing with this is.  As MESA
>>>>> has a HLLC solver in it, it also relies on the sound speed to get an
>>>>> estimate for the signal velocities and contact wave pressure.  As far as I
>>>>> can tell, it would be vulnerable to the same issues that I am encountering.
>>>>>
>>>>> So my question is two fold.
>>>>>
>>>>> 1. Is the negative gamma_1 physical? I believe it is, as it occurs
>>>>> near ionization zones.
>>>>>
>>>>> 2. What is the proper way of computing sound speed in this
>>>>> circumstances?
>>>>>
>>>>> Thanks in advance for any help.
>>>>>
>>>>> Cheers,
>>>>>
>>>>> Phil
>>>>>
>>>>> _______________________________________________
>>>>> mesa-users at lists.mesastar.org
>>>>> https://lists.mesastar.org/mailman/listinfo/mesa-users
>>>>>
>>>>>
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
>
>


-- 
Michael Zingale
Associate Professor

Dept. of Physics & Astronomy • Stony Brook University • Stony Brook, NY
11794-3800
*phone*:  631-632-8225
*e-mail*: Michael.Zingale at stonybrook.edu
*web*: http://www.astro.sunysb.edu/mzingale
github: http://github.com/zingale
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