[Mesa-users] sound speed and mesa eos

[Michael Zingale]

sorry -- convexity for an EOS means that d2p/d2rho | s > 0 (second
derivative of p wrt rho at constant entropy).  This can be violated at
phase transitions.  Some approximate Riemann solvers require convexity.

On Thu, May 31, 2018 at 8:02 PM, Philip Chang <chang65 at uwm.edu> wrote:

> Michael,
>
> What do you mean by convex? I am new to all this.
>
> Also I will write a short test code tomorrow to reproduce the issue.
>
> Cheers,
> Phil
>
> Get Outlook for Android <https://aka.ms/ghei36>
>
> ------------------------------
> *From:* Michael Zingale <michael.zingale at stonybrook.edu>
> *Sent:* Thursday, May 31, 2018 5:48:32 PM
> *To:* Philip Chang
> *Cc:* Francis Timmes; mesa-users
> *Subject:* Re: [Mesa-users] sound speed and mesa eos
>
> 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
>
>


-- 
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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