[mesa-users] bad angular_momentum_j

Kenny Van kvan at ualberta.ca
Thu Aug 4 17:02:07 EDT 2016


Hi Everyone,

So I've checked the units for Jdot and they seem fine, Jorb/Jdot is on the
order of 1e12. The issue I'm currently running into is that the code
doesn't quite seem to be doing what I think it should be doing.
For extra checks I also included:

         write(*,*) "starting modified MB"
         if (b% angular_momentum_j <= 0) then
            write(*,*), "angular_momentum_j <= 0", b% angular_momentum_j
            b% s1% dt_next = min(b% s1% dt * 0.50, b% s1% dt_next)
            extras_binary_startup = retry
         end if

to extra_binary_startup. Just to check if my initial timestep is
sufficiently small and the MESA code doesn't seem to be triggering this. I
have a similar portion of code in extras_binary_check_model,
but I haven't reached a point where the simulation breaks to determine if
this works or not. Does the file binary_evolve.f90 trigger and instantly
kill the MESA simulation before the code checks the
run_binary_extras.f file?



On 3 August 2016 at 21:25, Kenny Van <kvan at ualberta.ca> wrote:

> Hey Pablo,
>
> Thanks for the advice, I'll try out the time step adjustment to see how it
> goes. I'll also double check the units to be 100% sure that I haven't
> crated any jdots that are a few orders too big.
>
>
> On 3 August 2016 at 20:53, Pablo Marchant <pamarca at gmail.com> wrote:
>
>> Also, be sure you are getting your units right. That's an easy way to
>> create absurdly large jdots (been there). For the process you are
>> considering, what's the decay timescale for Jorb (ie. Jorb/Jdot)? If that
>> is absurdly tiny then I'd worry.
>>
>> On Thu, Aug 4, 2016 at 4:50 AM, Pablo Marchant <pamarca at gmail.com> wrote:
>>
>>> Kenny, I'd recommend you to manually adjust the timestep, this is
>>> something we discussed here in mesa-users a while ago, copy from Rob
>>> Farmer's answer to create a hard timestep limit
>>>
>>> (Untested)
>>>
>>> In extras_startup:
>>> s%xtra1=0.d0
>>>
>>> extras_finish_step:
>>> s%xtra1=s%log_R
>>>
>>> extras_check_model:
>>>
>>> if( abs( 10**s%xtra1_old - 10**s%log_R) > EPS) then
>>>     extras_check_model = retry
>>>     s% dt = s%dt * SOME_SCALE_FACTOR
>>> end if
>>>
>>> And to create a soft timestep limit:
>>>
>>> (also untested)
>>>
>>> if( abs( 10**s%xtra1_old - 10**s%log_R) > EPS) then
>>>     s% dt_next = min(s% dt_next, s%dt * SOME_SCALE_FACTOR)
>>> end if
>>>
>>> If the first timestep is the issue, then set a smaller initial timestep.
>>> Check this from defaults/star_job.defaults
>>>
>>>  435          !### set_initial_dt
>>>  436          !### years_for_initial_dt
>>>  437          !### seconds_for_initial_dt
>>>  438          ! if true, set initial timestep, dt, in years
>>>  439
>>>  440       set_initial_dt = .false.
>>>  441       years_for_initial_dt = 0
>>>  442       seconds_for_initial_dt = 0
>>>
>>> On Wed, Aug 3, 2016 at 4:56 PM, Kenny Van <kvan at ualberta.ca> wrote:
>>>
>>>> Hi,
>>>>
>>>> I'm currently working on adapting additional magnetic braking terms
>>>> into MESA using the run_binary_extras.f file. I'm currently running into an
>>>> issue where the amount of angular momentum being removed is too great in a
>>>> single timestep and causing the simulation to break. Looking at the code it
>>>> seems like the MESA binary evolution dies immediately if the angular
>>>> momentum loss is too great instead of retrying with a smaller timestep. Is
>>>> there a way to get MESA to retry with a smaller timestep when it encounters
>>>> this issue?
>>>>
>>>> Thanks
>>>>
>>>> ------------------------------------------------------------
>>>> ------------------
>>>>
>>>> _______________________________________________
>>>> mesa-users mailing list
>>>> mesa-users at lists.sourceforge.net
>>>> https://lists.sourceforge.net/lists/listinfo/mesa-users
>>>>
>>>>
>>>
>>>
>>> --
>>> Pablo Marchant Campos
>>> M.Sc on Astrophysics, Universidad Católica de Chile
>>> PhD student, Argelander-Institut für Astronomie
>>>
>>
>>
>>
>> --
>> Pablo Marchant Campos
>> M.Sc on Astrophysics, Universidad Católica de Chile
>> PhD student, Argelander-Institut für Astronomie
>>
>
>
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