[mesa-users] bad angular_momentum_j

Pablo Marchant pamarca at gmail.com
Thu Aug 4 19:00:06 EDT 2016


Are you running into these issues at the first timestep? If so, you need to
ensure the first step is small as well.

On Thu, Aug 4, 2016 at 11:02 PM, Kenny Van <kvan at ualberta.ca> wrote:

> 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
>>>
>>
>>
>


-- 
Pablo Marchant Campos
M.Sc on Astrophysics, Universidad Católica de Chile
PhD student, Argelander-Institut für Astronomie
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