[mesa-users] bad angular_momentum_j

[Kenny Van]

Yes, but I was also hoping to create an adaptive way for MESA to adjust the
first step if necessary

On 4 August 2016 at 17:00, Pablo Marchant <pamarca at gmail.com> wrote:

> 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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