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Re: [mesa-users] bad angular_momentum_j
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From: Kenny V. <kv...@ua...> - 2016-08-12 17:51:29
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Hi,
Unfortunately some of the models that I'm testing my modified MB on are
running into this odd issue. The angular momentum decreases more quickly
than the default
MB implemented in MESA but with a sufficiently small timestep this doesn't
appear to be a problem. What occurs after some time in evolution is the
angular momentum
suddenly goes negative. Now in the final step prior the the angular
momentum becoming negative the jdot does not appear to be large enough to
cause this sharp decrease.
The angular momentum near the final step is on the order of 10^52, while
the jdot is on order of 10^40. This jdot value is multiplied by the
timestep size converted to seconds
so the units are the same.
I added the following two lines into binary_evolove.f90 before the angular
momentum check
write (*,*) "angular_momentum_j", b% angular_momentum_j
write (*,*) "jdot", b% jdot * b% s_donor %time_step * secyer
So the jdot is taken directly from binary_evolve just to be sure.
I'm not sure if this is a problem that I have accidentally created with my
run binary_extras.f but I'm not sure how to fix this.
On 9 August 2016 at 10:37, Kenny Van <kv...@ua...> wrote:
> Hi Pablo,
>
> I figured out what the issue was. I didn't realize that the different
> timestep values were in different units so that caused issues.
>
> Thanks for the help
>
> On 8 August 2016 at 17:06, Kenny Van <kv...@ua...> wrote:
>
>> Hi Pablo,
>>
>> I'll verify the problem I'm running into and get back to you.
>>
>> As for the snippet I added before, that was just an attempt to see if I
>> could get MESA to decrease the timestep in the very first iteration. I
>> include a similar code in extra_binary_check_model and just use a small
>> initial timestep now.
>>
>> On 8 August 2016 at 17:02, Pablo Marchant <pa...@gm...> wrote:
>>
>>> Kenny, if you want to debug this just do some small edits to
>>> binary/private/binary_evolve.f90, in particular around these lines
>>>
>>> 257 ! get jdot and update orbital J
>>> 258 b% jdot = get_jdot(b, b% mtransfer_rate, b% xfer_fraction)
>>> 259 b% angular_momentum_j = b% angular_momentum_j + b% jdot*b%
>>> s_donor% time_step*secyer
>>> 260
>>> 261 if (b% angular_momentum_j <= 0) then
>>> 262 stop 'bad angular_momentum_j'
>>> 263 end if
>>>
>>> Since the stop condition literally has a check for negative angular
>>> momentum, I have a hard time believing what you say. You can put write
>>> statements in there to verify you are getting the numbers you expect. If
>>> this still gives you no answers, then if you want you can send a minimal
>>> example that fails (truly minimal please), and I can give it a look.
>>>
>>> PS:
>>>
>>> Just saw in more detail this snippet you posted before
>>>
>>> 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
>>>
>>> You said you add this to extras_binary_startup. That will do nothing,
>>> extras_binary_startup is only ran at the beginning of the simulation, and
>>> orbital angular momentum will be positive. You should be doing this in
>>> extras_binary_check_model.
>>>
>>> On Mon, Aug 8, 2016 at 9:12 PM, Kenny Van <kv...@ua...> wrote:
>>>
>>>> Hi,
>>>>
>>>> So unfortunately after some testing I've started running into some
>>>> problems that I cant quite solve. I've included a scaling factor in the
>>>> timestep check to try and retry the run if we encounter a problem with
>>>> angular momentum.
>>>> The problem that I'm running into now is that the code triggers the
>>>> "bad angular_momentum_j" portion even when the angular_momentum_j > 0. At
>>>> every step I have the extras_binary_check_model output the
>>>>
>>>> b% angular_momentum_j,
>>>>
>>>> as well as
>>>>
>>>> b% angular_momentum_j + b% jdot * b% s1% dt_next
>>>>
>>>> so I have an idea of what the current angular momentum is as well as
>>>> approx what it will be in the next timestep.
>>>>
>>>> At the point of the code breaking both of these values are positive and
>>>> I encounter the termination code
>>>>
>>>> STOP bad angular_momentum_j.
>>>>
>>>> I'm not quite sure what I can do from here.
>>>>
>>>> On 4 August 2016 at 21:40, Pablo Marchant <pa...@gm...> wrote:
>>>>
>>>>> You should be able to do that in extras_binary_startup. Anyhow, I'd
>>>>> just go for the simple approach of setting a small initial timestep, if its
>>>>> too small it will grow quite fast.
>>>>>
>>>>> On Fri, Aug 5, 2016 at 3:36 AM, Kenny Van <kv...@ua...> wrote:
>>>>>
>>>>>> 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 <pa...@gm...> 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 <kv...@ua...> 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 <kv...@ua...> 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 <pa...@gm...>
>>>>>>>>> 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 <pa...@gm...
>>>>>>>>>> > 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 <kv...@ua...>
>>>>>>>>>>> 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
>>>>>>>>>>>> mes...@li...
>>>>>>>>>>>> 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
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> 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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