[Mesa-users] Loss of angular moment
Rob Farmer
r.j.farmer at uva.nl
Mon Apr 23 05:37:49 EDT 2018
>Don't you think the same?
Ah i never ran your model long enough, its always easiest (and faster) to
send models that are "near" problem points, so people don't waste time
constantly rerunning uninteresting bits of evolution.
I think you have a scale issue in your calculation:
omega(1) ~ 10**-5
irot(1) ~10**21
jdot(1) ~10**-10
So the existing angular momentum of the surface is ~ 10**21 * 10**-5 =
10**16 to which you then try to -10**-10, even your -1 value is small
compared to the existing angular momentum.
> could it be that I'm not propagating properly back the loss of angular
moment?
if your not sure what the codes does, have a look at the code:
grep -rinI other_torque $MESA_DIR/star/p*/*
The look in star/private/solve_omega_mix.f90 then follow where extra_jdot
is used.
Rob
On 21 April 2018 at 16:52, Roque Caballero Navarro <rcaballeron at hotmail.com>
wrote:
> Hi Rob,
> I agree with you that it's needed a rotating model and I get it using
> the following configuration:
>
> * ! Rotation off until near ZAMS*
> * change_rotation_flag = .false.*
> * new_rotation_flag = .true.*
> * new_surface_rotation_v = 20 ! solar (km sec^1)*
> * set_near_zams_surface_rotation_v_steps = 10*
>
> The star starts to rotate with it approaches to the ZAMS. Using the
> "debug" option of my routine, I can confirm the other_torque hook is called
> as soon as the rotation is activated. I also dump the calculated loss of
> angular moment (and other partial results) in the history fie and non-zero
> values are reported. I'd say that the code is properly invoked. Don't you
> think the same? I'll do also some test with the rotation activated since
> the beginning.
>
> Regarding s% omega_avg_surf value, I've also checked that isn't null
> when other_torque is invoked. The same values are reported in the history
> file as well. Nevertheless, I'll follow your advice and take a deeper look
> into star_utils.
>
> So Rob, for me the question is, if the model is rotating and
> other_torque routine is invoked (let's put apart if the calculations done
> on it are right or not), could it be that I'm not propagating properly back
> the loss of angular moment? I'm assuming that even if I used an "absurd"
> value, an impact on s% omega_avg_surf value, right?
>
> Many thanks for your help.
>
> Kind regards,
>
> Roque
>
> On 04/20/2018 05:27 PM, Rob Farmer wrote:
>
> Hi
> To use other_torque you need a rotating model, you need to set:
>
> change_rotation_flag = .true.
>
> in your star_job inlist to change the rotation flag, new_rotation_flag
> only changes the rotation flag if change_rotation_flag = .true.
>
> The other issue is your using s% omega_avg_surf, but that gets set after
> the other_torque call. When using the other_ routine the best bet is to
> always "goto the source" of the stellar structure data, rather than any use
> any shorthand variables as they may not be set. In this case you'll want to
> look at the s% omega array which stores the rotation information for the
> star. See set_surf_avg_rotation_info in star/private/star_utils.f90 for how
> s% omega_avg_surf is implemented, you'll want to copy the relevant bits in
> your run_star_extras file for computing the surface averaged value.
>
> Rob
>
>
> On 20 April 2018 at 14:18, Roque Caballero Navarro <
> rcaballeron at hotmail.com> wrote:
>
>> Hi Rob,
>>
>> Please find attached the requested files.
>>
>> Kind regards,
>>
>> Roque
>> ------------------------------
>> *De:* Rob Farmer <r.j.farmer at uva.nl>
>> *Enviado:* viernes, 20 de abril de 2018 12:12
>> *Para:* Roque Caballero Navarro
>> *Cc:* mesa-users at lists.mesastar.org
>> *Asunto:* Re: [Mesa-users] Loss of angular moment
>>
>> Hi
>>
>> This is not enough information to help you. Please provide your inlists
>> and run_star_extras.f
>>
>> Rob
>>
>> On 20 April 2018 at 12:06, Roque Caballero Navarro via Mesa-users <
>> mesa-users at lists.mesastar.org> wrote:
>>
>> Dear all,
>>
>> I'm trying to implement a magnetic braking routine based on Matteo
>> Cantiello exercise propose during the Mesa school 2012 (here the details
>> <http://cococubed.asu.edu/mesa_market/ewExternalFiles/2012_cantiello.zip>.)
>> Well, for doing it I'm using the hook other_torque and the code is
>> implemented, as usual, in the run_extras_star.f file. Below you can see the
>> core part of the implementation:
>>
>> 1. * if (s% use_other_torque) then*
>> 2.
>> 3.
>> * !Star data *
>> 4.
>> * r_st = s% r(1) *
>> 5.
>> * m_st = s% m(1) *
>> 6.
>> * omega_surf = s% omega_avg_surf *
>> 7.
>> * m_dot = s% star_mdot *
>> 8.
>> 9.
>> * v_esc = 618 * (((Rsun/r_st)*(m_st/Msun)))**0.5 *
>> 10.
>> 11.
>> * v_inf = 1.92 * v_esc *
>> 12.
>> 13.
>> * B = s% x_ctrl(6) *
>> 14.
>> 15. *eta_surf = abs(((r_st/Rsun)**2/B**2)/(m_dot * v_inf))*
>> 16.
>> 17.
>> * j_dot = two_thirds * m_dot * omega_surf * (r_st/Rsun)**2 *
>> eta_surf *
>> 18.
>> 19. * s% extra_jdot(1) = j_dot*
>> 20. * !s% extra_jdot(1) = -1*
>> 21.
>> 22.
>> * if (debug_use_other_torque) then *
>> 23.
>> * write(*,*) "Rsun=", Rsun, "Msun=", Msun, "r_st=", r_st,
>> "m_st=", m_st, & *
>> 24.
>> * "v_esc=", v_esc, "v_inf", v_inf, "B", B, "m_dot",
>> m_dot, "eta_surf", eta_surf, & *
>> 25.
>> * "omega_surf", omega_surf, "j_dot", j_dot *
>> 26.
>> * end if *
>> 27.
>> 28.
>> * s% x_ctrl(7) = v_esc *
>> 29.
>> * s% x_ctrl(8) = v_inf *
>> 30.
>> * s% x_ctrl(9) = eta_surf *
>> 31.
>> * s% x_ctrl(10) = j_dot *
>> 32.
>> * s% x_ctrl(11) = m_dot *
>> 33.
>> 34. * end if*
>>
>> The input parameters for the calculation are the radius, mass, loss of
>> mass and velocity at surface (lines 4 to 7). After some calculations, I end
>> up with a loss of angular moment j_dot which I pass back using the array
>> extra_jdot (line 20). After running a simulation with this routine
>> activated, I'd expect to have lower values of velocity at surface but I
>> couldn't find any difference. I've even assigned an unreal value (line 20)
>> to the extra_jdot array but nothing changed. So, something must be wrong or
>> missing in the implementation. As you maybe has already noticed, I'm just
>> providing a value to one cell, the outermost one. I'm assuming that only
>> this layer is affected by the magnetic braking effect.
>>
>> As usual, any help is more than welcome.
>>
>> Kind regards,
>>
>> Roque
>>
>>
>>
>>
>>
>>
>>
>
>
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