[Mesa-users] Relaxing angular momentum

[Roque Caballero Navarro]

Dear all,

I'm aware of the existence of a number of "relax" options aimed to let some modifications be done gradually over several steps. In particular, I'm interesting in relaxing the angular momentum loss calculated in my other_torque routine.

According to MESA documentation, the following parameters are the relevant for my purpose:

relax_initial_angular_momentum = .false.
max_steps_to_relax_angular_momentum = 1000
timescale_for_relax_angular_momentum = 1d-10
max_dt_for_relax_angular_momentum = 1d-9
num_timescales_for_relax_angular_momentum = 1000
relax_angular_momentum_filename = ''

Additionally, it's mentioned that for relaxing angular momentum from current to specified over a certain amount of relaxation timescales. This is done by adding an extra torque term of the form and evolving the star without changing the composition for num_timescales_for_relax_angular_momentum times timescale_for_relax_angular_momentum.

s% extra_jdot(k) =  &
    (1d0 - exp_cr(-s% dt / (s% job% timescale_for_relax_angular_momentum*secyer))) * &
    (desired_angular_momentum(k) - s% j_rot(k)) / s% dt

I've some questions about how to modified the aforementioned parameters in a proper way, meaning that to make longer/shorter the period of time in which the angular momentum loss is applied:

  1.  If a want to extend the relaxing period, is it enough to assign to max_steps_to_relax_angular_momentum a bigger number, let's say 2000. What about num_timescales_for_relax_angular_momentum, should it be assigned the same value used in max_steps_to_relax_angular_momentum?
  2.  Which is the effect of modifying timescale_for_relax_angular_momentum and max_dt_for_relax_angular_momentum?

Basically I don't understand how to modify those parameters in the right way. I don't want just to throw there some values and try to figure out what's going on, so any hint about that will be very appreciated.


Kind regards,

Roque

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