[mesa-users] ] rotation: problem with smooth parameters

[Pierre Lesaffre]

  Dear Bill,

  I like your point about rotation and smoothing. It reminds me of my 
attempt to introduce full MLT in the cambridge STAR code, which resorts to
some kind of fudging factor to smooth things near the edges of convective 
regions. In Flash_the_Tortoise, the trick was to use two first order 
equations (for chemical composition and its gradient) instead of one 
second-order equation for the chemical composition equations. Then no
fugding is necessary and the full value of MLT diffusion can be used. 
  However, this means one needs to be careful at the edges with the 
boundary conditions for the gradients... where it relates to Dave's 
comment: I think indeed we (or at least I !) don't yet understand properly 
the physics of the boundary conditions between convective and radiative 
regions. 
  Rest well to finish off your flu, and may the only bugs you catch be the 
ones in MESA :) !

  Cheers,

Pierre.
  
On Thu, 24 Jan 2013, David Arnett wrote:

> Rotation and overshooting are not separate issues; they are both
> facets (and closely related) of fluid dynamics. The apparently better
> behavior of overshooting relative to rotation is an illusion, as 3D
> simulations make clear. We have a lot to learn before we can project
> this back into 1D. Matteo is right; we can compromise by using
> observational data, but really, we need to solve the physics before
> our stellar models will be predictive.
> 
> -- 
> David Arnett
> Regents Professor
> Steward Observatory
> University of Arizona
> 
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