[aspect-devel] Problem with active tracers & compositional fields

[Wolfgang Bangerth]

Felipe,

> For a target material body (e.g. a sphere) that has a compositional-density 
> contrast with respect to the environment, and having the system convecting (by 
> any means), what is the difference (in output, usefulness, etc.) between:
> 
>     a) Having the system domain fully mapped by active tracers and 
> compositional fields, some of which will track the kinematic evolution of the 
> target body.
> 
>     b) Having the system defined by compositional fields, and having the 
> target body mapped by passive tracers that track its kinematic evolution.

Using particles or fields achieves basically the same thing.

Traditionally, the mantle convection community has used particles, and so 
that's what you can do in ASPECT as well. On the upside, it allows you to keep 
interfaces sharp. On the downside, it may lead to poorly load-balanced 
problems if you work on large parallel computations. It also requires 
interpolating particle properties from particle locations to the locations of 
quadrature points, and this may introduce an error.

On the other hand, compositional fields are always well load balanced and 
don't require this interpolation, but they do introduce diffusion.

So it is essentially a *choice* whether you want to go with one or the other. 
You should give both a try.

Best
  W.

-- 
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Wolfgang Bangerth          email:                 bangerth at colostate.edu
                            www: http://www.math.colostate.edu/~bangerth/