[aspect-devel] Open boundaries + tracers

Lev Karatun lev.karatun at gmail.com
Sun Dec 4 19:32:33 PST 2016

Thanks Wolfgang, it's an important clarification - I indeed was attempting
to use the particles as alternative to compositional fields.

Best regards,
Lev Karatun.

2016-12-04 19:15 GMT-05:00 Wolfgang Bangerth <bangerth at tamu.edu>:

> On 11/25/2016 03:43 PM, Rene Gassmoeller wrote:
>> I recently added tracers to my models, they work great, thank you for
>> adding
>> them! I was trying to incorporate open boundaries (by Anne Glerum) into my
>> models, they work just fine too. However, when I included both of them, I
>> ran
>> into a problem: the cells near the open boundary, through which constant
>> inflow of material is happening end up not having enough tracers (and
>> later
>> not  having any tracers at all) (see attached screenshot). I decreased
>> the CFL
>> number from 0.5 to 0.1, but it didn't help. So I was wondering if you
>> could
>> tell me what the possible causes are?
> Lev -- I don't think this question was actually answered. The cause is
> that you start with particles everywhere, and then you let these particles
> be transported along with the flow. If you have inflow, then you have
> material flowing across the boundary into the domain (but this new material
> does not bring with it any particles), and material that was close to the
> boundary flowing further inside (taking along the particles that were close
> to the boundary). The result is that you have no particles close to the
> boundary after some time -- independent of how large or small your mesh
> size, time step, or CFL number are.
> What Rene and John describe is in essence a way to *generate particles in
> cells that have too few particles*, by "cloning" the ones that are in the
> vicinity. If all you care about is to use particles to visualize the flow,
> then that is appropriate. But if, for example, you wanted these particles
> to carry properties such as the accumulated strain, then this is not
> appropriate because the new particles will have the accumulated strain of
> the particles in the vicinity, not what would be appropriate for a new-born
> particle just making its way across the inflow boundary.
> For these sorts of cases, we would have to implement a way to create
> particles along inflow boundaries from scratch, rather than interpolating
> from existing particles. But this is not currently implemented.
> Best
>  W.
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth          email:                 bangerth at colostate.edu
>                            www: http://www.math.colostate.edu/~bangerth/
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