# [aspect-devel] cylindrical rigid body rotation

Ian Rose ian.rose at berkeley.edu
Mon Mar 3 13:53:18 PST 2014

Oops, sorry, missed that part.  I'm attaching
interpolate_onto_velocity_system().  Note that I have this rather than the
deal.ii version of the function because deal.ii can throw an exception that
the pressure element is non-interpolating (even though we are really only
interested in the velocity part).

I call the functions for computing the nullspace just before the solve, and
removing it just after.  Computing it should only be necessary if the mesh
has changed.

Cheers,
Ian

On Mon, Mar 3, 2014 at 1:41 PM, Wolfgang Bangerth <bangerth at math.tamu.edu>wrote:

> On 02/28/2014 03:36 PM, Ian Rose wrote:
>
>> It would be fairly easy to remove the net angular momentum as Wolfgang
>> described, and I may end up doing that, though what I have at the moment
>> takes
>> a different strategy.  Instead I explicitly construct rotation vectors and
>> project them out of the solution, i.e.
>>
>> v' = v - (v \cdot ( \omega \times r)) (\omega \times r)
>>
>> I don't know whether this or the angular momentum approach is preferable
>> (or
>> if there is some fatal flaw to my approach),  maybe somebody has some
>> insight
>> into that.
>>
>
> I don't know. If the density is constant, the two are equivalent. Either
> is fine to remove the null space. My inclination would be to remove the
> physical angular momentum. Do any of you geoscientists have preferences?
> Cedric?
>
>
> I need to write some glue code to make sure we only call this piece of
> code when it is necessary, i.e., if the geometry and the boundary
> conditions allow for a null space.
>
> @Ian: Can you also post your interpolate_onto_velocity_system() function?
> Where are the places where you call the functions that compute and remove
> the null space?
>
> Best
>
>  W.
>
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth               email:            bangerth at math.tamu.edu
>                                 www: http://www.math.tamu.edu/~bangerth/
>
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