Re: [Libmesh-users] Periodic boundaries for circular segment domains

[David K. <dav...@ak...>]

On Thu, Mar 1, 2018 at 10:50 AM, Roy Stogner <roy...@ic...>
wrote:

>
> On Wed, 28 Feb 2018, David Knezevic wrote:
>
> I would like to implement a periodic boundary condition on a model with
>> circular symmetry, e.g. solve on sector of a disk with periodicity. To
>> implement this it seems like all I'd need to do is subclass
>> PeriodicBoundary and override get_corresponding_pos() to impose the
>> appropriate rotation rather than just a translation, and then add the
>> PeriodicBoundary subclass object to the system in the usual way. Is that
>> indeed all that's required,
>>
>
> Yes, if it's working correctly!
>
> or would we need something more?
>>
>
> If you have something vector or tensor valued, like e.g. a *velocity*
> variable, and your formulation doesn't already use polar coordinates
> for the components of that variable, then you're in trouble if you
> want anything other than 0/90/180/270 degree rotations, because we
> don't currently have any way to specify a periodic BC for one variable
> as a weighted sum of other variables.


Ah, OK. I was hoping to do cases other than 0/90/180/270 degree rotations,
and I'm considering elasticity, hence (u,v,w) displacement variables. As a
result I think the current implementation won't work for me since I'd need
one variable to be a weighted sum of the others.

I can look into adding this, any suggestions on where to start?



> Has anyone tried this case before?
>>
>
> We actually have some CI coverage for it thanks to the MOOSE guys:
> tests/bcs/periodic/orthogonal_pbc_on_square.i
>

Thanks, I'll have a look.


John, regarding this:

We have support for user-defined forward and inverse periodic boundary
> transform functions in MOOSE if you'd like to check and see how it's done
> there.


I'd be interested to check that, can you point me to the relevant part of
MOOSE?

Thanks,
David