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

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

On Thu, Mar 1, 2018 at 12:00 PM, John Peterson <jwp...@gm...> wrote:

>
>
> On Thu, Mar 1, 2018 at 9:30 AM, David Knezevic <dav...@ak...
> > wrote:
>
>> 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?
>>
>
> It's just implemented by overriding get_corresponding_pos() as you said.
>
> https://github.com/idaholab/moose/blob/devel/framework/src/bcs/
> FunctionPeriodicBoundary.C
>


OK, thanks!

David