Re: [deal.II] Re: FE w/ Gauss Point DoFs

[Wolfgang Bangerth]

On 03/07/2018 08:43 AM, Jonathan Russ wrote:


Thank you for your fast reply. I'm sorry I'm not doing a great job of 
explaining this. Here is an example from elasticity that illustrates what I 
would like:
In this case there are displacement degrees of freedom at the nodes but the 
stress is a quantity typically derived from the displacements. However, one 
could make the stress an independent degree of freedom at the gauss points.


If all you're interested in is values at quadrature points (and not any 
associated "field"), then you may also want to take a look at the 
CellDataStorage and related classes. They were written with your specific 
application in mind, including the need to transfer data from one cell to its 
children or parents upon mesh refinement, and to other processors upon 
partitioning of the mesh.


Best
 W.

--

Wolfgang Bangerth  email: bange...@colostate.edu
   www: http://www.math.colostate.edu/~bangerth/

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Re: [deal.II] Re: FE w/ Gauss Point DoFs

[Jonathan Russ]

Bruno -

Thank you for your help. I see what you are saying. In this way I would 
need to make sure I have the same number of gauss points as nodes in the 
finite element since deal.II will assume that the stress degrees of freedom 
are associated with the nodes. For now I don't believe this is too strict 
of a limitation for me since I will likely choose the quadrature rule such 
that the number of quadrature points is equal to the number of nodes 
anyways. Perhaps there is a better way to handle this situation but I will 
try this for now. Thanks again!

Jonathan

On Wednesday, March 7, 2018 at 11:04:33 AM UTC-5, Bruno Turcksin wrote:
>
> Jonathan,
>
> 2018-03-07 10:43 GMT-05:00 Jonathan Russ  >:
>
>>
>> Thank you for your fast reply. I'm sorry I'm not doing a great job of 
>> explaining this. Here is an example from elasticity that illustrates what I 
>> would like:
>> In this case there are displacement degrees of freedom at the nodes but 
>> the stress is a quantity typically derived from the displacements. However, 
>> one could make the stress an independent degree of freedom at the gauss 
>> points. 
>>
>> So, in the element there would be displacement degrees of freedom at the 
>> nodes and stress degrees of freedom at the gauss points. Does this make 
>> sense?
>>
> I don't think there is a way to do that in deal unless you can split your 
> finite elements, i.e., you have one FE_Q for the displacement and another 
> FE_Q for the stress. Then, you can use FESystem. But do I understand 
> correctly that the stress is not describe by any finite element but you 
> would like to use dof_handler to help you manage some data. In that case, I 
> think that using a FESystem should work, you just will never call FEValues 
> for the stress since you don't care about the associated finite element but 
> the dof_handler will associate a degree of freedom to each quadrature point.
>
> Best,
>
> Bruno
>

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Re: [deal.II] Re: FE w/ Gauss Point DoFs

[Bruno Turcksin]

Jonathan,

2018-03-07 10:43 GMT-05:00 Jonathan Russ :

>
> Thank you for your fast reply. I'm sorry I'm not doing a great job of
> explaining this. Here is an example from elasticity that illustrates what I
> would like:
> In this case there are displacement degrees of freedom at the nodes but
> the stress is a quantity typically derived from the displacements. However,
> one could make the stress an independent degree of freedom at the gauss
> points.
>
> So, in the element there would be displacement degrees of freedom at the
> nodes and stress degrees of freedom at the gauss points. Does this make
> sense?
>
I don't think there is a way to do that in deal unless you can split your
finite elements, i.e., you have one FE_Q for the displacement and another
FE_Q for the stress. Then, you can use FESystem. But do I understand
correctly that the stress is not describe by any finite element but you
would like to use dof_handler to help you manage some data. In that case, I
think that using a FESystem should work, you just will never call FEValues
for the stress since you don't care about the associated finite element but
the dof_handler will associate a degree of freedom to each quadrature point.

Best,

Bruno

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