How to add degrees of freedom to a specified node

[wang yuan]

Hello everyone,

 I am using extended finite element method to do crack expansion. I have a question, can I increase the degree of freedom for the nodes designated around the crack in Deal? Meanwhile, another question is can I assign different numbers of Gaussian integral points to different elements? Thank you for your help!

[Wolfgang Bangerth]

Wang Yuan,

>  I am using extended finite element method to do crack expansion. I have a
> question, can I increase the degree of freedom for the nodes designated around
> the crack in Deal?

Not easily. deal.II enumerates degrees of freedom based on the finite element
used on a cell, so if you want to have extra degrees of freedom, you need to
describe that by using a different element on that cell (using the
hp-framework, in the same way as step-46 for example).

> Meanwhile, another question is can I assign different
> numbers of Gaussian integral points to different elements? Thank you for your
> help!

Yes! You can use a hp::QCollection together with hp::FEValues. Or you can do
it by hand: You create multiple quadrature rules and corresponding FEValues
objects, and then you choose which one is appropriate when you are on a
concrete cell.

Best
W.

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

[Simon Sticko]

Hi,

Since several XFEM papers formulate this as a Heaviside enrichment around the crack, you might find this class useful:

https://www.dealii.org/current/doxygen/deal.II/classFE__Enriched.html

Relating to Wolfgangs answer, note in particular the section "Using enriched and non-enriched FEs together".

Best,
Simon