On Wed, Mar 30, 2016 at 8:00 AM, David Knezevic <[email protected]>
wrote:
>
>
> Thanks for your comments. The problem I'm considering is plasticity, using
> the radial return algorithm. As far as I can tell, the code matches the
> text book, and it converges correctly. However, it doesn't match the finite
> difference Jacobian from FEMSystem. So there are two possibilities:
>
> 1) Somehow the finite difference Jacobian is inconsistent with the radial
> return algorithm. This doesn't seem impossible to me, given that the radial
> return algorithm is highly path-dependent.
>
This is very much a thing. What reference are you using? The Jacobian you
get from the equations vs. the Jacobian which includes the radial return
algorithm ("consistent tangent" as the community calls it) are different.
Simo and Hughes, "Computationally Inelasticity" has a good discussion of
this.
> 2) There is a bug somewhere in my analytical Jacobian.
>
> I'll look some more for a bug (I'll compare the elements, like you said).
> But I was wondering if you think 1) is a possibility?
>
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