On Wed, Mar 30, 2016 at 9:20 AM, Paul T. Bauman <[email protected]> wrote:
> > > On Wed, Mar 30, 2016 at 9:16 AM, David Knezevic < > [email protected]> wrote: > >> On Wed, Mar 30, 2016 at 9:11 AM, Paul T. Bauman <[email protected]> >> wrote: >> >>> >>> >>> 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. >>> >> >> >> I'm using Simo and Hughes. I implemented the algorithm in "Box 3.2" of >> that book for radial return, and it seems to be working fine. >> > > OK, cool. Just wanted to make sure you were aware (I figured you were). > > >> However, I would have thought that I could use a finite difference >> Jacobian based on the residual that is given by the radial return algorithm >> (i.e. the residual that uses the stress from radial return). I would have >> thought that yields a "consistent tangent", no? >> > > Agreed. I'd suspect a bug, or I'm forgetting something because I haven't > played with damage/plasticity in ~3 years. > OK. I was hoping there might be some reason that the finite difference could be wrong in this case... but I agree, it's more likely that there's just a bug. Do you get dramatic convergence behavior changes between the finite > difference version and the analytical version? If not, very likely there's > some small term that's missing/in error. > They both converge similarly, so yeah, there's probably a small term that's in error. Thanks, David ------------------------------------------------------------------------------ Transform Data into Opportunity. Accelerate data analysis in your applications with Intel Data Analytics Acceleration Library. Click to learn more. http://pubads.g.doubleclick.net/gampad/clk?id=278785471&iu=/4140 _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
