On Wed, Mar 30, 2016 at 9:16 AM, David Knezevic <david.kneze...@akselos.com> wrote:
> On Wed, Mar 30, 2016 at 9:11 AM, Paul T. Bauman <ptbau...@gmail.com> > wrote: > >> >> >> On Wed, Mar 30, 2016 at 8:00 AM, David Knezevic < >> david.kneze...@akselos.com> 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. 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. ------------------------------------------------------------------------------ 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 Libmesh-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-users