Problems with multi-step biphasic simulation using Ogden material

[lefeverj]

I am working on a biphasic, pressurized cavity problem with the Ogden
material model. I am ramping the internal fluid pressure over 800
seconds and then running 1000 more seconds.

When I use a single step with 14 timesteps of 200 seconds each, it
executes properly. However, when the simulation is divided into two
separate steps of 4 x 200 seconds and 10 x 1000 seconds, it yields a
negative Jacobian on the first time step of the second step and an
early termination.

I've also noticed that this behavior occurs with the Ogden material
but not with the neo-Hookean material. Attached are the files for the
two simulations. Can anyone explain this behavior?

Thanks,
Joel

[ateshian]

Hi Joel,

I downloaded both files and ran them, and they both completed successfully. Please make sure that you have the latest version of FEBio. There was a relatively recent fix that dealt with multi-step analyses using biphasic materials (see http://mrlforums.sci.utah.edu/forums...hp?issueid=353). Let me know if that fixes your problem.

Gerard

[lefeverj]

Gerard,
Thanks for the help. I have just run the simulation on a machine running Windows XP, with success.

Unfortunately I would like to eventually run the simulations on a machine running OSX. I believe it is the latest update of FEBio for OSX, 1.3.0.1358, and it continues to terminate early. Attached is a .log file from a failed simulation. Any ideas?

Joel

[ateshian]

Joel,

Dave Rawlins has uploaded the latest Mac and Linux version of FEBio on the software website. Please try it out and let me know if it works for your problem.

Gerard

[lefeverj]

Gerard,

That solved the problem. Thanks for the help.

Joel