Hello,
in ABAQUS/Standard the global time step size can be controlled from within umat using the variable PNEWDT. I wonder, if there is any variable in ANSYS Usermat that do the same.
Thanks
dnoack
Have you looked at the ANSYS user manuals?
An alternative to PNEWDT, that works in all FE codes, is to return a crazy stress. That way equilibrium will not be reached and the increment attempted again.
- Jorgen
Jorgen,
your last comment about crazy stresses sounds very interesting but regretfully I do not think I understand it at all.
Would you mind extending it with just a couple of lines?
Many thanks
Best Regards
Muzialis
I have not used the crazy stress approach, but I assume it should work as follows. Implicit FE increments are repeated until equilibrium is reached. If you return bad stresses then equilibrium will not be reached and the solver will be forced to cut time.
This, of course, is only used for implicit simulations.
- Jorgen
Jorgen,
many thanks for this clarification
Muzialis
Keycut variable
Hi,
in ANSYS Usermat you will find the keycut variable. If you set it to 1, ANSYS performs a bisection due to the ANSYS solution logic. A direct control of dt is not (yet) possible.
Armin
Hello all,
thank you for the hints and discussions of my problem. I recognized that there is nothing available in ANSYS for controlling the time increment efficiently from usermat.
Returning a crazy stress is not a clean solution, since it can produce wrong results or crash the job because of numerical problems in the FE-program.
The keycut variable seems to be a good option but is limited (yet) to bisectional cut. If the time step size should be reduced with factor eight, the keycut should returned three times.
Unfortunately both possibilities decreases the execution performance.
Many thanks
dnoack