Why is Contact Energy Higher Than Internal Energy in My LS-DYNA Simulation?

[smeenakshisu]

Hi all,

I'm running an explicit finite element simulation with significant sliding and friction (0.2) in LS-DYNA. In the energy summary, I've observed that the total contact energy (including friction) is higher than the internal energy at several stages during the simulation.

My understanding is that, even with friction, contact energy should generally remain a fraction of the internal energy (often <10–20%).

• Contact in my model uses CONTACT_AUTOMATIC_SURFACE_TO_SURFACE with FS/FD defined. SOFT=2, SBOPT=5, DEPTH=23

• There is significant sliding.

• My material can yield.

• I've checked for initial penetration, and there are none as I start with a open contact.

From a physical standpoint, is it ever correct for contact energy to exceed internal energy in an explicit LS-DYNA run?

[Dennis Chen]

Maybe consider looking into the exact definition of "contact energy".    This is not exactly a term that LS-Dyna subscribe to from the documentation.    what you are looking at is workbench, which is Ansys's version of dyna's postprocessor.   Check documentation for exactly what it means

In terms of actual energy you can check, database_matsum and database_SLEOUT gives you the KE, IE and sliding interface energy.  

sliding interface energy is a common check point for penalty based automatic contact pairs.   GLSTAT can also give global level energy look. 

if you have no friction, sliding interface energy should be way lower than IE.   If you do, ensure each contact pair doesn't have negative sliding interface energy from the database_SLEOUT.

I know Ansys won't promote this because workbench LS-Dyna is their product but compared to the full scope of what LS_Dyna can do in postprocessing, workbench is not adequate simply because it doesn't remotely capture the extent of what's possible in postprocessing.