Learning Forum

[javat33489]

Hello everyone, I encountered some errors in the solver when calculating in LS-Dyna.
1. When solving a problem without temperature analysis:

2. When solving with temperature analysis:

How can I fix them? Or is it not critical?

[Reno Genest]

Hello Javat,

Those are warning messages and not error messages; the simulation should continue until normal termination.

For the unattached nodes warning, you can display the unreferenced nodes in LSPP as follows:

 

Then, you can delete the unreferenced nodes as follows:

 

For the tied contact warning, you probably have a constraint based tied contact which might create to many constraint equations with a rigid body, hence the warning message. Try using penalty based tied contacts to see if the warning messages go away. You will find more information on contacts in LS-DYNA in the following training from our channel partner Oasys:

https://www.oasys-software.com/dyna/wp-content/uploads/2020/01/Intro-to-Contacts.pdf

And here is more information on tied contacts from our knowledge database:

"

Below is a description of each of the tied contact types,which may also help explain the differences:

*CONTACT_TIED_..._TO_SURFACE:   constraint-based, and slave nodes will be projected to master surface during initialization.

*CONTACT_TIED_..._TO_SURFACE_OFFSET:   penalty-based, and slave nodes will NOT be projected to master surface during initialization.   In general, we don't like to use this type of contact as it doesn't consider the moments induced by the gap between slave and master.

*CONTACT_TIED_..._TO_SURFACE_CONSTRAINED_OFFSET:   constraint-based, and slave nodes will NOT be projected to master surface during initialization.

 If the "..." above is NODES_TO_SURFACE or SURFACE_TO_SURFACE, the rotational DOF of nodes are not considered in the contact algorithm.   That's fine if you're tying solids to solids.

If the "..." above is SHELL_EDGE_TO_SURFACE, the rotation DOF of nodes ARE considered in the contact algorithm.   That what you want if shells or beams are included in the contact.

*CONTACT_TIED_SHELL_EDGE_TO_SURFACE has a BEAM_OFFSET variation that is penalty-based, and and slave nodes will NOT be projected to master surface during initialization.

Constraint-based tied contacts should not be used in explicit analysis IF there are other constraints (SPCs, prescribed motion, rigid bodies, etc) associated with the slave or master surface.   Otherwise, they should be fine.

Penalty-based tied contacts don't interfere with other constraints."



Reno.