no iterations using elements with different nodes

[cri]

Dear Professors and FEAP users,
I implemented a user element based on the Virtual Element Method. The implementation considers a generic number of nodes for the element.
If I perform a numerical analysis using elements with the same number of nodes, I get satisfactory results. Instead, if I use elements with different number of nodes, no iterations are performed after the first step of the analysis. As an example, I attach the 'L-file' and 'O-file' resulting from 2 linear elastic analyses in which:

- I use two elements with 6 nodes ('L66node' and 'O66node')
- I use one element with 6 nodes and one with 5 nodes ('L65node' and 'O65node')

Certainly, I always indicate the maximum number of nodes in the second line of the input file. I didn't attach my input files, because I'm using a user element, but I can send them if you need to better understand.
Can someone help me? Is there any other modification that I have to insert in the input file or in my user element?


Thanks for your support
Cristina

[Prof. R.L. Taylor]

If the  problem is plane stress or plane strain you do not have a boundary condition in the y direction. Nevertheless the solver is not losing digits and the 2-node gets a numerical zero.  But check to see if it is what you want.  Fix a b.c. and see if that helps.

If adding b.c. does not help. The output file says it converged for a couple of increments and then did not.  Very strange -- hard to tell without the program and input file???