29 April 2018
- Last edited 30 April 2018
I sent you email about using Adjust to Touch to close frictional contacts that had a small gap.
You say you are "using newton raphson residual to find out the place where its value is high" but I don't see any NR residual plots under the Solution Information folder in the screen image above, and NR residual plots were set to zero in the new beginnings model you sent me. I set NR residual plots to a value of 6 and made the adjust to touch change mentioned above. The plot below shows why the solver cannot find equilibrium. It is on this ligament:
It tells you the name of the component that has the Maximum NR residual force. This is usually very helpful, but only if you don't reuse the same name multiple times.
I duplicated that contact and took one vertex off the group contact so the duplicate can have just one vertex to the body. I changed the Bonded contact for that ligament to give it a known pinball radius and use MPC contact.
Here is the unconverged displacement, it looks like using this elements is not going to work for your model.
The next experiment I will do on your model is to convert all frictional contacts to bonded contacts. This is always my strategy, first solve as bonded contact, then convert to frictional.
So the next thing is to reduce the initial substep size by a factor of 2^3 = 8 and use the APDL command neqit,50 to get the solver to keep going!
Now with bonded contact, weak springs turned on and step 1 set to -2 N, this model finally started to converge!
Note that it took 163 substeps for step 1 to converge, then only 115 substeps to do the next 20 steps. That all took about 4 hours on 8 cores but is only half way to the final load.
To simplify things, why not use one ligament spring element between the spurs on the bones instead of a bunch of beams?