SOL 106- not converging
SOL 106- not converging
(OP)
There was a previous thread similar to this which I read, but in didnt prove helpful. So here I go posting this thread, hopeful that someone has run into a similar situation.
I am running SOL 106 for a beam-column type of analysis, nonlinearity for the displacements. The constraint is simply supported on one end, and roller on the other end, free to translate along the column's own axis. The actual loading case is an axial compressive load and distributed load along the column, which yielded a non convergent solution. The column is modeled by shells, and is loaded eccentrically by the compressive load.
Now, I did do a few tests by I varying the magnitude of the loads, and running only compressive and only distributed load. What i found is that I can find a convergent solution if i decrease the load enough. So there is a specific magnitude for which any runs with loads higher than that wont converge. If the model runs just fine with smaller loads, does that mean its an actual physical instability of the structure? which would mean that I need to re-design my part? Or is it only an algorithm occurence? Im leaning towards the first possibility. Please give me any kind of input- it will be appreciated. Thank you.
I am running SOL 106 for a beam-column type of analysis, nonlinearity for the displacements. The constraint is simply supported on one end, and roller on the other end, free to translate along the column's own axis. The actual loading case is an axial compressive load and distributed load along the column, which yielded a non convergent solution. The column is modeled by shells, and is loaded eccentrically by the compressive load.
Now, I did do a few tests by I varying the magnitude of the loads, and running only compressive and only distributed load. What i found is that I can find a convergent solution if i decrease the load enough. So there is a specific magnitude for which any runs with loads higher than that wont converge. If the model runs just fine with smaller loads, does that mean its an actual physical instability of the structure? which would mean that I need to re-design my part? Or is it only an algorithm occurence? Im leaning towards the first possibility. Please give me any kind of input- it will be appreciated. Thank you.





RE: SOL 106- not converging
The other thing to try out is to make more than one load cases and increase the number of increments on NLPARM card until you see any convergence. Note that convergence level ,and add another loadcase and rerun with higher number of increments. Try this several time , and you will see it converging unless you have very flexible part or mechanism.
RE: SOL 106- not converging
RE: SOL 106- not converging
RE: SOL 106- not converging
Usually, it need a small structural imperfection to have buckling. But sometimes, numerical roundoff can also introduce buckling.
RE: SOL 106- not converging
ThomasH,
I dont have any yield limits in the model. I have linear isotropic & orthrotropic materials in the model, so it shouldnt recognize yields.
EricZhao,
Ive already thought about that. I did a test where i imposed 2 of the same load cases, with different magnitudes, but I know both exceed the number that allows convergence. Both did not converge, and diverged at a percentage of the full load. One was at about 82% load, the other at 90% load. When i calculated the failure loads for these 2 cases, they werent the same magnitude. So it doesnt consistently give me the same buckling load. But, I still tend to believe that this might be hinting a physical geometric instability that actually exists. But i dont know this for sure.
RE: SOL 106- not converging
RE: SOL 106- not converging
Another thought. If the compressive load causes the beam to arch up into the distributed load then is it possible you are seeing some kind of snap through?
RE: SOL 106- not converging
I did do runs with less load and found that my solution converges. kellnerp, what do you mean by "collapse."? Is that something that would happen physically, or something in the algorithm?