Controls explanation

[saja11]

Hi,

I am trying to converge my complex model by trying to play with controls parameters. However, it would be appreciated is someone can help me in understanding what these controls represents?

I have tried to see manual but it would be nice if someone can help me in geeting these controls and how they effect solver's solution.

*Controls, parameters=constraints
, , , 3., 3., , ,5.
*Controls, parameters=line search
20, , , ,0.01
*Controls, analysis=discontinuous
*Controls, parameters=field, field=displacement
1500., 2., , 0.15, , , ,
*Controls, parameters=field, field=rotation
1000., 100., , , ,1.0 , ,
*Controls, parameters=field, field=pore fluid pressure
200., 2, , , , , ,

 

[FEA way]

Be careful with these options, in most cases they aren’t needed (unless there are extreme nonlinearities in the model, like in fracture mechanics analyses) and it’s recommended to resolve convergence issues without them if possible.

It would be hard to explain them all here. Please check the documentation chapter "Commonly used control parameters" (and other three short chapters mentioned in See Also) first.

If you tell us something about your model and convergence issues that you have then maybe we will be able to suggest a solution other than adjusting the solver settings.

 

[saja11]

It's a knee joint cartilage model and implemented with fibril reinforced poroviscoelastic material (UMAT). As material is very soft, I was facing convergence issues. But typically changing constraint and displacement controls (lower values than default), model do converges. Maybe not all but it would be helpful if u can explain *Controls, parameters=constraints and *Controls, parameters=field, field=displacement. Eg. how they effect convergence issues.

 

[FEA way]

This first set of parameters (constraints) mainly applies to specific, special types of elements and is rather rarely adjusted. So the question arises, which types of elements are used in your analysis ?

The second set of parameters (field) is more general and allows you to adjust the convergence criteria. That requires understanding the details of how Abaqus approaches nonlinear problems. Check the documentation chapter "Convergence criteria for nonlinear problems", it features a very comprehensive explanation.

You might be also interested in time incrementation parameters, there’s quite a lot of them.

In general, I would advise you to carefully examine the output in the Job Diagnostics dialog box first. It might help you find the actual cause of non-convergence.

 

[saja11]

Element is C3D8P-(8-node trilinear displacement and pore pressure).