convergence probleme in ansys apdl

[pashapatil67]

i m doing nonlinear analysis(material non linearity)...i have given cyclic load for 10 cycles..after reaching at 512 time solution is not get converged...error file shows following error

*** WARNING *** SUPPRESSED MESSAGE CP = 8.641 TIME= 15:54:45
Quadrilateral element 7031 has an angle between adjacent edges of 171
degrees, which exceeds the warning limit of 155 degrees.

*** WARNING *** SUPPRESSED MESSAGE CP = 8.641 TIME= 15:54:45
Quadrilateral element 7040 has an angle between adjacent edges of 171
degrees, which exceeds the warning limit of 155 degrees.

*** ERROR *** CP = 9469.375 TIME= 17:37:15
Excessive distortion of Element 4614.

*** ERROR *** CP = 9469.375 TIME= 17:37:15
Excessive distortion of Element 4618.

*** ERROR *** CP = 9611.922 TIME= 17:38:28
Excessive distortion of Element 5320.

i have tried with increasing no.of sub steps and reducing time step also...but couldnt get convergence..
so can anybody help me out from this and tell me what corrective actin should i take to get convergence

thank you
prashant patil
MTECH cad/cam

 

[albertoruenes]

Hi. the reason you are getting this error is because the model checks are throwing a geometrical error regarding the topology of an element, you can either remesh your model to obtain less distortion or relax the tolerance for the geometrical model checks.

 

[IceBreakerSours]

Tolerance is somewhat like a nuclear option in the modeling world: You better have a very strong case and you better know what the consequences are when playing with tolerances. And if you knew you had a strong case, you wouldn't be posting a message on a free-for-all online forum in the first place

In my experience, convergence errors are most often due to modeling issues. You have to play the detective in figuring modeling issues. In this case, you should remove all complexities from the model and run the simplest version you can. For instance, get rid of all nonlinearities (if you can) and see what happens. And turn on complexities one step at a time.

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[Dave442]

Hi,

I just wanted to reiterate what IceBreakerSours posted above - 99% of the times I have encountered relaxed convergence tolerances it has been to overcome convergence issues caused by bad assumptions or mistakes which were made elsewhere in the model.

As stated above, your problem stems from badly distorted elements. Check your loads/constraints to make sure they are reasonable and you have used consistent units. Also, look at the distorted elements during loading (the element numbers are given in the warning messages) and see what is going on to cause the excessive distortion. Maybe you have over constrained an element set somehow? If not, consider refining the mesh in that area or incorporating adaptive remeshing to automatically refine the mesh in regions of high distortion during the analysis.

Good Luck,
Dave