Learning Forum

[keey6tyl]

Hi, I am trying to perform a non-linear analysis on a rc slab. However, i encounter this error message stating "solver engine unable to converge on a solution for nonlinear problem. And after viewing a few forum discussion, may I ask is it possible to solve nonlinear problem using Ansys student license? Or is there anything wrong with my model?

[Ashish Khemka]

Did you check the Solver Output for what is the error which caused the non-convergence? Also please see if the following link helps:

Overcoming Convergence Difficulties in ANSYS Workbench Mechanical, Part II: Quick Usage of Mechanical APDL to Plot Distorted Elements ÔÇô PADT, Inc. ÔÇô The Blog (padtinc.com)

Regards Ashish Khemka

[keey6tyl]

Thanks for the link. However my error message was not as per said in the link.
It did not show any other reason but just the unconverged error. I tried manipulate the force and time steps around but everytime it just stops at one specific timing. However, I will still trying following the link solution and see where it leads.

[keey6tyl]

Again many thanks to your reply and link provided. However the solution in the link seems to be leading to nowhere for my situation cause I do not have error elements when checked in apdl. Do you have any other idea how to solve the convergence issue?

[Ashish Khemka]

Can you try applying the load more gradually by increasing the number of substeps? Also under Details of Solution Information, specify NR Residuals to be 3 and Element Violation to be 1:

This will help to identify regions where the force balance is not achieved for convergence and also show any distorted elements. With this change you may find slight increase in solution time.

Regards Ashish Khemka

[keey6tyl]

I have done another analysis as your suggestion. However the solution still loads to 36% and the solution time stopped at 4s. Also I have switched on the identify element violations option and may I ask where can I check for the result of element violations? I do see 3 newton-raphson residual forces but I am not sure what they meant. Also I changed my time steps to 10 steps with 100 initial substeps and 1000 max substeps, after applying the load gradually from 100kn to 1000kn with 100kn interval the model still fail to converge. Is there any other option I can use to observe the nonlinear behaviour of my model? Because that is my ultimate goal for my final year thesis.

[Ashish Khemka]

In the link shared earlier, Newton-Raphson Residual Force will allow seeing the location of force imbalance:
Overcoming Convergence Difficulties in ANSYS Workbench Mechanical, Part I: Using Newton-Raphson Residual Information ÔÇô PADT, Inc. ÔÇô The Blog (padtinc.com)


How to use this information is discussed in the post.
Regards Ashish Khemka

[keey6tyl]

Thanks for the assistance. I have found out my problem is with the menetry-william material properties assigned along with the multilinear isotropic hardening material. When i remove the menetry-william material properties the convergence problem is gone. Thanks for the help along the way.