Learning Forum

[Shannon Cheang]

Hi and good day, 

I am having issues being able to successfully get results when modelling a knee model with specific parts as viscoelastic materials, namely the femoral and tibial cartilages. I am using tetrahedrons. I've tried adding weak springs, changing contact stiffness, adding large deformation, but nothing I do seems to be working. I keep getting the error "An internal solution magnitude limit was exceeded.", so I've also tried adding the command "ncnv, ,1e30" but unfortunately to no avail.

It would really mean a lot to me if someone could please help me with this issue. This is my first time posting here, so please do let me know if I've left out any information that is necessary, 

My work file

 

[Sahil Sura]

Hello Shannon Cheang,
Thanks for sharing the images of the screen, as at Ansys we usually do not download any attachments.
The error might have been raised due to improper constraints or boundary conditions especially inappropriate loads or insufficient constraints, so a check on boundary conditions might help resolve the issue.
For the cases where there are no supports required, try considering 'Weak Springs' and if considered and still facing the issue, try updating the stiffness of the same. Using 'Inertia relief' might also work for such cases.
More on this can be found in the references section.

Apart from these, selecting an appropriate mesh size helps to give accurate results, the following video might also be useful for the same.
Specifying an Appropriate Element Size for Stress Analysis — Lesson 1 - ANSYS Innovation Courses

References -
1. An Internal Solution Magnitude Limit Was Exceeded. (ansys.com)
2. Solver Controls (ansys.com)
3. Bending Simulation on a Rat Femur | Ansys Innovation Courses
4. High Resolution FE Model of Bone - ANSYS Innovation Courses
5. Stress Analysis Simulation Examples | Ansys Innovation Courses
6. 4.9. Viscoelasticity (ansys.com)

Hope this helps!
Thanks,
Sahil
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