Learning Forum

[ningxin]

Dear Ansys community,

 

I'm trying to model blood pressure acting on the blood vessel in Static structural. 

Blood vessel was modelled using 5 parameter mooney-rivlin model with two layer mesh, and the surrounding muscle was linear elastic. 

As shown in the picture below, fixed boundary was applied to the muscle surrounding the vessel wall, and frictionless condition to the muscle surrounding inlet & outlets. Pressure was applied to the inner surface of blood vessel (yellow and green surfaces). 

I turned autotime stepping on with minimum number of steps of 100, and max of 400. However the solver failed to converge. I tried a few tricks I saw on the forum (KEYOPT, matid, 6, 1; KEYOPT, matid, 2, 1; NEQIT, 10; newton-raphson 3), but it's not helping.

Any suggestions?

 

Thanks,

[Akshay Maniyar]

Hi Max,

Debugging convergence issues with hyperelastic models is a tricky exercise. ANSYS provides various tools that can help in finding and resolving the issue. Commonly used tools for debugging are:
1. Force convergence plot.
2. Newton-Raphson residuals.
3. Solver output file.
4. Contact trackers (if contacts are present).

Also, do you have any interference which will be solved while running the model? Are your contact and target sides properly assigned? Please check the below video and see if it helps.

How to Designate the Contact | Ansys Innovation Courses

Also, check below KM for more details on hyperelastic modeling.

How simulate hyperelastic models in Workbench? - Ansys Knowledge

 

Thanks,

Akshay Maiyar

 

[ningxin]

Hi Akshay,

Thank you for your prompt response. I don't have contact surface, and the muscle and the blood vessel share the same nodes at the interface. 

As for the debugging tools, I do see them and I've attached some of them (solver output and force convergence) in the above thread. But I don't know how to interpret them and how to use them for debugging. 

In addition, I used mixed u-P formulation as suggested and I got the following message:

Any suggestions on how to interpret these debugging tools?

Thanks,