Learning Forum

[navidvd]

Hi

I have an issue with the FEA modelling of an artery with three layers. I tried to make it as simplified as possible. However, I got a couple of errors.

This is the list of errors that I got:

• An error occurred when the post processor attempted to load a specific result. Please review all messages.
• Current result file may not contain requested result data . Please clear the solution and solve again.
• The result file cannot be opened.
• Not enough constraints appear to be applied to prevent rigid body motion. This may lead to solution warnings or errors. Check results carefully.

I am wondering if anyone can suggest what I am doing wrong. Attached is also the archive format of the

try_3.wbpz

[peteroznewman]

What version of Ansys are you using?

[navidvd]

I am using Ansys 2021 R1

[peteroznewman]

Artery tissue is generally modelled using a Hyperelastic material model. Using Linear Elasticity is not going to represent reality very well.
Materials with a high Poisson's Ratio often benefit by using a mixed u-P element formulation, which is enabled by setting Keyopt(6) = 1.
To get the model solving faster, you could use two planes of symmetry and cut the geometry down to 1/4 of the size.
You have a pressure ramp up and then down over 1 second, but since the material is linear, there is no new information on the ramp down, so I only simulated 0.5 seconds.
This mesh has less than 25k nodes, your model had 871k nodes, which means you spend a lot of time waiting for the solver to finish.

[navidvd]

Thanks a lot Peter for your help. I tried to rerun the archive file. However, I got a bunch of errors. I believe the main one is:
The unit system of Command object(s) such asintima1>Commands (APDL) at the time of creation, differs from the solver unit system.Check your data and results accordingly.
I tried to change the unit system but not much success. Do you have any suggestions?
Thanks again

[Erik Kostson]

That error you mention is not an error it is just a warning - also it is a fine warning, since only sets a keyopt(6)=1 I believe, so it does not involve units, hence we can neglect that warning, and it should be all OK and have run through till the end. So under Solution there are only warning and no errors in your model most likely (errors prevent the solution to finish, warning do not and we need to assess if they are important or not, like in this case it is not).

Can you please show us the model after it has been solved as an inline image, and all the warnings under the solution and messages - thank you.

Erik

[navidvd]

Thanks for your reply. Here are some snapshots of the model:
Thanks for the help.
Cheers
Navid

[Erik Kostson]

Hi

See that error - something with the post processor - so it has solved.

First of all save the archive wbpz as a wbpj somewhere on your C drive. Then:

delete all of the result objects, resolve and add new results when it has solved.

Thank you

Erik

[navidvd]

I've done what you suggested.
Here is the model without asking for any results to calculate:
Which looks fine. However, once I add a result and press Evaluate, the same thing as previous happened:
Thanks again for possible suggestions

[Erik Kostson]

Hi

Firstly did you save the wbpz archive locally as a wbpj project?

If that is the case and the same error occurs the:
The error is that it can not open the results file. We do not know exactly why so I would just start from scratch and follow that model (same geometry (import it from), same loads, boundary conditions, I would initially skip the commands since it will probably solve without them,...).

Hope this helps

Erik

[navidvd]

Thanks, Erik for your help. I installed Ansys 2021R2 and rerun the archive file, and it worked well.
I do have another question. I used the linear elasticity model as a first step. Now I am going to add experimental material properties in longitudinal and circumferential directions for each layer. I got the material properties from a paper and used MCalibration software to extract a suitable format of experimental data for Ansys. As I only have experimental data for two directions (circumferential and longitudinal and no data for radial direction), my question is how to make sure that I assign correctly material properties for different directions? Should I define a cylindrical coordinate system? (I tried to add a cylindrical coordinate system and change the boundary conditions with the current settings, however Ansys failed to solve it) How can I tell Ansys to assign for example circumferential for x (in polar) and longitudinal for y (in polar)? what should I do with the third direction?

Any suggestions would be appreciated.
Thanks