[YoussefFath]

Hi!
I´m new in this forum and I search information about a FSI 2-way error.
I am trying to simulate a artery (cylinder) with the blood, with a variable pressure-input and a pressure-output in fluent. When I run the system coupling I had a error which said there was a elements with high distortion.
I tried very solutions but I don´t have any improvement.
I attached two images with the error

P.D: Sorry for my english and thank you.

Tags: FSI, system coupling, High distortion, biosimulation, transient structural

[RaiderDoctor]

Element distortion in the Mechanical solver is usually due to the load (in this case, from the fluid) being applied too quickly. The usual way to deal with this is to simply restart your analysis from a time step that was close to where it failed. This time, however, you want to decrease your step size so that the load is applied much more slowly.

Say, for instance, your original time step size was 0.002 s, and the simulation failed at 0.43 s. You would want to restart your simulation at a point close to 0.43 s, but this time with a step size of 0.001 s. That's the easy part.

Now, for the hard part: how do we do this? Unfortunately, this has to be done prior to running your simulation. Ansys is fickle, and will not hesitate to delete your solution files if you touch the wrong thing. Even if you change it back, the solution files are gone. A good practice, if you have the memory, is to save your simulation immediately after it fails so that you always have a back-up plan.

Setting up restart points is fairly simple, so that's the nice part. Check out this youtube video (Restarting a Coupled Analysis in ANSYS Fluent and Mechanical, https://www.youtube.com/watch?v=ef9XGXyuJHY) which should go over the basic steps. Check the documentation and write down what you do so that you can check back on it later.

If, in the instance, you already know how to do all of this, another issue might be your element quality. Check the quality and aspect ratio within mechanical and verify that it is still good. If it isn't, consider remeshing. Be warned, however, that this will delete your solution files and you will need to restart from scratch.

Good luck!