Learning Forum

[Jason Franzman]

I am currently trying to run a hyper elastic closed tube 2 way FSI in ansys 2022 R2 using CFX and transient mechanical.  Water is entering at a speed of 1 cm/s sin(100*t) normal to the inlet.  The tube is 30 cm long, 1 inch in diameter and .4mm walls.  I am using the neohookean material from the hyperelastic data base on ansys and a neohookean fitting curve to ensure that its not my material measurements that causing this issue.  I am trying to model the pulse wave as it travels through the material and see the interaction the reflected wave.

To do this:

I have read multiple forums about the methods of running hyper elastic materials and have done most of them except keyopt 6,1/ 2,1 and global stabilization which for some reason is not showing up under expert settings in the workbench system coupling gui.  I am using a super computing platform that uses linux which may be why my keyopts and stabilization are not working correctly.  

The basic set up is I have the capped end and inlet face fixed and the interior using system coupling.

I have 4 layers of elements through the wall of my cylindrical tube to and my element aspect ratio changes from 1.02 to 1.75 with nothing above 2.  The elements are nonlinear mechanical and linear.  The substeps for the transient mechanical are set to 100 and large deflection is set to on.  The time steps in the system coupling are at .001

I have already tried my setup with steel and it works and completed as is expected but when the material is turned to hyper elastic the simulation fails relatively quickly at coupled step 4 which leads me to believe there was to be some instability but I dont know how to correct this besides using the global or local stabilization.  I have tried adjusting th geometry so that it is more curved near the capped end however this just makes it so I have to use tet elements which does not work well.

Thank you for reading this and all the help.

Here are my results and warnings.

nd001-HDUP

nd001-MXUP

 

The final warning I recieved is this:

 

[RM]

Excessive element distortion errors may occur when using hyperelastic materials due to the highly non-linear nature of the simulations. This may lead to excessive distorsion in certain local regions of the model, leading to a non-physical shape of some elements in the mesh.

Please refer following course: How to Handle Element Distortion Errors in Hyperelastic Materials — Lesson 3 - ANSYS Innovation Courses

Hope this helps!