Learning Forum

[karankakroo]

Hello,
I hope this post finds you well! I have been simulating a 2-way FSI (fluid structure interaction) of a single wall mounted flexible flap in a transverse flow. For a highly flexible filament (using respective properties in engineering material), the filament in my simulation touches the bottom wall of the fluid domain and the mesh collapses at that instance and the Fluent solver throws me an error "Negative Volume Detected". Is there a way to fix this or resolve this issue? I believe I have to define a contact, so that ANSYS knows that there would be contact between the structure and the bottom wall after running for certain time when the oscillation is huge. However, I am not aware of how to define a contact in ANSYS, do I have to define it in Transient structural solver (solid solver) or ANSYS FLUENT solver (fluid solver), as I am using both the solvers using system coupling to perform a 2-way FSI simulation? If yes, how can i define a contact, kindly help on this? I would really appreciate any help. Please find the attached picture for your reference. (It shows the instant where the mesh collapses when the flexible filaments touch the bottom wall). Hoping to hear from you soon. Thank you!

[Rahul]

Hello Karan,

Please refer tutorial which explains the contact detection settings in fluent. You can find it on dynamic mesh task page. Reed Valve FSI Co-Simulation with Partial Setup Export from Workbench (Fluent-Mechanical) (ansys.com)

Hope this helps!

[chakrachand]

 

 

[karankakroo]

Thank you for the suggestion. I followed the tutorial and now the contact in the fluid component (FLUENT works fine as I can see the grid/cells being deleted when the contact is activated using a proximity threshold (0.004) defined in FLUENT. However, now the solid component (transient structual) throws a "highly distorted elements" error when the flap reaches the contact (defined by offset value of 0.001 in solid solver). Please seee the attached figre for reference. I beleive the contact force is significant that it deforms the flap. Is there a way to reduce the contact force or fix this "highly distorted elements" error. I have tried different contacts such as frictionless as well as friction contact, but nothing helps so far. Hoping to hear from you soon.

[Rahul]

Hello,

To overcome highly dostorted elements error, you can ensure good mesh quality by using elements that are less susceptible to distortion, using a mesh with appropriately shaped elements, or applying loads in smaller increments. Additionally, you need to ensure that the model is set up correctly, which includes using complete test data and a stable material model. In some cases, changes to the design geometry may be necessary to limit localized excessive element distortion.

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