Fluid-Structure Interactions: Flow past flap

[ateshian]

• The objective of this advanced tutorial is to demonstrate the use of the FSI solver in FEBio, which was introduced in version 2.8.
• This tutorial requires PreView 2.1.0 and PostView 2.3.0 or higher.
• FEBio uses a specialized fluid-solid mixture to model fluid domains whose mesh (defined on the solid constituent) may deform as a result of fluid-structure interactions (FSI).
• FSI analyses use the “fluid-FSI” module and the “fluid-FSI” material.
• For domains that are assigned a “fluid-FSI” material, users need to define boundary conditions for the fluid and solid constituents.

This problem analyzes pulsatile flow in a channel which is partially occluded by a flexible flap. As the upstream pressure is increased, flow initiates and causes the flap to deform and bend. The pressure is then reduced back to zero by time 0.5, held there until time 1.0, then the cycle of pressurization is repeated once more.



The detailed steps for this tutorial can be downloaded from here.

The FEBio file can be downloaded directly from FlowPastFlap.feb.zip.

Gerard Ateshian

[Abha]

Error termination in Flow past flap tutorial

Hello Gerard!
Thank you for this tutorial. I am a beginner in FEBio. I tried this but the simulation shows 'error termination' after ~600 steps, while as per the tutorial, it should run up to 1000 steps. It reads 'failed to converge at time : 1.21509' and 'Negative Jacobian was detected'. How should I solve this problem?

Thank you!
Abha

[ateshian]

Hi Abha,

Which version of FEBio are you using? And on which operating system?

This tutorial was created when FEBio 2.8 was released and it also runs fine with FEBio 2.9 (at least on my Mac).

If you a running it using the FEBio executable in the FEBioStudio beta version, that is a beta version of FEBio 3.0, so the issue may lie there.

Let me know, as this will help us debug this issue.

Best,

Gerard

[Abha]

Hi Gerard,

Thank you for your prompt reply. I am using FEBio 2.9.1 and PreView2.1.5 on Windows 8.1 Pro. I created and defined the geometry in PreView and ran the simulation there itself-FEBio 2.9.1. I do not use FEBioStudio. I have attached my .feb file if you would like to cross-check something.

Thank you!
AbhaFlowpastflap.feb

[ateshian]

Hi Abha,

I looked at the model you attached and it seems to have insufficient displacement constraints along the z-direction: You need to select the entire faces of the fluid and solid domains on the planes normal to the Z-direction and fix their z-displacement. (This becomes apparent because your model starts twisting out of the xy-plane as time progresses.)

Please try that and let me know if it resolves the convergence issue.

Best,

Gerard

[Abha]

Oh, it worked! I had made a blunder. Thank you very much.

[ateshian]

Hi Abha,

I changed all the CFD tutorials so that you can download the FEBio model files directly from the febio.org server. Please try downloading these again and let me know if you still have problem.

Best,

Gerard

[Abha]

Thank you very much, Gerard! I was able to download them.

Abha