[jtwilson]

Hi All-

I am currently performing a two-way iteratively implicit coupled FSI simulation using ANSYS Mechanical, Fluent, and system coupling. This is a biomedical application. I have a bi-leaflet valve that is encapsulated within a sinus with tubular segments on either end of the sinus. I am only modelling a quarter of the valve and sinus and making the assumption that the valve will open axisymmetrically (this will change in the future).

I am applying a time-varying pressure at the tubular inlet of the geometry (outlet is set at zero pressure). Eventually, the leaflet opens. However, during the time step when the opening occurs, I get oscillations in the force (monitored at the leaflet surface as the integral of the total pressure) and oscillations in the flow rate at the outlet.

The strange thing is that these oscillations don't occur until the end of the time step when the simulation crashes. I think the problem is derived within Fluent - the continuity residuals gets particularly high (on the order of 10s or 100s).

Eventually the solution crashes either with an error stating negative volumes within the fluid mesh or high distortions within the solid mesh.

I've tried increasing solution stabilization at the FSI interface within Fluent and also numerical damping within mechanical. However, these don't really seem to work well.

Has anyone come across such a problem before? Any help would be greatly appreciated. I am attaching some images of the geometry, oscillations that I am observing between flow and force and the distorted mesh after opening.

Any help/information would be greatly appreciated!