Discussion Forum

I'm working on a model to simulate the movement of a ventricle like structure caused by the pulsation of the fluid. I first started by simulating only the fluid part of the structure (inner structure) and it worked pretty well. Then I added the outer part (solid part) and that was the time when the problems occurred. - the 1st problem I encountered was the condition from the inlet of the fluid. I used "Fully developed flow" with "flow rate" set as 1.67e-7 m^3/s and multiplied it with a step function to ramp it up slowly and a rectangular function to generate the pulsation effect (open and then close and open). It worked pretty well with fluid only, but when i added the solid part into the model, it gave me an error message " Pointwise constraints for time derivatives are not supported.". And the interesting part here is when I switched my condition for inlet into "velocity", the problem solved. So I wonder what is the reason that it didnt allow me to use "fully developed flow" as my inlet for the FSI model but was ok when using only with laminar flow. - the 2nd problem is even when I switched my inlet to velocity, and started running my simulation, I received the following error message: "Nonlinear solver did not converge. Maximum number of segregated iterations reached. In Velocity u_fluid, Pressure p: There was an error message from the linear solver. Very ill-conditioned preconditioner. Time : 0 Last time step is not converged."

Is it because my mesh is too coarse, (i did try to increase the density of the mesh, but it didnt solve the problem). or was anything wrong with my initial settings?

thank you