Problem with FSI simulations

ufuk

Hello,

I am doing a FSI simulation in a slightly tapered tube. I setup fluid and solid cases and run them coupled through ansys launcher. I take E as 4E+06 and poisson ratio as 0.49. I apply a sinusoidal velocity inlet profile and a constant backpressure of 13.3 kPa at the outlet. My period is 1 s. Everything goes well for upto 0.4 s and then the middle part of tube begins to blow up. Then the outlet pressure drops abruptly and inlet pressure begins to oscillate. After some time the tube blows too far from reality. I tried decreasing the relaxation parameter for coupling between the fields down to 0.01. This delays the time of this blow up upto 1.4 s. But again after some point same thing happens. (My time step is 0.01s and for the tube both ends are fixed, also I tried decreasing time step but it doesnt help)

Does anybody have an idea what might be the reason and what can I do? Like introducing some damping coefficients to the solid part for the transient anlysis, how much should they be. I am solving for small displacements by the way.

Thanks a lot. ufuk