ERROR: nonlinear solver did not converge, when simulating ball movement in meso-size chamber.

Hi all,

I have seen several threads about this error and tried to figure it out myself using the sample cases but I still fail to simulate this. Any help will be greatly appreciated.

I am trying to simulate the movement of a 1 mm diameter ball inside a chamber. There is a water flow on the top of chamber, from left to right. I am using fluid structure interaction (FSI).

I keep getting the same error message that says
Nonlinear solver did not converge.
Time : 4.6875e-005
Segregated group 2

Attempt to evaluate real square root of negative number
Function: sqrt ... (and so on)

I also get a list of warning saying that "Inverted mesh element near coordinates ..., ...) that are located inside the ball (which is linear elastic solid material). I am also confused because it supposedly have less deformation compared to fluid area.

Any help or idea will be greatly appreciated. Thanks in advance.