[skabilan]

I am trying to simulate a transient flow through branching cylinders. The geometry is not complex. There was no problem with steady state solution. I prescribe the inlet pressure which is a positive sinewave. I get the following error

Time = 0.486

Mean and max Courant Numbers = nan nan
BICCG: Solving for Ux: solution singularity
BICCG: Solving for Uy: solution singularity
BICCG: Solving for Uz: solution singularity
ICCG: Solving for p: solution singularity
ExecutionTime = 481924 s ClockTime = 482478 s

Thanks in advance for any suggestions!