femlab-flow in a 3d channel
 

femlab-flow in a 3d channel
i have a cylinder with a flow inside of it; it is a very simple problem, with no slip conditions on the curved surface, an inflow velocity at the inlet and a pressure at the outlet. starting the simulation with an iterative method a window tells me that solution has not converged, and with direct methods the error is ''zero on the matrix diagonal''. what is the right method to solve it?
thank you in advance!