Dear Dave,
Thanks for your response. I actually could resolve the issue and could successfully run the 1D simulation on my network (with constant cross sectional areas, like the warning messages). When I compare the time series of flow rate out of the simulation with our MRI data, I found pretty good agreement. However, I don't know why the flow and velocity are almost constant along x at each time frame? I mean if I plot the flow rate (Q) as a function of x for each segment at each time step, I get a constant value. Do you think that it is because of the constant area in each segment, or maybe it it because of the wormesly velocity profile that I chose for the inlet faces? Shall I choose parabolic velocity profile instead?
Thanks so much for your response in advance,
Best,
Sohrab