Re : Help for EPANET - Network Ill conditioned at Node xx

[network2000]

Hello,

Please help me to correct the error in the attached .net file..It is giving Network Ill conditioned at Node xx error.. All nodes are connected with links..

Thank you
poun

 

[fel3]

I had only a few minutes to look at your model at lunchtime today and won't have any more time until next week. Unfortunetely, I'm also a bit rusty with EPANET, since I haven't used it in about two years.

Even so, I was able to find and fix one of the errors. The Status Report says that Dv4 is disconnected. Actually it's DV4 and its neighbors that are disconnected from the rest of the network. EPANET can handle isolated regions, but they must have a source, which this region does not. I added a pipe between nodes Dum6 and Dum126 and that took care of this problem.

The Status Report also says that your reservoir is closed, which would mean the model doesn't see an active source. I exported the network file (File|Export|Network) and saw that all of the pipes are open, so I can't figure out why the reservoir would be closed. I added a second reservoir with a higher head (1000 m) and connected it directly the system somewhere, that didn't work. The Status Report said my reservoir was closed also, even though I set its status to open.

I then tried closing all three pumps and bypassing the pumping station with a new pipe between the reservoir and node D8, increasing the head on your reservoir, connecting "disconnected" nodes with more pipes, giving all demand patterns a non-zero value at all time steps (I changed your zeros to 0.1), etc.. None of this worked for me.

This is going to take a bit more digging. One thing you might want to do, since you know this model much better than I do, is export the network file and see if you can spot something in your inputs that might be causing this problem.

Fred

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[fel3]

network2000…

I don't know if you figured out what was wrong with your model, but I did over the weekend. I found a total of six regions that were not connected to the main network. That was it. When I first looked at the model, I found just the one I mentioned above. This weekend I found five more.

The attached file includes an updated model with six new pipes (named FEL1 through FEL6) and the full output report. I sized the new pipes based on the adjoining pipes. With these six new pipes the model runs successfully. However, the results are not all good.
[ul]
[li]The pipe out of the reservoir and the suction and discharge pipes for the left and right pumps are very undersized at 87.8 mm.
Since this is your default diameter, I suspect these pipes never got completely edited. It happens.[/li]
[/ul]
[ul]
[li]Pressures range from over 90 m during some time slices to all negative at T=5:20 (the lowest pressures I saw at T=5:20 are below -110 m). The low pressures might be partially or completely fixed if the undersized pipes at the reservoir and pumping station are corrected, but I didn't get to that. However, all other time slices had positive pressures, so I suspect there is also a problem with the combination of demand patterns at T=5:20 that is requiring far more flow than the system can handle. As for the high pressures, I can't imagine needing to run a flat system like this at 90 m (which is more than 125 psi in my world).
One of the best ways I can think of to reduce your current pressure requirements (and thus reduce energy requirements at your pumping station) would be to upsize some (or more than some) of the upstream pipes in the system. [/li]
[/ul]
[ul]
[li]A few other pipes are also undersized, but you will have to look at all time slices to identify them all. I figured anything flowing above 1.8 m/s merited a look.[/li]
[/ul]

I hope this helps, and please let me know if you need further assistance. This was a fun little detective project.

--Fred

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill