I have only used one water modeling program that got this correct.Į. Considering inflows and demands from a mass balance perspective, inflows should be positive and demands should be negative, not the other way around.
WATERGEMS TANK ONE WAY FLOW SOFTWARE
This is an easy typo to make and it often results from not following the ridiculous sign convention that most water modeling software uses. Fixed inflows that are entered as demands (positive numbers), rather than as inflows (negative numbers). Pumps that are off or that have bad curve data. Rather than try to untangle this mess, we asked the city to get a clean copy of the model from the previous consultant.Ĭ. As I dug deeper into the model, I found some pipes with changed diameters, a tank that I had designed a few years before had been deleted, an entire section of the city had been disconnected (it had it's own tank, so the model would run, even if incorrectly), etc. As it turned out, one of the city's young engineers had tried to teach himself the program (not EPANET), but instead of working on a copy of the model, he used the master version of the model. When I tried to rerun the last consultant's scenarios, I didn't get his results. I once inherited a model from a city of 50,000 people that had a check valve incorrectly inserted into a 12" main. Pipes that are closed and control valves and check valves that hinder or block flow through their pipes. Regardless, the proper thing to do is to accurately model the physical elements in the system, rather than make things up.ī. Increasing the diameter of a tank won't change pressures, although this would cause pressures to increase and decrease more slowly during a time period simulation. Check all elevations to make sure they are correct. Tank(s) and/or reservoir(s) that are too low relative to the elevations of the other nodes. Negative pressures can have several causes, including, but not limited to the following:Ī. For example, a model that can't complete its iterations can generate this error.Ģ. For this case, the solution is to find and fix the other problems. Sometimes, however, there are other problems with the model that can generate a "disconnected nodes" error when there aren't actually any disconnected nodes. I never make this mistake myself, of course.
![watergems tank one way flow watergems tank one way flow](https://i.ytimg.com/vi/MjRf21CIjtU/maxresdefault.jpg)
I have seen this in other people's models quite a few times, both here and at work. For disconnected nodes, find all nodes that are truly disconnected (if any) and connect them to the network. That's not a lot of information, but I can give you a few things to start with:ġ.