Hi,
I am modelling a system with two elevated storage tanks (with an operating level of 950.5 and the other at 921.5). I am expecting that the 950.5 will be able to fill the 921.5 tank. The system has two supply wells. To add supply into the system, i am simply adding a negative demand at the well location. I don't have any information in regards to pump curves at the well locations, just the pump capacity flow. My current system demand is 2000 gpm. Once I my supply is less than 2000 gpm my model runs with no errors, however as soon as the supply is greater than 2000 gpm, the model give me the following errors: disconnected demand nodes detected. and junction (at various) locations is disconnected from reservoir or tanks?
Are you running an EPS? If the supply into the tanks is greater than the downstream demand, the tanks will eventually become full. When this happens, by default an altitude valve is assumed and will close the tank's inlet pipe, which could lead to disconnections. Try graphing the "percent full" for your tanks and if you find they are becoming full or empty, you may need to add controls to your model to prevent this. If the tanks in the real system will overflow when full, you can now model this as well.
See more information in the following related article: What happens when a tank becomes empty, full, overflows?
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
I am running a steady state analysis and running batch foreflows, not EPS. Is the way I modelled the supply correct?
If you have no tanks or reservoirs and only a negative demand as the inflow, if the demand is greater than the inflow value, you may see this. You will likely need to have some source of flow that can vary with the demand, like a tank or reservoir.
If there are tanks or reservoirs, you will want to make sure that the system isn't disconnected because of these. The tank being empty or full would be one cause of this, as mentioned above. If there is a pump on a reservoir and the pump is off, that would also cause a message like this.
If this doesn't help, we would need a copy of the model files.
Scott
if I model my well (supply) as a tank, how do i know what elevation to set the tank at?
Do you have any way of getting the pump information for the well? That would be the best option, since you would not only have the flow but the head being added by the pump.
Otherwise, you would need to know how much head is being added by the pumps and use that to get the elevation. Even this might be tricky in getting stable results. For instance, depending on what you enter, you could end up with flow from the tank representing the well pump into the other two tanks (depending on the hydraulic grade balance in the system).
Using or approximating the actual well pump information would be the best solution though.