Changing the solver engine and time step!

Mo7amed,

I'd like to see your model files before I comment on why the results you're seeing are different. What you should be certain of first is that you're comparing values at the same time steps when you're looking at the results of elements. If you're looking at two different time steps then it's possible the results could have changed pretty dramatically because something in your network could have changed, e.g. a pump turning on/off or a valve switching statuses. An important setting to check in your calculation options in order to make sure you're seeing all the time steps the "reporting time step". If you set that to <All> instead of Constant or Variable that might help out. I also noticed that you said you're using a time step of .02 hours and .01 hours, which are relatively small time steps. Do you have very fast changes in flows that you need to capture? If you don't you might want to consider using a slightly larger time step like 5 minutes.

If the above doesn't help there are two options for sharing your model on Communities. Either way, be sure to zip your files first. The first option is to attach to your reply on the forum using the Advanced Reply Editor (see link below and to the right of the reply box). If your data is confidential, use the instructions in the link below to send it via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley.

communities.bentley.com/.../7079.be-communities-secure-file-upload

If you upload the file to Sharefile, please post here with the name of the file so that we know it is available

We have a wiki article that I've linked to below that explains the user notification that you're seeing and how it can be resolved.

communities.bentley.com/.../24830.pumps-are-operating-at-a-much-higher-rate-than-the-design-point-pump-exceeds-the-maximum-operating-point-specified-for-the-pump-curve

Regards,
Mark

Hello
I uploaded the file and linked it to this URL.

please check why the model works fine when using WaterGEMS solver engine and with problems while using epanet solver engine (both under the same time step and other conditions)?

Thank you in advance

Thanks for your fast respond ,
I uploaded .WTG.SQLITE file.
This system is very simple, 5 pumps and 1 demand node, if you used the WaterGEMS solver, the system is balanced while if you used EPAnet, the pump will not work because it couldn't deliver head or flow. (there are not any control is the system)
Why is that and how can i overcome this problem while using the EPAnet solver.
Thanks

The solution is simple--use WaterGEMS instead of EPANET. The WaterGEMS solver has some features that make it more robust.

Plus WaterGEMS has a whole array of features that do things better than EPANET (e.g. symbology) or things that EPANET can't do at all (e.g. criticality, pressure zone manager).

I already knew the WaterGEMS is better !! But i must complete my work with EPAnet!!!!

if you know an answer, please share it with us!

Thanks

Hello,

I believe that this is because the flow required for some time steps between about 10 hours and 14 hours is higher than what the pumps can provide. If you graph the flow and pump head for the pumps, you will notice that that there results are okay. There are flow and pump head results for each pump for all time steps.

However, notice that the flows are higher than the highest flow value in the pump definition. It is likely that the EPANET solver to noticing this discrepancy and generating the user notification as a results. However, it does appear to be extrapolating the flow results beyond the maximum flow value in the pump definition.

The WaterGEMS solver is more robust in how it works in this case. So while the flow and pump head results are generally the same, no user notification is generated.

Regards,
Scott

To add to Scott's answer -

This is due to the fact that the two different solvers handle Multi-point pump curves differently (and you are using this type).

If you right click on one of the pumps, choose Pump Curve and select one of the times in question such 12 hours, you'll see that with the WaterGEMS solver, it has a curved shape and is extrapolated beyond the highest flow point entered on the curve. However with the EPANET solver, you'll see that linear interpolation is used and it does not show the extrapolation; the operating point is shown beyond the end of the curve, which causes that notification to be generated. It's able to select an estimated operating point, but the warning lets you know that it's beyond the curve.

If you navigate to the help topic "Engine Compatibility Calculation Option", you can read more. There is also some additional information here:

communities.bentley.com/.../24597.should-the-epanet-solver-and-the-watergemscad-solver-give-the-same-results-for-a-model

communities.bentley.com/.../9025.why-do-i-get-a-user-notification-stating-pump-cannot-deliver-flow-or-head

To add to Scott's answer -

This is due to the fact that the two different solvers handle Multi-point pump curves differently (and you are using this type).

If you right click on one of the pumps, choose Pump Curve and select one of the times in question such 12 hours, you'll see that with the WaterGEMS solver, it has a curved shape and is extrapolated beyond the highest flow point entered on the curve. However with the EPANET solver, you'll see that linear interpolation is used and it does not show the extrapolation; the operating point is shown beyond the end of the curve, which causes that notification to be generated. It's able to select an estimated operating point, but the warning lets you know that it's beyond the curve.

If you navigate to the help topic "Engine Compatibility Calculation Option", you can read more. There is also some additional information here:

communities.bentley.com/.../24597.should-the-epanet-solver-and-the-watergemscad-solver-give-the-same-results-for-a-model

communities.bentley.com/.../9025.why-do-i-get-a-user-notification-stating-pump-cannot-deliver-flow-or-head