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EPS Pump cannot deliver the flow

Dear Team, 

In my model, The nodes connected next to the pump in active topology has demand pattern( Grass lands) as  9-12 (3 hrs)  and 18-21 (3 hrs) in a day. There are 7 pumps in (BP-16,18,19,23,25,26,39) feeding to grass lands demand.

As per the my understanding of the model, i should get warning msg for all the 7 pumps "Pump cannot deliver the flow or head" in each interval of time. Say at 0 hr  7 pumps warnings, at 1 hr again 7 pumps warning, same upto 8th hr. Since, as per demand pattern up to 9 hrs there is no demand. If no demand on the downstream side of the  pump, then model has to give warning msg. 

But looking at the users notification, it is not happening so!!!. At different hrs different pumps are giving warning msg but all the connected nodes are with same demand pattern. I suppose to get all 7 pumps warning at every hr. But, if i operate in steady state no error warnings at all.

Is it my understanding wrong? or how to do it?

Suggestions please. I attached the file for your use.

With Regards,

RSP.

  • Hello RSP,

    This is likely related to modeling noise. Take a look at two of the pumps, such as BP-39 and BP-26. At time zero, you see a user notification for the first pump but not for the second one. Change the flow precision to look out 10 decimal places instead of the 2 decimal places in the model. Note that the flow for BP-39 is very slightly negative while the flow for BP-26 is very slightly positive. In both cases, the flow is zero.

    However since BP-39 has a very slightly negative flow, the program is essentially trying to add slightly more head than the shutoff head of the pump. You can see an illustration of this by looking at your pump definition. At zero flow, the head is 80 ft. However, you have a slightly negative flow, meaning that slightly more than 80 feet of head would need to be added. Since this is off the pump curve, the user notification is generated.

    You can try making some adjustments to the calculation options for this, but the modeling noise may still exist. The bottom line is that the pumps have zero flow except when there is demand, and the pump head seems to match with the pump definition. So, the program appears to be operating correctly.

    Regards,
    Scott

    Answer Verified By: Sushma Choure 

  • Dear Scott,

    Thanks for response. Yes What you mentioned is correct, but why even there is no supply there is a change in flow?. Since, it will be bit hard to explain to the client. In reality, if no demand then no change in downstream.

    Thanks again for the Bentley's support.

    With Regards,
    RSP
  • Hello,

    It's modeling noise. The program looks out ten decimal places when looking at results fields. For instance, the flow at BP-39 is -0.0000006646 m^3/hr. But has it is slightly negative, the user notification is generated. The bottom line is that the flow is treated as being zero and the results you see from the pumps confirm that.

    Regards,
    Scott