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Problems when modeling an EPS engine aqueduct system

Dear Bentley Master

I am modeling an aqueduct system in 2 periods "EPS and Steady State"
In the first part, it is modeled with Steady State, solving the multiple errors presented in it.
In the second part it is modeled with EPS, I make the following configurations:

  • EPS motor selection
  • In Patterns, adjustment is made in the Hydraulic option

  • I make the adjustment in the Demand Control Center for the different Junctions of the system

  • I carry out the Control for the Set to use according to the pumps that I have in the system

  • In the alternatives, I modify in operational the creation of a child scenario with the selection of the created Set

Note: Making it clear that the system has 2 pumps that supply a tank, leaving only pump 1 activated. But the tank gets 2 more reservoirs.

I generate multiple errors such as:

Network Unbalanced.

Disconnected demand nodes detected; hydraulic results are likely to be compromised

Demands and is disconnected from a reservoir or tank during the analysis.
This error occurs multiple times. System disconnected because of pipe ta1153, this error could not be solved and I believe that one time solving it, the others will be fixed
My doubts are enough.

I would like with the help of a bentley teacher to solve the many problems that the model presents.

I already made different applications of solutions for Network Unbalanced but I can't find the solution.

Can I model a tank as represented in the model, 2 pumps, 2 reservoirs?
I have been able to review different forums, videos, supplied by the bentley team and I have not been able to find a solution. Attached model for your required solution.

  • Hello Jefry, 

    Pump BOMBA 1 - 10HP is having issues in steady state as well before moving to EPS analysis, that pump cannot deliver flow or exceeds maximum operating point. 

    Could you please check if the correct pump curve is defined as second pump is BOMBA 2 - 15HP is off, so pump  BOMBA 1 - 10HP needs to deliver required flow. Please follow below troubleshooting steps. 

    User Notification: "Pump cannot deliver flow or head" 

    If you could provide at lease 3 point curve that would yield better solution. 

    Disconnected nodes are in model because of tank PTAP, as it becomes empty and full every time step as per controls defined. Make sure that tank neither becomes empty nor full to avoid disconnected nodes. 

    There are 3 reservoirs in model and 1 tank, are these 3 continuous sources of water or elevated tanks on field? You mentioned you are modeling aqueduct, could you elaborate more on that? 


    Sushma Choure

    Bentley Technical Suppport

  • Hi Sushma
    I have not been able to add more than 3 points for the curve of Pump 1 and Pump 2, this is because the aqueduct system is very old, there is almost no information on these pumps and the curves could only be made with 1 only point.
    There are 3 reservoirs in model and 1 tank, are these 3 continuous sources of water or elevated tanks on field? You mentioned you are modeling aqueduct, could you elaborate more on that?
    Answering the question, the 3 sources mentioned in the model are continuous water.
  • Hello Jefry,

    Thank for you for confirming the modeling case. 

    As mentioned earlier please revise the pump curve, if you don't have full pump curve i.e. fine, one point curve is to be used in such cases only. 

    The total downstream demand is around 150 lps and if only one pump is going to operate then you may need to revise the pump curve to cope up with the total demand. 

    Also the controls on the tank need to be set up correctly, you can either set level based or hydraulic grade based controls. It appears in second control below the level should be used instead of HGL, as HGL cannot be 0.05 m. 


    Sushma Choure

    Bentley Technical Suppport

  • Hola Sushma
    En primer lugar, gracias por su colaboración con respecto a las muchas preguntas que les he hecho.
    Realizar el ajuste del error encontrado en los Controles y presentar los mismos errores de 
    los de las uniones desconectadas, aplicar las posibles soluciones encontradas en un foro como
    comprobar si presento sectores desconectados pero ninguno, ajustar las opciones de cálculo para
    más interacciones, ajustar precisión.

    enlace de descarga adjunto
  • Hello Jefry,

    As Sushma pointed out in her earlier responses you need to revise the pump curve specifically for BOMBA-1 10 HP. Another thing I noticed was the size of the tank PTAP. It has a diameter of only 0.41 m. Are you sure the values entered for the tank are correct. 

    For testing I changed the value to 20 m (randomly) and the number of user notifications reduced. See the below snapshot;

    And here is the percent full graph for the tank PTAP;

    You can see that its more agreeable in this case and although the tank is getting 100% full at some timesteps, we don't have any disconnected nodes. With sufficient size the tank is not rapidly filling and emptying as before thereby not disconnecting the downstream and upstream pipes. 

    Check to see if the tank is as built or you can increase the volume of the tank. Note that I have randomly assumed a 20 m diameter and you would have to perform some mass balance calculations to determine the optimum capacity of the tank based on your demands downstream and the pumping capacity.

    Let me know if this helps.


    Yashodhan Joshi