This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

1. How can there be a flow supply without any flow demand? Can anyone help pe learn about it?

Parents
  • Hello Sifi, 

    As mentioned by Dr. Tom the flow is going from source reservoir into storage tanks. The "Flow Stored" is the net inflow into tanks at that time. 

    Since there are no demands in the model the water must be stored in tanks, which can be checked by Flow(In Net) result if is greater than zero, then the flow into the tank is greater than the flow out i.e. it is stored. 

    Here is summary about what does Flow supplied / demanded / stored mean in calculation summary results, for your reference,

    Calculation summary: Flow Supplied, Flow Demanded and Flow Stored 

    Regards,

    Sushma Choure

    Bentley Technical Suppport

    Answer Verified By: Engineer Sifi 

  • Likewise, I have a similar model in place of tanks I have demand nodes(junctions/ house connections). I want to keep the same flow as this model has.

    for example, I have copied all flows going to these tanks as a demand point in a different model.

    but, then when I am opening isolation valves the whole flow is changing. As I am learning water gems unable to find out how to keep the same flow in another model( demand nodes) when I open up isolation valves.

  • I have sent a copy of the model files by message to you sir.

  • What is the name of uploaded file? 

    Regards,

    Sushma Choure

    Bentley Technical Suppport

  •  I have attached models for your reference.

    • Model-1:   with demand nodes
    • Model-2: with tanks

    Likewise, I have two models one with tanks and another one with demand nodes(junctions/ house connections). I want to keep the same flow as model -2 in model 1.

    for example, I have copied all flows going to these tanks as a demand point in model-1. As I have considered it as current demand and exported it to model 2 demand nodes.

    but, then when I  open/close isolation valves in " model 2" the whole flow is changing, What can be the cause of it. As per this condition, I cannot keep the appropriate demand in model-1.

     What is your suggestion for it? How can I keep the flow as in model -2

    attached models for your reference.

    Model - 1.zipModel- 2.zip

  • Hello,

    I assume that the only isolation valve you are closing ISO-6. If that is not the case, let me know what valve you are closing. 

    The flow changes when you change the status of the isolating valve because WaterCAD is trying to balance the hydraulic grade in the system. If there are no demands in the system, the flow from between reservoirs and/or tanks is simply based on the difference in hydraulic grade. When the valve closes, this will force more flow through the parallel pipe and increase the headloss. This changes the hydraulic grade and can thus change the total flow in the system. (I will note that the change in flow in the system is relatively small when ISO-6 closed versus when it is open).

    In Model-1, there are demands in place. Since WaterCAD is a demand driven program, the demands will always be satisfied, no matter the impact on the hydraulic grade in the system. If there are tanks and reservoirs instead, like in Model-2, there can be changes in flow depending on what the hydraulic grade (and related results like headloss) is in the system.

    I would say that if you want to model a specific demand, I would use demands in the system. This is fairly common in a water system. If you need to model this with tanks and reservoirs, the flow may change depending on the status of elements in the system.

    Regards,

    Scott

    Answer Verified By: Engineer Sifi 

  • Thank you, for making it really easier to understand.

Reply Children
No Data