HELLO BENTLEY FAMILY,
I am trying to model a complex gravity flow system where water flows naturally by gravity from the reservoir (a river upstream) to several tanks downstream. Is there the best way to run the model and allow the system to deliver a reasonable amount of flow by automatically adjusting itself in accordance to the existing conditions(active topology/base physical elevations e,t,c) without the need to introduce Flow Control Valves before each tank?
My point is that in any real gravity flow system water tends to flow up to the maximum capacity the pipeline will hold/allow depending on the terrain surface and amount of energy to be overcome along that pipeline route without the need of introducing a flow control valve. We all understand that more rugged terrain surfaces will require more energy to be overcomed in the pipelines than smoother terrains which will enable the pipe to carry more water. In the real scenario, the natural low will apply and flow delivered will automatically adjust unlike in watergems where negative and even larger flows are experienced without the introduction of FCVs.
Is there a way to allow the software to automatically adjust the flow delivered in an open gravity system(reservoir to tank downstream) to be reasonable and match the existing ground conditions without the need of a FCV. (Lets maybe say: A PRESSURE DEPENDENT FLOW) which will maintain a positive residual head in the downstream side even if it is 0.000001m of water or soo.
Or is there any way to tackle this issue? I was thinking maybe the Pressure Dependent Function will sort me but I have tried and realized it won't. Can anyone please guide me by using the attached file.Let's say, pick a pipeline from the Reservoir to BPT1-Check the selection sets set they will help. With this pipeline, without the use of a FCV, can the software readjust itself into the normal conditions available and allow water to flow without any negative pressures experienced. Please find attached.
CHEPTAIS ANALYSIS.rar
Hello Mulongo,
The elevation of the reservoir feeding the system is very close to the elevations of the nodes downstream of this. With the headlosses in the pipes, I would expect negative pressures to occur, and the pressures will continue to drop. Are these elevations correct? Are the pipe diameters and other properties correct? If so, what are the flows in the actual system compared to the model results.
Regards,
Scott
Hello Scott,
Every element is as it is in the real situation. The pipe route and elevations were surveyed. In the actual system, the flow delivered is 23.6L/s. From the design data, the line from R-TIISI to BPT 1 can deliver only up to a maximum of 30L/S with which when surpassed negative pressure will be experienced meaning zero flow in the real world . Can the software be able to readjust itself to the existing ground/nodal elevation conditions and allow water to flow only up to a maximum(30L/S) but not the current value(150L/S or so) without the use of a flow control valve?
Hello Mulongo.
Pressure pipes in WaterCAD are always supposed to flow full, satisfying given demands.
If you want only certain amount of flow should be provided to tank from reservoir, you can put a control on pipe to close when 30 L/s is supplied, if you don't want to use FCV.
Or you could use pressure dependent demands, where demands will be satisfied based on available pressure.
Using Pressure Dependent Demands
Sushma Choure
Bentley Technical Suppport
Hello Sushma,
You seem to understand my point very well
Can you help by assisting to set up a PDD on the attached model please?The use of controls on the available pipes will actually sort me out.but I would rather use PDD .please set the percent of demand that is dependent to available pressure to be 100%.Pressure at the tanks is actually zero,I don't know if using the node immediately before the tank will work.
The use of controls doesn't work. Setting up a PDD on the same will assist. Can anyone illustrate by setting up a PDD on the attached document please