Hello guys.I have a complete water distribution system.The main challenge I am facing is how to meet the demands at specified nodes after running a criticality analysis tool.Can you guys please provide insights and assist me so that the model above can run successfully.I have set up measures and controls so that the tank will never get empty.After doing a criticality analysis on the model the hydraulic engine outputs unreasonable results.I think my question is, after running the criticality analysis(by unchecking the check valve option) and understanding which segments are facing outages then what next?Is there a way that I can incorporate during the design in order to avoid disconnection of certain segments due to demand shortfalls? I have worked on setting up new calculation options for the engine but still, I get unexpected results when I look at my flex table.
Please note that I don't want to use Pressure Dependent Demand or emitter coefficients and instead I only want to work in Steady state mode with fixed demands as they are.None of the elements is disconnected from the main model as seen in the network navigator toolbar.
Here are some links that may help you.
Thank you, Tom Walski, for getting in touch.Can you please give me a direct lead to the solution.I think my question is...after understanding which parts of my network are facing outages; that is after doing criticality analysis and segmentation to understand which segments have been disconnected due to demand shortfall then what should I do to avoid that.How do I work around with this Isolation valves or something of the sort to allow flow to this nodes without altering my demand so that I can achieve reasonable results?I don't want to use PDD or emitter coefficients.I only wanted to work with fixed demand in the Steady state.Thank you once more and sorry for asking many questions.I hope am not bothering you that much.Please have a look at the attached network I am confident it doesn't have any errors.All the controls have been set straight with none of the elements disconnected from the main network
t looks like my network, due to the long length of pipes and small pipe diameters it may be impossible for the demands to be met at the nodes as I had defined.I have decided to try and use pressure dependent Demand functions,can you please guide me through.Should I use the 0.5 ratios as it is the default function to derive my equation?and at the end will the engine display results with generated flows as a ratio to the residual pressure?4201.watercad.zip
I don't think pressure dependent demands will help you much, because the pressure at your demand nodes is quite high. I would just suggest these changes:
1. Your tank is empty at the start of the simulation, and this causes the "disconnected demand node" errors. Set the tank "Elevation (Initial)" value to a number between the base and maximum tank elevations - e.g. 1,490 m
2. Your pump controls should leave a small buffer between the tank-full and tank-empty levels. For example, you could set something like this:
IF T-1 Percent Full <=25% then PMP-3 Pump Status = On
IF T-1 Percent Full >=95% then PMP-3 Pump Status = Off
3. You should check your pump capacity against the demands. Currently the pump can't deliver enough water from the reservoir to the tank, so, if I run an extended period simulation, the tank empties after a couple of hours.
Answer Verified By: ALLAN MULONGO WAFULA
Hello Mal Sharkey!
Thank you so much for this reply.My network model is ok only that I did set the base elevation to be the same as the initial elevation of the tank.I followed your first instruction (in reference to your answers above: "1. Your tank is empty at the start of the simulation, and this causes the "disconnected demand node" errors. Set the tank "Elevation (Initial)" value to a number between the base and maximum tank elevations - e.g. 1,490 m", and I managed to compute and run the model successfully without any error!
Thank you for your time, Mal Sharkey!I will have to read more about TANK OPERATING RANGE in order to avoid mistakes later!
THANKS, SOO MUCH!
Here is some information in our Wiki, on tank operating range: Understanding Tank Operating Range
Jesse DringoliTechnical Support Manager, OpenFlows ProductsBentley Communities Site AdministratorBentley Systems, Inc.
Thank you Jesse