Parts of the network are disconnected due to demand shortfall

Here are some links that may help you.

https://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/4615/running-a-criticality-analysis

https://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/30968/why-does-the-criticality-analysis-return-0-segments-when-using-the-subset-scope-type

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

6136.watercad.zip

To add to Tom and Scott's reply - I see that you have posted a file, but it is only the .WTG file. The .SQLITE file would be needed in order to open the file. If you are using CONNECT Edition Update 1, you can go to File > Save to Package.

If you are encountering a specific error or issue with Criticality, please elaborate on what you are seeing.

If you are asking for general advice on what to do after a criticality analysis to improve things, please elaborate on a specific challenge you are having. For example are you seeing a large system shortfall when a certain segment is out of service, but do not know what to do to prevent such a large shortfall? This may largely a matter of engineering judgment. For example there may be a trade-off analysis, comparing the cost to loop the system in such a way to avoid the shortfall when the segment is out of service, compared to the benefit and chance that the segment will be out of service. If the segment in question in the one just downstream of your main pump station for example, it may be very costly to mitigate this, as it may involve installing a backup pump station. In other case, the "solution" to high demand shortfall may be to add a loop; piping that provides another path for flow, to go around the segment that is out of service.

You may find further useful engineering advice in the book Advanced Water Distribution Modeling and Management

Hello, for a clear and precise elaboration, please check the attached file6237.watercad.zip.

If I were to design the same system in an excel sheet with defined formulas I will get results.

My question is can I be able to successfully run the model above and still meet all the demand in all nodes?,and still be able to get the results without encountering any errors.

Hello, in order to understand my case better please check the attached3755.watercad.zip.

Hello Allan,

There doesn't seem to be a criticality study in the model. Do you have a version of the model where a criticality study is set up?

I did look into this a little, creating a criticality study. Since there are no valves in the model, I needed to set this up with the "Consider Valves" option unchecked. Basically, this set each pipe as its own outage segment. When I computed criticality for this, there were indeed cases where the demands could not be met. However, this would be as expected in many cases, based on the layout of the system. 

For instance, consider a case where pipe P187 is closed. If this pipe is closed, the demand at junction (Point)-75 will not be satisfied. There is no other path for the flow to get to the node. So in a case like this, I would expect there by be times when the demands cannot be satisfied if there is an outage at a given pipe or segment. 

In the future, if there are valves in the model, you may want to include these, if for no other reason than to minimize the number of outage segments. However, given the linear setup of the system, I would expect some shortfalls.

All that being said, I noticed that if you compute the model on its own (not including a criticality study) that there are user notifications related to disconnected demand nodes. If this is ultimately what the issue is, the reason for the disconnected demand nodes is because the tank T-1 is empty. Because this tank is empty, this results in pipe P52 being closed. This link has some details on this. To resolve this, I would change the initial elevation of tank to a value between the minimum and maximum elevation. When you do this and compute the model, the disconnected demand nodes no longer occur. The following link has more information on this issue: Disconnected Demand Nodes user notification when computing model. This link mentions an empty tank being a possible cause of the issue.

If the issue is with running criticality, I would still set the tank to a higher water elevation. Criticality uses the scenario as a basis for the analysis, so having a viable solution is needed. Setting the tank level to a higher elevation will still result in outages, since there are some demand nodes with only one path in which to satisfy the demand, but you will at least be computing criticality with a better starting point.

Regards,

Scott

The main challenge I am facing is how to meet the demands at specified nodes after running a criticality analysis tool.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 emit5367.watercad.zipter 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.

The main challenge I am facing is how to meet the demands at specified nodes after running a criticality analysis tool.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 emit5367.watercad.zipter 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.

There are several ways to improve the reliability of the distribution systems. The two most important are

1. Loop the system. Proving loops gives the water several ways to reach every customer. even during a shut down

2. Having a high density of isolation valves. this makes it possible to only isolate a small number of customers when you have a pipe break or other maintenance.

What do you mean by "unexpected results".

It 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?

Check the attached0525.watercad.zip