Using Skelebrator to reduce the number of pipes in a model

Product(s): WaterGEMS
Version(s): CONNECT Edition
Area: Modeling

Background

There can be cases when a user will want to reduce the number of pipes in a model. This may be because they want to simplify the model, such as removing pipes serving as laterals to a hydrant, or because they have license configuration that would require having fewer pipes. A user could manually remove pipes be deleting them or making them inactive or export a part of a model as a submodel to look at only a part of the system.

Skelebrator is a tool in WaterGEMS where a user can simplify a model and reduce the number of pipes in the system in a more automated manner. The information below includes the general workflow for this as well as the types of methods available in Skelebrator.

Before using Skelebrator, it is recommended that you make a copy of the model. Skelebrator does not include and “undo” feature, so once a change is made, it cannot be undone. In addition, note that when a pipe is removed from a model, it will be removed from all scenarios. If you want to remove pipes from only specific scenarios, please use Active Topology management instead (wiki). Finally, care should be taken for models with multiple scenarios. Please refer to the WaterGEMS Help topic “Skeletonization and Scenarios” for more information. You can find the Hep documentation by going to File > Help > WaterGEMS Help.

A note for WaterCAD users: If you have WaterCAD, you will need to upgrade to WaterGEMS to access Skelebrator. In the distant past, WaterCAD users could purchase Skelebrator separately, but this is no longer possible. Also, starting with CONNECT Edition Update 2 (10.02.00.43 and greater), the Skelebrator tool is no longer accessible from within the WaterCAD user interface.

Using Skelebrator

To open Skelebrator, go to the Tools tab and select Skelebrator Skeletonizer. You can also use the Ribbon search to access it.

There are few Skelebrator options: Branch Collapsing, Parallel Pipe Merging, Series Pipe Merging, Smart Pipe Removal, and Inline Isolating Valve Replacement. Information on each of these can be found below.

At the very bottom of the Skelebrator manager, you will see the current number of pipes and nodes in the model. When you preview a skelebration run, will see the number of elements included in this.

At the top, you can click the New button to choose the type of skelebration you want to run. In addition, to the Compute button, which runs the skelebration, there is an option to run a manual skelebration and a Preview button. The Preview option lets you see the elements that will be removed or combined during the skelebration.

On the right side of Skelebrator, there is a batch run option. If you set up multiple types of skelebration, you can use this option to run all of them at once.

In the Protected Elements tab, you have the option to pick elements that will not removed when you run Skelebrator. This is used if you have elements that are important and need to remain in the model after simplifying it. To pick the protected elements, click the Select in Drawing button to open the Select tool.

  

When you run Skelebrator, you may want to run a given skelebration type more than once. For instance, if you have five pipes in series and run Series Pipe Merging skelebration, only some of the pipes will be merged. Running this again will remove additional pipes.

Skelebrator and Demands

Since Skelebrator removes pipes and nodes, there are options to account for the demands on junctions that are removed from the model. Each type of skelebration handles this differently. The sections on the different types of skelebration will include information how demands are allocated.

Types of Skelebration

The following section is related to the different types of skelebration available. The type of skelebration will depend on the model, but more than one type of skelebation can be used on a model.

Branch Collapsing

Branch Collapsing is used when you want to eliminate dead ends in a system. Skelebrator will find branches in the system and remove the pipes and nodes.

After creating a Branch Collapsing, use the Settings tab on the right side of the Skelebrator manager to define how the skelebration runs. For the Maximum Number of Trimming Levels, you can define the number of trimming levels you want to allow. In Branch Collapsing, a single trimming level run to completion would trim every valid branch in the model back by one pipe link. Two trimming levels would trim every valid branch back two pipe links and so on.

For the Load Distribution Strategy, you would select how you want the demand allocated. If you set this to Move Load, the demand will move to the next junction upstream. If you select Don't Move Load, the demand will be deleted from the model along with the junction.

In the Conditions tab, you can set select parameters that determine which pipes are included in the skeletonizing process in the Conditions tab. In Branch Collapsing, the junctions referred to in junction conditions are the two end junctions of the pipe being trimmed. Tolerances can also be defined for junctions. Tolerances work by limiting the pipes skeletonized only to the ones that have the specified attribute within the specified tolerance. For example, in Branch Collapsing you can set a tolerance on junction elevation of 3 feet would limit skeletonization to pipes that had both end junctions with an elevation within three feet of each other. For pipes, you can enter condition related to diameter such that the only pipes that can be removed are less than a given size.

 

Parallel Pipe Merging

Parallel Pipe Merging looks for pipes that are in parallel with a shared start and stop nodes. If you have two pipes in parallel, Parallel Pipe Merging will remove on of these from the model. After creating a Parallel Pipe Merging, use the Settings tab to define how the skelebration will run. For the Maximum Number of Trimming Levels, you can define the number of trimming levels you want to allow. If you set this to 1, if there are three parallel pipes, it will be reduced to two pipes.

Dominant Pipe Criteria is used to determine which of the pipes is the dominant pipe, and thus the pipe whose properties are retained. For example, when merging a 6-in pipe and an 8-in pipe, if diameter is selected as the dominant pipe criteria then the larger diameter pipe (e.g., 8-in) will provide the properties for the new pipe. That is, the 8-in pipe's diameter, roughness, bulk reaction rate, etc., will be used for the new pipe.

If the field Use Equivalent Pipes is checked, Skelebrator will adjust the properties to accommodate the removal of other pipes. If selected, you would define the Equivalent Pipe Method by selecting if you want to modify the dominant pipe roughness or the dominant pipe diameter for the equivalent pipe calculations. If Modify Diameter is selected, the new pipe's roughness is kept constant and the diameter adjusted such that the head loss through the pipe remains constant. If Modify Roughness is selected, the new pipe's diameter is kept constant and the roughness adjusted such that the head loss through the pipe remains constant.

For the Minor Loss Strategy field, you select how you wans Skelebrator to manage minor losses. You can choose to ignore the minor loss, which means the merged pipes will have a minor loss of zero. If you choose Skip Pipe if Minor Loss > Max, you would protect pipes from being skeletonized if there is a minor loss greater than the maximum value you enter. If you choose 50/50 Split, the merged pipes will have 50% of the sum of the minor losses from the parallel pipes.

In the Conditions tab, you can set select parameters that determine which pipes are included in the skeletonizing process in the Conditions tab. With Parallel Pipe Merging, you can enter certain pipe conditions for the run. For example, you can enter condition related to diameter such that the only pipes that can be removed are less than a given size.

Series Pipe Merging

Series Pipe Merging takes pipes in series and combines them into a single equivalent pipe. The two pipes cannot be connected to another pipe or it will not be removed.

The Settings tab will define how the pipes will be removed and the demands distributed. The Maximum Number of Removal Levels defines the levels of pipes that get removed per iteration of the Series Pipe Merging operation. The Dominant Pipe Criteria determines the pipe whose properties are retained as appropriate. For example, when merging a 6-in. pipe and an 8-in. pipe, if diameter is selected as the dominant pipe criteria then the larger diameter pipe (e.g., 8-in.) will provide the properties for the new pipe. The Use Equivalent Pipes field is used when you want Skelebrator to adjust the merged pipe properties as such to attain equivalent hydraulics as the two merged pipes. The Equivalent Pipe Method field determines if the diameter or roughness is modified for the equivalent pipe. For example, if Modify Diameter is selected, the new pipe's roughness is kept constant and the diameter adjusted such that the head loss through the pipe remains constant.

If there is a junction removed during the Series Pipe Merging, you can define out the demand is distributed. If Equally Distributed is select, you can set the percentage that the demand is distributed to adjacent nodes. Proportional to Dominant Criteria assigns loads proportional to the attribute used to select the dominant pipe. For example, if diameter is the dominant attribute and one pipe is 6-in., while the other is 8-in. (14-in. total length), 8/14 of the load will go to the upstream node, while 6/14 will go to the downstream node. Proportional to Existing Load maintains the pre-skeletonization load proportions. User-Defined Ratio allows you to specify the percentage of the load applied to the upstream node in the post-skeletonized pipe.

The Apply Minor Losses field is used if you want the minor losses to be retained during the skelebration process. There is also an option to remove TCVs if they are in series.

The Conditions tap operates similar other skelebration types and defines the elements involved when using Skelebrator.

Smart Pipe Removal

Smart Pipe Removal is a data scrubbing technique that allows the user to remove small diameter pipes (including those that form parts of loops) while retaining network connectivity and important elements, like pumps and valves. The algorithm used marks elements that can be safely removed without causing this issue.

When using Smart Pipe Removal, check the box for Preserve Network Integrity to assure pipes are not removed that will inhibit the calculation of a model. By checking the box for Removed Orphaned Junctions, nodes that have no pipe connected to them will be removed from the model. If there are no demands on the orphaned nodes, the model will still compute, but you will see user notifications about nodes being disconnected from a reservoir or tank.

The Loop Retaining Sensitivity setting controls how sensitive the pipe removal algorithm is to retaining loops in your model. A low setting will mean a higher number of loops in the model and a high setting means fewer loops. This feature is only available when using the Preserve Network Integrity option.

There is an option to include pipe conditions in the Conditions tab for Smart Pipe Removal. Using pipe conditions is highly recommended when using this skelebration method. Smart Pipe Removal is largely used to remove small diameter pipes while retaining network connectivity. By including a pipe condition based on diameter, this will assure that larger diameter pipes are not inadvertently removed from the model.

Manual Skeletonization

Manual Skeletonization allows you to step through each individual removal candidate. The element can then be removed or marked to be excluded from the skeletonization. You can save this process and choices you made and reuse them in an automatic skeletonization of the same model.

Manual Skeletonization is based on one of the methods described above. For instance, if you are using Series Pipe Merging, the process will only look at pipes in series.

To access this, click the Manual button at the top of Skelebator.

A new dialog will open where you can review the elements that would be removed during the process. You would check each action in turn and either execute or protect the element. This method allows for complete control over the elements removed during the process.

  

Inline Isolating Valve Replacement

This is a special type of skeletonization used specifically to removing certain types of valves from a model and replace them with isolation valves. In the process of creating a model, you may have added a valve like a TCV or a GPV to act as an isolation valve. WaterGEMS and WaterCAD include an element type for isolation valves that works a little differently compared to other valve types. An isolation valve does not split a pipe. Instead is associated with a pipe and can have a setting of open or closed.

Inline Isolating Valve Replacement will identify existing TCVs, GPVs, and PBVs in a model and merge the pipes on either side of these valves. The valve will be replaced with an isolation valve that is associated with the new merged pipe.

In this method, you would select the types of valve you want to replace. Note that PRVs, PSVs, and FCVs are not included in this method. In most models, these have specific purposes other than acting as isolating valves. In addition, if there is a valve that should not be replaced by an isolation valve, this should be included as a protected element.

You will also have the option to set a maximum number of removal levels, similar to other skeletonization methods. You would also define the dominant pipe criteria, which determines the dominant pipe (the one that will be kept after the operation). The dominant pipe is the pipe whose properties are retained as appropriate. For example, when merging a 6-in. pipe and an 8-in. pipe, if diameter is selected as the dominant pipe criteria then the larger diameter pipe (e.g., 8-in.) will provide the properties for the new pipe. That is, the 8-in. pipe's diameter, roughness, bulk reaction rate, etc., will be used for the new pipe.

Use Equivalent Pipes is used if pipe diameters or pipe roughnesses are different on either side of the valve. This will create an equivalent pipe so that the hydraulics are similar once the pipes are merged. You can also apply minor losses to the new isolation valve by checking the box for Apply Minor Losses.

More information on Inline Isolating Valve Replacement can be found here: How to convert a TCV, GPV, or PBV to an isolation valve using Skelebrator.

See Also

How can I reduce the number of pipes in a model?

How to protect elements which are part of control sets in Skelebrator

Is there a recommended level of skelebration for different modeling conditions?

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