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The purpose of this technote is to discuss the Criticality feature available in the Bentley WaterGEMS and WaterCAD. Additional information can be found in the Help menu for the products. There is also a Quick Start Lesson available for Criticality until Help > Quick Start Lessons.
Bentley WaterGEMS V8i provides the user with a flexible tool to evaluate and identify the most critical elements in a water distribution system. Using this process, the user can shut down individual segments of the system and view the results on system performance. This is simulated in a single run rather than in a series of different scenarios.
A variety of indicators is reported for each outage during the criticality analysis. Depending on the type of run, criticality analysis can report the flow shortfall, volume shortfall or pressure shortfall in the distribution system for each segment outage.
Before conducting a criticality analysis, the segments to be removed from service during the analysis must be identified. Often this will be defined by the valves in the system, wherein a closed valve will disrupt service to parts of the model. Included in this, the user must identify which types of valves will be used in the analysis. The user will also have to decide which scenario will be used for the analysis.
Once identified, this information will be entered into the Criticality manager. The steps to do this and compute the criticality analysis are detailed below.
The Criticality manager can be opened by going to Analysis > Criticality, or by clicking the Criticality icon in the toolbar.
This will open the following dialog:
Next, click the Options tab. In this section, you will identify how the segments in the analysis will be defined.
The recommended procedure is to place isolation valves on the pipe elements. If you don’t have sufficient data on the location of isolating valves, each pipe element can be isolated. In this case, each distribution segment consists of a single pipe, not including the nodes at each end. You can set this up by way of the “Consider Valves?” option at the top of the page. By default, this item is checked. When it is checked, the segments are defined by the valves. If it is unchecked, the pipes are isolated individually.
When the “Consider Valves?” option is selected, the default status of the valves is available. By default, these will be set to “Always Use.” If you have some valve types that you don’t want used in the criticality analysis, change this field to “Do Not Use.” Note: if you don’t have a given valve type in the model, you can leave this with the default setting.
There is a valve override section at the bottom of the page. This item is used in cases where an individual valve will not be considered in the analysis, such as if the valve is broken open. Once the options are set as needed, click the New icon in the upper left and choose the scenario you will be using in the analysis. Once this is done, you will have to select the segmentation scope of the analysis. You can either choose a subset of the model or the entire network. With Subset is selected, you can select the subset by clicking the ellipsis button. If you choose Entire Network, all elements in the model will be used.
Next, click the green Compute icon. You may be prompted about update valve placement data. Typically, you will click Yes for this. The criticality analysis will then run. The results will be available in the Segmentation Results tab.
In the middle pane will be a list of all of the segments. In the right pane, you will see the distribution of segments and their properties, such as the number of pipes in a segment and the number of affected nodes. The displayed results are governed by the highlight segment in the middle pane.
Note: this is true of viewing results for the Outage Segments and Criticality sections below as well.
You can view the segments graphically by clicking the Highlight Segments icon at the top of the middle pane.
If you minimize Criticality manger, you can then view the segments on the model itself.
Once the segmentation is completed, you then do an outage analysis. This allows you to determine which segments are affected when a certain valve is closed. To do this, highlight “Outage Segment” in the left pane and select the green Compute icon.
The results from this section will show you how an outage affects a model, including the number of affected elements. You can also view these outage segments graphically in the model. Highlight one of the outage segments in the middle pane and select the Highlight Segment icon. When you minimize the window, the outage segment chosen will be highlighted.
The final step is to see how the outages affect the demand. This is the most important function of the criticality analysis. It will determine if the system can supply the needed demand if a section is closed, and if it cannot, how much demand is not supplied as a result of the closure.
Highlight “Criticality” in the left pane. At the top of the right pane is an item called “Run Hydraulic Engine?” If this is unchecked, the model will check the connectivity of the model with certain segments are closed. If you select the green Compute icon, you will be able sort the results to see which outage segments will cause the largest disruption by looking at the “System Demand Shortfall” column.
If you place a check in the “Run Hydraulic Engine?” icon, the program will hydraulically compute the model as well. If the demands are not met in that segment, the check box in the column “Are all demands met?” will not be checked.
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