The component importance of each individual pipe is calculated by comparing the total demand that the network is hydraulically able to satisfy when that pipe is out of service, with the total demand that the original network is able to supply. The calculation is computed over the entire simulation duration specified in the network model used – i.e., the unmet demand caused by each individual pipe failure is added for all time steps and compared with the total supplied by the original network over the entire simulation duration.
Component importance values are given between 0 (no demand is satisfied, over the simulation duration) and 1 (all demand is satisfied, over the simulation duration); e.g., a component importance of 0.81 for a specific pipe means that, in the absence of that pipe, the network is expected to be able to supply only 81% of the total demand. In addition, the actual value of expected unmet demand is shown for each pipe.
The NETWORKS Tool and its visualization capabilities may be invoked from this tool, namely as a swift shortcut to visualize the results on 2D or 3D maps – results become available for display in that tool as soon as they are produced.
The calculation of satisfied demand (actual consumption) is based on a simple relationship between available pressure and effective consumption for the particular simulation time step at each node. This relationship is built on two user-specified reference pressure values:
- the Required Minimum Pressure is the nodal pressure value above which the nodal demand is considered to be fully satisfied (e.g., 25 m/ 75 ft); and
- the Zero-Consumption Pressure is the value below which there is no physical consumption at the node (e.g., 8 m / 24 ft).
A linear interpolation is used for pressure values in between the two limits. Nodal demand is understood as the specified base-demand multiplied by the demand pattern’s factor and by any applicable demand multiplier.
The computation is based on full hydraulic response simulation as provided by the network model, where the nodal pressure values for each time step are computed for the reduced network (i.e., with the target pipe missing), and the expected satisfied demand at each node is calculated by applying the above relationship. The total demand for the network, which is used as the basis for the ratio, is computed in the same way but with the original network. The current version uses Epanet's standard demand-driven hydraulic model.
CIMP is launched from the AWARE-P main menu. The initial screen displays any existing component importance tables, and gives the option to create a new table. Creating a new component importance table requires an uploaded Epanet model.
A brief explanation of the tool is given at the top of the main CIMP window. In order to calculate the component importance of each pipe, the two input boxes Zero-consumption Pressure and Required Minimum Pressure must be filled out (default values are 15.0 m and 35.0 m, respectively). Pressing Calculate will compute the percentage of unmet demand caused by the closing of each pipe of the network.
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Wagner, J. M., Shamir, U., Marks, D. H. (1998). Water Distribution Reliability: Simulation Methods. Journal of Water Resources Planning and Management, 114(3), pp. 276-294.