The CIMP model calculates a component importance metric for each individual pipe in a network, based on the impact of the pipe's failure on nodal consumption across the network. The measure is computed based on the response of a hydraulic model, using full simulation capabilities.
Component importance is a crucial measure of a pipe failure’s consequence to the network, used e.g. in the assessment of risk associated with pipe failure. The component importance of each individual pipe is calculated by comparing the demand that the network is hydraulically able to satisfy when that pipe is out of service, to the total demand that the unreduced 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, calculated for a 24h cycle, means that, if that pipe is out, the network is expected to supply only 81% of the total demand in 24h. In addition, the actual value of expected unmet demand is given 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:
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.
Andrianov, A. (2010). MIKE NET and RELNet: which approach to reliability analysis is better? Available at: http://www.vateknik.lth.se/exjobb/E315.pdf [accessed: 19 July 2010]
CARE-W., 2003. Tests and validation of Technical Tools. Cemagref, INSA Lyon, NTNU, Brno University. Report.
CARE-W., 2004. Guidelines for the use of Technical Tools. Cemagref, SINTEF, INSA Lyon. Report.
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.
This software was developed through intensive colaboration in the framework of the AWARE-P research project.