Author(s): Rudy Gargano; Domenico Pianese
Linked Author(s): Domenico Pianese
Keywords: Water; Network; Reliability; Probability; Availability; Stochastic; Index
Abstract: A problem frequently encountered in studying the overall reliability of water distribution networks (WDNs) is that of minimising the computational workload generated by the extremely large number of operating conditions that normally have to be analysed. An approach is therefore proposed by which it is possible to fix the maximum approximation error in evaluating a WDN’s overall reliability (Max Err), and then to determine which of the distribution network’s operating conditions actually need to be investigated, choosing from the possible configurations that the network might assume following the outage of one or more components. More specifically, a criterion is suggested which makes it possible, once the characteristics of the WDN’s main electromechanical components and the stochastic structure of water demand are known, to assess the incidence of mechanical and hydraulic reliability on overall reliability. To this end, a hierarchic approach is proposed to estimate the overall reliability. In the first stage, a large set of daily users’demand is generated by using a stochastic approach. Starting from these data, for each of the various network operating conditions taken for reference (e. g. : WDN with all electromechanical components working; WDN with only one link withdrawn; WDN with only two links withdrawn, etc. ), the nodal heads and flow rate are evaluated by mathematical modelling. Then, by the Hydraulic Performance Indices (HPIs), the daily volumes of water supplied to the users are estimated and compared to actual demand. Subsequently, by statistical analysis of HPIs reliability is estimated, for each operating condition, by means of suitable Hydraulic Reliability Indices, HRIs. More specifically, HRI represents the probability that the index HPI is higher than a predefined threshold value*hpi. The last stage is to assess the Overall Reliability Indices (ORIs) by means of a weighted mean of the HRIs. The reliability evaluated by the ORIs represents the probability that the WDN will provide overall a distribution service level that is higher than a predefined standard, regardless of whether the electromechanical components are fully or partially operative. Finally, some relationships and charts are proposed that are particularly useful for identifying, for a fixed number of electromechanical components in the network and for a fixed value of their operation availability, the maximum number of components simultaneously out that need to be considered in order to evaluate the overall reliability so that the maximum error will be at most equal to the predetermined one.
Year: 1999