Environmental Engineering Reference
In-Depth Information
1.00
0.80
0.60
ADFavg
NBI
In
NPI
P BI
corrVjQj
0.40
0.20
0.00
1
2
3
4
5
6
7
8
9
10
-0.20
-0.40
Figure 7.22 Correlation between pipe flows and volumes and its relation to loss of demand - Table 7.18
7.8
CONCLUSIONS
The research presented in this chapter aims to assess the potential of water distribution
networks to sustain a certain level of failure based on analysis of their operational parameters
under regular supply conditions, namely the pressures, flows and head loss distribution.
Three different reliability measures have been proposed to describe the network operation,
namely the network power index (NPI), the pressure buffer index (PBI), and the network
residence time (NRT). Comparisons have been done with the reliability measures discussed
in Chapter 6, namely the available demand fraction ( ADF avg ), the network buffer index ( NBI )
and the network reliability index, I n . Furthermore, several statistical analyses have been
conducted to check the correlations between the pipe properties, specifically the volumes and
flows, as possible indicators of the loss of demand after the pipe failure. The conclusions
based on the simulation results can be summarised in the following bullets:
1. The results point fairly good matching between the reliability measures. The logical
response of the indices occurs after the demand and diameter increase, or having various
degree of network connectivity applied in the model.
2. NPI values are generally more susceptible to nodal elevations (i.e. the pressures) than are
the PBI values. Oppositely, the PBI values are more susceptible to the demand growth
(i.e. the friction losses) than are the NPI values.
3. Additional buffer achieved by the increase of pipe diameters shows different effect on the
improvement of network resilience, which can be observed on the diagrams showing the
reliability measures. The different form of the curves for the same reliability index results
from the presentation of that index in different range of ADF avg . After sufficient increase
of pipe diameters, each network enters the state where furthering this action has little
implication for the increase of ADF avg . A curve covering the entire range, starting from
optimised diameters, would be of S-shape ending with the saturation zone of ADF avg .
How big this zone will be, also depends on the available head in the network.
Nevertheless, more research should be done to solidify this conclusion.
4. The pipe correlations of geometric and hydraulic parameters show less consistent
patterns. Different network categories have been showing different level of correlations of
particular parameters. GA-optimised networks show generally better correlations between
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