Thesis (PhD (Logistics))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The design of a water distribution system (WDS) involves finding an acceptable trade-off between cost minimisation and the maximisation of numerous system benefits, such as hydraulic
reliability and surplus capacity. The primary design problem involves cost-effective specifica-
tion of a pipe network layout and pipe sizes (which are typically available in a discrete set
of commercial diameters) in order to satisfy expected consumer water demands within required
pressure limits. The problem may be extended to consider the design of additional WDS com-
ponents, such as reservoirs, tanks, pumps and valves. Practical designs must also cater for the
uncertainty of demand, the requirement of surplus capacity for future growth, and the hydraulic
reliability of the system under different demand and potential failure conditions.
A detailed literature review of exact and approximate approaches towards single-objective (minimum cost) WDS design optimisation is provided. Essential topics which have to be included in
any modern WDS design paradigm (such as demand estimation, reliability quantification, tank
design and pipe layout) are discussed. A number of formative concepts in multi-objective evo-
lutionary optimisation are also reviewed (including a generic problem formulation, performance
evaluation measures, comparative testing strategies, and suitable classes of metaheuristics).
The two central themes of this dissertation are conducting multi-objective WDS design optimi-
sation using metaheuristics, and a critical examination of surrogate measures used to quantify
WDS reliability. The aim in the first theme is to compare numerous modern metaheuristics, in-
cluding several multi-objective evolutionary algorithms, an estimation of distribution algorithm
and a recent hyperheuristic named AMALGAM (an evolutionary framework for the simulta-
neous incorporation of multiple metaheuristics applied here for the first time to a real-world
problem), in order to determine which approach is most capable with respect to WDS design
optimisation. Several novel metaheuristics are developed, as well as a number of new variants
of existing algorithms, so that a total of twenty-three algorithms were compared.
Testing with respect to eight small-to-large-sized WDS benchmarks from the literature reveals
that the four top-performing algorithms are mutually non-dominated with respect to the vari-
ous performance metrics. These algorithms are NSGA-II, TAMALGAMJndu, TAMALGAMndu
and AMALGAMSndp (the last three being novel variants of AMALGAM). However, when these
four algorithms are applied to the design of a very large real-world benchmark, the AMALGAM
paradigm outperforms NSGA-II convincingly, with AMALGAMSndp exhibiting the best perfor-
mance overall. As part of this study, a novel multi-objective greedy algorithm is developed by
combining several heuristic design methods from the literature in order to mimic the design
strategy of a human engineer. This algorithm functions as a powerful local search. However,
it is shown that such an algorithm cannot compete with modern metaheuristics, which employ
advanced strategies in order to uncover better solutions with less computational effort.
The second central theme involves the comparison of several popular WDS reliability surro-
gate measures (namely the Resilience Index, Network Resilience, Flow Entropy, and a novel
mixed surrogate measure) in terms of their ability to produce designs that are robust against
pipe failure and water demand variation. This is the first systematic study on a number of
WDS benchmarks in which regression analysis is used to compare reliability surrogate measures
with probabilistic reliability typically derived via simulation, and failure reliability calculated
by considering all single-pipe failure events, with both reliability types quantified by means of
average demand satisfaction. Although no single measure consistently outperforms the others,
it is shown that using the Resilience Index and Network Resilience yields designs that achieve
a better positive correlation with both probabilistic and failure reliability, and while the Mixed
Surrogate measure shows some promise, using Flow Entropy on its own as a quantifier of re-
liability should be avoided. Network Resilience is identified as being a superior predictor of
failure reliability, and also having the desirable property of supplying designs with fewer and
less severe size discontinuities between adjacent pipes. For this reason, it is recommended as
the surrogate measure of choice for practical application towards design in the WDS industry.
AMALGAMSndp is also applied to the design of a real South African WDS design case study
in Gauteng Province, achieving savings of millions of Rands as well as significant reliability
improvements on a preliminary engineered design by a consulting engineering firm. / AFRIKAANSE OPSOMMING: Die ontwerp van waterverspreidingsnetwerke (WVNe) behels die soeke na ’n aanvaarbare afruiling tussen koste-minimering en die maksimering van ’n aantal netwerkvoordele, soos hidroliese
betroubaarheid en surpluskapasiteit. Die primere ontwerpsprobleem behels ’n koste-doeltreffende spesifikasie van ’n netwerkuitleg en pypgroottes (wat tipies in ’n diskrete aantal kommersiele
deursnedes beskikbaar is) wat aan gebruikersaanvraag binne sekere drukspesifikasies voldoen.
Die probleem kan uitgebrei word om die ontwerp van verdere WVN-komponente, soos op-
gaardamme, opgaartenks, pompe en kleppe in ag te neem. Praktiese WVN-ontwerpe moet
ook voorsiening maak vir onsekerheid van aanvraag, genoegsame surpluskapsiteit vir toekom-
stige netwerkuitbreidings en die hidroliese betroubaarheid van die netwerk onder verskillende
aanvraag- en potensiele falingsvoorwaardes.
’n Omvattende literatuurstudie word oor eksakte en benaderde oplossingsbenaderings tot enkel-
doelwit (minimum koste) WVN-ontwerpsoptimering gedoen. Sentrale temas wat by heden-
daagse WVN-ontwerpsparadigmas ingesluit behoort te word (soos aanvraagvooruitskatting, die
kwantifisering van betroubaarheid, tenkontwerp en netwerkuitleg), word uitgelig. ’n Aantal
basiese konsepte in meerdoelige evolusionˆere optimering (soos ’n generiese probleemformulering,
werkverrigtingsmaatstawwe, vergelykende toetsingstrategie¨e, en sinvolle klasse metaheuristieke
vir WVN-ontwerp) word ook aangeraak.
Die twee sentrale temas in hierdie proefskrif is meerdoelige WVN-ontwerpsoptimering deur mid-
del van metaheuristieke, en ’n kritiese evaluering van verskeie surrogaatmaatstawwe vir die
kwantifisering van netwerkbetroubaarheid. Die doel in die eerste tema is om ’n aantal moderne
metaheuristieke, insluitend verskeie meerdoelige evolusionere algoritmes en die onlangse hiper-
heuristiek AMALGAM (’n evolusionere raamwerk vir die gelyktydige insluiting van ’n aantal
metaheuristieke wat hier vir die eerste keer op ’n praktiese probleem toegepas word), met
mekaar te vergelyk om sodoende ’n ideale benadering tot WVN-ontwerpoptimering te identi-
fiseer. Verskeie nuwe metaheuristieke sowel as ’n aantal nuwe variasies op bestaande algoritmes
word ontwikkel, sodat drie en twintig algoritmes in totaal met mekaar vergelyk word.
Toetse aan die hand van agt klein- tot mediumgrootteWVN-toetsprobleme uit die literatuur dui
daarop dat die vier top algoritmes mekaar onderling ten opsigte van verskeie werkverrigtings-
maatstawwe domineer. Hierdie algoritmes is NSGA-II, TAMALGAMJndu, TAMALGAMndu
en AMALGAMSndp, waarvan laasgenoemde drie nuwe variasies op AMALGAM is. Wanneer
hierdie vier algoritmes egter vir die ontwerp van ’n groot WVN-toetsprobleem ingespan word,
oortref die AMALGAM-paradigma die NSGA-II oortui-gend, en lewer AMALGAMSndp die
beste resultate. As deel van hierdie studie is ’n nuwe meerdoelige gulsige algoritme ontwerp
wat verskeie heuristiese ontwerpsmetodologiee uit die literatuur kombineer om sodoende die on-
twerpstrategie van ’n ingenieur na te boots. Hierdie algoritme funksioneer as ’n kragtige lokale
soekprosedure, maar daar word aangetoon dat die algoritme nie met moderne metaheuristieke,
wat gevorderde soekstrategie¨e inspan om beter oplossings met minder berekeningsmoeite daar
te stel, kan meeding nie.
Die tweede sentrale tema behels die vergelyking van ’n aantal gewilde surrogaatmaatstawwe vir
die kwantifisering van WVN-betroubaarheid (naamlik die elastisiteitsindeks, netwerkelastisiteit,
vloei-entropie en ’n gemengde surrogaatmaatstaf ) in terme van die mate waartoe hul gebruik kan
word om WVNe te identifiseer wat robuust is ten opsigte van pypfaling en variasie in aanvraag.
Hierdie proefskrif bevat die eerste sistematiese vergelyking deur middel van regressie-analise van
’n aantal surrogaatmaatstawwe vir die kwantifisering van WVN-betroubaarheid en stogastiese
betroubaarheid (wat tipies via simulasie bepaal word) in terme van ’n aantal toetsprobleme in
die literatuur. Alhoewel geen enkele maatstaf as die beste na vore tree nie, word daar getoon
dat gebruik van die elastisiteitsindeks en netwerkelastisiteit lei na WNV-ontwerpe met ’n groter
positiewe korrelasie ten opsigte van beide stogastiese betroubaarheid en falingsbetroubaarheid.
Verder toon die gebruik van die gemengde surrogaatmaatstaf potensiaal, maar die gebruik
van vloei-entropie op sy eie as kwantifiseerder van betroubaarheid behoort vermy te word.
Netwerkelastisiteit word as ’n hoe-gehalte indikator van falingsbetroubaarheid geidentifiseer en
het ook die eienskap dat dit daartoe instaat is om ontwerpe met ’n kleiner aantal diskontinuiteite
sowel as van ’n minder ekstreme graad van diskontinuiteite tussen deursnedes van aangrensende
pype daar te stel. Om hierdie rede word netwerkelastisiteit as die surogaatmaatstaf van voorkeur
aanbeveel vir toepassings van WVN-ontwerpe in die praktyk.
AMALGAM word ook ten opsigte van ’n werklike Suid-Afrikaanse WVN-ontwerp gevallestudie
in Gauteng toegepas. Hierdie toepassing lei na die besparing van miljoene rande asook noe-
menswaardige verbeterings in terme van netwerkbetroubaarheid in vergeleke met ’n aanvanklike
ingenieursontwerp deur ’n konsultasiefirma.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6617 |
| Date | 03 1900 |
| Creators | Raad, Darian Nicholas |
| Contributors | Van Vuuren, Jan H., Sinske, Alexander, University of Stellenbosch. Faculty of Economic and Management Sciences. Dept. of Logistics. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 334 p. : ill., maps |
| Rights | University of Stellenbosch |
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