Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Waterborne sewage system design and expansion objectives are often focused on
minimising initial investment while increasing system capacity and meeting
hydraulic requirements. Although these objectives make good sense in the short
term, the solutions obtained might not represent the optimal cost-effective
solution to the complete useful life of the system. Maintenance and operation of
any system can have a significant impact on the life-cycle cost. The costing
process needs to be better understood, which include maintenance and operation
criteria in the design of a sewer system. Together with increasing public
awareness regarding global warming and environmental degradation,
environmental impact, or carbon cost, is also an important factor in decisionmaking
for municipal authorities. This results in a multiplicity of different
objectives, which can complicate the decisions faced by waterborne sewage
utilities.
Human settlement and migration is seen as the starting point of expansion
problems. An investigation was conducted into the current growth prediction
models for municipal areas in order to determine their impact on future planning
and to assess similarities between the models available. This information was used
as a platform to develop a new method incorporating indirect costs into models
for planning waterborne sewage systems.
The need to balance competing objectives such as minimum cost, optimal
reliability, and minimum environmental impact was identified. Different models
were developed to define the necessary criteria, thus minimising initial
investment, operating cost and environmental impact, while meeting hydraulic
constraints. A non-dominated sorting genetic algorithm (NSGA-II) was applied to
certain waterborne sewage system (WSS) scenarios that simulated the
evolutionary processes of genetic selection, crossover, and mutation to find a
number of suitable solutions that balance all of the given objectives. Stakeholders
could in future apply optimisation results derived in this thesis in the decision making process to find a solution that best fits their concerns and priorities.
Different models for each of the above-mentioned objectives were installed into a
multi-objective NSGA and applied to a hypothetical baseline sewer system
problem. The results show that the triple-objective optimisation approach supplies
the best solution to the problem. This approach is currently not applied in practice
due to its inherent complexities. However, in the future this approach may become
the norm. / AFRIKAANSE OPSOMMING: Spoelafvoering rioolstelsel ontwerp en uitbreiding doelwitte is dikwels gefokus op
die vermindering van aanvanklike belegging, terwyl dit die verhoging van stelsel
kapasiteit insluit en ook voldoen aan hidrouliese vereistes. Alhoewel hierdie
doelwitte goeie sin maak in die kort termyn, sal die oplossings verkry dikwels nie
die optimale koste-effektiewe oplossing van die volledige nuttige lewensduur van
die stelsel verteenwoordig nie. Bedryf en instandhouding van 'n stelsel kan 'n
beduidende impak op die lewensiklus-koste hê, en die kostebepalings proses moet
beter verstaan word en die nodige kriteria ingesluit word in die ontwerp van 'n
rioolstelsel. Saam met 'n toenemende openbare bewustheid oor aardverwarming
en die agteruitgang van die omgewing, is omgewingsimpak, of koolstof koste, 'n
belangrike faktor in besluitneming vir munisipale owerhede. As gevolg hiervan,
kan die diversiteit van die verskillende doelwitte die besluite wat munisipale
besluitnemers in die gesig staar verder bemoeilik.
Menslike vestiging en migrasie is gesien as die beginpunt van die uitbreiding
probleem. 'n Ondersoek na die huidige groeivoorspelling modelle vir munisipale
gebiede is van stapel gestuur om hul impak op die toekomstige beplanning te
bepaal, en ook om die ooreenkomstes tussen die modelle wat beskikbaar is te
asesseer. Hierdie inligting is gebruik as 'n platform om ‘n nuwe metode te
ontwikkel wat indirekte kostes inkorporeer in die modelle vir die beplanning van
spoelafvoer rioolstelsels.
Die behoefte is geïdentifiseer om meedingende doelwitte soos minimale
aanvanklike koste, optimale betroubaarheid en minimum invloed op die
omgewing te balanseer. Verskillende modelle is ontwikkel om die bogenoemde
kriteria te definiëer, in die strewe na die minimaliseering van aanvanklike
belegging, bedryfskoste en omgewingsimpak, terwyl onderhewig aan hidrouliese
beperkinge. ‘n Nie-gedomineerde sorteering genetiese algoritme (NSGA-II),
istoegepas op sekere spoelafvoering rioolstelsel moontlikhede wat gesimuleerde
evolusionêre prosesse van genetiese seleksie, oorplasing, en mutasie gebruik om 'n aantal gepaste oplossings te balanseer met inagname van al die gegewe
doelwitte. Belanghebbendes kan in die toekoms gebruik maak van die resultate
afgelei in hierdie tesis in besluitnemings prosesse om die bes-passende oplossing
vir hul bekommernisse en prioriteite te vind. Verskillende modelle vir elk van die
bogenoemde doelwitte is geïnstalleer in die nie-gedomineerde sorteering genetiese
algoritme en toegepas op 'n hipotetiese basislyn rioolstelsel probleem. Die
resultate toon dat die drie-objektief optimalisering benadering die beste oplossing
vir die probleem lewer. Hierdie benadering word tans nie in die praktyk toegepas
nie, as gevolg van sy inherente kompleksiteite. Desnieteenstaande, kan hierdie
benadering in die toekoms die norm word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6824 |
| Date | 03 1900 |
| Creators | Bester, Albertus J. |
| Contributors | Jacobs, H. J., University of Stellenbosch. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 174 p. : ill. |
| Rights | University of Stellenbosch |
Page generated in 0.0022 seconds