Browsing by Author "De Villiers, Nico-Ben"

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    Optimality in sewer network design
    (Stellenbosch : Stellenbosch University, 2018-03) De Villiers, Nico-Ben; Van Rooyen, G. C.; Sinske, A. N.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: Sewer networks form a vital part of urban infrastructure and represent a capital intensive expense in the public sector. In South Africa, a recent estimation stated that R44.75 billion is required to provide basic sanitation services to those in need, while the budget allocation for sanitation was approximately R3.2 billion nation wide. This state of affairs is not limited to South Africa alone. It is clear that funds allocated to sanitation have to be spent as effectively as possible. It is within this space that this dissertation makes a contribution, by exploiting modern digital computing power and optimization techniques to find more cost effective solutions to sewer network design and analysis problems. This investigation proposes and evaluates new solutions that address critical shortcomings in existing sewer network optimization algorithms. The distinct lack of adequate benchmark problems to test and compare the performance of new sewer network optimization algorithms is addressed and a thorough investigation into the nature of optimal solutions is made by capturing trial solutions of optimization algorithms at regular intervals. The characteristics of the solutions are quantified through proposed network characteristic parameters. The evolution of trial solution characteristics allow insight and understanding into how the network changed over the course of the algorithm's life cycle. This information is then exploited to propose heuristic influence factors which guide the optimization procedures toward decisions favouring characteristics which have demonstrated good solution fitness. In this way the proposed sewer network optimization algorithms, which are shown to perform better than the algorithms it took inspiration from, are further improved through the use of heuristics. The heuristics, and their formulation, reveal characteristics of optimal sewer network designs which can be used by future researchers as well as design engineers, to improve their solutions.
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    Sewer network design layout optimisation using ant colony algorithms
    (South African Institution of Civil Engineering, 2018) De Villiers, Nico-Ben; Van Rooyen, G. C.; Middendorf, Martin
    The optimal design of sewer networks typically comprises two sub-problems. The first is to determine an optimal layout of the network elements, and the second to optimally design the network components. In this article the focus is on the optimisation of gravity sewer network layouts, which requires simultaneous optimisation of hydraulic design. The layout is optimised using ant colony algorithms with four proposed node and edge-based selection strategies, while a heuristic optimisation algorithm is used for the hydraulic optimisation. The resulting simultaneous optimisation algorithm is shown to perform very well. The selection strategies are shown to be effective, but no clear best strategy is identified, as the performance of the layout algorithms is shown to depend heavily on characteristics of the network under consideration. However, some strategies are shown to perform inconsistently and worse than others on average.