Comparing Low and HighLevel Hybrid Algorithms on

Authors: Qi Wang Enrico Creaco Marco Franchini Dragan Savić Zoran Kapelan

Publish Date: 2014/10/30

Volume: 29, Issue: 1, Pages: 1-16

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Abstract

This paper presents the comparison of two hybrid methodologies for the twoobjective cost and resilience design of water distribution systems The first method is a lowlevel hybrid algorithm LLHA in which a main controller the nondominated sorting genetic algorithm II NSGAII coordinates various subordinate algorithms The second method is a highlevel hybrid algorithm HLHA in which various subalgorithms collaborate in parallel Applications to four case studies of increasing complexity enable the performances of the hybrid algorithms to be compared with each other and with the performance of the NSGAII In the case study featuring low/intermediate complexity the hybrid algorithms especially the HLHA successfully capture a more diversified Pareto front although the NSGAII shows the best convergence When network complexity increases instead the hybrid algorithms especially the LLHA turn out to be superior in terms of both convergence and diversity With respect to both the HLHA and the NSGAII the LLHA is capable of detecting the final front in a single run with a lower computation burden In contrast the HLHA and the NSGAII which are more affected by the initial random seed require numerous runs with an attempt to reach the definitive Pareto front On the other hand a drawback of the LLHA lies in its reduced ability to deal with general problem formulations ie those not relating to water distribution optimal designThe first author would like to appreciate the financial support given by both the University of Exeter and the China Scholarship Council towards the PhD research The work of the second and third author was carried out as part of the PRIN 2012 “Devices and Procedures for an Advanced and Substainable management of Water Distribution Systems” and under the framework of TerraAcqua Tech Laboratory Axis I activity 11 of the POR FESR 2007–2013 project funded by EmiliaRomagna Regional Council Italy We also appreciate the comments and suggestions given by anonymous reviewers which helped improve the quality of this paper substantially

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